Chapter 20. Defenses Against Disease

Organs, Tissues & Cells of the Immune System

Nonspecific Defenses

Specific Defenses

Induced Immunity

Disorders of Immunity

The Immune System: protects against Diesease

• Nonspecific: defend against and/or attack any pathogen without need to develop special cells or chemicals; no immunological memory formed

• Specific: involves selection of special immune system cells that target specific pathogens; immunological memory results

The lymphatic Organs

thymus

spleen

red bone marrow

lymph nodes

• Primary Lymphatic Organs– sites of lymphocyte

formation and/or maturation

• Secondary Lymphatic Organs– sites where lymphocytes and

other immune system cells encounter and bind antigens

Primary Lymphatic Organs• Red Bone Marrow: site of all

blood cell formation including lymphocytes– B lymphocytes formed and

mature in red bone marrow

• Thymus: site of T-lymphocyte maturation– T lymphocytes formed in red

bone marrow, but mature in thymus

– T lymphocytes that leave thymus can mount an immune response, but tolerate “self”

Secondary Lymphatic Organs• Spleen

– filters blood and stores, contains lymphocytes that participate in immune responses

• Lymph Nodes– filter lymph, contains

lymphocytes that participate in immune responses

• Lymphatic Vessels– transport lymph to blood

stream, pass through lymph nodes on the way

Tissues & Cells of the Immune System

• Tonsils: aggregations of lymphatic nodules in the pharynx

• Peyer’s Patches: aggregations of lymphatic tissue in the wall of the intestine

• Appendix: concentrations of lymphatic tissue• Note: lymphatic tissue can be found in the loose

connective tissues throughout the body, especially in the walls of organs lined by mucus membranes

NonSpecific Body Defenses

• Physical Barriers• Inflammatory Reaction• Protective Body Cells• Protective Proteins

Barriers to Entry

• Skin and Mucus Membranes– secretions of these organs are toxic to bacteria (lysozymes,

acids)

– some organs have resident “beneficial” bacteria that exclude pathogens

Inflammatory Reaction

Protective Body Cells

• phagocytes: neutrophils, macrophages

• natural killer cells: lymphocytes that can attack pathogens and cancer cells without an immune response

Protective Proteins• Complement: Proteins that attack pathogens directly• Interferon: Proteins that are produced by virus infected

cells that signal nearby cells to activate antiviral infection mechanisms

Specific Defenses

B lymphocytes

produce antibodies (=antibody mediated or humoral immunity)

T lymphocytes

attack abnormal body cells, such as those infected with virus (=cell-mediated immunity)

Antibody Mediated Immunity

• clonal selection: only a B cell with the antigen receptor that can bind to the antigen is selected

• it undergoes proliferation (needs cytokines from helper T cells)

• some clonal cells become antibody producing plasma cells

• plasma cells undergo apoptosis when infection is destroyed, but other clone members remain behind as memory cells

Structure of IgG (antibody)

• Y-shaped protein

• each arm has a “heavy” (long) peptide and a “light” (short) peptide

• each peptide has a “constant and a variable region

• the variable region binds to the antigen

• there are 4 other classes of antibodies: IgM, IgA, IgD, IgE

Antibody Structure

Antibody

Cell-Mediated Immunity• Similar to Antibody mediated, but T Cells cannot

bind free antigen in body fluids, antigen must be “presented” by antigen presenting cells (APCs)

• T cell that can bind presented antigen is activated (selected)

• undergoes clonal expansion, produces cytokines and a variety of T cell types (killers, helpers, etc.)

• after immune response most T lymphocytes undergo apoptosis

• some T cells remain as memory cells

How T Cells “Kill”

Cytotoxic, I.e., “Killer” T Cells

attacking a cancer cell

Helper T Cells

• provide chemical signals, cytokines, that that regulate and enhance the function of other immune cells

• HIV virus attacks and destroys Helper T Cells, thereby destroying the immune system

Immunosuppression• HIV destroys immune system resulting in immune

deficiency• radiation, by destroying bone marrow, also

suppresses immunity• various environmental pollutants, dioxins, pesticides

suppress immunity• certain drugs, such as steroids, suppress the immune

system– immunosuppression is desirable in organ transplant

recipients, but not in most individuals

• some people are born with a part of their immune system not working

Induced Immunity

• Active immunity: acquired by infection• Artificial (induced) immunity: acquired by medical

intervention– active immunity: individual produces their own immunity

by being challenged with the “antigen”

– passive immunity: individual is given antibodies that convey immunity

Immunization (Vaccination)

University of Port Harcourt Teaching

Hospital Study, Port Harcourt,

Nigeria • 14 year old boy unconcious

with cerebral malaria in Nigeria

• 10.2 % of childhood deaths

Two year old with severe measles

• Measles infects 30 to 40 million children per year

• Measles kills over 500,000 children per year

• it costs $1 to immunize a child against measles

58%

26%

777,000 deaths worldwide

DPT = combined Diptheria, Pertussis, Tetanus vaccine

Childhood Mortality: Then & Now

Passive Immunity by Breastfeeding