Fischer E M, Mouhoub A, Maillet F, Frémeaux-Bacchi V, Krief C, Gould H, Berrih-Aknin S, Kazatchkine M D
INSERM U430, Hôpital Broussais, 96 rue Didot, 75014 Paris, France.
Int Immunol. 1999 Nov;11(11):1841-9. doi: 10.1093/intimm/11.11.1841.
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.
CD21是C3d/CD23/爱泼斯坦-巴尔病毒（EBV）受体，在T细胞系细胞上低密度表达。未成熟胸腺细胞高密度表达CD21。在本研究中，我们分析了T细胞胸腺内成熟过程中CD21的表达情况。在双阴性阶段和早期获得CD4的阶段观察到CD21的强烈染色。在双阳性和单阳性阶段，CD21表达降低，随后达到与外周血T细胞相似的水平。胸腺切片染色显示，在皮质区进入胸腺的胸腺细胞上有明亮的荧光信号。利用高表达CD21（CD21(++)）细胞的未成熟表型，我们去除胸腺细胞悬液中的CD3(+)和CD8(+)细胞，以研究该细胞亚群上CD21的特性。用其配体iC3b、CD23和抗CD21单克隆抗体触发CD21，并未改变胸腺细胞对IL-7的增殖反应，也未诱导早期细胞分化为CD4(+)CD8(+)胸腺细胞。免疫沉淀未发现任何与CD21相关的分子可在胸腺细胞中发挥信号作用。最后，EBV诱导CD21(++)胸腺细胞中CD21下调和CD1上调。综上所述，我们的观察结果表明CD21在人胸腺细胞上的表达受到调控，提示CD21(++)亚群可能是EBV的靶标。我们进一步认为，早期胸腺细胞上的CD21作为胸腺中表达CD23细胞的配体发挥作用。
