IDENTIFICATION OF M-CELLS AND THEIR DISTRIBUTION IN RABBIT INTESTINALPEYER PATCHES AND APPENDIX

The distribution of intestinal membranous (M) cells has been studied w ithin the follicle-associated epithelium of rabbit Peyer's patches and appendix. Vimentin expression has been assessed as a primary criterio n to identify rabbit M cells in tissue sections and in whole tissue pr eparations. This criterion has been compared to the use of the absence of alkaline phosphatase which, due to its heterogeneous distribution within the enterocyte population, is less reliable than vimentin expre ssion as a marker for rabbit M cells. The pattern of vimentin immunost aining revealed that the majority of M cells are located in the periph ery of the follicle-associated epithelium, the dome apex being largely free of M cells. This distribution was confirmed by scanning electron microscopy. Vimentin is also expressed by follicle-associated epithel ial cells in the vicinity of crypts which lack the typical lymphocyte- containing pocket of M cells. Cytoplasmic peanut agglutinin binding co incides with vimentin-expression throughout the follicle-associated ep ithelium but is absent from vimentin-negative enterocytes. The co-loca lisation of these two phenotypic markers in both M cells and epithelia l cells adjacent to crypts, which lack the typical morphology of fully developed rabbit M cells, suggests that they correspond to immature M cells which by their location appear to derive directly from undiffer entiated crypt stem cells and not from mature columnar enterocytes.