V-specific IgG responses induced by various V vaccine regimens in mice: codon optimized V DNA vaccine alone (V-DNA), V DNA vaccine prime followed by V protein boost formulated with IFA (V-DNA + Prot/IFA), V protein formulated with IFA (V-Prot/IFA), V protein alone (V-Prot), or empty DNA vaccine vector alone (Vector). Panels A and B: V-specific antibody titers were measured by ELISA against V protein in mouse sera collected at 2 weeks after the prime (1st immunization) (Panel A) or at 2 weeks after the boost (2nd immunization) (Panel B). Panel C: V-specific IgG concentrations at 2 weeks after the boost (2nd) immunization. Each bar represents the mean V-specific IgG titers or concentrations in each group of 5 mice with standard error. Statistically significant differences (p < 0.05) are indicated as “*”, “#” or “^” when comparing V-DNA, V-DNA + Prot/IFA, and V-Prot/IFA groups.