Gm types of sera from Caucasians and Negroes, of myeloma globulins, and of specific antibodies were investigated. In particular the relationship between the recently identified gene Gmf and other Gm genes was analyzed.

1. Caucasians were, with rare exceptions, either Gm(b+f+) or Gm(b-f-).

2. In Negroes, on the other band, type Gm(b+f-) was found to be common.

3. No myeloma globulins appeared to contain the product of more than 1 of the 3 genes Gma, Gmb, and Gmf, even though the large majority of normal individuals, as well as myeloma patients, possess 2 or all 3 of these genes.

4. The types Gm(a+b-f-) and Gm(a-b-f+) represented the 2 major groups among the γ2-myeloma globulins; each comprised roughly 40 per cent. The types Gm(a- b+f-) and Gm(a-b-f-) are minor groups.

5. All Gm(x+) myeloma globulins were also Gm(a+). Approximately half of the Gm(a+) myeloma globulins were Gm(x+).

6. In the majority, but not in all, of Gm(a+) sera the anti-Rh antibodies were clearly Gm(a+). Similarly, the anti-Rh antibodies of Gm(f+) sera were most often, but not always, also Gm(f+). In contrast, only a minor proportion of Gm(b+) anti-Rh sera sensitized red cells to anti-Gm(b).

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