Effects of the expansion of bacterial colonies into the intervillous spaces on the localization of several lymphocyte lineages in the rat ileum

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The effect of bacterial colonies expanded into the intervillous spaces on the localization of several lymphocyte lineages was immunohistochemically investigated in two types of mucosa: ordinary mucosa of rat ileum, which consists of mucosa without any mucosal lymphatic tissue; and follicle-associated mucosa (FAM), which accompanies the parafollicular area under the muscularis mucosae in the rat ileal Peyer’s patch. The results showed that bacterial colonies in the intervillous spaces induced increased populations of CD8⁺ cells in the epithelium of the intestinal villus in ordinary mucosa (IV) and intestinal villus in FAM (IV-FAM). Bacterial colonies in the intervillous spaces were also associated with increased numbers of IgA⁺ cells, which were mainly localized in the lamina propria of basal portions of IV and IV-FAM, and with expanded localization of IgA⁺ cells into the villous apex in both IV and IV-FAM. Moreover, IgA⁺ cells around the intestinal crypts adjacent to IV or IV-FAM were also increased in response to bacterial colonies. In the IV-FAM, but not IV, L-selectin⁺ cells, which were found to be immunopositive for TCRαβ or CD19, were drastically increased in the lamina propria from the crypt to middle portion of IV-FAM and in the lumen of central lymph vessel of IV-FAM in response to the bacterial colonies in the intervillous spaces. These findings revealed that the expansion of bacterial colonies into the intervillous spaces accompanies the change of histological localization of the lymphocyte lineage in both the ordinary mucosa and FAM.