Morphometric evidence against lymphocyte-induced differentiation of M cells from absorptive cells in mouse Peyer's patches.

As the result of our morphometric study of mouse follicle-associated epithelium, we obtained evidence against the hypothesis that absorptive cells of this epithelium, under the influence of contact with intraepithelial lymphoid cells, transform into cells with short and sparse microvilli--M cells. The evidence consists of the following: (a) lack of correlation was demonstrated between the length (or density) of microvilli of absorptive cells and the number of lymphoid cells in contact with a given absorptive cell; (b) no intermediate forms between absorptive cells and M cells were found to exist; (c) the proportion of M cells among the epithelial cells in the follicle-associated epithelium was not significantly reduced in mice housed under specified pathogen-free conditions as compared with that in conventionally housed mice (9% and 11%, respectively), despite almost twofold depletion of the intraepithelial lymphoid cells in specified pathogen-free mice.