Expression of CD21 is developmentally regulated during thymic maturation of human T lymphocytes.
CD21, the C3d/CD23/Epstein-Barr virus (EBV), receptor is expressed at low density on cells of the T lineage. Immature thymocytes express CD21 with high density. In the present study, we have analyzed the expression of CD21 during intrathymic maturation of T cells. An intense staining for CD21 was observed at the double-negative stage and at the stage of early acquisition of CD4. CD21 expression was decreased at the double-positive and single-positive stages, to then reach levels similar to those of peripheral blood T cells. Staining of thymus sections showed a bright fluorescent signal on thymocytes entering the thymus in the cortical region. Taking advantage of the immature phenotype of cells expressing high amounts of CD21 (CD21(++)), we depleted thymocyte suspensions in CD3(+) and CD8(+) cells to study the properties of CD21 on this cell subset. Triggering of CD21 with its ligands iC3b, CD23 and anti-CD21 mAb did not alter the proliferative response of thymocytes to IL-7, and did not induce the differentiation of early cells into CD4(+)CD8(+) thymocytes. Immunoprecipitation did not reveal any molecule associated with CD21 that could play a signaling role in thymocytes. Finally, EBV induced a down-regulation of CD21 and an up-regulation of CD1 in CD21(++) thymocytes. Taken together, our observations demonstrate a regulated expression of CD21 on human thymocytes and suggest that the CD21(++) subset may be a target for EBV. We further suggest that CD21 on early thymocytes acts as a ligand for CD23-expressing cells in the thymus.
Fischer
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INSERM U430, Hôpital Broussais, 96 rue Didot, 75014 Paris, France.
Mouhoub
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Maillet
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Frémeaux-Bacchi
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Krief
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Gould
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Berrih-Aknin
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Kazatchkine
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D002454:Cell Differentiation; D002478:Cells, Cultured; D020031:Epstein-Barr Virus Infections / Q000276:immunology; D018507:Gene Expression Regulation, Developmental / Q000276:immunology*; D004854:Herpesvirus 4, Human / Q000276:immunology; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008213:Lymphocyte Activation; D011233:Precipitin Tests; D017464:Receptors, Complement 3d / Q000276:immunology / Q000378:metabolism*; D017455:Receptors, IgE / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology* / Q000821:virology; D013950:Thymus Gland / Q000166:cytology* / Q000276:immunology
D017464:Receptors, Complement 3d; D017455:Receptors, IgE