However, this classical Th1/Th2 paradigm has been challenged by recent findings in humans and some mouse models: for instance, IL-4−/− and IL-4Rα−/− BALB/c mice are not resistant against all L. major strains [7], and, whereas IL-4−/− and IL-4Rα−/− BALB/c mice are resistant to infection with L. amazonensis, IL-4−/− C57BL/6 and IL-4−/− C3H mice are not [8], [9]. This evidence concerns the gene IL4R and infection.