MONOCYTE CHEMOATTRACTANT PROTEIN-1 EXPRESSION AND MONOCYTE RECRUITMENT IN OSSEOUS INFLAMMATION IN THE MOUSE

In bone, early events in inflammation involve the production and relea se of primary proinflammatory cytokines, such as interleukin-1 beta. B y activation of target cells, these cytokines are thought to induce a second wave of cytokines, including monocyte chemoattractant protein-1 (MCP-1). MCP-1 is a cytokine that stimulates chemotaxis of monocytes. Experiments were undertaken to examine the expression of MCP-1 in bon e-associated cells in vivo. To observe in vivo expression of MCP-1, an inflammatory lesion was created in the murine mandible. Immunohistoch emistry experiments using specific antibodies to MCP-1 were conducted to identify MCP-1-expressing cells in inflamed and noninflamed bone. W e found that osteoblasts were the principal cells expressing MCP-1 in inflamed bone. There was little or no MCP-1 expression in noninflamed bone. Immunohistochemistry experiments were carried out to assess mono cyte recruitment during osseous inflammation. The number of MCP-1-posi tive cells was significantly correlated to the number of monocytes/mac rophages present (n = 15; r = 0.69; P < = 0.01). These in vivo results strongly suggest that MCP-1 is an important mediator involved in the recruitment of monocytes/macrophages in inflamed bone.