The expression of BAFF in the muscles of patients with dermatomyositis

A B-cell activating factor of the tumor necrosis factor (TNF) family (BAFF) plays a crucial role in B-cell survival and maturation. An elevated serum BAFF level has been linked to several autoimmune diseases such as Sjögren syndrome, systemic lupus erythematosus and rheumatoid arthritis. Dermatomyositis (DM), one of autoimmune inflammatory myopathies, is characterized by inflammatory cell infiltration (CD4(+) T cells and B cells) in skeletal muscle. Serum BAFF level was significantly high in DM, but the role of BAFF is not well understood. We investigated the role of BAFF in the immunopathogenesis of DM. To examine the transcriptional increase of BAFF gene expression, we performed RT-PCR analysis with skeletal muscle tissue that contained 4 controls and 9 patients with DM. Next, in order to detect BAFF expression and cellular localization in DM, we executed immunostaining in cryosection of biopsied muscle tissue with 4 controls and 8 patients and we adopted to double immunostaining to find which inflammatory cells expressed BAFF-receptor (BAFF-R). BAFF mRNA level was increased in DM patients compared with normal controls. BAFF expression was markedly increased at muscle fibers in the perifascicular area but not blood vessels. BAFF-R was expressed in inflammatory cells in skeletal muscle tissues of DM patients. We found that BAFF expression in muscle tissue may be associated with an increased number of CD4(+) T cells and CD19(+) B cells in DM. Our study results suggest that BAFF might play an important role in the pathogenesis of DM.