[Endotheliitis in COVID-19]

COVID-19 disease is a systemic inflammatory viral reaction starting with the viral phase followed by the inflammatory phase. The first phase is rather mild and asymptomatic with only a small subset of infected patients turning into the inflammatory phase with high mortality. Patients with pre-existing cardiovascular diseases and cardiovascular risk factors pose a considerably higher risk to develop severe or lethal COVID-19 disease course. COVID-19 affects not only the epithelial cells of the lung parenchyma via ACE2, but also endothelial cells across the whole body thus leading to generalized endothelial damage and inflammation, so-called endotheliitis. The histological morphology of endotheliitis comprises the accumulation of lymphocytes, plasma cells and macrophages beneath the endothelial cells and within the perivascular spaces. Endothelial cells play an important role in the regulation of vascular tone and the maintenance of vascular homeostasis. Endotheliitis thus can shift the vascular equilibrium towards more pronounced vasoconstriction with subsequent organ ischemia, inflammation with associated tissue edema and a procoagulant state. Patients with pre-existing endothelial dysfunction (male sex, smoking, hypertension, diabetes, obesity, and established cardiovascular disease) are particularly vulnerable and have adverse outcomes in COVID-19. This is a rationale for approaches to stabilize the endothelium. Most of these findings have been established from autopsies since the outbreak of the pandemic.