INCLUSION-BODY MYOSITIS IN HIV-1 AND HTLV-1 INFECTED PATIENTS

Sporadic inclusion body myositis (IBM) is the most common inflammatory myopathy affecting patients over the age of 50 years. Dysimmune and d egenerative aetiologies have been postulated, but viral infections hav e not been associated with the disease. Two HIV-1 (human immunodeficie ncy virus type 1) infected men and one woman infected with HTLV-1 (hum an T cell leukaemia virus type 1) developed progressive proximal muscl e weakness unrelated to antiretroviral therapy. Their muscle biopsies were studied by light and electron microscopy, by immunocytochemistry to determine the expression of major histocompatibility complex (MHC) molecules and identify the type of infiltrating cells and T cell recep tor (TCR) subunits, and by reverse transcription-polymerase chain reac tion (RT-PCR) and single or double immunocytochemistry to search for r etrovirally infected endomysial cells. The clinical features were cons istent with sporadic IBM. The muscle biopsies showed primary endomysia l inflammation red-rimmed vacuoles, amyloid deposits, eosinophilic inc lusions, and small round fibres in groups, all diagnostic of IBM. The muscle fibres expressed MHC class-I antigens and were invaded primaril y by CD8+ T-lymphocytes preferentially bearing TCR V beta 5.1 and V be ta 13 chains. The HIV-1 or HTLV-1 antigens were detected only on endom ysial macrophages on or around muscle fibres, but not within the muscl e fibres. We conclude that IBM occurs in HIV-1 and HTLV-1 infected ind ividuals and has a clinical, histological and immunological pattern id entical to sporadic IBM in the non-retrovirally infected patients. Ret roviruses do not directly infect the muscle, but persistent retroviral infections may provide superantigenic stimulation and trigger an endo mysial inflammatory response identical to that occurring in sporadic I BM.