MT1-MMP activity is required for MCP-1–stimulated migration of monocytes on FN, VCAM-1, or ICAM-1. Monocyte migration was analyzed in Transwell assays on 3 μm–pore filters coated with 20 μg/mL FN, 10 μg/mL VCAM-1 or ICAM-1, or none (A, B, C, and D, respectively). 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. Migrated cells were quantitated after 2 hours as described in “Materials and methods” and are represented as a percentage of cellular input. The arithmetic means and SD of n independent experiments run in triplicate are shown (n = 4 for FN, n = 3 for VCAM-1, n = 4 for ICAM-1, and n = 3 for none). ^***P < .01.