Antigen Antibody Reaction Seminar

8/3/2019 Antigen Antibody Reaction Seminar

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Antigen-Antibody

Reaction

Under Supervision of

Dr Punit Saraswat

HOD,Department of zoology

LMC,Jodhpur

Submitted by-

Monika Prajapat

MSc Previous Zoology



What is antigen ?

A substance that enters the body and stimulates

the production of an antibody to fight what the

immune system perceives as an invader.

An antigen is any substance that causes your

immune system to produce antibodies against it.

An antigen may be a foreign substance from the

environment such as chemicals, bacteria,viruses, or pollen.

An antigen may also be formed within the body,

as with bacterial toxins or tissue cells.





What is antibody ?

Antibodies (also known as immunoglobulins,abbreviated Ig) are gamma globulin proteins thatare found in blood or other bodily fluids of

vertebrates, and are used by the immunesystem to identify and neutralize foreign objects,such as bacteria and viruses.

They are typically made of basic structural

units²each with two large heavy chains and twosmall light chains²to form, for example,monomers with one unit, dimers with two units or pentamers with five units.



Antibodies are produced by a kind of white blood

cell called a plasma cell. There are several different types of antibody

heavy chains, and several different kinds of antibodies, which are grouped into different

''isotypes'' based on which heavy chain theypossess.

Five different antibody isotypes are known inmammals, which perform different roles, and

help direct the appropriate immune response for each different type of foreign object theyencounter.



Antibody Structure

Monomer: A flexible Y-shaped molecule withfour protein chains:

2 identical light chains

2 identical heavy chains

Variable Regions: Two sections at the end of Y¶s arms. Contain the antigen binding sites(Fab). Identical on the same antibody, but varyfrom one antibody to another.

Constant Regions: Stem of monomer and lower parts of Y arms.

Fc region: Stem of monomer only. Importantbecause they can bind to complement or cells.



Antibody Structure





I mmunoglobulin Classes

I. IgG

II. IgM

III. IgA

IV. IgD

V. IgE



ANTIGEN-ANTIBODY REACTIONS

The antigens and the antibodies combinespecifically with each other. This interactionbetween them is called Antigen-Antibody

reaction. It may be abbreviated as Ag-Ab reaction.

These form the basis for humoral immunity or antibody mediated immunity. These reactions

form the basis for detection of infectious diseasecausing agents and also some non-specific Ag¶slike enzymes. When Ag-Ab reactions occur invitro, they are known as serological reactions.



The reactions between Ag and Ab occur in

three stages.

1. Primary stage- This reaction involves formationof Ag-Ab complex. The reaction is rapid and itobeys the general laws of physical chemistryand thermodynamics. The two molecules are

held together by non-covalent forces,hydrogen bonding, ionic bonding andsometimes hydrophobic bonding.

2. The second stage leads to visible events like

precipitation, agglutination, lysis of cells, killingof Ag, neutralization of toxins, fixation of complement and enhancement of phagocytosis.

3. The third stage includes destruction of Ag or its

neutralization.



Salient features of Ag-Ab reactions:

1) Immune complex

2) Specificity of Ag-Ab reaction

3) Binding sites of Ag and Ab

4) Binding forces of Ag and Ab

5) Avidity6) Bonus effect

7) Cross reaction



Measurement of Ag-Ab reactions:

Methods

Many methods are available for themeasurement of Ag¶s and Ab¶s participating inthe Ag-Ab reactions.

Measurement may be done in terms of mass or in terms of titer values. (The degree of dilution of asubstance such as an antibody, reflecting the strength of the solution. )

The two important parameters effectingserological tests are the specificity and thesensitivity .



A sensitive test should be able to measure

even very minute quantities of Ag or Ab.

Specificity refers to the ability of the test todetect the reactions between homologous

Ag¶s and Ab¶s and not with others.



The Ag-Ab reactions can be detected by

the following techniques.

1. Precipitation

2. Agglutination

3. Lysis and complement fixation

4. Neutralization test

5. Flocculation

6. Opsonisation

7. Immunofluorescence

8. Enzyme Immunosorbent assay

9. Radio allegro sorbent test10. Radio Immunosorbent test

11. Immunoblotting

12. Immunoprecipitation

13. ELISPOT



P

recipitation reactions:

When a soluble Ag combines with its Ab in the

presence of an electrolyte (NaCl) at a particular temperature and pH, it forms an insoluble

precipitate of Ag-Ab complex. The Ab causing

precipitation is called Precipitin.





NEUTRALIZATION TESTS

Virus neutralization test

Toxin-antitoxin ractions

FLOCCULATION

In these tests Ag-Ab reaction results in

visible floccules which do not sediment butremain dispersed in the medium.



AGGLUTINATION REACTIONS:

When a particular Ag is mixed with its Ab¶s in thepresence of electrolytes at a suitabletemperature and pH, the particles are clumped

or agglutinated. The Ab of the serum causes the cellular Ag¶s to

form clumps and these are called Agglutinins.

The particulate antigens that are aggregated are

termed Agglutinogens. This reaction occurs optimally when Ag¶s and

Ab¶s react in equivalent proportions.





Mechanism of Agglutination:

1. Slide agglutination

2. Tube agglutination

3. Haemagglutination inhibition test

4. Coombs test (anitglobulin test)

5. Passive agglutination test

6. Brucella agglutination test for Brucellosis

7. Cold agglutinatin test for Pneumonia,Malaria and Trypnosomiasis



ELISA (Enzyme Linked ImmunoSorbent

Assay)

ELISA is of 3types.

Indirect ELISA

Sandwich ELISA

Competitive ELISA



ELISPOT





Documents

Antigen Antibody Reaction Seminar