uPA-mediated remodeling of CCL21 gradients regulates lymphatic migration of dendritic cells.

Dendritic cell (DC) migration via afferent lymphatics to draining LNs (dLNs) occurs in distinct steps that require the chemokine C-C motif ligand 21 (CCL21). In addition to full-length CCL21, which forms an immobilized perilymphatic gradient, a truncated soluble variant with enhanced gradient-forming capacity (CCL21-ΔC) was recently identified in tissues. We show that in skin, plasmin is continuously activated in a urokinase plasminogen activator (uPA)-dependent manner on lymphatic endothelial cells (LECs) and cleaves full-length CCL21, generating CCL21-ΔC. Inflammatory conditions, while promoting overall DC migration, markedly enhance this process, reducing immobilized perilymphatic CCL21 and increasing dermal CCL21-ΔC levels. Inhibition of uPA-mediated CCL21 cleavage causes full-length CCL21 to accumulate around dermal lymphatics, while CCL21-ΔC levels decline in the skin and dLN subcapsular sinus. Consequently, DC entry into afferent lymphatics is diminished, whereas DC egress from the subcapsular sinus into the LN parenchyma is enhanced. These findings reveal uPA/plasmin-dependent regulation of lymphatic CCL21 gradients and identify CCL21-ΔC as critical for DC migration.