Anaphylatoxin in its relation to the complement system.

The fifth component of complement that reacts hemolytically in the guinea pig or rat complement system, C'3b, is intimately associated with the generation of anaphylatoxin. Anaphylatoxin was formed (i) if this purified component reacted with a washed, intermediate complex consisting of antigen, antibody, and the first four components of complement; (ii) if the component was treated with trypsin; or (iii) if the component was incubated with a material isolated from cobra venom together with a fraction from serum other than complement. The significance of this fifth component as anaphylatoxinogen is discussed, and a common mechanism is proposed for the generation of anaphylatoxin in whole serum.