Serodiagnostic value of 23 Mycobacterium tuberculosis proteins and a novel protein combination

To identify novel serological targets for improving the serodiagnosis of Mycobacterium tuberculosis (MTB) infection, a total of 23 MTB proteins were clone into the Escherichia coli, and the serodiagnostic values of these proteins and a novel combined protein were evaluated. By a two-step selection process, 21 proteins having cross-reaction with TB antibody were identified. In these proteins, the most frequently recognized antigens were Rv0934 and Rv2185c, which were found in 45.6% of TB patients, while the specificity of Rv0934 was only 93.3% which was lower than that of Rv2185c. Subsequently, Rv2031c, Rv2185c, Rv2537c, Rv2785c and Rv3354 were combined equally and the combined protein had 100% specificity and relatively high sensitivity. The sensitivity of the combined protein was 76% which was close to that of purified protein derivative (PPD) test; the specificity of combined protein was 96 similar to 98%, which was higher than that of PPD test (76 similar to 92%) in the detection of 150 TB patients and 150 healthy subjects. In addition, the specificity of combined protein was significantly higher than that of PPD in the detection of TB antibody in subjects' negative, positive and strong positive for PPD skin test, but the positive rates of the same protein were not significantly different. Three months after bacillus calmette-guerin (BCG) vaccination, the positive rate of combined protein was lower than that of PPD testing. The combination of proteins with high specificity is an effective method to improve the sensitivity of TB serological diagnosis.