Anti-interferon-γ autoantibody-associated adult-onset immunodeficiency with occult immunological abnormalities and sequential intracellular infections: a case report.

Adult-onset immunodeficiency associated with anti-interferon-γ (IFN-γ) autoantibodies (AIGA) is a rare immune disorder that neutralizes IFN-γ activity and compromises defense against intracellular pathogens. It is predominantly reported in Southeast Asia and predisposes affected individuals to recurrent and multiple intracellular bacterial infections, which can be life-threatening. As a "silent disruptor," AIGA often go unnoticed due to their insidious nature, leading to a lack of sufficient clinical awareness. This report presents the case of a 59-year-old male patient from Wenzhou, Zhejiang Province, China, who experienced multiple severe infections over one year. These included disseminated bloodstream infection caused by Salmonella enteritidis, pneumonia caused by Legionella pneumophila, and osteomyelitis (an infection of bone and bone marrow caused by microbial pathogens) of the right scapula caused by Talaromyces marneffei, which are rarely observed consecutively in immunocompetent individuals. The patient exhibited no distinct immune phenotypic abnormalities, leading to the insidious nature of the disease. After receiving short-term targeted antimicrobial therapy, long-term rituximab treatment and prophylactic anti-infective therapy, the patient eventually recovered and was discharged, with regular follow-up to monitor AIGA titers. This case suggests that AIGA-associated immunodeficiency should be considered in adults presenting with unexplained or recurrent intracellular infections, even when their immunophenotypic features appear unremarkable. Prompt detection of AIGA is essential for establishing an accurate diagnosis and initiating appropriate treatment. Immunomodulatory therapy with rituximab, in combination with targeted antimicrobial therapy and close long-term follow-up, can achieve favorable clinical outcomes. Ongoing clinical experience and research are needed to establish standardized therapeutic strategies and determine the optimal treatment duration for this rare immunodeficiency.