Transcriptomics- and 3D imaging-based characterization of the lymphatic vasculature in human skin.

Afferent lymphatic vessels (LVs) are present in most vascularized tissues and exert important immune and drainage functions, yet human afferent LVs remain poorly studied. Performing single-cell RNA sequencing of lymphatic endothelial cells (LECs) from human skin and subcutaneous adipose tissue, we identified various LEC subsets, including two valve LEC populations located on the upstream and downstream sides of the valve leaflets. The cell adhesion molecule CD24 emerged as a specific marker of upper valve leaflet LECs in human skin and contributed to lymphatic valve development in murine mesentery. Three-dimensional imaging further revealed several unique features of the human dermal lymphatic network, including a high proportion of LYVE-1+ pre-collecting vessels containing intraluminal valves, virtually no collectors, and absence of lymphatic muscle cell coverage. Moreover, LECs in blind-ended capillaries and around valves in pre-collectors displayed mixed junctional and morphological phenotypes. These findings reveal key differences between human and murine dermal afferent lymphatics and provide a deeper understanding of human lymphatic-related (patho)physiological processes.