LAUSR

Endothelial cells are known to form a single-cell layer of endothelium that plays an important role in cardiovascular homeostasis by regulating blood fluidity, fibrinolysis, vascular tone and permeability, angiogenesis, monocyte adhesion, and platelet aggregation (1). Recent findings have demonstrated similarities between endothelial cells (ECs) and macrophages (2–5). Whereas they generally are not viewed as classic immune cells, ECs express a variety of innate immune receptors including Toll-like receptors (TLRs) and NOD-like receptors (NLRs), which activate intracellular inflammatory pathways mediated by nuclear factor kappa B (NF-kB) and the mitogen-activated protein kinases (MAPKs) (2, 6, 7). More interestingly, ECs and macrophages share evolutionarily conserved defense mechanisms such as phagocytosis and autophagy (8, 9). Macrophages are considered professional phagocytes and are highly specialized in the detection and removal of pathogens, apoptotic cells, and cell debris (3, 10). Additionally, macrophages are classical immune cells and play important roles in the innate immune system (11). Based on recent findings and considering the similar functions and mechanistic events shared by ECs and macrophages, we explore the opinion that ECs should be considered macrophage-like gatekeepers.