Role of endothelial dysfunction in the severity of COVID­19 infection (Review).

COVID­19 patients with severe infection have been observed to have elevated auto­antibodies (AAs) against angiotensin II receptor type 1 (AT1R) and endothelin (ET) 1 receptor type A (ETAR), compared with healthy controls and patients with favorable (mild) infection. AT1R and ETAR are G protein­coupled receptors, located on vascular smooth muscle cells, fibroblasts, immune and endothelial cells, and are activated by angiotensin II (Ang II) and ET1 respectively. AAs that are specific for these receptors have a functional role similar to the natural ligands, but with a more prolonged vasoconstrictive effect. They also induce the production of fibroblast collagen, the release of reactive oxygen species and the secretion of proinflammatory cytokines (including IL­6, IL­8 and TNF­α) by immune cells. Despite the presence of AAs in severe COVID­19 infected patients, their contribution and implication in the severity of the disease is still not well understood and further studies are warranted. The present review described the major vascular homeostasis systems [ET and renin­angiotensin­aldosterone system (RAAS)], the vital regulative role of nitric oxide, the AAs, and finally the administration of angiotensin II receptor blockers (ARBs), so as to provide more insight into the interplay that exists among these components and their contribution to the severity, prognosis and possible treatment of COVID­19.