Anti-interferon-γ autoantibody in a patient with disseminated Mycobacterium avium complex

We report the case of a 44-year-old woman with disseminated Mycobacterium avium complex (MAC) infection involving multiple bone lesions despite a normal healthy status until 6 months previously. Because she was suspected to have acquired immunodeficiency, we tested interferon (IFN)-γ production by peripheral blood mononuclear cells (PBMC) after phytohemagglutinin (PHA) or anti-CD3 stimulation, and found that these cells produced no, or undetectable, levels of IFN-γ in the presence of the patient’s plasma, but produced nearly normal levels of IFN-γ in the presence of healthy donor plasma. Since the IgG fraction of the patient’s plasma was capable of blocking in vitro responses to IFN-γ, the cause of disseminated MAC infection in this case appeared to be anti-IFN-γ autoantibodies. To reduce the titer of anti-IFN-γ autoantibodies, the patient received intravenous immunoglobulin (IVIG). However, titer of autoantibodies changed little compared to that before IVIG administration. According to our literature search, this is only the second case of disseminated MAC infection associated with anti-IFN-γ autoantibodies in Japan.