Antigen antibody interactions play important role in immunological assays which help in detection of disease.Such interaction are of various types e.g.Precipitation,Flocculation, Agglutination, Complement fixation, ELISA,RIA, Immunoflourescence,Immunoprecipitation.

1. Antigen-Antibody reaction
Prepared by
Nidhi A Jodhwani

2.  Ag-Ab reaction is bimolecular association similar to
enzyme-substrate interaction.
 Association between Ag-Ab involves non-covalent
bonds between epitopes and variable region of
Antibodies.
 This interaction is very specific that it leads to
development of various immunological assays.
INTRODUCTION

3. Types of bonds involved

4.  Reaction is very specific.(some time cross reactivity
observed due to same antigenic property)
 When antigenic part of large molecule react with Ab
,whole molecule is agglutinated.
 There is no denaturation of Antigen or Antibody during
reaction.
 Ag-Ab complex is firm but reversible.The strength of
bond depends upon affinity (attraction) between Ag &
Ab.
 Both Ag & Ab are pequired for precipitation reaction.
General features

5. Types of Antigen-Antibody
reaction
1)Precipitation
2)Flocculation
3)Agglutination
4)Compliment fixation
5)ELISA
6)RIA
7)Immunoflourecence
8)Immuno precipitation

6.  Precipitation is the reaction in which a soluble antigen
reacts with soluble antibody to give insoluble product or
precipitate.
 Soluble antibodies =‘precipitins’
 Soluble antigens=‘precipitogens’
PRECIPITATION

7. MECHANISM OF PRECIPITATION
 Precipitation can be explained by Lattice hypothesis.
 This hypothesis was given by Marrack in 1934

8.  This reaction is greatly affected by concentration of
Antigen&Antibody
 This effect can be explained by precipitatin curve.

9.  In this curve three zones are oberved
1)Zone of antibody excess (Prozone)
2)Zone of equivalence
3)Zone of antigen excess (postzone)

10.  In this zone antigen concentration is very low compared to
antibody concentration as a result no large Antigen-
Antibody complex are formed
 No precipitation is observed
PROZONE

11. • In this zone precipitation is observed
maximum.
• Large visible Antigen-Antibody
complex are formed.
Zone of equivalence

12. • In this zone antigen concentration is very
much higher compared to antibody
concentration
• As a result Antigen-Antibody
complex are too small to
be precipitate.
POSTZONE

13. Application of precipitation reaction
 RID-radial immuno diffussion

14. Double diffusion

15.  immunoelectrophoresis

16.  Basic mechanism is same as same as the precipitation
reaction.
 If insoluble complex remains suspended in solution instead
of sedimentation the reaction is known as ‘flocculation’.
FLOCCULATION

17.  Interaction between antibody and a particulate
antigen results in visible clumping ,is known as
agglutination.
 The main difference between agglutination and
precipitation is about the size of antigen.
 In agglutination reaction,antigens are insoluble
AGGLUTINATION

18. Application of agglutination reaction
1)Bacterial agglutination
- In this patient’s serum is tested for the presence of Ab
against bacterial antigens.

19. 2)Hemagglutination
-If antigens are present on RBC are to be detected ,process is
known as hemagglutination.
e.g. ABO group typing

20. 3)Passive agglutination
-In this, soluble antigens are coated on carrier
particles and after addition of antibodies,
agglutination of carrier particles takes place.
Carrier particles
Artificial Biological
-Latex -RBC
-Charcoal
-polymethylmethylacrylate

22. • compliment proteins are able to bind
with ag-ab complex & are able to lyse
RBCs
compliment fixation test

25. • In this technique, flourescence property
of dyes are used to demonstrate ag-ab
reactions
 Direct. Indirect
Immunoflourescence

26. • Commonly used dyes are :
Flourescein isothiocynate-blue green
Lissamine rhodomine-orange red

27. • Enzyme Linked Immuno Sorbent Assay
• There are dour types of ELISA
1)Direct ELISA
2)Indirect ELISA
3)Sandwich ELISA
4)Competetive ELISA
ELISA

28. • Radio immuno assay
• In thistechniquee, radioactive isotopes
are used to demonstrate ag-ab reactions.
RIA

30. Two type:
1)Direct immnunoprecipitation:
In this ,antibodies are coated
with insoluble inert material
(microbeads)
Immunoprecipitation

31. 2)Indirectimmunoprecipitate
Here secondary antibodies are
coated with microbeads.