Podoplanin interactions with CLEC-2 regulate dendritic cell migration (44.4)

Abstract

Abstract The migration of dendritic cells (DCs) from peripheral tissues to lymph nodes (LNs) is critical for the generation of protective immune responses and maintenance of self-tolerance. In our studies of DC trafficking we observed that migratory DCs, arriving in LNs from inflamed skin, exhibited elevated surface levels of the C-type lectin, CLEC-2. CLEC-2 activation in DCs was found to induce actin polymerization and increased protrusive activity, directly linking CLEC-2 to altered cytoskeletal dynamics and DC motility. CLEC-2 binds to podoplanin, a 38kDa surface glycoprotein required for correct formation of lymphatic vessels. Interestingly, podoplanin is normally expressed by both lymphatic endothelium (LECs) and fibroblastic reticular cells (FRCs); two stromal cell subtypes that directly interact with migratory DCs en route to the LN paracortex. Using a 3D in vitro culture system combined with time-lapse confocal microscopy we found that FRCs promote migration of DCs in a CCR7-independent manner. Podoplanin localizes to sites of contact between FRCs and DCs, and is required for DC migration along FRC scaffolds. Furthermore, hydrodynamic intradermal injection of podoplanin siRNA, used to silence podoplanin expression by LECs and FRCs, significantly impaired migration of DCs from skin to draining LNs. Our data illuminate important new features of DC-stromal cell interactions and reveal a critical role for podoplanin and its receptor CLEC-2 in regulating DC trafficking to LNs.