(1) in a precipitation test, the presence of uncombined antigen in excess of 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; could be tolerogenic.