Three Naturally-Occurring Inhibitors of Components of Complement in Guinea Pig and Rabbit Serum

Abstract

At the present time, the complement (C′) system may be defined as consisting of nine hemolytic components and of at least three inhibitors or inactivators of specific components (1). In this report, some properties of three naturally-occurring inactivators of components in guinea pig and rabbit C′ are described. One is similar to a heat labile α-globulin of human serum which inhibits C′1 esterase (2–4) and to an ether labile factor in guinea pig serum which was shown by Klein in 1960 (5) to inactivate C′1 bound to sensitized sheep erythrocytes (EAbC′1). The existence of an inactivator with different specificity originally was suggested in experiments of Nishioka and Linscott (6). In 1965, we isolated and characterized this substance as a specific inactivator of C′3 (7). In 1966, one of us discovered yet another naturally-occurring inactivator in rabbit serum which is specific for C′6 (8).