Autoimmune diatheses and T lymphocyte immunoincompetences in BB rats

BB rats were found to have autoantibodies to gastric parietal cells, thyroid colloid antigens, smooth muscle, and thymocytes. No autoantibodies reactive with pancreatic islet cells (cytoplasmic), thyroid epithelial cells, adrenal cortex, testes, or anterior pituitary sections were identified. BB rats with gastric parietal autoantibodies had modest degrees of lymphocytic gastritis, but none developed iron or vitamin B12 deficiencies. These results suggest that BB rats have an underlying autoimmune diathesis. In addition, reports of peripheral T lymphopenia in such rats were confirmed, and markedly reduced helper T cell and cytotoxic-suppressor T cell subsets were demonstrated. Histological studies also revealed depletions of the T cell areas of spleen and lymph nodes. Furthermore, BB rats exhibited a profound inability to reject skin grafts across major and minor histocompatibility barriers. This was confirmed by mixed lymphocyte culture studies in vitro. BB-rat lymphocytes from either spleen or peripheral blood also showed profoundly reduced responses to T cell mitogens. Although BB-rat lymphocytes could produce normal levels of interleukin-2, they were unable to respond to this T cell growth factor. However, examination of thymuses from BB rats showed largely normal histologies, normal numbers of thymocyte subsets, and good mitogenic responses to con A. Thus, it appears that BB rats may have a thymic or post thymic defect in T lymphocyte maturation. The relevance of the immunologic lesion to the etiology of IDD in BB rats remains to be shown.