[Immunohistologic study of the localization of ICAM-1 (intercellular cell adhesion molecule 1) in alveolar epithelium in the human lung]

The intercellular cell adhesion molecule 1 (ICAM-1) is expressed in the endothelium of pulmonary blood vessels, in the alveolar epithelium and in the bronchial epithelium. Because of conflicting reports in the literature on the question whether ICAM-1 is exclusively expressed in pneumocytes Type I or also in pneumocytes Type II, the present study aimed at characterising the cell types in normal human alveolar epithelium which show immunoreactivity for ICAM-1. Immunohistochemistry for ICAM-1 was performed on a series of 19 specimens of normal human lung. In addition, double staining procedures of ICAM-1 together with cell type specific antigens were performed. To detect pneumocytes Type II an antibody to cytokeratin 18 (CK 18) was used. Alveolar macrophages were marked by an antibody to the monocyte macrophage-specific leukocyte antigen CD 68. Vascular endothelium was stained by common endothelial markers (Ulex europaeus agglutinin Type I, anti-von Willebrand factor). The alveolar septa showed intense surface staining for ICAM-1 that could be localised predominantly to pneumocytes Type I. There were also single ICAM-1 positive cells having the characteristics of pneumocytes Type II in respect of their morphological appearance and their cytokeratin pattern. For the interpretation of these results the fact had to be considered that pneumocytes Type I can partly cover up pneumocytes Type II. This was confirmed by ultrastructural observations. Our findings suggest that ICAM-1 plays a part in the interaction between intraalveolar leukocytes and the alveolar epithelium.