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Immunobiological properties of a 30 kDa secretory protein of Mycobacterium tuberculosis H37Ra
R K Sinha1, I Verma, G K Khuller
1Department of Biochemistry, Postgraduate Institute of Medical Education and Research, Chandigarh, India.
Abstract:
Six different secretory proteins of molecular weights (15, 26, 30, 41, 55 and 70 kDa) were isolated from 8-day-old culture filtrate of Mycobacterium tuberculosis H37Ra using different column chromatography techniques. These proteins were further examined for their ability to induce cell mediated (T-cell proliferation assay) and humoral immune response (ELISA) in mice immunized with total culture filtrate proteins. Out of six proteins, three proteins showed good reactivity. However, the activity was at a maximum with 30 kDa antigen. The immune response induced by 30 kDa antigen emulsified in Freund's incomplete adjuvant (FIA) was investigated and was found to be dose dependent. The T-cell response induced by this protein was skewed towards T-helper (Th1) cells as determined by the pronounced secretion of interleukin-2 (IL-2) and gamma-interferon (IFN-gamma). The protective activity of the 30 kDa protein was also evaluated and compared with reference to Bacillus Calmette Guerin (BCG) vaccine in the mice challenged with virulent M. tuberculosis H37Rv. The degree of protection afforded by the 30 kDa antigen on the basis of mortality and the significant decrease in c.f.u.'s recovered from different organs (lung, liver, spleen) after 30 days of challenge with LD50 of M. tuberculosis H37Rv was significantly higher in comparison to BCG vaccinated animals. However, the degree of immunity induced by this antigen decreased with time (when challenged 8 and 12 weeks post-immunization) but it was still comparable with BCG. These findings suggest that 30 kDa secretory protein of M. tuberculosis is the key immunoprotective antigen and may be a suitable candidate for the development of an alternative subunit vaccine against tuberculosis.
Insights
A 30 kDa secretory protein from Mycobacterium tuberculosis demonstrated significant protective immunity in mice, outperforming BCG in early protection against tuberculosis. This key antigen shows promise for developing a new subunit vaccine.
Area of Science:
- Immunology
- Microbiology
- Vaccinology
Background:
- Mycobacterium tuberculosis (M. tuberculosis) causes tuberculosis, a significant global health concern.
- Current vaccines like Bacillus Calmette Guerin (BCG) have limitations in efficacy and duration.
- Identifying novel immunodominant and protective antigens is crucial for developing improved tuberculosis vaccines.
Purpose of the Study:
- To isolate and characterize secretory proteins from M. tuberculosis H37Ra.
- To evaluate the immunogenicity and protective efficacy of these proteins in a murine model.
- To identify key antigens for potential subunit vaccine development against tuberculosis.
Main Methods:
- Isolation of six secretory proteins (15-70 kDa) from M. tuberculosis culture filtrate using chromatography.
- Assessment of cell-mediated (T-cell proliferation) and humoral (ELISA) immune responses in immunized mice.
- Evaluation of protective efficacy against virulent M. tuberculosis H37Rv challenge, comparing a 30 kDa antigen with BCG vaccine.
Main Results:
- Three of the six isolated proteins showed significant immune reactivity, with a 30 kDa antigen exhibiting maximum activity.
- The 30 kDa antigen induced a dose-dependent T-helper (Th1) cell response, evidenced by increased interleukin-2 and gamma-interferon secretion.
- Mice vaccinated with the 30 kDa antigen showed significantly higher protection (reduced mortality and bacterial load) compared to BCG early after challenge, though protection waned over time but remained comparable to BCG.
Conclusions:
- The 30 kDa secretory protein of M. tuberculosis is identified as a key immunoprotective antigen.
- This antigen demonstrates potential as a candidate for a novel subunit vaccine against tuberculosis.
- Further research into this 30 kDa antigen could lead to more effective tuberculosis vaccines.