ANTIGEN, ANTIBODY AND COMPLEMENTS.TYPES OF IMMUNE RESPONSES AND HYPERSENSITIVITY REACTIONS.

Raju Kaiti

Optometrist, Dhulikhel Hospital-Kathmandu University Hospital

REFERENCES

Short text book of medical microbiology, 6th edition, Satish Gupte

Lippincott’s microbiology Robbin’s pathology Immunopathology of the eye by A. H. S. Rahi and A.

Garner Ocular Pathology by Myron Yanoff and Ben S. Fine Internet Class notes

IMMUNITY

Greek word Immunis:- Free from burden Sequence of cellular and molecular events

designed to rid the host of an offending stimulus

Pathogenic organism\toxic substances\cellular debris\ neoplastic cells

Immunology Science which deals with the body’s response

to antigenic challenge.

Deals with the vital immune system.

Immune system is an interacting set of specialized cells and proteins designed to identify and destroy foreign invaders or abnormal substances before they damage the body.

Two arms of immune system

1.Innate (or natural) immune systema. Non specific Physical barrier: skin, mucus Proteins in serum and in tissues: Lysozyme, interferon,

complements. (eg. In tears…….)

b. Specific Antibody mediated Cell mediated

2.Adaptive(or acquired)specific immune system

Active Passive1.Produced actively by the immune system of host

1.Received passively by the host and the immune system doesn’t participate.

2.Induced by infection or by contact with immunogen.

2.Conferred by introducing ready made antibody.

3. Immune response-durable and effective

3. Immune response-short lived and less effective

4.Immunity develops only after a lag period.

4.Immunity effective immediately.

5.Immunological memory presumed.

5.No immunological memory.

6.Serves no purpose in immunodeficient host.

6.Applicable in immuno-deficient host.

7.No inheritance of immunity.

7.May be acquired from mother

Innate Immunity Components :

Macrophages Granulocytes Natural killer cells Complement Other chemicals eg. HCl, Lysozymes

Characteristics: Immediate action Non-specific response

Adaptive Immunity

Humoral

B cells Antibodies Complements

Cell-mediated

Antigen Presenting Cells T cells

Characteristics: Specific response

Late response

Cells of Immune system

T-Lymphocytes Thymus derived lymphocytes Role in cellular or cell-mediated immunity. Constitutes 60-70% of peripheral lymphocytes Differentiation of T-cells

Helper T cells Essential to the differentiation of B-cells into plasma

cells and their subsequent secretion of Antibodies. Each helper T-cell is capable of activating hundreds of

specific B-cells

Suppressor T-cells :

inhibit the development of B-cells in to plasma cells

regulate the activity of killer T-cells and suppress the production of Abs when they

become excessive. Also suppress auto-immune responses.

Killer T-cells

Have specific receptor for antigenic determinants.

Killer T-cell migrate from lymphoid tissue to the site of foreign cell invasion where they secrete small protein, lymphokines.

Prevent the reproduction of invading micro-organisms, infected host cells or viruses inside host cells.

Memory T-cells

The T-cells that remain potentially active and viable even after the antigen has been inactivated.

Upon 2nd encounter memory cells proliferate, differentiate into plasma cells and secrete Abs so rapidly that the symptoms of the disease may not even be observed.

Humoral immunity Cellular immunity

15

Types of Immunity

Antigens Basically Exogenous

Occasionally may be derived from body’s own tissues

Protein molecules or part which have specific AA sequence folded in tertiary shapes.

Substances that stimulate Ab production when they react.

Molecular wt. : 8000 or more

Properties of antigens

Foreignness Size

Types :

Complete antigen Partial antigen

Hapten e.g lipid,nucleic acid

Two types:Complex hapten andSimple hapten

Immunogen Vs antigen All immunogens are antigens but not all the

antigens are immunogens.

Antibody

o Specific glycoprotein molecules generated by ß –cells in response to antigens.

o Also called immunoglobulins.

o Humoral substance found in serum,lymphs and other body fluids.

o Highly specific in nature.

Organs producing Antibodies

Spleen, lymphnodes and bone marrow

Tissues like peyer’s patches, appendix, thymus

These structures contains lymphocytes macrophages and plasma cells

FUNCTIONS

Neutralization of toxins.

Activation of complement (results in improved opsonisation)

Lysis of invading microorganisms.

Immunoglobulin

Immunoglobulins are synthesized by plasma cells and also by lymphocytes.

All antibodies are Immunoglobulins but all Immunoglobulins may not be antibodies.

Immunoglobulin is the structural and chemical concept while antibody is biological and functional concept.

Classification:# Types based on Size, Carbohydrate

content and amino acid analysis:

IgG IgM IgA IgD IgE

Immunoglobulin

IgG: comprises 70% of total Ig. Shortest half life of 21 days Lowest mol. Wt. and found in highest concn in body. crosses placenta and provides much of maternal antibody. Responsible for late immune response. Bivalent in structure. Four sub classes: IgG1, IgG2, IgG3, IgG4.

IgA:

•In body secretion like milk, tears, saliva, urine etc.

•Also called secretory immunoglobulins

•Antibacterial and antiviral

•Present as either monomer or dimer

•Majorly generated in bone marrow

IgM: Highest mol.wt Present in serum as pentamer Constitute only 10% of serum immunoglobin Can’t cross transplacental barrier. Responsible for early immune response.

IgE:

Play role in parasitic and allergic disease. Shortest half life. Present in small quantities.

Contd…

IgD:

Present in the surface of the lymphocytes.

Least abundant of all. Mainly intravascular

distribution.

Chemistry of immunoglobulins

All immunoglobulins composed of same basic units.

Consists two light (L) and two heavy (H) chains.

L chains and H chains linked together by a disulphide bond.

Two H chains linked similarly.

Enzyme action breaks the structure into three. Two identical Fab fragments Third Fc fragment Two classes of L chains – Kappa (k) and Lamda (λ) Five classes of H chains µ- IgM α- IgA γ- IgG δ- IgD ε- IgE

Different regions

Constant region ‘C’

Variable region ‘V’

Adjuvants are substances which enhance the immune response

Weak antigens also evoke high order of antibody production

Complements

Protein substance involved in immune response

Synthesized by hepatocytes, blood monocytes, epithelial cell of GI tract and tissue macrophages

Functions include opsonisation, target cytolysis, inflamation and immune complex clearence with lysis of bacterial cells

2 pathway of complement activation. complement system

classical alternateBrought about by Ag-Ab complex.

Involves activation of nine major proteins C1 to C9

Brought about by certain bacterial polysaccharides, endo-toxin

Activated by agregated IgA

Contd…

Refers to series of factors occuring in normal serum activated by Ag-Ab interaction

Concentration is fairly constant for each species of animal

10% of human serum globulin. Concentration decreased in acute glomerulo-nephritis,

serum sickness Concentration increased in carcinomatosis, coronary

occlusion and rheumatic fever

Components of Complement

Known to have nine distinct components

One of which have three protein subunits making total 11 proteins

C1: 3 proteins held by calcium ions.

Biosynthesis of Complement

C1 – synthesized in interstitial epithelium C2 and C4 – macrophages C5 and C8 – in spleen C3, C6 and C9 – in liver C7 – not known

Features of antigen antibody reactions

Reactions highly specific Entire molecules react and not fragment No de-naturation of antigen or antibody during reaction Combination is formed but reversible Both Ag and Ab participate in formation of agglutinates

or precipitates Ag and Ab may combine in varying proportion

Cross reactions Particular antibody may react with other antigens

also

Heterophile antigens Antigens those are cross reacting with other

antibodies

Heterophile antibodies Antibodies those are cross reacting with or

antigens

Antibody title highest dilution of patient serum where visible

antigen antibody reaction takes place

Factors influencing antibody production

Age Nutritional status Root of adminstration Size and no. of doses

Critical dose and immunological paralysis

Multiple antigens Adjuvants Immunosuperssive agents

Figure of Ag-Ab Reation

Immune Response

Specific reactivity induced in host by antigenic stimulus

Primary response Secondary responseHumoral

Cell-mediated

Slow, sluggish, short lived with a long lag phage and low antibody production, Predominantly IgM

Prompt, powerful, prolonged with much higher level of Ab production predominantly IgG

Ocular Immune Responses

Conjunctiva

Tear film: Washes away debris and irritants lysosyme, betalysin, lactoferrin, IgA

Well vascularized, Langerhans cells, dendritic cells and macrophages

Conjunctiva

Papillary reaction in allergic conjunctivitis

CORNEA

No localized immune processing

Immune Privilege: Normal limbal physiology, avascularity, absence of APCs and lymphatics, intact immunoregulatory systems of anterior chamber

Cornea

Transplantation Immunology: type of rejection reactions:

High success rate of graft (90%): Immune privilege

Failure of Immune system

Immune system

Hypersensitivity

(Overactive immune response)

Immunodeficiency

(ineffective immune response)

Autoimmunity

(mistaken recognition of self antigens)

Hypersensitivity Term used to describe immune responses

that cause host tissue damage Detrimental effect on hosts

Fever shock Inflammatory nature Spasm of smooth muscle Gastrointestinal and pulmonary disorders Fatal circulatory collapse

Hypersensitivity

State in which the introduction of an antigen into the body elicits an unduly severe immunological reaction.

4 types: -1. Anaphylaxis, atopic or Type I reaction.2. Cytotoxic or Type II3. Immune complex, Arthus-Type III4. Delayed hypersensitivity Type IV

Hypersensitivity

Type I Exaggerated IgE response to relatively harmless

environmental antigens

Genetic predisposition

Results in release of several active substances including histamine, slow reacting substance and an eosinophil chemo tactic factor

Type I

Eg: Hay fever, atopic dermatitis, systemic anaphylaxis Atopic conjunctivitis

Diagnosis: In vivo skin testing with batteries of allergens In vitro RAST test (quantitate specific IgE levels

Allergic conjunctivitis

Type II

Antibody mediated hypersensitivity against self cells or receptors or membranes

Mediated by IgG or IgM antibodies against tissue antigens, resulting in organ-specific antibody production

Type II

Antibody binds to cells or tissues and causes local complement activation, influx of leukocytes, and tissue destruction by: ADCC Degranulation by phagocytes Production of oxygen radicals

Type II Diagnosis:

Detect immunoglobulins on affected cells or tissues

Detect complement in affected tissueDetect autoantibody or auto reactive T

cells

Type II

eg

Mooren’s ulcer Hemolytic disease of the newbornGoodpasture syndromeHyper acute graft rejection

Type III

Due to high levels of circulating, soluble immune complexes overwhelming the ability of the mononuclear phagocyte system to remove them

Damage is caused by antigen-antibody complex.

Type III

The excess complexes deposit in various tissues and activate complement

Subsequent attempt by neutrophils to remove them results in degranulation and tissue damage.

Type III

Can take one of two forms according to whether the immune complex develops in circulating blood or in tissues

Arthus reaction Local manifestation in tissue

Serum sickness Systemic form of type III hypersensitivity

Type III

Eg. Arthus reaction, serum sickness, Lupus, Rheumatoid

arthritis, etc. Immune ring formation in cornea in Herpes simplex

keratitis

Diagnosis: very low levels of complements in blood, esp. c3 and

c4

Immune ring formation in herpes simplex keratitis

Peripheral corneal thinning in rheumatoid arthritis

Type IV No role of antibody or complement One aspect of cell mediated immunity Antigen activates specifically macrophages

and sensitized T-lymphocytes leading to secretions of lymphokines

Due to activity of thymus dependent lymphocytes and clinically has a delayed onset

Two types: Classical or Tuberculin type Granulomatous reactions

Type IVExample:

Allergic Dermatoconjunctivitis, disciform keratitis

Example Corneal graft rejection Sympathetic ophthalamitis Vogt Koyonagi Harada’s syndrome Optic neuritis Recurrent herpetic keratitis Bacterial, fungal, viral, protozoal and parasytic

infection.

69

AIDS Ocular manifestations

Kaposi’s sarcoma of conjunctiva CMV retinitis Recurrent infections Viral infections

Auto-immune Diseases Myasthenia gravis Pemphigus vulgaris Ocular cicatricial Pemphigoid Sympathetic ophthalmitis Phacogenic uveitis Multiple sclerosis Auto immune hemolytic

anemia Idiopathic thrombocytopenic

purpurae

Organ-specific

Idiopathic leucopenia Primary billiary cirrhosis Active chronic hepatitis Cryptogenic cirrhosis Ulcerative colitis SjÖgren’s syndrome Rheumatoid arthritis Dermatomyositis Scleroderma Discoid lupus erythematosus

Non-organ specific

Antibody-mediated Diseases

Vernal conjunctivitis : Mostly affects children & adolescents

Occurs only in warm season of year.

Produces giant papillae (cobblestone) of tarsal conjunctiva.

Rheumatoid Diseases affecting the eye Juvenile rheumatoid arthritis

Females>males

C/F uveitis extensive synechia formation Cataract Secondary glaucoma

Reiter’s diseases males>females

C/F Self limited papillary conjunctivitis Acute iridocyclitis or both eyes occasionally with

hypopyn.

76

Other antibody mediated Diseases

Systemic lupus erythematosus Occlusive vasculitis of nerve fiber layer of retina. Infarcts results in cytoid bodies or cotton-wool spots in

retina.

Pemphigus vulgaris Intraepithelial bullae of conjunctiva

Lens induced Uveitis

Rare condition associated with circulating Ab to lens protein.

In individuals whose lens capsule is permeable to to these protein as a result of trauma or other Diseases.

Cell mediated Diseases

Ocular sarcoidosis Panuveitis with inflammatory involvement of

optic nerve and retinal blood vessels. Acute iridocyclitis Conjunctival erythema.

Sympathetic ophthalmitis

Inflammation of 2nd eye after the other has been damaged by penetrating injury.

Symptoms Floating spots Loss of accommodative power. Ultimately may lead to

Pappilloedema and 20 glaucoma

Thank You!Thank You! Suggestions!Suggestions!