Suppressive Role of Endogenous Endothelial Monocyte Chemoattractant Protein–1 on Monocyte Transendothelial Migration In Vitro

Abstract

Monocyte chemoattractant protein–1 (MCP-1, or monocyte chemotactic and activating factor) is thought to play an important role in monocyte infiltration into tissue, but little is known about its effect on monocyte-endothelium interaction. We examined the effect of MCP-1 produced by cytokine-activated endothelial cells (ECs) on monocyte-endothelium adhesion and subsequent transendothelial migration by using a double-chamber vessel model. Unstimulated ECs showed no MCP-1 expression, but exposure to interleukin-1β (IL-1β, 25 U/mL) induced marked MCP-1 mRNA expression and protein synthesis. When placed in the lower compartment, recombinant human (rh) MCP-1 (100 ng/mL) produced a 1.9-fold and a 2.7-fold increase in adhesion and migration, respectively, compared with a corresponding 51% and 59% decrease when placed in the upper compartment. Migration of monocytes was dependent on a gradient of rh–MCP-1 from the apical to basilar side of the EC layer. Furthermore, a forward gradient of MCP-1 induced adherent cells to increase their subsequent migration, whereas a reverse gradient induced the cells to detach and completely inhibited their subsequent migration. Pretreatment with IL-1β for 4 and 24 hours produced a 20% and 63% increase in monocyte migration, respectively. In the presence of anti–MCP-1 antibody, the increase was further enhanced by 52% and 152%, respectively. These results suggest that endogenous endothelial MCP-1, when secreted by IL-1–stimulated ECs, suppresses monocyte migration in the presence of MCP-1 on the basilar side of the EC layer. This process may be useful for preventing excessive infiltration of monocytes from the circulating blood into atherogenic tissue during the early stages of atherogenesis.