KLK4 and COVID-19: Since soluble or cell surface gC1qR can activate the classical pathway of complement and the kinin-kallikrein system (KKS)–both of which play a significant role in the pathogenesis of COVID-19–we postulated that if any of the SARS-CoV-2 structural proteins bind gC1qR, then the gC1qR-decorated viral particles could potentially provide a platform for the simultaneous activation of both the complement and the KKS pathways.