Comparison of various procedures for the detection of antigen-antibody complexes.

The described test of inhibition of AA activity proved to be a procedure of exquisite sensitivity and specificity for detection of immune complexes. This could have been expected since AA is an antibody specifically combining with IgG antibody that suffered molecular transformation in the reaction with its corresponding antigen. Complexes formed at or close to the equivalence zone were most active in inhibiting AA, whereas those at extreme antigen excess did not inhibit it at all. Inhibition of AA was capable of detecting circulating immune complexes as well as immune complexes deposited in the tissues. It was also shown that by using this procedure, identification of the antigen participating in immune complex formation is feasible since excess of the specific antigen converts inhibitory complexes into inactive complexes.