Frémeaux-Bacchi V, Bernard I, Maillet F, Mani J C, Fontaine M, Bonnefoy J Y, Kazatchkine M D, Fischer E
INSERM U430, Hôpital Broussais, Paris, France.
Eur J Immunol. 1996 Jul;26(7):1497-503. doi: 10.1002/eji.1830260714.
We report on a soluble (s) form of CD21 (the C3dg/Epstein-Barr virus receptor, CR2) that is spontaneously released by B and T lymphocytes. Immunoprecipitation with anti-CD21 mAb of culture supernatants of surface and biosynthetically labeled B and T cell lines revealed a single band with an apparent molecular mass of 135 kDa. The molecule exhibited a molecular mass 10 kDa lower than that of membrane CD21. The release of soluble CD21 (sCD21) was time dependent and correlated with a parallel decrease in the expression of the membrane-associated molecule. The protein was also found in culture supernatants of tonsillar B cells and normal human thymocytes. Epitopic analysis using combinations of anti-CD21 monoclonal antibodies (mAb) indicated that sCD21 and membrane CD21 were similarly recognized by mAb directed against short consensus repeats (SCR) 1-2, SCR 4-5 and SCR 9-11. Affinity-purified sCD21 was capable of binding to purified human iC3b and to human recombinant CD23, as assessed by enzyme-linked immunosorbent assay and by using the BIAcore technology. In addition, normal human serum was found to contain a soluble form of CD21 that exhibited a similar molecular mass to that of the molecule shed by B and T cells in culture. The serum form of CD21 was recognized by all anti-CD21 mAb that we tested and showed a high reactivity with mAb directed against SCR 1-2. Our observations suggest that B and T cells shed the extracellular portion of CD21 and release a soluble molecule that retains the ligand-binding properties of CD21, thus having a potential role in immunoregulation.
我们报道了一种可溶性（s）形式的CD21（C3dg/爱泼斯坦-巴尔病毒受体，CR2），它由B淋巴细胞和T淋巴细胞自发释放。用抗CD21单克隆抗体对表面和经生物合成标记的B细胞系及T细胞系的培养上清进行免疫沉淀，显示出一条表观分子量为135 kDa的单一带。该分子的分子量比膜结合型CD21低10 kDa。可溶性CD21（sCD21）的释放具有时间依赖性，且与膜相关分子表达的平行下降相关。在扁桃体B细胞和正常人胸腺细胞的培养上清中也发现了该蛋白。使用抗CD21单克隆抗体（mAb）组合进行的表位分析表明，针对短共有重复序列（SCR）1-2、SCR 4-5和SCR 9-11的mAb对sCD21和膜结合型CD21的识别相似。通过酶联免疫吸附测定和BIAcore技术评估，亲和纯化的sCD21能够结合纯化的人iC3b和人重组CD23此外，发现正常人血清中含有一种可溶性形式的CD21，其分子量与培养中的B细胞和T细胞所释放分子的分子量相似血清中的CD-21形式被我们测试的所有抗CD21 mAb所识别，并与针对SCR 1-2的mAb表现出高反应性。我们的观察结果表明，B细胞和T细胞释放CD21的细胞外部分，并释放一种保留CD21配体结合特性的可溶性分子，因此在免疫调节中可能发挥作用。
