Objective To understand whether the rat model can be used in the immunogenicity study for Streptococcus pneumoniae polysaccharide conjugate vaccine by analysing the correlation between the concentration of serotype-specific IgG binding antibody and the titer of the functional antibody in the serum of rats immunized with Streptococcus pneumoniae conjugate vaccine.

Methods Five different doses of 24-valent Streptococcus pneumoniae polysaccharide conjugate vaccine (PCV24) were intramusculally injected to Sprague-Dawley rats according to three immunization schedules respectively on day 0, 0/14 and 0/14/28, and serum samples of the rats were collected at different time points. the standardized quantitative enzyme-linked immunosorbent assay recommended by World Health Organization was used to detect the concentrations of serotype-specific IgG binding antibody, and multiplexed opsonophagocytosis assay was used to detect the titers of functional antibody. The correlation between the concentration of serotype-specific IgG binding antibody and the titer of functional antibody was analyzed by using statistical software Minitab 17.

Results After immunization with different doses of PCV24 based on three different immunization schedules, good consistency in the changes was observed between the concentration of serotype-specific IgG binding antibody and the titer of the functional antibody in rat serum. The concentration of serotype-specific IgG binding antibody and the titer of the functional antibody in rat serum had a good correlation (r≥0.600, P < 0.05) except for serotype 10A in 24 serotypes.

Conclusion After immunization with PCV24, the concentration of serotype-specific IgG binding antibody and the titer of the functional antibody in rat serum could reflect the dynamic change of antibody level with good consistency. This study showed that the rat model can be used to evaluate the immunogenicity of Streptococcus pneumoniae polysaccharide conjugate vaccine.