Gm Factors in Normal γ-Globulin Fractions, Myeloma Proteins, and Microglobulins

The Gm groups in man are genetically determined properties of normal serum γ-globulins. In the present study, Gm factors (a), (b), and (x) were measured in fractions of normal serum γ-globulin obtained by anion-exchange (DEAE) cellulose chromatography. Gm factors appeared to be present in the same proportion in all the normal human γ-globulin fractions, with ultracentrifugal sedimentation coefficient of about 6.6S. However, the normal fraction, composed primarily of 18S globulin, had no detectable activity. Myeloma proteins, classified immunoelectrophoretically as γ-type and having a single 6.6S component in the ultra-centrifuge, varied in their Gm activities. Two Gm factors were undoubtedly present on one such protein. Other myeloma proteins appeared to have only one of the two or three Gm factors present in normal γ-globulins. Several myeloma proteins showed activity equal to that of normal γ-globulin for one Gm factor, but other Gm factors were found at very low levels. The quantitative differences in Gm activity of the individual γ-type myeloma globulins are believed to reflect qualitative differences in the proteins. Myeloma proteins classified immunoelectrophoretically as β2A-type and having multiple (6.6S, 9S, 11S, and 13S) components in the ultra-centrifuge did not have demonstrable Gm factors. The γ-18S macroglobulins (β2M on immunoelectrophoresis) similarly were without Gm factors. Reduction of these macromolecules to smaller units with sedimentation coefficients of about 6.6S did not uncover masked or latent Gm activity. The finding of Gm activity on γ-myeloma globulins indicates that malignant plasma cells retain certain genetic features of normal plasma cells.