Table 1.

Titre of West Nile virus (WNV) antigen-specific antibodies in sera of immunized mice with or without challenge with WNV

Vaccination	WNV challenge	Date of sera harvest	Antibody titre
No treatment	–		Negative control1
p458	–	7 days after 3rd immunization	Negative control1
p458-Ep15	–	7 days after 3rd immunization	25 600
Ep15	–	7 days after 3rd immunization	Not detected2
p431-Ep15	–	7 days after 3rd immunization	Not detected2
p458-Ep15	104 PFU	10 days after challenge	51 200
Ep15	104 PFU	10 days after challenge	3200
p431-Ep15	104 PFU	10 days after challenge	6400
p458	104 PFU	10 days after challenge	1600

Three-week-old mice were immunized three times with the different peptides (equimolar amounts, emulsified in incomplete Freund’s adjuvant), at 7-day intervals. Seven days after the last immunization, the mice were bled and then challenged intraperitoneally with a lethal dose of WNV-ISR98 strain. Ten days after the challenge, surviving mice were bled, sera from each group were pooled and tested by enzyme-linked immunosorbent assay as described in the Materials and methods.

¹For calculation of cut-offs at a confidence level of 99·5%,⁶² we employed two negative controls, namely pooled sera from (i) naive mice and (ii) p458-immunized mice.

²The detection level for WNV antigen-specific antibody titre in this experiment was 400.

PFU, plaque-forming units