IgG antibody responses against HIV Env after immunization with SHIV VLPs. A) HIV Env-specific total IgG antibody. Sera were collected before immunization and 2 weeks after every immunization. Results are expressed as the arithmetic mean ± SD of 100-fold diluted serum samples from 6 mice per group. Error bars indicate standard deviation (SD). The ANOVA test from the PC-SAS program showed significant differences between 3G-dV2−1G and WT (**: P < 0.001) and between WT and 3G (*: P <0.05). B) V3 loop peptide specific total IgG antibody. After the 2nd boost immunization, total IgG antibody binding to the V3 loop peptide (100 fold-diluted sera) was determined. Gag: HIV Env-negative SIV Gag VLPs, WT: SHIV VLPs with wild type HIV Env 89.6, dV1V2: SHIV VLPs with dV1V2 mutant HIV Env, 3G: SHIV VLPs with 3G mutant HIV Env, 3G-dV2−1G: SHIV VLPs with 3G-dV2−1G mutant HIV Env. (*: P < 0.05, **: P < 0.001).