The immunologic response to sheep erythrocytes was compared in mice treated with Cobra venom (CoF) and with pneumococcal capsular antigen S III. Suppression of the immunologic response in both cases was attributed to the ability of both tested substances to activate the third component of complement. CoF and S III both changed the organ localization of labeled antigens capable of activating the complement system. No evidence for an alternative pathway by which S III could activate the complement system was found. On the basis of the literature data and experimental findings, the properties of CoF and S III were compared in the light of their ability to suppress the immunologic response.
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