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Immunology Syllabus 2013

Department of Immunology and Allergy Volgograd State Medical University

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COVER DESCRIPTION A strikingly designed stainless steel sculpture dedicated to Richard A. Lerner, president

of The Scripps Research Institute, was installed at the entrance to the main building on the new Scripps Florida campus.

The 12-foot-high sculpture features an enormous ring surrounding a fully realized model of a human antibody, an immune molecule that recognizes and helps fight off the body's foreign invaders, such as bacteria or viruses. Entitled "Angel of the West," the sculpture was created by Julian Voss-Andreae, a former physicist who now works as a sculptor in Portland, Oregon.

The sculpture, donated anonymously by a Palm Beach County resident, hails Lerner's "vision, pioneering spirit, and perseverance" that helped make the Scripps Florida campus a reality. Lerner, who became president of Scripps Research in 1987, is well known scientifically for his pioneering work with catalytic antibodies and combinatorial antibody libraries. These advances have lead to new uses for antibodies, including as human therapeutics.

"I am honored and deeply moved by Julian Voss-Andreae's work," Lerner said. "By using the structure of the human antibody, the sculpture can be seen as a universal statement about the complexity and beauty of human biology. The dedication should really be shared with all the scientists at Scripps Florida who, through their own deep commitment to biomedical research, are helping to eradicate disease and alleviate human suffering."

The artist, Julian Voss-Andreae, 38, was born in Hamburg, Germany and studied physics at the Free University of Berlin and Edinburgh University. As a graduate student at the University of Vienna, he was part of a team that conducted ground-breaking experiments in quantum mechanics in 1999. Voss-Andreae moved to the United States in 2000 and graduated from the Pacific Northwest College of Art in 2004 with a B.F.A. in sculpture. He lives and works in Portland, Oregon.

Much of Voss-Andreae's work is inspired by molecular structures. "When I started thinking about a sculpture based on the human antibody, I found a

fascinating visual analogy between human proportions, as illustrated in Leonardo da Vinci's Vitruvian Man, and the structure of an antibody," Voss-Andreae said. "My sculpture plays on the connection between Renaissance culture, symbolized by Leonardo's highly recognizable iconic drawing, and the antibody, the central molecule of the immune system."

The sculpture is called "Angel of the West" for a number of reasons, he said: "The title references the monumental piece Angel of the North by British sculptor Antony Gormley erected in Gateshead in northeast England, while mine refers to Western medicine's almost miraculous promises of healing. Most importantly, the title makes clear that antibodies are, in fact, like an enormous army of angels constantly protecting us from sickness and disease."

Voss-Andreae began design of the sculpture in mid-2005, and spent much of 2006 developing the software that would translate details of the antibody structure into complex cutting instructions for the special grade stainless steel needed to complete the structure.

"The sculpture was built from 1,400 laser-cut pieces of corrosion-resistant stainless steel," Voss-Andreae said. "Constructing the sculpture, which involved bending and welding each of the pieces and then grinding and sanding them, was very labor intensive. I began assembly in 2007 and finished earlier this year."

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IMMUNOLOGY SYLLABUS 2013 – TABLE OF CONTENTS

Оглавление IMMUNOLOGY SYLLABUS 2013 – TABLE OF CONTENTS ..............................................3

COURSE SCHEDULE (WEEK – TOPIC) (TENTATIVE! SUBJECT TO CHANGE!): ..........4

COURSE DESCRIPTION ......................................................................................................5

1) STAFF AND CONTACTS...............................................................................................5

2) COURSE ORGANIZATION ...........................................................................................5

3) COURSE MATERIALS...................................................................................................5

4) GRADING .......................................................................................................................6

5) MISSING CLASSES POLICIES.....................................................................................6

REQUIRED READINGS ........................................................................................................6

IMMUNOLOGY CLINICAL CORRELATION .........................................................................7

ASSIGNMENTS .....................................................................................................................8

1. MEDICAL IMPORTANCE OF THE IMMUNE SYSTEM [HOW THE IMMUNE SYSTEM WORKS]. CELLS AND ORGANS OF THE IMMUNE SYSTEM. innate immunity .....8

A) Subtopics ....................................................................................................................8

B) Objectives ...................................................................................................................8

C) Keywords....................................................................................................................8

D) Reading: .....................................................................................................................8

BASIC CONCEPTS AND DEFINITIONS .......................................................................9

CELLS AND ORGANS OF THE IMMUNE SYSTEM. INNATE IMMUNITY ................18

F) Study questions for class discussion .......................................................................26

2. ANTIGENS. MHC structure and activities....................................................................28

A) Subtopics ..................................................................................................................28

B) Objectives .................................................................................................................28

C) Keywords..................................................................................................................28

D) Reading: ...................................................................................................................28

ANTIGENS ....................................................................................................................29

MHC STRUCTURE AND ACTIVITIES .........................................................................35

F) Study questions for class discussion .......................................................................42

APPENDIX ...........................................................................................................................45

Timeline of Immunology ...................................................................................................45

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COURSE SCHEDULE (WEEK – TOPIC) (TENTATIVE! SUBJECT TO CHANGE!):

1. Overview and Elements of the Immune System 2. Antigens. Innate immunity. MHC Structure and activities. 3. Antibodies and T cell Receptors – Structure and Functions 4. Complement. Antigen-antibody interactions – ImmunoAssays 5. T cell-mediated immunity 6. Regulatory functions of T cells 7. Cytokines. Immune tolerance. 8. Immune system and Infectious disease 9. Tumor immunology. Reproductive immunology. Immunobiotechnology. Autoimmune diseases 10. Age-related immunology. Immune function assessment (reading: http://www.ncbi.nlm.nih.gov/pubmed/23755371) 11. Immunopathology. Hypersensitivity reactions. IgE-mediated diseases: natural course, diagnosis and treatment 12. Food allergy 13. Allergic respiratory diseases 14. Drug allergy 15. Primary Immune deficiencies 16. Secondary immune deficiencies 17. Immune therapies

Essay Assignment due: TBD

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COURSE DESCRIPTION

1) STAFF AND CONTACTS

Director of the department: Dr. Eleonora Belan, M. D., Ph.D., D.Sc. (belan05@mail.ru)

Office hours: by appointment Lecturers:

Eleonora Belan, M. D., Ph. D., D. Sc. Pavel Nesmiyanov, M. D., Ph. D. (nesmiyanovp@volgmed.ru) Instructors:

Eleonora Belan, M. D., Ph. D., D. Sc. Pavel Nesmiyanov, M. D., Ph. D. Mikhail Gutov, M. D. (gutmich@mail.ru)

Department contacts:

Department phone number: +7-961-080-1010 Department official site: http://www.volgmed.ru/ru/depts/list/67/ Public discussions: http://forum.volgmed.ru/index.php?showforum=60 Social Network: http://vk.com/club14643818 Student support site: http://immunology-allergy.org/students Animations: http://immunology-allergy.org/animations/

2) COURSE ORGANIZATION

The purpose of the Immunology course is to provide a basic knowledge of the immune response and its involvement in health and disease. All lectures will be presented as stated in general faculty schedule. An effort has been made to increase clinical relevance and problem-solving skills through an essay assignment and faculty presented clinical correlations.

Any questions on the lecture material should be addressed to Dr. Belan or directly to that lecturer. If you have general problems or comments regarding the course, your grades, or the faculty, please contact any instructor. If the problem is not resolved, you should make an appointment to see Dr. Belan.

3) COURSE MATERIALS

a) Lectures. The student is responsible for all material covered in lectures and faculty

presented clinical correlations, as well as for any additional handouts or assignments (whether provided in this syllabus or at a later time). Immunology is a rapidly advancing area, so the lectures may contain new information not covered in the textbooks. Therefore you should make every effort to attend lecture and take complete and accurate notes.

b) Reading. Two textbooks are required for the course. Chapter assignments are listed

directly in the syllabus chapter. The books are available in the library. Additional readings will be provided by the department.

c) Web assisted education. You are encouraged to make use of all the web sites listed

above. Websites will be actively updated during the course to include information that will assist in understanding of course materials.

d) Department contests. Students who participate in contests are eligible for extra credit

points. Further information will be available.

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e) Study questions. Additional study questions are provided at each class. The purpose

of these questions is to encourage you to read additional texts, journal papers and actively participate in process of your education. They also serve to make studies more object-oriented and to extend your learning beyond rote memorization toward more „cognitive‟ learning. The study questions may not be graded, but questions related to these assignments will appear in the examinations. It can be comfortable for you to print out pages with these questions so that you can write down the answers during your preparation for the class.

f) Office hours and other assistance. Students are encouraged to approach the

instructors if they need assistance in understanding the course material. All instructors are available in the office by individual appointment or by phone or email.

4) GRADING

Grading policy is in accordance to University grading policy. a) Examinations. There will be two major exams consisting of multiple choice, matching

and other questions. Exam answers will be posted according to accepted policies of the university. There will be minor testing every class, sessions may be scheduled for question review after each testing.

b) Essay assignment. The essay assignment is required. Topic list will be provided by

your instructor. You are encouraged to propose your own topic for an essay. Grading will be based on adherence to the format described in this syllabus, thoroughness, and application of your budding medical knowledge and logic. The due date will be posted.

c) Extra curricular activities. Extra curricular activities may include lab work with

instructor in clinical setting or on a one of the department‟s projects, or some special activities (such as „grant proposal‟). Please be aware that department may not be able to host each willing student due to time or space limit. Please understand that not everyone can be accepted though we make everything possible to „host‟ any willing person.

5) MISSING CLASSES POLICIES

Persons missing the seminars must provide written notice explaining circumstances for not attending. Written approval must be obtained from the Office of Educational/Student Affairs prior to consideration for any makeup seminar or alternate assignment.

REQUIRED READINGS

Khaitov R. M. Immunology (+CD-ROM). GEOTAR-Media Publishing, Moscow, 2000

Abul Abbas, Andrew H. Lichtman, Shiv Pillai. Cellular and Molecular Immunology (7th

ed.) Philadelphia : Elsevier/Saunders, 2012 Owen J., Punt J, Stranford S. Kuby Immunology. 7th ed. New York: W.H. Freeman and

Company, 2013 R.S. Geha and Notarangelo, L. Case Studies in Immunology: A Clinical Companion.

(6th ed.) Garland Publishing, New York, 2012.

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IMMUNOLOGY CLINICAL CORRELATION

Reading for topic:

Required readings (from R.S. Geha and Notarangelo, L. Case

Studies in Immunology: A Clinical Companion. (6th ed.) Garland Publishing, New

York, 2012)

Cells and Organs 30. Congenital Asplenia Innate Immunity 15. Chediak-Higashi Syndrome

25. Neutropenia 26. Chronic Granulomatous disease 27. Leukocyte Adhesion Deficiency

Antigens

Other topics TBD

Required readings complement lectures and presented materials. It is highly encouraged

to view these clinical cases. Case materials may not be covered in full during lectures, however, all required case

study readings contain material that may be tested on exams.

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ASSIGNMENTS

1. MEDICAL IMPORTANCE OF THE IMMUNE SYSTEM [HOW THE IMMUNE SYSTEM WORKS]. CELLS AND ORGANS OF THE IMMUNE SYSTEM. INNATE

IMMUNITY

A) Subtopics

1. The early stage of the development of immunology (ancient experience; B. Jesty‟s and E. Jenner‟s achievements). L. Pasteur as a founder of immunology as a science. The discovery of two types of immunity (Y. Metchnikoff, P. Erlich). The development and most important achievements of immunology in XX century.

2. The subject, tasks and basic definitions in immunology. 3. Central immune system. Anatomy and basic functions. 4. Peripheral immune system. Anatomy and basic functions. 5. Innate immunity: phagocytosis, natural killer cells, ADCC

B) Objectives

1. To appreciate the components of the human immune response that work together to protect the host

2. To understand the concept of immune-based diseases as either a deficiency of components or excess activity as hypersensitivity

3. To introduce the main concepts of the course 4. Identify cell types involved in specific and non-specific immune responses 5. Present the developmental pathway of immune system cells 6. Understand structure and function of primary and secondary lymphoid organs 7. Introduce innate immune defense mechanisms 8. Define chemical mediators involved in inflammation 9. Review cell types involved in innate immune responses, and their role in inflammation 10. Define ADCC, chemokines, and Pattern-recognition receptors

C) Keywords

Immunodeficiency, hypersensitivity, Reticuloendothelial System, Leukocytes, Myeloid

Cells, Lymphocytes, Antigen Presenting Cells (APC), GALT, MALT, BALT, Cluster of Differentiation (CD), Inflammasome, PRRs, DAMPs, Innate Immunity, Innate Defense Barriers, Neutrophils, Monocytes, Macrophages, Natural Killer (NK) cells, Phagocytosis, APC, ADCC, Chemokines, Complement

D) Reading:

Khaitov R. M. Immunology (+CD-ROM). GEOTAR-Media Publishing, Moscow, 2000

Abul Abbas, Andrew H. Lichtman, Shiv Pillai. Cellular and Molecular Immunology (7th

ed.) Philadelphia : Elsevier/Saunders, 2012 Owen J., Punt J, Stranford S. Kuby Immunology. 7th ed. New York: W.H. Freeman and

Company, 2013 R.S. Geha and Notarangelo, L. Case Studies in Immunology: A Clinical Companion.

(6th ed.) Garland Publishing, New York, 2012. Web Resource: http://www.immunology-allergy.org/students

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BASIC CONCEPTS AND DEFINITIONS

The chief function of immunity is to discriminate between self and non-self.

The immune cells and organs of the body comprise the primary defense system against invasion by microorganisms and foreign pathogens. A functional immune system confers a state of health through effective elimination of infectious agents (bacteria, viruses, fungi, and parasites) and through control of malignancies by protective immune surveillance. In essence, the process is based in functional discernment between self and non-self, a process which begins in utero and continues through adult life.

Immune responses are designed to interact with the environment to protect the host against pathogenic invaders. The goal of these chapters is to appreciate the components of the human immune response that work together to protect the host. Furthermore, we will strive to present a working clinical understanding of the concept of immune-based diseases resulting from either immune system component deficiencies or excess activity.

Immunological memory as the basis for vaccine efficacy

Continued discrimination for health depends upon immunological memory where the adaptive immune system can more efficiently respond to previously encountered antigen. This results in resistance to repeated infection with pathogens and the resulting clinical syndrome. This principle accounts for the clinical utility of vaccines which have done more to improve mortality rates worldwide than any other medical discovery in recorded history.

The clinical immunologist is a physician who has specialized in the diagnosis and treatment of disorders of the immune system. Many other clinical specialties (such as oncology, hematology, infectious diseases, transplant surgery, etc.) also deal with immunologicallybased diseases in their area of specialization. Much of the work of modern clinical immunologists revolves around refining diagnostic techniques for greater clinical utility and evaluating new therapeutic modalities such as recombinant cytokines and cytokine modulators.

Protection against foreign pathogens

Normal physiologic functions of the immune system include the ability to discern self from non-self, and recognition of foreign pathogens. This represents recognition of environmental challenges in an attempt to preserve homeostasis while responding to pathogenic agents. The goal is to respond with specificity, allowing sufficient intensity and duration to protect the host without causing damage to self. The Immune system protects against foreign pathogens, of which four major classes can be defined. These include (1) Extracellular bacteria, parasites and fungi; (2) Intracellular bacteria and parasites; (3) Viruses (intracellular); and (4) Parasitic worms (extracellular).

Immunodeficiency and dysfunction as the basis of disease Immunological diseases can be grouped into two large categories – deficiency and

dysfunction. Immunodeficiency diseases occur as the result of the absence (congenital or

acquired) of one or more elements of the immune system. Immune dysfunction occurs when a particular immune response occurs that is detrimental to the host. This response may be against a foreign antigen or self antigen. It may also be an inappropriate regulation of an effector response resulting in the absence of a protective response. Notwithstanding, the host is adversely affected. A healthy immune system occurs as a result of balance between innate and adaptive immunity, cellular and humoral immunity, inflammatory and regulatory networks and small biochemical mediators (cytokines). Because specific mechanism affects prognosis as well as therapeutic approaches, Gel and Coombs classified these dysfunctional immune responses into hypersensitivity diseases.

Hypersensitivities will be discussed throughout the course, and in much greater detail in a later chapter. There is considerable overlap in underlying mechanisms that contribute to the hypersensitive responses. The major mechanisms are outlined on the following page.

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Type I (also called immediate hypersensitivity) is due to aberrant production and activity

of IgE against normally nonpathogenic antigens (commonly called allergens). The IgE binds to mast cells via high affinity IgE receptors. Subsequent antigen exposure results in crosslinking of mast cell bound IgE with activation of mast cells that release preformed mediators (eg. histamine, leukotrienes, etc.) and synthesize new mediators (i.e. chemotaxins, cytokines). These mediators are responsible for the signs and symptoms of allergic diseases. [A = Allergic]

Type II is due to antibody directed against cell membrane-associated antigen that results

in cytolysis. The mechanism may involve complement (cytotoxic antibody) or effector lymphocytes that bind to target cell-associated antibody and effect cytolysis via a complement independent pathway (Antibody dependent cellular cytotoxicity, ADCC). Cytotoxic antibodies mediate many immunologically-based hemolytic anemias while ADCC may be involved in the pathophysiology of certain virus-induced immunological diseases. [C = Cytotoxic]

Type III results from soluble antigen-antibody immune complexes that activate

complement. The antigens may be self or foreign (i.e. microbial). Such complexes are deposited on membrane surfaces of various organs (i.e. kidney, lung, synovium, etc). The byproducts of complement activation (C3a, C5a) are chemotaxins for acute inflammatory cells. These result in the inflammatory injury seen in diseases such as rheumatoid arthritis, systemic lupus erythematosus, postinfectious arthritis, etc). I = Immune Complex]

Type IV (also called Delayed Type Hypersensitivity, DTH) involves macrophage-T

cellantigen interactions that cause activation, cytokine secretion and potential granuloma formation. Diseases such as tuberculosis, leprosy and sarcoidosis as well as contact dermatitis are all clinical examples where the tissue injury is primarily due to the vigorous immune response rather than the inciting pathogen itself. D = DTH]

Clinical suspicion for immunodeficiency may be made when patients present with chronic

infection or chronic inflammatory status, poor wound healing, constant fatigue and malaise, or when unresponsive to vaccine administration. Certain infections with organisms may be suggestive of deficiency in an immune related component. Alternatively, disruptions in homeostasis may lead to immunodeficiency, such as those induced inadvertently by a physician through medical treatment (iatrogenic). The mechanisms for clinical immunodeficiency are varied, and will be examined (in part) throughout the remainder of the course.

Therapeutic intervention for immune based diseases Therapy for these diseases has historically been nonspecific, centering on repair of the damaged tissues and inhibition of the aberrant immune responses with

immunosuppressive drugs. Recent work using such cutting edge techniques as recombinant

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DNA technology, gene therapy, and stem-cell research have opened up an entire new avenue to address these diseases by providing diagnostic and therapeutic modalities not previously available. For immunodeficiency states, we have developed the g ability to replace elements through marrow transplants, recombinant immune molecule administration and, soon, gene therapy.

INTRODUCTION TO 7 MAIN CONCEPTS TOWARDS UNDERSTANDING MEDICAL

IMMUNOLOGY

1. The chief function of the immune system is to distinguish between self and non-self. Health – effective elimination or control of health-threatening agents Infectious agents – bacteria, viruses, fungi, parasites Tumors – the immune system also plays an important role in the control of malignant

cells through a mechanism called immune surveillance Hyporeactivity – inability to recognize and control health-threatening agents

(immunodeficiency) Congenital immunodeficiency – immune defects due to genetic defects Acquired immunodeficiency – caused by multiple agents, including Human

Immunodeficiency Virus and tumors Malnutrition – severe malnutrition compromises the immune system Young/Old Age – increased susceptibility to infection

Hyperreactivity – aberrant immune responses Systemic autoimmunity – e.g. systemic lupus erythematosus Organ-Specific autoimmunity – e.g. thyroiditis Allergies and Asthma – aberrant immune response to environmental allergens or

chemicals Immunopathology – general term for damage to normal tissue due to the immune

reaction to infectious agents or other antigens (e.g. rheumatic fever, leprosy)

Figure: Immune based diseases can be caused by lack of specific functions

(immune deficiency) or excessive activity (hypersensitivity).

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2. The immune system consists of two overlapping compartments: the innate immune system and the adaptive immune system.

Innate immune system

Most primitive type of immune system; found in virtually all multicellular animals (arguably also in plants!) Always present and active, constitutively expressed Nonspecific; not specifically directed against any particular infectious agent or tumor Same every time; no „memory‟ as found in the adaptive immune system First line of defense against infection Includes:

o Physical barriers (skin, mucus lining of gastrointestinal, respiratory and

genitourinary tracts) o Phagocytic cells – neutrophils, macrophages o Protective chemicals – acid pH of stomach, lipids on skin surface o Enzymes – lysozyme in saliva, intestinal secretions; digests cell walls of bacteria o Alternate complement pathway – cascade of serum proteins that are activated

by bacterial cell wall components

Adaptive or acquired immune system Found only in vertebrates (fish, amphibians, birds and mammals) Must be induced to be active against infections or tumors Antigen-specific – adaptive immune responses recognize antigens, which can be

proteins, carbohydrates, lipids and nucleic acids. Memory – response against a given antigen is much stronger after the first (primary)

response. This heightened reactivity is called secondary responses, and is due to increased numbers of memory B and T cells to that antigen Regulation – discriminates between self and non-self, prevents autoimmune reactions

in most individuals o B lymphocytes – differentiate into plasma cells that produce antibodies o T lymphocytes – subdivided into CD4+ and CD8+ populations

- Helper activity – help other lymphocytes respond to antigen (mostly CD4+ T

cells, subdivided into phenotypic responders) - Delayed type hypersensitivity – activate macrophages to phagocytose, kill

pathogens (mostly CD4+ T cells) - T cell-mediated cytotoxicity – cytotoxic T cells (mostly CD8+ T cells) bind to

and kill target cells (e.g. virus-infected cells and tumor cells) - Suppressor T cells/Treg cells – down-regulate the responses of other

lymphocytes

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3. The antigenic specificity of the adaptive immune system is due to antigen-specific receptors.

Immunoglobulins (also called antibodies) – produced by B cell lineage o IgM, IgD, IgG, IgA, and IgE subtypes o Surface immunoglobulin (Ig) – antigen-specific receptor of B lymphocytes o Secreted immunoglobulin (Ig) – Ig molecules secreted by plasma cells

T cell receptor (TCR) – antigen-specific receptor of T lymphocytes o αβ and γλ TCR subtypes

The basic reaction in immunology is the binding of antigen to an antigen-specific

receptor. The affinity of this interaction is similar to that of an enzyme binding to its substrate.

Ag + Ab ↔ AgAb

Typically, each antibody or T cell receptor molecule recognizes a single epitope, a small region (e.g. 6-10 amino acids) of an antigen. In a given B- or T-cell, the antigen-specific receptors of all are identical. Exception – IgM

and IgD can be coexpressed on certain B cells Each B cell and T cell has its own antigenic specificity, determined by the amino acid

sequence of its surface Ig or TCR. The region of the Ig or TCR that binds to the antigen is called the paratope. In each person, there are ~106 to 108 different Igs and TCRs, giving rise to an almost

endless supply of antigenic specificities. This is called diversity.

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4. The generation of antigen-binding diversity occurs prior to antigen exposure through a DNA rearrangement process called VDJ joining.

The “business end” of an antibody or TCR is the variable region. This region contains the antigen-binding site that binds to the epitope (meaning: the conformational shape recognized).

The variable region is formed during B and T cell development. This process occurs

prior to exposure to a given antigen. The DNA encoding the variable region is subdivided into V, D, and J gene segments.

There are multiple V, D, and J gene segments in the Ig and TCR genetic loci. In most cells, these gene segments are spread out, so that all the V segments are

together, all the D segments are together, and all the J segments are together. This is called the germline configuration, because it is the arrangement seen in sperm and ova.

The V, D, and J gene segments are brought together to form a contiguous exon encoding the variable region. The V, D, and J segments are selected randomly in each cell, giving rise to combinatorial diversity.

The light chain gene locus (and some TCR genes) has only V and J regions. There are several other mechanisms for generating diversity, as will be discussed in a

later class.

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5. To generate an active immune response against a certain antigen, a small number of B and T cell clones that bind to the antigen with high affinity undergo activation, proliferation, and differentiation into plasma cells (for B cells) or activated T cells. This process is called ‘clonal selection’.

B and T cells are resting cells that lack functional activity until they undergo activation, proliferation, and differentiation into plasma cells or activated T cells. This process

takes several days, which explains the lag between being exposed to an infectious agent and eventually getting better when the immune response „kicks in‟. Of the millions of different specificities of B and T cells produced, only a few will have

surface Ig or TCRs that bind the antigen with high affinity. However, we produce B and T cells that will react with virtually any antigen, including those that are man-made and are not found in nature (e.g. di-nitrophenol). In nearly all cases, activation of a B or T cell requires two signals: binding of the

antigen-specific receptor to the antigen, and exposure to proteins called cytokines

expressed by helper T cells. The blast cells resulting from activation undergo proliferation, resulting in a ~100-fold

expansion of the number of cells reactive to the antigen. Some of these cells become effector cells (plasma cells and activated T cells that

express activities that help to eliminate the pathogen. Others become memory cells that can give rise to secondary responses as described below.

6. The adaptive immune system has memory, meaning that the response against an antigen is much greater after the first exposure.

The first response to an antigen is called the primary response, and responses thereafter are called secondary responses.

The different properties of secondary responses are due to memory cells generated during the primary responses. Secondary responses have

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o Higher antibody levels o Increased proportion of IgG and other immunoglobulin isotypes o Shorter lag period o Higher affinity for antigen

Vaccination is effective because it primes the immune system to provide secondary

responses when the individual is exposed to an infectious agent. Each exposure to an antigen tends to increase the secondary response. This is why

booster immunizations are often used in vaccinations.

Figure: Primary and secondary antibody responses. The adaptive immune system

has memory, allowing for maturation of a rapid secondary immune response with higher specificity and magnitude directed against foreign substances.

7. The immune system is tightly regulated.

Self-reactive B and T cell clones are generated as a natural part of the random VDJ recombination process. The adaptive immune system has developed several mechanisms to eliminate or inhibit

self-reactive B and T cells. o Elimination of self-reactive cells during their development through apoptosis. o Permanent inactivation of self-reactive cells through a process called clonal

anergy.

o Inhibition of self-reactive cells by suppressor cells, inhibitory cytokines, and other factors

Each immune response requires a combination of multiple factors, thereby limiting the number of spurious responses.

SUMMARY – MEDICAL IMPORTANCE OF THE IMMUNE SYSTEM AND HOW THE

IMMUNE SYSTEM WORKS

Thus it can be said that the healthy immune system occurs as a result of balance – between innate and adaptive immunity, cellular and humoral immunity, inflammatory and

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regulatory networks and even cytokine modulators. Disease occurs when the balance is altered either by deficiency or dysfunction.

Current and future research efforts center about defining exact hypersensitivity and/or immunodeficiency mechanisms in specific diseases, developing diagnostic assays that have individual patient relevance and finding more specific agents that can regulate or eliminate aberrant immune responses while leaving the rest of the system intact. Research opportunities abound in the broadening area of clinical immunology.

SUMMARY The immune response is designed to interact with the environment to protect the host

against pathogenic invaders. Immune-based diseases are either because of a lack of specific elements (immune

deficiency) or excess activity (hypersensitivity). 1. The chief function of the immune system is to distinguish between self and nonself. 2. The immune system consists of two overlapping compartments: the innate immune

system and the adaptive immune system. 3. The antigenic specificity of the adaptive immune system is due to antigen-specific

receptors. 4. The generation of antigen-binding diversity occurs prior to antigen exposure through a

DNA rearrangement process called VDJ joining. 5. To generate an active immune response against a certain antigen, a small number of B

and T cell clones that bind to the antigen with high affinity undergo activation, proliferation, and differentiation into plasma cells (for B cells) or activated T cells. This process is called „clonal selection‟.

6. The adaptive immune system has memory, meaning that the response against an antigen is much greater after the first exposure.

7. The immune system is tightly regulated.

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CELLS AND ORGANS OF THE IMMUNE SYSTEM. INNATE IMMUNITY

Immune system cells are derived from pluripotent hematopoietic stem cells in the bone marrow. These cells can be functionally divided into groups that are involved in two major categories of immune responses: innate (natural) and acquired. Innate immunity is present

from birth and consists of non-specific components. Acquired immunity by definition requires recognition specificity to foreign (non-self) substances. The major properties of the acquired immune response are specificity, memory, adaptiveness, and discrimination between self and non-self.

The acquired immune response is subdivided into humoral and cellular immunity, based on participation of two major cell types. In Humoral Immunity, B lymphocytes synthesize and secrete antibodies. Cellular Immunity (CMI) involves effector T lymphocytes which secrete immunoregulatory factors following interaction with antigen presenting cells (APCs).

Figure. The developmental pathway of pluripotent bone marrow stem cells. Coico

and Sunshine, 2009. Fig. 2.1

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Figure. The interrelationship between innate and acquired immunity. An intricate

communication system allows components of innate and acquired immunity to work in concert to combat infectious disease. Coico and Sunshine, 2009. Fig. 2.12.

Cluster of Differentiation (CD): Cell surface molecules are identifiable by monoclonal

antibodies. In humans, these molecules have been given number designations. The acronym CD describes the cluster of antigens with which the antibody reacts; the number describes the order in which it was discovered. As of 2010, the list of determinants officially identified 350 individual and unique markers (link to Human CD Molecules). Surface expression of a particular CD molecule may not be specific for just one cell or even a cell lineage. However, many are useful for characterization of cells.

CD-specific monoclonal antibodies have been useful for 1) determining the functions of CD proteins; 2) identifying the distribution of CD proteins in different cell populations in normal individuals; 3) measuring changes in the proportion of cells carrying these markers in patients with disease (e.g. decrease in CD4+ T cells is a hallmark of HIV infection); 4) developing therapeutic measures for increasing or decreasing the numbers or activities of certain cell populations.

Reticuloendothelial System

Cells of the RES provide natural immunity against microorganisms by 1) a coupled process of phagocytosis and intracellular killing, 2) recruiting other inflammatory cells through

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the production of cytokines, and 3) presenting peptide antigens to lymphocytes for the production of antigen-specific immunity. The RES consists of 1) circulating monocytes; 2) resident macrophages in the liver, spleen, lymph nodes, thymus, submucosal tissues of the respiratory and alimentary tracts, bone marrow, and connective tissues; and 3) macrophage-like cells including dendritic cells in lymph nodes, Langerhans cells in skin, and glial cells in the central nervous system.

Leukocytes Leukocytes provide either innate or specific adaptive immunity. These cells are derived

from myeloid or lymphoid lineage. Myeloid cells include highly phagocytic, motile neutrophils, monocytes, and macrophages that provide a first line of defense against most pathogens. The other myeloid cells, including eosinophils, basophils, and their tissue counterparts, mast cells, are involved in defense against parasites and in the genesis of allergic reactions. Cells from the lymphoid lineage are responsible for humoral or cell mediated immunity.

Myeloid Cells Neutrophils: Neutrophils are the most highly adherent, motile, phagocytic leukocytes and

are the first cells recruited to acute inflammatory sites. They ingest, kill, and digest pathogens, with their functions dependent upon special proteins, such as adherence molecules, or via biochemical pathways (respiratory burst).

Eosinophils: Eosinophils defend against parasites and participate in hypersensitivity

reactions via cytotoxicity. Their cytotoxicity is mediated by large cytoplasmic granules, which contain eosinophilic basic and cationic proteins.

Basophils/Mast cells: Basophils, and their tissue counterpart mast cells, produce

cytokines that help defend against parasites, and also cause allergic inflammation. These cells display high affinity surface membrane receptors for IgE antibodies, and have many cytoplasmic granules containing heparin and histamine. The cells degranulate when cell-bound IgE antibodies are crosslinked by antigens, and produce low-molecular weight vasoactive mediators (e.g. histamine).

Monocytes/Macrophages: Monocytes and macrophages are involved in phagocytosis

and intracellular killing of microorganisms. Macrophages are differentiated monocytes, which are one of the principal cells found to reside for long periods in the RES. These monocytes/macrophages are highly adherent, motile and phagocytic; they marshal and regulate other cells of the immune system, such as T lymphocytes; they serve as antigen processing-presenting cells.

Dendritic Cells: Dendritic cells provide a link between innate and adaptive immunity by interacting with T cells in a manner to deliver strong signals for development of memory responses. Dendritic cells recognize foreign agents and pathogens through a series of pattern recognition receptors (non-specific), and are able to present antigen to both T helper and T cytotoxic cells to allow those lymphocytes to mature towards functionality.

Lymphoid Cells

Lymphoid cells provide efficient, specific and long-lasting immunity against microbes/pathogens and are responsible for acquired immunity. Lymphocytes differentiate into three separate lines: (1) thymic-dependent cells or T lymphocytes that operate in cellular and humoral immunity; (2) B lymphocytes that differentiate into plasma cells to secrete antibodies; and (3) natural killer (NK)

B Lymphocytes: B lymphocytes differentiate into plasma cells to secrete antibodies. The

genesis of mature B cells from pre-B cells is antigen-independent. The activation of B cells into antibody producing/secreting cells (plasma cells) is antigen-dependent. Mature B cells can have 1-1.5 x 105 receptors for antigen embedded within their plasma membrane. Once specific antigen binds to surface Ig molecule, the B cells differentiate into plasma cells that produce and secrete antibodies of the same antigen-binding specificity. If B cells also interact with T helper cells, they proliferate and switch the isotype (class) of immunoglobulin that is produced, while

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retaining the same antigen-binding specificity. T helper cells are thought to be required for switching from IgM to IgG, IgA, or IgE isotypes. In addition to antibody formation, B cells also process and present protein antigens.

T Lymphocytes: T lymphocytes are involved in the regulation of the immune response

and in cell mediated immunity, and help B cells to produce antibody. Mature T cells express antigen-specific T cell receptors (TCR). Every mature T cell also expresses the CD3 molecule, which is associated with the TCR. In addition mature T cells usually display one of two accessory molecules, CD4 or CD8, which define whether a T cell will be a helper T lymphocyte, or a cytotoxic T lymphocyte (CTL). The TCR/CD3 complex recognizes antigens associated with the major histocompatibility complex (MHC) molecules on target cells (e.g. virus-infected cell).

Development of T lymphocytes

During differentiation in the thymus, immature T cells undergo rearrangement of their TCR α and β genes to generate a diverse set of clonotypic TCRs. Immature thymocytes are selected for further maturation only if their TCRs do not interact with self-peptides presented in the context of self-major histocompatibility complex (MHC) molecules on antigen presenting cells.

T Helper Cells: T helper cells (Th) are the primary regulators of T cell- and B cell-

mediated responses. They 1) aid antigen-stimulated subsets of B lymphocytes to proliferate and differentiate toward antibody-producing cells; 2) express the CD4 molecule; 3) recognize foreign antigen complexed with MHC class II molecules on B cells, macrophages or other antigen-presenting cells; and 4) aid effector T lymphocytes in cell-mediated immunity.

Currently, it is believed that there are many helper subsets of importance. T helper 1 (Th1) cells aid in the regulation of cellular immunity, and T helper 2 (Th2) cells aid B cells to produce certain classes of antibodies (e.g., IgA and IgE). The functions of these subsets depend upon the specific types of cytokines that are generated, for example interleukin-2 (IL-2) and interferon-gamma (IFN-gamma) by Th1 cells; IL-4, IL-6 and IL-10 by Th2 cells. Th17 cells,

characterized by IL-17 secretion, are thought to be involved as effector cells for autoimmune disease progression, and protect surfaces (skin, gut) from extracellular bacteria. Tfh cells (follicular helper T cells) also provide help to B cells enabling them to develop into antibody-

secreting plasma cells. They function inside of follicular areas of lymph nodes. Finally, although no longer prevalent in the literature, a subclass called Th3 cells were historically identified as

secreting IL-4 and TGF-β to provide help for IgA production; they were thought to be suppressive for Th1 and Th2 cells.

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Cytotoxic Cells: T cytotoxic cells (CTLs) are cytotoxic against tumor cells and host cells infected with intracellular pathogens. These cells 1) usually express CD8, and, 2) destroy infected cells in an antigen-specific manner that is dependent upon the expression of MHC class I molecules on antigen presenting cells.

T Regulatory Cells: T regulatory cells (Tregs) affect T cell response, with many cells

characterized as CD4+CD25+, TGF-β secretors. Tregs regulate/suppress other T cell activities, and help prevent development of autoimmunity.

Natural Killer T Cells: Natural killer T cells (NKT) are a heterogeneous group of T cells

that share properties of both T cells and natural killer (NK) cells. These cells recognize an antigenpresenting molecule (CD1d) that binds self- and foreign lipids and glycolipids. They constitute only 0.2% of all peripheral blood T cells. The term “NK T cells” was first used in mice to define a subset of T cells that expressed the natural killer (NK) cell-associated marker NK1.1 (CD161). It is now generally accepted that the term “NKT cells” refers to CD1d-restricted T cells coexpressing a heavily biased, semi-invariant T cell receptor (TCR) and NK cell markers. Natural killer T (NKT) cells should not be confused with natural killer (NK) cells.

Natural Killer Cells: NK cells are large granular “innate” lymphocytes that nonspecifically

kill certain types of tumor cells and virus-infected cells. NK cells share many surface molecules with T lymphocytes. These circulating large granular lymphocytes are able to kill “self” in the absence of antigen-specific receptors. NK cells are especially effective against viral infected cells, and keep the expansion of virus in check until adaptive immunity kicks in. In this regard, they also secrete interferon-gamma, which is an effective immunoregulator. NK cells can also kill via antibody-dependent cellular cytotoxic mechanisms (ADCC) via their Fc receptors. NK cells express a large number of receptors that deliver either activating or inhibitory signals, and the relative balance of these signals controls NK cell activity.

Antigen Presenting Cells (APCs) are found primarily in the skin, lymph nodes, spleen

and thymus. They may also be present throughout the diffuse lymphoid system. Their main role is to present antigens to antigen-sensitive lymphoid cells. APCs may be characterized by their ability to phagocytose antigens, location in body, and expression of Major Histocompatibility Complex (MHC) related molecules. Two main types of APCs are Dendritic Cells and Macrophages. Of note, B cells are a special class of APCs; because they have antigen-specific antibody receptors they are enabled to internalize and process targeted antigens.

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Lymphoid Organs

The lymphatic organs are tissues in which lymphocytes mature, differentiate and proliferate. Lymphoid organs are comprised of epithelial and stromal cells arranged either into discretely capsulated organs or accumulations of diffuse lymphoid tissue. The primary (central) lymphoid organs are the major sites of lymphopoiesis, where B and T lymphocytes differentiate from stem cells into mature antigen recognizing cells. The secondary lymphoid organs, therefore, are those tissues in which antigen-driven proliferation and differentiation take place.

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Historically, the primary lymphoid organ was first discovered in birds, in which B cells undergo maturation in the bursa of Fabricius, an organ situated near the cloaca. Humans do not have a cloaca, nor do they possess a bursa of Fabricius. In embryonic life, B cells mature and differentiate from hematopoietic stem cells in the fetal liver. After birth, B cells differentiate in the bone marrow. Maturation of T cells occurs in a different manner. Progenitor cells from the bone marrow migrate to the thymus where they differentiate into T lymphocytes. The T lymphocytes continue to differentiate after leaving the thymus, and are driven to do so by encounter with specific antigen in the secondary lymphoid organs.

Primary Lymphoid Organs Thymus Gland: The lymphoid organ in which T lymphocytes are educated, mature and

multiply. It is a lymphoepithelial organ composed of stroma (thymic epithelium) and lymphocytes, almost entirely of the T-cell lineage. This is where T lymphocytes learn to recognize self antigens as self, and where these cells differentiate and express specific receptors for antigen. Only 5-10% of maturing lymphocytes survive and leave the thymus.

Fetal Liver and Adult Bone Marrow: Islands of hematopoietic cells in the fetal liver and in the adult bone marrow give rise directly to B lymphocytes

Secondary Lymphoid Organs The spleen and lymph nodes are the major secondary lymphoid organs. Additional

secondary lymphoid organs include the tonsils, appendix, and Peyer‟s patches. Aggregates of cells in the lamina propria of the digestive tract lining may also be included in this category, as well as any tissue described as MALT (mucosa-associated lymphoid tissue), GALT (gut-associated lymphoid tissue) or BALT bronchus-associated lymphoid tissue). Last but not least, the bone marrow can serve as an important secondary lymphoid organ. In addition to being a site of B cell generation, the bone marrow contains many mature T cells and plasma cells.

Figure. Distribution of lymphoid tissues in the body. Actor, Elsevier’s Integrated

Immunology and Microbiology. 2012

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Lymph Node: Lymph nodes form part of the network which filters antigen from tissue fluid or lymph during its passage from the periphery to the thoracic duct. Histologically, the lymph node is composed of a B cell cortex containing primary and secondary follicles, a T cell paracortex, and a central medulla which contains cords of lymphoid tissue.

Spleen: The spleen is a filter for blood, and is actively involved in the removal of dying

and dead erythrocytes. There are two main types of tissue; red pulp and white pulp. The white pulp contains the lymphoid tissue, arranged around a central arteriole as a periarteriolar lymphoid sheath (PALS). The PALS is composed of T and B cell areas, and contains germinal

centers. Dendritic reticular cells and phagocytic macrophages can be found in germinal centers where they work to present antigen to lymphocytes.

Review your histology chapters dealing with Hematopoiesis and the Immune System!

Clinical Vignette - Congenital Asplenia (Case 30 in Geha and Notarangelo): Mr. and

Mrs. Vanderveer had five children. Their 10 month old daughter developed a cold, followed by upper respiratory infection. The child became feverish, convulsive and died; the causative agent was Haemophilus influenza which was isolated from the throat and cerebrospinal fluid. At autopsy she was found to have no spleen. How does the lack of a spleen affect B cell function, and what implications does this have towards immune responses to infective agents? In adults? In children?

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F) Study questions for class discussion

1. Pathogens are caught by specialized immune organs with a surveillance function. Describe the filtration mechanism of one such organ. From where do microbes originate that are trapped by this filter?

2. Name one characteristic of bacteria that is used by cells of innate immune responses to

detect them. How is this feature recognized? Name one cell with innate detection and response capabilities.

3. Explain why Gram negative bacteria like E.coli cannot prevent detection by the

macrophage LPS receptor and thus prevent phagocytosis. 4. Explain why neutrophils and macrophages typically must exit the blood circulation in

order to attempt phagocytic eradication of a bacterial infection. Why can they not fight most bacterial infections by remaining in the blood circulation?

5. List at least 3 distinct microbicidal mechanisms by which activated macrophages kill

endocytosed bacteria.

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6. What organ is depicted on a presented slide? Explain the answer (define/give a description for the structures).

7. What organ is depicted on a presented slide? Explain the answer (define/give a description for the structures).

Organ name

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2. ANTIGENS. MHC STRUCTURE AND ACTIVITIES

A) Subtopics

1. Antigens. Definition. Chemical nature. Structure. Classification of antigens. 2. Antigen determinants (epitops). Definition. Chemical nature. Structure. Types of determinants. Factors influencing antigen power. 3. Properties of antigens. Specificity types. 4. Mechanisms of antigen persisting in the body (antigen ways of entry into the body, localization, ways of elimination). 5. Presentation of endogenous antigens to immune cells. 6. Presentation of exogenous antigens to immune cells

B) Objectives

1. To learn the molecular attributes and properties of compounds which render them immunogenic and antigenic 2. To compare and contrast immunogen, antigen and hapten 3.To describe the factors influencing immunogenicity 4. To define the chemical nature of immunogens 5. To compare the structures of T-independent and T-dependent antigens 6. To introduce the concept of hapten-carrier conjugates and to describe their structure 7. To characterize antigenic determinants 8. To introduce the concept of superantigens 9. To understand the process of antigen presentation

C) Keywords

Immunogen, antigen, hapten, epitope, adjuvant.

D) Reading:

Khaitov R. M. Immunology (+CD-ROM). GEOTAR-Media Publishing, Moscow, 2000

Abul Abbas, Andrew H. Lichtman, Shiv Pillai. Cellular and Molecular Immunology (7th

ed.) Philadelphia : Elsevier/Saunders, 2012 Owen J., Punt J, Stranford S. Kuby Immunology. 7th ed. New York: W.H. Freeman and

Company, 2013 R.S. Geha and Notarangelo, L. Case Studies in Immunology: A Clinical Companion.

(6th ed.) Garland Publishing, New York, 2012. Web Resource: http://www.immunology-allergy.org/students

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ANTIGENS

I. DEFINITIONS

A. Immunogen: A substance that induces a specific immune response. B. Antigen (Ag): A substance that reacts with the products of a specific immune

response. C. Hapten: A substance that is non-immunogenic but which can react with the products of

a specific immune response. Haptens are small molecules which could never induce an immune response when administered by themselves but which can when coupled to a carrier molecule. Free haptens, however, can react with products of the immune response after such products have been elicited. Haptens have the property of antigenicity but not immunogenicity.

D. Epitope or Antigenic Determinant: That portion of an antigen that combines with the products of a specific immune response.

E. Antibody (Ab) A specific protein which is produced in response to an immunogen and

which reacts with an antigen. II. FACTORS INFLUENCING IMMUNOGENICITY A. Contribution of the Immunogen 1. Foreignness The immune system normally discriminates between self and non-self

such that only foreign molecules are immunogenic. 2. Size There is not absolute size above which a substance will be immunogenic.

However, in general, the larger the molecule the more immunogenic it is likely to be. 3. Chemical Composition In general, the more complex the substance is chemically the

more immunogenic it will be. The antigenic determinants are created by the primary sequence of residues in the polymer and/or by the secondary, tertiary or quaternary structure of the molecule.

4. Physical form In general particulate antigens are more immunogenic than soluble

ones and denatured antigens more immunogenic than the native form. 5. Degradability Antigens that are easily phagocytosed are generally more immunogenic.

This is because for most antigens (T-dependant antigens, see below) the development of an immune response requires that the antigen be phagocytosed, processed and presented to helper T cells by an antigen presenting cell (APC).

B. Contribution of the Biological System 1. Genetic Factors Some substances are immunogenic in one species but not in another.

Similarly, some substances are immunogenic in one individual but not in others ( i.e. responders and non-responders). The species or individuals may lack or have altered genes that code for the receptors for antigen on B cells and T cells or they may not have the appropriate genes needed for the APC to present antigen to the helper T cells.

2. Age Age can also influence immunogenicity. Usually the very young and the very old have a diminished ability to mount and immune response in response to an immunogen.

C. Method of Administration 1. Dose The dose of administration of an immunogen can influence its immunogenicity.

There is a dose of antigen above or below which the immune response will not be optimal. 2. Route Generally the subcutaneous route is better than the intravenous or intragastric

routes. The route of antigen administration can also alter the nature of the response 3. Adjuvants Substances that can enhance the immune response to an immunogen are

called adjuvants. The use of adjuvants, however, is often hampered by undesirable side effects such as fever and inflammation.

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III. CHEMICAL NATURE OF IMMUNOGENS A. Proteins The vast majority of immunogens are proteins. These may be pure proteins

or they may be glycoproteins or lipoproteins. In general, proteins are usually very good immunogens.

B. Polysaccharides Pure polysaccharides and lipopolysaccharides are good

immunogens. C. Nucleic Acids Nucleic acids are usually poorly immunogenic. However, they may

become immunogenic when single stranded or when complexed with proteins. D. Lipids In general lipids are non-immunogenic, although they may be haptens.

IV. TYPES OF ANTIGENS A. T-independent Antigens T-independent antigens are antigens which can directly

stimulate the B cells to produce antibody without the requirement for T cell help In general, polysaccharides are T-independent antigens. The responses to these antigens differ from the responses to other antigens.

Properties of T-independent antigens

1. Polymeric structure These antigens are characterized by the same antigenic determinant repeated many times as illustrated in Figure:

2. Polyclonal activation of B cells Many of these antigens can activate B cell clones

specific for other antigens (polyclonal activation). T-independent antigens can be subdivided into Type 1 and Type 2 based on their ability to polyclonally activate B cells. Type 1 T-independent antigens are polyclonal activators while Type 2 are not.

3. Resistance to degradation T-independent antigens are generally more resistant to

degradation and thus they persist for longer periods of time and continue to stimulate the immune system.

B. T-dependent Antigens T-dependent antigens are those that do not directly stimulate

the production of antibody without the help of T cells. Proteins are T-dependent antigens. Structurally these antigens are characterized by a few copies of many different antigenic determinants as illustrated in the Figure below:

V. HAPTEN-CARRIER CONJUGATES A. Definition Hapten-carrier conjugates are immunogenic molecules to which haptens

have been covalently attached. The immunogenic molecule is called the carrier. B. Structure tructurally these conjugates are characterized by having native antigenic

determinants of the carrier as well as new determinants created by the hapten (haptenic determinants) as illustrated in the Figure below. The actual determinant created by the hapten

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consists of the hapten and a few of the adjacent residues, although the antibody produced to the determinant will also react with free hapten. In such conjugates the type of carrier determines whether the response will be T-independent or T-dependent.

VI. ANTIGENIC DETERMINANTS A. Determinants recognized by B cells 1. Composition Antigenic determinants recognized by B cells and the antibodies

secreted by B cells are created by the primary sequence of residues in the polymer (linear or sequence determinants) and/or by the secondary, tertiary or quaternary structure of the molecule (conformational determinants).

2. Size In general antigenic determinants are small and are limited to approximately 4-8

residues. (amino acids and or sugars). The combining site of an antibody will accommodate an antigenic determinant of approximately 4-8 residues.

3. Number Although, in theory, each 4-8 residues can constitute a separate antigenic

determinant, in practice, the number of antigenic determinants per antigen is much lower than what would theoretically be possible. Usually the antigenic determinants are limited to those portions of the antigen that are accessible to antibodies as illustrated in the Figure 4 (antigenic determinants are indicated in black).

Antigenic determinants on a carbohydrate antigen are usually less diverse than on a

protein antigen. Carbohydrate antigens are found on bacterial cell walls and on red blood cells (the ABO blood group antigens). Protein antigens are complex because of the variety of three-dimensional shapes that proteins can assume, and are especially important for the immune responses to viruses and worm parasites. It is the interaction of the shape of the antigen and the complementary shape of the amino acids of the antigen-binding site that accounts for the chemical basis of specificity (Figure).

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Figure: A typical protein antigen has multiple antigenic determinants, shown by the

ability of T cells with three different specificities to bind to different parts of the same antigen

Although the figure above shows T cell receptors interacting with antigenic determinants

directly, the mechanism that T cells use to recognize antigens is, in reality, much more complex. T cells do not recognize free-floating or cell-bound antigens as they appear on the surface of the pathogen. They only recognize antigen on the surface of specialized cells called antigen-presenting cells. Antigens are internalized by these cells. Antigen processing is a mechanism that enzymatically cleaves the antigen into smaller pieces. The antigen fragments are then brought to the cell‟s surface and associated with a specialized type of antigen-presenting protein known as a major histocompatibility complex (MHC) molecule. The MHC is the

cluster of genes that encode these antigen-presenting molecules. The association of the antigen fragments with an MHC molecule on the surface of a cell is known as antigen presentation and results in the recognition of antigen by a T cell. This association of antigen

and MHC occurs inside the cell, and it is the complex of the two that is brought to the surface. The peptide-binding cleft is a small indentation at the end of the MHC molecule that is furthest away from the cell membrane; it is here that the processed fragment of antigen sits. MHC molecules are capable of presenting a variety of antigens, depending on the amino acid sequence, in their peptide-binding clefts. It is the combination of the MHC molecule and the fragment of the original peptide or carbohydrate that is actually physically recognized by the T cell receptor

B. Determinants recognized by T cells 1. Composition Antigenic determinants recognized by T cells are created by the primary

sequence of amino acids in proteins. T cells do not recognize polysaccharide or nucleic acid antigens. This is why polysaccharides are generally T-independent antigens and proteins are generally T-dependent antigens. The determinants need not be located on the exposed surface of the antigen since recognition of the determinant by T cells requires that the antigen be proteolytically degraded into smaller peptides. Free peptides are not recognized by T cells, rather the peptides associate with molecules coded for by the major histocompatibility complex (MHC) and it is the complex of MHC molecules + peptide that is recognized by T cells.

2. Size In general antigenic determinants are small and are limited to approximately 8-15

amino acids.

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3. Number Although, in theory, each 8-15 residues can constitute a separate antigenic determinant, in practice, the number of antigenic determinants per antigen is much less than what would theoretically be possible. The antigenic determinants are limited to those portions of the antigen that can bind to MHC molecules. This is why there can by differences in the responses of different individuals.

VII. SUPERANTIGENS

When the immune system encounters a conventional T-dependent antigen, only a small fraction (1 in 104 -105) of the T cell population is able to recognize the antigen and become activated (monoclonal/oligoclonal response). However, there are some antigens which polyclonally activate a large fraction of the T cells (up to 25%). These antigens are called superantigens(Figure below).

Examples of superantigens include: Staphylococcal enterotoxins (food poisoning),

Staphylococcal toxic shock toxin (toxic shock syndrome), Staphylococcal exfoliating toxins (scalded skin syndrome) and Streptococcal pyrogenic exotoxins (shock). Although the bacterial superantigens are the best studied there are superantigens associated with viruses and other microorganisms as well.

The diseases associated with exposure to superantigens are, in part, due to hyper activation of the immune system and subsequent release of biologically active cytokines by activated T cells.

VIII. DETERMINANTS RECOGNIZED BY THE INNATE IMMUNE SYSTEM

Determinants recognized by components of the innate (nonspecific) immune system differ from those recognized by the adaptive (specific) immune system. Antibodies, and the B and T cell receptors recognize discrete determinants and demonstrate a high degree of specificity, enabling the adaptive immune system to recognize and react to a particular pathogen. In contrast, components of the innate immune system recognize broad molecular patterns found in pathogens but not in the host. Thus, they lack a high degree of specificity seen in the adaptive immune system. The broad molecular patterns recognized by the innate immune system have been called PAMPS (pathogen associated molecular patterns) and the receptors for PAMPS are called PRRs (pattern recognition receptors). A particular PRR can recognize a molecular pattern that may be present on a number of different pathogens enabling the receptor to recognize a variety of different pathogens. Examples of some PAMPs and PRRs are illustrated in Table1.

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Table 1 Examples of pathogen associated molecular patterns and their receptors

PAMP PRR Biological Consequence of

Interaction

Microbial cell wall components

Complement Opsonization, Complement activation

Mannose-containing carbohydrates

Mannose-binding protein

Opsonization Complement activation

Polyanions Scavenger receptors Phagocytosis Lipoproteins of Gram +

bacteria Yeast cell wall components

TLR-2 (Toll-like receptor 2)

Macrophage activation, secretion of

inflammatory cytokines

Double stranded RNA TLR-3 Production of interferon (antiviral)

LPS (lipopolysaccharide of Gram negative

bacteria)

TLR-4 Macrophage activation, secretion of

inflammatory cytokines Flagellin (bacterial

flagella) TLR-5 Macrophage activation,

secretion of inflammatory cytokines

U-rich Single stranded viral RNA

TLR-7 Production of interferon (antiviral)

CpG containing DNA

TLR-9 Macrophage activation, secretion of inflammatory cytokines

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MHC STRUCTURE AND ACTIVITIES

HISTORICAL OVERVIEW

Cell-cell interactions of the adaptive immune response are critically important in protection from pathogens. These interactions are orchestrated by the immunological synapse whose primary components are the T cell antigen receptor (TCR) and the Major histocompatibility complex (MHC) molecule. The major function of the TCR is to recognize antigen in the correct context of MHC and to transmit an excitatory signal to the interior of the cell. Since binding of peptide within the MHC is not covalent, there are many factors while help stabilize the immunological synapse.

Gene products encoded in the MHC were first identified as being important in rejection of transplanted tissues. Furthermore, genes in the MHC were found to be highly polymorphic (i.e. in the population there were many different allelic forms of the genes). Studies with inbred strains of mice showed that genes in the MHC were also involved in controlling both humoral and cell-mediated immune responses. For example, some strains of mice could respond to a particular antigen but other strains could not and these strains differed only in one or more of the genes in the MHC. Subsequent studies showed that there were two kinds of molecules encoded by the MHC – Class I molecules and class II molecules which are recognized by different classes of T cells. Class I molecules were found on all nucleated cells (not red blood cells) whereas class II molecules were found only on antigen presenting cells, (APCs) which included dendritic cells, macrophages, B cells and a few other types (Figure).

It was not until the discovery of how the TCR recognizes antigen that the role of MHC

genes in immune responses was understood. The TCR was shown to recognize antigenic peptides in association with MHC molecules. T cells recognize portions of protein antigens that are bound non-covalently to MHC gene products. Cytotoxic T cells (Tc) recognize peptides bound to class I MHC molecules and helper T cells (Th) recognize peptides bound to class II MHC molecules. The three dimensional structures of MHC molecules and the TCR have been determined by X-ray crystallography so that a clear picture of how the TCR, MHC gene products and antigen interact has emerged.

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STRUCTURE OF CLASS I MHC MOLECULES The molecule

Class I MHC molecules are composed of two polypeptide chains, a long α chain and a short β chain called β2-microglobulin (figure). The α chain has four regions.

A cytoplasmic region, containing sites for phosphoylation and binding to

cytoskeletal elements. A transmembrane region containing hydrophic amino acids by which the

molecule is anchored in the cell membrane. A highly conserved α3 immunoglubilin-like domain to which CD8 binds. A highly polymorphic peptide binding region formed from the α1 and α2 domains.

The β2- microglobulin associates with the α chain and helps maintain the proper conformation of the molecule.

THE ANTIGEN-BINDING GROOVE

An analysis of which part of the class I MHC molecules is most variable demonstrates that variability is most pronounced in the α1 and α2 domains, which comprise the peptide binding region (Figure below).

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The structure of the peptide binding groove, revealed by X-ray crystallography, shows that the groove is composed of two α helices forming a wall on each side and eight β-pleated sheets forming a floor. The peptide is bound in the groove and the residues that line the groove make contact with the peptide (Figure below).

These are the residues that are the most polymorphic. The groove will accommodate peptides of approximately 8-10 amino acids long. Whether a particular peptide will bind to the groove will depend on the amino acids that line the groove. Because class I molecules are polymorphic, different class I molecules will bind different peptides. Each class I molecule will bind only certain peptides and will have a set of criteria that a peptide must have in order to bind to the groove. For example, Figure 5 shows that one class I molecule will bind peptides that have a leucine (L) as the carboxy-terminal amino acid and either tyrosine (Y) or phenylalanine (F) as the 4th amino acid from the carboxy-terminal end. As long as these two conditions are met a peptide will bind, regardless of what the other amino acids are. Similarly a different class I molecule will bind any peptide that has a tyrosine (Y) as the second amino acid from the amino-terminal end and either a valine (V), isoleucine (I) or leucine (L) at the carboxy-terminal end (Figure below).

Thus, for every class I molecule, there are certain amino acids that must be a particular

location in the peptide before it will bind to the MHC molecule. These sites in the peptide are referred to as the “anchor sites”. The ends of the peptide are buried within the closed ends of the class I binding groove while the center bulges out for presentation to the TCR.

Within the MHC there are 6 genes that encode class I molecules HLA-A, HLA –B, HLA-C, HLA-E, HLA-F and HLA-G. Among these HLA-A, HLA –B, and HLA-C are the most important

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and are most polymorphic. Table below shows the degree of polymorphism at each of these loci.

Locus Number of alleles

(allotypes)

HLA-A 218

HLA-B 439 HLA-C 96

HLA-E, HLA-F and HLA-G Relatively few alleles

STRUCTURE OF CLASS II MHC MOLECULES The molecule

Class II MHC molecules are composed of two polypeptide chains an α and a β chain of approximately equal length (Figure).

Both chains have four regions: A cytoplasmic region containing sites for phosphoylation and binding to

cytoskeletal elements A transmembrane region containing hydrophic amino acids by which the

molecule is anchored in the cell membrane A highly conserved α2 domain and a highly conserved β2 domain to which CD4

binds A highly polymorphic peptide binding region formed from the α1 and β1 domains

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The antigen-binding groove As with Class I MHC molecules, an analysis of which part of the class II MHC molecule is

most variable demonstrates that variability is most pronounced in the α1 and β1 domains, which comprise the peptide binding region (Figure).

The structure of the peptide binding groove, revealed by X-ray crystallography, shows

that, like class I MHC molecules, the groove is composed of two α helices forming a wall on each side and eight β-pleated sheets forming a floor. Both the α1 and β1 chain contribute to the peptide binding groove. The peptide is bound in the groove and the residues that line the groove make contact with the peptide. These are the residues that are the most polymorphic. The groove of Class II molecules is open at one end so that the groove can accommodate longer peptides of approximately 13-25 amino acids long with some of the amino acids located outside of the groove. Whether a particular peptide will bind to the groove will depend on the amino acids that line the groove. Because class II molecules are polymorphic, different class II molecules will bind different peptides. Like class I molecules, each class II molecule will bind only certain peptides and will have a set of criteria that a peptide must have in order to bind to the groove (i.e. “anchor sites”).

Within the MHC there are 5 loci that encode class II molecules, each of which contains a gene for an α chain and at least one gene for a β chain. The loci are designated as HLA-DP, HLA –DQ, HLA-DR, HLA-DM, and HLA-DO. Among these, HLA-DP, HLA –DQ, and HLA-DR are the most important and are most polymorphic. Table 2 shows the degree of polymorphism at each of these loci.

IMPORTANT ASPECTS OF MHC

Although there is a high degree of polymorphism for a species, an individual has maximum of six different class I MHC products and only slightly more class II MHC products (considering only the major loci).

Each MHC molecule has only one binding site. The different peptides a given MHC molecule can bind all bind to the same site, but only one at a time.

Because each MHC molecule can bind many different peptides, binding is termed degenerate.

MHC polymorphism is determined only in the germline. There are no recombinational mechanisms for generating diversity.

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MHC molecules are membrane-bound; recognition by T cells requires cell-cell contact.

Alleles for MHC genes are co-dominant. Each MHC gene product is expressed on the cell surface of an individual nucleated cell.

A peptide must associate with a given MHC of that individual, otherwise no immune response can occur. That is one level of control.

Mature T cells must have a T cell receptor that recognizes the peptide associated with MHC. This is the second level of control.

Cytokines (especially interferon-γ) increase level of expression of MHC. Peptides from the cytosol associate with class I MHC and are recognized by Tc

cells. Peptides from within vesicles associate with class II MHC and are recognized by Th cells. Polymorphism in MHC is important for survival of the species.

Locus Number of alleles

(allotypes)

HLA-DPA HLA-DPB

12 88

HLA-DQA HLA-DQB

17 42

HLA-DRA HLA-DRB1 HLA-DRB3 HLA-DRB4 HLA-DRB5

2 269 30 7 12

HLA-DM and HLA-DO Relatively few alleles

HOW DO PEPTIDES GET INTO THE MHC GROOVE?

Peptides from the cytosol associate with class I MHC and are recognized by CTL cells. The peptides enter the endoplasmic reticulum and bind in the MHC class I groove. This complex is then exported to the cell surface through the Golgi. MHC class II molecules are formed with an invariant (Ii) chain as a place holder while in the ER and Golgi. The Ii chain is cleaved and removed once the complex is in a vesicle. Peptides from within the vesicle associate with class II MHC and are then exported to the cell surface where they are recognized by Th cells.

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Figure . Assembly and disassembly of the peptide-loading complex at the ER membrane. De novo synthesized MHC I heavy chain (hc) initially assembles with the chaperones and ER-resident lectin calnexin. After association with β2m, calnexin is replaced by its soluble counterpart calreticulin. This MHC I subcomplex docks to tapasin-ERp57, which is recruited to the TAP translocation machinery by its unique, extra N-terminal domain TMD0. After peptide loading, a peptide–MHC complex is released and can traffic to the cell surface for inspection by cytotoxic T-lymphocytes. X-ray structures of tapasin-ERp57 (3F8U.pdb) [19] and MHC I (HLA-A*0201) (1DUY.pdb) [65] are shown in a cartoon style, whereas the putative structure of calreticulin, modeled on its homolog calnexin (2JHN.pdb) [66] is depicted as a surface representation. Calreticulin binds to the N-glycan of MHC I and via its proline-rich domain to ERp57. Structural and mechanistic details of the 3D model of the TAP transport complex are given in [9]. The extra, N-terminal TMD0 (four-helix bundle) is shown as surface model and single TMs are schematically illustrated.

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F) Study questions for class discussion

1. Describe clearly why MHC-I presentation proteins can only be loaded by peptides derived from cytoplasmic proteins and can NOT be loaded which peptides generated from extracellular antigen.

2. Explain the basis why CD4+ helper T cells can only respond to extracellular

antigen. 3. What is the correct sequence of events for activation of a B cell by a T-dependent

antigen?

4. Explain the difference between thymus-dependent (TD) and thymus-independent

(TI) antigens.

5. Cross-linking of immunoglobulin by antigen is essential but not always sufficient

to initiate the signal cascade for B-cell activation. Stimulation of additional receptors is also necessary for the full activation and differentiation of naive B cells. Describe these receptors and their ligands, and outline how they help activate the B cell.

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6. Give an example of a type 1 thymus-independent antigen (TI-1) and describe how such antigens bypass the requirement for T-cell help.

7. Repeat this for TI-2 antigens.

8. Some molecules seem to act as TI-1 antigens when part of a bacterial surface but

need T-cell help if purified and administered on their own. Explain why this might be so.

9. TRUE OR FALSE? TI-2 polysaccharide antigens are commonly used in vaccines administered to

infants because they stimulate strong antibody responses.

10. Give an example of how pathogens may use antigen presentation system to

evade immune response

Use the article provided below in this package:- Rupert Abele and Robert Tampe. Peptide trafficking and translocation across membranes in cellular signaling and self-defense strategies. Current Opinion in Cell Biology 2009, 21:508–515.

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11. What processes are depicted in the figure below? Give an explanation for all the numbered stages of the process. What are the major differences between left and right parts of the figure?

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APPENDIX

TIMELINE OF IMMUNOLOGY

Sources: Wikipedia, Timeline of Immunology; Immunology History IV, History of Immunology

Time Line (Keratin.com); Stewart Sell and Scott L. Rodkey, A short history of Immunopathology.

– Fever (Mesopotamia) - Recognition of “adaptive” protection against disease (Egypt, China)

– Anatomic identification of organs (Hippocrates) – Acquired resistance to poinsons (Mithridate Eupator, King of Pontus)

– Four cardinal signs of inflammation (Celsus) – “Snuff” variolation for smallpox (Sung Dynasty, China) – Bursa of birds described (Fabricius) – Lymphoid tissue identified in small intestine (Peyer)

- Lady Mary Wortley Montagu, the wife of the British ambassador to Constantinople,

observed the positive effects of variolation on the native population and had the technique performed on her own children.

- First demonstration of vaccination smallpox vaccination (Edward Jenner) - First description of the role of microbes in putrefaction and fermentation

(Theodore Schwann)

- Confirmation of the role of yeast in fermentation of sugar to alcohol (Charles Cagniard-Latour) 1840 - First "modern" proposal of the germ theory of disease (Jakob Henle)

- Demonstration of the contagious nature of puerperal fever (childbed fever) (Ignaz

Semmelweis) – Tuberculous granulomas identified (Rokitansky) – Langhans Giant Cells identified (Langhans)

1857-1870 - Confirmation of the role of microbes in fermentation (Louis Pasteur) - phagocytosis (Ernst Haeckel) - First aseptic practice in surgery using carbolic acid (Joseph Lister) - First demonstration that microbes can cause disease-anthrax (Robert Koch) - Mast cells (Paul Ehrlich) - Confirmation and popularization of the germ theory of disease (Louis Pasteur) – Birth of Cellular Pathology (Virchow) - 1881 -Theory that bacterial virulence could be attenuated by culture in vitro and

used as vaccines. Proposed that live attenuated microbes produced immunity by depleting

host of vital trace nutrients. Used to make chicken cholera and anthrax "vaccines" (Louis Pasteur)

- 1905 - Cellular theory of immunity via phagocytosis by macrophages and microphages

(polymorhonuclear leukocytes) (Elie Metchnikoff) - Introduction of concept of a "therapeutic vaccination". First report of a live

"attenuated" vaccine for rabies (Louis Pasteur) – Anti-rattlesnake venom discovered (Sewall) - Identification of bacterial toxins (diphtheria bacillus) (Pierre Roux and Alexandre

Yersin) 1888 - Bactericidal action of blood (George Nuttall)

- Demonstration of antibody activity against diphtheria and tetanus toxins. Beginning

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of humoral theory of immunity. (Emil von Behring) and (Shibasaburo Kitasato). Attempt to cure tetanus with passive immunotherapy (Behring)

- Demonstration of cutaneous (delayed type) hypersensitivity (Robert Koch) - Use of live bacteria and bacterial lysates to treat tumors-"Coley's Toxins"

(William B. Coley)

- Bacteriolysis (Richard Pfeiffer) - An antibacterial, heat-labile serum component (complement) is described (Jules

Bordet) - Antibody formation theory “side chain theory” “horror autotoxicus” (Paul Ehrlich) - blood groups (Karl Landsteiner) -8 Carl Jensen & Leo Loeb, Transplantable tumors - Immediate hypersensitivity anaphylaxis (Paul Portier) and (Charles Richet)

ul Portier & Charles Richet, Anaphylaxis - Intermediate hypersensitivity, the "Arthus reaction" (Maurice Arthus) - Opsonization (Almroth Wright & Stewart Douglas) - "Serum sickness" allergy (Clemens von Pirquet and (Bela Schick) – successful organ transplantation (Correl and Guthrie) – Clemens von Priquet, coined word “allergy” - Svante Arrhenius, coined the term immunochemistry - Emil von Dungern, & Ludwik Hirszfeld, Inheritance of ABO blood groups - Peyton Rous, Viral immunology theory - 2nd demonstration of filterable agent that caused tumors (Peyton Rous) - Clarence Little, Genetics theory of tumor transplantation -20 - Leonell Strong & Clarence Little, Inbred mouse strains

7 - hapten (Karl Landsteiner) - Cutaneous allergic reactions (Carl Prausnitz and Heinz Küstner) – Fleming found lysozyme and penicillin - Reticuloendothelial system (Aschoff) – Chemical mediators of inflammation (Lewis) - Lloyd Felton & GH Bailey, Isolation of pure antibody preparation

- Peter Gorer, Identification of the H-2 antigen in mice

1938 – Gammaglobulin identified (Tiselius and Kabat) - Antigen-Antibody binding hypothesis (John Marrack) - Identification of the Rh antigens (Karl Landsteiner and Alexander Weiner) – Hemolytic disease of the newborn (Rh antigens) (Levine) - Albert Coons, Immunofluorescence technique - Anaphylaxis (Karl Landsteiner and Merill Chase) - Adjuvants (Jules Freund and Katherine McDermott) - hypothesis of allograft rejection (Peter Medawar) - Passive transfer of cell mediated immunity (Chase) - identification of mouse MHC (H2) by George Snell and Peter A. Gorer – Twins do not demonstrate transplant rejection (Owen) - antibody production in plasma B cells (Astrid Fagraeus)

1949 - growth of polio virus in tissue culture, neutralization with immune sera, and demonstration of attenuation of neurovirulence with repetitive passage (John Enders) and (Thomas Weller) and (Frederick Robbins)

- immunological tolerance hypothesis (Macfarlane Burnet & Frank Fenner) - Richard Gershon and K Kondo, Discovery of suppressor T cells

- Ogden and Bruton, discovery of agammagobulinemia (antibody immunodeficiency)

- vaccine against yellow fever - Graft-versus-host disease (Morton Simonsen and WJ Dempster) - immunological tolerance hypothesis (Rupert Billingham, Leslie Brent, Peter

Medwar, & Milan Hasek)

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- James Riley & Geoffrey West, Discovery of histamine in mast cells -1959 - Niels Jerne, David Talmage, Macfarlane Burnet, Clonal selection theory - Clonal selection theory (Frank Macfarlane Burnet) - Discovery of interferon (Alick Isaacs & JeanLindermann)

-1962 - Discovery of human leukocyte antigens (Jean Dausset and Snell) -1962 - Discovery of antibody structure (independently elucidated by Gerald

Edelman and Rodney Porter)

- Discovery of lymphocyte circulation (James Gowans) - Discovery of lymphocyte "blastogenic transformation" and proliferation in

response to mitogenic lectins-phytohemagglutinin (PHA) (Peter Nowell)

-1962 Discovery of thymus involvement in cellular immunity (Jacques Miller) - Demonstration that glucocorticoids inhibit PHA-induced lymphocyte proliferation

(Peter Nowell) – Classification of immune mechanisms (Gell and Coombs) - Development of the plaque assay for the enumeration of antibody-forming cells

in vitro (Niels Jerne) (Albert Nordin)

- Jaques Oudin et al., antibody idiotypes 1964-1968 T and B cell cooperation in immune

response (Anthony Davis) 1964 – Mixed lymphocyte reaction (Bain, Vas, et al.)

- Discovery of the first lymphocyte mitogenic activity, "blastogenic factor" (Shinpei Kamakura) and (Louis Lowenstein) (J. Gordon) and (L.D. MacLean)

- Discovery of "immune interferon" (gamma interferon) (E.F. Wheelock) - Secretory immunoglobulins (Thomas Tomasi et al.) - Identification of T and B cells (Claman) - Identification of IgE as the reaginic antibody (Kimishige Ishizaka) - Passenger leukocytes identified as significant immunogens in allograft rejection

(William L. Elkins and Ronald D. Guttmann) – Accessory cell role in immune response (Mosier) - The lymphocyte cytolysis Cr51 release assay (Theodore Brunner) and (Jean-

Charles Cerottini)

– Immune response genes (Benacerraf and McDevitt) - Donald Bailey, Recombinant inbred mouse strains - Peter Perlmann and Eva Engvall at Stockholm University invented ELISA - Structure of the antibody molecule – Network theory for antibody control on immune response (Niels K. Jerne)

1974 - T-cell restriction to major histocompatibility complex (Rolf Zinkernagel and (Peter Doherty)

- Generation of the first monoclonal antibodies (Georges Köhler) and (César Milstein)

– Identification of natural killer cells (Kiessling, et al.) - Identification of somatic recombination of immunoglobulin genes (Susumu

Tonegawa) - Generation of the first monoclonal T cells (Kendall A. Smith)

0 – Immunoglobulin structure (Kabat) -1983 - Discovery and characterization of the first interleukins, 1 and 2 IL-1 IL-2

(Kendall A. Smith) - Discovery of the IL-2 receptor IL2R (Kendall A. Smith) – Appearance of AIDS on a global scale - Discovery of the T cell antigen receptor TCR (Ellis Reinherz) (Philippa Marrack)

and (John Kappler) (James Allison)

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- Discovery of HIV (Luc Montagnier) - The first single cell analysis of lymphocyte proliferation (Doreen Cantrell) and

(Kendall A. Smith) - Robert Good, Failed treatment of severe combined immunodeficiency (SCID,

David the bubble boy) by bone marrow grafting

-1987 - Identification of genes for the T cell receptor (Leroy Hood, et al.; Hedrick Davis, Mak)

85 Tonegawa, Hood et al., Identification of immunoglobulin genes, somatic generation of

Ig variable regions -onwards - Rapid identification of genes for immune cells, antibodies, cytokines

and other immunological structures

- Structure of MHC I defined (Wiley and Strominger) - Hepatitis B vaccine produced by genetic engineering - Th1 vs Th2 model of T helper cell function (Timothy Mosmann) - Discovery of biochemical initiators of T-cell activation: CD4- and CD8-p56lck

complexes (Christopher E. Rudd) – Catalytic antibody cleavage of peptide bonds (Sudhir Paul) - Yamamoto et al., Molecular differences between the genes for blood groups O

and A and between those for A and B 1990 - Gene therapy for SCID using cultured T cells

- Role of peptide for MHC Class II structure (Sadegh-Nasseri & Germain) – Hepatitis A vaccine developed - NIH team, Treatment of SCID using genetically altered umbilical cord cells - 'Danger' model of immunological tolerance (Polly Matzinger) - Regulatory T cells (Shimon Sakaguchi) -1998 - Identification of Toll-like receptors - Discovery of FOXP3 - the gene directing regulatory T cell development - Development of human papillomavirus vaccine (Ian Frazer) – Nobel Prize awarded to Bruce A. Beutler, Jules A. Hoffmann, and Ralph M.

Steinman for landmark discoveries indicating TLRs are gatekeepers of innate immunity