L-asparaginase: suppression of the immune response of mice to sheep red blood cells.

L-asparaginase was immunosuppressive in mice. A single injection of 1000 I.U. of L-asparaginase markedly suppressed the direct haemolytic plaque forming cell response to immunization with sheep red blood cells. The effect was not due to cytotoxicity but to delayed proliferation of plaque forming cells. Haemagglutinin production was delayed by a single injection and was suppressed when the enzyme was given daily from 3 days before immunization to the day before antiserum collection. L-asparaginase in this dosage form both reduced total antibody production and markedly prolonged 2-ME sensitive antibody production. L-asparaginase treatment was only weakly immunosuppressive and none of the animals studied showed complete suppression of the immune response. It was suggested that asparaginase would be most effective in the prevention of the development of primary immunity when combined with another agent with an independent mechanism of action.