S100A9 and idiopathic pulmonary fibrosis: Proteomic comparative analysis of BALF in stable IPF patients vs. AE-IPF revealed that proteins involved in the propagation of β-catenin WNT transduction signal, proteins upregulated in lung carcinogenesis (IGKC, S100A9, PEDF, IGHG1, ALDOA, A1AT, HPT, CO3, and PIGR), as well as acute phase proteins involved in protease–antiprotease imbalance (such as a1 antithrypsin fragments) correlated to AE-IPF [93].