Suppressor activity of blood lymphocytes from guinea-pigs treated with ALS.

PHA-induced transformation of guinea-pig lymphocytes was profoundly inhibited by the injection of antilymphocyte serum (ALS). This effect, seen 24 h after ALS administration, disappeared within 3 days. Lymphocytes of animals injected with ALS 24 h earlier inhibited the blast transformation of autologous normal lymphocytes. The supernatants of short term cultures of such cells, even after pre-treatment with puromycin, exhibited the same inhibitory activity. It is suggested that the immunosuppressive effect of ALS is not limited to its direct action on lymphocytes.