Interaction of C1q subcomponent with immunoglobulin M.

The affinity of human C1q subcomponent for IgM of normal human serum and Waldenström macroglobulins of patients Sew and Zuk were investigated by the polyethylene glycol 6,000 immune complexes precipitation test. This test was calibrated with heat-aggregated gamma-globulin (HAGG); maximum fixation of C1q ranged from 60 to 80% (measured as percentage of radioactivity of the immune complexes precipitate) and was observed when the C1q:HAGG concentration ratio was about 1:250. At the ratio of 1:20 the radioactivity of the precipitate was about 43% of the total. The capacity of polyclonal IgM and Waldenström macroglobulins for C1q fixation is low and variable. The percentage of C1q fixed at the C1q:IgM ratio of 1:20 for polyclonal IgM and Zuk macroglobulin was about 9%, whereas for Sew it was only about 1%.