Expression of granulysin in polymyositis and inclusion-body myositis

Background: Granulysin, a recently defined cytolytic molecule, is expressed in cytotoxic T cells and natural killer cells in a similar way to perforin, which is reported to have a major role in the pathogenesis of polymyositis and inclusion-body myositis (IBM). Objective: To clarify the role of granulysin in polymyositis and IBM. Methods: The expression of granulysin and perforin was examined by double staining with CD8, CD4 and CD56 in endomysial infiltrating cells and autoinvasive cells in muscle biopsy specimens of 17 patients with polymyositis (6 steroid resistant and 11 steroid responsive) and of 7 patients with IBM. Results: Similar to perforin, granulysin was expressed in CD8, CD4 or CD56 cells in patients with polymyositis and IBM. The ratio of cells double positive for granulysin and CD8 to all CD8 cells at endomysial sites was notably higher in steroid-resistant polymyositis than in steroid-responsive polymyositis and IBM. Conclusion: Granulysin expression in CD8 cells seems to be correlated with steroid resistance in polymyositis.