Lymphocyte subpopulations in high endothelial venules and lymphatic capillaries of bronchus-associated lymphoid tissue (BALT) in the rat

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Abstract
The subpopulations of lymphocytes and non‐lymphoid cells in high endothelial venules (HEV) and in lymphatic capillaries surrounding lymphoid follicles in bronchus‐associated lymphoid tissue (BALT) were examined by electron microscopy after preembedding the tissue and staining with an immunoperoxidase technique. The results were compared with those obtained in gut‐associated lymphoid tissue (GALT) reported previously. Monoclonal mouse‐anti‐rat T cell, IgG, IgM, IgA, and Ia antisera were used. Plasma cells that were reactive to anti‐IgG, anti‐IgM, and anti‐IgA were detected as cells in which the 3′, 3′ ‐diaminobenzidine tetrahydroxychloride reaction product was localized in rough endoplasmic reticulum and perinuclear spaces but not on plasma membranes. These plasma cells did not occur in either lymphatic capillaries or HEV in BALT as they did in GALT. Cells with surface Ig (sIg cells), T‐cell antigen (T cells), and Ia antigen (Ia cells) were present in BALT. T cells were located predominantly in the follicular area opposite the bronchial epithelium; IgM‐ and IgG‐reactive cells were found in the follicular area adjacent to the bronchial epithelium; and IgA‐positive cells were found in the lateral part of the area where the T cells were localized (T‐cell area). Ia cells were abundant throughout BALT and in moderate numbers in the epithelium. A striking observation was the presence of “nurse‐cell”‐like structures in the periphery of BALT. The percentages of T, sIgG, sIgM, and sIgA cells in the HEV were 54.7%, 2.4%, 28.9%, and 27.3%, respectively, and in the lymphatic capillaries, 41.2%, 3.8%, 38.2%, and 21.2%, respectively. Non‐lymphoid cells with Ia antigen, presumably interdigitating cells (IDC), were often seen in the two types of vessels. The percentage was 4. 3% in the HEV and 5.6% in the lymphatic capillaries. The results indicate that the largest common lymphocyte subpopulation in the two types of vessels surrounding follicles in BALT is T cells, followed by sIgM or sIgA cells as seen in GALT; IDC may be one of the main migrating cells within BALT.