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[High endothelial venule and lymphocyte homing of the musk shrew palatine tonsil].

Homing of lymphocytes into secondary lymphoid organs is essential for an adequate immune response in vivo. Adherence of the lymphocytes to the high endothelial venule (HEV) is the crucial step of the homing. In contrast to lymph nodes and Peyer's patch, study of lymphocyte homing to the palatine tonsil has been hampered by the lack of useful laboratory animals that possess the tonsil. Herein, we examined the preferential adhesion of lymphocytes to the tonsillar HEV using the musk shrew; a new laboratory animal which has a pair of immunocompetent palatine tonsils. The palatine tonsils of the musk shrew had the morphologically detectable HEV in the parafollicular region. Immunofluorescent staining showed that more B cells were located in the lumen of the tonsillar HEV rather than T cells. The in vitro lymphocyte-HEV binding assay indicated some preferential adhesion of the lymphocytes to the tonsillar HEV. First, adhesion of B cells to the tonsillar HEV was more preferential than that of T cells, which was consistent with the result in the assay of Peyer's patch. Second, adhesion of the lymphocytes from axillar and inguinal lymph nodes was similar to that of the lymphocytes from the mesenteric lymph nodes, that differed from the result in the assay of Peyer's patch. These findings suggest that, in the musk shrew, the regulation of lymphocyte homing through the HEV has differences between tonsil and Peyer's patch, at least in part. This may be related to the role of the lymphoid organs in each local immune response.