GDF15 and idiopathic pulmonary fibrosis: Among the top-ranked proteins with increased expression in IPF matrix compared with healthy lung matrix, there is a number of collagen proteins (COL10, COL14, COL7), immune response-related proteins (CXCL13, LGALS3, IGHV3-9), and GDF15, a TGF-β family member (Figure 1, G and H).