Specifically, control of the infection relies on a successful macrophage activation via interferon-γ (IFN-γ), produced mainly by proinflammatory CD4+ T helper type 1 (Th1) cells and natural killer (NK) cells stimulated by interleukin (IL)-12, that promotes leishmanicidal activity mediated by nitric oxide (NO) (12, 15–17). This evidence concerns the gene IFNG and infection.