This phase is polarized by two types of response: the first is Th1 response with the production of interferon gamma (IFN-γ) and tumour necrosis factor alpha (TNF-α), which leads to the activation of the oxidative stress machinery; still protecting the host cell against the parasite, it may induce a Th2 type response with the production of, mainly, interleukin 4 (IL-4) that leads to the phenotype of susceptibility to infection [8]. This evidence concerns the gene IL4 and infection.