Complement interaction with immune serum globulin and immune globulin intravenous

Abstract

Three complement assays, C1q binding activity, C3 activation in normal human serum, and enhancement of alternative pathway activity, have been used to evaluate the in vitro anticomplementary activity of untreated and heat-aggregated (63 °C, 10 minutes) immune serum globulin and immune globulin intravenous prepared by partial reduction and alkylation. Unheated immune globulin intravenous marginally activated endogenous C3 in normal serum, had a fivefold lower affinity for 125I C1q but was very similar to immune serum globulin in enhancing complement alternative pathway activity. Heat-aggregated immune globulin intravenous was about twofold less effective than heat-aggregated immune serum globulin in the activation of C3 in normal serum and had approximately a threefold lower affinity for 125I C1q. The ability of immune globulin intravenous to retain specific complement receptor activity suggests that it would also retain in vivo efficacy in complement-mediated amplification of host defense reactions but that it is safe for intravenous use due to a lower capacity to initiate nonspecific complement activation.