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Gm, Am and Km allotypes were investigated in two Tunisian populations (236 samples from Mahdia and 142 samples from Sfax). These populations descend from immigrants and, therefore, the results were compared with those obtained in other populations living in the Near East and in North Africa. The subclass heavy chain allotypes G1m, G2m, G3m and A2m are inherited in fixed combinations. There were five main and four minor Gm-Am haplotypes that could be deduced from the phenotypes. This led to the conclusion that the populations studied are Caucasoids with some African admixture (about 10%) and a very low oriental contribution. Furthermore, there were 11 samples which showed 8 uncommon Gm-Am phenotypes. These could be explained by the assumption of five different uncommon Gm-Am haplotypes. Four of these may have arisen by equal crossing over of prevalent haplotypes. The fifth may be the result of unequal crossing over of prevalent haplotypes. The fifth may be the result of unequal crossing over, since it was proven, by family study, that more markers are transmitted together than are present in the prevalent haplotypes.

Allotypes of IgG1, IgG2, IgG3, and IgA2 subclasses were investigated in seven Lebanese communities (three Moslem and four Christian). The Gm-Am haplotypes found were mainly those prevalent in Caucasians with a low frequency of haplotypes usually observed in Africans and Orientals. The difference between highlanders and lowlanders as expressed by G2m(23) was highly significant and suggested a possible adaptation to selective pressure related to the gamma2 genes, possibly due to endemic malaria in the past. Exceptional Gm-Am haplotypes were unambiguously determined by family studies. Some were characterized either by a deletion or a repression or, in contrast, by a partial or total duplication of gamma genes. Two others had uncommon combinations of allotypes: Gm17;23;5,10,11,13,14 A2m1, where G1m (17) was present without G1m (1); and Gm3;23;5,14 A2m1, where the CH3 allotypes G3m (10,11,13) were lacking.

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Three hundred and ninety-seven sera from 185 melanoma patients were studied. These sera were classified into three groups according to stage of disease. An alteration in the level of the IgG4 subclass was found. It was related to the dissemination of disease. The percentage of abnormalities (either increased or decreased levels of IgG4) was more frequent in patients with stage II and III diseases (55 and 53%, respectively) than in patients with stage I(19%). The higher frequencies of high titers of IgG4 were essentially detected in advanced disease. The biologic significance of the increase of IgG4 in melanoma remains obscure. The increase may be related to the development of facilitating antibodies of the IgG4 subclass.

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