Qualitative and quantitative investigations on the reactions of normal and myeloma IgG with antisera to IgG.

Ten different antisera specific for the γ-chain of IgG were tested in gel diffusion tests and radioimmuno assays with isolated normal IgG and myeloma proteins of all four IgG subclasses. In Ouchterlony analyses, eight antisera revealed anti-genic deficiency of several myeloma proteins compared to normal IgG. The most pronounced deficiency was associated with IgG4 meloma proteins. Only two antisera gave reactions of antigenic identity between normal IgG and all myeloma proteins. Radial immunodiffusion plates were prepared with four of the antisera. When normal IgG and myeloma proteins were applied at the same concentrations (1 mg/ml), areas of the precipitin discs of most myeloma proteins were larger than the discs obtained with normal IgG. The largest discs were obtained with IgG4 myeloma proteins. The same four antisera were used for a solid phase radioimmuno-assay. Binding of I-labelled normal IgG to the insolubilized globulin fractions of the antisera was inhibited by normal IgG and myeloma proteins at various concentrations. Binding inhibition curves for normal IgG, IgG1 and IgG2 myeloma proteins were similar. However, pronounced differences in binding inhibition capacity were found among the IgG3 and IgG4 myeloma proteins. It was concluded that antisera to IgG can detect immunochemical differences between normal and myeloma IgG on the one hand and between various IgG myeloma proteins on the other, and that several myeloma proteins, particularly of the IgG4 subclass, lack some of the antigenic determinants of normal IgG and other myeloma proteins.