IL-10 secreted by Tregs are involved in persistence of parasites, regulation of Th2 cell expansion, and control of cell-mediated lesion development in leishmaniasis (Powrie et al., 1994; Sacks and Kamhawi, 2001; Aseffa et al., 2002; Xu et al., 2003; Mendez et al., 2004; Ji et al., 2005). The gene discussed is IL10; the disease is leishmaniasis.