Effect of cytokines on gelatinase activity of CD34⁺ cells from BM and PB. The cells were incubated for 24 hours in serum-free IMDM in the absence (control) or presence of a cytokine, and then zymography was performed on 10% (A, left panel) or 12% (A, right panel, and B) acrylamide containing 2 mg/mL gelatin. Data are representative of at least three experiments using CD34⁺ cells from both BM and PB sources. The final concentrations of cytokines are given in Materials and Methods. Media conditioned by HT-1080 cells was used as the standard (Std) showing the positions of the 92-kD (MMP-9) and 72-kD (MMP-2) activities in the gel. To establish the identity of the band having molecular weight lower than 72 kD, cell-conditioned media in the presence of TNF- was preincubated with 1 mmol/L APMA for 30 minutes before loading of the gel (B, left panel). (C) Densitometric analysis of gelatinolytic activities (MMP-9 and MMP-2). The intensities of the bands were quantitated relative to the control and expressed as fold increase ± standard deviations from two or three zymograms. The asterisks indicate where statistical differences exist (P < .05) in MMP-9 and MMP-2 activities of CD34⁺ cells from BM versus PB in response to each cytokine.