The immunogenicity of Streptococcus pneumoniae type 6 alginate conjugate and diphtheria toxoid in BALB/C mouse model

Streptococcus pneumoniae is one of the infectious pathogenic bacteria in humans. It is considered the cause of pneumonia. It is colonized in the respiratory system of susceptible people such as immunocompromised and AIDS patients and causes chronic and treatment-resistant infections. The aim of the present study is to prepare a vaccine with a conjugated antigen combination and with the ability to induce antibodies and memory immunity experimentally against Streptococcus pneumoniae type 6 in the BALB/C mouse model.

Streptococcus pneumoniae type 6 strain was cultured in Mueller Hinton agar and at the end of the logarithmic phase of growth, it was extracted and concentrated by normal NaOH. The polysaccharide capsule was attached to diphtheria toxoid using (ADH) adipic acid dihydrazide and EDAC. After chromatography, prepare by mixing the polysaccharide capsule conjugate (CPS-DT) with diphtheria toxoid and alginate solution of the desired antigen. The prepared antigens were injected into 4 groups of 15 mice intraperitoneally with two-week intervals. In serum samples, antibody responses were measured by ELISA method.

According to the results of the ELISA test, total IgG titer increased from 315 to 1680. Also, IgM and IgA antibody titers increased from 90 to 610 and 18 to 28, respectively. The serum antibodies of the group vaccinated with diphtheria toxoid alginate (ALG-DT) increased statistically significantly after each injection. So that the titer of total IgG, IgM and IgA produced against alginate in the groups vaccinated with conjugate showed a significant increase compared to specific alginate in three injections.

The results obtained for the above antibodies were CPS-DT > CPS > DT, and the antibody titer against DT-CPS in IgG was higher than other antibodies, which shows that microparticles Alginate polysaccharide capsule of Streptococcus pneumoniae in conjugated form with diphtheria toxoid increases antibodies. The increase in antibody titer in the groups vaccinated with alginate conjugate indicates the activation of T cells and the creation of immune memory. Therefore, the conjugate of alginate and diphtheria toxoid can be a suitable candidate for preparing a vaccine. The results of the antibody titer obtained against Micro CPS-DT in the groups were IgG>IgM>IgA.