The role and mechanism of cobra venom factor-induced suppression of the humoral immune response in guinea pigs.

The cobra venom factor (CVF)-mediated suppression of the humoral immune response to bacteriophage phi X 174, a T cell-dependent antigen, was investigated in guinea pigs. The suppression was markedly dependent on the amount of antigen used: decomplementation of animals diminished the humoral immune response when immunizing with low doses of antigen, whereas increasing the antigenic dose resulted in little or no diminution by CVF. In contrast to the results with normal animals, CVF had no influence on the humoral immune response of genetically C2-deficient guinea pigs; i.e., no suppression occurred above that due to the inherited complement deficiency state alone. We therefore postulate that CVF suppresses the humoral immune response by the depletion of C3, with no measurable role for complement split products under these experimental conditions.