Aggregation of macrophages in the tips of intestinal villi in guinea pigs: their possible role in the phagocytosis of effete epithelial cells.

Numerous macrophages were found aggregated in the lamina propria at the tips of villi in the small intestine of guinea pigs. These macrophages extended their pseudopodia into the epithelial lining and internalized fragments of effete enterocytes in their phagosomes. The epithelium of the villus tips was found to be infiltrated with numerous lymphocytes. They possessed electron-dense granules characteristic of natural killer cells, and actively interdigitated with the enterocytes. The latter were either fragmented or extensively lost in their basal cytoplasm, often leaving an attenuated apical cytoplasm of the cell. Immunohistochemical labeling using bromodeoxyuridine demonstrated that at 96 h after its administration, immunolabeled nuclei were encountered in the cytoplasm of macrophages in the lamina propria at the villus tips. These findings suggest that in the guinea pig, effete enterocytes are not simply exfoliated into the lumen, but are damaged by intraepithelial lymphocytes possessing a natural killer cytotoxicity, and subsequently phagocytosed by subepithelial macrophages.