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Figure 1: Morphology of human lung lymphatic endothelial cells (HL-LEC). (a)–(d): phase contrast microscopy. (a): an example of a mixed cell population obtained after enzymatic digestion of lung fragments. The black rectangle includes an area shown at higher magnification in (b) to illustrate a cluster of cells with cobblestone-like morphology, suggestive of an endothelial phenotype. (c): confluent monolayer of lymphatic endothelial cells selected by double immunomagnetic sorting with CD31 and Pdn antibodies. (d): fibroblastoid morphology of the CD31 negative cell population eluted after immunomagnetic sorting. (e)–(j): Transmission Electron Microscopy (TEM). (e): microphotograph of a single HL-LEC showing numerous surface microvilli. (f)–(h): ultrastructural characteristics of the lymphatic endothelium are documented by the presence of prominent micropinocytotic vesicles (MV), a well-developed rough endoplasmic reticulum (RER) and Weibel-Palade bodies (WP). (i)-(j): ultrastuctural image of a HL-LEC showing multiple Weibel-Palade bodies (white arrowheads) Two adjacent WPBs (asterisk), one transversally and one obliquely oriented, are shown at higher magnification in (j) to appreciate microtubular-like structures. M: mitochondria. N: nucleus. Scale bars: (a), (c), and (d) = 500 μm; (b) = 200 μm; (e) = 2 μm; (f) and (g) = 0.5 μm; (h) and (j) = 0.2 μm; (i) = 1 μm.