Interdigitating Cells

Abstract: The lymph node is composed of functionally different compartments, each with a characteristic type of macrophage. In the marginal zone the plasmacell reaction is induced, in the germinal centre the memory B-cells are generated and in the paracortex recirculating T-cells are stimulated in thymus dependent humoral responses and in cell mediated responses. In normal lymph nodes, the reticulum and endothelial cells composing the stroma of these areas, are clearly distinguished from the macrophages and the lymphocytes (Hoefsmit 1975). Marginal zone macrophages, tingible body macrophages (TBM) and interdigitating cells (IDC) seem to differ in functional activity only.

Abstract: Blood lymphocytes and lymph nodes from three patients with acquired immunodeficiency syndrome (AIDS) and two cases with AIDS-related complex (ARC) were studied during the course of the disease. The lymph node histomor-phology could be grossly categorized into three stages: follicle hyperplasia, follicle degeneration and the depleted stage. In the first stage, follicles show large and sometimes irregular-sized germinal centres and narrow B-cell mantles. Dendritic reticulum cells in the germinal centres reveal disruption of their fine dendritic processes; often indentations are visible, filled with small B- and T-lymphocytes of follicle mantle and paracortical origin. These lesions may be the first signs of follicle degeneration, in which only hyalinized remnants of follicle centres are found. The changes in the paracortex are less prominent than those in the follicles. The disturbance in the numerical balance of T-cell subsets of helper–inducer and suppressor–cytotoxic phenotypes is less than that found in the blood. In some cases the paracortex reveals a high density of T6-positive elements resembling interdigitating cells, suggestive of continuous antigen exposure. We found follicle hyperplasia in ARC, follicle degeneration in one case of ARC and in full-blown AIDS, while the depleted stage was found in lymph nodes at autopsy of AIDS patients. Lymph node changes do not completely correlate with the changes in the blood lymphocyte pool. Investigations on lymph nodes may be of value in the assessment of the prognosis of the disease.

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.

Abstract: Frozen sections of pannus tissue taken from the joints of patients with rheumatoid arthritis have been investigated using immunohistological methods to determine the distribution of subsets of macrophage-like cells in this area. A panel of monoclonal antibodies including reagents specific in normal tissue for interdigitating cells (RFD1), macrophages (RFD7), epithelioid cells, (RFD9), monocytes (UCHMI), and osteoclasts (263C), were used. Indirect immunoperoxidase and combination indirect immunofluorescence procedures revealed the phenotypes of macrophage-like cells in four histologically distinct areas of the tissue: the synovial lining layers, the deeper stroma, areas of perivascular infiltration, and the articular cartilage junction where degeneration was occurring. It was discovered that 80% of the lining cells and a majority of macrophage-like cells of the stroma, express the phenotype RFD1+ RFD7+ UCHMI+. Cells with a typical 'dendritic cell' phenotype (RFD1+ RFD7-) were only present in the perivascular infiltrates, while 'classic macrophages' (RFD7+ RFD1-) were the cells accumulating at the cartilage junction. No significant numbers of RFD9+ epithelioid cells were seen. 263C+ osteoclasts were present in small numbers distributed throughout the stroma but did not appear to be involved in areas of cartilage degradation. This cellular distribution in the pannus is compared with previous studies on the rheumatoid synovium proper. It is concluded that a distinct inflammatory reaction occurs in the pannus and that classic activated macrophages are the cells involved in cartilage degradation.