Local expression of monocyte chemoattractant protein-1 (MCP-1) in idiopathic inflammatory myopathies

The idiopathic inflammatory myopathies (IIM), including dermatomyositis (DM), polymyositis (PM), and inclusion body myositis (IBM), are a group of autoimmune diseases characterized by the recruitment of lymphocytes and monocytes to the site of affection. The mechanism for recruitment of these cells likely involves chemokines. The monocyte chemoattractant protein-1 (MCP-1), a chemoattractant to T lymphocytes and monocytes, may play an important role in the pathogenesis of IIM. Frozen muscular tissues were obtained from eight cases of DM, five PM, and four IBM. We investigated the MCP-1 expression by the reverse transcription-PCR technique, immunohistochemistry and in situ hybridization. MCP-1 mRNA was markedly expressed in all the IIM cases. Greater amounts of MCP-1 mRNA were observed in DM, and in situ hybridization showed MCP-1 mRNA accumulation in perivascular mononuclear cells. Immunohistochemistry showed MCP-1 expression in vessels (endothelial cells and walls of veins and arteries) in all IIM cases. Very few mononuclear cells in DM perivascular infiltrates expressed MCP-1, whereas in PM and IBM, it was strongly expressed by mononuclear cells partially invading non-necrotic muscle fibers. These findings suggest that MCP-1 can contribute to the inflammatory response by attracting monocytes and T lymphocytes to sites of cell-mediated immune injury. The morphological characteristics and distribution of positive cells indicate that macrophages, lymphocytes, and endothelial cells previously reported to produce MCP-1, contribute to its production in IIM lesions.