Lymphopenia and abnormal lymphocyte subsets in the "BB" rat: relationship to the diabetic syndrome.

The "BB" rat spontaneously develops insulitis followed by impaired glucose tolerance (IGT) and/or an insulin-dependent diabetic syndrome like that in man. All diabetic rats in this study showed marked lymphopenia in blood, lymph nodes, spleen, and thymus. Peripheral blood lymphopenia antedated glucoregulatory disturbances. All rats showing either insulitis with or without IGT or diabetes were lymphopenic. None with normal lymphocyte counts developed any abnormality. Diabetics showed marked decrease in the proportions of T+ lymphocytes in all tissues. The proportion of B (Ia+) lymphocytes was normal in blood, spleen and thymus, but increased in lymph nodes. However, in absolute terms both T and Ia+ lymphocytes were decreased. The subset decreased by the greatest proportion in all tissues was that which includes helper T lymphocytes. Thus: a) generalized lymphopenia most marked for T lymphocytes has been shown, b) helper T lymphocytes show proportionally the greatest reduction, c)thymic helper T deficit suggests a thymic origin of the lymphopenia, d) lymphopenia is a possible marker for susceptibility to the syndrome.