C3 and COVID-19: In addition, SARS-CoV-2 infection contributes to the potent activation of complement mediators including C5a, C3a, factor P, factor I, factor C4-BP, and factor H. Despite the advantage of complement activation and protection against COVID-19, there is a strong association in the pathogenesis of SARS-CoV-2, especially in tissue inflammation and coagulation.