Figure 2

Immunohistochemical staining for claudins 1, 3, 4, 5 and 7 in the canalicular period i.e. weeks 16-28. 2A. Epithelial cells including pretype II cells of developing alveoli are negative for claudin-1. Scale bar = 80 μm. 2B. Positive immunoreactivity for claudin-3 is observed in the epithelial cells of a bronchiole (on the left) and in the pretype II cells of developing alveoli. Scale bar = 80 μm. 2C. Pretype II cells of developing alveoli are positive for claudin-3 (arrow). Scale bar = 25 μm. 2D-2E. Epithelium of a bronchiole (short arrow in the Fig 2D) and pretype II cells lining alveoli (arrows in the Figs 2D and 2E) are positive for claudin-4. Scale bar = 80 μm in the Fig 2D, scale bar = 25 μm in the Fig 2E. 2F. Endothelial cells of alveolar capillaries (arrow) and an artery (arrowhead), pretype II cells lining alveoli (asterisk) and epithelium of bronchioles (short arrow) are positive for claudin-5. Scale bar = 80 μm. 2G. Alveolar (arrows) and bronchiolar epithelium (short arrow) are positive for claudin-7. Scale bar = 80 μm. 2H. Negative control in which the primary antibody has been substituted with PBS with haematoxylin counterstain. Scale bar = 80 μm.