Uptake of a Gram-positive bacterium (Streptococcus pneumoniae R36a) by the M cells of rabbit Peyer's patches

The epithelium associated with the lymphoid follicles of Peyer's patches differs from the villi epithelium by the presence of M cells. The main function of these cells is to take up antigens (inert material, viruses and bacteria) from the intestinal lumen. The M cells are able to internalize various different gram-negative bacteria. In order to show the M cells ability to interact and take up a gram-positive bacterium, we exposed rabbit Peyer's patches to Streptococcus pneumoniae R36a. Using the isolated ileal loop technique, Peyer's patches were incubated with a bacterial suspension for varying periods (15, 30, 60, 100 minutes). The bacteria were found outside and inside the M cells. The internalized streptococci could be found in the M cell cytoplasm, in the cytoplasmic "pockets" and inside the intraepithelial lymphoid cells. The finding of internalized bacteria with their damaged walls suggests the possibility that M cells are able to modify internalized antigens in the same way as the antigen presenting cells.