Progress in understanding the human immune responses to Mycobacterium tuberculosis

Clinical evaluation of the T-SPOT.TB test for detection of tuberculosis infection in northeastern Guangdong Province, China

OBJECTIVE

We evaluated clinical performance of the T-SPOT.TB test for detecting tuberculosis (TB) infection in Meizhou, China.

METHODS

We enrolled 2,868 patients who underwent T-SPOT.TB, smear, and TB-DNA at the same time. The tests' sensitivity and specificity were evaluated and compared in different groups, and in pulmonary TB (PTB) and extrapulmonary TB (EPTB) subgroups. Receiver operator characteristic (ROC) curve analysis was used to evaluate T-SPOT.TB's diagnostic value and determine its cutoff value.

RESULTS

T-SPOT.TB, TB-DNA, and sputum smear sensitivity was 61.44%, 37.12%, and 14.02%; and specificity was 76.49%, 99.20% and 99.60%, respectively. The T-SPOT.TB positive rate was higher in the PTB and EPTB subgroups than in patients with other pulmonary diseases (61.38% and 61.76% vs. 23.34%). The T-SPOT.TB test had better diagnostic accuracy and sensitivity when the positive cutoff value of marker ESAT-6 was 2.5 [area under ROC curve = 0.701, 95%CI 0.687-0.715] and marker CFP-10 was 6.5 [area under ROC curve = 0.669, 95%CI 0.655-0.683].

CONCLUSION

T-SPOT.TB sensitivity was higher than that of TB-DNA or sputum smear, but the specificity was lower. T-SPOT.TB had moderate sensitivity and specificity for diagnosing TB. T-SPOT.TB's new positive cutoff value may be clinically valuable according to ROC analysis.

The anti-tuberculosis agents under development and the challenges ahead

Tuberculosis (TB) is a serious health problem causing 1.5 million deaths worldwide. After the discovery of first-line anti-TB drugs, the mortality rate declined sharply, however, the emergence of drug-resistant strains and HIV co-infection have led to increased incidence of this disease. A number of new potential antitubercular drug candidates with novel modes of action have entered clinical trials in recent years. Compounds such as gatifloxacin, moxifloxacin and linezolid, the already known antibiotics are currently being evaluated for their anti-TB activity. OPC-67683 and TMC207 have been approved for the treatment of MDR-TB patients recently, while PA-824, SQ109, PNU-100480, AZD5847, LL3858, SQ609, SQ641, BTZ043, DC-159a, CPZEN-45, Q-203, DNB1, TBA-354 are in various phases of clinical and preclinical developments. This review evaluates the current status of TB drug development and future aspects.

Human IL-32 expression protects mice against a hypervirulent strain of Mycobacterium tuberculosis

Silencing of interleukin-32 (IL-32) in a differentiated human promonocytic cell line impairs killing of Mycobacterium tuberculosis (MTB) but the role of IL-32 in vivo against MTB remains unknown. To study the effects of IL-32 in vivo, a transgenic mouse was generated in which the human IL-32γ gene is expressed using the surfactant protein C promoter (SPC-IL-32γTg). Wild-type and SPC-IL-32γTg mice were infected with a low-dose aerosol of a hypervirulent strain of MTB (W-Beijing HN878). At 30 and 60 d after infection, the transgenic mice had 66% and 85% fewer MTB in the lungs and 49% and 68% fewer MTB in the spleens, respectively; the transgenic mice also exhibited greater survival. Increased numbers of host-protective innate and adaptive immune cells were present in SPC-IL-32γTg mice, including tumor necrosis factor-alpha (TNFα) positive lung macrophages and dendritic cells, and IFN-gamma (IFNγ) and TNFα positive CD4(+) and CD8(+) T cells in the lungs and mediastinal lymph nodes. Alveolar macrophages from transgenic mice infected with MTB ex vivo had reduced bacterial burden and increased colocalization of green fluorescent protein-labeled MTB with lysosomes. Furthermore, mouse macrophages made to express IL-32γ but not the splice variant IL-32β were better able to limit MTB growth than macrophages capable of producing both. The lungs of patients with tuberculosis showed increased IL-32 expression, particularly in macrophages of granulomas and airway epithelial cells but also B cells and T cells. We conclude that IL-32γ enhances host immunity to MTB.

Increased frequency of regulatory T cells and T lymphocyte activation in persons with previously treated extrapulmonary tuberculosis

Extrapulmonary tuberculosis may be due to underlying immune compromise. Immunosuppressive regulatory T cells (Treg cells), and CD4(+) T lymphocytes in general, are important in the host immune response to Mycobacterium tuberculosis. We evaluated T lymphocytes from patients after recovery from extrapulmonary tuberculosis, which may reflect conditions before M. tuberculosis infection. A case-control study was conducted among HIV-uninfected adults with previously treated extrapulmonary tuberculosis and 3 sets of controls: (i) subjects with previously treated pulmonary tuberculosis, (ii) close tuberculosis contacts with M. tuberculosis infection, and (iii) close tuberculosis contacts with no infection. Monocyte-depleted peripheral blood mononuclear cells (PBMC-M) were stained for CD4(+) CD25(hi) CD127(low) FoxP3(+) cell (Treg cell) and T lymphocyte activation. Both characteristics were compared as continuous variables between groups with the Kruskal-Wallis test. There were 7 extrapulmonary tuberculosis cases, 18 pulmonary tuberculosis controls, 17 controls with M. tuberculosis infection, and 18 controls without M. tuberculosis infection. The median Treg cell proportion was highest among persons with previous extrapulmonary tuberculosis (1.23%) compared to subjects with pulmonary tuberculosis (0.56%), latent M. tuberculosis infection (0.14%), or no M. tuberculosis infection (0.20%) (P = 0.001). The median proportion of CD4(+) T lymphocytes that expressed the activation markers HLA-DR and CD38 was highest for CD4(+) T lymphocytes from persons with previous extrapulmonary tuberculosis (0.79%) compared to subjects with pulmonary tuberculosis (0.44%), latent M. tuberculosis infection (0.14%), or no M. tuberculosis infection (0.32%) (P = 0.005). Compared with controls, persons with previously treated extrapulmonary tuberculosis had the highest Treg cell frequency, but also the highest levels of CD4(+) T lymphocyte activation. Immune dysregulation may be a feature of individuals at risk for extrapulmonary tuberculosis.

Biological functions of Mycobacterium tuberculosis-specific CD4+T cells were impaired by tuberculosis pleural fluid

The local milieu at the site of Mycobacterium tuberculosis infection that modulates T-cell functions is the main battleground for the host to build counter-M. tuberculosis immune responses. CD4+T cells are enriched predominantly in tuberculosis pleurisy and their roles are of considerable importance, but their nature and functional profiles linked with local condition remain elusive. Here we evaluated the functions of M. tuberculosis-specific CD4+T cells from the major three profiles: cytokines production, cell activation and division. Results showed that pleural fluid (PF) from tuberculosis patients in a dose dependent manner inhibited the production of IFN-γ, IL-2 and TNF-α by M. tuberculosis-specific peptides or BCG activated CD4+T cells from pleural fluid mononuclear cells (PFMCs). Surface staining for activation molecules indicated that PF could also blunt cell activation process. CFSE labeling showed that antigen-specific CD4+T cell division ceased following co-incubation with PF. Pre- or post-treatment with PF could disturb subsequent cell activities. The strong inhibitory effect mediated by PF on CD4+T cells was functional predominance. Moreover, application of inhibitors of IDO, adenosine, neutralizing Abs to IL-10 and TGF-β could partially reverse IFN-γ production. Our current research provided novel information that the functions of antigen-specific CD4+T cells coincubated with PF were apparently impaired, which were distinct from cells that cultured in fresh culture medium. We concluded that CD4+T cell mediated antigen-specific cellular immune response that occurred locally might be impaired by PF.