Precipitin

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

The precipitin reaction provided the first quantitative assay for antibody. The precipitin reaction is based upon the interaction of antigen with antibody leading to the production of antigen-antibody complexes.

To produce a precipitin reaction, varying amounts of soluble antigen are added to a fixed amount of serum containing antibody. As the amount of antigen added:

The small, soluble immune complexes formed in vivo in the zone of antigen excess can cause a variety of pathological syndromes.

Antibody can only precipitate antigenic substrates that are multivalent—that is, only antigens that have multiple antibody-binding sites epitopes. This allows for the formation of large antigen:antibody complexes.

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