Previous research demonstrated that mice pre-exposed to the salivary gland extract (SGE) of sand flies followed by infection with Leishmania major in the presence of SGE have a five-fold increase in infiltrating leukocytes in the skin, augmented IFN-γ, decreased interleukin (IL)-4, and, remarkably, are protected against the severe disease [12], [16]. The gene discussed is IL4; the disease is infection.