Antigenic analysis of enterovirus 71

[[abstract]]Background: Enterovirus 71 (EV71) is a non-enveloped RNA virus of the family Picornaviridae and contains a single molecule of plus sense ssRNA. The icosahedral viral capsid is composed of 60 identical units that consist of VP1, VP2, VP3 and VP4 structural proteins. Most EV71 infections manifest as mild cases of hand-foot-mouth disease (HFMD). Recently, it has caused large-scale epidemics in Asian children with life-threatening neurological and cardiopulmonary complications. Therefore, development of EV71 vaccines has become a public health priority in several Asian countries. EV71 has single serotype as measured by hyperimmune animal antisera but can be phylogenetically classified into three genogroups (A, B and C) and 11 genotypes (A, B1-B5 and C1-C5). Recently, it has been observed in Taiwan that different genotypes, rather than cocirculating, tend to prevail at a given time period, i.e., C2 in 1998, B4 in 2000-2001, C4 in 2004-2005, and B5 in 2008, an epidemiological pattern suggestive of genotype replacement. This observation, in conjunction with the observed antigenic variations among different EV71 genogroups in human studies, has kindled the interest to establish animal models to monitor the potential antigenic evolution of EV71. Methods: In the present study, a rabbit model was developed to produce EV71 antisera for monitoring antigenic variations of EV71 viruses. EV71 viruses of 11 genotypes were grown in rhabdomyosarcoma (RD) or Vero cells. Virus particles were purified by consecutive sucrose ultracentrifugations. The EV71 particles detected in the 33-43% sucrose fractions had the highest viral infectivity, which were collected to immunize rabbits. EV71-specific rabbit antisera were further employed to measure cross-reactive neutralizing antibody titers against all 11 EV71 genotypes. Results: In the initial results, serology data showed that rabbits immunized with genogroup B and C consistently have a lower neutralizing antibody titers against genogroup A (>4-fold difference) and antigenic variations between genogroup B and C can be detected but did not have a clear pattern. Conclusion: Compared with human serological data, the rabbit model has similar cross-reactive EV71 neutralizing antibody profiles to that observed in human studies and can be incorporated in enterovirus surveillance system to monitor antigenic variations of EV71 viruses