PADI4 and viral infectious disease: Similarly, defensin β1, encoded by DEFB1, is expressed by monocytes, macrophages, and certain dendritic cells (DCs) and has antiviral effects in humans (33, 34); peptidyl arginine deiminase 4, encoded by PADI4, plays an important role in inflammation and immune response (35); and the plasma protein inter-alpha-trypsin inhibitor heavy chain H4, encoded by ITIH4, is abundant in the sera of survivors of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection (36) and is involved in the acute-phase response to virus infection or inflammation (37, 38).