title: Mechanism of complement activation by radiographic contrast media.
abstract: Activation of the complement system by radiographic contrast media (RCM) was demonstrated by in vitro haemolytic and immunological assays. Such activation was found to be a function of the RCM molar concentration. Iodipamide was the most active of five RCM tested. When RCM was incubated with normal human serum (NHS) in the presence of ethylene glycol-tetra-acetic acid and magnesium ions, conditions which block activation of the classical pathway but permit activation of the alternative pathway, haemolytically active C3, properdin and factor B were found to be decreased but haemolytically active C4 was normal. Using counterimmunoelectrophoresis, the activation of complement was further demonstrated by detection of C3 and factor B-split products. Finally, when radiolabelled complement proteins were reacted with RCM in vitro and studied by density-gradient ultracentrifugation, it was demonstrated that a large complex was formed with a sedimentation of 22S, similar in characteristics to the C5b-C9 complex. It was postulated that the mechanisms of in vitro consumption of complement by RCM was mainly through the alternative pathway.
mesh_terms: D003176:Complement C3; D003165:Complement System Proteins / Q000378:metabolism*; D003287:Contrast Media / Q000494:pharmacology*; D003378:Counterimmunoelectrophoresis; D004305:Dose-Response Relationship, Drug; D006801:Humans; D066298:In Vitro Techniques; D011414:Properdin
chemical_list: D003176:Complement C3; D003287:Contrast Media; D011414:Properdin; D003165:Complement System Proteins