[Gm(28), a new allotypic marker on human IgG3: peculiar interest of its study within Negroid populations (author's transl)].

A new allotype in the Gm system (Gm(28)) was described and studied. Among Caucasoids and Mongoloids, it was found with rare exceptions, in samples containing Gm(21), segregating with Gm1,17,21 and Gm1,2,17,21 haplotypes. This new antigenic determinant was found to be of particular interest among Negroid populations in which its frequency is variable. It can be detected with all--common or uncommon--haplotypes. The degree to which it is associated with some haplotypes in different populations may prove useful in the characterization of Negroid populations. This new allotypic determinant is located on the CH3 homology region of IgG3 subclass.