Gene expression across the two subsets did not suggest an association with acute exacerbations of IPF; for example, some published markers of acute IPF exacerbations (MMP1, MMP7) were higher in Subset 2, while others (AGER, DEFA3) were lower in Subset 2 or not significantly different (COL1A2, CCNA2) [52]. Here, COL1A2 is linked to idiopathic pulmonary fibrosis.