CYTOSOLIC DISTRIBUTION OF VILLIN IN M-CELLS FROM MOUSE PEYERS-PATCHESCORRELATES WITH THE ABSENCE OF A BRUSH-BORDER

Background & Aims: The follicle-associated epithelium (FAE) of Peyer's patches mainly consists of two cell types: absorptive enterocytes wit h a brush bolder and M cells without this apical specialization. To st udy the controversial ontogeny of M cells (mesenchymal vs. epithelial origin), the expression pattern of tissue-specific cytoskeletal protei ns, markers of cell origin that play a crucial role in the specific sh ape of epithelial cells and brush border assembly, was investigated. M ethods: The localization of cytokeratins, vimentin, and villin was det ermined on mouse FAE using immunocytochemistry and electron microscopy . Results: Epithelial-specific cytokeratins were expressed in both abs orptive enterocytes and M cells, whereas vimentin was not detected in mouse FAE. Villin, a tissue-specific, actin-binding protein of the bru sh border, was expressed in the two cell types. This protein had an un usual cytoplasmic distribution in FAE cells lacking a brush border and in cells having an intraepithelial pocket filled with lymphocytes. Co nclusions: The presence of villin and the absence of vimentin in M cel ls support the intestinal origin of M cells. The cytoplasmic distribut ion of villin provides a new identification criteria for M cells and r eflects the reorganization of the F-actin network, which correlates wi th the inability of M cells to assemble a brush border.