MUC5B and idiopathic pulmonary fibrosis: Compared to the SCGB3A2high club cells, the IPF-induced MUC5B+ club cells had a unique signature gene set, which included genes related to mucous cell differentiation (SPDEF, MUC5B, TFF3 and AGR2), growth factors related to host defense (LCN2, BPIFB1 and BPIFA1) and immune cell attractants (CXCL1, CXCL6, CXCL8 and CX3CL1) (Fig 3A).