Similar ‘self-regulating’ Th1 cells that co-produce IL-10 and IFN-γ were first identified in the lungs of patients with active pulmonary tuberculosis [64] and have since been observed in mice infected with Toxoplasma gondii[65] and Leishmania major[66] as well as in humans with visceral leishmaniasis [67]. The gene discussed is IFNG; the disease is visceral leishmaniasis.