CDKN1A and pulmonary fibrosis: Utilizing the widely used mouse model of bleomycin (BLM)-induced pulmonary fibrosis, the authors demonstrate that fibrotic lung tissue of BLM-treated mice is highly enriched in cells expressing p21 and other senescence markers, pro-inflammatory SASP factors, ECM components, and immune cell infiltrates both 10 and 21 days after BLM administration.