Matrix metalloproteinase (MMP) secretion in a co-culture of CD14+ monocytes and human fibroblast cells (HFC). (a) Gel zymography detection of MMP-2 and MMP-9 in human CD14+ monocytes from rheumatoid arthritis (RA) patients, in HFC and in a co-culture of the two. An elevated release and activation of MMP-9 and MMP-2 was seen in the co-culture cells compared with those in the cultures of human monocytes or HFC alone. (b) Gel zymography detection of MMP-2 and MMP-9 in human CD14+ monocytes of normal control monocytes, in HFC, and in a co-culture of the two. MMP-2 and MMP-9 release was higher in the co-culture cells. (c) Effects of antagonistic peptide 9 (AP9) on pro-MMP-9, MMP-9 and MMP-2 release in a co-culture of human CD14+ monocytes and HFC. The zymography gels above were scanned and the gray density of strips was counted. The release and activation of pro-MMP-9, MMP-9 and MMP-2 was significantly reduced when AP9 was added. Asterisks indicate a p-value <0.01. HFC, Human fibroblast cells.