CD4 and infection: Our data show that the hierarchical importance of target cells interacting with the IL-4Rα and its ligands (IL-4 and IL-13) is a dynamic interaction, largely influenced by cytokines secreted in the vicinity of target and non-target cells, heterogenous CD4+ T cell populations, autocrine versus paracrine signaling, the Leishmania species/strain initiating infection, and the timing of the immune response.