Use of solid-phase C1Q to remove soluble antigen/antibody complexes in an inhibition ELISA for streptococcal cell membrane antigens.

Solid-phase C1q was used to remove antigen/antibody complexes in an inhibition ELISA for low molecular weight streptococcal cell membrane (SCM) polypeptide antigens. To selectively fix IgM monoclonal antibody bound to antigen, binding was carried out in C1q-coated ELISA plates; transfer of supernatants to SCM-coated plates for ELISA permitted measurement of residual antibody. When inhibition occurred in the presence of C1q, the maximal binding was 72-98%. In the absence of C1q the maximum apparent binding was only 45-50%, which we attribute to displacement of the initially bound SCM antigen by solid phase SCM antigen. Removal of antigen/antibody complexes by solid-phase Clq during inhibition assays may facilitate analysis of low affinity antigen/antibody interactions.