COL5A1 and pulmonary fibrosis: Under conditions of AEC2/FB co-culture, but not tri-culture, we found that FBs retained elevated expression of contractile markers (Acta2, Myl9), as seen in the cultured FB isolate; and were enriched for pathways (mTORC1 signaling, reactive oxygen species [ROS] metabolism) and matrix-related molecules (Tgfb1, Col5a1, Col12a1) that are characteristic of FBs in pulmonary fibrosis, but that are minimally expressed in native lung FBs (Fig. 4c, d, Supplementary Fig. 7e, f, and Supplementary Data 3)57,58.