Immuno- and enzymehistochemical characterization of 'plasmacytoid T-cells' in formalin-fixed paraffin-embedded tissue of reactive lymph nodes.

In eight (10.4%) of 77 randomly selected cases of lymphadenitis, foci of 'plasmacytoid T-cells' (PTCs) were found. We characterized the PTCs in formalin-fixed paraffin-embedded tissue by immuno- and enzymehistochemical techniques. In each case the PTCs formed nodular and patchy infiltration patterns around the high endothelial venules in the paracortex of the lymph nodes. The PTCs in half of the cases were present near the intermediary peritrabecular sinuses. The PTCs were found to be positive for CD 45 (LCA), CD 45 R (4 KB 5) and CD 43 (MT 1), but not for CD 45 RO (UCHL 1), L 26 (CD 20), myeloperoxidase, naphthol AS-D chloroacetate esterase, Mac 387, alpha-1-antichymotrypsin or S 100 protein and anti-dendritic reticulum cell antibody. Some lysozyme+ PTCs were mingled in and around the foci in each case. In five cases the PTCs showed weaker positive reactions for CD 68 (EBM 11) and HLA-DR than for T-zone macrophages and sinus histiocytes. Related to the degree of desintegration of the nodular PTC-foci increasing numbers of T- and B-lymphocytes, T-zone macrophages and interdigitating reticulum cells with HLA-DR were detected in the foci. In two cases, where there was no HLA-DR expression by PTCs, small amounts of HLA-DR in secondary lymph follicles and a decrease of HLA-DR+ T-zone macrophages and interdigitating reticulum cells were observed. Our results suggest that there is a high degree of interaction between PTCs and other cellular components in the lymph node. The PTC may represent a special type of resident macrophage with secretory capacities.