Interleukin 2 enhances specific and nonspecific immune responses in experimental Chagas' disease

Mice infected with Trypanosoma cruzi develop an early and profound immunosuppression of responses to heterologous antigens. Recently it has been demonstrated that this immunosuppression is linked, in part, to deficiency in the production of interleukin 2 (IL-2), and that the addition of IL-2 to cultures of normally unresponsive spleen cells from infected mice will restore responsiveness to sheep erythrocytes (SRBC) and enhance parasite-specific immune responses. In the present study, the effect of administration of ultrapure or recombinant IL-2 on immune responses to SRBC and parasite-specific responses in vivo was examined. It was found that a single injection of 1,500 U of IL-2 provided at the same time as SRBC more than doubled the number of direct plaque-forming cells to SRBC and that multiple injections of 1,500 U of IL-2 were no more restorative than a single injection. Anti-SRBC responses of normal mice were unaffected by injection of IL-2. Single or multiple injections of recombinant human IL-2, with and without gelatin, into highly susceptible C3H(He) mice induced greater parasite-specific immunity as reflected by significantly reduced levels of parasitemia and increased longevity. Three injections of 1,500 U each of recombinant human IL-2 on days 10, 14, and 18 was found to be the most efficacious in reducing parasitemia and increasing longevity. Injection of IL-2 with gelatin did not enhance the effect of IL-2 alone.