Interaction of a serum inhibitor of C'I-esterase with intermediate complexes of the immune haemolytic system. I. Specificity of inhibition of C'I activity associated with intermediate complexes.

Abstract

An investigation is described of the interaction of a highly purified human serum inhibitor of C′1-esterase with various intermediate complexes of sensitized sheep erythrocytes and human or guinea-pig complement. The inhibitor reacted with and blocked specifically the activity of C′1 on these complexes. There was a direct correlation, by several criteria, between the ability of the inhibitor to block esterolytic activity of C′1-esterase in solution and its ability to inhibit C′1 activity on the intermediate complexes, implying the participation of C′1-esterase in immune haemolysis. Prior interaction of the inhibitor with complexes between sensitized erythrocytes and C′1 and C′4 prevented subsequent reaction of these complexes with C′2. However, once the complex between sensitized erythrocytes and C′1, C′4 and C′2 had been formed, the inhibitor was no longer effective in preventing haemolysis. These data suggested a biochemical function for C′1-esterase in reactions involving C′4 and C′2 but not in further steps leading to immune haemolysis.