Dermal endothelial cells, fluorescence light micrograph. This tissue (from the skin) is endothelial, from the inner surface of blood vessels and lymphatic vessels. The tissue is described as lymphatic and microvascular in nature. The cells have been stained for CD31 (PECAM-1, green), a protein found here at endothelial cell intercellular junctions. The cell nuclei have been stained red using propidium iodide (PI). This sample is from human tissue.