CLDN4 and idiopathic pulmonary fibrosis: Here, we found that, similar to the human transitional AEC2s or ABI1s, the cluster 1 transitional cells from each of the mouse models downregulated AEC2 markers and upregulated classic transitional state markers such as Krt8, Cldn4, and Itgb6, whereas similar to the KRT17+KRT5– AEC2s or ABI2s, the murine cluster 7 cells and the human IPF KRT17+KRT5– cells upregulated basal cell genes (Figure 7L).