Visceral leishmaniasis is characterized by fever, malaise, anemia, leukopenia, thrombocytopenia, hepatosplenomegaly, hypergammaglobulinemia, and a strong suppression of the cellular immune response (47), mainly due to an intense decrease of the CD4+ T helper lymphocyte population, which is responsible for the resistance to the infection (86, 87). This evidence concerns the gene CD4 and infection.