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Volume 47, Number 1, February 2014

Evaluation of protective efficacy conferred by a recombinant Mycobacterium bovis BCG expressing a fusion protein of Ag85A-ESAT-6 


Yi-Hao Deng, Hong-Yun He, Ben-Si Zhang


Received: October 9, 2012    Revised: November 1, 2012    Accepted: November 27, 2012   

 

Corresponding author:

Corresponding author. Yi-Hao Deng, Department of Human Anatomy, College of Preclinical Medicine, Dali University, Dali 671000, China. 



 

Background and purpose: 

We previously constructed a recombinant bacille Calmette-Guérin (rBCG-AE) strain that could express a fused Ag85A-ESAT-6 protein. That study suggested that the rBCG-AE strain was able to induce a higher titer of antibody and elicit a more long-lived and stronger Th1-type cellular immune responses than the parental BCG strain, the rBCG-A strain (i.e., expressing Ag85A), or the rBCG-E strain (i.e., expressing ESAT-6). 



 

Methods:

In the current study, we further investigated the strain's protective efficacy against Mycobacterium tuberculosis H37Rv infection in BALB/c mice through evaluating organ bacterial loads, lung histopathology, lung immunohistochemistry, and net weight gain or loss by using conventional BCG, rBCG-A, and rBCG-E as the controls. 



 

Results:

From the 3rd to 9th weeks after the challenge infection, the bacterial counts were significantly lower in tissues (e.g., spleen and lung tissues) in the mice immunized with rBCG-AE than in the control group, but were higher than the counts in the BCG group. The pathological damage in the lung tissues of the rBCG-AE group gradually improved from the 6th to 9th weeks after being infected with M. tuberculosis H37Rv, but the score of pathological changes in the rBCG-AE group was obviously higher than the score in the BCG group. There was no difference in the percentage of IFN-γ and iNOS positive cells in the lung tissues of the rBCG-AE and BCG groups. 



 

Conclusion:

The results suggest that rBCG-AE can not promote protective efficacy against M. tuberculosis H37Rv infection, compared to the BCG vaccine. 



 

Key words:

Ag85A, ESAT-6, Protective efficacy, Recombinant Mycobacterium bovis bacillus Calmette-Guérin (rBCG)