The role of Fc:Fc interactions in insoluble immune complex formation and complement activation

Abstract

The initial rate of formation of insoluble immune complexes from rabbit IgG and ovalbumin was approximately 12 times that for formation of F(ab') 2-ovalbumin complexes. At low IgG concns, in the range 0.7–2.7 n M, the formation of insoluble immune complexes was characterised by a lag phase, especially for complexes formed in low antigen excess, compared to antibody excess. Guanidine HC1 (at concns up to 0.5 M) and urea (at concns up to 1 M) decreased the initial rates of formation of IgG immune complexes more than F(ab') 2 immune complexes. Pre-formed IgG immune complexes were solubilised at lower guanidine HC1 concns than were F(ab') 2 immune complexes. Clq enhanced the initial rate of formation of IgG immune complexes at Clq:IgG ratios up to 1:1. Higher Clq concns decreased the initial rate of formation of the complexes. Urea (1 M) blocked the Clq mediated enhancement of immune complex formation.