Leishmanin skin test lymphoproliferative responses and cytokine productionafter symptomatic or asymptomatic Leishmania major infection in Tunisia

Resistance to Leishmania parasite infection requires the development of a c ellular immune response that activates macrophage leishmanicidal activity. In this study we have investigated the lymphoproliferative responses and in vitro cytokine production of peripheral blood mononuclear cells (PBMC) fro m individuals living in an endemic area for L. major infection in Tunisia. The results were compared with the DTH reaction of the leishmanin skin test (LST). Sixty-seven individuals were included in the study: 22 persons (age range 9-60 years) who developed, 2 years before the present study, a paras itologically confirmed localized cutaneous leishmaniasis (LCL) that healed spontaneously, and 45 individuals (age range 18-20 years) born and living i n the same area, with no previous history of LCL. LST was positive (skin in duration greater than or equal to 5 mm) in 20/22 cured cases of LCL and in 75% of healthy individuals without history of LCL. LST+ individuals express ed vigorous Leishmania-specific lymphoproliferative responses associated wi th in vitro production of interferon-gamma (IFN-gamma) but not IL-4. Intere stingly, IL-10 was detected in parallel with the highest levels of IFN-gamm a in PBMC supernatants from 3/20 cured LCL and 8/25 individuals without his tory of LCL. Our results showed a 98% concordance between the DTH reaction assessed by LST and the in vitro proliferative assay induced by soluble lei shmanial antigens. Moreover, proliferative assays as well as cytokine analy sis did not show any significant difference of the immune memory to parasit e antigens developed by patients who had overt cutaneous leishmaniasis and those who had apparently asymptomatic infection.