Figure 3: IgG, IgG1, IgG2a and G2b antibody responses. Groups of mice were intramuscularly immunized with HA-NA-M1 Vlp at 3 week intervals, and blood samples were collected at various time points (weeks 1 and 4) after the final immunization. The sera from individual mice were used, and the average antibody response from each group was determined. Immulon microtiter plates were coated with inactivated influenza H5N1 virus, and mouse antibodies were detected with a horseradish peroxidase-conjugated antibody. The ELISA endpoint titers are expressed as the highest dilutions that yielded optical densities greater than the mean optical density plus 3 standard deviations of similarly diluted negative control sera. (A) IgG antibody reactive to the whole inactivated influenza H5N1 virus. (B) IgG1 antibody reactive to the inactivated influenza H5N1 virus. (C) IgG2a and IgG2b isotype antibodies reactive to the inactivated influenza H5N1 virus.