National Institute for Veterinary Research, Brussels, Belgium.
Avian Pathol. 1996 Dec;25(4):751-68. doi: 10.1080/03079459608419179.
This study has confirmed, by the use of immunological and molecular tools, that the recent failures of vaccination against infectious bursal disease (IBD) encountered in Europe were not related to antigenic variation, but to increased virulence of the circulating IBD virus strains. Neutralizing monoclonal antibodies (Mabs) showed that the vaccines of intermediate virulence and the pathogenic strain 849VB had a similar pattern of reactivity in ss neutralization tests. Four distinct epitopes could be defined in seroneutralization and addition ELISA tests. All neutralizing Mabs bound to the structural VP2 protein only in its native form. Moreover, Mabs which did not neutralize some strains precipitated well the VP2 protein from extracts of cells infected with the same virus. This suggests that slight changes in the conformation of the epitope were sufficient to allow the virus to escape to neutralization. VP2 sequencing results confirmed that the neutralizing epitopes are clustered in the variable domain which is highly hydrophobic and flanked by two major hy-drophilic peaks. Three potential 'minor' antigenic sites were identified within the hydrophobic region. Comparison of the VP2 sequence of 849VB strain with other highly virulent isolates showed that they are close together and clearly distinct from 'classical' strains. Moreover, sequencing of IBD vaccines revealed that some of them had not been cloned.
本研究通过免疫和分子工具证实，近期在欧洲发生的传染性法氏囊病（IBD）疫苗免疫失败并非由于抗原变异，而是由于流行的 IBD 病毒株毒力增强。中和单克隆抗体（Mabs）表明，中等毒力疫苗和致病性毒株 849VB 在 ss 中和试验中的反应模式相似。在血清中和和加样 ELISA 试验中可定义四个不同的表位。所有中和性 Mab 仅在其天然形式下与结构 VP2 蛋白结合。此外，一些不能中和某些毒株的 Mab 很好地沉淀了相同病毒感染的细胞提取物中的 VP2 蛋白。这表明表位构象的微小变化足以使病毒逃避中和。VP2 测序结果证实，中和表位聚集在高度疏水的可变区，两侧是两个主要的亲水峰。在疏水区域内还鉴定出三个潜在的“次要”抗原位点。与其他高毒力分离株的 849VB 株 VP2 序列比较表明，它们彼此接近，与“经典”株明显不同。此外，IBD 疫苗的测序表明，其中一些疫苗没有被克隆。
