SFTPB and idiopathic pulmonary fibrosis: While the mature SFTPB is too hydrophobic to circulate in the bloodstream, immature SFTPB proteins are less hydrophobic, and are detectable in the serum, where they might serve as biomarkers for pulmonary diseases with alveolar or interstitial damage, such as ILDs and especially IPF (30, 31).