Kala azar is a lethal disease caused by infection with the protozoan parasite Leishmania donovani. Alain Dessein and colleagues, at INSERM UMR 906, France, have now obtained new insight into the human immune responses responsible for protection against kala azar.
Although the immune molecules IL-17 and IL-22, which are produced by immune cells known as Th17 cells, provide protection against some bacteria and fungal pathogens in animal models, their role in protection against microbes has not been determined in humans. In this study, analysis of a subset of blood cells (peripheral blood mononuclear cells) from individuals who were infected with Leishmania donovani and developed kala azar and those who were infected with the protozoan parasite but did not develop kala azar showed that IL-17 and IL-22 were strongly and independently associated with resistance to kala azar.
Further analysis indicated that peripheral blood mononuclear cells from individuals who developed kala azar produced lower levels of the factors required for the induction of Th17 cells. As peripheral blood mononuclear cells from healthy individuals produced high levels of IL-17 and IL-22 when exposed to Leishmania donovani in vitro, the authors conclude that IL-17 and IL-22 have important complementary roles in protecting individuals from developing kala azar following infection with Leishmania donovani.
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