precipitin reaction

precipitin reaction n the specific reaction of a precipitin with its antigen to give an insoluble precipitate

* * *

the formation of an insoluble precipitate by reaction of antigen and antibody; it occurs only with multivalent antigens and is dependent on electrolyte concentration, pH, temperature, and the relative concentrations of antigen and antibody, the amount of precipitate formed increasing to a maximum and then decreasing as the relative antigen concentration is increased.

Schematic of precipitin reactions with different proportions of antigen and antibody. Antigenic proteins that elicit antibody responses are depicted as having three different antibody-binding sites on their surface. Polyclonal antibodies with three different specificities (box, triangle, circle) are also depicted. (A), Under conditions of antigen–antibody equivalence, there is maximum cross-linking and visible precipitin formation. (B), With antigen excess, the resulting small soluble immune complexes do not form a visible precipitate. (C), With antibody excess, small soluble complexes are also formed; lattice formation is insufficient to cause visible precipitation. (D), Under conditions of equivalence but in the presence of monoclonal, rather than polyclonal, antibodies, each antigen binds only at a single site; there is no cross-linking and no visible precipitate.


Medical dictionary. 2011.

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