Distribution of hepatocyte growth factor activator inhibitor type 1 (HAI-1) in human tissues: Cellular surface localization of HAI-1 in simple columnar epithelium and its modulated expression in injured and regenerative tissues

We used a specific monoclonal antibody to human hepatocyte growth factor ac tivator inhibitor type 1 (HAI-1) in immunohistochemical procedures to deter mine the distribution and localization of HAI-1 in human tissues. In normal adult tissues, HAI-1 was predominantly expressed in the simple columnar ep ithelium of the ducts, tubules, and mucosal surface of various organs. In a ll cases, HAI-1 was localized predominantly on the cellular lateral (or bas olateral) surface. By contrast, hepatocytes, acinar cells, endocrine cells, stromal mesenchymal cells, and inflammatory cells were hardly stainable wi th the antibody, and stratified squamous epithelium showed only faint immun oreactivity on the surface of cells of the basal layer. In the gastrointest inal tract, the surface epithelium was strongly stained. RNA blot analysis confirmed the presence of specific mRNA transcript in the gastrointestinal mucosa, and in situ hybridization revealed that HAI-1 mRNA showed a similar cellular distribution pattern. Although HAI-1 was not expressed in normal hepatocytes, strong immunoreactivity was observed on the epithelium of pseu do-bile ducts and on the surface of scattered hepatocytes in fulminant hepa titis. The enhanced expression was also noted in regenerating tubule epithe lial cells of the kidney after infarction. We conclude that HAI-1 is prefer entially expressed in the simple columnar epithelium of the mucosal surface and duct, that the predominant localization of HAI-1 is the cell surface, and that the expression of HAI-1 can be modulated by tissue injury and rege neration.