DIFFERENTIAL EXPRESSION OF LECTIN-BINDING SITES DEFINES MOUSE INTESTINAL M-CELLS

We investigated the binding of four lectins to the follicle-associated epithelium (FAE) overlying fixed mouse small intestinal Peyer's patch es to identify M-cell-specific surface markers. Wheat germ agglutinin and peanut agglutinin displayed heterogeneous staining patterns, bindi ng 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 sc anning 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 s tained 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% (6/3 61) enterocytes, and 5.3% (1/19) goblet cells. The M-cell specificity of the lectin binding was further demonstrated by localization of hors eradish peroxidase (HRP)-conjugated lectins under the transmission ele ctron microscope (TEM). This is the first demonstration of carbohydrat es in the glycocalyx of M-cells that are not expressed elsewhere on th e FAE surface. These carbohydrates not only provide a means to identif y mouse M-cells by LM but may also contribute to the occurrence of spe cific interactions between microorganisms and the M-cell apical membra ne.