CD8+ T cells and lysis of parasitized macrophages seem to be important in the resistance to murine leishmaniasis. In the present study, we evaluated peripheral blood mononuclear cell (PBMC) from patients with either cutaneous (CL) or mucosal (ML) leishmaniasis in cell lysis assays using 51-Cr-labeled Daudi or K562 cells, or autologous antigen-pulsed macrophages as targets. Results are reported as lytic units (number of cells required for 30% lysis) per million PBMC. Exposure of patient PBMC (n = 12) to lysate from Leishmania amazonensis promastigotes led to an increase in cytotoxic activity compared to unstimulated patient cells against Daudi (81.8 +/- 14.9 vs 13.6 +/- 5 lytic units (LU) per million PBMC; mean +/- SEM) and K562 (65.7 +/- 8.4 vs 13.1 +/- 5 LU/10(6) PBMC). ML had higher responses than CL in both targets (80.4 +/- 11.0 vs 46.4 +/- 11.6 LU/10(6) PBMC for K562, and 104.3 +/- 23.8 vs 59.3 +/- 14.3 LU/10(6) PBMC for Daudi). Normal control PBMC, stimulated with L. amazonensis antigen had 6.32 +/- 3.72 LU/10(6) PBMC against Daudi cells and 9.06 +/- 2.78 LU/10(6) PBMC against K562. The cell responsible for lysis of the K562 cells was characterized as NK, by means of cell separation employing magnetic beads coupled to antibodies. Addition of recombinant TGF-beta or recombinant human IL-10 reduced L. amazonensis-induced cytotoxicity by 90% and 70%, respectively. Cytotoxicity of antigen-stimulated PBMC was also demonstrated against autologous L. amazonensis antigen-pulsed macrophages in the range of 6.7 to 41.7 LU/10(6) PBMC.(ABSTRACT TRUNCATED AT 250 WORDS)