MONOCYTE CHEMOATTRACTANT PROTEIN-2 IS A POTENT AGONIST OF CCR2B

The binding and functional activity of the CC chemokines monocyte chem oattractant protein-1 (MCP-1), MCP-2, and MCP-3 have been characterize d using Chinese hamster ovary DXB-11 cells transfected with the chemok ine receptor CCR2B. Receptor binding studies demonstrated that I-125-l abeled MCP-1 bound to a single class of high-affinity receptors with a K-d of 0.14 (0.07-0.32) nM. In competition studies MCP-1, MCP-2, and MCP-3 completely inhibited I-125-labeled MCP-1 binding with K-i values of 0.3 (0.16-0.46), 8.8 (3.4-26), and 12.2 (0.6-22) nM, respectively, In calcium mobilization studies, MCP-1 and MCP-3 induced robust eleva tions in intracellular calcium concentrations, whereas MCP-2 was only weakly active, In contrast, using changes in extracellular acidificati on rate as a functional readout, all three chemokines were identified as potent agonists of CCR2B. These data demonstrate that MCP-2, in add ition to MCP-1 and MCP-3, is a potent agonist of CCR2B and furthermore that MCP-2 activates either different or a subset of the signaling pa thways activated by MCP-1 and MCP-3.