BCG-specific IgG-secreting peripheral plasmablasts as a potential biomarker of active tuberculosis in HIV negative and HIV positive patients

Inflammatory immune profiles associated with disease severity in pulmonary tuberculosis patients with moderate to severe clinical TB or anemia

Background

Immune control of Mycobacterium tuberculosis (Mtb) infection is largely influenced by the extensive disease heterogeneity that is typical for tuberculosis (TB). In this study, the peripheral inflammatory immune profile of different sub-groups of pulmonary TB patients was explored based on clinical disease severity, anemia of chronic disease, or the radiological extent of lung disease.

Methods

Plasma samples were obtained from n=107 patients with active pulmonary TB at the time of diagnosis and after start of standard chemotherapy. A composite clinical TB symptoms score, blood hemoglobin status and chest X-ray imaging were used to sub-group TB patients into 1.) mild and moderate-severe clinical TB, 2.) anemic and non-anemic TB, or 3.) limited and extensive lung involvement. Plasma levels of biomarkers associated with inflammation pathways were assessed using a Bio-Plex Magpix 37-multiplex assay. In parallel, Th1/Th2 cytokines were quantified with a 27-multiplex in matched plasma and cell culture supernatants from whole blood stimulated with M. tuberculosis-antigens using the QuantiFERON-TB Gold assay.

Results

Clinical TB disease severity correlated with low blood hemoglobin levels and anemia but not with radiological findings in this study cohort. Multiplex protein analyses revealed that distinct clusters of inflammation markers and cytokines separated the different TB disease sub-groups with variable efficacy. Several top-ranked markers overlapped, while other markers were unique with regards to their importance to differentiate the TB disease severity groups. A distinct immune response profile defined by elevated levels of BAFF, LIGHT, sTNF-R1 and 2, IP-10, osteopontin, chitinase-3-like protein 1, and IFNα2 and IL-8, were most effective in separating TB patients with different clinical disease severity and were also promising candidates for treatment monitoring. TB patients with mild disease displayed immune polarization towards mixed Th1/Th2 responses, while pro-inflammatory and B cell stimulating cytokines as well as immunomodulatory mediators predominated in moderate-severe TB disease and anemia of TB.

Conclusions

Our data demonstrated that clinical disease severity in TB is associated with anemia and distinct inflammatory immune profiles. These results contribute to the understanding of immunopathology in pulmonary TB and define top-ranked inflammatory mediators as biomarkers of disease severity and treatment prognosis.

Beyond the Clinic: The Activation of Diverse Cellular and Humoral Factors Shapes the Immunological Status of Patients with Active Tuberculosis

Mycobacterium tuberculosis (Mtb), the etiologic agent of tuberculosis (TB), has killed nearly one billion people in the last two centuries. Nowadays, TB remains a major global health problem, ranking among the thirteen leading causes of death worldwide. Human TB infection spans different levels of stages: incipient, subclinical, latent and active TB, all of them with varying symptoms, microbiological characteristics, immune responses and pathologies profiles. After infection, Mtb interacts with diverse cells of both innate and adaptive immune compartments, playing a crucial role in the modulation and development of the pathology. Underlying TB clinical manifestations, individual immunological profiles can be identified in patients with active TB according to the strength of their immune responses to Mtb infection, defining diverse endotypes. Those different endotypes are regulated by a complex interaction of the patient's cellular metabolism, genetic background, epigenetics, and gene transcriptional regulation. Here, we review immunological categorizations of TB patients based on the activation of different cellular populations (both myeloid and lymphocytic subsets) and humoral mediators (such as cytokines and lipid mediators). The analysis of the participating factors that operate during active Mtb infection shaping the immunological status or immune endotypes of TB patients could contribute to the development of Host Directed Therapy.

Discovery of Novel Transketolase Epitopes and the Development of IgG-Based Tuberculosis Serodiagnostics

Despite advances in rapid molecular techniques for tuberculosis (TB) diagnostics, there is an unmet need for a point-of-care, nonsputum-based test. Previously, through a T7 phage antigen display platform and immunoscreening, we identified that the serum IgGs of active TB patients differentially bind to several antigen-clones and that this immunoreactivity discriminates TB from other respiratory diseases. One of these high-performance clones has some homology to the transketolase of Mycobacterium tuberculosis (M.tb TKT). In this study, we developed a direct enzyme-linked immunosorbent assay (ELISA) detecting IgG against the TKT antigen-clone (TKTμ). Through sequence alignment and in silico analysis, we designed two more peptides with potential antigenicity that correspond to M.tb-specific transketolase (M.tb TKT1 and M.tb TKT3) epitopes. After the development and standardization of a direct peptide ELISA for three peptides, we tested 292 subjects, including TB (n = 101), latent tuberculosis infection (LTBI) (n = 49), healthy controls (n = 66), and sarcoidosis (n = 76). We randomly assigned 60% of the subjects to a training set to create optimal models to distinguish positive TB samples, and the remaining 40% were used to validate the diagnostic power of the IgG-based assays that were developed in the training set. Antibodies against M.tb TKT3 yielded the highest sensitivity (0.845), and these were followed by TKTμ (0.817) and M.tb TKT1 (0.732). The specificities obtained by TKTμ, M.tb TKT3, and M.tb TKT1 on the test sets were 1, 0.95, and 0.875, respectively. The model using TKTμ obtained a perfect positive predictive value (PPV) of 1, and this was followed by M.tb TKT3 (0.968) and M.tb TKT1 (0.912). These results show that IgG antibodies against transketolase can discriminate active TB against LTBI, sarcoidosis, and controls. IMPORTANCE There is an unmet need for a point-of-care, nonsputum-based TB test. Through the immunoscreening of a novel T7 phage library, we identified classifiers that specifically bind to IgGs in active TB sera. We discovered that one of these clones is aligned with Mycobacterium tuberculosis transketolase (TKT). TKT is an essential enzyme for Mycobacterium tuberculosis growth. We designed three TKT epitopes (TKTμ, TKT1, and TKT3) to detect TKT-specific IgGs. After the development and standardization of three different ELISA-utilizing TKT peptides, we tested 292 subjects, including active TB, LTBI, healthy controls, and sarcoidosis. Rigorous statistical analyses using training and validation sets showed that ELISA-based detections of specific IgGs against TKT3 and TKTμ have the greatest sensitivity, specificity, and accuracy to distinguish active TB subjects from others, even LTBI. Our work provides a novel scientific platform from which to further develop a point-of-care test, thereby aiding in faster TB diagnoses.

Distinct and shared B cell responses of tuberculosis patients and their household contacts

This study was aimed at identifying the B cell responses which could distinguish between 'latent tuberculosis infection (LTBI)' and active TB disease. Study subjects were smear-positive TB patients (n = 54) and their disease-free household contacts (HHCs, n = 120). The sera were used for determination of antibody levels (ΔOD values) against Mycobacterium tuberculosis membrane (MtM) antigens by ELISA and for visualisation of seroreactive MtM antigens by immunoblotting. B cell subsets in whole blood samples were determined by flow cytometry. In TB sera, levels of IgG antibodies were significantly higher than IgM and IgA whereas IgM and IgA antibody levels were comparable. Conversely, HHC sera had significantly higher IgM antibody levels than IgG and IgA. The ratio of IgM to IgG antibodies in HHCs were also significantly higher than in patients. Immunoblotting revealed that some of the MtM antigens (<10, ~12 and ~25 kDa) reacted with TB as well as HHC sera whereas some other antigens (~16, ~36, ~45 and ~60 kDa) reacted with most of TB and a subset of HHC sera. Frequencies of classical memory B cells (cMBCs, CD19+CD27+) were significantly higher, and of IgG+ cMBCs were significantly lower in HHCs than in patients. Frequencies of IgA+ cMBCs in HHCs and patients were comparable but both were significantly higher than the corresponding frequencies of IgG+ cMBCs. Frequencies of IgA+ atypical MBCs (aMBCs, CD19+CD27-) in HHCs and patients were also comparable and significantly higher than the IgG+ aMBCs. The plasmablast (CD19+CD27++CD38++) frequencies in HHCs and patients were comparable. These results suggest that the IgM/IgG antibody ratio, antibody binding to selected MtM antigens and relative frequencies of MBC subsets could indicate protective or pathogenic immune responses following the primary infection with Mtb. Responses that orchestrate protection leading to a 'quiescent' LTBI may provide clues to an effective vaccination strategy against TB.

Impaired Circulating Antibody-Secreting Cells Generation Predicts the Dismal Outcome in the Elderly Septic Shock Patients

Purpose

Sepsis is a condition that derives from a dysregulated host response to infection. Although B lymphocytes play a pivotal role in immune response, little is known about status of their terminally differentiated cells, antibody-secreting cells (ASCs) during immunosuppressive phase of sepsis, especially in elderly patients. Our aim was to extensively characterize the immune functions of ASCs in elderly septic patients.

Patients and Methods

Clinical and laboratory data were collected on days 1, 3, and 7 of hospitalization. Circulating ASCs were evaluated by flow cytometry from fresh whole blood in elderly septic patients at the onset of disease. RNA sequencing analyzed ASCs gene expression profile. Receiver operating characteristic (ROC) curve analysis and logistic regression predicted the survival rate of 28-day mortality.

Results

A total of 103 septic patients were enrolled. The number and proportion of ASCs among total lymphocytes dramatically increased in septic patients, and RNA sequencing analysis showed that ASCs from septic patients exhibited a different gene expression profile. Furthermore, we found these ASCs could promote the function of T cells. Logistic regression analysis showed ASCs population was an independent outcome predictor in septic shock patients.

Conclusion

Our study revealed the complex nature of immune disorders in sepsis and identified circulating ASCs population as a useful biomarker for predicting mortality in elderly septic patients, which provided a novel clue to combat this severe disease.

Past and Present Approaches to Diagnosis of Active Pulmonary Tuberculosis

Tuberculosis disease continues to contribute to the mortality burden globally. Due to the several shortcomings of the available diagnostic methods, tuberculosis disease continues to spread. The difficulty to obtain sputum among the very ill patients and the children also affects the quick diagnosis of tuberculosis disease. These challenges warrant investigating different sample types that can provide results in a short time. Highlighted in this review are the approved pulmonary tuberculosis diagnostic methods and ongoing research to improve its diagnosis. We used the PRISMA guidelines for systematic reviews to search for studies that met the selection criteria for this review. In this review we found out that enormous biosignature research is ongoing to identify host biomarkers that can be used as predictors of active PTB disease. On top of this, more research was also being done to improve already existing diagnostic tests. Host markers required more optimization for use in different settings given their varying sensitivity and specificity in PTB endemic and non-endemic settings.

FasL regulatory B-cells during Mycobacterium tuberculosis infection and TB disease

Tuberculosis (TB) disease remains a major health crisis. Infection with Mycobacterium tuberculosis (M.tb) cause a range of diseases ranging from latent infection to active TB disease. This active state of the disease is characterised by the formation of granulomas (a physical barrier in the lung), a structure thought to protect the host by controlling the infection through preventing the growth of the bacilli. Subsequently, the surviving bacteria become inactive and in most cases, TB reactivation is prevented by the immune response of the host. B-cells perform numerous immunological functions beyond antibody production to positively regulate the response to pathogenic assault. A subgroup of B-cells with regulatory functions express death-inducing ligands, such as Fas ligand (FasL). Expression and interaction of the Fas receptor-ligand promotes the induction of apoptosis and the induction of T-cell tolerance. Here, we focus on the significance of B-cells by addressing their FasL phenotype and regulatory functions during TB, with reference to disease in humans, non-human primates and mice.

Slow radiological improvement and persistent low-grade inflammation after chemotherapy in tuberculosis patients with type 2 diabetes

Background

Diabetes mellitus type 2 (DM) may impede immune responses in tuberculosis (TB) and thus contribute to enhanced disease severity. In this study, we aimed to evaluate DM-mediated alterations in clinical, radiological and immunological outcomes in TB disease.

Methods

Newly diagnosed pulmonary TB patients with or without DM (TB n = 40; TB-DM n = 40) were recruited in Dhaka, Bangladesh. Clinical symptoms, sputum smear and culture conversion as well as chest radiography were assessed. Peripheral blood and sputum samples were collected at the time of diagnosis (baseline) and after 1, 2 and 6 months of standard anti-TB treatment. Blood samples were also obtained from healthy controls (n = 20). mRNA expression of inflammatory markers in blood and sputum samples were quantified using real-time PCR.

Results

The majority of TB-DM patients had poor glycemic control (HbA1c > 8%) and displayed elevated pulmonary pathology (P = 0.039) particularly in the middle (P < 0.004) and lower lung zones (P < 0.02) throughout the treatment period. However, reduction of clinical symptoms and time to sputum smear and culture conversion did not differ between the groups. Transcripts levels of the pro-inflammatory cytokines IL-1β (P = 0.003 at month-1 and P = 0.045 at month-2) and TNF-α (P = 0.005 at month-1) and the anti-inflammatory cytokine IL-10 (P = 0.005 at month-2) were higher in peripheral blood after anti-TB treatment in TB-DM compared to TB patients. Conversely in sputum, TB-DM patients had reduced CD4 (P < 0.009 at month-1) and IL-10 (P = 0.005 at month-1 and P = 0.006 at month-2) transcripts, whereas CD8 was elevated (P = 0.016 at month-2). At 1- and 2-month post-treatment, sputum IL-10 transcripts were inversely correlated with fasting blood glucose and HbA1c levels in all patients.

Conclusion

Insufficient up-regulation of IL-10 in the lung may fuel persistent local inflammation thereby promoting lung pathology in TB-DM patients with poorly controlled DM.

Mycobacterium tuberculosis-specific plasmablast levels are differentially modulated in tuberculosis infection and disease

Background

While T cell responses to Mycobacterium tuberculosis (Mtb) have been extensively studied, the role of B-cells and antibodies are less well characterised. The aim of this study was to assess levels of Mtb-specific IgG + plasmablasts across the Mtb infection spectrum.

Methods

Patients with active TB were analysed at baseline and 6 months of therapy (n = 20).Their exposed household contacts (HHC) included individuals with latent TB infection (LTBI; n = 20); evident at baseline; individuals with a negative Tuberculin Skin Test (TST) at baseline who became; positive at 6 months (converters; n = 11) and those who remained negative (non-converters; n = 10). An e x-vivo B-cell ELISPOT was performed to analyse plasmablast responses.

Results

Frequencies of ESAT-6/CFP-10 (EC)- but not Whole Cell Lysate (WCL)-specific plasmablasts were significantly higher in patients with active TB pre-treatment compared to post-treatment (p = 0.002) and compared to HHC with LTBI (p < 0.0001). Conversely, total IgG + plasmablasts were significantly decreased in TB patients at baseline. No difference was seen in levels of plasmablasts between TST converters and non-converters at baseline.

Conclusions

We show that EC-specific plasmablast levels are differentially modulated during TB infection and disease, with levels highest during active TB. These data provide new insights into TB biomarker development and avenues for novel immune interventions.

The role of antibodies in Bacille Calmette Guérin-mediated immune responses and protection against tuberculosis in humans: A systematic review

BACKGROUND

The mechanisms underlying Bacille Calmette-Guérin (BCG) vaccine's protective effects against tuberculosis (TB) are incompletely understood but are proposed to involve a predominantly cell-mediated process. However, there is increasing evidence for the involvement of antibodies in the control of Mycobacteria tuberculosis and in the immune response to BCG.

METHODS

We did a systematic review of studies investigating anti-BCG antibodies in individuals with active or latent TB, and in the response to BCG vaccination.

RESULTS

Of 1417 articles screened, 70 were relevant, comprising 52 investigating anti-BCG antibodies in TB and 18 investigating the anti-BCG antibody response to BCG-vaccination. Individuals with active TB have higher levels of anti-BCG antibodies compared with individuals with latent TB or healthy individuals. Antibodies to BCG are present after BCG vaccination. There is some evidence for the in utero transfer of maternal anti-BCG antibodies to infants.

CONCLUSIONS

BCG vaccination induces a humoral response. Antibodies targeted against BCG and its antigens may play a role in protection against active TB.

Antibody-Secreting Cells To Diagnose Mycobacterium tuberculosis Infection in Children in Pakistan

Tuberculosis (TB) in children represents a missed opportunity for diagnosis and preventive therapy. The magnitude or burden of disease in children is not fully understood due to our limitations with respect to exploring sensitive diagnostic algorithms. In a setting of TB endemicity in Pakistan, we carried out a proof-of-concept study to evaluate for the first time the performance of B cell analyses by the use of well-defined diagnostic criteria and NIH consensus guidelines as “culture-confirmed,” “probable,” and “possible” TB groups. In contrast to detection of serum antibody, we focused on mycobacterial-antibody-secreting cell (MASC) detection as a marker of active disease in children with a strong suspicion of TB. Further work exploring a larger panel of inflammatory biomarkers and enrichment of B cells with the objective of increasing the sensitivity of the current MASC assay would lead to the development of a field-friendly assay for timely diagnosis of childhood TB.

Reliance on microbiologic methods to diagnose Mycobacterium tuberculosis infection is a suboptimal approach for children due in part to the paucibacillary nature of the disease. A blood-based biomarker assay, such as the mycobacterial-antibody-secreting cell (MASC) assay, could be a major advance for the field of study of pediatric tuberculosis (TB). Children <15 years of age with clinical concern for TB and age-matched children with no concern for TB were enrolled from outpatient clinics in Karachi, Pakistan. MASC, ferritin, and C-reactive protein (CRP) assays were performed, and results were compared among cases and controls, as well as among children with a case definition of “confirmed TB,” “probable TB,” or “possible TB.” MASC responses were significantly higher among children with TB than among controls (0.41 optical density [OD] versus 0.28 OD, respectively, P < 0.001), and the differences were largely driven by the data from children with confirmed TB (P = 0.002). Ferritin and CRP values were significantly higher among those with confirmed TB than among those with the other disease states and controls (P = 0.004 and P = 0.019, respectively). The use of the MASC assay as a blood-based biomarker for TB disease shows some promise among children with microbiologically confirmed disease; however, the performance characteristics for the majority of young children with unconfirmed TB were suboptimal in this cohort.

IMPORTANCE Tuberculosis (TB) in children represents a missed opportunity for diagnosis and preventive therapy. The magnitude or burden of disease in children is not fully understood due to our limitations with respect to exploring sensitive diagnostic algorithms. In a setting of TB endemicity in Pakistan, we carried out a proof-of-concept study to evaluate for the first time the performance of B cell analyses by the use of well-defined diagnostic criteria and NIH consensus guidelines as “culture-confirmed,” “probable,” and “possible” TB groups. In contrast to detection of serum antibody, we focused on mycobacterial-antibody-secreting cell (MASC) detection as a marker of active disease in children with a strong suspicion of TB. Further work exploring a larger panel of inflammatory biomarkers and enrichment of B cells with the objective of increasing the sensitivity of the current MASC assay would lead to the development of a field-friendly assay for timely diagnosis of childhood TB.

Bcells and their regulatory functions during Tuberculosis: Latency and active disease

Tuberculosis (TB) is a global epidemic with devastating consequences. Emerging evidence suggests that B-cells have the ability to modulate the immune response and understanding these roles during Mycobacterium tuberculosis (M.tb) infection can help to find new strategies to treat TB. The immune system of individuals with pulmonary TB form granulomas in the lung which controls the infection by inhibiting the M.tb growth and acts as a physical barrier. Thereafter, surviving M.tb become dormant and in most cases the host's immunity prevents TB reactivation. B-cells execute several immunological functions and are regarded as protective regulators of immune responses by antibody and cytokine production, as well as presenting antigen. Some of these B-cells, or regulatory B-cells, have been shown to express death-inducing ligands, such as Fas ligand (FasL). This expression and binding to the Fas receptor leads to apoptosis, a major immune regulation mechanism, in addition to the ability to induce T-cell tolerance. Here, I discuss the relevance of B-cells, in particular their non-humoral functions by addressing their regulatory properties during M.tb infection.

Evaluation of cytokines in peripheral blood mononuclear cell supernatants for the diagnosis of tuberculosis

INTRODUCTION

There is active interest in leveraging host immune responses as biomarkers of tuberculosis (TB) disease activity. We had previously evaluated an immunodiagnostic test called the antibody in lymphocyte supernatant (ALS) assay. Here, we aimed to evaluate a panel of inflammatory mediators and associate the responses with the ALS results to identify a biosignature to distinguish TB cases from controls.

METHODOLOGY

In this case-control study, adults with TB were compared to controls who were hospitalized for non-infectious conditions. Blood was collected at baseline and after 4 weeks of TB treatment (from TB cases only). Peripheral blood mononuclear cells were isolated and cultured without antigenic stimulation for 72 hours. Inflammatory mediators were measured using the Multiplex cytokine kit and compared between TB cases and controls; among TB cases, responses were compared over time. ALS and inflammatory mediator results were evaluated using generalized discriminant analysis to identify the optimal biosignature to predict TB.

RESULTS

When comparing inflammatory mediators between groups, IL-1ra, IL-1β, and granulocyte macrophage-colony stimulating factor (GM-CSF) were lower in TB cases (P<0.002). Fibroblast growth factor-basic significantly increased from baseline to week-4 (P=0.002). Generalized discriminant analysis yielded a model with IL-2, tumor necrosis factor-alpha, vascular endothelial growth factor, and ALS, providing a sensitivity of 82.2% and specificity of 76.2%.

CONCLUSION

Our results suggest that IL-1ra, IL-1β, and GM-CSF might be used as diagnostic biomarkers to distinguish between TB cases and non-TB cases. We could not identify a group of mediators that outperformed the diagnostic accuracy of the ALS alone.

Characterising antibody avidity in individuals of varied Mycobacterium tuberculosis infection status using surface plasmon resonance

There is increasing evidence supporting a role for antibodies in protection against tuberculosis (TB), with functional antibodies being described in the latent state of TB infection. Antibody avidity is an important determinant of antibody-mediated protection. This study characterised the avidity of antibodies against Ag85A, an immunodominant Mycobacterium tuberculosis (M.tb) antigen and constituent of several anti-TB vaccine candidates, in individuals of varied M.tb infection status. Avidity of Ag85A specific antibodies was measured in 30 uninfected controls, 34 individuals with latent TB infection (LTBI) and 75 active pulmonary TB (APTB) cases, employing the more commonly used chaotrope-based dissociation assays, and surface plasmon resonance (SPR). Chaotrope-based assays indicated that APTB was associated with a higher antibody avidity index compared to uninfected controls [adjusted geometric mean ratio (GMR): 1.641, 95% confidence interval (CI): 1.153, 2.337, p = 0.006, q = 0.018] and to individuals with LTBI [adjusted GMR: 1.604, 95% CI: 1.282, 2.006, p < 0.001, q <0.001]. SPR assays showed that APTB was associated with slower dissociation rates, an indication of higher avidity, compared to uninfected controls (adjusted GMR: 0.796, 95% CI: 0.681, 0.932, p = 0.004, q = 0.012) and there was also weak evidence of more avid antibodies in the LTBI compared to the uninfected controls (adjusted GMR: 0.871, 95% CI: 0.763, 0.994, p = 0.041, q = 0.123). We found no statistically significant differences in anti-Ag85A antibody avidity between the APTB and LTBI groups. This study shows that antibodies of increased avidity are generated against a principle vaccine antigen in M.tb infected individuals. It would be important to determine whether TB vaccines are able to elicit a similar response. Additionally, more research is needed to determine whether antibody avidity is important in protection against infection and disease.

Vitamin D₃ Status and the Association with Human Cathelicidin Expression in Patients with Different Clinical Forms of Active Tuberculosis

Low vitamin D (vitD₃) is one of the most common nutritional deficiencies in the world known to be associated with numerous medical conditions including infections such as tuberculosis (TB). In this study, vitD₃ status and its association with the antimicrobial peptide, human cathelicidin (LL-37), was investigated in Ethiopian patients with different clinical forms of TB. Patients with active TB (n = 77) and non-TB controls (n = 78) were enrolled in Ethiopia, while another group of non-TB controls (n = 62) was from Sweden. Active TB included pulmonary TB (n = 32), pleural TB (n = 20), and lymph node TB (n = 25). Concentrations of 25-hydroxyvitamin D₃ (25(OH)D₃) were assessed in plasma, while LL-37 mRNA was measured in peripheral blood and in samples obtained from the site of infection. Median 25(OH)D₃ plasma levels in active TB patients were similar to Ethiopian non-TB controls (38.5 versus 35.0 nmol/L) and vitD₃ deficiency (.

Evaluation of serum inflammatory biomarkers as predictors of treatment outcome in pulmonary tuberculosis

OBJECTIVE

To evaluate C-reactive protein (CRP), globulin and white blood cell (WBC) count as predictors of treatment outcome in pulmonary tuberculosis (PTB).

METHODS

An observational study of patients with active PTB was conducted at a tertiary centre. All patients had serum CRP, globulin and WBC measured at baseline and at 2 months following commencement of treatment. The outcome of interest was requirement for extension of treatment beyond 6 months.

RESULTS

There were 226 patients included in the study. Serum globulin 45 g/l was the only baseline biomarker evaluated that independently predicted requirement for treatment extension (OR 3.42, 95%CI 1.597.32, P 0.001). An elevated globulin level that failed to normalise at 2 months was also associated with increased requirement for treatment extension (63.9% vs. 5.1%, P 0.001), and had a low negative likelihood ratio (0.07) for exclusion of requirement for treatment extension. On multivariable analysis, an elevated globulin that failed to normalise at 2 months was independently associated with requirement for treatment extension (OR 6.13, 95%CI 2.2316.80, P 0.001).

CONCLUSIONS

Serum globulin independently predicts requirement for treatment extension in PTB and outperforms CRP and WBC as a predictive biomarker. Normalisation of globulin at 2 months following treatment commencement is associated with low risk of requirement for treatment extension.

Use of QuantiFERON®-TB Gold in-tube culture supernatants for measurement of antibody responses

QuantiFERON®-TB Gold in-tube (QFT-GIT) supernatants may be important samples for use in assessment of anti-tuberculosis (TB) antibodies when only limited volumes of blood can be collected and when a combination of antibody and cytokine measurements are required. These analytes, when used together, may also have the potential to differentiate active pulmonary TB (APTB) from latent TB infection (LTBI). However, few studies have explored the use of QFT-GIT supernatants for investigations of antibody responses. This study determined the correlation and agreement between anti-CFP-10 and anti-ESAT-6 antibody concentrations in QFT-GIT nil supernatant and serum pairs from 68 TB household contacts. We also explored the ability of Mycobacterium tuberculosis (M.tb) specific antibodies, or ratios of antibody to interferon gamma (IFN-γ) in QFT-GIT supernatants, to differentiate 97 APTB cases from 58 individuals with LTBI. Sputum smear microscopy was used to define APTB, whereas the QFT-GIT and tuberculin skin test were used to define LTBI. There were strong and statistically significant correlations between anti-CFP-10 and anti-ESAT-6 antibodies in unstimulated QFT-GIT supernatants and sera (r = 0.89; p<0.0001 for both), and no significant differences in antibody concentration between them. Anti-CFP-10 & anti-ESAT-6 antibodies differentiated APTB from LTBI with sensitivities of 88.7% & 71.1% and specificities of 41.4% & 51.7% respectively. Anti-CFP-10 antibody/M.tb specific IFN-γ and anti-ESAT-6 antibody/M.tb specific IFN-γ ratios had sensitivities of 48.5% & 54.6% and specificities of 89.7% and 75.9% respectively. We conclude that QFT-GIT nil supernatants may be used in the place of sera when measuring antibody responses, reducing blood volumes needed for such investigations. Antibodies in QFT-GIT nil supernatants on their own discriminate APTB from LTBI with high sensitivity but have poor specificity, whereas the reverse is true when antibodies are used in combination with M.tb specific cytokines. Further antibody and antibody/cytokine combinations need to be explored to achieve better diagnostic accuracy.

Human Immunology of Tuberculosis

Immunology is a central theme when it comes to tuberculosis (TB). The outcome of human infection with Mycobacterium tuberculosis is dependent on the ability of the immune response to clear or contain the infection. In cases where this fails, the bacterium replicates, disseminates within the host, and elicits a pathologic inflammatory response, and disease ensues. Clinical presentation of TB disease is remarkably heterogeneous, and the disease phenotype is largely dependent on host immune status. Onward transmission of M. tuberculosis to new susceptible hosts is thought to depend on an excessive inflammatory response causing a breakdown of the lung matrix and formation of lung cavities. But this varies in cases of underlying immunological dysfunction: for example, HIV-1 infection is associated with less cavitation, while diabetes mellitus comorbidity is associated with increased cavitation and risk of transmission. In compliance with the central theme of immunology in tuberculosis, we rely on detection of an adaptive immune response, in the form of interferon-gamma release assays or tuberculin skin tests, to diagnose infection with M. tuberculosis. Here we review the immunology of TB in the human host, focusing on cellular and humoral adaptive immunity as well as key features of innate immune responses and the underlying immunological dysfunction which associates with human TB risk factors. Our review is restricted to human immunology, and we highlight distinctions from the immunological dogma originating from animal models of TB, which pervade the field.

The Antibody-Secreting Cell Response to Infection: Kinetics and Clinical Applications

Despite the availability of advances in molecular diagnostic testing for infectious disease, there is still a need for tools that advance clinical care and public health. Current methods focus on pathogen detection with unprecedented precision, but often lack specificity. In contrast, the host immune response is highly specific for the infecting pathogen. Serological studies are rarely helpful in clinical settings, as they require acute and convalescent antibody testing. However, the B cell response is much more rapid and short-lived, making it an optimal target for determining disease aetiology in patients with infections. The performance of tests that aim to detect circulating antigen-specific antibody-secreting cells (ASCs) has previously been unclear. Test performance is reliant on detecting the presence of ASCs in the peripheral blood. As such, the kinetics of the ASC response to infection, the antigen specificity of the ASC response, and the methods of ASC detection are all critical. In this review, we summarize previous studies that have used techniques to enumerate ASCs during infection. We describe the emergence, peak, and waning of these cells in peripheral blood during infection with a number of bacterial and viral pathogens, as well as malaria infection. We find that the timing of antigen-specific ASC appearance and disappearance is highly conserved across pathogens, with a peak response between day 7 and day 8 of illness and largely absent following day 14 since onset of symptoms. Data show a sensitivity of ~90% and specificity >80% for pathogen detection using ASC-based methods. Overall, the summarised work indicates that ASC-based methods may be very sensitive and highly specific for determining the etiology of infection and have some advantages over current methods. Important areas of research remain, including more accurate definition of the timing of the ASC response to infection, the biological mechanisms underlying variability in its magnitude and the evolution and the B cell receptor in response to immune challenge. Nonetheless, there is potential of the ASC response to infection to be exploited as the basis for novel diagnostic tests to inform clinical care and public health priorities.

Evaluation of the Antibody in Lymphocyte Supernatant Assay to Detect Active Tuberculosis

BACKGROUND

We aimed to evaluate the antibody in lymphocyte supernatant (ALS) assay as a biomarker to diagnose tuberculosis among adults from Tanzania with and without HIV.

METHODS

Adults admitted with suspicion for tuberculosis had sputa obtained for GeneXpert MTB/RIF, acid-fast bacilli smear and mycobacterial culture; blood was obtained prior to treatment initiation and after 4 weeks. Adults hospitalized with non-infectious conditions served as controls. Peripheral blood mononuclear cells were cultured unstimulated for 72 hours. Anti-mycobacterial antibodies were measured from culture supernatants by ELISA, using BCG vaccine as the coating antigen. Median ALS responses were compared between cases and controls at baseline and between cases over time.

RESULTS

Of 97 TB cases, 85 were microbiologically confirmed and 12 were clinically diagnosed. Median ALS responses from TB cases (0.366 OD from confirmed cases and 0.285 from clinical cases) were higher compared to controls (0.085, p<0.001). ALS responses did not differ based on HIV status, CD4 count or sputum smear status. Over time, the median ALS values declined significantly (0.357 at baseline; 0.198 after 4-weeks, p<0.001).

CONCLUSIONS

Robust ALS responses were mounted by patients with TB regardless of HIV status, CD4 count, or low sputum bacillary burden, potentially conferring a unique niche for this immunologic biomarker for TB.

B in TB: B Cells as Mediators of Clinically Relevant Immune Responses in Tuberculosis

The protective role of B cells and humoral immune responses in tuberculosis infection has been regarded as inferior to cellular immunity directed to the intracellular pathogen Mycobacterium tuberculosis. However, B-cell–mediated immune responses in tuberculosis have recently been revisited in the context of B-cell physiology and antigen presentation. We discuss in this review the diverse functions of B cells in tuberculosis, with a focus on their biological and clinical relevance to progression of active disease. We also present the peptide microarray platform as a promising strategy to discover unknown antigenic targets of M. tuberculosis that could contribute to the better understanding of epitope focus of the humoral immune system against M. tuberculosis.

T7 Phage Display Library a Promising Strategy to Detect Tuberculosis Specific Biomarkers

One-third of the world's population is infected with tuberculosis, only 10% will develop active disease and the remaining 90% is considered to have latent TB (LTB). While active TB is contagious and can be lethal, the LTB can evolve to active TB. The diagnosis of TB can be challenging, especially in the early stages, due to the variability in presentation and nonspecific signs and symptoms. Currently, we have limited tools available to diagnose active TB, predict treatment efficacy and cure of active tuberculosis, the reactivation of latent tuberculosis infection, and the induction of protective immune responses through vaccination. Therefore, the identification of robust and accurate tuberculosis-specific biomarkers is crucial for the successful eradication of TB. In this commentary, we summarized the available methods for diagnosis and differentiation of active TB from LTB and their limitations. Additionally, we present a novel peptide microarray platform as promising strategy to identify TB biomarkers.

Fluctuating Behavior and Influential Factors in the Performance of the QuantiFERON-TB Gold In-Tube Assay in the Diagnosis of Tuberculosis

Background

The QuantiFERON-TB Gold In-Tube (QFT-GIT) is a newly developed but widely used interferon-γ release assay for diagnosing tuberculosis (TB). However, research has not determined whether age or the use of an immune suppressive or anti-TB treatment influences this assay’s ability to detect TB. We assessed the QFT-GIT diagnostic performance for active tuberculosis (ATB) in children and adults in an endemic country and explored the effects of glucocorticoids and anti-TB therapy on the diagnostic value of the QFT-GIT.

Methods

A total of 60 children and 212 adults with suspected ATB were evaluated with the QFT-GIT. The association between the QFT-GIT diagnostic value and pretreatment factors was qualitatively and quantitatively assessed.

Results

The sensitivity of the QFT-GIT was 83.9% (95% CI 66.3%-94.6%) in children, and 73.7% (95% CI 57.8%-85.2%) in adults. Glucocorticoids affected the mitogen-stimulated response in both children and adults. In subjects undergoing glucocorticoid pretreatment, 25.0% of the children presented with false-negative QFT-GIT results, 28.6% of adults presented with indeterminate results. For subjects pre-treated with anti-TB drugs, 44.4% presented with false-negative QFT-GIT results.

Conclusions

The QFT-GIT has higher sensitivity and specificity in children than adults. Glucocorticoid treatment negatively impacts the diagnostic value of the QFT-GIT in all age groups. Anti-TB treatment decreases the sensitivity of the QFT-GIT. Therefore, we recommend that the QFT-GIT assay be performed before TB-specific treatment is initiated and the test should not be used on people undergoing immunosuppression treatment, regardless of their age. A quantitative analysis of the QFT-GIT could be useful for assessing and monitoring TB-specific and non-specific immunity during conversion of the disease.

Inflammation and tuberculosis: host-directed therapies

Tuberculosis (TB) is an airborne infectious disease that kills almost two million individuals every year. Multidrug-resistant (MDR) TB is caused by strains of Mycobacterium tuberculosis (M. tb) resistant to isoniazid and rifampin, the backbone of first-line antitubercular treatment. MDR TB affects an estimated 500,000 new patients annually. Genetic analysis of drug-resistant MDR-TB showed that airborne transmission of undetected and untreated strains played a major role in disease outbreaks. The need for new TB vaccines and faster diagnostics, as well as the development of new drugs, has recently been highlighted. The major problem in terms of current TB research and clinical demands is the increasing number of cases of extensively drug-resistant and 'treatment-refractory' TB. An emerging scenario of adjunct host-directed therapies is intended to target pulmonary TB where inflammatory processes can be deleterious and lead to immune exhaustion. 'Target-organ-saving' strategies may be warranted to prevent damage to infected tissues and achieve focused, clinically relevant and long-lasting anti-M. tb cellular immune responses. Candidates for such interventions may be biological agents or already approved drugs that can be 're-purposed' to interfere with biologically relevant cellular checkpoints. Here, we review current concepts of inflammation in TB disease and discuss candidate pathways for host-directed therapies to achieve better clinical outcomes.

Biomarkers of tuberculosis: a research roadmap

Tuberculosis (TB) continues to represent a major public health problem worldwide. Prompt and accurate diagnosis and effective treatment are fundamental to reducing morbidity and mortality and curtailing spread of infection. Furthermore, tackling the large reservoir of latent infection is the cornerstone to TB control in many high income low TB incidence countries. However, our existing toolkit for prevention, diagnosis and treatment remains outdated and inadequate. Here, we discuss the key targets for biomarker research and discovery in TB and recent developments in the field. We focus on host biomarkers, in particular: correlates of vaccine efficacy and sterilizing immunity; biomarkers of latent TB infection, including diagnosis, risk of progression to active TB and response to treatment; and markers of active TB, including diagnosis, response to treatment and risk of relapse. Recent scientific and technological advances have contributed to significant recent progression in biomarker discovery. Although there are clear remaining paucities, continued efforts within scientific, translational and clinical studies are likely to yield a number of clinically useful biomarkers of TB in the foreseeable future.

Long-lived memory B-cell responses following BCG vaccination

The role of T-cells in immunity against Mycobacterium tuberculosis (M. tuberculosis) infection has been extensively studied, however, that of B-cells still remains comparatively unexplored. In this study, we determined the presence and frequencies of mycobacteria-specific memory B-cells (MBCs) in peripheral blood from clinically healthy, Bacillus Calmette Guerin (BCG) vaccinated (n = 79) and unvaccinated (n = 14) donors. Purified protein derivative (PPD)-specific MBCs were present in most donors (both vaccinated and unvaccinated) but their frequencies were significantly higher in vaccinated than in unvaccinated donors. MBCs specific for other mycobacterial antigens [antigen-85A (Ag85A), antigen-85B (Ag85B), 6 kDalton early secretory antigenic target (ESAT-6) and the 10 kDalton-culture filtrate protein (CFP-10)] were less prevalent than those recognising PPD. Furthermore, PPD-specific MBCs were detected in BCG vaccinated donors without ESAT-6 and CFP-10 specific responses. Together, these results indicate that BCG vaccination induces long-lived MBC responses. Similar patterns of response were seen when we examined mycobacteria-specific antibody and T-cell responses in these donors. Our data show for the first time that BCG vaccination elicits long-lived mycobacteria-specific MBC responses in healthy individuals, suggesting a more substantial role of B-cells in the response to BCG and other mycobacterial infections than previously thought.