IgA response to ESAT-6/CFP-10 and Rv2031 antigens varies in patients with culture-confirmed pulmonary tuberculosis, healthy Mycobacterium tuberculosis-infected and non-infected individuals in a tuberculosis endemic setting, Ethiopia

Prolonged survival of a patient with active MDR-TB HIV co-morbidity: insights from a Mycobacterium tuberculosis strain with a unique genomic deletion

Coinfection of HIV and multidrug-resistant tuberculosis (MDR-TB) presents significant challenges in terms of the treatment and prognosis of tuberculosis, leading to complexities in managing the disease and impacting the overall outcome for TB patients. This study presents a remarkable case of a patient with MDR-TB and HIV coinfection who survived for over 8 years, despite poor treatment adherence and comorbidities. Whole genome sequencing (WGS) of the infecting Mycobacterium tuberculosis (Mtb) strain revealed a unique genomic deletion, spanning 18 genes, including key genes involved in hypoxia response, intracellular survival, immunodominant antigens, and dormancy. This deletion, that we have called "Del-X," potentially exerts a profound influence on the bacterial physiology and its virulence. Only few similar deletions were detected in other non-related Mtb genomes worldwide. In vivo evolution analysis identified drug resistance and metabolic adaptation mutations and their temporal dynamics during the patient's treatment course.

An anti-LpqH human monoclonal antibody from an asymptomatic individual mediates protection against Mycobacterium tuberculosis

Tuberculosis (TB) is an airborne disease caused by Mycobacterium tuberculosis (Mtb). Whilst a functional role for humoral immunity in Mtb protection remains poorly defined, previous studies have suggested that antibodies can contribute towards host defense. Thus, identifying the critical components in the antibody repertoires from immune, chronically exposed, healthy individuals represents an approach for identifying new determinants for natural protection. In this study, we performed a thorough analysis of the IgG/IgA memory B cell repertoire from occupationally exposed, immune volunteers. We detail the identification and selection of a human monoclonal antibody that exhibits protective activity in vivo and show that it targets a virulence factor LpqH. Intriguingly, protection in both human ex vivo and murine challenge experiments was isotype dependent, with most robust protection being mediated via IgG2 and IgA. These data have important implications for our understanding of natural mucosal immunity for Mtb and highlight a new target for future vaccine development.

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.

IgA Serological Response for the Diagnosis of Mycobacterium abscessus Infections in Patients with Cystic Fibrosis

The immunoglobulin A (IgA) status of cystic fibrosis (CF) patients, presenting with or without a non-tuberculous mycobacterial (NTM) infection, has to date not been fully elucidated toward two antigenic preparations previously described. We have chosen to determine the clinical values of an IgA ELISA for the diagnosis of NTM and/or Mycobacterium abscessus infections in CF patients. One hundred and 73 sera from CF patients, comprising 33 patients with M. abscessus positive cultures, and 31 non-CF healthy controls were assessed. IgA levels were evaluated by indirect ELISAs using a surface antigenic extract named TLR2eF for TLR2 positive extract and a recombinant protein, the phospholipase C (rMAB_0555 or rPLC). These assays revealed a sensitivity of 52.6% (95% CI = 35.8% to 69%) and 42.1% (95% CI = 26.3% to 59.2%) using TLR2eF and rPLC, respectively, and respective specificities of 92.6% (95% CI = 87.5% to 96.1%) and 92% (95% CI = 86.7% to 95.7%) for samples culture positive for M. abscessus. Overall sensitivity and specificity of 66.7% and 85.4%, respectively, were calculated for IgA detection in M. abscessus-culture positive CF patients, when we combine the results of the two used antigens, thus demonstrating the efficiency in detection of positive cases for these two antigens with IgA isotype. CF patients with a positive culture for M. abscessus had the highest IgA titers against TLR2eF and rPLC. The diagnosis of NTM infections, including those due to M. abscessus, can be improved by the addition of an IgA serological assay, especially when cultures, for example, are negative. Based on these promising results, a serological follow-up of a larger number of patients should be performed to determine if the IgA response may be correlated with an active/acute infection state or a very recent infection. IMPORTANCE Mycobacterium abscessus is currently the most frequently isolated rapid growing mycobacterium in human pathology and the major one involved in lung infections. It has recently emerged as responsible for severe pulmonary infections in patients with cystic fibrosis (CF) or those who have undergone lung transplantation. In addition, it represents the most antibiotic resistant mycobacterial species. However, despite its increasing clinical importance, very little is known about the use of M. abscessus parietal compounds and the host response. This has led to the development of serological tests to measure the antibody response in infected patients, and potentially to link this to the culture of respiratory samples. Herein, we describe an important analysis of the serological IgA response from CF patients, and we demonstrate the full diagnostic usefulness of this assay in the diagnosis of NTM infections, and more particularly M. abscessus, in CF patients.

Diagnostic Potential of the Serological Response to Synthetic Peptides from Mycobacterium tuberculosis Antigens for Discrimination Between Active and Latent Tuberculosis Infections

Diagnosis and treatment of active tuberculosis (ATB) as well as latent tuberculosis infection (LTBI) are required for effective tuberculosis (TB) control, especially in TB endemic area. The usefulness of conventional tests to distinguish between ATB and LTBI has remained challenging. The present study was aimed to demonstrate the usefulness of the serological response to synthetic peptides from Mycobacterium tuberculosis (Mtb) antigens for discrimination between ATB and LTBI in Warao Amerindians. Serum IgG antibody levels were measured by the indirect ELISA assay using 22 designed and synthesized peptides derived from immunogenic Mtb ESAT-6 and Ag85A proteins. A total of 211 adult Warao Amerindians were included; cases with active TB (ATB, n = 75), latent TB infection (LTBI, n = 85) and non-infected (NI, n = 51). The approach’s diagnostic information was compared using receiver operating characteristic (ROC) curves. For ATB diagnostic performance between ATB and NI; ESAT-6; P-12037 had 100% of sensitivity (AUC = 0.812; 0.733 to 0.891 95% CI); and Ag85A; P-10997 had 100% of specificity (AUC = 0.691; 0.597 to 0.785 95% CI); and ATB and LTBI; Ag85A; P-29878 had 100% of sensitivity (AUC = 0.741; 0.666–0.817 95% CI), and P-29879 had 99% of specificity (AUC = 0.679; 0.593–0.765 95% CI). While that ESAT-6 P-12037 also allowed differentiation between LTBI and NI or healthy ones. It had 98.8% of sensitivity and 98.0% of specificity (AUC = 0.640; 0.545–0.735 95% CI). The potential of combination-antigen immunoassays with peptides could discriminate between Warao Amerindians with ATB, LTBI and NI. Further validation of this approach could lead to developing a complementary tool for rapid diagnosis of TB infections.

Concurrent evaluation of cytokines improves the accuracy of antibodies against Mycobacterium tuberculosis antigens in the diagnosis of active tuberculosis

BACKGROUND

Antibodies against mycobacterial proteins are highly specific, but lack sensitivity, whereas cytokines have been shown to be sensitive but not very specific in the diagnosis of tuberculosis (TB). We assessed combinations between antibodies and cytokines for diagnosing TB.

METHODS

Immuoglubulin (Ig) A and IgM antibody titres against selected mycobacterial antigens including Apa, NarL, Rv3019c, PstS1, LAM, "Kit 1" (MTP64 and Tpx)", and "Kit 2" (MPT64, Tpx and 19 kDa) were evaluated by ELISA in plasma samples obtained from individuals under clinical suspicion for TB. Combinations between the antibody titres and previously published cytokine responses in the same participants were assessed for diagnosing active TB.

RESULTS

Antibody responses were more promising when used in combination (AUC of 0.80), when all seven antibodies were combined. When anti-"Kit 1"-IgA levels were combined with five host cytokine biomarkers, the AUC increased to 97% (92-100%) with a sensitivity of 95% (95% CI, 73-100%), and specificity of 88.5% (95% CI, 68.7-97%) achieved after leave-one-out cross validation.

CONCLUSION

When used in combination, IgA titres measured with ELISA against multiple Mycobacterium tuberculosis antigens may be useful in the diagnosis of TB. However, diagnostic accuracy may be improved if the antibodies are used in combination with cytokines.

Alteration of Endocrine Hormones and Antibody Responses in Different Spectrum of Tuberculosis Disease

Effective control of Mycobacterium tuberculosis (Mtb) infection is mediated by multifaceted factors that involve both the endocrine and immune system. Profiling hormones and antibodies in different stages of TB provides insight in the pathogenesis of the disease. In this study, we profiled endocrine hormones (dehydroepiandrosterone (DHEA), cortisol, testosterone, estradiol, growth hormone and leptins) and Mtb strain H37RV lipoarabinomannan (LAM)-specific antibody levels in plasma samples, collected from pulmonary TB (PTB) patients, TB lymphadenitis (TBLN) patients and latently infected (QFT-positive) or uninfected (QFT-negative) apparently healthy individuals using ELISA. Plasma levels of leptin and DHEA were significantly low in PTB and TBLN patients compared to healthy controls (P<0.0001 and P=0.02, respectively), whereas these levels significantly increased following anti-TB treatment (P=0.002 and P=0.0001, respectively) among TB patients. The levels of estradiol and testosterone significantly improved following anti-TB treatment (P=0.03 and P=0.0003, respectively), whereas cortisol and growth hormones declined significantly (P <0.05). Similarly, LAM-specific IgG, IgM and IgA were significantly higher in PTB patients compared to other groups, whereas levels of IgG1 subtype were significantly higher among LTBI groups compared to both TB patients and QFT-negative individuals (P<0.0001). Overall, we observed significantly variable levels of endocrine hormones as well as immunoglobulins across the spectrum of TB illness and such profiling has a significant contribution in selection of effective biomarkers that have roles in TB treatment monitoring or diagnostics. Although this study did not show a functional association between hormones and antibodies, alterations in the levels of these biomarkers suggest the key roles these markers play in TB pathogenesis.

Immunological Characterization of Proteins Expressed by Genes Located in Mycobacterium tuberculosis-Specific Genomic Regions Encoding the ESAT6-like Proteins

The 6 kDa early secreted antigen target (ESAT6) is a low molecular weight and highly immunogenic protein of Mycobacterium tuberculosis with relevance in the diagnosis of tuberculosis and subunit vaccine development. The gene encoding the ESAT6 protein is located in the M. tuberculosis-specific genomic region known as the region of difference (RD)1. There are 11 M. tuberculosis-specific RDs absent in all of the vaccine strains of BCG, and three of them (RD1, RD7, and RD9) encode immunodominant proteins. Each of these RDs has genes for a pair of ESAT6-like proteins. The immunological characterizations of all the possible proteins encoded by genes in RD1, RD7 and RD9 have shown that, besides ESAT-6 like proteins, several other proteins are major antigens useful for the development of subunit vaccines to substitute or supplement BCG. Furthermore, some of these proteins may replace the purified protein derivative of M. tuberculosis in the specific diagnosis of tuberculosis by using interferon-gamma release assays and/or tuberculin-type skin tests. At least three subunit vaccine candidates containing ESAT6-like proteins as antigen components of multimeric proteins have shown efficacy in phase 1 and phase II clinical trials in humans.

IgA and FcαRI: Versatile Players in Homeostasis, Infection, and Autoimmunity

Mucosal surfaces constitute the frontiers of the body and are the biggest barriers of our body for the outside world. Immunoglobulin A (IgA) is the most abundant antibody class present at these sites. It passively contributes to mucosal homeostasis via immune exclusion maintaining a tight balance between tolerating commensals and providing protection against pathogens. Once pathogens have succeeded in invading the epithelial barriers, IgA has an active role in host-pathogen defense by activating myeloid cells through divers receptors, including its Fc receptor, FcαRI (CD89). To evade elimination, several pathogens secrete proteins that interfere with either IgA neutralization or FcαRI-mediated immune responses, emphasizing the importance of IgA-FcαRI interactions in preventing infection. Depending on the IgA form, either anti- or pro-inflammatory responses can be induced. Moreover, the presence of excessive IgA immune complexes can result in continuous FcαRI-mediated activation of myeloid cells, potentially leading to severe tissue damage. On the one hand, enhancing pathogen-specific mucosal and systemic IgA by vaccination may increase protective immunity against infectious diseases. On the other hand, interfering with the IgA-FcαRI axis by monovalent targeting or blocking FcαRI may resolve IgA-induced inflammation and tissue damage. This review describes the multifaceted role of FcαRI as immune regulator between anti- and pro-inflammatory responses of IgA, and addresses potential novel therapeutic strategies that target FcαRI in disease.

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Nutritional status positively impacts humoral immunity against its Mycobacterium tuberculosis, disease progression, and vaccine development

Nutritional status contributes to the regulation of immune responses against pathogens, and malnutrition has been considered as a risk factor for tuberculosis (TB). Mycobacterium tuberculosis (Mtb), the causative agent of TB, can modulate host lipid metabolism and induce lipid accumulation in macrophages, where the bacilli adopt a dormant phenotype. In addition, serum lipid components play dual roles in the regulation of and protection from Mtb infection. We analyzed the relationship between nutritional status and the humoral immune response in TB patients. We found that serum HDL levels are positively correlated with the serum IgA specific for Mtb antigens. Analysis of the relationship between serum nutritional parameters and clinical parameters in TB patients showed that serum albumin and CRP levels were negatively correlated before treatment. We also observed reduced serum LDL levels in TB patients following treatment. These findings may provide insight into the role of serum lipids in host immune responses against Mtb infection. Furthermore, improving the nutritional status may enhance vaccination efficacy.

Diagnostic Potential of IgG and IgA Responses to Mycobacterium tuberculosis Antigens for Discrimination among Active Tuberculosis, Latent Tuberculosis Infection, and Non-Infected Individuals

Tuberculosis remains a major public health problem. Conventional tests are inadequate to distinguish between active tuberculosis (ATB) and latent tuberculosis infection (LTBI). We measured antibody responses to Mycobacterium tuberculosis antigens (Mycobacterium tuberculosis chorismate mutase (TBCM), antigen 85B (Ag85B), early secreted antigen-6 (ESAT-6), and culture filtrate protein-10 (CFP-10) in ATB, LTBI, and non-infected (NI) individuals. Serum immunoglobulin G (IgG) and immunoglobulin A (IgA) levels were measured and the QuantiFERON-TB Gold In-Tube assay was used to diagnose LTBI. IgG levels against TBCM were significantly higher in LTBI than NI subjects. IgG and IgA levels against Ag85B and IgG levels against CFP-10 were significantly higher in ATB, followed by LTBI, and then NI. When the ATB group was subdivided, IgG levels against Ag85B and CFP-10 were significantly higher in each subgroup compared with those in LTBI and NI groups. Positive correlation trends between interferon-gamma and IgG levels against Ag85B, TBCM, and CFP-10 and IgA levels against Ag85B in LTBI and NI subjects were observed. Age- and sex-adjusted models showed that IgG against TBCM and CFP-10 was independently related to LTBI diagnosis, and IgG against Ag85B was independently related to the diagnosis of ATB and could distinguish between LTBI and ATB. Overall, IgG antibody responses to TBCM, Ag85B, and CFP-10 can discriminate among ATB, LTBI, and NI groups.

Use of DosR Dormancy Antigens from Mycobacterium tuberculosis for Serodiagnosis of Active and Latent Tuberculosis

As more than two billion people possibly have a latent tuberculosis (LTB) infection, early LTB diagnosis is crucial for the efficient control and elimination of tuberculosis (TB). The aim of this study is to detect the serum antibody responses to dormancy-related DosR regulon antigens of Mycobacterium tuberculosis for the diagnosis of active and latent TB infections. A membrane array with 25 latency antigens detected by silver-enhanced gold nanoparticles was used to determine the corresponding cognate antibody levels in clinical serum samples from healthy controls, TB patients, and individuals with LTB. The array is sized to fit into a 24-well ELISA plate and follows an ELISA-like experimental procedure without expensive instrumentation. Linear discriminant analysis (LDA) of the resulting antibody profiling data set identified a panel of nine DosR antigens with significant discriminatory capability among different subjects with ≥90% sensitivity, specificity, and overall accuracy. Furthermore, the high predictive performance validated by an independent test sample set reflects the robustness and reliability of the LDA classification model. Our current data demonstrate that the nine DosR antigen combination associated with the proposed membrane array platform is a clinically feasible approach for distinguishing different TB infection statuses. The proposed methodology in this study could be further developed for multiple disease serodiagnoses with high sensitivity and specificity.

Immune responses to Mycobacterium tuberculosis membrane-associated antigens including alpha crystallin can potentially discriminate between latent infection and active tuberculosis disease

Changes in expression of membrane antigens may accompany the transition of Mycobacterium tuberculosis (Mtb) from ‘dormant’ to ‘active’ states. We have determined whether antibody and T cell responses to Mtb membrane (MtM)-associated antigens, especially the latency-induced protein alpha crystallin (Acr), can discriminate between latent tuberculosis infection (LTBI) and active TB (ATB) disease. Study subjects comprised a previously described cohort of healthcare workers (HCWs, n = 43) and smear-positive ATB patients (n = 10). HCWs were further categorized as occupational contacts (OC, n = 30), household contacts of TB (HC, n = 8) and cured TB (CTB, n = 5). Levels (ΔOD) of serum antibody isotypes (IgG, IgA and IgM) were determined by ELISA and blood T cell proliferative responses were determined by flow cytometry using Ki67 protein as marker for DNA synthesis. Antibodies to MtM and Acr were predominantly IgG and their levels in HCWs and ATB did not differ significantly. However, HCWs showed a significantly higher level of anti-MtM IgM and a significantly lower level of anti-Acr IgA antibodies than the ATB patients. Also, a larger proportion of HCWs showed a high (>1) ΔOD_Acr/ΔOD_MtM ratio for IgG. HCWs also showed a higher, though not significantly different from ATB, avidity of anti-MtM (IgG) antibodies. A higher proportion of HCWs (35% of OC, 62.5% of HC and 20% of CTB), compared with ATB (10%) showed a positive T cell response to Acr along with significant difference (P <0.05) between HC and ATB. A significant correlation (r = 0.60, P <0.0001) was noted between T cell responses of HCWs towards Acr and MtM (reported earlier by us) and both responses tended to decline with rising exposure to the infection. Even so, positive responses to Acr (38.5%) were significantly lower than to MtM (92%). Neither antibody nor T cell responses to either antigen appeared affected by BCG vaccination or reactivity to tuberculin. Results of the study suggest that the levels of IgM antibodies to MtM, IgA antibodies to Acr and proliferative T cell responses to both the antigens can potentially discriminate between LTBI and active TB disease. They also underscore the necessity of SOPs for antibody assays.

The Mycobacterial HBHA Protein: A Promising Biomarker for Tuberculosis

A major goal in tuberculosis (TB) research is the identification, among the subjects infected with Mycobacterium tuberculosis (Mtb), of those with active TB, or at higher risk of developing active disease, from the latently infected subjects. The classical heterogeneity of Mtb infection and TB disease is a major obstacle toward the identification of reliable biomarkers that can stratify Mtb infected subjects based on disease risk. The heparin-binding haemagglutinin (HBHA) is a mycobacterial surface antigen that is implicated in tuberculosis (TB) pathogenesis. The host immune response against HBHA varies depending on the TB status and several studies are supporting the role of HBHA as a useful biomarker of TB.

Longitudinal Evaluation of Humoral Immunity and Bacterial and Clinical Parameters Reveals That Antigen-Specific Antibodies Suppress Inflammatory Responses in Active Tuberculosis Patients

A novel tuberculosis vaccine to replace BCG has long been desired. However, recent vaccine trials focused on cell-mediated immunity have failed to produce promising results. It is worth noting that most commercially available successful vaccines rely on humoral immunity. To establish a basic understanding of humoral immunity against tuberculosis, we analyzed and evaluated longitudinal levels and avidity of immunoglobulin to various tuberculosis antigens compared with bacterial and clinical parameters during treatment. We found that levels of IgG antibodies against HrpA and HBHA prior to treatment exhibited a positive correlation with bacterial burden. Analysis of changes in CRP during treatment revealed an association with high levels of specific IgG and IgA antibodies against mycobacterial antigens. Levels of CRP prior to treatment were negatively associated with IgG avidity to CFP-10 and MDP1 and IgA avidity to HrpA, while IgA avidity to MDP1 and Acr exhibited a negative correlation with CRP levels after 60 days of treatment. These results may provide insight for the development of a novel tuberculosis (TB) vaccine candidate to induce protective humoral immunity against tuberculosis.

Detection of a combination of serum IgG and IgA antibodies against selected mycobacterial targets provides promising diagnostic signatures for active TB

Immunoglobulin G (IgG) based tests for the diagnosis of active tuberculosis (TB) disease often show a lack of specificity in TB endemic regions, which is mainly due to a high background prevalence of LTBI. Here, we investigated the combined performance of the responses of different Ig classes to selected mycobacterial antigens in primary healthcare clinic attendees with signs and symptoms suggestive of TB. The sensitivity and specificity of IgA, IgG and/or IgM to LAM and 7 mycobacterial protein antigens (ESAT-6, Tpx, PstS1, AlaDH, MPT64, 16kDa and 19kDa) and 2 antigen combinations (TUB, TB-LTBI) in the plasma of 63 individuals who underwent diagnostic work-up for TB after presenting with symptoms and signs compatible with possible active TB were evaluated. Active TB was excluded in 42 individuals of whom 21 has LTBI whereas active TB was confirmed in 21 patients of whom 19 had a follow-up blood draw at the end of 6-month anti-TB treatment. The leading single serodiagnostic markers to differentiate between the presence or absence of active TB were anti-16 kDa IgA, anti-MPT64 IgA with sensitivity and specificity of 90%/90% and 95%/90%, respectively. The combined use of 3 or 4 antibodies further improved this performance to accuracies above 95%. After successful completion of anti-TB treatment at month 6, the levels of 16 kDa IgA and 16 kDa IgM dropped significantly whereas LAM IgG and TB-LTBI IgG increased. These results show the potential of extending investigation of anti-tuberculous IgG responses to include IgM and IgA responses against selected protein and non-protein antigens in differentiating active TB from other respiratory diseases in TB endemic settings.

L. M. C. F, Ottenhoff THM. IgA and IgG against Mycobacterium tuberculosis Rv2031 discriminate between pulmonary tuberculosis patients, Mycobacterium tuberculosis-infected and non-infected individuals

As part of a major project to investigate protective and diagnostic immune markers against tuberculosis (TB), we measured antibody isotype responses to Mycobacterium tuberculosis (Mtb) antigens (LAM, Rv2031, and HBHA) in cohorts of 149 pulmonary tuberculosis patients (PTBP), 148 household contacts (HHCs), and 68 community controls (CCs) in an endemic setting. ELISA was used to measure levels of IgA, IgG, and IgM from sera of cohorts at baseline, and at 6 and 12 months from entry. The results show that there were significant differences in IgA, IgG, and IgM responses to the different antigens and in the three cohorts. At baseline, the level of IgM against RV2031 and LAM did not vary between cohorts, but the levels of IgA and IgG against Rv2031 were significantly higher in PTB patients than HHCs and CCs, followed by HHCs, and the lowest in CCs. In patients, there was a significant variation in antibody responses before and after chemotherapy. The levels of IgA and IgG against HBHA, and IgA against Rv2031 decreased significantly and remained low, while IgA and IgG against LAM increased significantly and remained high following chemotherapy. However, the levels of IgM against Rv2031 and LAM increased at 6 months but decreased again at 12 months. IgM against HBHA did not show any significant variation before and after chemotherapy. Similarly, there were also significant variations in antibody responses in HHCs over time. Our results show that there are significant variations in IgA, IgG and IgM responses to the different antigens and in the three cohorts, implying that not all antibody isotype responses are markers of clinical TB. In addition, the current and previous studies consistently show that IgA and IgG against Rv2031 discriminate between clinical disease, Mtb-infected and non-infected individuals.

Determination of Lipoprotein Z-Specific IgA in Tuberculosis and Latent Tuberculosis Infection

Tuberculosis (TB) remains one of the most severe infectious diseases. It is still of paramount importance to establish more accurate, rapid, and efficient diagnostic methods. Since infection with Mycobacterium tuberculosis (M. tb) is largely mediated through the respiratory tract, IgA responses against mycobacterial proteins are worthy of investigation for their potential clinical utility. In this study, the IgA response targeting lipoprotein Z (LppZ) was determined by using a homemade ELISA with plasma of TB patients (N = 125), LTBI individuals (N = 92), healthy controls (HCs) (N = 165), as well as TB patients undergoing anti-TB treatment (N = 9). In parallel the antigen-specific IFN-γ release from PBMCs triggered by LppZ and M. tb-specific ESAT-6 or CFP-10 was detected by using an ELISPOT assay. It was found that the LppZ-specific IgA level was dramatically higher in TB patients than in HCs (p < 0.0001). Compared to that before anti-TB treatment, the LppZ-specific IgA level decreased substantially after 2 months of anti-TB treatment (p = 0.0297) and remained at low levels until the end of the treatment. What is more, pulmonary TB patients exhibited significantly higher LppZ-specific IgA-values than extra-pulmonary TB patients (p = 0.0296). Interestingly, the LppZ-specific IgA-values were negatively correlated to the amounts of IFN-γ released in response to LppZ with statistical significance (r = -0.5806, p = 0.0002). LppZ-specific IgA level was also higher in LTBI individuals than in HCs (p < 0.0001). Additionally there were some PPD⁺ HC individuals with high LppZ-specific IgA levels but the potential of this assay for identifying leaky LTBI in PPD⁺ HCs needs to be further investigated through follow-up studies. The sensitivity of detecting TB solely with ESAT-6 or CFP-10-specific IFN-γ release was increased by including the LppZ-specific IgA results, respectively, from 86.11 to 100% and 88.89 to 100%; the sensitivity of screening for LTBI was increased from 80.36 to 83.93% and 57.14 to 69.64%, respectively. The higher LppZ-specific IgA responses in TB and LTBI populations than in controls indicated high immunoreactivity to LppZ upon M. tb infection. Although the assay was not efficient enough for independent application in sero-diagnosis, LppZ-specific IgA might become a complementary biomarker for the improvement of TB and LTBI screening.

The dynamics of immune responses to Mycobacterium tuberculosis during different stages of natural infection: A longitudinal study among Greenlanders

Objective

Understanding human immunity to Mycobacterium tuberculosis (Mtb) during different stages of infection is important for development of an effective tuberculosis (TB) vaccine. We aimed to evaluate immunity to Mtb infection by measuring immune responses to selected Mtb antigens expressed during different stages of infection over time and to observe sustainability of immunity.

Methods

In a cohort study comprising East Greenlanders aged 17–22 years (2012 to 2014) who had either; undetectable Mtb infection, ongoing or prior Mtb infection at enrolment, we measured immunity to 15 antigens over a one-year period. Quantiferon-TB Gold testing (QFT) defined Mtb infection status (undetected/detected). The eligible study population of East Greenlanders aged 17–22 years was identified from the entire population using the Civil Registration System. From the source population 65 participants were selected by stratified random sampling according to information on Mtb infection stage. Retrospective and prospective information on notified TB (including treatment) was obtained through the mandatory TB notification system and was used to characterise Mtb infection stage (ongoing/prior). Immunity to 15 antigens including two QFT antigens, PPD and 12 non-QFT antigens (representing early, constitutive and latent Mtb infection) was assessed by measuring immune responses using whole-blood antigen stimulation and interferon gamma measurement.

Results

Of 65 participants, 54 were considered Mtb-infected. Immunity to Mtb infection fluctuated with high annual risk of conversion (range: 6–69%) and reversion (range: 5–95%). During follow-up, five (8%) participants were notified with TB; neither conversion nor reversion was associated with an increased risk of progressing to TB.

Conclusions

Our findings suggest that human immunity to natural Mtb infection over time is versatile with fluctuations, resulting in high levels of conversion and reversion of immunity, thus human immunity to Mtb is much more dynamic than anticipated. The study findings suggest future use of longitudinal assessment of immune responses when searching for TB vaccine candidate antigens.

Early Secreted Antigenic Target of 6-kDa of Mycobacterium tuberculosis Stimulates IL-6 Production by Macrophages through Activation of STAT3

As early secreted antigenic target of 6 kDa (ESAT-6) of Mycobacterium tuberculosis (Mtb) is an essential virulence factor and macrophages are critical for tuberculosis infection and immunity, we studied ESAT-6 stimulated IL-6 production by macrophages. ESAT-6 stimulated significantly higher IL-6 secretion by murine bone marrow derived macrophages (BMDM) compared to culture filtrate protein 10 kDa (CFP10) and antigen 85A. Polymyxin B, an LPS blocker, did not affect ESAT-6 stimulated macrophage IL-6 production. ESAT-6 but not Pam3CSK4 induced IL-6 by TLR2 knockout BMDM. ESAT-6 induced phosphorylation and DNA binding of STAT3 and this was blocked by STAT3 inhibitors but not by rapamycin. STAT3 inhibitors suppressed ESAT-6-induced IL-6 transcription and secretion without affecting cell viability. This was confirmed by silencing STAT3 in macrophages. Blocking neither IL-6Rα/IL-6 nor IL-10 affected ESAT-6-induced STAT3 activation and IL-6 production. Infection of BMDM and human macrophages with Mtb with esat-6 deletion induced diminished STAT3 activation and reduced IL-6 production compared to wild type and esat-6 complemented Mtb strains. Administration of ESAT-6 but not CFP10 induced STAT3 phosphorylation and IL-6 expression in the mouse lungs, consistent with expression of ESAT-6, IL-6 and phosphorylated-STAT3 in Mtb-infected mouse lungs. We conclude that ESAT-6 stimulates macrophage IL-6 production through STAT3 activation.

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.

Evaluation of Humoral Immunity to Mycobacterium tuberculosis-Specific Antigens for Correlation with Clinical Status and Effective Vaccine Development

Although tuberculosis remains a major global health problem, Bacille Calmette-Guérin (BCG) is the only available vaccine. However, BCG has limited applications, and a more effective vaccine is needed. Cellular mediated immunity (CMI) is thought to be the most important immune response for protection against Mycobacterium tuberculosis (Mtb). However, the recent failure of a clinical trial for a booster BCG vaccine and increasing evidence of antibody-mediated immunity prompted us to evaluate humoral immunity to Mtb-specific antigens. Using Enzyme-Linked ImmunoSpot and Enzyme-Linked ImmunoSorbent Assays, we observed less correlation of both CMI and IgG titers with patient clinical status, including serum concentration of C reactive protein. However, IgA titers against Mtb were significantly correlated with clinical status, suggesting that specific IgA antibodies protect against Mtb proliferation. In addition, in some cases, IgA antibody titers were significantly associated with the serum concentration of total albumin, which supports the idea that humoral immunity can be influenced by the nutritional status. Based on these observations, we propose that the induction of humoral immunity should be included as an option in TB vaccine development strategies.

A Subgroup of Latently Mycobacterium tuberculosis Infected Individuals Is Characterized by Consistently Elevated IgA Responses to Several Mycobacterial Antigens

Elevated antibody responses to Mycobacterium tuberculosis antigens in individuals with latent infection (LTBI) have previously been linked to an increased risk for progression to active disease. Studies in the field focussed mainly on IgG antibodies. In the present study, IgA and/or IgG responses to the mycobacterial protein antigens AlaDH, NarL, 19 kDa, PstS3, and MPT83 were determined in a blinded fashion in sera from 53 LTBI controls, 14 healthy controls, and 42 active TB subjects. Among controls, we found that elevated IgA levels against all investigated antigens were not randomly distributed but concentrated on a subgroup of <30%—with particular high levels in a small subgroup of ~5% comprising one progressor to active TB. Based on a specificity of 100%, anti-NarL IgA antibodies achieved with 78.6% sensitivity the highest accuracy for the detection of active TB compared to healthy controls. In conclusion, the consistently elevated IgA levels in a subgroup of controls suggest higher mycobacterial load, a risk factor for progression to active TB, and together with high IgG levels may have prognostic potential and should be investigated in future large scale studies. The novel antigen NarL may also be promising for the antibody-based diagnosis of active TB cases.

An evaluation of the use of immunoglobulin A antibody response against mycobacterial antigens for the diagnosis of Mycobacterium bovis infection in cattle

Antibody responses are useful indicators of Mycobacterium bovis infection in cattle. Many studies have evaluated the ability of immunoglobulin G (IgG) to serodiagnose bovine tuberculosis (TB). In the current study, immunoglobulin A (IgA) and IgG responses against the MPB70 and MPB83 antigens of M. bovis, the 38 kDa phosphate-binding lipoprotein (PstS1) that is a well-known serodiagnostic M. tuberculosis antigen, and a newly identified protein, termed Rv1483c, were compared in M. bovis-infected and noninfected cattle as well as in field samples. The diagnostic utility of the IgA antibody to MPB70 and MPB83 for bovine TB was superior or comparable to that of the IgG antibody, and the sensitivity of serodiagnosis increased when the results of antigen binding by IgA and IgG were combined. The sensitivities of the IgG and IgA antibodies to the Rv1483c and PstS1 proteins were significantly lower than those to MPB70 and MPB83, and no diagnostic utility for Rv1483c was observed in field samples. Importantly, the IgA antibody reacted strongly to the MPB70 and MPB83 antigens and differentiated cattle with TB from healthy cattle in a multiantigen printed immunoassay. The results of this study support the feasibility of using IgA antibody against the MPB70 and MPB83 antigens to detect bovine TB. In addition, approaches using assays for both IgA and IgG antibodies may increase detection accuracy.

A Mycobacterium bovis BCG-naked DNA prime-boost vaccination strategy induced CD4⁺ and CD8⁺ T-cell response against Mycobacterium tuberculosis immunogens

Mycobacterium tuberculosis infection is still a major global public health problem. Presently the only tuberculosis (TB) vaccine available is Bacille Calmette-Guérin (BCG), although it fails to adequately protect against pulmonary TB in adults. To solve this problem, the development of a new effective vaccine is urgently desired. BCG-prime DNA-booster vaccinations strategy has been shown to induce greater protection against tuberculosis (TB) than BCG alone. Some studies have demonstrated that the two genes (Rv1769 and Rv1772) are excellent T-cell antigens and could induce T-cell immune responses. In this research, we built BCG-C or BCG-P prime-recombination plasmid PcDNA3.1-Rv1769 or PcDNA3.1-Rv1772 boost vaccinations strategy to immunize BALB/c mice and evaluated its immunogenicity. The data suggests that the BCG-C+3.1-72 strategy could elicit the most long-lasting and strongest Th1-type cellular immune responses and the BCG-C+3.1-69 strategy could induce the high level CD8+ T-cell response at certain time points. These findings support the ideas that the prime-boost strategy as a combination of vaccines may be better than a single vaccine for protection against tuberculosis.