Figure 3

Electron microscopy pictures of lymphangiogenesis in vivo. Lymphangiogenesis was observed after thermal cauterization of the cornea (A-G) and in lymphangioma (H, I). (A): Lymphatic endothelial cells (LEC) form long processes containing vesicles and delimitating extracellular spaces devoid of matrix or with reminiscent matrix fragments. Note the presence of intracellular vesicles in endothelial processes. (B): Endothelial cells are joined by interdigitations. (C): Intracellular vesicle contains matrix fragments (d). (D): Aligned endothelial cells form a tubular structure that delimits a narrow lumen (lu). The luminal surface of endothelial cells is ruffled with small cell processes. A mitotic endothelial cell is visible (*). (E): LEC are anchored to the matrix through anchoring filaments (arrow). (F): Tubular structures containing a lumen (lu) are lined by long cytoplasmic extensions of LEC. (G): Connection of two cell extensions delineates an extracellular space containing degradation products of the matrix that are reminiscent of collagen fibrils. (H, I): LEC are aligned and surrounded by matrix-free extracellular spaces. Note the presence of coalescent vacuoles. Scale bars in (A-C; F-H): 1 μm, in (D, I): 2 μm, and in (E): 0.5 μm.