Human pathology
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Because diffuse alveolar damage, bronchiolitis obliterans-organizing pneumonia, and usual interstitial pneumonia are all related to acute lung injury, we postulated that the proliferative activity of fibroblasts and epithelium would be similar in all 3, and that of fibroblasts would be similar to skin scars. Ki-67 staining was assessed in 16 usual interstitial pneumonia, 9 bronchiolitis obliterans-organizing pneumonia, and 8 diffuse alveolar damage cases, 5 incidental fibroblast foci, 5 skin scars, and 5 keloids. The proliferative activity of alveolar macrophages was also measured and compared with that of 10 respiratory bronchiolitis cases. ⋯ Our results suggest different reactions to acute injury in usual interstitial pneumonia and bronchiolitis obliterans-organizing pneumonia compared with diffuse alveolar damage. The similar low proliferative activity of fibroblasts in usual interstitial pneumonia and keloids supports the hypothesis of abnormal wound healing in usual interstitial pneumonia. The high proliferative activity of macrophages in usual interstitial pneumonia suggests a role in the pathogenesis of usual interstitial pneumonia.