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Medical Definition of Antigen excess
1. In a precipitation test, the presence of uncombined antigen above that required to combine with all of the antibody; precipitation may be inhibited because the presence of excess antigen gives rise to soluble antigen-antibody complexes, in vivo the resultant antigen-antibody interaction in such an antigen excess may give rise to immune complexes, which have a potential to induce cellular damage; such injury underlies the pathologic changes seen in certain immune complex diseases. (05 Mar 2000)