Monitoring the efficacy of antituberculosis therapy is crucial both for the individual patient and for better control of the spread of tuberculosis. We studied 18 patients with microbiologically confirmed tuberculosis, both at the time of diagnosis and 3 months after they started therapy, using an in vitro assay that detects T cell-mediated interferon- gamma response to selected peptides of Mycobacterium tuberculosis-specific early secretory antigenic target 6 (ESAT-6) protein. All patients had positive results at diagnosis; however, 3 months later, the response to ESAT-6 peptides was still detectable only in the 5 patients with microbiological isolation and/or absence of clinical improvement after treatment. On the basis of these data, we conclude that our assay is a useful tool in monitoring the efficacy of antituberculosis therapy.
Hypersensitivity to beryllium (Be) is found in 1–16% of exposed workers undergoing immunological screening for beryllium disease using the beryllium lymphocyte proliferation test (BeLPT). However, only ∼50% of BeLPT-positive workers present with lung granulomas (i.e.berylliosis). As berylliosis is associated with the human leukocyte antigen (HLA)-DP supratypic marker DPGlu69, the authors asked whether this marker is differentially associated with disease presentation.A population of 639 workers from a beryllium factory undergoing BeLPT screening was evaluated in a nested case-control study for the prevalence of HLA-DPGlu69, the HLA-DPB1, HLA-DQ and HLA-DR alleles and of the biallelic tumour necrosis factor (TNF)-;α polymorphism TNF-;α-;308 in 23 individuals presenting as “sensitized” (i.e.BeLPT-positive without lung granulomas) and in 22 presenting as “diseased” (i.e.BeLPT-positive with granulomas in the lung biopsy).The HLA-DPGlu69 marker was associated with “disease” (odds ratio (OR) 3.7, p=0.016, 95% confidence interval (CI) 1.4–10.0), whilst the high TNF-;α production-related TNF-;α-;308*2 marker was associated with both a positive BeLPT (OR 7.8, corrected p<0.0001, 95% CI 3.2–19.1) with no difference between “sensitization” and “disease”. Furthermore, the HLA-DRArg74 marker was associated with “sensitization” without disease (OR 3.96, p=0.005, 95% CI 1.5–10.1).The data indicate that tumour necrosis factor-;α, human leukocyte antigen-DR and human leukocyte antigen-DP markers play different roles in beryllium sensitization and granuloma formation in beryllium-exposed workers.
The information available on the specific function of HLA-DP and the structure-function relationships is very limited. Here, single amino acid substitutions of HLA-DPB1*02012 have been used to analyze the role of polymorphic residues of the DPbeta1 domain on DP-mediated T cell allorecognition and peptide binding. Using a panel of specific anti-HLA-DP mAb, we identified the HLA-DP residues involved in the recognition by these mAb, with a crucial role for DPbeta56 for most of the mAb assayed. Individual substitutions at residues 9, 11, 35, 55, 56 and 69 completely abrogated T cell recognition mediated by two different HLA-DPw2-allospecific T cell clones (8.3 and 8.9). Interestingly single changes at positions 9, 11, 35 and 55 of HLA-DPbeta also altered the binding of peptides AAII(12-27) and IIP(53-65), natural ligands of the HLA-DPB1*02012 molecule. Individual changes at residues located in pocket 1 (84, 85, 86 and 87 from HLA-DPbeta) led to a partial reduction in cytotoxic T lymphocyte-mediated lysis and also partially affected peptide binding. However, the simultaneous substitution of these positions completely abolished both T cell allorecognition and peptide binding, suggesting a major role for polymorphisms at pocket 1 in HLA-DP function. Molecular modeling, used to predict changes induced by amino acid substitutions, supported the functional data. Taken together, these results strongly suggest that polymorphic residues 84, 85, 86 and 87 at pocket 1, residues 9, 35 and 55 at pocket 9, and residues 11 and 69 at pockets 6 and 4 respectively play a key role in HLA-DP function, probably by modifying the way the peptide is bound within the groove of HLA-DP2 and determining changes in the conformation of the MHC-peptide complex recognized by the TCR.
We recently set up a gamma interferon (IFN-␥) enzyme-linked immunospot assay (ELISPOT), using selected early secreted antigenic target 6 (ESAT-6) peptides, that appears specific for active tuberculosis (A-TB). However, ELISPOT is difficult to automate. Thus, the objective of this study was to determine if the same selected peptides may be used in a technique more suitable for routine work in clinical laboratories, such as whole-blood enzyme-linked immunosorbent assay (WBE). For this purpose, 27 patients with A-TB and 41 control patients were enrolled. Our WBE, using the already described selected peptides from ESAT-6 plus three new ones from culture filtrate protein 10, was performed, and data were compared with those obtained by ELISPOT. Using our selected peptides, IFN-␥ production, evaluated by both WBE and ELISPOT, was significantly higher in patients with A-TB than in controls (P < 0.0001). Statistical analysis showed a good correlation between the results obtained by WBE and ELISPOT (r ؍ 0.80, P < 0.001). To substantiate our data, we compared our WBE results with those obtained by QuantiFERON-TB Gold, a whole-blood assay based on region of difference 1 (RD1) overlapping peptides approved for TB infection diagnosis. We observed a slightly higher sensitivity with QuantiFERON-TB Gold than with our WBE (89% versus 81%); however, our test provided a better specificity result (90% versus 68%). In conclusion, results obtained by WBE based on selected RD1 peptides significantly correlate with those generated by ELISPOT. Moreover, our assay appears more specific for A-TB diagnosis than QuantiFERON-TB Gold, and thus it may represent a complementary tool for A-TB diagnosis for routine use in clinical laboratories.
BackgroundThe clinical application of IFN-γ release assays (IGRAs) has recently improved the diagnosis of latent tuberculosis infection. In a multicenter study of the Tuberculosis Network European Trialsgroup (TBNET) we aimed to ascertain in routine clinical practice the accuracy of a novel assay using selected peptides encoded in the mycobacterial genomic region of difference (RD) 1 for the diagnosis of active tuberculosis in comparison with tuberculin skin test (TST), QuantiFERON-TB GOLD In-Tube (Cellestis Ltd., Carnegie, Australia) and T-SPOT.TB (Oxfordimmunotec, Abingdon, UK).Principal Findings425 individuals from 6 different European centres were prospectively enrolled. We found that sensitivity of the novel test, TST, QuantiFERON-TB GOLD In-Tube and T-SPOT.TB was respectively 73.1%, 85.3%, 78.1%, and 85.2%; specificity was respectively 70.6%, 48.0%, 61.9% and 44.3%; positive likelihood ratios were respectively 2.48, 1.64, 2.05, and 1.53; negative likelihood ratios were respectively 0.38, 0.31, 0.35, 0.33. Sensitivity of TST combined with the novel test, QuantiFERON-TB GOLD In-Tube and T-SPOT.TB increased up to 92.4%, 97.7% and 97.1%, respectively. The likelihood ratios of combined negative results of TST with, respectively, the novel test, QuantiFERON-TB GOLD In-Tube and T-SPOT.TB were 0.19, 0.07 and 0.10.ConclusionsThe assay based on RD1 selected peptides has similar accuracy for active tuberculosis compared with TST and commercial IGRAs. Then, independently of the spectrum of antigens used in the assays to elicit mycobacterial specific immune responses, the novel test, IGRAs, and the TST do not allow an accurate identification of active tuberculosis in clinical practice. However, the combined use of the novel assay or commercial IGRAs with TST may allow exclusion of tuberculosis.
The early secretory antigenic target (ESAT)-6 purified protein and peptides from Mycobacterium tuberculosis were evaluated as antigens for the immunodiagnosis of tuberculosis (TB). Because the control of TB requires improved diagnostic procedures, efforts have increased to identify Mycobacterium tuberculosis-specific epitopes for the immunodiagnosis of active TB and to discriminate between active and latent states of infection. Two multiepitopic peptides from ESAT-6 protein were selected by computational analysis. Patients with active TB (7 HIV + and 20 HIV-) and control patients (17 HIV + and 28 HIV-) were enrolled. Enzyme-linked immunospot assay analysis for interferon-γ expression by peripheral blood mononuclear cells was quantified after stimulation with selected ESAT-6 peptides, purified protein derivative, or the intact ESAT-6 protein. During active TB, 20 of 27 patients responded in vitro to ESAT-6 peptides and 23 of 27 patients to purified protein derivative. None of the controls without active TB, including individuals with latent TB infection, recognized ESAT-6 peptides. By contrast, latently infected individuals did respond in vitro to both intact ESAT-6 protein and purified protein derivative. Thus, high T-cell response frequencies to ESAT-6 peptides are present only during active TB and can be used to discriminate between active and latent forms of infection.
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