Mice were immunized on weeks 0, 2, 4 and 6 with each protein (E3R4, E12R4 and R4) or E3 peptide formulated with Freunds adjuvant, and sera were collected at week 8. Dilutions of each of HPV L1/L2 pseudovirus, including PsV16, 18, 45, 52, 58, 6, 11 and 5, were coated in ELISA plates and used to determine the cross-reactive antibody titers of the antiserum. The binding titer was determined as the reciprocal of the highest serum dilution with an OD 490 greater than 0.2 and 2-fold higher than control sera at the same dilution. The experiment was repeated twice. The horizontal bars represent the geometric mean antibody titers. The statistically significant differences (using one-way ANOVA and Bonferroni multiple comparison test) were indicated by: ***, P<0.001.