REN and diabetes mellitus: Although immunity is not the main focus of this manuscript it is tempting to speculate that the severity of the clinical manifestations such as the acute respiratory failure and also failure in other organs depend on the state of the immune system which decreases with age or diseases such as diabetes.The involvement of ACE2 in the renin-angiotensin system as antagonist of ACE in regulating blood pressure via Angiotensin II, vasoconstriction, dilation and its protective role against lung injury41 are additional factors which correlate with age50.