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Antigen antibody interaction

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Antigen-antibody interaction, or antigen-antibody reaction, is a specific chemical interaction between antibodies produced by B cells of the white blood cells and antigens during immune reaction. It is the fundamental reaction in the body by which the body is protected from complex foreign molecules, such as pathogens and their chemical toxins. In the blood, the antigens are specifically and with high affinity bound by antibodies to form an antigen-antibody complex. The immune complex is then transported to cellular systems where it can be destroyed or deactivated.

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Antigen antibody interaction

  2. 2.  Antigen-Antibody reaction is a bimolecular association similar to enzyme-substrate interaction  The association between antigen-antibody involves non-covalent bonds between antigenic determinants or epitopes and variable regions of antibodies  The interaction is very specific that leads to the development of various immunological assays
  3. 3.  Hydrogen bond  Ionic bond  Hydrophobic bond  Vander Wall interaction
  4. 4. The combined strength of non-covalent interaction between a single antigen binding site on an antibody and a single epiptope is the affinity of antibody. The association between a binding site on antibody(Ab) with a monovalent antigen(Ag) is described as follows: Ag + Ab ⇆ Ag-Ab k1 = forward (association) rate constant k-1 = reverse (dissociation) rate constant where, k1/k-1 = Ka, association constant and measure of affinity. Hence Ka = [Ag-Ab] [Ag] [Ab]
  5. 5.  Avidity is the strength of multiple interaction between the multivalent antigen and antibody  avidity of an Ab is a better measure of its binding capacity within biological system (e.g., the reaction of an antibody with antigenic determinants on a virus or bacterial cell) than the affinity of its individual binding sites  high avidity can compensate for low affinity
  6. 6.  When an antibody elicited by one antigen can react with an related antigen, the phenomenon is called cross-reactivity  Such cross-reactivity occurs if two different antigens share an identical or very similar epitope  The antibody’s affinity for the cross-reacting epitope is usually less than that for the original epitope  ABO blood group is a good example of cross-reactivity
  7. 7.  When antibody and soluble antigen interact in aqueous solution, it form a lattice that eventually develops into a visible precipitate  Antibodies that aggregate soluble antigens are called precipitin  Formation of an Ag-Ab lattice depends on the valency of both the antibody and antigen  The antibody must be bivalent; a precipitate will not form with monovalent Fab fragments  The Ag must be either bivalent or polyvalent; that is, it must have at least two copies of the same epitope, or have different epitopes that react with different antibodies present in polyclonal antisera
  8. 8.  Zone of antibody excess:Precipitation is inhibited and antibody doesn't bind to antigen and can be detected in supernatent  Zone of equivalence:Antigen-antibody binding is optimum and precipitation shows  Zone of antigen excess:Precipitation is inhibited and antigen not bound to antibody can be detected in suprernatent
  9. 9.  When antigen and antibody are diffused in Agar medium, a visible line of precipitation will form in the zone of equivalence  Two types of immunodiffusion reactions can be used to determine relative concentrations of antibodies or antigens to compare antigens or to determine the relative purity of an antigen preparation are  Radial immunodiffusion (the Mancini method)  Double immunodiffusion(the Ouchterlony method)
  10. 10. Immunoelectrophoresis: The antigens are electrophoresed in agarose, then the antibody applied.
  11. 11.  The interaction between antibody and a particulate antigen results in visible clumping called agglutination  Antibodies that produce such reactions are called agglutinins.  Antibody excess can inhibit agglutination reactions, which is called prozone effect  Antibodies that bind univalently cannot crosslink one Ag to another
  12. 12. RBC’s mixed with antisera to the A or B blood group antigens on a slide,if antigen is present on the cells, they agglutinate, forming a visible clump on slide Clumping of RBC’ less or other particles
  13. 13. It is modification of the agglutination reaction, called agglutination inhibition, provides a highly sensitive assay for small quantities of an antigen. It is used in pregnancy test.
  14. 14. Some of the techniques of immunoassay are:  Radioimmunoassay  Enzyme-Linked immunosorbent assay
  15. 15.  One of the most sensitive techniques for detecting antigen or antibody  Principle involves competitive binding of radiolabeled Ag and unlabeled Ag to a high affinity Ab  Ratio of Ab to radioactive Ag is chosen such that the number of epitopes presented by the labeled Ag always exceeds the total number of Ab binding sites  This insures that any unlabeled Ag added to the sample mixture will compete with radiolabeled Ag for the limited supply of Ab
  16. 16.  Estimation of recent and long term malaria transmission in a population by antibody testing to multiple Plasmodium falciparum antigen.8 sept,2014,oxford journal, James S.Hodge,David E.Lunar,Sheetij Dutta,Candy C .John,10.1093/infdis/jiju225.  Current approaches of fine mapping of antigen-antibody interaction. 11July,2014,British society for immunology,W.Mark Abott,David C. Lowe,DOI:10.1111/imm.12284.
  17. 17. Antigen-antibody interaction is vital process of our immune system of the body . This chemical interaction elicits an immune response in the body against the foreign substances. The specificity of the interaction has lead to the development of a variety of immunological assay which can be used for detection of presence of antigen or antibody and widely used as immunodiagnostics.
  18. 18. Owen, Judy; Punt, Jenni; Stanford, Sharon A.; Jones, Patricia (2013): Kuby Immunology. Seventh Edition. W.H Freeman and Company. New York. pp. 517-536. ISBN-13: 978-14292-1919-8. Murphy, Kenneth (2012). Janeway's Immunobiology: 8th ed. Chapter 15: Garland Science. pp. 611–668. ISBN 0815342438. Chakravarty, Ashim K (2007): Immunology and Immunotechnology. 2nd Edition. Oxford University Press. New Delhi. pp 412-424. ISBN-13: 978-0-19-567688-4