Antigen antibody interactions

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 J odhwani

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

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

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

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

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

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

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

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