IgG, IgM and IgA antibodies against the novel polyprotein in active tuberculosis

Abstract

Background: The present study was aimed to evaluate whether IgG, IgM and IgA antibodies levels detected against a novel Mycobacterium tuberculosis polyprotein 38 F-64 F (with 38 F being the abbreviation for 38kD-ESAT6-CFP10 and 64 F for Mtb8.4-MPT64-TB16.3-Mtb8) are suitable for diagnosing active tuberculosis, and for monitoring the efficacy of chemotherapy on TB patients.

Methods: In this study, a total of 371 active TB patients without treatment were selected and categorized into S+/C+group (n=143), S-/C+group (n=106) or S-/C- group (n=122). A series of serum samples were collected from 82 active TB patients who had undergone anti-TB chemotherapy for 0-6 months at one month interval. Humoral responses (IgG, IgM and IgA) were determined for the novel Mycobacterium tuberculosis polyprotein using indirect ELISA methods in all of serum samples.

Results: For S+/C+, S-/C+and S-/C- active tuberculosis patients before anti-TB chemotherapy, the sensitivities of tests based on IgG were 65.7%, 46.2% and 52.5% respectively; the sensitivities based on IgM were 21.7%, 24.5% and 18.9%; and the sensitivities based on IgA were 25.2%, 17.9% and 23.8%. By combination of three isotypes, for all active tuberculosis patients, the test sensitivity increased to 70.4% with the specificity being 91.5%. After anti-TB chemotherapy, there were no significant differences between groups with different courses of anti-TB chemotherapy.

Conclusions: The novel Mycobacterium tuberculosis polyprotein 38 F-64 F represents potential antigen suitable for measuring IgG, IgM and IgA antibodies. However, the serodiagnostic test based on the 38 F-64 F polyprotein appears unsuitable for monitoring the efficacy of chemotherapy.

Figure 1

The serodiagnostic performance of the novel 38 F-64 F indirect ELISA assay in active TB patients at their first visit to the outpatient clinic without treatment. Levels of serum IgG, IgM and IgA against the novel 38 F-64 F polyprotein in S+/C+, S-/C + and S-/C- TB patients (A1, B1 and C1) and in total TB patient (A2, B2 and C2) were presented as scatter grams respectively. Each bar represents the mean OD value. The ROC curves of the novel 38 F-64 F indirect ELISA assay based on measuring IgG (A3), IgM (B3) and IgA (C3) were shown and the areas under the curve (AUC) for IgG, IgM and IgA were 0.81, 0.68 and 0.62 respectively.

Figure 2

The positive rates of sputum smear/culture with or without integration of serodiagnostic test. The integration of serodiagnostic test with sputum smear or sputum culture increased the positive rates from 38.54% to 79.78% or from 67.12% to 90.03%, respectively.

Figure 3

Levels of serum IgG (A), IgM (B) and IgA (C) against the novel 38 F-64 F polyprotein in active TB patients with different course of chemotherapy. 0 M = patients at their first visit to the outpatient clinic, 1 M-6 M = patients received anti-TB chemotherapy for 1–6 months. The mean antibody level and the standard deviation of each group were shown. There was no significant difference between the patients at their first visit to the outpatient clinic without anti-TB chemotherapy and those receiving anti-TB chemotherapy for 1–6 months. All of the p values between each of two groups were greater than 0.05.

Figure 4

Changes in IgG (A1, A2 and A3), IgM (B1, B2 and B3) and IgA (C1, C2 and C3) antibody levels against the novel 38 F-64 F polyprotein after initiation of anti-TB chemotherapy. After initiation of anti-TB chemotherapy, patients showed three different IgG, IgM and IgA antibody responses patterns, i.e., decrease, increase and maintaining at stable level.