Depletion of long-lived lymphocytes in old New Zealand black mice.

Labelling studies with tritiated thymidine in NZB mice revealed that old mice of this strain with established Coombs positive haemolytic anaemia were depleted predominantly of long-lived small lymphocytes. Lymphopoiesis in the bonemarrow was relatively less affected suggesting that the peripheral destruction or deviation of re-circulating lymphocytes and not a precursor cell deficiency may account for the depletion of these cells. Old NZB mice in which the development of Coombs positive haemolytic anaemia, but not other disease features, has been prevented by thymectomy and treatment with anti-lymphocyte globulin several months earlier were equally deficient in this population of lymphocytes. C57BL mice, subjected to the same regime largely regenerated this population during the subsequent 12 months and rejected skin homografts in the same time as young controls of the same strain. Loss of lymphocytes responsible for antigen recognition would account for the impaired cellular immunity of old NZB mice observed in this study and described earlier by other authors. This process appears to accompany the progression of the spontaneous disease in this strain.