Control of parasites is correlated with the production of IFN-γ by CD4+ T cells, whilst uncontrolled infections have an absence of IFN-γ in these mice (12, 18–20) using C57BL/6 mice have shown that CD4+ T cells can play a pathogenic role in L. amazonensis infection, in which mice with MHC-2 depletion and lymphocyte depletion, in transgenic mice lacking the recombinant activation gene 2 (RAG-2−/− mice), were more resistant to infection, presenting smaller lesions in relation to wild-type animals. The gene discussed is CD4; the disease is infection.