INDUCTION OF MONOCYTE CHEMOATTRACTANT PROTEIN-1 SYNTHESIS IN HUMAN MONOCYTES DURING TRANSENDOTHELIAL MIGRATION IN-VITRO

Monocyte chemoattractant protein-1 (MCP-1, or monocyte chemotactic and activating factor) plays important roles in the recruitment of monocy tes and thus in the development of atherosclerosis. In this study, we determined whether MCP-1 synthesis was induced by the cellular interac tion between monocytes and endothelial cells during the process of tra nsendothelial migration. We found that when human peripheral blood mon ocytes (2.5X10(6) cells) and umbilical vein endothelial cells (HUVECs; 5.0x10(5) cells) were cocultured for 5 hours, 7.9 ng/mL MCP-1 was sec reted into the medium, whereas when the two were cultured separately, MCP-1 levels were 1.0 and 0.9 ng/mL, respectively. Furthermore, the us e of interleukin-1 beta (IL-1 beta)-pretreated HUVECs in cocultures in duced twice the levels of MCP-1 as in unstimulated HUVEC culture. Cond itioned medium had transendothelial chemotactic activity for monocytes , and this activity was completely abolished by addition of anti-MCP-1 antibody. Although MCP-1 mRNA levels were very low or undetectable in HUVECs or monocytes alone, message could be detected after 2 hours of coculture in total mRNA preparations from both monocytes and HUVECs. mRNA levels increased by 4 hours and had declined slightly by 24 hours . The rapid induction of message suggests that cell contact between mo nocytes and HUVECs induces the de novo synthesis of MCP-1 protein. Ant i-interleukin (IL)-1 alpha/beta and anti-tumor necrosis factor-alpha a ntibodies, or anti-lymphocyte function-associated antigen-1 and very l ate antigen-4 antibodies, had little or no inhibitory effects on MCP-1 secretion by cocultures. Immunohistochemistry revealed that monocytes adherent to or having migrated across unstimulated HUVEC monolayers a s well as the HUVECs themselves expressed MCP-1 protein. However, nona dherent monocytes failed to express it. This finding suggests that the monocyte- endothelial cell adhesive interaction results in an MCP-1-i nductive signal to each cell type. MCP-1 expression by migrated monocy tes may indicate that monocytes are primed to produce MCP-1 during tra nsmigration and can secrete it in normal tissue in which inflammatory cytokines that induce MCP-1 are otherwise absent.