DOES INTERLEUKIN-2 RESTORE LYMPHOCYTE-RESPONSES SUPPRESSED BY TRYPANOSOMA-CRUZI

There has been disagreement about the ability of exogenous interleukin -2 (IL-2) to restore responsiveness to lymphocytes from either Trypano soma cruzi-infected animals or normal individuals co-cultured with thi s parasite. The discrepancy has been attributed to the use of differen t strains of mice or T. cruzi isolates, or to the use of lymphoid cell s from different organs. As T. cruzi inhibits the expression of IL-2 r eceptors by activated lymphocytes in vitro, we were able to test wheth er restoration of responsiveness by exogenous IL-2 might depend on the level of suppression present in the system. Human or mouse lymphocyte s stimulated with phytohaemagglutinin (PHA) exhibited gradual decrease s in IL-2 receptor expression, [H-3]thymidine incorporation and IL-2 s ecretion as the concentration of T. cruzi in the culture increased. Ex ogenous IL-2 afforded a degree of restoration of both IL-2 receptor ex pression and [H-3]thymidine uptake which was substantial at the lower, but very small-if any-at the higher, parasite concentrations tested. Trypanosoma cruzi could not have competed with the lymphocytes for IL- 2 because it did not bind significant amounts of this cytokine. These results suggested that the controversy about the corrective effects of IL-2 may be more apparent than real, reflecting variations in the ext ent of immunosuppression present in different model systems of T. cruz i-associated immunosuppression.