Objective: To explore the roles of BCG-depleted immunodominant antigens derived from M. tuberculosis in serological tests for tuberculosis (TB).
Methods: Four different combinations of current mainstream antigens used for serological diagnosis of TB were selected: Reagent A [Mycobacterium TB immunoglobulin G (IgG) antibody assay kit]; Reagent B (Mycobacterium TB detection kit); Reagent C (M. tuberculosis-specific antibody detection kit); Reagent D [Active TB antibody detection enzyme-linked immunosorbent assay (ELISA) system]. Immunological methods of Western blot, colloidal gold and ELISA were developed to test the antibodies in 109 patients with active tuberculosis (TB) and 97 healthy populations. They were divided into purified protein derivative of tuberculin (PPD) positive and negative groups. Bayesian statistical analysis was used to analyze the influences of variable combinations of different antigens on the detection accuracy of TB.
Results: For Reagent A, B, C, D, the detection rates of IgG antibodies in the patients with active TB were 80.0%, 66.7%, 80.7%, 56.0% versus 23.9%, 8.9%, 6.6% and 1.0% respectively in healthy populations. The TB antibody detection rates in four TB patient populations were all higher than that in healthy populations (χ(2) = 47.53, 51.59, 90.48, 69.68, all P < 0.01). The TB antibody detection rates of Reagents A and B increased with the intensity of positive reaction to PPD in healthy populations (χ(2) = 2.124, 2.220, all P < 0.05) while those of Reagents C, D in healthy populations were irrelevant to PPD reaction. (χ(2) = 0.122, 0.479, all P > 0.05). Reagent D has the highest accuracy. The immunoglobulin M (IgM) antibody detection rate of Reagent D was only 2.1% in the patients with active TB.
Conclusions: The detecting sensitivity of TB IgG antibodies is associated with antigen selection. And it is also positively correlated with the number of combined antigens. High-sensitivity detection is often accompanied by a loss of specificity. With the BCG-depleted antigens derived from M. tuberculosis, the specificity of serological test for TB may significantly improve.