2 The endothelial cells also provide a crucial interface in host defences, forming the front line of encounter with bloodborne pathogens, thus sensing danger threatening the organism in a concerted fashion, sending early warning signals of infection, invasion, or injury.
The endothelium displays a tightly regulated palette of functions that control vasomotion, inflammation, oxidative stress, vascular permeability, and structure. The endothelium furnishes one of the only surfaces, either natural or synthetic, that under physiological conditions maintains blood in a liquid state during prolonged contact. 1 The endothelium possesses a series of remarkable properties that contribute capitally to homeostasis ( Figure 1, left). The endothelial monolayer that lines the intima of arteries, veins, and microvessels measures up to 7000 m 2 in surface area. The vascular endothelium provides the crucial interface between the blood compartment and tissues. The concept of COVID-19 as an endothelial disease provides a unifying pathophysiological picture of this raging infection, and also provides a framework for a rational treatment strategy at a time when we possess an indeed modest evidence base to guide our therapeutic attempts to confront this novel pandemic.Įndothelium, Thrombosis, Cytokine, Inflammation, Microvasculature Introduction The endgame of COVID-19 usually involves a cytokine storm, a phlogistic phenomenon fed by well-understood positive feedback loops that govern cytokine production and overwhelm counter-regulatory mechanisms. Cytokines, protein pro-inflammatory mediators, serve as key danger signals that shift endothelial functions from the homeostatic into the defensive mode. This essay explores the hypothesis that COVID-19, particularly in the later complicated stages, represents an endothelial disease. It produces protean manifestations ranging from head to toe, wreaking seemingly indiscriminate havoc on multiple organ systems including the lungs, heart, brain, kidney, and vasculature. SARS-CoV-2, the aetiological agent of COVID-19, causes the current pandemic. While these functions participate in the moment-to-moment regulation of the circulation and coordinate many host defence mechanisms, they can also contribute to disease when their usually homeostatic and defensive functions over-reach and turn against the host. This tightly regulated palette of functions includes control of haemostasis, fibrinolysis, vasomotion, inflammation, oxidative stress, vascular permeability, and structure. The vascular endothelium provides the crucial interface between the blood compartment and tissues, and displays a series of remarkable properties that normally maintain homeostasis.
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