CD4 and infection: To better understand the specific cell subsets in the host that render IL-4Rα-/- mice resistant to CL, recent studies have shown that deficiency of IL-4Rα signaling on CD4+ T cells protects mice from L. major infections but the protection is sex-dependent in L. mexicana-infected BALB/c mice; with controlled infection in female mice, but persistent infection in male mice (21, 22).