Complement system, plasma coagulation, their interaction and role in the pathogenesis of coronavirus infection

The interaction between plasma coagulation and the complement system is a topic of active research, but it remains poorly understood. Nevertheless, it may have played a significant role in the pathogenesis of coronavirus infection. This review describes the complement system, the plasma coagulation pathway, including the extrinsic and intrinsic (contact) activation pathways, the kallikrein-kinin system, their role in protecting the body, as well as studies on the direct interaction between these systems. The review also outlines the scheme and role of these interactions in coronavirus infection. Available data suggest that the direct interaction between plasma coagulation and the complement system is extremely limited and is most likely mediated by complement activation through kallikrein. This may be important for protecting the body and highlights the role of the contact pathway as part of the innate immune system. During coronavirus infection, complement system activation could be enhanced by the activation of the contact pathway and the kallikrein-kinin system, which, in turn, may amplify complement activity. Neutrophils played an important role in this interaction. Mutual activation of these systems could have been one of the reasons for the severity of coronavirus disease.