Comprehensive Mapping of Common Immunodominant Epitopes in the West Nile Virus Nonstructural Protein 1 Recognized by Avian Antibody Responses

Encheng Sun,Zhigao Bu,Yinhui Yang,Qingyuan Xu,Nihong Liu,Linfa Wang,Tao Yang,Donglai Wu,Jing Zhao,Yongli Qin,Ross A Lunt,Robyn Klein

doi:10.1371/journal.pone.0031434

Abstract

West Nile virus (WNV) is a mosquito-borne flavivirus that primarily infects birds but occasionally infects humans and horses. Certain species of birds, including crows, house sparrows, geese, blue jays and ravens, are considered highly susceptible hosts to WNV. The nonstructural protein 1 (NS1) of WNV can elicit protective immune responses, including NS1-reactive antibodies, during infection of animals. The antigenicity of NS1 suggests that NS1-reactive antibodies could provide a basis for serological diagnostic reagents. To further define serological reagents for diagnostic use, the antigenic sites in NS1 that are targeted by host immune responses need to be identified and the potential diagnostic value of individual antigenic sites also needs to be defined. The present study describes comprehensive mapping of common immunodominant linear B-cell epitopes in the WNV NS1 using avian WNV NS1 antisera. We screened antisera from chickens, ducks and geese immunized with purified NS1 for reactivity against 35 partially overlapping peptides covering the entire WNV NS1. This study identified twelve, nine and six peptide epitopes recognized by chicken, duck and goose antibody responses, respectively. Three epitopes (NS1-3, 14 and 24) were recognized by antibodies elicited by immunization in all three avian species tested. We also found that NS1-3 and 24 were WNV-specific epitopes, whereas the NS1-14 epitope was conserved among the Japanese encephalitis virus (JEV) serocomplex viruses based on the reactivity of avian WNV NS1 antisera against polypeptides derived from the NS1 sequences of viruses of the JEV serocomplex. Further analysis showed that the three common polypeptide epitopes were not recognized by antibodies in Avian Influenza Virus (AIV), Newcastle Disease Virus (NDV), Duck Plague Virus (DPV) and Goose Parvovirus (GPV) antisera. The knowledge and reagents generated in this study have potential applications in differential diagnostic approaches and subunit vaccines development for WNV and other viruses of the JEV serocomplex.

Highlights

West Nile virus (WNV) is a medically important pathogen that is prevalent in many areas around world, including Africa, Europe, Russia, the Middle East, India, Australia and North America [1]
Prior to each immunization, serum was collected from each bird to measure the nonstructural protein 1 (NS1)-reactive antibody titers by immunofluorescence assay (IFA)
Immunization with recombinant WNV NS1 protein elicits high-titer NS1-reactive antibodies in chickens, ducks and geese

Summary

Introduction

West Nile virus (WNV) is a medically important pathogen that is prevalent in many areas around world, including Africa, Europe, Russia, the Middle East, India, Australia and North America [1]. It is serologically classified into the Japanese encephalitis virus (JEV) serocomplex, which includes WNV, JEV, Saint-Louis encephalitis virus (SLEV) and Murray Valley fever virus (MVEV) [2]. Deaths in American crows (AMCR) due to WNV infection were especially prevalent in New York City in 1999 [22], and crow mortality has been adopted as an epidemiological indicator to monitor WNV transmission in the United States and has proven useful in predicting an increased risk for human infection [23,24,25]

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