KLK4 and systemic inflammatory response syndrome: HFRS represents a systemic inflammatory response syndrome, with a multifactorial pathogenesis [7], including increased cleavage of high molecular weight kininogen, higher enzymatic activities of FXIIa/kallikrein, and increased liberation of bradykinin from endothelial cells, resulting in overactivation of the kallikrein-kinin system and increased endothelial cell permeability [8].