In this article, it was shown that exposure to PM2.5 leads to an activation of the TGF-β1 receptor that plays a fundamental role in the pathological process of pulmonary fibrosis, promoting ENDMT in the MHC cells, increasing the levels of Col1 and Acta2 and reducing the expression of CD31 and CDH5 after 48 h. This evidence concerns the gene PECAM1 and pulmonary fibrosis.