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Specific cytoloxic T cells against intracellular pathogens may be generated in vitro. On the other hand it is well known that cytokines can regulate almost every aspect of immune function. The aim of this study was to evaluate the effect of some cytokines on the generation of cytotoxic T cells with specificity for Mycobacterium leprae- or PPD-pulsed autologous macrophages from leprosy patients and normal controls. Peripheral blood mononuclear cells from M. bovis BCG-immunized controls or from leprosy patients were stimulated with antigen, in the presence or absence of cytokines, for 7 days. These were used as effector cells in a 4-h [5lCr]-release assay. Our results show that development of cytotoxic T cells may be enhanced by γ-IFN, IL-6 or the combination of IL-6 and IL-2. Addition of IL-2 or TNF-a alone did not modify the generation of cytotoxic activity. IL-4 down-regulated the cytotoxic response and γ-IFN was able to counteract this effect. Hence, the generation of specific cytotoxic T cells can be modulated by cytokines. Whether this cytotoxic mechanism contributes to protection or tissue damage in M. leprae infection remains to be determined.