Precipitin

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A precipitin is an antibody which can precipitate out of a solution.

[edit] The Precipitin Reaction

The precipitin reaction provided the first quantitative assay for antibody but is now made redundant by current technology and diagnostic techniques such as ELISA (enzyme linked immunosorbant assay) and RIA (Radioimmunoassay). The precipitin reaction was based upon the interaction of antigen with antibody leading to the productiuon of antigen:antibody complexes.

In the precipitin reaction, varying amounts of soluble antigen are added to a fixed amount of serum containing antibody. As the amount of antigen added increases, the amount of precipitate generate also increases up to a maximum and then declines.

  • At low concentrations of antigen antibody complexes are formed under conditions of antibody excess so that each molecule of antigen is bound extensively by antibody and crosslinked to other molecules of antigen.
  • At the point of "Equivalence", the formation of precipitin complexes are optimal. Large lattices of antigen and antibody are formed by cross-linking.
  • At high concentrations of antigen antibody complexes are broken up to account for the excess antigen to bind.

NB: the small, soluble immune complexes formed in the zone of antigen excess are the cause of many pathological syndromes in vivo.

Antibody may precipitate antigenic substrates that have several antibody-binding sites. This allows for the formation of large antigen:antibody complexes.



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