Figure 4: Comparison of antibody responses induced by immunization with the HIV Env-DNA and SHIV 89.6 VLP vaccines in different combinations. Mice were immunized by different vaccine preparations as described in Figure 2. Sera were collected at 2 weeks after the second immunization and analyzed for antibodies specific for HIV 89.6 gp120 by ELISA. The levels of antibody responses are expressed as the quantity (ng) of antibodies binding to HIV 89.6 gp120 in 1 mL sera from each mouse. (a) Total IgG antibodies against gp120. (b) IgG1 subtype antibodies against gp120. (c) IgG2a subtype antibodies against gp120. Error bars indicate the standard deviations for each immunization group. * indicates the groups with significantly higher levels of antibody responses than Group 2 that received the HIV Env-DNA vaccine only ().