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.
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
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
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
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.