A new marker for cup cells in the rabbit small intestine: expression of vimentin intermediate filament protein.

Cup cells in the intestinal lining in mammals are largely limited to the ileum, suggesting a specific but undetermined function. The investigation of these cells has been hindered by the lack of a suitable marker for immunohistochemistry. The small intestine of rabbits was examined for a potential molecular marker. Segments of New Zealand white rabbit small intestine, with and without Peyer's patches, were removed, rinsed, fixed with periodate-lysine-2% paraformaldehyde (PLP), and frozen for immunohistochemistry, or fixed in 2.5% glutaraldehyde solution for electron microscopy. The sections were stained with monoclonal antibodies (V9, 3B4) against vimentin, which is known to be absent in enterocytes other than antigen-sampling M cells, and observed by immunohistochemistry and immunoelectron microscopy. Epithelial expression of vimentin intermediate filament proteins was limited to a subpopulation of villus-associated cells and to cells over Peyer's patch domes. Immunoreactivity with vimentin antibodies was selectively found in cells with a cup-like indentation in the brush border in villous epithelium and in M cells in Peyer's patch follicle epithelium. Immunoelectron microscopy revealed that the labeled cells in villous epithelium had shorter microvilli than the adjacent absorptive cells, and small, sparse, mitochondria, which are ultrastructural characteristics of cup cells. Vimentin filaments were recognized in the area surrounding the nucleus and extending beneath the plasma membrane of cup cells. In rabbit small intestine, vimentin is useful for the detection of cup cells, as well as M cells, and may facilitate the investigation of these little understood cells.