Examining the correlation between cytokine levels and control of infection, we observed a significant inverse relationship between peak parasitemia and a broad Th1 cytokine response (comprising parasite-induced IFN-γ, TNF, and IL-2) when comparing all combinations of mouse strains that were challenged and the different species of parasites (homologous and heterologous) (r = −0.7835; P = 0.0214; Fig. 6E). This evidence concerns the gene TNF and infection.