Pathogenesis of HTLV-I positive polymyositis

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Patients with polymyositis (PM) in Kagoshima, Japan exhibit seropositivity to human T-cell lymphotropic virus type I (HTLV-I), which is higher than in the general population. A direct HTLV-I infection of muscle fibers was previously reported by in situ hybridization (ISH) in a patient dually infected with HIV and HTLV-I.While using the same technique of ISH,we could not detect HTLV-I in patients with PM infected with HTLV-I alone. We obtained biopsied muscle specimens from 5 HTLV-I positive PM patients, 5 HTLV-I negative PM patients, an autopsied muscle specimen from a HAM patient, and a lymph node from a patient with adult T-cell leukemia (ATL) as a positive control. Employing in situ PCR,we found the HTLV-I provirus in some of the CD4-positive infiltrating cells in HTLV-I-positive PM but not within the muscle fibers. Among HTLV-I-positive PM,we performed double staining of immunohistochemistry for CD4 or macrophage and in situ PCR for HTLV-I provirus on the same sections to determine the exact cell types of HTLV-I containing cells. We found HTLV-I in CD4-positive cells but not in macrophages. This finding suggests that most of the HTLV-I containing CD4-positive cells are not macrophages but lymphocytes.