Phenotypic characterization of cells participating in transport of prion protein aggregates across the intestinal mucosa of sheep.

The oral route is considered to be the main entry site of several transmissible spongiform encephalopathies or prion diseases of animals and man. Following natural and experimental oral exposure to scrapie, sheep first accumulate disease associated prion protein (PrP (d) ) in Peyer's patch (PP) lymphoid follicles. In this study, recombinant ovine prion protein (rPrP) was inoculated into gut loops of young lambs and the transportation across the intestinal wall studied. In particular, the immunohistochemical phenotypes of cells bearing the inoculated prion protein were investigated. The rPrP was shown to be transported across the villi of the gut, into the lacteals and submucosal lymphatics, mimicking the transport route of PrP (d) from scrapie brain inoculum observed in a previous intestinal loop experiment. The cells bearing the inoculated rPrP were mainly mononuclear cells, and multicolor immunofluorescence procedures were used to show that the rPrP bearing cells were professional antigen presenting cells expressing Major histocompatibility complex II (MHCII). In addition, the rPrP bearing cells labeled with CD205, CD11b and the macrophage marker CD68, and not with the dendritic cell markers CD11c and CD209. Others have reported that cells expressing CD205 and CD11b in the absence of CD11c have been shown to induce T cell tolerance or regulatory T cells. Based on this association, it was speculated that the rPrP and by extension PrP (d) and scrapie infective material may exploit the physiological process of macromolecular uptake across the gut, and that this route of entry may have implications for immune surveillance.