Complement-mediated inhibition of non-specific aggregation of highly-dinitrophenyl-conjugated human serum albumin

125I-labelled dinitrophenylated human serum albumin (DNP35HSA) was shown to form large aggregates after incubation either in normal human serum (NHS) containing ethylene diamine tetraacetate (EDTA), or in heat treated NHS, whereas much smaller aggregates were formed after incubation in NHS or NHS containing ethylene glycol tetraacetate (EGTA) and Mg2+. It is proposed that serum complement inhibits the formation of DNP35HSA aggregates after activation of the alternative pathway in the absence of specific antibodies. The phenomenon is probably explained by increased electrostatic repulsion.