ARG1 and immune system disorder: Inflammation and immune disorders are considered as the main factors in the initiation and development of pulmonary fibrosis (6); in particular, alveolar macrophages or their prototype monocytes, especially can mediate and respond to the fibrosis related inflammatory stimulus or immune factors, such as interleukin 6 (IL-6), transforming growth factor-β (TGF-β), arginase-1 (Arg-1), etc. (7, 8).