Although TGFβ1 alone was sufficient to induce interstitial collagen gene (COL1A1) expression (Figure 4—figure supplement 2), HIF stabilisation significantly increased the ratio of PLOD2 and LOXL2 gene expression relative to fibrillar collagen (COL1A1) gene expression while TGFβ1 did not (Figure 4e and f), suggesting that TGFβ activity alone may be insufficient to promote the altered collagen cross-linking that is present in IPF lung tissue. This evidence concerns the gene PLOD2 and idiopathic pulmonary fibrosis.