How do orally ingested infectious prions find their way to the brain? An article by Ricki Lewis in this issue of The Scientist (See "Portals for Prions?") describes recent hypotheses about trafficking of prions from gastrointestinal tract via lymphoid cells to the central nervous system. The most attractive point of entry for the ingested prions seems to be directly in the gut, where contaminated food is first deposited. Gastroenterologists have long known about the specialized subpopulation of enterocytes, m cells, whose function is to sample gut antigens and to pass them on for inspection to the immune system.1 m cells are embedded in gut epithelial surfaces, where they overlay mucosal lymphoid tissues populated by T cells, B cells and various antigen presenting cells (APC) including dendritic cells (DC) and macrophages.

Recent studies suggest that m cells do not break down orally administered antigens; this function, and the subsequent...

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