KL-6 is increased in serum of several ILDs including IPF [47,49,53,55,56,57] In one study, KL-6 levels in BALF seems to be a specific diagnostic marker in IPF compared with other ILDs [58] while Bennet et al. proved that higher levels of BALF KL-6 are related to a more severe and extended disease [56]. This evidence concerns the gene MUC1 and idiopathic pulmonary fibrosis.