Decreased Apoptosis in the Ileum and Ileal Peyer's Patches: a Feature after Infection with Rabbit EnteropathogenicEscherichia coli O103

Light micrographs of rabbit ileum (A, C, F, G, and H) and ileal PP (B, D, and E), uninfected (A to F) or after severe infection with REPEC O103 (G and H) after H&E (A, B, F, and H), TUNEL (C to E), or Gram (G) staining. (A) Ileal absorptive villi (v) display their physiological long shape, while ileal crypt regions (c) are short (magnification, ×400). (B) Germinal centers (gc) and domed villi (d) of ileal PP are separated by absorptive villi (v) (magnification, ×160). (C) At the tips of ileal villi (v), numerous apoptotic cells can be distinguished from adjacent cells by their distinctive dark brown stain, forming an apoptotic cuff (magnification, ×800). (D) A number of dark-brown-stained apoptotic cells are evenly distributed in a PP domed villus (d) (magnification, ×500). (E) Numerous apoptotic cells scattered in a PP germinal center (gc) are recognizable as tiny dark-brown-stained spots (magnification, ×330). (F) A cell in the early stages of apoptosis is indicated (arrowhead). Note the two masses of chromatin which have condensed to form sharply circumscribed masses that abut the nuclear membrane. Several apoptotic bodies containing small rounded pieces of chromatin are also shown (arrows) (magnification, ×1,000). (G) Bacteria attached to ileal absorptive villi (v), heavily covering most parts of their surfaces (arrowheads). Villi are stunted, blunted, and fused together (magnification, ×500). (H) Ileal villi are fused together. They gained in width due to the influx of inflammatory cells (arrows). At villus tips, the cell layer is disrupted and cells are being shed into the lumen (arrowheads) (magnification, ×660).

Light micrographs of rabbit ileal PP (A, B, G, and H) and ileum (C, D, E, and F) after severe infection with REPEC O103. Sections were stained with H&E (A to D) or TUNEL (E to H). (A) Domed villi (d) have dwindled. Absorptive villi (v) are thickened and fused together. Note the prominent increase in the amount of goblet cells (arrows), resulting in distinct enlargement of the crypt region (magnification, ×132). (B) Early apoptosis cell (arrowhead) showing two masses of condensed chromatin abutting the nuclear membrane. Later, this cell will bud to form apoptotic bodies. Several apoptotic bodies containing uniformly dense masses of chromatin (arrows) are also indicated (magnification, ×1,000). (C) Bacteria diffusely cover the tip of an ileal villus (arrowheads). An apoptotic cell contains several small masses of condensed chromatin (apoptotic bodies, black arrow). Two other cells in the later stages of apoptosis both contain two small, uniformly dense masses of chromatin (white arrows) (magnification, ×1,000). (D) Bacteria diffusely cover the tip region of an ileal villus (arrowheads). Two cells in the late stages of apoptosis are indicated (arrows). Note the single rounded mass of nuclear chromatin (magnification, ×1,000). (E) Masses of dark-brown-stained bacteria line the surfaces of ileal villi (arrowheads) that are mainly fused. Occasionally, apoptotic cells with condensed chromatin (arrows) can still be seen. However, note the lack of apoptotic cells beneath adherent bacteria, in contrast to the apoptotic cuff observed in uninfected tissue (magnification, ×660). (F) Masses of dark-brown-stained bacteria are diffusely attached to the ileal surface (arrowheads). Apoptotic cells cannot be seen beneath attachment sites. Instead, they can occasionally be found in the deeper tissue or shed into the lumen (arrows) (magnification, ×660). (G) A domed villus (d) diminished in size and flanked by absorptive villi (v) that are fused. Note that the incidence of dark-brown-stained apoptotic cells is greatly decreased in the domed villus (magnification, ×500). (H) Apoptotic cells can still be seen in PP germinal centers (gc). However, cell counts reveal that the apoptotic incidence has dropped compared to that in uninfected tissue (magnification, ×400).