Porto Conte Ricerche, Science and Technology Park of Sardinia, Tramariglio, Alghero (Sassari), Italy.
Department of Clinical, Surgical, Diagnostic and Pediatric Sciences, University of Pavia, Italy.
Clin Infect Dis. 2018 Apr 17;66(9):1342-1351. doi: 10.1093/cid/cix1006.
Several tools have been proposed for serodiagnosis of cystic echinococcosis (CE), but none seems promising for cyst viability assessment. Antigens with stage-specific diagnostic value have been described, but few studies with well-characterized antigens and human serum samples have been performed. Antigen B (AgB) proteoforms hold promise as markers of viability, due to their differential stage-related expression and immunoreactivity.
Four AgB subunits (AgB1, AgB2, AgB3, AgB4) were synthesized and structurally characterized. Based on the preliminary evaluation of the subunits by western immunoblotting and enzyme-linked immunosorbent assay (ELISA), AgB1 and AgB2 were further tested in two ELISA setups and extensively validated on 422 human serum samples.
All subunits showed a high degree of spontaneous oligomerization. Interacting residues within oligomers were identified, showing that both the N-terminal and C-terminal of each subunit are involved in homo-oligomer contact interfaces. No hetero-oligomer was identified. AgB1 and AgB2 ELISAs revealed different sensitivities relative to cyst stage. Of note, besides high specificity (97.2%), AgB1 revealed a higher sensitivity for active-transitional cysts (100% for CE1, 77.8% for CE2, 81.5% for CE3a, and 86.3% for CE3b) than for inactive cysts (41.7% for CE4 and 11.1% for CE5) and postsurgical patients (44%). Interestingly, 19 of 20 patients with spontaneously inactive cysts and 6 of 9 treated with albendazole >5 years earlier were negative on the AgB1 assay.
The structural characterization of subunits provides insights into the synthetic antigen conformation. The stage-related sensitivity of synthetic AgB1 holds promise as part of a multiantigen setting and deserves further longitudinal evaluation as marker of cyst viability.
已有多种工具被提出用于囊型包虫病（CE）的血清学诊断，但似乎没有一种方法能够很好地评估包虫囊的活力。已经描述了具有阶段特异性诊断价值的抗原，但很少有使用特征明确的抗原和人类血清样本进行的研究。由于其差异相关的表达和免疫反应性，抗原 B（AgB）的蛋白变体有望成为活力标志物。
合成了四个 AgB 亚单位（AgB1、AgB2、AgB3、AgB4）并对其结构进行了表征。基于 AgB 亚单位的初步western 免疫印迹和酶联免疫吸附试验（ELISA）评估，AgB1 和 AgB2 在两种 ELISA 方案中进行了进一步测试，并在 422 个人类血清样本中进行了广泛验证。
所有亚单位均显示出高度的自发性寡聚化。鉴定出寡聚体中的相互作用残基，表明每个亚基的 N 端和 C 端均参与同型寡聚体接触界面。未鉴定出异型寡聚体。AgB1 和 AgB2 ELISA 相对于囊型阶段显示出不同的敏感性。值得注意的是，除了高特异性（97.2%）外，AgB1 对活动性过渡性囊肿（CE1 为 100%，CE2 为 77.8%，CE3a 为 81.5%，CE3b 为 86.3%）的敏感性高于非活动性囊肿（CE4 为 41.7%，CE5 为 11.1%）和手术后患者（44%）。有趣的是，19 例自发性非活动性囊肿和 6 例接受阿苯达唑治疗>5 年的患者在 AgB1 检测中均为阴性。
亚单位的结构特征为合成抗原构象提供了深入了解。合成 AgB1 的与阶段相关的敏感性有望成为多抗原检测的一部分，并值得进一步进行纵向评估作为囊活力的标志物。
