To further assess the fundamental role of IL-17A in mediating PM-induced pulmonary fibrosis, homozygous IL-17A−/− mice and wildtype (WT) littermate (20 mice/group) were subjected to 8-week and 16-week PM exposure in real-ambient PM exposure system in the winter season of 2020. The gene discussed is IL17A; the disease is pulmonary fibrosis.