Mode of action of anti-lymphocyte globulin. II. Changes in the lymphoid cell population in rats treated with anti-lymphocyte globulin.

Lymphopenia in rats which had been made tolerant to normal rabbit immunoglobulin G(IgG) was induced by the administration of rabbit anti-rat immunoglobulin G(IgG). The rats were injected with tritiated thymidine ([H] thymidine) and the labelling pattern in lymphoid tissues was studied. The thymus weight decreased with continued lymphopenia and this could be explained by the release of small lymphocytes into the circulation. Lymphopoiesis in the thymus and spleen was not inhibited by anti-lymphocyte globulin. Plasmacytosis was noted in the lymph nodes. These findings support the idea that anti-lymphocyte globulin acts mainly on peripheral lymphocytes and suppresses the immune function mediated by these cells.