The molecular basis of antibody-mediated neutralization of West Nile virus

West Nile Virus (WNV) is a mosquito-borne flavivirus that causes disease in humans ranging from a mild febrile illness to lethal encephalitis. Infection results in a robust antibody response against the envelope protein (E) that is critical for control of infection. The antibody response may also contribute to severe disease in some flavivirus infections through the mechanism of antibody dependent enhancement (ADE): antibodies bind virus and enhance uptake into FcgammaR bearing cells such as macrophages. These conflicting roles of antibody have resulted in intense study of the antibody response generated in a flavivirus infection such as WNV. The E protein has three structural domains that have been implicated in various functions in the viral life cycle and in eliciting antibodies. Domain III has been implicated in receptor binding and strongly neutralizing monoclonal antibodies (mAbs) map to this domain. Domain II contains the fusion loop that mediates endosomal fusion of the virus envelope. Neutralizing mAbs have also been mapped to this domain. Domain I connects domains II and III and appears to have some potential to generate neutralizing antibodies. While specific epitopes have been identified that interact with neutralizing antibodies, it is unclear the exact role epitope specificity has in determining antibody function. The aim of this thesis is to determine how epitope location on the WNV E protein impacts antibody function. To address this, a panel of ∼164 mAbs that bind to the WNV envelope protein was generated. Using a novel yeast display system, an epitope was identified in domain III that elicits highly neutralizing and protective antibodies. Other epitopes in all three domains elicit antibodies with reduced efficacy both in vitro and in vivo. These antibodies also displayed a greater potential to facilitate ADE. The presence of antibodies in the serum of infected mice and humans that bind to the strongly neutralizing epitope as well as a less-protective epitope at the fusion loop was assessed using recombinant proteins. Significant species-specific differences were observed in that, antibodies to the strongly neutralizing epitope in domain III are generated at lower levels in human patients than mice. This work has implications in both therapeutic and vaccine design.