ELISA results of total (kappa), total IgG, and IgM antibody titers of pooled day 21 sera from mice immunized with CRM197 conjugates 1a and 2a, using HSA conjugates 1b and 2b as the capture antigens and AP-linked goat anti-mouse kappa, IgG, and IgM antibodies as the secondary antibodies to detect total, total IgG, and IgM antibodies specific to the monomer and dimer epitopes of the repeating unit of type Ia CPS, respectively. Antibody titer was defined as the serum dilution number at which the OD450 value reached 0.10 and was shown as the mean value of three parallel experiments for each serum. The error bar represented the standard error of mean (SEM). *p < 0.05 between two groups.