FIG. 2.

Comparison of the PPS14 antibody response to PPS14-C3d with that induced by a conjugate of PPS14 and OVA, a T-dependent protein carrier. BALB/c mice (5 animals per group) were immunized subcutaneously on day 0 with 1 μg of PPS14 either as unmodified PPS14 (left graph) or as PPS14 conjugated to C3d (middle graph) or OVA (right graph). For mice receiving PPS14 conjugates (right two graphs), one group of mice received PPS14 conjugate on both day 0 and day 70 (closed circles) and another group of mice received PPS14 conjugate on day 0 followed by unmodified PPS14 on day 70 (open triangles). The mice were bled 10, 25, 45, and 63 days after the primary immunization and 10, 27, and 42 days after the secondary immunization. Serum anti-PPS14 immunoglobulin concentrations were determined by RABA. Data points represent the GMC for each group of mice. The error bars represent the 95% CI of the geometric mean for each group of sera. The arrowheads indicate the day of secondary immunization. Serum anti-PPS14 concentrations were significantly greater for mice receiving two injections of either conjugate preparation than for those receiving two injections of PPS14 (P ≤ 0.02 at all time points). They were also significantly increased for mice reimmunized with unmodified PPS14 after primary immunization with PPS14-C3d or PPS14-OVA (P ≤ 0.05 at all time points). Reimmunization with unmodified PPS14 after primary immunization with either conjugate did not cause a significant increase in serum anti-PPS14 compared with values 7 days prior to secondary immunization (P ≥ 0.1 at all time points after secondary immunization).