In vitro secretion of cytokines by human mononuclear cells of individuals during and after cutaneous leishmaniasis infection.

Human peripheral blood mononuclear cells were incubated in the presence of Leishmania major promastigotes. The culture supernatants were collected after 24 and 72 h and the cytokine content was measured. It was found that mononuclear cells from cured individuals, in the presence of L. major promastigotes, had increased leishmanicidal activity and secreted increased levels of interferon gamma (IFN gamma), interleukin-2 (IL-2) and tumour necrosis factor alpha (TNF). The levels of IL-6, on the other hand, did not differ from the levels secreted by cells from unexposed individuals. The secretion of cytokines by cells from patients in the course of the disease was sometimes elevated, but the pattern they presented was more heterogeneous than that of cured individuals, and showed less correlation with leishmanicidal effector activity. Addition of IFN and IL-2, but not TNF, to cultures from unexposed individuals caused increased leishmanicidal activity, suggesting that these factors play a role in controlling the parasite infection; the role of TNF is not yet clear, and is probably concentration-dependent.