Morphologic characteristics of the epithelial surface of aggregated lymphoid follicles (Peyer's patches) in the small intestine of newborn gnotobiotic calves and pigs.

Scanning electron microscopic studies of the dome epithelium of aggregated lymphoid follicles (Peyer's patches) of gnotobiotic newborn calves and pigs revealed distinct characteristics. The dome epithelium in the calves was characterized by a uniform population of lymphoepithelial cells (M cells). These cells were columnar, with a luminal surface that bulged toward the intestinal lumen forming intercellular crevices. Bovine M cells were covered by densely packed blunt microvilli that were irregular, short and thick and that differed from microvilli of absorptive epithelial cells. The dome epithelium in the pigs had 2 distinct cell populations. The majority had surface characteristics indistinguishable from those of ordinary absorptive epithelial cells. Interspersed among the absorptive-like epithelial cells were numerous M cells with distinctive surface morphologic characteristics. Porcine M cells were covered by densely packed, long microvilli that were irregular and thick and that projected above the microvilli of adjacent epithelial cells. The epithelium of aggregated lymphoid follicles in calves differed from that of primates and rodents. The organization of the dome epithelium in pigs resembled that of rodents. However, the surface morphologic features of porcine M cells were unlike that of rodents and human beings.