Immunosuppressive effects of lymphocyte (type II) and leucocyte (type I) interferon on primary antibody responses in vivo and in vitro.

We have tested the hypothesis that type II interferon (IF), released by immune lymphocytes after in vivo stimulation with tuberculin, has immunosuppressive effects. Mycobacterium bovis (BCG) infected mice injected with tuberculin showed a very intense suppression of antibody response to sheep erythrocytes. Sera containing lymphocyte IF strongly inhibited primary immune responses to sheep erythrocytes in cultures. Addition of macrophages could not counteract the in vitro immunosuppressive effects of lymphocyte IF, suggesting that the main effect is exerted directly on lymphocytes. Sendai virus-induced leucocyte (type I) IF was also shown to have suppressive effects in vivo and in vitro. However, lymphocyte IF was shown to be much more immunosuppressive than a preparation of type I interferon with equivalent antiviral potency. Thus type II IF, as a product of activated lymphocytes, may have a major immunoregulatory role.