Human cutaneous leishmaniasis: in-vitro parasite--mononuclear cell interactions in immune and naive individuals

The aim of this study was to compare the ability of Leishmania parasites to survive in mononuclear cells from immune individuals with their ability to survive in cells from naive individuals. For this purpose we established an in vitro system based on the co-culture in suspension of human peripheral blood leukocytes derived from immune and naive subjects and L. major promastigotes. The proportion of monocytes containing intracellular parasites and the number of amastigotes per 100 infected monocytes (parasite burden) were determined 24 and 72 h after in-vitro infection. The proportion of infected cells from naive individuals did not change, and the number of amastigotes either did not change or increased by 1.2 to 1.7-fold between 24 and 72 h incubation. In contrast, in the immune subjects, the proportion of infected monocytes 24 h after infection was lower than in the naive individuals, and a 30-90% decrease in both the proportion of infected monocytes and the parasite burden was observed after 72 h incubation. Based on these results, three characteristics of leishmanicidal activity of mononuclear cells from immune individuals were determined: (a) the proportion of infected monocytes 24 h after infection was lower than 22%; (b) there was a decrease of more than 30% in the proportion of infected monocytes between 24 and 72 h after infection; and (c) there was a significant decrease in the number of amastigotes between 24 and 72 h after infection. The results of this study demonstrate an enhanced leishmanicidal activity of mononuclear cells from immune individuals.