Lamina propria macrophages in the human gastrointestinal mucosa: their distribution, immunohistological phenotype, and function.

In this study we systematically investigated the cellular distribution, immunohistochemical phenotype, and mucosal disposal function of macrophages in the lamina propria of the human gastrointestinal mucosa (lamina propria macrophages; LPMs). In all tissues examined, most of these LPMs accumulated beneath the epithelial layer that covered the apex of the lamina propria of the mucosa. These cells expressed normal levels of common macrophage markers such as CD68, LN5, lysozyme, ferritin, and alpha 1-anti-chymotrypsin. In addition, they expressed high levels of 25F9 (a market for a certain subpopulation of macrophages), MHC Class II molecules, and CD74 (MHC Class II-associated invariant chain). Interestingly, LPMs possessed some epithelial cell-associated antigens such as cytokeratin, carcinoembryonic antigen (CEA), and Ber-Ep4 in their cytoplasm. Ultrastructurally, these antigens were associated with cellular debris ingested by LPMs, which were recognized as apoptotic fragments by in situ end-labeling. Furthermore, double positive-labeled granules were seen in LPMs by double staining for epithelial cell-associated antigens and in situ end-labeling. These observations suggest that one of the major functions of LPMs is the disposal of apoptotic epithelial cells and that LPMs may be involved in the regulation of mucosal epithelial renewal.