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We investigated the binding of four lectins to the follicle-associated epithelium (FAE) overlying fixed mouse small intestinal Peyer's patches to identify M-cell-specific surface markers. Wheat germ agglutinin and peanut agglutinin displayed heterogeneous staining patterns, binding most avidly to the intestine goblet cells. In contrast, the lectins Ulex europaeus 1 (UEA 1) and Psophocarpus tetragonolobus (winged bean; WBA) were almost exclusively M-cell specific. When confocal laser scanning images of tissues stained with fluorescein isothiocyanate (FITC)-conjugated UEA1 or WBA were compared with the appearance of the same tissues under the scanning electron microscope (SEM), UEA1 strongly stained 97.2% (106/109) of M-cells, 0.6% (3/516) enterocytes, and 0% (0/28) goblet cells, whereas WBA stained 100% (83/83) M-cells, 1.7% (6/361) enterocytes, and 5.3% (1/19) goblet cells. The M-cell specificity of the lectin binding was further demonstrated by localization of horseradish peroxidase (HRP)-conjugated lectins under the transmission electron microscope (TEM). This is the first demonstration of carbohydrates in the glycocalyx of M-cells that are not expressed elsewhere on the FAE surface. These carbohydrates not only provide a means to identify mouse M-cells by LM but may also contribute to the occurrence of specific interactions between microorganisms and the M-cell apical membrane.

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Quantitative analysis of Yersinia pseudotuberculosisinfection of murine gut loops revealed that significantly more wild-type bacteria associated with Peyer’s patch M cells than with dome enterocytes or goblet cells. An invasin-deficient mutant was significantly attenuated for M-cell invasion, while β1 integrin expression was demonstrated in the apical membranes of M cells but not enterocytes. M-cell targeting by Yersinia pseudotuberculosis in vivo may, therefore, be mediated primarily by the interaction of invasin with cell surface β1 integrins.

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