Generation of Mycobacterium tuberculosis-specific recombinant antigens and evaluation of the clinical value of antibody detection for serological diagnosis of pulmonary tuberculosis

Rapid diagnosis of pulmonary tuberculosis (TB) infection is critical inclinical practice. To establish an effective serological diagnostic technique,we generated the several Mycobacterium tuberculosis (MTB)-specific immunogenicantigens and evaluated the clinical benefits of detection of immunoglobulin G(IgG) and IgM antibodies raised against these target antigens for the diagnosisof patients with active TB. The genes encoding the MTB-specific antigens 6-kDaearly secretory antigenic target of MTB (ESAT-6), 10-kDa culture filtrate protein(CFP-10), ESX-1 substrate protein C (ESPC), 14KD/38KD and ESAT-6/14KD/38KD, wereamplified from the MTB genome by PCR. Prokaryotic vectors were constructed forthe expression of the individual MTB antigens. The target recombinant proteinwas expressed in Escherichia coli (BL21/DE3) and purified using immobilized metalaffinity chromatography (IMAC). An ELISA based immunoassay was set up using thesetarget antigens for the diagnosis of active TB. The detection samples included98 patients with active TB and 102 healthy control volunteers. The cutoff OD valuefor IgG and IgM antibodies was selected according to a receiver operating characteristic(ROC) analysis. The sensitivity, specificity and positive likelihood ratio werealso determined. We successfully cloned, expressed and purified the ESAT-6, CFP-10,ESPC, 14KD/38KD and ESAT‑6/14KD/38KD recombinant antigens of MTB. The mean levelsof IgG antibodies were significantly higher in patients with pulmonary TB comparedwith control groups. The target MTB-specific antigens can distinguish a TB infectionfrom a non-TB infection, showing significant difference in statistics (P<0.001).The sensitivity of the IgG test ranged from 69.4% (ESAT-6) to 77.6% (ESAT-6/14KD/38KD)in the active TB patients; the specificity of assays varied from 78.4% (CFP-10)to 90.2% (14KD+38KD) in the healthy control groups. The IgM antibody test cannot distinguish a TB infection from a non-TB healthy control. In conclusion, clinicaluse of the ESAT-6, CFP-10, ESPC, 14KD/38KD and ESAT-6/14KD/38KD antigens basedon serodiagnostic IgG assay is of significant value for the rapid diagnosis ofTB and for the discrimination between active TB patients and healthy controls.