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Evaluation of protective immunity responses against pneumococcal PhtD and its C-terminal in combination with
Mohammadali Malekan1, Seyed Davar Siadat2,3, Mohammadreza Aghasadeghi4
1Department of Microbiology, Pasteur Institute of Iran, Tehran, Iran.
Insights
Polyhistidine triad protein D (PhtD) and its fragment PhtD-C were tested as pneumococcal vaccine candidates. Combinations with alum and outer-membrane vesicles (OMVs) showed promising immune responses and survival rates in mice.
Area of Science:
- Vaccinology
- Microbiology
- Immunology
Background:
- Streptococcus pneumoniae is a major human bacterial pathogen.
- Existing pneumococcal vaccines have limitations.
- Serotype-independent pneumococcal proteins are desirable vaccine candidates.
Purpose of the Study:
- To evaluate recombinant polyhistidine triad protein D (PhtD) and its C-terminal fragment (PhtD-C) as pneumococcal vaccine candidates.
- To assess the immunogenicity and efficacy of PhtD and PhtD-C when formulated with alum and outer-membrane vesicles (OMVs) as adjuvants.
Main Methods:
- Recombinant PhtD and PhtD-C were prepared.
- Mice were immunized with PhtD/PhtD-C combined with alum or OMVs.
- Humoral immune responses (total IgG, specific IgG, IgG1, IgG2a) were measured.
- Serum bactericidal assays and opsonophagocytosis tests were conducted.
- Survival rates after pneumococcal challenge were assessed.
Main Results:
- Specific IgG and IgG1 levels increased significantly after PhtD/PhtD-C immunization with alum or OMVs.
- Opsonophagocytosis and serum bactericidal assays demonstrated significant killing of Streptococcus pneumoniae.
- Mice immunized with PhtD/PhtD-C plus alum or OMVs showed increased survival rates post-challenge.
Conclusions:
- PhtD and PhtD-C, particularly with alum adjuvant, elicit robust immune responses against Streptococcus pneumoniae.
- The combination of PhtD/PhtD-C with alum demonstrated optimal results compared to OMVs.
- These findings support the potential of PhtD-based vaccines for preventing pneumococcal infections.
Abstract:
Introduction. Streptococcus pneumoniae is a significant bacterial pathogen in humans. Currently, there are two types of pneumococcal vaccines, but there are concerns regarding their application.Aim. Since many pneumococcal proteins are serotype-independent, polyhistidine triad protein D (PhtD) has been selected as a vaccine candidate.Methodology. We prepared recombinant PhtD and its C-terminal fragment (PhtD-C) using alum and outer-membrane vesicles (OMVs) as adjuvants. The combinations were injected intraperitoneally into mice, and then total immunoglobulin G (IgG) and specific IgG, IgG1 and IgG2a were measured. A serum bactericidal assay and opsonophagocytosis were also performed as complementary tests. Meningococcal OMVs were used as an adjuvant.Results. The levels of specific IgG and IgG1 against combinations of PhtD and its C-terminal with OMVs and alum as adjuvants increased at the time of the third mouse immunization on day 35. Forty per cent and 60% of S. pneumoniae ATCC 6303 (serotype 3) as a virulent pneumococcal strain, respectively, were killed in the opsonophagocytosis test and these results could also be observed in the serum bactericidal assay. Mice mmunized iwith PhtD and its C-terminal with OMVs and alum as adjuvants survived after 10 days of pneumococcal challenge.Conclusion. The combination of PhtD and PhtD-C with alum produced optimal results, but the combination of PhtD and PhtD-C with OMVs produced minimal results by comparison. The survival rates were also measured, and these corresponded with the results of the immunological assessments. Our findings showed that mice receiving PhtD and PhtD-C plus OMV and alum had higher survival rates than the mice in the other groups.
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