Cup cells: Further structural characterization of the brush border and the suggestion that they may serve as an attachment site for an unidentified bacillus in guinea pig ileum

We recognized a low incidence, spontaneously occurring colonization of guinea pig ilea by an unidentified strain of gram-negative bacteria. By thick section, bacteria were associated with 28% of cup cells but with only 0.4% of absorptive cells. Additionally, noncolonized guinea pig ileum was subsequently studied by a variety of morphologic techniques to further define the normal functional anatomy of cup cells. Cup cells have glycocalyces that are more extensive than those of absorptive cells. As judged by ruthenium red staining, cup cells are comparable to absorptive cells in the density of glycocalyceal anionic sites; thus cup cells would not be expected to bind negatively charged plasma membranes (like those of bacteria) simply on the basis of having diminished negative charge of the glycocalyx. Sequential studies of ileal loops exposed to cationized ferritin suggest cup cell microvilli are able to internalize small quantities of membranebound molecules but, like absorptive cells, transport these substances to lysosomelike compartments. Finally, we show that cup cells, unlike absorptive cells, readily display morphologically detectable cholesterol on their microvillus membranes, even though it is likely that cup cell microvillus membranes are highly stabilized by underlying cytoskeleton as are those of absorptive cells, which label poorly for morphologically detectable cholesterol. These studies further define cup cell structure and suggest that these cells may represent preferential sites for attachment of at least some strains of bacilli.