INHIBITION OF COMPLEMENT BY A SUBSTANCE ISOLATED FROM HUMAN ERYTHROCYTES .2. STUDIES ON SITE AND MECHANISM OF ACTION

Extracts from human E stromata were found to be capable of causing inhibition of the complement mediated lysis of antibody sensitized sheep red cells. The partially purified inhibitor (I-H) could apparently bind spontaneously to sheep E, but another form of the inhibitor which was obtained by butanol extraction of human E stromata at a low ionic strength (I-L) would not bind. The latter material was employed in experiments designed to elucidate the site of inhibitory action. The low ionic strength form of the inhibitor was found to cause inactivation of shepp EAbC′la, 4, 2a, EAbC′la, 4, 2a, 3, and EAbC′la, 4, 2a, 3, 5 compelement component intermediate complexes. Indications were that the inhibition resulted from an increase in the rate of SAbC′la, 4, 2a decay to the SAbC′la, 4 state. Guinea pig C′3 was also observed to accelerate SAbC′la, 4, 2a decay. © 1969.