To establish an early infection, L. major inhibits the NK cell proliferation and IFN-γ production (26) and L. donovani evades inducible nitric oxide synthase (iNOS)-dependent killing of intracellular amastigotes in MΦs via downregulation of iNOS mRNA expression (27, 28) and induction of arginase expression (29) as the arginine is a common substrate for both iNOS and arginase enzymes. This evidence concerns the gene IFNG and infection.