Immunopathologic study of skin lesions in dermatomyositis

To determine the phenotype of skin infiltrates in affected and uninvolved skin from patients with dermatomyositis, immunohistochemical studies with 10 murine monoclonal antibodies were carried out on 25 skin biopsy specimens. Dermal infiltrates consisted predominantly of HLA-DR-expressing macrophages and T lymphocytes, especially of the CD4 subset. B lymphocytes, as defined by positive staining for Leu-12, were absent. Epidermal Langerhans cells were absent or decreased in some areas of affected skin but the total number was normal. OKT6+ cells were present in some dermal mononuclear infiltrates in close contact with lymphocytes. We observed reduced HLA-DR positivity of dermal capillary endothelia. These findings are apparently different from dermatomyositis muscle infiltrates but are similar to those in skin affected by cutaneous lupus erythematosus. Our observations support the concept that, in autoimmune diseases, cellular infiltrates may be more organ-specific than disease-specific.