Abstract:

Objective To investigate the role of FadD9 recombinant protein of Mycobacterium tuberculosis（MTB） for the diagnosis of active tuberculosis. Methods FadD9 recombinant protein was prepared and identified. C57BL/6 mouse model was used to evaluate its immunogenicity. Using Ag85A protein as positive reference antigen,the specific antibody levels of FadD9 recombinant protein in serum samples of 145 active tuberculosis patients（active tuberculosis group）,38 close-contact tuberculosis patients（MTB close-contact group） and 101 healthy subjects（healthy control group） were determined. The FadD9 recombinant protein was incubated with blood samples of 58 tuberculosis patients and 34 non-tuberculosis patients at 37 ℃ for 20-24 h,and then was determined by interferon-gamma release assay（IGRA）. The results were compared with the standard tube in IGRA kit,and the sensitivity and specificity of FadD9 recombinant protein in the diagnosis of tuberculosis were analyzed by receiver operating characteristic（ROC）curve. Results FadD9 recombinant protein could induce a high level of humoral immune response in mice,which was close to that of Ag85A. Serum anti-FadD9 antibody level in active tuberculosis group was higher than those in healthy control group and MTB close-contact group（P<0.000 1）. There was no statistical significance between MTB close-contact group and healthy control group（P>0.05）. There was no statistical significance among the 3 groups in the level of anti-Ag85A antibody（P>0.05）. For the diagnosis of tuberculosis,the area under curve（AUC） of FadD9 recombinant protein was 0.682,the optimal cut-off value was 0.343,and the sensitivity and specificity were 96.8% and 37.5%,respectively. Conclusions FadD9 recombinant protein is potential in the diagnosis of active tuberculosis.

Key words: FadD9 recombinant protein, Interferon-gamma release assay, Mycobacterium tuberculosis