CD4 and protozoa infectious disease: Nevertheless in several virulent protozoal infections (PyL, Toxoplasma gondii, Leishmania major SD and L. donovani), adaptive IL-10-producing CD4+ T cells are required to regulate the fulminant Th1-effector responses that are induced whereas classical (Foxp3+) Treg appear to be sufficient to regulate the effector response to a less virulent (healing) strain of L. major[15].