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). Here, NOS2 is linked to pulmonary fibrosis.