The document discusses the antigen-antibody (Ag-Ab) reaction, which involves non-covalent bonds between epitopes and antibodies, leading to various immunological assays. It outlines different types of Ag-Ab reactions, such as precipitation, flocculation, agglutination, and different assay techniques like ELISA and RIA. The mechanisms, application, and features of these reactions are also explained, highlighting the specific interactions crucial for immunological testing.

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.