The lumen is filled with plasma and red blood cells. Immunohistochemistry (IHC), alkalyne phosphatase. C: Normal human lung. Expression of ENaC in PI. Group of PII with nuclei marked by TTF1 (long arrow) is seen inside the alveolar lumen, close to the epithelial cell lining which exhibits few PII (short arrow). IHC, double labelling. D: Enlarged, possibly hypertrophic PI expressing ENaC made up mostly of the alveolar epithelium in leptospirosis. Groups of PII with nuclei expressing TTF1 are also part of the alveolar lining. IHC, double labelling. E and F: Normal human lung PI expressing aquaporin 5. The endothelial like shape of PI and the marked cytoplasmic expression of aquaporin 5 are present. IHC, DAB. G and H: Many enlarged, apparently hypertrophic PI expressing aquaporin 5 covers alveoli filled with plasma and red blood cells. PII are also present as part of the alveolar lining. IHC, 1G double labelling.