CD4 and infection: •  Lymph node cells produce low Leishmania-induced IFN-γ levels at the initiation of infection. •  Lymph node cells produce normal IFN-γ levels later in infection. •  Mice produce considerable levels of IL-4 at the initial of infection. •  Susceptibility to L. major is limited to the initial stages of infection. •  The IP administration of anti-IL-4 antibody (every 4 days for the first 4 weeks of after infection) improves the IFN-γ production and host resistance. •  The treatment with blocking anti-IL-4 antibody increases the number of IL-17+ CD4+ cells.