Precipitation (immunology)

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Schematic representation of the precipitation
Change in the degree of precipitation with increasing concentration of antibodies

In immunology, the precipitation of antigens and antibodies describes the formation of antigen-antibody immune complexes (an immunoprecipitate ), which lead to clumping (synonym agglutination ) and subsequent precipitation (synonym precipitation , from Latin praecipitatio "falling down") from a solution leads.

properties

Precipitation occurs when multivalent antigens with repeated epitopes (ie antigens with several identical epitopes ) bind to bivalent antibodies (antibodies with two paratopes ) and form a network. With individual Fab fragments , there is no precipitation after binding to an antigen. It takes place faster when heated (below the denaturation temperature ) and slower when cooled. At pH values below 4 or above 10, the precipitation is inhibited.

An antigen can be detected through the precipitation with the aid of known antibodies and vice versa. Substances that trigger precipitation are sometimes referred to as "precipitating agents ".

A prerequisite is that antibodies with 2 ( IgG ) or 10 ( IgM ) binding sites bind to antigens, which in turn have several binding sites that can be occupied by other antibodies. The binding reaction leads to a crosslinking of numerous antibodies and antigens, so that these finally form a gel-like complex and, due to their mass, fall out of the solution.

The amount of precipitated antigen-antibody complexes depends on the ratio in which the two partners are in the solution. If there is a significant excess of one of the components, the formation of larger complexes hardly occurs and the precipitation is low (this is the so-called prozone phenomenon ).

The method is used in immunology and biochemistry e.g. B. in the Gruber-Widal reaction , in the immunodiffusion test , in nephelometry , as a hemagglutination inhibition test , as a serum precipitin test and as immunoprecipitation including their special form chromatin immunoprecipitation .

Individual evidence

  1. ^ A b Alfred Pingoud : Working methods of biochemistry. Walter de Gruyter, 2013, ISBN 978-3-110-80769-1 , p. 215.
  2. ↑ I. Roitt: Guide to Immunology. Springer-Verlag, 2013, ISBN 978-3-642-97770-1 , p. 117.
  3. ↑ a b Wolfgang Heizmann : Short textbook medical microbiology and immunology. Schattauer Verlag, 1999, ISBN 978-3-794-51961-3 , p. 296.
  4. ↑ Hybridoma antibody . European patent EP 0150309 A2