Abstract
Abstract A series of human myeloma proteins were prepared in highly purified form by standard chromatographic techniques. Aliquots were aggregated with bisdiazo-benzidine (BDB) over a wide range of protein and BDB concentrations. The aggregated proteins were tested for their ability to activate the alternate complement pathway in C4-deficient guinea pig serum, as evidenced by their ability to lower the titer of C3-9 after incubation in serum for 1 hr at 37°C. The number of proteins which led to C3-9 fixation/total number of proteins tested was as follows: IgG1, 2/2; IgG2, 1/1; IgG3, 1/1; IgG4, 3/5; IgM, 2/2; IgE, 1/1; IgA, 2/7. Incubation of C4-deficient serum with IgG1 led to most complement fixation. IgG4 was least active on a milligram basis. Both a and b subgroups of IgG4 and both α1 and α2 subgroups of IgA fixed C3-9 in individual cases. In no instance did the unaggregated protein lower the titer of C3-9.
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