The document discusses antigen-antibody interactions and various immunological techniques. It explains that antigen-antibody binding is specific and involves non-covalent bonds between epitopes and antibody variable regions. It also describes affinity, avidity, cross-reactivity, precipitation, agglutination, radioimmunoassay, enzyme-linked immunosorbent assay, and how these techniques can be used for immunodiagnostics and detection of antigens or antibodies.

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
k1 = forward (association) rate constant
k-1 = reverse (dissociation) rate constant
where,
k1/k-1 = Ka, association constant and measure of affinity.
Hence
Ka = [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 Fab fragments
 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 prozone effect
 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
falciparum antigen.8 sept,2014,oxford journal, James
S.Hodge,David E.Lunar,Sheetij Dutta,Candy C
.John,10.1093/infdis/jiju225.
 Current approaches of fine mapping of antigen-antibody
interaction. 11July,2014,British society for
immunology,W.Mark Abott,David C.
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.

23. Owen, Judy; Punt, Jenni; Stanford, Sharon A.; Jones, Patricia
(2013): Kuby Immunology. Seventh Edition. W.H Freeman and
Company. New York. pp. 517-536. ISBN-13: 978-14292-1919-8.
Murphy, Kenneth (2012). Janeway's Immunobiology: 8th ed.
Chapter 15: Garland Science. pp. 611–668. ISBN 0815342438.
Chakravarty, Ashim K (2007): Immunology and
Immunotechnology. 2nd Edition. Oxford University Press. New
Delhi. pp 412-424. ISBN-13: 978-0-19-567688-4