REN and viral infectious disease: Viral infections cause endothelial dysfunction via several mechanisms, as follows: (1) the inflammatory response elicited by the infection directly activates the renin angiotensin system to increase the production of reactive oxygen species; (2) the viral infection can directly increase the production of reactive oxygen species and activate nuclear factor kappa B, which inactivates NO by converting it to peroxynitrite and reduces NO production by uncoupling it from endothelial NO synthase; (3) several cytokine receptors can directly or indirectly impair endothelial function.