Antibody-induced suppression and postsuppression stimulation of complement in vitro: I. Effects of anti-C4 on cultured guinea pig peritoneal cells

Suppression of the fourth component of complement in vitro was examined by exposing cultured guinea pig peritoneal cells to anti-C4 alloantisera or to control sera. We found that in contrast to similar experiments in vivo, C4 production could be suppressed by specific anti-C4 antisera over a wide range of doses with complete regularity. The suppression was not permanent, however, and postsuppression stimulation of C4 was frequently seen after recovery from suppression. Production of C2 and β-glucuronidase were also measured in these experiments. C2 was not suppressed by the anti-C4 treatment but stimulation of C2 was seen in those instances where C4 production was stimulated. β-Glucuronidase was neither suppressed nor stimulated. Purified IgG₁ IgG₂ and (Fab′)₂ fragments were as effective in causing suppression and postsuppression stimulation as whole antibody preparations. This suggests that complement activation, Fc receptors, and complement receptors do not play a significant role in these in vitro phenomena.