Antigen antibody interaction

Antigen-antibody interaction, or antigen-antibody reaction, is a specific chemical interaction between antibodies produced by B cells of the white blood cells and antigens during immune reaction. It is the fundamental reaction in the body by which the body is protected from complex foreign molecules, such as pathogens and their chemical toxins. In the blood, the antigens are specifically and with high affinity bound by antibodies to form an antigen-antibody complex. The immune complex is then transported to cellular systems where it can be destroyed or deactivated.

1. PRESENTED BY
BIPUL JYOTI DAS
M.Sc BIOTECHNOLOGY
DIBRUGARH UNIVERSITY

2. Antigen-Antibody reaction is a bimolecular association
similar to enzyme-substrate interaction
The association between antigen-antibody involves
non-covalent bonds between antigenic determinants or
epitopes and variable regions of antibodies
The interaction is very specific that leads to the
development of various immunological assays

3. Hydrogen bond
Ionic bond
Hydrophobic bond
Vander Wall interaction

4. The combined strength of non-covalent interaction between a single
antigen binding site on an antibody and a single epiptope is the affinity
of antibody.
The association between a binding site on antibody(Ab) with a
monovalent antigen(Ag) is described as follows:
Ag + Ab⇆Ag-Ab
k
1= forward (association) rate constant
k
-1= reverse (dissociation) rate constant
where,
k
1/k
-1= K
a,association constant and measure of affinity.
Hence
K
a= [Ag-Ab]
[Ag] [Ab]

5. Avidity is the strength of multiple interaction between the
multivalent antigen and antibody
avidity of an Ab is a better measure of its binding capacity within
biological system (e.g., the reaction of an antibody with antigenic
determinants on a virus or bacterial cell) than the affinity of its
individual binding sites
high avidity can compensate for low affinity

6. When an antibody elicited by one antigen can react with an related
antigen, the phenomenon is called cross-reactivity
Such cross-reactivity occurs if two different antigens share an
identical or very similar epitope
The antibody’s affinity for the cross-reacting epitope is usually
less than that for the original epitope
ABO blood group is a good example of cross-reactivity

7. When antibody and soluble antigen interact in aqueous solution, it
form a lattice that eventually develops into a visible precipitate
Antibodies that aggregate soluble antigens are called precipitin
Formation of an Ag-Ab lattice depends on the valency of both the
antibody and antigen
The antibody must be bivalent; a precipitate will not form with
monovalent Fabfragments
The Ag must be either bivalent or polyvalent; that is, it must have
at least two copies of the same epitope, or have different epitopes
that react with different antibodies present in polyclonal antisera

9. Zone of antibody excess:Precipitation is inhibited and antibody
doesn't bind to antigen and can be detected in supernatent
Zone of equivalence:Antigen-antibody binding is optimum and
precipitation shows
Zone of antigen excess:Precipitation is inhibited and antigen not bound
to antibody can be detected in suprernatent

11. When antigen and antibody are diffused in Agar medium, a visible
line of precipitation will form in the zone of equivalence
Two types of immunodiffusion reactions can be used to determine
relative concentrations of antibodies or antigens to compare
antigens or to determine the relative purity of an antigen
preparation are
Radial immunodiffusion (the Mancini method)
Double immunodiffusion(the Ouchterlony method)

13. Immunoelectrophoresis:
The antigens are electrophoresed
in agarose, then the antibody
applied.

14. The interaction between antibody and a particulate antigen results
in visible clumping called agglutination
Antibodies that produce such reactions are called agglutinins.
Antibody excess can inhibit agglutination reactions, which is
called prozoneeffect
Antibodies that bind univalently cannot crosslink one Ag to
another

15. RBC’s mixed with antisera to the A or B blood group antigens on a slide,if
antigen is present on the cells, they agglutinate, forming a visible clump
on slide
Clumping of RBC’ less or other particles

16. It is modification of the agglutination reaction, called agglutination
inhibition, provides a highly sensitive assay for small quantities of an
antigen. It is used in pregnancy test.

17. Some of the techniques of immunoassay are:
Radioimmunoassay
Enzyme-Linked immunosorbent assay

18. One of the most sensitive techniques for detecting antigen or
antibody
Principle involves competitive binding of radiolabeled Ag and
unlabeled Ag to a high affinity Ab
Ratio of Ab to radioactive Ag is chosen such that the number of
epitopes presented by the labeled Ag always exceeds the total
number of Ab binding sites
This insures that any unlabeled Ag added to the sample mixture
will compete with radiolabeled Ag for the limited supply of Ab

21. Estimation of recent and long term malaria transmission in a
population by antibody testing to multiple Plasmodium
falciparumantigen.8 sept,2014,oxford journal, James
S.Hodge,DavidE.Lunar,SheetijDutta,CandyC
.John,10.1093/infdis/jiju225.
Current approaches of fine mapping of antigen-antibody
interaction. 11July,2014,British society for
immunology,W.MarkAbott,DavidC.
Lowe,DOI:10.1111/imm.12284.

22. Antigen-antibody interaction is vital process of our immune
system of the body . This chemical interaction elicits an immune
response in the body against the foreign substances. The
specificity of the interaction has lead to the development of a
variety of immunological assay which can be used for detection of
presence of antigen or antibody and widely used as
immunodiagnostics.

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