Control of Leishmania infantum infection is associated with CD8(+) and gamma interferon- and interleukin-5-producing CD4(+) antigen-specific T cells.

Visceral leishmaniasis is a severe and lethal disease caused by the protozoan parasites of the genus Leishmania. In areas where leishmaniasis is endemic, most infected individuals control the infection and remain asymptomatic; chemotherapy of visceral leishmaniasis restores some immunity which protects against relapses. In the present study, Leishmania-specific T-cell clones were established from six asymptomatic and five cured patients. Cytokines production by these clones was analyzed. A large fraction of the parasite-specific T-cell clones from asymptomatic patients were CD8(+) and produced high amounts of gamma interferon (IFN-gamma). Most CD4(+) T-cell clones from two asymptomatic subjects exhibited an unusual phenotype: production of high levels of IFN-gamma low levels of interleukin-4, (IL-4), but high levels of IL-5. In contrast, only few parasite-specific CD8(+) T-cell clones were obtained from cured patients after chemotherapy; moreover, CD4(+) T-cell clones from these patients exhibited an heterogeneous profile of cytokines from Th1-like to Th2-like phenotypes. These results point to CD8(+) T cells and to IL-5- and IFN-gamma-producing CD4(+) T cells as possible contributors to human resistance to Leishmania infection. They should stimulate new immunological approaches in the control of this disease.