Analysis identified two unique club cell sub-populations, a SCGB1A1+ club cell sub-population highly expressing SCGB3A2, another club cell marker [14, 15], and a second SCGB1A1+ sub-population expressing MUC5B, a known genetic risk gene for IPF [16]. Here, SCGB1A1 is linked to idiopathic pulmonary fibrosis.