Expression of intercellular adhesion molecule-1 on rat vascular smooth muscle cells by pro-inflammatory cytokines

Infiltration of mononuclear cells is an early pathological finding in human and experimental atherosclerosis. However, the cellular and molecular basis for cell infiltration is incompletely understood. While the intercellular adhesion molecule-1 (ICAM-1) is expressed on endothelial cells and promotes the adhesion of mononuclear cells, there is little information on the expression of ICAM-1 on vascular smooth muscle cells (SMC). In this study, we investigated the expression of ICAM-1 on cultured rat SMC and its regulation by pro-inflammatory cytokines, interleukin 1 alpha (IL-1 alpha), interleukin 6 (IL-6) and monocyte chemoattractant protein 1 (MCP-1). In immunohistochemical staining, ICAM-1 molecules were constitutively expressed on the surface of SMC. In flow cytometric and ELISA analyses, ICAM-1 molecule expression on SMC was significantly upregulated by IL-1 alpha and MCP-1, but not by IL-6, in a dose-dependent manner. The effects of IL-1 alpha and MCP-1 were observed as early as 4 h. In Northern blot analysis, ICAM-1 mRNA was slightly detectable in unstimulated SMC, but its expression was clearly observed following exposure to IL-1 alpha or MCP-1. These results suggest that ICAM-1 on SMC, as well as on endothelial cells, could participate in the focal accumulation of mononuclear cells in human atherosclerotic lesions.