The protein and mRNA expressions of GDF-15 in the lung of AE-IPF subjects were increased significantly compared with HCs and S-IPF cases by WB and RT-PCR (p < 0.001, p = 0.007 and p < 0.001, p = 0.026, respectively) (Figures 2A–C). This evidence concerns the gene GDF15 and idiopathic pulmonary fibrosis.