Mechanism of aggregates generated by heating human serum

Heating normal human serum produced aggregates that can be detected with a F(ab')2 anti-C3 enzyme-linked immunosorbent assay (FaC3 ELISA) for circulating immune complexes. Using this we studied the production mechanism of these aggregates. Heating serum with the inactivated complement system produced aggregates which included IgG and C3/C3 fragments. The aggregates also incorporated IgA, IgM, and albumin as well as IgG and C3/C3 fragments. These results indicate that the production of the aggregates was not due to activation of the complement system by aggregated IgG generated by heating, but mainly resulted from aggregation of serum proteins induced by heating. This study suggests that there are heating conditions under which the hemolytic activity of complement system is abolished, but aggregates are not detected with FaC3 ELISA.