Mallet V, Blaschitz A, Crisa L, Schmitt C, Fournel S, King A, Loke YW, Dohr G, Le Bouteiller P. HLA-G in the human thymus: a subpopulation of medullary epithelial but not CD83(+) dendritic cells expresses HLA-G as a membrane-bound and soluble protein.
Int Immunol 1999;
11:889-98. [PMID:
10360962 DOI:
10.1093/intimm/11.6.889]
[Citation(s) in RCA: 100] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The human MHC class Ib gene HLA-G is transcribed and translated in different placental cell subpopulations during pregnancy. In addition to this restricted tissue distribution, HLA-G proteins were also recently detected in the thymus of HLA-G transgenic mice, as well as in some human thymic epithelial cells (TEC). There was a need to further define the phenotype of the HLA-G-expressing cells in the human thymus as well as the type of translated forms that they produce. Using several HLA-G-specific mAb and immunohistochemistry performed on cryosections of human thymi at different ages, we found that the HLA-G-expressing cells are present on medullary cells exhibiting the epithelial morphological type 6. Co-localization experiments performed by double or triple immunofluorescence staining demonstrate that these HLA-G-expressing cells express various cytokeratins, epithelial cell markers but not the CD83 dendritic cell marker. We further show by ELISA measurements that a subset of primary cultured human TEC also expresses soluble HLA-G. Therefore, HLA-G protein tissue distribution is not restricted solely to placental cells. A subpopulation of medullary TEC also expresses HLA-G both at their cell surface and in secreted form, raising the question of the functional significance of such MHC class Ib molecules. Whether thymic soluble and/or membrane-bound HLA-G contribute to inhibit NK cells or to a negative selection of autoreactive T cells which could be harmful in case of pregnancy and/or to a positive selection of viral peptides/HLA-G-restricted CD8(+) T cells remains to be demonstrated.
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