Molecular phenotyping has led to the development of biomarkers that specifically target Th2 responses in the lung: Woodruff and colleagues identified periostin (POSTN), chloride channel regulator 1 (CLCA1), and serpin peptidase inhibitor, clade B, member 2 (SERPINB2) as epithelial genes that were specifically induced in asthma and directly regulated by IL-13 in vitro (48). Here, IL13 is linked to asthma.