The gene for the T lymphocyte alloantigen, RT6, is not linked to either diabetes or lymphopenia and is not defective in the BB rat.

In an outcross between a diabetic BB/H rat and a healthy Long Evans Hooded rat, the segregation of the RT6 gene was studied in the 207 F2 animals to look for linkage with diabetes or lymphopenia. The recessive gene, albino (c), was used as a marker for the RT6 gene because of the close proximity of these two genes on chromosome 1. Though most of the albino F2 rats should have been homozygous for the BB RT6 gene, we found no increase in the incidence of diabetes or lymphopenia among them when compared to their hooded littermates. Therefore, the RT6 gene was not linked to diabetes or lymphopenia in the BB rat. Moreover, the non-lymphopenic albino rats displayed normal RT6 expression when compared to the normal hooded rats showing that the RT6 gene from the BB/H grandfather was not defective. Any alteration in lymphocyte composition which could be specifically related to diabetes was studied by measuring all F2 rats for the major lymphocyte subsets including the RT6+ subset. We found that the typical pattern of lymphopenia described in diabetic BB rats was displayed by both diabetic and non-diabetic lymphopenic rats in the F2 generation. Thus, all these lymphocyte abnormalities including the depletion in RT6+ T lymphocytes appeared as a consequence of lymphopenia alone and could not be specifically related to diabetes.