Reduced immune adherence of antigen/antibody complexes formed in the presence of complement in vivo and in vitro.

The adherence of complement-reacted immune complexes (ICs) to cells bearing C3b receptors depends on the characteristics of the IC used. The immune adherence of preformed ICs exposed in vitro or in vivo to complement has been well established, and was confirmed using different types of ICs-antigens used: BSA; BSA dimers and trimers; tetanus toxoid, and hepatitis B surface antigen. In contrast the same ICs did not bind to human red blood cells when formed in the presence of serum in vitro. ICs remained negative for immune adherence as well, when formed directly in vivo by the sequential injection of antibody and antigen in guinea pigs. These results suggest that in many circumstances, the elimination of ICs formed in the circulation does not involve immune adherence reactions, possibly because complement in itself inhibits the formation of the large ICs that would bind to C3b receptor-bearing cells.