Rokhlin O W, Cohen M B, Kubagawa H, Letarte M, Cooper M D
Department of Medicine, University of Alabama at Birmingham 35294, USA.
J Immunol. 1995 May 1;154(9):4456-65.
Endoglin, a glycoprotein that is expressed by human endothelial cells, binds TGF-beta 1 and -beta 3 with high affinity. It was originally identified with the 44G4 mAb that was produced against a human pre-B cell line. We now report that another anti-pre-B cell mAb, 29-G8, reacts with pro-B and pre-B leukemic cells, but not with mature B and T cells, and recognizes a different epitope of endoglin. The 29-G8 mAb bound specifically to recombinant endoglin and immunoprecipitated a phosphorylated homodimeric glycoprotein with subunits of M(r) 95,000 from the 697 pre-B cell line. This new Ab removed all of the molecules identified by the prototypic 44G4 anti-endoglin Ab, but the reverse was not true. A subpopulation of 29-G8+ endoglin molecules on this pre-B cell line was unreactive with the 44G4 mAb, thus suggesting that these anti-endoglin Abs see different epitopes that may discriminate different species of endoglin molecules. Flow cytometric analysis with the 29-G8 mAb revealed two endoglin-positive subpopulations in fetal bone marrow: early B-lineage precursor cells (CD19+ and CD34+), and proerythroblasts (CD71+ and glycophorin A+). In adult bone marrow, only the proerythroblast subpopulation was observed. Stromal cells derived from fetal bone marrow also reacted strongly with the 29-G8 and 44G4 Abs, and these cells responded with enhanced proliferation after stimulation with either TGF-beta 1 or the anti-endoglin Abs. Thus, endoglin, a specialized component of the TGF-beta receptor system, may play a physiologic role in the stromal-hemopoietic cell interactions occurring during development.
内皮糖蛋白是一种由人内皮细胞表达的糖蛋白，它能以高亲和力结合转化生长因子-β1和-β3。它最初是用针对人前B细胞系产生的44G4单克隆抗体鉴定出来的。我们现在报告，另一种抗前B细胞单克隆抗体29-G8与前B和前B白血病细胞发生反应，但不与成熟B和T细胞发生反应，并且识别内皮糖蛋白的不同表位。29-G8单克隆抗体特异性结合重组内皮糖蛋白，并从697前B细胞系中免疫沉淀出一种磷酸化的同型二聚体糖蛋白，其亚基的分子量为95,000。这种新抗体去除了由原型44G4抗内皮糖蛋白抗体鉴定出的所有分子，但反之则不然。该前B细胞系上29-G8 +内皮糖蛋白分子的一个亚群与44G4单克隆抗体无反应，因此表明这些抗内皮糖蛋白抗体识别的不同表位可能区分不同种类的内皮糖蛋白分子。用29-G8单克隆抗体进行的流式细胞术分析显示，胎儿骨髓中有两个内皮糖蛋白阳性亚群：早期B系前体细胞（CD19 +和CD34 +），以及早幼红细胞（CD71 +和血型糖蛋白A +）。在成人骨髓中，仅观察到早幼红细胞亚群。源自胎儿骨髓的基质细胞也与29-G8和44G4抗体强烈反应，并且在用转化生长因子-β1或抗内皮糖蛋白抗体刺激后，这些细胞增殖增强。因此，内皮糖蛋白作为转化生长因子-β受体系统的一个特殊成分，可能在发育过程中发生的基质-造血细胞相互作用中发挥生理作用。
