C5 and COVID-19: Several clinical trials are currently ongoing to investigate the protective effects of purified/recombinant complement regulators (e.g. C1-esterase inhibitor) or complement inhibitors directed against MASP-2, C3, C5, or the C5a receptor on COVID-19 outcomes ranging from changes in oxygenation to mortality (31)(https://www.trialsitenews.com/category/masp-2/).