Isolated myeloma proteins and anti-Rh antibodies were utilized for determination of the distribution among the γ-globulin molecules of various Gm(b) and Gm(f) determinants. All of these genetic factors are as a rule inherited together in Caucasians, but not in other races. The Gm(b) determinants, except (b2), were found together in the same Caucasian myeloma globulins of the Vi H chain group, which never carried Gm(f) or (b2). The Gm(f) and (b2) determinants were found together in other myeloma globulins, of the We group. Anti-Rh antibody molecules appeared to be similar to myeloma molecules in these respects. A few myeloma proteins and anti-Rh antibodies were encountered which reacted with some but not other anti-Gm(b) or anti-Gm(f) reagents; the only available Vi type myeloma protein from a Negro, specifically lacked the Gm(b3) factor.

The observations might be explained by the following hypothesis: In Caucasians with the common Gmf Gmb gene complex the Gm(b) antigenic determinants, except (b2), co-occur in certain molecules, which contain a polypeptide chain determined by the Gmb gene; the Gm(f) and (b2) determinants co-occur in other molecules, which contain a polypeptide chain determined by the Gmf gene. Individuals that lack some Gm(b) or Gm(f) determinants most likely have a gene partly different from Gmb or Gmf.

The value of studies with myeloma proteins from individuals of different racial groups was apparent from this study. One myeloma protein from a Chinese was unique in that it was both Gm(a+) and Gm(f+).

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