Lepromatous leprosy and mucosal leshmaniasis, two opposite polar forms of these diseases, were observed in peripheral blood mononuclear cells culture from patients co-infected, which during active leprosy, the M. leprae antigens induced suppression of the IFN-у response to Leishmania braziliensis antigen, and this suppression was abolished by IL-10 neutralization. The gene discussed is IFNA1; the disease is leprosy.