[Immunity characteristics induced by a genetic vaccine expressing Ag85B-ESAT6 fusion protein].
OBJECTIVE
To evaluate the humoral and cell-mediated immune responses induced by a genetic vaccine expressing the Ag85B-ESAT6 fusion protein, and to investigate its protective effect against Mycobacterium tuberculosis (MTB) challenge.


METHODS
Fifty BALB/c mice were randomized into 5 groups and subjected to the following treatments respectively: immunization with normal saline, BCG, pcDNA3, A(Z)-pcDNA3-E(F) and E(Z)-pcDNA3-A(F) for 3 times at 2-week intervals. The stimulation index (SI) of the splenic lymphocytes from the immunized mice was measured by the methyl thiazolyl tetrazolium (MTT) method, and the level of secreted IFN-gamma upon antigen-specific stimulation was detected by ELISA. The immunized mice were intravenously infected with 10(5) colony forming unit (CFU) of MTB H(37)Rv. The numbers of MTB CFU in spleens were determined 4 weeks later.


RESULTS
The specific antibody titers in the sera of mice immunized with plasmid A(Z)-pcDNA3-E(F) and E(Z)-pcDNA3-A(F) were 1:1,000 and 1:1,500 respectively, and the SI was 2.2 and 2.4 respectively, while the SI of the normal saline group and the plasmid pcDNA3 immunized group was only 0.9 and 1.1 respectively. The IFN-gamma concentrations in cultured supernatant of splenic lymphocytes from mice immunized with plasmid A(Z)-pcDNA3-E(F) [(5.48 +/- 0.38) ng/ml] and E(Z)-pcDNA3-A(F) [(5.76 +/- 0.51) ng/ml] were significantly higher than those of the normal saline group [(0.50 +/- 0.25) ng/ml] and the plasmid pcDNA3 immunized group [(1.20 +/- 0.33) ng/ml, P < 0.05], but were not significantly different with that of the BCG immunized group [(5.55 +/- 0.31) ng/ml]. Compared with plasmid pcDNA3 immunized group, the bacterial load (lg, CFU/g) in spleen was 6.08 +/- 0.25 which dramatically reduced in mice immunized with recombinant plasmids, but the protective efficacy of mice immunized with plasmid A(Z)-pcDNA3-E(F) (4.63 +/- 0.11) or E(Z)-pcDNA3-A(F) (4.50 +/- 0.32) was lower than that of the BCG vaccination group (4.09 +/- 0.27).


CONCLUSIONS
The cell-mediated immune response induced by genetic vaccine expressing the Ag85B-ESAT6 fusion protein was similar to that induced by BCG immunization.
Shi
Chang-hong
CH
Department of Microbiology, Faculty of Preclinical Medicine, Fourth Military Medical University, Xi'an 710033, China. changhong@fmmu.edu.cn
Wang
Xiao-wu
XW
Zhu
De-sheng
DS
Xu
Zhi-kai
ZK
Bai
Yin-lan
YL
Xue
Ying
Y
D000217:Acyltransferases / Q000235:genetics / Q000276:immunology*; D000818:Animals; D000942:Antigens, Bacterial / Q000235:genetics / Q000276:immunology*; D001426:Bacterial Proteins / Q000235:genetics / Q000276:immunology*; D007111:Immunity, Cellular; D007371:Interferon-gamma / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D009169:Mycobacterium tuberculosis / Q000276:immunology*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000276:immunology; D014376:Tuberculosis / Q000276:immunology / Q000517:prevention & control; D032581:Tuberculosis Vaccines / Q000276:immunology*; D019444:Vaccines, DNA / Q000276:immunology*
D000942:Antigens, Bacterial; D001426:Bacterial Proteins; C093276:ESAT-6 protein, Mycobacterium tuberculosis; D011993:Recombinant Fusion Proteins; D032581:Tuberculosis Vaccines; D019444:Vaccines, DNA; D007371:Interferon-gamma; D000217:Acyltransferases; C121433:antigen 85B, Mycobacterium tuberculosis