C3 and COVID-19: In this study, we aimed to examine differences in serum levels of neutrophil elastase and granzyme B proteases, and to examine the anti-protease activity of their associated serpins, alpha-1-antitrypsin (ATT) and alpha-1-antichymotrypsin (ACT) as well as complement activation activity of factor 3 (C3) and complement factor 3 a (C3a) in context of COVID-19 severity.