Fibroblasts are responsive to soluble signaling factors produced by asthma AECs, as in vitro transfer of asthma AEC conditioned medium to normal fibroblasts induced robust upregulation of COL1A1, COL3A1, and FN1 that was not observed in non-asthma AEC conditioned medium transfer [59]. Here, COL3A1 is linked to asthma.