Surface plasmon resonance. Antibody affinity analysis for DIII of WNV was performed by surface plasmon resonance (BIAcore 3000, Biacore, Inc). Binding curves and kinetic parameters were obtained as follows: we captured E16 antibodies by flowing (300 nM, rate of 5 µl/min for 2 min) them over immobilized F(ab)'2 fragment specific for goat anti-human or mouse IgG with Fc region specificity. Subsequently, DIII of the New York 1999 strain of WNV E protein (amino acids 296-415), which was generated in E. coli, was injected (6.25-200 nM, flow rate 70 µl/min for 1.5 min and then allowed to dissociate over 5 min). The F(ab)'2 surface was regenerated by pulse injection of 10 mM glycine (pH 1.5) and 100 mM NaOH before each E16 injection. We analyzed curves with a global fit 1:1 binding algorithm with drifting baseline.