WT1 and idiopathic pulmonary fibrosis: Immunostaining for WT1 supported earlier findings that WT1 is selectively upregulated in mesothelial cells and spindle-shaped mesenchymal cells in fibrotic lesions of pleura and distal lung parenchyma of IPF lungs; however, there was limited or no staining observed in either mesothelial or other lung cells in control individuals (Figure 3A and Supplemental Figure 7).