SOX9 and HES1 stained the nuclei of some KRT5+ cells (Fig. 8c, d), indicating the presence of KRT5+SOX9+, KRT5+SOX9-, KRT5+HES1+ and KRT5+HES1- subpopulations amongst the IPF basal cell progenitors. Here, KRT5 is linked to idiopathic pulmonary fibrosis.