The activation of complement components by aggregates of antibodies and their fragments

The relative consumption of the complement components C1, C2, C3 and C4 from guinea pig serum on addition of rabbit antibody-antigen aggregates, papain digested aggregates, heat aggregated rabbit IgG and Fc has been measured. It has been found that antibody-antigen aggregates are much more efficient with respect to consumption of all four components than heat aggregated IgG which in turn is more efficient than heat aggregated Fc. In the latter two preparations the inefficiency is most marked with C2 and C3 consumption. The results suggest that splitting of C2 may depend on prior association with bound C4b which yields a bound C42 complex to the Fab section of the aggregated antibody.