C2 and COVID-19: In SARS-CoV-2-positive patients, proteomic changes were consistent with reported features of COVID-19 pathophysiology, including neutrophil activation (e.g., FCGR3B, PGLYRP2), moderate coagulation and acute-phase responses (FGA, FGB, SAA1/4), and early complement cascade activation (C2, C8A), consistent with classical innate immune engagement and endothelial injury [45,46,47,48,49,50,51,52].