While it is well-established that protective immunity against leishmaniasis, whether cutaneous or visceral, relies upon an IL-12-driven type 1 response and IFN-γ production, the contribution of IL-4, IL-13, and signaling via IL-4Rα to the outcome of Leishmania infection is very much parasite-species dependent [reviewed (21, 40)]. This evidence concerns the gene IL4 and leishmaniasis.