Electron microscopy of lung parenchyma in ALIp and ALIexp. Photomicrographs are representative of data obtained from lung sections of five animals per group. Type II epithelial cell (PII) damage with bizarre lamellar bodies (Lb) and apoptosis of epithelial (PII) and endothelial cells (End) are visible in all groups. In ALIp, PCV-Sigh was associated with greater endothelial cell damage as well as with interstitial edema (asterisks), whereas PSV-Sigh was associated with comparatively less alveolar-capillary damage. In ALIexp, the blood-gas barrier (Bgb) was thickened from edema in PSV-Sigh animals compared to PCV-Sigh and PSV-Non-Sigh animals. AS, intra-alveolar space; Cap, capillary; E, erythrocyte; ED, edema; IC, interstitial cell; Neu, neutrophil.