Restoration of mycobacterial antigen-induced proliferation and interferon-γ responses in peripheral blood mononuclear cells of tuberculosis patients upon effective chemotherapy

Abstract

Peripheral blood mononuclear cells (PBMC) were obtained from culture-proven tuberculosis (TB) patients before and after 2 and 6 months of chemotherapy with a multi-drug regimen. PBMC were tested for cellular responses in antigen-induced proliferation and interferon-gamma (IFN-gamma) assays in response to complex mycobacterial antigens (whole cell Mycobacterium bovis BCG and M. tuberculosis, cell walls and short-term culture filtrate [ST-CF] of M. tuberculosis), fractionated ST-CF antigens (fractions F1-F10) and ESAT-6. The responses in TB patients before anti-TB treatment were low (median stimulation index (SI)=1-7, median delta IFN-gamma=0-12 U ml(-1), and percent responders=13-67%) to all the antigenic preparations. Following the administration of anti-TB chemotherapy for 2 months, there were significant (P<0.05) improvements in the cellular responses (median SI=9-76, median delta IFN-gamma=3-70 U ml(-1), and percent responders=33-100%) to most of the antigenic preparations tested. However, concanavalin A-induced proliferation responses of PBMC from the same patients before and after 2 months of chemotherapy were high and comparable (median SI=101 and 114, respectively, P>0.05, 100% responders). A further increase in IFN-gamma responses (median delta IFN-gamma=14-250 U ml(-1) and percent responders=43-100%) to mycobacterial antigens was observed in patients receiving chemotherapy for 6 months. Among the ST-CF fractions, F1 and F2 containing low molecular mass proteins resulted in the highest responses, whereas ESAT-6 showed responses comparable to these fractions only in a minority of the patients. HLA-DR typing of these patients showed heterogeneity in the expression of molecules encoded by HLA-DRB genes. These results show that effective chemotherapy restores cellular responses of TB patients to a large number of M. tuberculosis antigens, which could be useful in monitoring the efficacy of anti-TB treatment.

The effect of antituberculosis treatment on interferon-γ release assay results

“…A previous study [7] showed that after 2 months of treatment T-cells proliferation response was restored to the same level as 6 months after, without a linear relationship: however, this study was based on only 15 patients. Our study performed on a significantly larger number of individuals and the method of data collection (random assignation to the month of assay) and statistical analysis (random effect model) allowed a more accurate estimation of changes over time.…”

“…According to this hypothesis, other studies have shown that CD4+ T cells responsive to a large array of MTB epitopes are compartmentalised at the site of the disease, appearing in the peripheral blood after effective chemotherapy which reverses the state of relative hypoanergy usually observed in these patients [24,25]. Other contributing factors in the restoration of cellular response could be the shift in cytokine production by mononuclear blood cells [7,10,26].…”

“…Another limitation of our study was the lack of T-cell measurement: however, only a minority of studies relied on cellular assessment, showing a firm correlation between mononuclear blood cell count and INF-γ concentration [7].…”

“…Some studies have shown that interferon-γ response to ESAT-6 decreased more or less consistently during treatment in patients with active tuberculosis [2][3][4], while others have suggested that treatment could result either in increases [5][6][7][8][9] or in insignificant changes [10][11][12][13][14], with both T-Spot and Quanti-FERON©-TB assays used for the study of INF-γ release.…”

Diagnostic and Vaccine Potentials of ESAT-6 Family Proteins encoded by M. tuberculosis genomic regions absent in M. bovis BCG

“…Although, these genes have only 10-35% homology to esat6, they are approximately of the same size (ca 100 aa) and share a similar genomic organization. Because of the immunodominance of ESAT-6 (ESXA) [12][13][14][15][16][17][18], other ESAT-6 family proteins have also received considerable attention for immunological evaluation [19][20][21]. As given below, the genes of some of these proteins are present in M. tuberculosis-specific genomic regions, and therefore they have been considered useful in the diagnostic and vaccine applications [2][3][4][5][6].…”