We investigated the distribution of T lymphocytes, B lymphocytes, and S-100 protein-immunoreactive dendritic-like in the anal tonsil of the laboratory shrew, Suncus murinus. In adult animals, T lymphocytes were located mainly at the periphery of the anal tonsil, especially around small blood vessels. B lymphocytes were located in the central and subepithelial region of the anal tonsil, which includes primary lymphoid follicles, and in which there are small numbers of scattered T lymphocytes. B and T lymphocytes were distributed over 72.7 and 27.3% of the tonsillar area, respectively. However, their areas of distribution were not clearly distinguished. The areas containing B lymphocytes were enriched in S-100 protein antibody-immunoreactive cells, which exhibited a dendritic shape. These S-100-positive cells appeared to be identical to the follicular dendritic cells (FDC) seen in the follicles of lymphoid organs. These results suggest that the anal tonsils constitute one of the gut-associated lymphoid tissues (GALT), and that a function of the anal tonsil includes the capture of intruding antigens that would generate protective antibody responses.
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