Heterogeneity of epithelial cells in the human thymus |
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Authors: | Frank P. van de Wijngaert Marion D. Kendall Henk-Jan Schuurman Ph.D. Loek H. P. M. Rademakers Louis Kater |
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Affiliation: | (1) Division of Immunopathology, Departments of Internal Medicine and Pathology, University Hospital, Utrecht, The Netherlands;(2) Department of Anatomy, St. Thomas's Hospital Medical School, London, England;(3) Division of Electron microscopy, Institute for Pathology, University of Utrecht, The Netherlands;(4) Division of Immunopathology, Department of Internal Medicine, University Hospital, 101 Catharijnesingel, 3511 GV Utrecht, The Netherlands |
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Abstract: | Summary To evaluate interrelationships among epithelial cells, and between morphology and function in the microenvironment, we studied the ultrastructural morphology of epithelial cells in sections of human thymus from donors aged 2 months to 31 years. Six types of epithelial cells were observed: subcapsular-perivascular (type 1); pale (type 2); intermediate (type 3); dark (type 4); undifferentiated (type 5); and large-medullary (type 6). Cells of types 2, 3 and 4 were found throughout the organ. The type-2 to -4 epithelial cells may represent various stages in a differentiation process. In this, type-2 cells are very active and type-4 cells are possibly degenerating elements. Type-4 cells can also contribute to Hassall's corpuscles. Type-5 cells were located mainly in the cortico-medullary region and showed the morphological characteristics of undifferentiated elements. Type-6 cells were located exclusively in the medulla and displayed characteristics of cellular activity. Small Hassall's corpuscles consisted of type-6 epithelial cells; in larger corpuscles many nuclei of type-6 cells were found. Cells of types 2 and 6 contained tubular structures (diameter approximately 20 nm).Concerning the function of thymus epithelial cells, the features associated with protein synthesis observed in cellular types 2 and 6 make them likely candidates for humoral factor-producing and/or secreting elements. In addition, type-2 and -3 cells in the cortex appear to contribute to a special pattern of epithelium-lymphocyte interaction (thymic nurse cells), as demonstrated by the intracytoplasmic location of lymphocytes in the epithelial cells. The various steps in intrathymic T-cell maturation occur at locations in a microenvironment composed of morphologically distinct epithelial cells. |
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Keywords: | Thymus Epithelial cells Hassall's Man |
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