Inhibition of host cell signal transduction by Leishmania: observations relevant to the selective impairment of IL-12 responses.

Leishmania parasites are able to delay the onset of cell-mediated immunity by selectively impairing the ability of infected macrophages to produce interleukin (IL)-12. Leishmania infection arrests the JAK/STAT-mediated signal transduction involved in activation of the IL-12 p40 promoter; the phosphorylation defects may be initiated by ligation of the phagocyte receptors used by these organisms to gain entry into the host cell.