Mucin-related epitopes distinguish M cells and enterocytes in rabbit appendix and Peyer's patches

The biochemical composition of the apical membranes of epithelial M cells o verlying the gut-associated lymphoid tissues (GALT) is still largely unknow n. We have prepared monoclonal antibodies (MAbs) directed against carbonate -washed plasma membranes from epithelial cells detached with EDTA from rabb it appendix, a tissue particularly rich in GALT. As determined by immunoflu orescence microscopy, several MAbs specifically recognized either M cells o r enterocyte-like cells of the domes from rabbit appendix, sacculus rotundu s, and Peyer's patches. M cells were identified by their large ventral pock et containing lymphoid cells and by specific labeling with antivimentin. Am ong various characterized MAbs, MAb 104 recognized rabbit immunoglobulins a nd was used as an apical marker for M cells in the rabbit appendix, MAb 58 selectively stained an integral membrane glycoprotein of greater than 205 k Da located at the apex of M cells, and MAb 214 stained a smaller soluble gl ycoprotein associated with the apical surfaces from neighboring enterocytes . In addition, both MAbs 58 and 214 also labeled luminal mucus and secretor y granules in goblet cells. The selective association of mucin-related mole cules at the surfaces of either M cells or enterocyte-like cells of the fol licle associated epithelium suggests that specific carbohydrate antigens ar e differentially expressed by epithelial cells and could account for the di fferential binding properties of pathogens.