Lymphatic endothelial cells (LECs) release extracellular chemokines to guide the migration of dendritic cells. In this study, Researchers at the Medical University of Vienna report that LECs also release basolateral exosome-rich endothelial vesicles (EEVs) that are secreted in greater numbers in the presence of inflammatory cytokines and accumulate in the perivascular stroma of small lymphatic vessels in human chronic inflammatory diseases. Proteomic analyses of EEV fractions identified >1,700 cargo proteins and revealed a dominant motility-promoting protein signature. In vitro and ex vivo EEV fractions augmented cellular protrusion formation in a CX3CL1/fractalkine-dependent fashion and enhanced the directional migratory response of human dendritic cells along guidance cues. The researchers conclude that perilymphatic LEC exosomes enhance exploratory behavior and thus promote directional migration of CX3CR1-expressing cells in complex tissue environments.
Endothelial monolayer transmigration assay with fluorescently stained human mature MMDCs migrating in the presence of EEV fractions from ss LECs on primary LECs that were transduced with a lentiviral construct encoding CCL21. Brightfield and fluorescence images were acquired every 2.2 s for 40 min, and the last 30 min were used for generating the image sequence (frame rate, 90 frames/s; playback speed, 3.3 min/s). Transmigrated MMDCs have a spread out morphology and show decreased red fluorescence intensity. Bar, 50 µm.