KLK4 and cardiovascular disorder: The balance of KLKB1 is quite tenuous; plasma kallikrein promotes vascular disease and thrombosis in the intravascular compartment, but at low concentrations, it facilitates platelet aggregation induced by adenosine diphosphate, collagen, and adrenaline (reviewed by Xie et al. [53]), but on the contrary, its inhibition may improve cardiovascular disease and thrombosis [53,55].