IL-4 is a cytokine associated with susceptibility to L. (L.)amazonensis infection and IL-4-deficient BALB/c mice are more resistant to infection, depending on the initial parasite inoculum, developing smaller lesions and a higher Th1 response, with higher IFN-γ, and IgG2a production than WT mice (Guimarães et al., 2006). The gene discussed is IFNG; the disease is infection.