The 581 antibody reacts with human CD34, an ~105 - 120 kDa type 1 transmembrane glycoprotein expressed on the surface of most human hematopoietic stem and progenitor cells (HSPCs) as well as on mesenchymal stem cells, embryonic fibroblasts, endothelial cells, neurons, and some tumor cell lines. CD34 is expressed only transiently during hematopoiesis, so the frequency of CD34+ cells is low in bone marrow or cord blood (~1 - 5%) and very low (~0.1 - 0.5%) in peripheral blood. CD34 is a marker used to identify and isolate HSPCs capable of cell engraftment. CD34 is thought to mediate attachment of stem cells to the bone marrow extracellular matrix or directly to stromal cells during early hematopoiesis, and to be involved in lymphocyte recruitment through binding to the ligands L- and E-selectin. Distinct epitope groups have been assigned to CD34 based on their sensitivity to enzymatic cleavage, with the 581 antibody recognizing a class III epitope (resistant to neuraminidase and O-glycoprotease). This antibody clone has been verified for purity assessments of cells isolated with EasySep™ Human CD34 Positive Selection Kit (Catalog #18056) and for labeling human mesenchymal cells grown in MesenCult™ Proliferation Kit (Human; Catalog #05411).

581抗体与大多数人类造血干细胞和祖细胞（HSPC）以及间充质干细胞，胚胎成纤维细胞，内皮细胞，神经元和表面上表达的人CD34（〜105-120kDa 1型跨膜糖蛋白）一些肿瘤细胞系。 CD34在造血过程中仅仅是短暂表达的，所以CD34 +细胞在骨髓或脐带血中的频率（1-5％）很低，外周血非常低（〜0.1-0.5％）。 CD34是用于鉴定和分离能够细胞植入的HSPC的标记。 CD34被认为介导干细胞在骨髓细胞外基质或在造血早期直接到基质细胞的附着，并通过与配体L-和E-选择素结合而参与淋巴细胞募集。根据其对酶切割的敏感性，将不同的表位组分配到CD34上，581抗体识别III类表位（对神经氨酸酶和O-糖蛋白酶具有抗性）。

已经验证了用EasySep TM人CD34阳性选择试剂盒（货号18056）分离的细胞的纯度评估和用于标记在MesenCult TM增殖试剂盒（Human;货号05411）中生长的人间充质细胞的纯度。