Antiserum to lymphocytes and procarbazine compared as immunosuppressants in mice.

As an immunosuppressant procarbazine was as potent as an antiserum to lymphocytes in mice. Both agents significantly prolonged survivals of skin allografts by 4 to 6 weeks. At the maximum tolerated dosage, procarbazine suppressed both circulating hemagglutinins to sheep erythrocytes and plaque-forming cells in the spleen. The antiserum to lymphocytes reduced the numbers of circulating hemagglutinins and plaque-forming cells by 94 percent. Procarbazine was administered to mice for 3 weeks before their exposure to antigen. Exposure for only 9 days, commencing 48 hours before injection of sheep erythrocytes, was less effective in suppressing the titers of hemagglutinins.