Differences in IgG responses against infection phase related Mycobacterium tuberculosis (Mtb) specific antigens in individuals exposed or not to Mtb correlate with control of TB infection and progression

Assessing the risk of TB progression: Advances in blood-based biomarker research

This review addresses the significant advancements in the identification of blood-based prognostic biomarkers for tuberculosis (TB), highlighting the importance of early detection to prevent disease progression. The manuscript discusses various biomarker categories, including transcriptomic, proteomic, metabolomic, immune cell-based, cytokine-based, and antibody response-based markers, emphasizing their potential in predicting TB incidence. Despite promising results, practical application is hindered by high costs, technical complexities, and the need for extensive validation across diverse populations. Transcriptomic biomarkers, such as the Risk16 signature, show high sensitivity and specificity, while proteomic and metabolic markers provide insights into protein-level changes and biochemical alterations linked to TB. Immune cell and cytokine markers offer real-time data on the body's response to infection. The manuscript also explores the role of single-nucleotide polymorphisms in TB susceptibility and the challenges of implementing novel RNA signatures as point-of-care tests in low-resource settings. The review concludes that, while significant progress has been made, further research and development are necessary to refine these biomarkers, improve their practical application, and achieve the World Health Organization's TB elimination goals.

A mucosal vaccine formulation against tuberculosis by exploiting the adjuvant activity of S100A4-A damage-associated molecular pattern molecule

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), remains one of the top three causes of death. Currently, the only licensed vaccine against TB is the bacillus Calmette-Guerin (BCG), which lacks efficacy in preventing and controlling pulmonary TB in adults. We aimed to evaluate a nasal TB vaccine formulation composed of the Mtb-specific vaccine antigen ESAT-6, an Mtb-associated protein that can trigger protective immune responses, and S100A4, a recently characterized novel mucosal adjuvant. Mice were intranasally given recombinant ESAT-6 in the presence or absence of S100A4 as an adjuvant. We have provided experimental evidence demonstrating that S100A4 admixed to ESAT-6 could induce Mtb-specific adaptive immune responses after intranasal immunization. S100A4 remarkably augmented the levels of anti-ESAT-6 IgG in serum and IgA in mucosal sites, including lung exudates, bronchoalveolar lavage fluid (BALF) and nasal lavage. Furthermore, in both lung and spleen tissues, S100A4 strongly promoted ESAT-6-specific expansion of CD4 T cells. Both CD4 and CD8 T cells from these tissues expressed increased levels of IFN-γ, TNF-α, and IL-17, cytokines critical for antimicrobial activity. Antigen-reencounter-induced T cell proliferative responses, a key vaccine performance indicator, were augmented in the spleen of S100A4-adjuvanted mice. Furthermore, CD8 T cells from the spleen and lung tissues of these mice expressed higher levels of granzyme B upon antigen re-stimulation. S100A4-adjuvanted immunization may predict good mucosal protection against TB.

Intravenous Bacillus Calmette-Guérin (BCG) Induces a More Potent Airway and Lung Immune Response than Intradermal BCG in Simian Immunodeficiency Virus-infected Macaques

Tuberculosis (TB), caused by Mycobacterium tuberculosis, is one of the leading causes of death due to an infectious agent. Coinfection with HIV exacerbates M. tuberculosis infection outcomes in people living with HIV. Bacillus Calmette-Guérin (BCG), the only approved TB vaccine, is effective in infants, but its efficacy in adolescents and adults is limited. In this study, we investigated the immune responses elicited by BCG administered via i.v. or intradermal (i.d.) routes in SIV-infected Mauritian cynomolgus macaques (MCM) without the confounding effects of M. tuberculosis challenge. We assessed the impact of vaccination on T cell responses in the airway, blood, and tissues (lung, thoracic lymph nodes, and spleen), as well as the expression of cytokines, cytotoxic effectors, and key transcription factors. Our results showed that i.v. BCG induces a robust and sustained immune response, including tissue-resident memory T cells in lungs, polyfunctional CD4+ and CD8αβ+ T cells expressing multiple cytokines, and CD8αβ+ T cells and NK cells expressing cytotoxic effectors in airways. We also detected higher levels of mycobacteria-specific IgG and IgM in the airways of i.v. BCG-vaccinated MCM. Although i.v. BCG vaccination resulted in an influx of tissue-resident memory T cells in lungs of MCM with controlled SIV replication, MCM with high plasma SIV RNA (>105 copies/ml) typically displayed reduced T cell responses, suggesting that uncontrolled SIV or HIV replication would have a detrimental effect on i.v. BCG-induced protection against M. tuberculosis.

Role of dormancy survival regulator and resuscitation-promoting factors antigens in differentiating between active and latent tuberculosis: a systematic review and meta-analysis

BACKGROUND

Dormancy survival regulator (DosR) and resuscitation-promoting factor (Rpf) antigens of Mycobacterium tuberculosis are activated during dormant phase of tuberculosis (TB). This study evaluates the differential immunogenicity potentials of DosR and Rpf antigens in individuals with latent tuberculosis infection (LTBI) and active TB patients.

METHODS

After a literature search in electronic databases, studies were selected by following precise eligibility criteria. Outcomes were synthesized systematically, and meta-analyses were performed to estimate standardized mean differences (SMDs) in interferon-gamma (IFNγ) levels, and IFNγ positive immune cells between individuals with LTBI and active TB patients.

RESULTS

Twenty-six studies (1278 individuals with LTBI and 1189 active TB patients) were included. DosR antigens Rv0569 (Standardized mean difference; SMD 2.44 [95%CI: 1.21, 3.66]; p < 0.0001), Rv1733c (SMD 0.60 [95%CI: 0.14, 1.07]; p = 0.011), Rv1735c (SMD 1.16 [95%CI: 0.44, 1.88]; p = 0.002), Rv1737c (SMD 1.26 [95%CI: 0.59, 1.92]; p < 0.0001), Rv2029c (SMD 0.89 [95%CI: 0.35, 1.42]; p = 0.002), RV2626c (SMD 1.24 [95%CI: 0.45, 2.02); p = 0.002), and Rv2628 (SMD 0.65 [95%CI: 0.38, 0.91]; p < 0.0001) and Rpf antigens Rv0867c (SMD 1.33 [95%CI: 0.48, 2.18]; p = 0.002), Rv1009 (SMD 0.65 [95%CI: 0.05, 1.25]; p = 0.034), and Rv2450c (SMD 1.54 [95%CI: 0.92, 2.16]; p < 0.0001) elicited higher IFNγ levels in individuals with LTBI in comparison with active TB patients. IFNγ-positive immunoresponsive cells were significantly higher in individuals with LTBI than in active TB patients for antigens Rv1733c (SMD 1.02 [95%CI: 0.15, 1.88]; p = 0.021), Rv2029c (SMD 0.57 [95%CI: 0.05, 1.09]; p = 0.031), and Rv2628 [SMD 0.38 [95%CI: 0.15, 0.61]; p = 0.001).

CONCLUSION

DosR antigens Rv0569, Rv1733c, Rv1735c, Rv1737c, RV2626c, Rv2628, and Rv2029c, and Rpf antigens Rv0867c, Rv1009, and Rv2450c are found to elicit immune responses differently in individuals with LTBI and active TB patients.

Intravenous BCG induces a more potent airway and lung immune response than intradermal BCG in SIV-infected macaques

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is one of the leading causes of death due to an infectious agent. Coinfection with HIV exacerbates Mtb infection outcomes in people living with HIV (PLWH). Bacillus Calmette-Guérin (BCG), the only approved TB vaccine, is effective in infants, but its efficacy in adolescents and adults is limited. Here, we investigated the immune responses elicited by BCG administered via intravenous (IV) or intradermal (ID) routes in Simian Immunodeficiency Virus (SIV)-infected Mauritian cynomolgus macaques (MCM) without the confounding effects of Mtb challenge. We assessed the impact of vaccination on T cell responses in the airway, blood, and tissues (lung, thoracic lymph nodes, and spleen), as well as the expression of cytokines, cytotoxic molecules, and key transcription factors. Our results showed that IV BCG induces a robust and sustained immune response, including tissue-resident memory T (TRM) cells in lungs, polyfunctional CD4+ and CD8αβ+ T cells expressing multiple cytokines, and CD8αβ+ T cells and NK cells expressing cytotoxic effectors in airways. We also detected higher levels of mycobacteria-specific IgG and IgM in the airways of IV BCG-vaccinated MCM. Although IV BCG vaccination resulted in an influx of TRM cells in lungs of MCM with controlled SIV replication, MCM with high plasma SIV RNA (>105 copies/mL) typically displayed reduced T cell responses, suggesting that uncontrolled SIV or HIV replication would have a detrimental effect on IV BCG-induced protection against Mtb.

Impact of in-utero exposure to HIV and latent TB on infant humoral responses

Introduction

Latent tuberculosis infection (LTBI) is a common coinfection in people living with HIV (PWH). How LTBI and HIV exposure in utero influence the development of infant humoral immunity is not well characterized. To address this question, we assessed the relationship between maternal humoral responses in pregnant women with HIV or with HIV/LTBI on humoral responses in infants to BCG vaccination and TB acquisition.

Methods

Plasma samples were obtained from mother infant pairs during pregnancy (14-34 wks gestation) and in infants at 12 and 44 wks of age from the IMPAACT P1078 clinical trial. LTBI was established by Interferon gamma release assay (IGRA). Progression to active TB (ATB) disease was observed in 5 women at various times after giving birth. All infants were BCG vaccinated at birth and tested for IGRA at 44 weeks. Mtb (PPD, ESAT6/CFP10, Ag85A, LAM), HIV (GP120), and Influenza (HA) specific IgG, IgM, and IgA were measured in plasma samples using a bead based Luminex assay with Flexmap 3D.

Results

In maternal plasma there were no differences in Mtb-specific antibodies or viral antibodies in relation to maternal IGRA status. ATB progressors showed increases in Mtb-specific antibodies at diagnosis compared to study entry. However, when compared to the non-progressors at entry, progressors had higher levels of Ag85A IgG and reduced ESAT6/CFP10 IgG and LAM IgG, IgM, and IgA1. All infants showed a decrease in IgG to viral antigens (HIV GP120 and HA) from 12 to 44 weeks attributed to waning of maternally transferred antibody titers. However, Mtb-specific (PPD, ESAT6/CFP10, Ag85A, and LAM) IgG and IgM increased from 12 to 44 weeks. HIV and HA IgG levels in maternal and 12-week infant plasma were highly correlated, and ESAT6/CFP10 IgG and LAM IgG showed a relationship between maternal and infant Abs. Finally, in the subset of infants that tested IGRA positive at 44 weeks, we observed a trend for lower LAM IgM compared to IGRA- infants at 44 weeks.

Discussion

The results from our study raise the possibility that antibodies to LAM are associated with protection from progression to ATB and support further research into the development of humoral immunity against TB through infection or vaccination.

Latent tuberculosis diagnostics: current scenario and review

This review presents a comprehensive examination of the contemporary landscape pertaining to latent tuberculosis infection (LTBI) diagnostics, with a particular emphasis on the global ramifications and the intricacies surrounding LTBI diagnosis and treatment. It accentuates the imperative of bolstering diagnostic, preventive, and treatment modalities for tuberculosis (TB) to fulfill the ambitious targets set forth by the World Health Organization aimed at reducing TB-related mortalities and the incidence of new TB cases. The document underscores the significance of addressing LTBI as a means of averting the progression to active TB, particularly in regions burdened with high TB prevalence, such as India. An in-depth analysis of the spectrum delineating latent and active TB disease is provided, elucidating the risk factors predisposing individuals with LTBI to progress towards active TB, including compromised immune functionality, concurrent HIV infection, and other immunosuppressive states. Furthermore, the challenges associated with LTBI diagnosis are elucidated, encompassing the absence of a definitive diagnostic assay, and the merits and demerits of tuberculin skin testing (TST) and interferon-γ release assays (IGRAs) are expounded upon. The document underscores the necessity of confronting these challenges and furnishes a meticulous examination of the advantages and limitations of TST and IGRAs, along with the intricacies involved in interpreting their outcomes across diverse demographics and settings. Additionally, attention is drawn towards the heritability of the interferon-γ response to mycobacterial antigens and the potential utility of antibodies in LTBI diagnosis.

Mycobacterium tuberculosis resisters despite HIV exhibit activated T cells and macrophages in their pulmonary alveoli

To understand natural resistance to Mycobacterium tuberculosis ( Mtb ) infection, we studied people living with HIV (PLWH) in an area of high Mtb transmission. Given that alveolar leukocytes may contribute to this resistance, we performed single cell RNA-sequencing of bronchoalveolar lavage cells, unstimulated or ex vivo stimulated with Mtb . We obtained high quality cells for 7 participants who were TST & IGRA positive (called LTBI) and 6 who were persistently TST & IGRA negative (called resisters). Alveolar macrophages (AM) from resisters displayed more of an M1 phenotype relative to LTBI AM at baseline. Alveolar lymphocytosis (10%-60%) was exhibited by 5/6 resisters, resulting in higher numbers of CD4 + and CD8 + IFNG -expressing cells at baseline and upon Mtb challenge than LTBI samples. Mycobactericidal granulysin was expressed almost exclusively by a cluster of CD8 + T cells that co-expressed granzyme B, perforin and NK cell receptors. For resisters, these poly-cytotoxic T cells over-represented activating NK cell receptors and were present at 15-fold higher numbers in alveoli compared to LTBI. Altogether, our results showed that alveolar lymphocytosis, with increased numbers of alveolar IFNG -expressing cells and CD8 + poly-cytotoxic T cells, as well as activated AM were strongly associated with protection from persistent Mtb infection in PLWH.

Mycobacterium tuberculosis virulence protein ESAT-6 influences M1/M2 polarization and macrophage apoptosis to regulate tuberculosis progression

BACKGROUND

Tuberculosis (TB) is an infectious disease caused by infection with Mycobacterium tuberculosis (Mtb), and it remains one of the major threats to human health worldwide. To our knowledge, the polarization of M1/M2 macrophages were critical innate immune cells which play important roles in regulating the immune response during TB progression.

OBJECTIVE

We aimed to explore the potential mechanisms of M1/M2 macrophage polarization in TB development.

METHODS

THP-1 macrophages were treated with early secreted antigenic target of 6 kDa (ESAT-6) protein for an increasing time. The polarization profiles, apoptosis levels of M1 and M2 macrophages were detected by RT-qPCR, immunofluorescence, Western blot and flow cytometry.

RESULTS

ESAT-6 initially promoted the generation of pro-inflammatory M1-polarized macrophages in THP-1 cells within 24 h, which were suppressed by further ESAT-6 treatment at 30-42 h. Interestingly, ESAT-6 continuously promoted M2 polarization of THP-1 cells, thereby maintaining the anti-inflammatory response in a time-dependent manner. In addition, ESAT-6 promoted apoptotic cell death in M1-polarized macrophages, which had little effects on apoptosis of M2-phenotype of macrophages. Then, the potential underlying mechanisms were uncovered, and we verified that ESAT-6 increased the protein levels of TLR4, MyD88 and NF-κB to activate the TLR4/MyD88/NF-κB pathway within 24 h, and this signal pathway was significantly inactivated at 36 h post-treatment. Interestingly, the following experiments confirmed that ESAT-6 TLR4/MyD88/NF-κB pathway-dependently regulated M1/M2 polarization and apoptosis of macrophage in THP-1 cells.

CONCLUSION

Our study investigated the detailed effects and mechanisms of M1/M2 macrophages in regulating innate responses during TB development, which provided a new perspective on the development of treatment strategies for this disease.

Mucosal and systemic antigen-specific antibody responses correlate with protection against active tuberculosis in nonhuman primates

BACKGROUND

Increasing evidence supports that antibodies can protect against active tuberculosis (TB) but knowledge of potentially protective antigens, especially in the airways, is limited. The main objective of this study was to identify antigen-specific airway and systemic immunoglobulin isotype responses associated with the outcome of controlled latent Mycobacterium tuberculosis (Mtb) infection (LTBI) versus uncontrolled infection (TB) in nonhuman primates.

METHODS

In a case-control design, using non-parametric group comparisons with false discovery rate adjustments, we assessed antibodies in 57 cynomolgus macaques which, following low-dose airway Mtb infection, developed either LTBI or TB. We investigated airway and systemic IgG, IgA, and IgM responses in paired bronchoalveolar lavage and plasma samples prior to, two-, and 5-6-months post Mtb infection using an antigen-unbiased approach with Mtb glycan and proteome-wide microarrays.

FINDINGS

Macaques that developed LTBI (n = 36) had significantly increased airway and plasma IgA reactivities to specific arabinomannan (AM) motifs prior to Mtb infection compared to those that developed TB (n = 21; p < 0.01, q < 0.05). Furthermore, LTBI macaques had higher plasma IgG reactivity to protein MTB32A (Rv0125) early post Mtb infection (p < 0.05) and increasing airway IgG responses to some proteins over time.

INTERPRETATION

Our results support a protective role of pre-existing mucosal (lung) and systemic IgA to specific Mtb glycan motifs, suggesting that prior exposure to nontuberculous mycobacteria could be protective against TB. They further suggest that IgG to Mtb proteins early post infection could provide an additional protective mechanism. These findings could inform TB vaccine development strategies.

FUNDING

NIH/NIAID AI117927, AI146329, and AI127173 to JMA.

Diagnosis and Management of Latent Tuberculosis Infection: Updates

India has the largest problem of tuberculosis (TB) infection globally (estimated at about 35-40 crores cases), and around 18-36 lakh develop active tuberculosis annually. Latent TB is defined as a state of persistent immune response to stimulation by Mycobacterium tuberculosis antigens with no evidence of clinically manifested active TB. The progression of a latent infection to active tuberculosis increases several-fold in children < 5 years of age and in people with some or the other form of an immunocompromising condition. Therefore, to cater to this gigantic problem of tuberculosis, it is necessary to have awareness about latent tuberculosis infection (LTBI) amongst clinicians and to prioritise its diagnosis and treatment in high-risk groups. India plans to end TB well before the deadline set by the World Health organisation (WHO). However, this can only be achieved with effective strategies targeting LTBI. Multiple treatment regimens have been approved for LTBI treatment, and all have comparable efficacy. The selection of one regimen over the other depends on various factors, such as availability, risk of adverse events, age, and drug interactions. Recently, the WHO, as well as the Revised National TB Control Programme (RNTCP), have updated their guidelines on TB preventive treatment in 2020 and 2021, respectively. This review has been especially prepared to acknowledge the differences in approach to LTBI in developed and developing countries.

Intravenous Bacille Calmette-Guérin vaccination protects simian immunodeficiency virus-infected macaques from tuberculosis

Tuberculosis, caused by Mycobacterium tuberculosis (Mtb), is the most common cause of death in people living with human immunodeficiency virus (HIV). Intra-dermal Bacille Calmette-Guérin (BCG) delivery is the only licensed vaccine against tuberculosis; however, it offers little protection from pulmonary tuberculosis in adults and is contraindicated in people living with HIV. Intravenous BCG confers protection against Mtb infection in rhesus macaques; we hypothesized that it might prevent tuberculosis in simian immunodeficiency virus (SIV)-infected macaques, a model for HIV infection. Here intravenous BCG-elicited robust airway T cell influx and elevated plasma and airway antibody titres in both SIV-infected and naive animals. Following Mtb challenge, all 7 vaccinated SIV-naive and 9 out of 12 vaccinated SIV-infected animals were protected, without any culturable bacteria detected from tissues. Peripheral blood mononuclear cell responses post-challenge indicated early clearance of Mtb in vaccinated animals, regardless of SIV infection. These data support that intravenous BCG is immunogenic and efficacious in SIV-infected animals.

Latent Tuberculosis: Challenges in Diagnosis and Treatment, Perspectives, and the Crucial Role of Biomarkers

Tuberculosis (TB) is the major cause of morbidity and mortality globally, which is caused by a single infectious agent Mycobacterium tuberculosis. For years, many TB control programmes are established for effective diagnosis and treatment of active TB cases, but these approaches alone are insufficient for TB eradication. This review aims to discourse on the crucial management of latent tuberculosis infection. This review will first summarize the current status, and methods for diagnosing latent tuberculosis then describes the challenges involved in the diagnosis and treatment of latent tuberculosis, and finally encounters the purpose of biomarkers as predicting tool in latent tuberculosis.

Identification of New Mycobacterium bovis antigens and development of a multiplexed serological bead-immunoassay for the diagnosis of bovine tuberculosis in cattle

Serological assays for bovine tuberculosis diagnosis require the use of multiple Mycobacterium bovis specific antigens to ensure the detection of infected animals. In the present study, identification and selection process of antigens, based on data from published proteomic studies and involving the use of bioinformatics tools and an immuno-screening step, was firstly performed for identifying novel antigens that elicit an antibody response in M. bovis infection. Based on this approach, a panel of 10 M. bovis antigens [with known relevance (MPB70, MPB83, MPB70/83, and ESAT6/CFP10) and novel (Mb1961c, Mb1301c, Mb3871, Mb1403, Mb0592, and PE25/PPE41)] were constructed and thenused to develop a new multiplexed serological assay based on Luminex technology. The performance of the Luminex-bTB immunoassay was evaluated using sera from cattle with known tuberculosis status. Among the proteins whose ability to detect bovine tuberculosis was evaluated for the first time, PE25/PPE41 and Mb1403, but not Mb3871, showed good detection capacity. Following multiple antigen combination, the final Luminex-bTB immunoassay included seven antigens (MPB70, MPB83, MPB70/83, ESAT6/CFP10, PE25/PPE41, Mb1403, and Mb0592) and showed better global performance than the immunoassay using the four usual antigens (MPB70, MPB70/83, MPB83 and ESAT6/CFP10). The specificity and sensitivity values were, respectively, of 97.6% and 42.8% when the cut-off of two-positive antigens was used to classify samples as positive. With the use of the more-restrictive criterion of three-positive antigens, the specificity increased to 99.2% but the sensitivity decreased to 23.9%. The analysis of antigen profiles generated with the Luminex-bTB immunoassay showed that mainly serodominant proteins were recognized in samples from infected cattle. The detection of Mb1961c and Mb1301c appeared to be associated with presumed false-positive results. Moreover, sera from cattle originating from bTB-outbreaks but having inconclusive or negative skin test results were identified as positive by the Luminex-bTB immunoassay and showed an antigen pattern associated with M. bovis infection. The Luminex-bTB immunoassay including seven antigens may be useful as adjunct test for the detection of M. bovis-infected herds, and different cut-offs could be applied according to the bovine tuberculosis epidemiological context.

No impact of helminth coinfection in patients with smear positive tuberculosis on immunoglobulin levels using a novel method measuring Mycobacterium tuberculosis-specific antibodies

Helminth/tuberculosis (TB)-coinfection can reduce cell-mediated immunity against Mycobacterium tuberculosis (Mtb) and increase disease severity, although the effects are highly helminth species dependent. Mtb have long been ranked as the number one single infectious agent claiming the most lives. The only licensed vaccine for TB (BCG) offers highly variable protection against TB, and almost no protection against transmission of Mtb. In recent few years the identification of naturally occurring antibodies in humans that are protective during Mtb infection has reignited the interest in adaptive humoral immunity against TB and its possible implementation in novel TB vaccine design. The effects of helminth/TB coinfection on the humoral response against Mtb during active pulmonary TB are however still unclear, and specifically the effect by globally prevalent helminth species such as Ascaris lumbricoides, Strongyloides stercoralis, Ancylostoma duodenale, Trichuris trichiura. Plasma samples from smear positive TB patients were used to measure both total and Mtb-specific antibody responses in a Peruvian endemic setting where these helminths are dominating. Mtb-specific antibodies were detected by a novel approach coating ELISA-plates with a Mtb cell-membrane fraction (CDC1551) that contains a broad range of Mtb surface proteins. Compared to controls without helminths or TB, helminth/TB coinfected patients had high levels of Mtb-specific IgG (including an IgG1 and IgG2 subclass response) and IgM, which were similarly increased in TB patients without helminth infection. These data, indicate that helminth/TB coinfected have a sustained humoral response against Mtb at the level of active TB only. More studies on the species-specific impact of helminths on the adaptive humoral response against Mtb using a larger sample size, and in relation to TB disease severity, are needed.

Peptide microarray-based identification of dormancy-associated Mycobacterium tuberculosis antigens inducing immune responses among latent tuberculosis infection individuals in Thailand

Multi-stage tuberculosis (TB) vaccines composed of active- and dormancy-associated antigens are promising to trigger the immune protection against all TB stages. However, scientists are still in quest of the suitable vaccine candidates. In this study, we identified the potential targets for this vaccine in a high TB burden country, Thailand. Peptide microarray was applied to gauge IgA and IgG antibodies specific to 16,730 linear epitopes of 52 dormancy-associated Mycobacterium tuberculosis (M. tb) proteins in three study groups: active tuberculosis (ATB), latent tuberculosis infection (LTBI) and endemic healthy control (EHC). Preferential IgA recognition against epitopes of dormancy-associated proteins was identified in LTBI group. Validation of these findings revealed that LTBI subjects exhibited the greater levels of Rv2659c- and Rv1738-specific IgA than those of household contacts, but less than did ATB subjects. Frequencies of IFNγ-producing CD4⁺ and CD8⁺ T cells induced by proteins Rv2659c and Rv1738 were higher in LTBI than ATB individuals. The results indicated that LTBI group in a high TB burden country demonstrated cell-mediated immune response to proteins Rv2659c and Rv1738 stronger than those of ATB. These immune responses likely contribute to natural protection against dormant M. tb and might be potential targets for a multi-stage TB vaccine.

Challenges and the Way forward in Diagnosis and Treatment of Tuberculosis Infection

Globally, it is estimated that one-quarter of the world's population is latently infected with Mycobacterium tuberculosis (Mtb), also known as latent tuberculosis infection (LTBI). Recently, this condition has been referred to as tuberculosis infection (TBI), considering the dynamic spectrum of the infection, as 5-10% of the latently infected population will develop active TB (ATB). The chances of TBI development increase due to close contact with index TB patients. The emergence of multidrug-resistant TB (MDR-TB) and the risk of development of latent MDR-TB has further complicated the situation. Detection of TBI is challenging as the infected individual does not present symptoms. Currently, there is no gold standard for TBI diagnosis, and the only screening tests are tuberculin skin test (TST) and interferon gamma release assays (IGRAs). However, these tests have several limitations, including the inability to differentiate between ATB and TBI, false-positive results in BCG-vaccinated individuals (only for TST), false-negative results in children, elderly, and immunocompromised patients, and the inability to predict the progression to ATB, among others. Thus, new host markers and Mtb-specific antigens are being tested to develop new diagnostic methods. Besides screening, TBI therapy is a key intervention for TB control. However, the long-course treatment and associated side effects result in non-adherence to the treatment. Additionally, the latent MDR strains are not susceptible to the current TBI treatments, which add an additional challenge. This review discusses the current situation of TBI, as well as the challenges and efforts involved in its control.

Exploring the eligibility of all reported lipoarabinomannan-testing assays in different clinical situations: a systematic review and meta-analysis of 97 articles

OBJECTIVES

How to choose proper lipoarabinomannan-testing assays for diagnosing tuberculosis (TB) in different populations baffles clinicians. This work assessed all reported lipoarabinomannan assays' performance and aimed to identify the eligibility of each assay and offer guidance for clinicians.

METHODS

We searched PubMed, Embase, and Web of Science until August 23, 2020. The risk of bias was evaluated by QADAS-2. Heterogeneity was evaluated by the Cochran Q test and I². Sensitivity and specificity were pooled by a bivariate mixed model (register number: CRD42021270506).

RESULTS

A total of 97 articles, covering 144 trials, 16 assays, 45,679 participants, and eight sample types, were divided into five groups. Electrochemiluminescence (ECL) had a sensitivity of 65%, specificity of 92%, and an area under curve (AUC) of 0.85 in diagnosing pulmonary TB in adults. ECL showed a promising diagnostic ability (sensitivity: 78%; specificity: 88%; AUC: 0.88) in patients with HIV, especially for urine detection (sensitivity: 90%; specificity: 89%; AUC: 0.95). The enzyme-linked immune assay showed a preference for diagnosing TB in Asians and Africans, especially in Africans who were smear-positive (sensitivity: 80%; specificity: 88%; AUC: 0.91).

CONCLUSION

ECL was recommended for diagnosing pulmonary TB in adults, especially for TB/HIV co-infection. Taking urine as a sample further enhanced ECL's diagnostic performance. Enzyme-linked immune assay was recommended as an additional TB-related detection for smear-positive Africans.

Culture filtrate protein 32 as a potential target to attenuate the heterogeneous antibody response against Mycobacterium tuberculosis Antigens in different endemic settings

Background

We previously reported the development of an enzyme-linked immunosorbent assay for the detection of the immunoglobulin G (IgG) response to Mycobacterium tuberculosis virulence factor - culture filtrate protein 32 (CFP32). The assay achieved high performance in comparing healthy Bacillus Calmette-Guerin-vaccinated controls with active tuberculosis (TB) patients from the Tunisian population. Herein, we aimed to assess the anti-CFP32 IgG response in suspected or confirmed active pulmonary TB individuals in different endemic settings.

Methods

Serum samples were obtained from 224 donors from African and Latin American countries with variable levels of TB endemicity and different ethnical origins. Receiver operating characteristic curve was used to evaluate the performance of the serological assay.

Results

The area under the curve was 0.70. The use of a cutoff level of 0.65 gave 67% and 68% sensitivity and specificity, respectively, regardless of ethnicity and endemicity. Except for the suspected Latin American group, overall multiple comparisons of medians pointed out the stability of the anti-CFP32 IgG response across the different endemic settings. Therefore, endemicity and ethnicity seem not to affect anti-CFP32 IgG response, mainly for detecting confirmed active TB individuals.

Conclusions

These findings suggest that the inclusion of CFP32 epitopes in multi-antigen TB assay could attenuate serological differences related to heterogeneous endemicity and ethnicity. For this purpose, we further identified B-cell epitopes belonging to CFP32 by an in silico analysis.

Defining Discriminatory Antibody Fingerprints in Active and Latent Tuberculosis

Tuberculosis (TB) is among the leading causes of death worldwide from a single infectious agent, second only to COVID-19 in 2020. TB is caused by infection with Mycobacterium tuberculosis (Mtb), that results either in a latent or active form of disease, the latter associated with Mtb spread. In the absence of an effective vaccine, epidemiologic modeling suggests that aggressive treatment of individuals with active TB (ATB) may curb spread. Yet, clinical discrimination between latent (LTB) and ATB remains a challenge. While antibodies are widely used to diagnose many infections, the utility of antibody-based tests to diagnose ATB has only regained significant traction recently. Specifically, recent interest in the humoral immune response to TB has pointed to potential differences in both targeted antigens and antibody features that can discriminate latent and active TB. Here we aimed to integrate these observations and broadly profile the humoral immune response across individuals with LTB or ATB, with and without HIV co-infection, to define the most discriminatory humoral properties and diagnose TB disease more easily. Using 209 Mtb antigens, striking differences in antigen-recognition were observed across latently and actively infected individuals that was modulated by HIV serostatus. However, ATB and LTB could be discriminated, irrespective of HIV-status, based on a combination of both antibody levels and Fc receptor-binding characteristics targeting both well characterized (like lipoarabinomannan, 38 kDa or antigen 85) but also novel Mtb antigens (including Rv1792, Rv1528, Rv2435C or Rv1508). These data reveal new Mtb-specific immunologic markers that can improve the classification of ATB versus LTB.

The Biological and Clinical Aspects of a Latent Tuberculosis Infection

Tuberculosis (TB), caused by bacilli from the Mycobacterium tuberculosis complex, remains a serious global public health problem, representing one of the main causes of death from infectious diseases. About one quarter of the world’s population is infected with Mtb and has a latent TB infection (LTBI). According to the World Health Organization (WHO), an LTBI is characterized by a lasting immune response to Mtb antigens without any TB symptoms. Current LTBI diagnoses and treatments are based on this simplified definition, although an LTBI involves a broad range of conditions, including when Mtb remains in the body in a persistent form and the immune response cannot be detected. The study of LTBIs has progressed in recent years; however, many biological and medical aspects of an LTBI are still under discussion. This review focuses on an LTBI as a broad spectrum of states, both of the human body, and of Mtb cells. The problems of phenotypic insusceptibility, diagnoses, chemoprophylaxis, and the necessity of treatment are discussed. We emphasize the complexity of an LTBI diagnosis and its treatment due to its ambiguous nature. We consider alternative ways of differentiating an LTBI from active TB, as well as predicting TB reactivation based on using mycobacterial “latency antigens” for interferon gamma release assay (IGRA) tests and the transcriptomic analysis of human blood cells.

The knowns and unknowns of latent Mycobacterium tuberculosis infection

Humans have been infected with Mycobacterium tuberculosis (Mtb) for thousands of years. While tuberculosis (TB), one of the deadliest infectious diseases, is caused by uncontrolled Mtb infection, over 90% of presumed infected individuals remain asymptomatic and contain Mtb in a latent TB infection (LTBI) without ever developing disease, and some may clear the infection. A small number of heavily Mtb-exposed individuals appear to resist developing traditional LTBI. Because Mtb has mechanisms for intracellular survival and immune evasion, successful control involves all of the arms of the immune system. Here, we focus on immune responses to Mtb in humans and nonhuman primates and discuss new concepts and outline major knowledge gaps in our understanding of LTBI, ranging from the earliest events of exposure and infection to success or failure of Mtb control.

Impact of knockdown LincRNA-Cox2 on apoptosis of macrophage infected with Bacillus Calmette-Guérin

Mycobacterium tuberculosis (Mtb)-induced apoptosis of alveolar macrophages plays an important role in the pathogenesis of tuberculosis. Previous studies indicated that massive LncRNAs could deteriorate MTB invasion or latent infection by regulating macrophage's apoptosis. However, whether LincRNA-Cox2 is involved in apoptosis of macrophage infected with Mtb is unclear. In this study, we found Bacillus Calmette-Guerin(BCG)infection induced cell apoptosis with a increasing LincRNA-Cox2 expression in RAW264.7 cells. Furthermore, the activation of TLR signal pathway elevated the expression of lincRNA-Cox2. In this regard, we used small interfering RNA to explore the role of LincRNA-Cox2 on regulating apoptosis of RAW264.7 cells infected with BCG. The results showed that si-LincRNA-Cox2 was capable of increased the expression of apoptosis-associated proteins and accumulation of ROS in BCG-infected RAW264.7 cells. Mechanically, si-LincRNA-Cox2 facilitated BCG-induced macrophage apoptosis by activating the intrinsic apoptotic pathway as well as increased the genes expression of PERK/eIF2α/CHOP. These results provide novel insights into host-pathogen interactions and highlight the potential role of LincRNA-Cox2 in regulating apoptosis induced by BCG-infection.

Diagnosis for Latent Tuberculosis Infection: New Alternatives

Latent tuberculosis infection (LTBI) is a subclinical mycobacterial infection defined on the basis of cellular immune response to mycobacterial antigens. The tuberculin skin test (TST) and the interferon gamma release assay (IGRA) are currently used to establish the diagnosis of LTB. However, neither TST nor IGRA is useful to discriminate between active and latent tuberculosis. Moreover, these tests cannot be used to predict whether an individual with LTBI will develop active tuberculosis (TB) or whether therapy for LTBI could be effective to decrease the risk of developing active TB. Therefore, in this article, we review current approaches and some efforts to identify an immunological marker that could be useful in distinguishing LTBI from TB and in evaluating the effectiveness of treatment of LTB on the risk of progression to active TB.

IFN-γ and IgG responses to Mycobacterium tuberculosis latency antigen Rv2626c differentiate remote from recent tuberculosis infection

Tuberculin skin test (TST) and IFN-γ release assays are currently used to detect Mycobacterium tuberculosis (Mtb) infection but none of them differentiate active from latent infection (LTBI). Since improved tests to diagnose Mtb infection are required, we studied the immune response to Mtb latency antigen Rv2626c in individuals exposed to the bacteria during different periods. Tuberculosis patients (TB), TB close contacts (CC: subjects exposed to Mtb for less than three months) and healthcare workers (HW: individuals exposed to Mtb at least two years) were recruited and QuantiFERON (QFT) assay, TST and IFN-γ secretion to Rv2626c were analyzed. Twenty-two percent of the individuals assessed had discordant results between QFT and TST tests. Furthermore, QFT negative and QFT positive individuals produced differential levels of IFN-γ against Rv2626c, in direct association with their exposure period to Mtb. Actually, 91% of CC QFT negative subjects secreted low levels of IFN-γ to Rv2626c, whereas 43% of HW QFT negative people produced elevated IFN-γ amounts against Rv2626c. Conversely, 69% of CC QFT positive subjects didn´t produce IFN-γ to Rv2626c. Interestingly, a similar pattern of IgG anti-Rv2626c plasma levels was observed. Therefore, determination of IFN-γ and IgG levels against the dormancy antigen Rv2626c allows to identify established LTBI.

Evaluation of Salmonella Typhi antigen YncE alongside HlyE for the detection of typhoid fever and its carriers

Typhoid fever is a disease caused by Salmonella Typhi that was implicated in millions of illnesses worldwide annually. Individuals that do not recover fully from typhoid fever can become asymptomatic carriers of the disease. Host antibodies against the S. Typhi antigens, HlyE (for acute typhoid) and YncE (for carriers) were previously reported to be useful biomarkers for the disease. Here, we expressed and purified recombinant HlyE and YncE antigens and tested the IgG, IgA and IgM responses in 422 sera samples retrieved from acute typhoid patients, other febrile, food handlers, and healthy individuals. The results showed that HlyE-IgG, -IgA and -IgM ELISAs have a collective sensitivity of 83% while YncE-IgG and -IgA ELISAs identified 16 possible carriers based on their antibody profiles. The identification of sensitive biomarkers for typhoid carrier detection is crucial for disease eradication.

Lipoarabinomannan in Active and Passive Protection Against Tuberculosis

Glycolipids of the cell wall of Mycobacterium tuberculosis (Mtb) are important immunomodulators in tuberculosis. In particular, lipoarabinomannan (LAM) has a profound effect on the innate immune response. LAM and its structural variants can be recognized by and activate human CD1b-restricted T cells, and emerging evidence indicates that B cells and antibodies against LAM can modulate the immune response to Mtb. Anti-LAM antibodies are induced during Mtb infection and after bacille Calmette-Guerin (BCG) vaccination, and monoclonal antibodies against LAM have been shown to confer protection by passive administration in mice and guinea pigs. In this review, we describe the immune response against LAM and the potential use of the mannose-capped arabinan moiety of LAM in the construction of vaccine candidates against tuberculosis.

Emerging Themes for the Role of Antibodies in Tuberculosis

The best way to debunk a scientific dogma is to throw irrefutable evidence at it. This is especially true if the dogma in question has been nurtured over many decades, as is the case with the apparent redundancy of antibodies (Abs) against intracellular pathogens. Although not fully compelling yet, that ‘hard core’ evidence is nevertheless now slowly beginning to emerge. This is true for several clinically relevant infections but none more so than Mycobacterium tuberculosis, the archetype intracellular pathogen that poses a great health challenge to the mankind. Here, prompted by a spate of recent high-profile reports on the effects of Abs in various experimental models of tuberculosis, we step back and take a critical look at the progress that has been made in the last 5 years and highlight some of the strengths and shortcomings of the presented evidence. We conclude that the tide of the opinion has begun to turn in favour of Abs but we also caution against overinterpreting the currently available limited evidence. For, until definitive evidence that can withstand even the most rigorous of experimental tests is produced, the dogma may yet survive. Or indeed, we may find that the truth is hidden somewhere in between the dogma and the unfulfilled scientific prophecy.

Genome wide approaches discover novel Mycobacterium tuberculosis antigens as correlates of infection, disease, immunity and targets for vaccination

Every day approximately six thousand people die of Tuberculosis (TB). Its causative agent, Mycobacterium tuberculosis (Mtb), is an ancient pathogen that through its evolution developed complex mechanisms to evade immune surveillance and acquire the ability to establish persistent infection in its hosts. Currently, it is estimated that one-fourth of the human population is latently infected with Mtb and among those infected 3-10% are at risk of developing active TB disease during their lifetime. The currently available diagnostics are not able to detect this risk group for prophylactic treatment to prevent transmission. Anti-TB drugs are available but only as long regimens with considerable side effects, which could both be reduced if adequate tests were available to monitor the response of TB to treatment. New vaccines are also urgently needed to substitute or boost Bacille Calmette-Guérin (BCG), the only approved TB vaccine: although BCG prevents disseminated TB in infants, it fails to impact the incidence of pulmonary TB in adults, and therefore has little effect on TB transmission. To achieve TB eradication, the discovery of Mtb antigens that effectively correlate with the human response to infection, with the curative host response following TB treatment, and with natural as well as vaccine induced protection will be critical. Over the last decade, many new Mtb antigens have been found and proposed as TB biomarkers and vaccine candidates, but only a very small number of these is being used in commercial diagnostic tests or is being assessed as candidate TB vaccine antigens in human clinical trials, aiming to prevent infection, disease or disease recurrence following treatment. Most of these antigens were discovered decades ago, before the complete Mtb genome sequence became available, and thus did not harness the latest insights from post-genomic antigen discovery strategies and genome wide approaches. These have, for example, revealed critical phase variation in Mtb replication and accompanying gene -and therefore antigen- expression patterns. In this review, we present a brief overview of past methodologies, and subsequently focus on the most important recent Mtb antigen discovery studies which have mined the Mtb antigenome through "unbiased" genome wide approaches. We compare the results for these approaches -as far as we know for the first time-, highlight Mtb antigens that have been identified independently by different strategies and present a comprehensive overview of the Mtb antigens thus discovered.