Evidence That Cobra Venom Factor (CoF) Is Cobra C3

Abstract

The presence in cobra venom of an anticomplementary activity has been known for over 80 years. More recent studies have demonstrated that purified CoF incubated with mammalian sera results in an alternative pathway mediated attack on C3. Lachmann and Nicol have pointed out that CoF is “C3b-like” in its ability to activate C3 and later components. The present studies strongly suggest that CoF is, in fact, altered cobra C3. Potent rabbit antiserum to CoF cross-reacts with human C3. On immunofixation of cobra serum after prolonged agarose gel electrophoresis, a single reactive band was found in the β1-region. Multiple slower bands were found in cobra venom or purified CoF, suggesting that CoF is an altered form of the serum molecule. When cobra serum was incubated at 37°C, slow conversion to a more rapidly migrating form was observed in immunoelectrophoresis. Much more rapid conversion occurred when cobra serum was incubated with endotoxin at 37°C.