PECAM1 and COVID-19: In COVID-19 the homeostatic equilibrium between TREG cells (IL-10) and Th17 cells (IL-17) is broken: inflammatory cytokine levels (IL-1, TNF) are elevated in the lungs of COVID-19 patients, resulting in an increase in HA-synthase-2 (HAS2) in alveolar epithelial cells CD31+, EpCAM+ and fibroblasts.