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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.

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Antigen antibody interactions

  1. 1. Antigen-Antibody reaction Prepared by Nidhi A Jodhwani
  2. 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. 3. Types of bonds involved
  4. 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. 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. 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. 7. MECHANISM OF PRECIPITATION  Precipitation can be explained by Lattice hypothesis.  This hypothesis was given by Marrack in 1934
  8. 8.  This reaction is greatly affected by concentration of Antigen&Antibody  This effect can be explained by precipitatin curve.
  9. 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. 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. 11. • In this zone precipitation is observed maximum. • Large visible Antigen-Antibody complex are formed. Zone of equivalence
  12. 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. 13. Application of precipitation reaction  RID-radial immuno diffussion
  14. 14. Double diffusion
  15. 15.  immunoelectrophoresis
  16. 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. 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. 18. Application of agglutination reaction 1)Bacterial agglutination - In this patient’s serum is tested for the presence of Ab against bacterial antigens.
  19. 19. 2)Hemagglutination -If antigens are present on RBC are to be detected ,process is known as hemagglutination. e.g. ABO group typing
  20. 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. 21. • compliment proteins are able to bind with ag-ab complex & are able to lyse RBCs compliment fixation test
  22. 22. • In this technique, flourescence property of dyes are used to demonstrate ag-ab reactions  Direct. Indirect Immunoflourescence
  23. 23. • Commonly used dyes are : Flourescein isothiocynate-blue green Lissamine rhodomine-orange red
  24. 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. 25. • Radio immuno assay • In thistechniquee, radioactive isotopes are used to demonstrate ag-ab reactions. RIA
  26. 26. Two type: 1)Direct immnunoprecipitation: In this ,antibodies are coated with insoluble inert material (microbeads) Immunoprecipitation
  27. 27. 2)Indirectimmunoprecipitate Here secondary antibodies are coated with microbeads.