Trafficking of tissue dendritic cells (DCs) via lymph is critical for the generation of cellular immune responses in draining lymph nodes (LNs). In the current study we found that DCs docked to the basolateral surface of lymphatic vessels and transited to the lumen through hyaluronan-mediated interactions with the lymph-specific endothelial receptor LYVE-1, in dynamic transmigratory-cup-like structures. Furthermore, we show that targeted deletion of the gene Lyve1, antibody blockade or depletion of the DC hyaluronan coat not only delayed lymphatic trafficking of dermal DCs but also blunted their capacity to prime CD8 T cell responses in skin-draining LNs. Our findings uncovered a previously unknown function for LYVE-1 and show that transit through the lymphatic network is initiated by the recognition of leukocyte-derived hyaluronan.

The lymphatic endothelial receptor LYVE-1 has been implicated in both uptake of hyaluronan (HA) from tissue matrix and in facilitating transit of leukocytes and tumor cells through lymphatic vessels based largely on in vitro studies with recombinant receptor in transfected fibroblasts. Curiously, however, LYVE-1 in lymphatic endothelium displays little if any binding to HA in vitro, and this has led to the conclusion that the native receptor is functionally silenced, a feature that is difficult to reconcile with its proposed in vivo functions. Nonetheless, as we reported recently, LYVE-1 can function as a receptor for HA-encapsulated Group A streptococci and mediate lymphatic dissemination in mice. Here we resolve these paradoxical findings and show that the capacity of LYVE-1 to bind HA is strictly dependent on avidity, demanding appropriate receptor self-association and/or HA multimerization. In particular, we demonstrate the prerequisite of a critical LYVE-1 threshold density and show that HA binding may be elicited in lymphatic endothelium by surface clustering with divalent LYVE-1 mAbs. In addition, we show that cross-linking of biotinylated HA in streptavidin multimers or supramolecular complexes with the inflammation-induced protein TSG-6 enables binding even in the absence of LYVE-1 cross-linking. Finally, we show that endogenous HA on the surface of macrophages can engage LYVE-1, facilitating their adhesion and transit across lymphatic endothelium. These results reveal LYVE-1 as a low affinity receptor tuned to discriminate between different HA configurations through avidity and establish a new mechanistic basis for the functions ascribed to LYVE-1 in matrix HA binding and leukocyte trafficking in vivo.