Impact of West Nile Virus Envelope Domain III Surface Loop Residues on Antigenicity and Virulence

West Nile virus (WNV) is an encephalitic flavivirus that is maintained worldwide in a transmission cycle between birds and mosquitoes. Domain III of its envelope protein is the target of highly specific and potently neutralizing antibodies, and is thought to bind the host cell receptors. To determine the role of individual surface loop residues in the function and antigenicty of WNV EIII, a panel of mutants was generated. Changes in antibody neutralization, in vitro replication kinetics, and in vivo virulence were characterized. In general, it was found that diversity in the surface loops was well tolerated and that all surface loop residues had at least some contribution to antigenicity. Residue T332 was especially important from an antigenic standpoint. Changes at T332 resulted in escape from neutralization by monoclonal and polyclonal antibodies both in vitro and in vivo. Changes at residues G331, D333, and N368 resulted in attenuation, suggesting a possible functional patch involved in receptor binding.