C4A and COVID-19: Among the most prominently upregulated proteins in COVID-19 lungs were members of the complement activation cascade (e.g. C4, C3, C5, B, C2, H, C9), different interferon-induced proteins (e.g. Interferon-induced GTP-binding protein Mx1 (MX1)) as well as inter-alpha-trypsin inhibitor family (ITIH) proteins, known acute phase proteins that are upregulated during inflammation [18].