Distribution of prion protein in the ileal Peyer's patch of scrapie-free lambs and lambs naturally and experimentally exposed to the scrapie agent

A sensitive immunohistochemical procedure was used to investigate the prese nce of prion protein (PrP) in the ileal Peyer's patch of PrP-genotyped lamb s, including scrapie-free lambs and lambs naturally and experimentally expo sed to the scrapie agent. The tyramide signal amplification system was used to enhance the sensitivity of conventional immunohistochemical procedures to show that PrP was widely distributed in the enteric nervous plexus suppl ying the gut wall. In scrapie-free lambs, PrP was also detected in scattere d cells in the lamina propria and in the dome and interfollicular areas of the Peyer's patch. In the follicles, staining for PrP was mainly confined t o the capsule and cells associated with vascular structures in the light ce ntral rone, In lambs naturally exposed to the scrapie agent, staining was p rominent in the dome and neck region of the follicles and was also found to be associated with the follicle-associated epithelium, Similar observation s were made in lambs that had received a single oral dose of scrapie-infect ed brain material from sheep with a homologous and heterologous PrP genotyp e 1 and 5 weeks previously. These studies show that the ileal Peyer's patch in young sheep may be an important site of uptake of the scrapie agent and that the biology of this major gut-associated lymphoid tissue may influenc e the susceptibility to oral infection in sheep. Furthermore, these studies suggest that homology or heterology between PrP genotypes or the presence of PrP genotypes seldom associated with disease does not impede uptake of P rP.