Keck Zhen-Yong, Li Ta-Kai, Xia Jinming, Bartosch Birke, Cosset François-Loïc, Dubuisson Jean, Foung Steven K H
Stanford Medical School Blood Center, 3373 Hillview Ave., Palo Alto, CA 94304, USA.
J Virol. 2005 Nov;79(21):13199-208. doi: 10.1128/JVI.79.21.13199-13208.2005.
Hepatitis C (HCV) E2 glycoprotein is involved in virus attachment and entry, and its structural organization is largely unknown. Characterization of a panel of human monoclonal antibodies (HMAbs) to HCV by competition studies has led to an immunogenic organization model of E2 with three domains designated A, B, and C and epitopes in each domain having similar structural and functional properties. Domain A contains nonneutralizing epitopes, and domains B and C contain neutralizing epitopes. The isolation and characterization of three new HMAbs within domain A for a total of six provide support for this model. All six domain A HMAbs do not neutralize HCV retroviral pseudotype particle (HCVpp) infection on Huh-7 cells, and all six HMAbs have similar binding affinity and maximum binding, B(max), a relative indicator of epitope density, as other neutralizing HMAbs, suggesting that neutralization is epitope specific and not by binding to any surface epitope. The dose-dependent neutralizing activity of CBH-7, an HMAb to a domain C epitope in spatial proximity to domain A, and of CBH-5, a domain B HMAb to a more distant epitope, were tested in the presence and absence of each domain A HMAb. No enhancement or reduction in CBH-7 or CBH-5 neutralizing activity was observed, indicating that the potential induction of nonneutralizing antibodies should not be a central issue for HCV vaccine design. To assess whether domain A is involved in the structural changes as part of a pH-dependent virus envelope fusion process, changes in antibody binding patterns to normal pH and acid pH-treated HCVpp were measured. Antibody binding affinity of HMAbs to HCVpp was not affected by low pH. However, the B(max) values for low-pH-treated HCVpp with antibodies to domain A increased 46%, for domain C (CBH-7) they increased 23%, and for domain B (CBH-5) there was a decrease of 12%. Collectively, the organization and function of HCV E2 antigenic domains are roughly analogous to the large envelope glycoprotein E organizational structure for other flaviviruses with three distinct structural and functional domains.
丙型肝炎病毒（HCV）E2糖蛋白参与病毒的附着和进入，但其结构组织在很大程度上尚不清楚。通过竞争研究对一组针对HCV的人单克隆抗体（HMAbs）进行表征，得出了E2的免疫原性组织模型，该模型有三个结构域，分别命名为A、B和C，每个结构域中的表位具有相似的结构和功能特性。结构域A包含非中和表位，结构域B和C包含中和表位。在结构域A内分离并表征了三种新的HMAbs，加上之前的共有六种，这为该模型提供了支持。所有六种结构域A的HMAbs均不能中和Huh-7细胞上的HCV逆转录病毒假型颗粒（HCVpp）感染，并且所有六种HMAbs与其他中和性HMAbs一样，具有相似的结合亲和力和最大结合量B(max)（表位密度的相对指标），这表明中和作用具有表位特异性，而非通过与任何表面表位结合。在存在和不存在每种结构域A的HMAb的情况下，测试了CBH-7（一种针对与结构域A空间邻近的结构域C表位的HMAb）和CBH-5（一种针对更远表位的结构域B的HMAb）的剂量依赖性中和活性。未观察到CBH-7或CBH-5中和活性的增强或降低，这表明非中和抗体的潜在诱导不应成为HCV疫苗设计的核心问题。为了评估结构域A是否作为pH依赖性病毒包膜融合过程的一部分参与结构变化，测量了抗体与正常pH和酸处理的HCVpp结合模式的变化。HMAbs与HCVpp的抗体结合亲和力不受低pH影响。然而，用结构域A抗体处理的低pH处理的HCVpp的B(max)值增加了46%，用结构域C（CBH-7）处理的增加了23%，用结构域B（CBH-5）处理的则下降了12%。总体而言，HCV E2抗原结构域的组织和功能大致类似于其他黄病毒具有三个不同结构和功能结构域的大包膜糖蛋白E的组织结构。
