Figure 7 shows that networks PSA (5a, 8, 13b) which regulate T-cell functions by regulating Arginase 1, are targeted by mir-107 and mir-21 in microRNA cluster U (Figure 6). Arginine deficiency increases mir-21 expression and inflammation by lowering endothelial nitric oxide production (338). Arginine supplementation increases mir-21 expression levels in clinical studies and shown to reduce the duration of in-hospital stays and the need for respiratory support in COVID-19 patients (339). Here, ARG1 is linked to COVID-19.