Abstract: Objective  To evaluate the diagnostic value for active tuberculosis (TB) by detecting antibodies secreted from Mycobacterium tuberculosis-specific plasma cells in peripheral blood. Methods  The study period was from April 2013 to July 2013, and the study sample included 3 groups of subjects: 104 patients with active TB; 26 cases with latent TB infection (LTBI); and 33 healthy volunteers as a control group. The active TB patients were enrolled from the Outpatient Department of Shenzhen 3^rd People’s Hospital while the LTBI and healthy volunteers were enrolled from Health Examination Clinic of Shenzhen 3^rd People’s Hospital. Peripheral blood mononuclear cells(PBMCs) from all study subjects were isolated and cultured in vitro for 4 days, and then the supernatants of each group were collected. Mycobacterium tuberculosis-specific antibodies in lymphocyte supernatant were tested by ELISA and Western blot and the differences among the three groups were analyzed. GraphPad Prism 5.0 was used for data analysis. The diagnostic value of ELISA was evaluated by receiver operating characteristic (ROC) curve. The Kruskal-Wallis test was used for comparison among multi-groups and the Dunn multiple comparison test was used for comparison between two groups. The difference was considered to be statistically significance if the P-value was <0.05. Results  The A_450nm value of Mycobacterium tuberculosis-specific antibodies measured by ELISA was higher in the group of patients with active TB (0.593±0.206) than those in the group of cases with LTBI (0.342±0.152) and in the group of healthy persons (0.246±0.121) respectively, the differences had statistically significance (H=77.27, P<0.001). Areas under the curve (AUC) of Mycobacterium tuberculosis-specific antibodies which used for distinguish active TB and LTBI, active TB and healthy person were 0.857 and 0.944 respectively; when the value of 0.42 was used as a diagnostic threshold, the sensitivity and specificity for districting active TB and LTBI were 77.9% (81/104) and 80.8%(21/26) respectively, and sensitivity and specificity for distinguishing active TB and health people were 77.9% (81/104) and 93.9% (31/33) respectively. The sensitivity, specificity, and accuracy of Western blot test in detecting active TB patients and healthy person were respectively 79.2% (61/77), 100.0% (11/11) and 81.8% (72/88) (χ²=24.8, P<0.001). Conclusion  The specificity of both ELISA and Western blot tests are high in detecting Mycobacterium tuberculosis-specific antibodies secreted from peripheral blood plasma cells, so they can be used for diagnosis of active TB as new methods in clinical laboratory.

Key words: Tuberculosis/diagnosis, Mycobacterium tuberculosis, Antibodies, bacterial, Leukocytes, mononuclear