Detection and measurement of multivalent antigen in the presence of low affinity antigen-antibody complexes.

Multivalent antigen which is bound to antibody can be difficult to measure and detect. There are 2 reasons for this phenomenon: (a) The antibody can mask the antigen so that it cannot react with antibody in the in vitro test system and (b) Complexes of multivalent antigen and antibody can precipitate spontaneously. In this study solutions to these problems were developed for the special case in which the antigen-antibody bond is of low affinity. The masking effect of low affinity antibody could be overcome by using a very high affinity antibody (K = 10(10) M-1) in the test system. The precipitation problem could be minimized by using fresh or thawed fresh frozen serum. In cases where antigen detection, rather than quantitation, is required, analysis of precipitates may be preferable because antigen is often selectively concentrated in the redissolved precipitates over serum values.