MT1-MMP plays a role in MCP-1–induced transmigration of monocytes through activated endothelial cells. Monocyte transmigration was analyzed in Transwell assays on 3 μm–pore filters coated either with endothelial monolayers previously activated with 20 ng/mL TNF-α for 2 hours (A) or with resting endothelial monolayers (B). MCP-1 (100 ng/mL) or vehicle was added to the lower chamber. Monocytes were pretreated with PBS or 15 μg/mL anti–MT1-MMP LEM-2/15 mAb or the isotype-matched control anti–MHC-I W6/32 mAb. Transmigrated cells were quantitated after 2 hours as described in “Materials and methods” and are represented as the percentage of cellular input. The arithmetic means and SD of 3 independent experiments run in triplicate are shown. ^***P < .01.