The assessment of cytokines in Quantiferon supernatants for the diagnosis of latent TB infection in a tribal population of Melghat, India

Summary: The tuberculin skin test (TST) and interferon-gamma release assays (IGRA), namely, the QuantiFERON-TB Gold test (QFT), remain the standard immunological diagnostic tools for latent tuberculosis (TB) infection (LTBI). However, the sub-optimal detection rates of both of these tests are major impediments in recognizing the population at risk. This study was aimed at evaluating additional cytokines besides interferon-gamma (IFN-γ) as biomarkers for improving LTBI diagnosis in the tribal population of Melghat, India. Seventy-four close TB contacts were stratified by QFT and TST results into: (i) QFT+/TST+ (n = 26), (ii) QFT+/TST− (n = 12), (iii) QFT−/TST− (n = 35) and (iv) QFT−/TST+ (n = 1) groups. A panel of cytokines (IL-6, IL-10, TNF-α and IL-2R) was then evaluated in antigen-stimulated QFT cell-free culture supernatants using IMMULITE-1000, an automated immunoassay analyzer. Cytokine estimation showed significantly higher levels of IL-6 in the QFT+/TST+ group, while significantly higher levels of IL-10 were found in the QFT−/TST− group. Correlation analysis identified a positive correlation between IL-6 and the QFT response (r = 0.6723, P < 0.0001), while a negative correlation was seen between QFT and IL-10 expression (r = −0.3271, P = 0.0044). Similarly, IL-6 was positively correlated with TST levels (r = 0.6631, P < 0.0001), and conversely, a negative correlation was found between TST and IL-10 expression (r = −0.5698, P < 0.0001). The positive and negative predictive values of IL-6 were found to be 92.59 and 93.33%, respectively, and the positive and negative predictive values of IL-10 were 96.55 and 91.18%, respectively. No significant impact of the demographic characteristics on cytokine positivity was observed. Our preliminary results suggest that the evaluation of additional cytokines in QFT cell-free culture supernatants may be valuable for the identification of LTBI. Combining IL-6 and IL-10 with QFT and/or TST could markedly improve the detection accuracy of LTBI. Our observations require investigation in larger well-characterized cohorts along with follow-up studies to further confirm the study outcome. Keywords: Cytokines, LTBI, TST, QF

Mycobacterial Dormancy Regulon Protein Rv2623 as a Novel Biomarker for the Diagnosis of Latent and Active Tuberculous Meningitis

The present study was designed to investigate Rv2623 antigen, a major dormancy regulon protein of Mycobacterium tuberculosis (MTB) in CSF of suspected latent and active tuberculous meningitis (TBM) patients. A total of 100 CSF samples from TBM (n=31), suspected latent TBM (n=22), and suitable noninfectious control subjects (n=47) were collected and evaluated for Rv2623 antigen level using ELISA protocol. A significantly high (P<0.05) mean absorbance was observed in samples of suspected latent TBM and active TBM patients as compared to non-TBM control patients. However, no significant difference in Rv2623 level was observed between suspected latent TBM and TBM patients. Our preliminary findings suggest that Rv2623 may be useful as a potential biomarker for the diagnosis of the latent as well as active TBM infection. Futher evaluation of this biomarker in large number of samples is therefore needed to confirm the result

Latent TB infection diagnosis in population exposed to TB subjects in close and poor ventilated high TB endemic zone in India.

The present study was designed to investigate the utility of Quantiferon TB gold (QFT-G) and Tuberculin skin test (TST) for diagnosis of latent TB infection (LTBI) in high crowding TB endemic zone of Nagpur, India and their comparison with associated risk factors.Out of 342 eligible participants, QFT-G and TST were performed in 162 participants.The prevalence of LTBI observed according to QFT-G and TST was 48% and 42% respectively, with an agreement of 52.47%. QFT-G positivity was associated with age while TST positivity was associated with body mass index (BMI). Duration of exposure emerged as a key risk factor significantly associated with both the tests.The prevalence of LTBI was quite high in the studied zone as detected by both the evaluated tests and thus, the combination of both the tests will be best predictive for LTBI in such high TB endemic regions

Correlation between the QFT-G and TST assays in exposed population (<i>n</i> = 162).

<p>Correlation between the QFT-G and TST assays in exposed population (<i>n</i> = 162).</p

Study flow diagram.

<p>Study flow diagram.</p

Multinomial univariate logistic regression to determine the correlation of risk factors with concordant and discordant test results.

<p>*<i>P</i><0.05;</p><p>**<i>P</i><0.0001;</p><p>QFT−/TST – as reference level.</p

General characteristics of TB exposed cases (<i>n</i> = 162).

†<p>Out of 117.</p

Correlation between patient characteristics and QFT results obtained through bivariate and multivariable logistic regression analysis (<i>n</i> = 162).

<p>*<i>P</i><0.05;</p><p>**<i>P</i><0.0001;</p>‡<p>Bivariate analysis;</p>†<p>Parsimonious multivariate logistic regression model;</p>+<p><i>n</i> = 117 (45 unknown).</p

QFT and TST assay in initial and Follow studies and their correlation with Baseline characteristics.

<p>NA - Not Available.</p><p>ND - Not Done.</p><p>*Conversion of QFT Test into positive after follow up.</p>#<p>QFT Test still remains positive after follow up.</p>$<p>QFT Test still remains negative after follow up.</p>¥<p>Conversion of TST Test into positive after follow up.</p>¶<p>TST Test still remains positive after follow up.</p>Φ<p>TST was not done in follow up cases.</p