NFKB1 and pulmonary fibrosis: Although multiple signaling pathways have been proposed as positive and negative regulators of AT2 progenitor proliferation in the adult lung (13–16, 34–37), their interaction with the NF-κB pathway in the injured lung remains largely undefined, though a recent study by Sieber et al. reports NF-κB–driven airway proliferation in human idiopathic pulmonary fibrosis airway epithelial/fibroblast cocultures (38).