WT1 and idiopathic pulmonary fibrosis: As a further validation of the in vitro and in vivo findings, immunohistochemical analysis of human IPF lung sections showed Wilms tumor-1 (WT-1)-positive mesothelial cells in the pleura and lung parenchyma, which corresponded with immunostaining of the mesothelial cell marker calretinin (Zolak et al., 2013; Karki et al., 2014).