血管生成素2（angiopoietin-2, Ang-2)是Ang家族的成员之一，是特异性血管生成刺激因子，也是恶性肿瘤早期的标志分子。Ang-2与Ang-1 60%同源，相互间易形成异二聚体结构，自身也常以同源二聚体及多聚体结构存在。Ang-2的生物学功能与Ang-1完全相反。Ang-1与血管内皮细胞的Tie-2受体结合，促进血管成熟及稳定，Ang-2与Tie-2结合，不使Tie-2磷酸化而激活Tie-2，反而拮抗Ang-1的生物活性，破坏血管完整性，影响内皮细胞之间及其与支持细胞之间的连接。在肿瘤发生的早期，Ang-2参与破坏瘤体周边原有的正常血管，而促进肿瘤新生血管的生成，在瘤体周边形成所谓的血管共择（co-option）区。当肿瘤形成以后，Ang-2与血管内皮生长因子（VEGF）有协同作用，共同促进肿瘤血管生成，并阻碍血管的完整性，使得肿瘤新生血管能在各种因子的刺激下不断增生。
本试剂盒应用双抗体夹心酶标免疫分析法测定标本中ANG-2水平。用纯化的抗体包被微孔板，制成固相抗体，往包被抗体的微孔中依次加入ANG-2、生物素化的抗ANG-2抗体、HRP标记的亲和素，经过彻底洗涤后用底物TMB显色。TMB在过氧化物酶的催化下转化成蓝色，并在酸的作用下转化成最终的黄色。颜色的深浅和样品中的ANG-2呈正相关。用酶标仪在450nm波长下测定吸光度（OD值），计算样品浓度。
Intended use
This immunoassay kit allows for the specific measurement of human Angiopoietin-2,ANG-2 concentrations in cell culture supernates ,serum ,plasma and saliva.
Introduction
Angiopoietin-2 (Ang-2) is a secreted glycoprotein that plays a complex role in vascular development. Ang-2 contains an N-terminal coiled-coildomain, 58 - 254 amino acids (aa) and a C-terminal fibrinogen-like domain, 281 - 467 aa, that is also found in other proteins including fibrinogen, tenascin, and ficolin. Located at the N-terminus are stretches of hydrophobic residues typical of secretory signal sequences. While Ang-2 is widely expressed in the mouse embryo, it is restricted postnatally to pro-angiogenic regions including the placenta, ovaries, and uterus.
Although likely playing different functional roles, both Ang-1 and Ang-2 are ligands for the endothelial cell receptor tyrosine kinase Tie-2.The regulation of Tie-2 activity by Ang-2 is complex, leading to inhibition in certain cell types or conditions, and activation in others.Initial in vitrostudies using immortalized human umbilical vein endothelial cells (HUVECs) demonstrated that Ang-1, but not Ang-2, could stimulate Tie-2 tyrosine phosphorylation and suggested that Ang-2 could act as a competitive inhibitor of Ang-1 signaling.Consistent with its role as an Ang-1/Tie-2 inhibitor, transgenic overexpression of Ang-2 leads to disruption of embryonic blood vessel formation, a phenotype similar to that of Tie-2 knockouts .In contrast, altering incubation times or elevating Ang-2 concentrations,can under some circumstances, result in Tie-2 activation in HUVECs.It has also been proposed that Ang-2may play a pro-angiogenic role by mediating destabilizing interactions between endothelial and perivascular cells, enhancing the effects of pro-angiogenic proteins including vascular endothelial growth factor (VEGF). Alone, Ang-2 promotes endothelial cell death and vessel regression, but can act in synergy with VEGF to promote new vessel formation.
Ang-2 has been implicated in cancer development due to its role in angiogenesis.Ang-2-mediated destabilization of mature vessel structures accompanied by the presence of VEGF, may contribute to the angiogenesis associated with tumor tissues. Ang-2 is elevated in colon carcinoma,gastric carcinoma ,glioblastoma,glioma ,hepatocellular carcinoma,neuroblastoma and non-small cell lung cancer .Furthermore, Ang-2 levels appear to correlate with advancing tumor stage progression and poor prognosis.
Test principle
This assay employs the quantitative sandwich enzyme immunoassay technique. A monoclonal antibody specific for ANG-2 has been pre-coated onto a microplate. Standards and samples are pipetted into the wells and any ANG-2 present is bound by the immobilized antibody. An enzyme-linked monoclonal antibody specific for ANG-2 is added to the wells. Following a wash to remove any unbound antibody-enzyme reagent, a substhumane solution is added to the wells and color develops in proportion to the amount of ANG-2 bound in the initial step. The color development is stopped and the intensity of the color is measured.
