CD8 T cells that produce IFN-γ followed by the induction of nitric oxide synthetase (NOS) (Klotz et al., 1995; Doolan and Hoffman, 1999) might be physiologically relevant to the process of elimination of LS parasites: IFN-γ inhibits the hepatic stages of rodent and human malaria both in vitro and in vivo (Mellouk et al., 1987); injection of IFN-γ protects mice against sporozoite challenge (Ferreira et al., 1986); and immunization with γ-spz fails to generate protection in IFN-γR KO mice (Tsuji et al., 1995). This evidence concerns the gene IFNG and malaria.