Figure 3: Serum IgG and isotype endpoint titers. Serum antibodies specific for M2e peptide and MDCK expressed M2 were determined. The highest dilution that gave an OD450 of twice that of the naive group at the lowest dilution was designated as the Ab endpoint titer. G1: Soluble tetrameric M2e protein (stM2e), G2: tM2e VLPs; G3: tM2e/tFliC VLPs; G4: tM2e VLP + tFliC VLPs; G5: tM2e VLP + soluble flagellin; G6: soluble flagellin. (a) Serum IgG; (b) IgG1; (c) IgG2a. Each group has 6 mice. The asterisk (*) indicates a significant difference between G2 and G1, G3 and G1, G4 and G1, and G5 and G1. The “+” indicates a significant difference between G3 and G2, G4 and G2, and G5 and G2.