Comparative evaluation of immunogenicity of pneumococcal conjugate vaccine in two strains of BALB/c and DBA/2 mice : Preclinical study

Streptococcus pneumoniae is easily transmitted from humans to animals and causes pneumonia, especially in horses. Extensive human vaccination prevents the transmission of the disease to the horse host. The immunogenicity of a vaccine is evaluated by various methods. The aim of this study was to design a test to evaluate the immunogenicity of pneumococcal conjugate vaccine as part of pre-clinical studies of vaccine production. After culturing Streptococcus pneumoniae serotype 19F in blood agar medium, the obtained colonies were labeled using fluorescence dye. On the other hand, the serum of BALB/c and DBA/2 mice immunized with Pneumococcal Conjugate Vaccine was collected to determine antibodies with phagocytosis properties against Streptococcus pneumoniae. After proximity of serum dilutions with labeled bacteria, the ability of bacteria to phagocytosis by serum opsonins (opsonophagocytosis) was read by adding mouse macrophage cells by flow cytometry. In both strains, the percentage of cells in the serum that phagocytosed the bacterium decreased with decreasing serum dilution. Opsonophagocytic titers were reported 128 in BALB/c mice and 64 in DBA/2 mice. On the other hand, flow cytometry results were significantly different from the results of manual colony count test (r = 0.89, p≤0.001). According to the results of the present study, the BALB/c strain of mice was a better host to determine the efficacy of the vaccine. Also, using flow cytometry method has more advantages than manual assay method. As a result, the data of this study bring us one step closer to producing an effective vaccine.