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;
2. 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.