Dendritic cells in muscle lesions of sarcoidosis

Sarcoidosis is a chronic systemic granulomatous disorder of unknown etiology. The precise mechanism by which granulomatous lesions form is still obscure. Dendritic cells (DCs) are the most efficient antigen presenting cells; however, pathologic investigations of dendritic cells in the affected lesions of sarcoidosis are quite limited. We immunohistochemically examined the localization and phenotypes of dendritic cells and the expressions of CD40 and CD40L (CD154), which are key molecules in dendritic cell activation, in the muscles of 5 patients with muscular sarcoidosis, 8 patients with muscular disorders without inflammation, and 4 patients with histologically normal muscles as controls. In muscular sarcoidosis, CD1c-positive myeloid dendritic cells were scattered mainly in the lymphocyte layers of granulomas and the endomysium around the granulomas. Double immunostaining revealed that some CD1c-positive cells expressed the mature dendritic cell marker CD83, but immature dendritic cell marker CD1a-positive cells were not found. Smaller numbers of Blood dendritic cell antigen (BDCA)-2-positive plasmacytoid dendritic cells were found in the lymphocyte layers of granulomas. In the controls, small numbers of CD1c-positive cells were seen in the endomysium, whereas BDCA-2-positive cells were not observed except in 1 case. In muscular sarcoidosis, CD40 was expressed on mononuclear cells, on the interstitium around the muscle fibers and granulomas, and on the endothelium of vessels. CD40L was positive on mononuclear cells scattered within and around granulomas in 3 of 5 patients. In the controls, CD40 was expressed on the endothelium of the vessels and sparse mononuclear cells in the lesions of muscle fiber necrosis, whereas CD40L was not seen in any. In muscular sarcoidosis, recruitment of myeloid dendritic cells and less plasmacytoid dendritic cells and up-regulation of the CD40/CD40L system in affected muscles suggest that myeloid dendritic cells may be mainly involved in granulomatous inflammation through antigen presentation in a Th1 immune milieu.