Infection of mice with both 1000 and 100 PFU of WNV Eg101 induced high titers of WNV specific IgM and IgG antibodies, and cross-reactive neutralizing antibodies, which were detectable as early as day 6 after infection and neutralized both WNV Eg101 and WNV NY99 strains with similar efficiency. This evidence concerns the gene CD40LG and infection.