Effect of intravenous immunoglobulin therapy on plasma complement.

The effect of the intravenous immunoglobulin preparation (Sandoglobulin) on the complement system and the formation of circulating immune complexes (CIC) was investigated in 10 patients with primary humoral immunodeficiency and in 12 normal volunteers. Infusion of 9 g of the pH4 treated preparation did not show relevant changes in total hemolytic complement activity, plasma levels of C4, C3, and factor B. C3dg fragments, however, increased markedly in some individuals in both groups immediately after infusion. CIC measured by 125 I-C1q binding were not detectable. Furthermore, the initially low C1q concentrations in immune-deficient patients correlated with the pre-infusion IgG levels (p < 0.05) and rose significantly 24 h after therapy (p < 0.001). In contrast, in vitro incubation of the immunoglobulin preparation with normal human serum did not reveal spontaneous anticomplementary activity nor did it lead to formation of immune aggregates. The results indicate that immunoglobulin infusions may moderately activate complement in vivo, as evidenced by increased C3dg fragments; in addition, partial C1q deficiency in hypogammoglobulinemia seems to be related to IgG concentration and can be corrected by immunoglobulin substitution.