2. Ag- Ab interaction
•The anitgens and the antibodies combine specifically with each
other. This interaction between them is called antigen-antibody
interaction.
•These form the basis for homoral and antibody mediated
immunity.
•The reaction between Ag and Ab occur in 3 stages:
1.In the first stage the reaction involves formation of Ag-Ab
complex
2.This leads to visible events like precipitation, agglutination etc.
3.The third stage includes destruction of Ag or its neutralization.
4. Salient features of Ag-Ab
interaction
Specificity of antibody
Immune complex
Binding site of antigen- antibody reaction
Binding fore of antigen- antibody reaction
Ag + Ab = Ag-Ab complex
6. Binding force or strength of Ag-Ab reaction
1. Affinity
2. avidity
3. Cross reactivity
• The bonds that hold the antigen to the antibody
combining site are all non covalent in nature.
These include hdrogen bonds, electrostatic bonds,
van der waals forces and hydrophobic bonds.
7. AGGLUTINATION REACTION
•The reaction between antibody and a particulate antigen results in visible
clumping called agglutination.
•Antibodies that produce such reactions are called agglutinins and the
antigens that aggregate are called agglutinogens.
8. Excess of an antibody also inhibits
agglutination reaction; this inhibition is
called prozone phenomemon.
Agglutination occurs optimally when
antigens and antibodies react in
equivalent proportions.
Incomplete or monovalent antibodies
do not show agglutination though the
bind with the antigen. They may act as
blocking antibodies, inhibiting
agglutination by the complete antibody
added subsequently.
12. Applications
1. Cross matching and blood grouping
2. Identification of bacteria eg. Serotyping of
salmonella typhi and paratyphi
3. To detect the presence and relative amount of
specific antibody in a patients serum.
4. Detection of unknown antigen in various
clinical specimens.
