MT1-MMP expression is up-regulated in human monocytes attached to FN in a manner dependent on α4β1 and α5β1 integrins. (A) MT1-MMP cell-surface expression was analyzed by flow cytometry in freshly isolated monocytes (thin solid line) and in monocytes attached to plates coated with 0.5% BSA, 20 μg/mL FN, or 10 μg/mL FN fragments H89 and FN80 for 16 hours (thick solid line). LPS stimulation (10 ng/mL) for 16 hours was included as a positive control. X63 was used as a negative control of staining (dotted line). One independent experiment of 6 is represented. (B) The arithmetic means and SD are shown of the percentage of MT1-MMP–positive monocytes (subtracting X63 negative control values) under different conditions. n = 6. ^*P < .05 (versus fresh) and ^**P < .04 (versus BSA). (C) MT1-MMP cell-surface expression was analyzed as described in panel A in monocytes adhered for 16 hours to different doses of BSA, FN, or FN fragments H89 and FN80 as indicated. The arithmetic means of the percentage of MT1-MMP–positive monocytes (subtracting X63 negative control values) are represented for each condition. n = 3. (D, top) MT1-MMP protein content was estimated by Western blot analysis of total cellular extracts from fresh monocytes or monocytes attached to plates coated as described for panel A. Anti–MT1-MMP LEM-2/15 mAb recognizes immature and mature forms of MT1-MMP of 63 and 60 kDa, respectively. (D, bottom) The arithmetic means and SD of the fold induction of the ratio of MT1-MMP to β-actin levels estimated by densitometry are represented (an arbitrary value of 1 was assigned to the MT1-MMP/β-actin ratio in freshly isolated monocytes). n = 4. ^***P < .01.