Moreover, the upregulation of ACE2 and TMPRSS2 in the same cells of IPF, such as FSP-1+ lung fibroblasts, with or without PM exposure may help to explain why the prognosis of patients with IPF who infected with SARS-CoV-2 is worse than that of the general population. Here, ACE2 is linked to idiopathic pulmonary fibrosis.