Human G myeloma (7S γ2-myeloma) proteins were investigated for relationships between Gm and Inv genetic factors and the different antigenic types of heavy polypeptide chains (γ-chains) and light polypeptide chains.

Myeloma proteins were isolated from the sera of 1 Chinese, 60 white and 28 Negro individuals. These 89 proteins were tested for eight Gm factors [Gm(a), Gm(x), Gm(b2), Gm(f), Gm(b1), Gm(b3), Gm(b4), and Gm(c)], and two Inv factors [Inv(l) and Inv(b)]. Results of the tests were correlated with the four γ-chain subclasses (γ2a, γ2b, γ2c and γ2d) and the two types of light polypeptide chains, κ-chains (type K or I) and λ-chains (type L or II) found in human IgG molecules.

1. Gm factors were limited to myeloma proteins with heavy polypeptide chains of the γ2b- and γ2c-subclasses. No Gm factors were detected on γ2a- and γ2d-myeloma proteins or on a "heavy-chain" disease protein of subclass γ2d.

2. γ2b-Proteins were positive for at least one Gm factor and were either Gm(a+), Gm(a + x+), or Gm(b2+ f+).

3. γ2c-Myeloma proteins, and one γ2c-"heavy-chain" disease protein, were positive for at least one Gm factor and contained various combinations of factors Gm(b1), (b2), (b4), and (c). Myeloma proteins from 3 Negroes were included in this group.

4. Inv factors (l) and (b) were limited to myeloma proteins with κ-light polypeptide chains. These Inv factors were not detected on proteins with λ-light polypeptide chains.

5. Most (70 per cent) of the γ2b- and γ2c-proteins with κ-chains were Inv(l+) or Inv(b+). None of the γ2a- or γ2d-proteins with κ-chains, however, contained these Inv factors.

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