During COVID-19, a dysregulated KKS is hypothesised to be caused by reduced des-Arg(9)-bradykinin degradation through virus-associated ACE 2 inhibition on the one hand and increased bradykinin production via alternative cleavage of bradykinin precursors or induction of the bradykinin-forming enzyme kallikrein on the other hand [5, 9–11]. Here, KLK4 is linked to COVID-19.