CCL5-enhanced human immature dendritic cell migration through the basement membrane in vitro depends on matrix metalloproteinase-9

The proinflammatory chemokine CC chemokine ligand 5 (CCL5) is a potent chemoattractant of immature dendritic cells (iDCs). It remains to be elucidated whether CCL5 may also enhance iDC migration through the basement membrane by affecting matrix metalloproteinase (MMP)‐9 secretion. In this study, iDCs were differentiated in vitro from human monocytes of healthy donors. Zymographic analysis of cellular membranes of nontreated iDCs revealed a basal secretion of the pro‐ and active MMP‐9, whereas only pro‐MMP‐9 was detected in conditioned media. Increasing concentrations of CCL5 significantly enhanced MMP‐9 secretion by iDCs, peaking at 100 ng/ml, which optimally increased iDC migration through a reconstituted basement membrane (Matrigel™) in vitro. The CCL5‐enhanced secretion of MMP‐9 occurred early (2 h) and was maintained at least for 10 h. A significant increase in MMP‐9 mRNA synthesis was detected by reverse transcriptase‐polymerase chain reaction, only at 6 h of CCL5 treatment, which suggests that the early effect of CCL5 (0–4 h) on MMP‐9 secretion was independent of mRNA synthesis, whereas the more delayed effect (6–10 h) could be mediated through an increase in MMP‐9 gene expression. In a Matrigel migration assay, the CCL5‐enhanced iDC migration was reduced significantly by specific inhibitors of MMP‐9, such as tissue inhibitor of metalloproteinase‐1 or an anti‐MMP‐9 antibody, which indicates that iDC migration through the basement membrane depends on MMP‐9. These results suggest that under inflammatory conditions, the chemokine CCL5 may enhance iDC migration through the basement membrane by rapidly increasing their MMP‐9 secretion.