Expression of B7-homolog 1 in Polymyositis

Costimulatory molecules are increasingly recognized as crucial for stimulation and/ or inhibition of immune responses. The present study was undertaken to examine the expression and functional relevance of B7-homolog 1 (B7-H1) attributed significant immunoregulatory functions in polymyositis in vivo.

43 muscle biopsy specimens obtained from patients with polymyositis, 26 cases with limb girdle muscular dystrophies (LGMD) 2B and 21 normal muscle samples were analyzed by immunohistochemistry for B7-H1 expression. The clinical and histopathologic data were analyzed.

B7-H1 was not detectable on normal muscle fibers and rarely detectable from patients with LGMD-2B. In contrast, its expression was markedly increased on muscle fibers from patients with polymyositis, even after short-term immunosuppressive treatment. Positive staining mainly localized at the surface of the muscle tissue, rarely in the cytoplasm, focused in areas where inflammatory cells lay in close apposition to damaged, necrotic or degenerative muscle fibers. The expression of B7-H1 was correlated to the degrees of muscular necrosis and clinical muscular strength.

Our results demonstrate that human muscle cells express B7-H1 in polymyositis. The muscle-related expression of B7-H1 may be helpful in the diagnosis of polymyositis and might be an indicator of prognosis of polymyositis.