Tumor necrosis factor-α expression in muscles of polymyositis and dermatomyositis

Abstract

We evaluated the expression of tumor necrosis factor-α (TNF-α) mRNA in muscle biopsy specimens from patients with polymyositis (PM) and dermatomyositis (DM) to clarify its role in the pathogenesis of PM and DM. We performed non-radioactive in situ hybridization studies for TNF-α combined with immunohistochemistry for cell type-specific markers on muscles from ten PM and five DM patients. TNF-α-positive infiltrating cells present in the endomysium and perimysium were found in all PM and DM muscles. The frequency of TNF-α-positive cells against total infiltrating cells was similar among PM and DM (27.1 ± 7.4% in PM and 28.5 ± 13.6% in DM). However, TNF-α/CD8-positive lymphocytes and TNF-α-positive macrophages invading the non-necrotic muscle fiber were observed only in PM but not in DM. TNF-α was more highly expressed in PM and DM than was previously thought, and it was suggested that TNF-α plays a role in muscle fiber degeneration in PM.