The studies of Lehman et al [39] confirmed that in visceral leishmaniasis a Th1 dominated immune response is protective against L. donovani parasites and furthermore, the capacity to produce IFN-γ rather than the presence of IL-4 determines the efficacy of the immune response in susceptible miceHigh levels of IL-4 and IL-10 in control animals supported a view that marked up-regulation of these two cytokines is accompanied by susceptibility, disease progression and depressed Th1 type of cell mediated immunity with decreased production of IFN-γ and IL-12 [40]. The gene discussed is IFNG; the disease is visceral leishmaniasis.