MECHANISM OF COMPLEMENT ACTIVATION BY RADIOGRAPHIC CONTRAST-MEDIA

Abstract

Activation of the complement [C] system by radiographic contrast media (RCM) was demonstrated by in vitro hemolytic and immunological assays. Such activation was a function of the RCM molar concentration. Iodipamide was the most active of 5 RCM tested. When RCM was incubated with normal human serum (NHS) in the presence of ethylene glycol-tetraacetic acid and Mg ions, conditions which block activation of the classical pathway but permit activation of the alternative pathway, hemolytically active C3, properdin and factor B were decreased, but hemolytically active C4 was normal. Using counterimmunoelectrophoresis, the activation of C was further demonstrated by detection of C3 and factor B-split products. When radiolabeled complement proteins were reacted with RCM in vitro and studied by density-gradiant ultracentrifugation, a large complex was formed with a sedimentation of 22S, similar in characteristics to the C5b-C9 complex. The mechanisms of in vitro consumption of C by RCM apparently was mainly through the alternative pathway.