ARG1 and bronchopulmonary dysplasia: In the bronchopulmonary dysplasia (BPD) model, after uptake of BMSC-Exos by alveolar macrophages, the expression levels of pro-inflammatory factors secreted by M1 macrophages such as TNF-α, IL-6, and CCL5 were blocked, and the expression levels of anti-inflammatory factors secreted by M2 macrophages such as arginase-1 (Arg-1) were increased, that is, macrophages transformed from M1 to M2, and the process occurred in a dose-dependent manner (Willis et al., 2018).