Relationship of C3 and Factor a of the Properdin System

Abstract

Abstract Early investigations of the properdin system by Pillemer and coworkers demonstrated a requirement for a hydrazine-sensitive component (factor A) for preferential inactivation of terminal components of C by zymosan. The relationship of factor A to C3 and C4, C components known to be hydrazine sensitive, was therefore investigated. The loss of C3 and C4 hemolytic activity in normal human serum incubated at 37°C for 60 min with various concentrations of hydrazine showed strikingly similar patterns, 6 × 10-4 M hydrazine being required in each case for 50% inactivation. Similarly, factor A activity declined in direct proportion to the loss of C3 and C4 activity. Restoration of factor A activity in serum rendered deficient in factor A by treatment with hydrazine could be demonstrated with several preparations of purified C3 and was proportional to the amount of hemolytically active C3 added to the serum with restored factor A. Purified C4 showed no factor A activity when tested in this fashion. Treatment of purified C3 with three concentrations of hydrazine caused the destruction of 100%, 48%, and 8% of the hemolytic activity. The first of these showed no factor A activity while the others showed activity proportional to their residual hemolytic activity. These findings are in agreement with those of Müller-Eberhard and Götze (J. Exp. Med., 135: 1003, 1972) that C3 is identical to the hydrazine-sensitive factor of the C3 activator system and further support the relationship of this system to the properdin system. (Supported by Grants AI-00438 and AI-08251, United States Public Health Service.)