Fine structure of the dome in Peyer's patches of mice.

The dome area of Peyer's patches in adult mice was studied by electron microscopy. The cellular constituents of the area are lymphocytes, plasma cells, macrophages and reticular cells. Macrophages are filled with numerous lysosomal bodies containing dead lymphocytes or plasma cells. The epithelium covering the dome is infiltrated with numerous lymphocytes, a few plasma cells and macrophages. These wandering cells first are found intercellularly but later appear to penetrate into the epithelial cell cytoplasm just beneath the cell apex. The epithelial cells containing the wandering cells in the supranuclear portion protrude into the intestinal lumen, and their microvilli are short and scanty. The epithelial cells covering the dome often have inclusion bodies containing dead wandering cells. Such modification of the epithelial cells may be related to the presence of underlying follicles. The results suggest that the dome including the covering epithelium is a site in which antigens from the intestinal lumen might come in direct contact with lymphocytes or other wandering cells.