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 aut oimmune diseases characterized by the recruitment of lymphocytes and monocy tes 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 ro le in the pathogenesis of IIM. Frozen muscular tissues were obtained from e ight cases of DM, five PM, and four TBM. We investigated the MCP-1 expressi on 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 hybridizat ion showed MCP-1 mRNA accumulation in perivascular mononuclear cells. Immun ohistochemistry showed MCP-1 expression in vessels (endothelial cells and w alls 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 mu scle fibers. These findings suggest that MCP-1 can contribute to the inflam matory 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 c ells previously reported to produce MCP-1, contribute to its production in IIM lesions.