Alveolar basement membrane breaks down in diffuse alveolar damage: An immunohistochemical study

Sequential structural changes of the alveoli in diffuse alveolar damage (DAD) were examined by immunohistochemical methods. Lung specimens obtained at autopsy from 52 patients with DAD were stained with antibodies to laminin, 7S collagen (7S) and type IV collagen (type IV) for alveolar basement membrane, to von Willebrand factor, CD‐31 and thrombomodulin (TM) for the alveolar capillary endothelial cell, and to epithelial membrane antigen and surfactant apo‐protein (PE‐10) for the alveolar epithelium. Forty‐two of the patients had the exudative form of DAD; 10 of the patients had the proliferative form of DAD. The results were summarized as follows: (i) laminin was most easily impaired both in the epithelial and capillary basement membrane in the early exudative stage; (ii) following laminin, 7S and type IV in the capillary basement membrane were also injured in the early exudative stage, and recovered in the proliferative stage; (iii) subsequently, 7S and type IV in the epithelial basement membrane were also impaired in the late exudative stage, and remained impaired even in the proliferative stage; and (iv) alveolar epithelium regenerated almost completely in the late exudative stage, but staining for TM in the alveolar capillary recovered in the proliferative stage. Because the alveolar basement membrane must govern the homeostasig of alveolar tissue architecture, it was concluded that its preservation is necessary to avoid the abnormal remodeling of the alveoli in the reparative stage of DAD, if the patient survives the acute episodes of the disease.