ARG1 and pulmonary fibrosis: Macrophage polarization plays an important role in the etiology of pulmonary fibrosis.20 In this study, to evaluate whether SiO2 administration resulted in the activation and apoptosis of U937-derived macrophages (UDMs), western blot was performed to detect M1 and M2 marker proteins, including NOS2 (iNOS), ARG1 (Arginase 1), and SOCS3 (suppressor of cytokine signaling 3).