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Extrafollicular reticulum cells in lymph nodes are heterogeneous. They express cytokeratins, desmin, and/or vimentin as their intermediate filament profile. Using those markers, we undertook an immunohistochemical study of human lymph nodes under various pathologic conditions. Samples included 15 simple reactive lymph nodes, 7 follicular hyperplasia, 1 necrotizing lymphadenitis, 4 tuberculous lymphadenitis, 13 malignant lymphoma (9 non-Hodgkin's and 4 Hodgkin's lymphomas), and 11 metastatic adenocarcinoma. In lymph nodes with follicular hyperplasia, cytokeratin and/or desmin expressing reticulum cells displayed a characteristic dendritic meshwork in the subcapsular, perisinusoidal, and paracortical regions. In other forms reactive lymph nodes, they were similarly distributed but were less prominent. By SDS-PAGE and immunoblotting, cytokeratin polypeptides were identified. In necrotizing lymphadenitis, they were increased and the pattern of distribution was disturbed. In tuberculous lymphadenitis, they were also increased and located at nongranulomatous as well as in perigranulomatous areas. In lymphomas the reticular meshwork was entirely obliterated. Cytokeratin or desmin expressing reticulum cells were rarely seen within tumors. The reticular meshwork was also obliterated in metastatic carcinoma. However, the meshwork was maintained in uninvolved areas. In conclusion, extrafollicular reticulum cells displayed characteristic patterns of distribution under various pathologic conditions, and may be implicated in the pathogenesis of those pathologic conditions in human lymph nodes.
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