T cell-mediated immunity is critical in resistance against Leishmania parasites, and T cell activation requires signals provided by costimulatory molecules. Herein we evaluated the role of costimulatory molecules on cytokine production and T cell surface molecule expression by peripheral blood mononuclear cells (PBMC) from cutaneous leishmaniasis (CL) patients. PBMC from CL patients were stimulated with soluble Leishmania antigen (SLA, 10 microg/ml), in the presence or absence of soluble CTLA4-Ig to block CD28-B7 interaction or in the presence or absence of anti-human CD40L to block CD40-CD40L interaction. Supernatants were harvested to evaluate tumor necrosis factor alpha (TNF-alpha), interleukin 10 (IL-10), transforming growth factor beta (TGF-beta) and interferon gamma (IFN-gamma) production by ELISA. Cells were harvested after 48 h of culture, stained for specific activation markers and analyzed by flow cytometry. Results show that the blockade of CD28-B7 interaction by CTLA4-Ig downmodulated IFN-gamma, IL-10, and TNF-alpha secretion by PBMC from CL patients. No alteration was detected on either TGF-beta production or the expression of CTLA44 or CD25 on CD4+ and CD8+ T cells. When the CD40-CD40L interaction was blockade using anti-CD40L, we did not observe changes in cytokine production or in surface molecule expression. The blockade of the CD28-B7 interactions by CTLA4-Ig also did not alter cytokine production in volunteers immunized against tetanus toxoid (TT). Taken together, these data suggest that the interaction of CTLA4 and CD28-B7 is a TGF-beta-independent mechanism that specifically downmodulates the immune response in cutaneous leishmaniasis patients.