Progress in serodiagnosis of Mycobacterium tuberculosis infection

A novel Mycobacterium Tuberculosis antigen, MTB48 enhances inflammatory response in LPS-induced RAW264.7 macrophage immune cells

Mtb (Mycobacterium tuberculosis) is a pathogenic bacterium that causes tuberculosis infection (TB). Mtb-secreted proteins have recently been investigated as virulence factors, as well as therapeutic and vaccine possibilities. The early-secreted antigen target MTB48 is one of these proteins that has been explored as a cocktail antigen in the serodiagnosis of active tuberculosis. However, there exists no information about the function or control of MTB48's inflammatory activity in macrophages at the site of inflammation. As a result, the goal of this research was to figure out what processes are involved in MTB48's function. MTB48 stimulated inflammation in LPS induced macrophages at both the protein and mRNA levels, which was interesting. MTB48 aided LPS induced IB phosphorylation and NF-κB translocation. MTB48 also led to the phosphorylation of MAPK signaling protein. These findings imply that MTB48 can enhance inflammatory activity via NF-κB and MAPK signaling by upregulating COX-2, iNOS, NO and PGE2. Many tuberculosis antigens have been tested for the development of rapid serological diagnosis. The results of this study suggest that MTB48 is a very high conservative antigen and is a major factor causing inflammatory reactions, suggesting that it can help control and diagnose tuberculosis.

Antibodies as clinical tools for tuberculosis

Tuberculosis (TB) is a leading cause of morbidity and mortality worldwide. Global research efforts to improve TB control are hindered by insufficient understanding of the role that antibodies play in protective immunity and pathogenesis. This impacts knowledge of rational and optimal vaccine design, appropriate diagnostic biomarkers, and development of therapeutics. Traditional approaches for the prevention and diagnosis of TB may be less efficacious in high prevalence, remote, and resource-poor settings. An improved understanding of the immune response to the causative agent of TB, Mycobacterium tuberculosis (Mtb), will be crucial for developing better vaccines, therapeutics, and diagnostics. While memory CD4+ T cells and cells and cytokine interferon gamma (IFN-g) have been the main identified correlates of protection in TB, mounting evidence suggests that other types of immunity may also have important roles. TB serology has identified antibodies and functional characteristics that may help diagnose Mtb infection and distinguish between different TB disease states. To date, no serological tests meet the World Health Organization (WHO) requirements for TB diagnosis, but multiplex assays show promise for improving the sensitivity and specificity of TB serodiagnosis. Monoclonal antibody (mAb) therapies and serum passive infusion studies in murine models of TB have also demonstrated some protective outcomes. However, animal models that better reflect the human immune response to Mtb are necessary to fully assess the clinical utility of antibody-based TB prophylactics and therapeutics. Candidate TB vaccines are not designed to elicit an Mtb-specific antibody response, but evidence suggests BCG and novel TB vaccines may induce protective Mtb antibodies. The potential of the humoral immune response in TB monitoring and control is being investigated and these studies provide important insight into the functional role of antibody-mediated immunity against TB. In this review, we describe the current state of development of antibody-based clinical tools for TB, with a focus on diagnostic, therapeutic, and vaccine-based applications.

The PE-PPE Family of Mycobacterium tuberculosis: Proteins in Disguise

Mycobacterium tuberculosis has thrived in parallel with humans for millennia, and despite our efforts, M. tuberculosis continues to plague us, currently infecting a third of the world's population. The success of M. tuberculosis has recently been attributed, in part, to the PE-PPE family; a unique collection of 168 proteins fundamentally involved in the pathogenesis of M. tuberculosis. The PE-PPE family proteins have been at the forefront of intense research efforts since their discovery in 1998 and whilst our knowledge and understanding has significantly advanced over the last two decades, many important questions remain to be elucidated. This review consolidates and examines the vast body of existing literature regarding the PE-PPE family proteins, with respect to the latest developments in elucidating their evolution, structure, subcellular localisation, function, and immunogenicity. This review also highlights significant inconsistencies and contradictions within the field. Additionally, possible explanations for these knowledge gaps are explored. Lastly, this review poses many important questions, which need to be addressed to complete our understanding of the PE-PPE family, as well as highlighting the challenges associated with studying this enigmatic family of proteins. Further research into the PE-PPE family, together with technological advancements in genomics and proteomics, will undoubtedly improve our understanding of the pathogenesis of M. tuberculosis, as well as identify key targets/candidates for the development of novel drugs, diagnostics, and vaccines.

Gene Expression Study of Host and Mycobacterium tuberculosis Interactions in the Manifestation of Acute Tuberculosis

Mycobacterium tuberculosis (M.tb) could induce type IV hypersensitivity. The chemotaxis of the leukocytes toward the site of infection and producing matrix metalloproteinases (MMPs) are key factors in the immune pathogenesis of tuberculosis (TB). Mononuclear cells were isolated from bronchoalveolar lavage (BAL) specimens, and the target from genomic DNA was used for qPCR TB diagnosis and cDNA for specific RT-qPCR gene expression. The subjects were then classified into TB⁺ and TB^- groups, and the expression levels of CFP-10, ESAT-6, CCR1, CCR12 and MMP3,9 were evaluated. The mean level of CCR1 expression in TB⁺ and TB^- patients' BAL was 1.71 ± 0.78 and 0.5 ± 0.22, respectively, which was statistically different (p = 0.01). The CCR2 level, in TB⁺ (2.07 ± 1.4), was higher than in TB^- patients (1.42 ± 0.89, p = 0.01). The MMP9 expression in TB⁺ was 2.56 ± 0.68, also higher than in TB^- patients (1.13 ± 0.35), while MMP3 was lower in TB⁺ (0.22 ± 0.09) than in TB^- (0.64 ± 0.230, p = 0.05). The CCR2/CCR1 and MMP3/MMP9 balance in TB⁺ were reduced, compared to the TB^-. The CFP-10 and ESAT-6 were highly expressed in TB⁺ patients. The CFP-10 expression had a strong negative correlation with albumin (r =  - 0.93, p = 0.001), and a negative correlation with neutrophil (r =  - 0.444, p = 0.1 with 90% CI). The MMP-9 expression showed a positive correlation with WBC count (r = 0.61, p = 0.02), in TB⁺, and had a negative correlation with BMI (r = 0.59, p = 0.02) in TB^-. The M.tb CFP-10 might be implicated in lowering CCR2 and MMP3 expression in favour of M.tb dissemination. Moreover, the balance of CCR2/CCR1 and MMP3/MMP9 can be used as prognostic factors in the severity of TB.

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.

Diagnosis of osteoarticular tuberculosis by immuno-PCR assay based on mycobacterial antigen 85 complex detection

Diagnosis of osteoarticular tuberculosis (OATB) exhibits serious challenges owing to paucibacillary nature of specimens and localization of disease at sites that are difficult to access. We recently developed indirect immuno-PCR (I-PCR) and real-time I-PCR (RT-I-PCR) assays for the detection of mycobacterial antigen 85 complex (Ag85) in OATB patients. Detection limits for the purified Ag85 protein were found to be 1 and 41 fg ml^-1 by I-PCR and RT-I-PCR, respectively, which were at least 10⁵ -fold lower than respective ELISA. While spiking synovial fluids of non-TB control subjects with the purified Ag85 protein, LODs of 100 and 120 fg ml^-1 were obtained by I-PCR and RT-I-PCR, respectively, thus demonstrating the sample matrix effect. Sensitivities of 87·5 and 70·5% were observed in bodily fluids of confirmed (n = 8) and clinically suspected (n = 51) OATB cases, respectively, by I-PCR, with a specificity of 93·9% (n = 33). Markedly, the sensitivities obtained by I-PCR/RT-I-PCR were significantly higher (P < 0·05-0·01) than ELISA and GeneXpert assay (n = 30). However, no substantial difference in sensitivity was observed between the I-PCR and RT-I-PCR assays. After further improving the accuracy of I-PCR, this test may lead to development of an attractive diagnostic kit.

Serological biomarkers for the diagnosis of Mycobacterium abscessus infections in cystic fibrosis patients

BACKGROUND

Culture conditions sometimes make it difficult to detect non-tuberculous mycobacteria (NTM), particularly Mycobacterium abscessus, an emerging cystic fibrosis (CF) pathogen. The diagnosis of NTM positive cases not detected by classical culture methods might benefit from the development of a serological assay.

METHODS

As part of a diagnostic accuracy study, a total of 173 sera CF-patients, including 33 patients with M. abscessus positive cultures, and 31 non-CF healthy controls (HC) were evaluated. Four M. abscessus antigens were used separately, comprising two surface extracts (Interphase (INP) and a TLR2 positive extract (TLR2eF)) and two recombinant proteins (rMAB_2545c and rMAB_0555 also known as the phospholipase C (rPLC)).

RESULTS

TLR2eF and rPLC were the most efficient antigens to discriminate NTM-culture positive CF-patients from NTM-culture negative CF-patients. The best clinical values were obtained for the detection of M. abscessus-culture positive CF-patients; with sensitivities for the TLR2eF and rPLC of 81.2% (95% CI:65.7-92.3%) and 87.9% (95% CI:71.9-95.6%) respectively, and specificities of 88.9% (95% CI:85.3-94.8%) and 84.8% (95% CI:80.6-91.5%) respectively. When considering as positive all sera, giving a positive response in at least one of the two tests, and, as negative, all sera negative for both tests, we obtained a sensitivity of 93.9% and a specificity of 80.7% for the detection of M. abscessus-culture positive CF-patients.

CONCLUSION

High antibody titers against TLR2eF and rPLC were obtained in M. abscessus-culture positive CF-patients, allowing us to consider these serological markers as potential tools in the detection of CF-patients infected with M. abscessus.

Microarray-based selection of a serum biomarker panel that can discriminate between latent and active pulmonary TB

Bacterial culture of M. tuberculosis (MTB), the causative agent of tuberculosis (TB), from clinical specimens is the gold standard for laboratory diagnosis of TB, but is slow and culture-negative TB cases are common. Alternative immune-based and molecular approaches have been developed, but cannot discriminate between active TB (ATB) and latent TB (LTBI). Here, to identify biomarkers that can discriminate between ATB and LTBI/healthy individuals (HC), we profiled 116 serum samples (HC, LTBI and ATB) using a protein microarray containing 257 MTB secreted proteins, identifying 23 antibodies against MTB antigens that were present at significantly higher levels in patients with ATB than in those with LTBI and HC (Fold change > 1.2; p < 0.05). A 4-protein biomarker panel (Rv0934, Rv3881c, Rv1860 and Rv1827), optimized using SAM and ROC analysis, had a sensitivity of 67.3% and specificity of 91.2% for distinguishing ATB from LTBI, and 71.2% sensitivity and 96.3% specificity for distinguishing ATB from HC. Validation of the four candidate biomarkers in ELISA assays using 440 serum samples gave consistent results. The promising sensitivity and specificity of this biomarker panel suggest it merits further investigation for its potential as a diagnostic for discriminating between latent and active TB.

TB or not to be: what specificities and impact do antibodies have during tuberculosis?

Tuberculosis, an infectious disease caused by Mycobacterium tuberculosis (Mtb), is a major cause of global morbidity and mortality. The primary barrier to the development of an effective tuberculosis vaccine is our failure to fully understand the fundamental characteristics of a protective immune response. There is an increasing evidence that mobilization of antibody and B cell responses during natural Mtb infection and vaccination play a role in host protection. Several studies have assessed the levels of Mtb-specific antibodies induced during active disease as well as the potential of monoclonal antibodies to modulate bacterial growth in vitro and in vivo. A major limitation of these studies, however, is that the specific antigens capable of eliciting humoral responses are largely unknown. As a result, information about antibody dynamics and function, which might fundamentally transform our understanding of host Mtb immunity, is missing. Importantly, Mtb infection also induces the recruitment, accumulation and colocalization of B and T cells in the lung, which are positively correlated with protection in humans and animal models of disease. These ectopic lymphoid tissues generally support local germinal center reactions for the proliferation and ongoing selection of effector and memory B cells in the mucosa. Efforts to leverage such responses for human health, however, require a more complete understanding of how antibodies and B cells contribute to the local and systemic host Mtb immunity.

ESAT-6 and Ag85A Synthetic Peptides as Candidates for an Immunodiagnostic Test in Children with a Clinical Suspicion of Tuberculosis

Background

Tuberculosis (TB) is being underdetected in children as most are smear-negative. This work was aimed at evaluating ESAT-6 and Ag85A synthetic peptides' serodiagnostic potential for diagnosing children having a clinical suspicion of TB.

Methods

The study involved 438 children: 77 Creole nonindigenous (13 suspected of having TB and 64 healthy ones) and 361 Warao indigenous children (39 suspected of TB and 322 healthy children). The approach's diagnostic information was compared using operational characteristics and receiver-operating characteristic (ROC) curves.

Results

Ag85A P-29879 had 94.6% sensitivity (AUC = 0.741: 0.651 to 0.819 95% CI) in indigenous children. ESAT-6 P-12036 and P-12037 had 100% and 92.3% of sensitivity (AUC = 0.929: 0.929: 0.846 to 0.975 95% CI and 0.791: 63.9 to 98.7 95% CI, respectively) in Creole children. ESAT-6 peptides also allowed a differentiation between children with TB and healthy ones.

Conclusions

Further validation of this approach could lead to developing a complementary tool for rapid TB diagnosis in children.

emPAI-assisted strategy enhances screening and assessment of Mycobacterium tuberculosis infection serological markers

Discovering new serological markers of Mycobacterium tuberculosis (MTB) infection and establishing a rapid and efficient detection technology is of great significance for the prevention and control of tuberculosis. In this study, we established an exponentially modified protein abundance index (emPAI) value-assisted strategy to investigate and improve the screening efficiency of serological biomarkers of tuberculosis. First, we used LC-MS/MS to analyse MTB culture filtrate proteins (MTB-CFPs), and 632 MTB proteins were identified. Then, the characteristic values of MTB-CFPs - including emPAI value, molecular weight (Mw), isoelectric point (pI), grand average of hydropathy (GRAVY), transmembrane domain (TMD) and functional groups were calculated. Next, we successfully prepared 10 MTB proteins with emPAI value > 1.0 and recombinantly expressed these proteins in Escherichia coli. At the same time, 3 MTB proteins with emPAI between 0.1 and 0.5 were randomly selected as the control groups, and the immunogenicity of the recombinant MTB proteins was detected using ELISA. The sensitivity and receiver operating characteristic (ROC) curves were calculated for each recombinant MTB protein. The results showed that the areas under the curve (AUC) value of Rv2031c, Rv0577, Rv0831c, Rv0934 and Rv3248c were all higher than those of Rv3875 (AUC, 0.6643). Further analysis of the relationship between emPAI value and antibody sensitivity, AUC value and antibody affinity in mice immunized with recombinant MTB protein showed that emPAI values were positively correlated with them, and R-squared value ranged from 0.64 to 0.79. The only exception was ESAT-6 (encoded by the Rv3875 gene), which AUC value was relatively low owing to its strong immunosuppressive properties. This study provides a rationale for the serological marker screening of emPAI-assisted tuberculosis clinical test. The results also provide new technical support for the screening of candidate serological markers of infectious diseases in the future.

Serodiagnostic evaluation of fusion proteins from multiple antigens of Mycobacterium tuberculosis for active TB

Tuberculosis (TB) is a global health problem, being prevalent in the developing countries. A rapid, reliable and cost effective diagnostic method would help in controlling TB in the endemic populations. Development of suitable fusion molecules detecting multiple antibodies produced against Mycobacterium tuberculosis antigens would enhance sensitivity of serodiagnostic assays. In this study, EspC, CFP7 and PPE57 antigens of M. tuberculosis were selected for constructing fusion molecules after prediction of B-cell epitopes using in silico tools. Fusion proteins EspC-CFP7, HspX-EspC-CFP7 and HspX-EspC-CFP7-PPE57 were expressed in E.coli (BL21). The serodiagnostic potential of the individual antigens and their fusions was analyzed by screening 230 plasma samples of pulmonary TB patients. The single antigens HspX, EspC, CFP7, PPE57 showed sensitivities of 30%, 31%, 22% and 35%, respectively. The fusion protein EspC-CFP7 showed sensitivity of 43%. Linking of HspX antigen to the N-terminus of EspC-CFP7 fusion molecule increased sensitivity to 58%, while joining PPE57 antigen to the C-terminus of HspX-EspC-CFP7 increased sensitivity to 69%. The fusion protein HspX-EspC-CFP7-PPE57 seems to be a promising molecule for use in the development of fusions with higher sensitivity.

Enhanced serodiagnostic potential of a fusion molecule consisting of Rv1793, Rv2628 and a truncated Rv2608 of Mycobacterium tuberculosis

Serodiagnosis of tuberculosis (TB) can be rapid, reliable and cost-effective if the issue of variable antibody responses of TB patients against different Mycobacterium tuberculosis (Mtb) antigens can be overcome by developing fusion proteins containing epitopes from multiple antigens of Mtb. In this study, Mtb antigens Rv1793, Rv2628, Rv2608 and a truncated variant produced by removing non-epitopic region from N-terminal of Rv2608 (tnRv2608), and the fusion protein Rv1793-Rv2628-tnRv2608 (TriFu64), were expressed in E. coli and purified. Plasma samples from TB patients characterized by sex, age and sputum/culture positivity, were used to compare the sensitivity of the single antigens with the fusion protein. Sensitivity of Rv1793, Rv2628 and Rv2608, was 27.8%, 39% and 36.3%, respectively. Truncation of Rv2608 increased sensitivity by approximately 35% in confirmed TB cases. Sensitivity of the fusion construct, TriFu64 increased to 66% with a specificity of 100%. Importantly, tnRv2608 was better able to detect sputum and culture negative patients, and this carried through to the fusion protein. We demonstrate that fusion of Mtb proteins ensures broad sensitivity across disease types, sex and age groups in a Pakistani population.

Characterization of antibody response against 16kD and 38kD of M. tuberculosis in the assisted diagnosis of active pulmonary tuberculosis

Background

In view of the inability of traditional etiological methods to diagnose pulmonary tuberculosis rapidly and effectively, the antibody responses against 38kD and 16kD-antigens of Mycobacterium tuberculosis (M. tuberculosis) were both detected in order to obtain a better serological detection method for M. tuberculosis.

Methods

M. tuberculosis-secreted protein 38kD and membrane protein 16kD were prokaryotically expressed and purified, and then used as detection antigens. A novel evolved immunoglobulin-binding molecule (NEIBM)-ELISA method was used to detect antibody levels against 38kD and 16kD in active tuberculosis patients (confirmed tuberculosis cases and clinically diagnosed cases), to explore the significance of these two antigens in serological detection of M. tuberculosis, and to study the diagnostic value of the combined detection of the two antigens in active pulmonary tuberculosis.

Results

The results showed that the positive detection rates of the 16kD antigen and 38kD antigen of M. tuberculosis were higher (about 44%) in the confirmed cases of tuberculosis, and there was no significant difference in the positive detection rates of the two antigens (P=0.786). The combined detection of these two antigens showed that the positive detection rate could be increased to 61.5%, which was significantly better than the detection effect of the two antigens alone. The positive detection rates of 16kD and 38kD antigens were 26–30% in clinically diagnosed tuberculosis cases, which were lower than those in confirmed tuberculosis cases, and there was no significant difference in the positive detection rates of the two antigens (P=0.242). The detection effect of the two combined antigens was better than that of the 16kD and 38kD antigens alone, but the detection rate was still lower than that of the confirmed tuberculosis cases.

Conclusions

This study found that the detection effect of 16kD and 38kD antigens was similar in confirmed cases and clinically diagnosed cases of pulmonary tuberculosis, and that the detection effect needs to be further improved. The combined detection of the two antigens showed a significantly better detection effect than the two antigens alone, suggesting that the combined detection of multiple antigens can be used for serological diagnosis of M. tuberculosis infection in clinic.

IgA and IgG antibody detection of mycobacterial antigens in pleural fluid and serum from pleural tuberculous patients

Background

A previous study demonstrated pleural fluid (PF) IgA immunodominance for the fused MT10.3:MPT64 protein in pleural tuberculosis (PLTB) cases. However, no clue on the role of IgA and IgG against this and other antigens in PF and serum concerning improved diagnosis is available. Thus, the aim of the present study was to validate PF IgA-MT10.3:MPT64 and evaluate PF and serum IgA and IgG reactivity against this protein, its peptides (F2) and single MPT64, MT10.3 and the PPE59 mycobacterial specific antigens. IgA and IgG ELISA were measured against the antigen in PLTB (n = 29) and other non-TB pleurisy (n = 39) patient samples.

Results

The immunodominance of PF IgA-MT10.3:MPT64 was confirmed in PLTB (86.2%) followed by PPE59 (62%), while serum IgA-F2 exhibited 51.7% sensitivity. PF and serum IgG-MT10.3:MPT64 led to 65.5 and 51.7% sensitivity, respectively. However, MT10.3 and MPT64 displayed overall lower sensitivity (≤34.5) for both antibodies. All results at 95% fixed specificity. Combinatory results indicated 93.1% sensitivity for PF IgA-MT10.3:MPT64/−PPE59 and IgA/IgG-MT10.3:MPT64 at 92.3% specificity, followed by IgA-MT10.3:MPT64/−MPT64 or /−F2 (89.6%) without jeopardizing specificity (94.9%). The combinatory results of the PF adenosine deaminase test (ADA) and IgA-MT10.3:MPT64/−F2 demonstrated the highest sensitivity (96.6%), with a specificity of 92.3%.

Conclusions

The PF IgA-MT10:MPT64 immune dominance was validated in PLTB, and its combinatory results with PPE59 or MPT64 or F2 antigens as well as with IgG, are reported herein for the first time, improving their potential to assist diagnosis. Combining PF-ADA and IgA-MT10.3:MPT64/−F2 results achieved better accuracy. Moreover, serum IgG, although less accurate, displays potential beyond microbiological tests.

Proteomic Analysis of Antigen 60 Complex of M. bovis Bacillus Calmette-Guérin Reveals Presence of Extracellular Vesicle Proteins and Predicted Functional Interactions

Tuberculosis (TB) is ranked among the top 10 causes of death worldwide. New biomarker-based serodiagnostics and vaccines are unmet needs stalling disease control. Antigen 60 (A60) is a thermostable mycobacterial complex typically purified from Bacillus Calmette-Guérin (BCG) vaccine. A60 was historically evaluated for TB serodiagnostic and vaccine potential with variable findings. Despite containing immunogenic proteins, A60 has yet to be proteomically characterized. Here, commercial A60 was (1) trypsin-digested in-solution, analyzed by LC-MS/MS, searched against M. tuberculosis H37Rv and M. bovis BCG Uniprot databases; (2) analyzed using STRING to predict protein-protein interactions; and (3) probed with anti-TB monoclonal antibodies and patient immunoglobulin G (IgG) on Western blot to evaluate antigenicity. We detected 778 proteins in two A60 samples (440 proteins shared), including DnaK, LprG, LpqH, and GroEL1/2, reportedly present in mycobacterial extracellular vesicles (EV). Of these, 107 were also reported in EVs of M. tuberculosis, and 27 key proteins had significant protein-protein interaction, with clustering for chaperonins, ribosomal proteins, and proteins for ligand transport (LpqH and LprG). On Western blot, 7/8 TB and 1/8 non-TB sera samples had reactivity against 37-50 kDa proteins, while LpqH, GroEL2, and PstS1 were strongly detected. In conclusion, A60 comprises numerous proteins, including EV proteins, with predicted biological interactions, which may have implications on biomarker and vaccine development.

Enhancement of the stability of Mycobacterium tuberculosis recombinant antigen expressed in Escherichia coli using cell lysis additives

BACKGROUND

Mycobacteria tuberculosis (Mtb), the causative agent of tuberculosis, is a slow-growing bacterium. Expression in Escherichia coli is a widely used method for large-scale production of diagnostic antigenic recombinant proteins. Expression of Mtb antigen in E. coli offers a rapid and, inexpensive alternative to conventional protein synthesis from Mtb. The addition of stabilizing additives during cell lysis or storage of Mtb antigenic protein plays a vital role in enhancing antigen stability. In this study, we evaluated the effects of additives on the stability of Mtb antigens expressed in E. coli.

METHODS

Immunodominant Mtb antigens, i.e., CFP-10, Rv3872, TB7.7, and TB9.7, were cloned, and recombinant proteins overexpressed in E. coli were gradually degraded in a time-dependent manner by incubation at 37 °C. Various stabilizing additives during storage or cell lysis before protein purification were investigated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analysis.

RESULTS

CFP-10 and Rv3872 were mainly expressed in soluble form. The degraded form of the expressed protein after incubation at 37 °C was easily observed after 1 week. Increased stability was observed in a solution containing glycine for recombinant CFP-10 and Rv3872. TB9.7 was stable in a solution containing trehalose or mannitol. TB7.7 was stable in a solution containing sucrose, glycine, or polyethylene glycol.

CONCLUSION

Recombinant Mtb antigen stabilization using chemical additives inhibited protein degradation, leading to increased antigen stability and purification efficiency.

Ribokinase screened from T7 phage displayed Mycobacterium tuberculosis genomic DNA library had good potential for the serodiagnosis of tuberculosis

Tuberculosis caused by Mycobacterium tuberculosis (M. tuberculosis) is the leading cause of death among infectious diseases in the worldwide. Lack of more sensitive and effective diagnostic reagents has increased the awareness of rapid diagnosis for tuberculosis. In this study, T7 phage displayed genomic DNA library of M. tuberculosis was constructed to screen the antigens that specially bind with TB-positive serum from the whole genome of M. tuberculosis and to improve the sensitivity and specificity of tuberculosis serological diagnosis. After three rounds of biopanning, results of DNA sequencing and BLAST analysis showed that 19 positive phages displayed four different proteins and the occurrence frequency of the phage which displayed ribokinase was the highest. The results of indirect ELISA and dot immunoblotting indicated that representative phages could specifically bind to tuberculosis-positive serum. The prokaryotic expression vector containing the DNA sequence of ribokinase gene was then constructed and the recombinant protein was expressed and purified to evaluate the serodiagnosis value of ribokinase. The reactivity of the recombinant ribokinase with different clinical serum was detected and the sensitivities and specificities in tuberculosis serodiagnosis were 90% and 86%, respectively by screening serum from tuberculosis patients (n = 90) and uninfected individuals (n = 90) based on ELISA. Therefore, this study demonstrated that ribokinase had good potential for the serodiagnosis of tuberculosis.

The diagnostic accuracy of Th1 (IFN-γ, TNF-α, and IL-2) and Th2 (IL-4, IL-6 and IL-10) cytokines response in AFB microscopy smear negative PTB- HIV co-infected patients

Acid Fast Bacilli (AFB) microscopy smear remains the most widely used laboratory diagnostic technique for Pulmonary Tuberculosis (PTB) in low-and-middle income countries. Although it is highly specific, the sensitivity varies between 20-80% in immune-competent people, with only 50% case detection among HIV/TB co-infected patients, hence the need to determine the diagnostic accuracy of Th1 and Th2 cytokine response in AFB microscopy smear negative PTB-HIV co-infected patients. A total of 86 participants were recruited; 70 (81.4%) AFB microscopy smear negative and 16 (18.6%) AFB microscopy smear positive. The AFB microscopy smear negative samples were then cultured using Lowenstein Jensen Medium with 46 being culture-negative and 24 being culture-positive. Blood samples were also collected, cultured using QFT-GIT and the supernatant (plasma) harvested to evaluate cytokine profiles using Enzyme-Linked Immunosorbent Assay. IFN-γ (P < 0.001), TNF-α (P = 0.004), IL-2 (P = 0.004) and IL-4 (P = 0.009) median levels were elevated in PTB culture-positive (AFB microscopy smear negative) as compared to PTB culture-negative (AFB microscopy smear negative) participants. Finally, when Th1 cytokines (IFN-γ, TNF-α and IL-2), Th2 cytokines (IL-6 and IL-10) and T cells were included in the logistic regression fit for PTB outcome, the predictive power of discriminating between those who were AFB smear negative in the diagnosis of PTB was good with cross validated area under the curve (AUC) being 0.87 (95% CI: 0.78, 0.96). This study provides evidence for the ability of Th1 and Th2 cytokines to determine PTB status in AFB microscopy smear negative patients co-infected with HIV.

Detection of the tuberculosis biomarker mannose-capped lipoarabinomannan in human serum: Impact of sample pretreatment with perchloric acid

The development of an accurate and rapid diagnostic test for tuberculosis (TB) to use at point of need is vital to efforts aimed at reducing the global burden from this disease. This paper builds on our previous studies of mannose-capped lipoarabinomannan (ManLAM) as a serum biomarker for active TB infection by means of a heterogeneous immunoassay. That work found that complexation with components in serum (e.g., proteins) sterically hindered the capture and/or labeling of ManLAM in an immunoassay at levels <10 ng mL-1, compromising the clinical utility of this biomarker for detection of active TB infection. We also showed that the acidification of ManLAM-containing serum samples with perchloric acid improved the detectability of ManLAM by 250× by complex disruption when compared to measurements of untreated serum. The present study examined what effects the PCA treatment of serum samples may have on the recovery and structural integrity of ManLAM, owing to its potential susceptibility to acid hydrolysis. Recovery was assessed with an enzyme-linked immunosorbent assay (ELISA). The possible impact of acid hydrolysis on the ManLAM structure was investigated by gas chromatography-mass spectrometry and carbohydrate chemical degradation methods. The ELISA study indicated that while the signal strength for ManLAM in the serum spike-in experiments was significantly stronger after PCA pretreatment when compared to untreated human serum, it was only ∼20% of the ManLAM measured in physiological buffer. This loss in detectability was shown by structural analysis to arise mainly from the acid-induced degradation of the arabinan domains of ManLAM that are targeted by antibodies used for antigen capture and/or tagging. The implications of these findings in terms of the detection of this important biomarker for TB are also discussed.

Antibody response against Mycobacterium avium complex in cystic fibrosis patients measured by a novel IgG ELISA test

BACKGROUND

Early signs of Mycobacterium avium complex pulmonary disease can be missed in patients with cystic fibrosis due to subclinical infection or delays in mycobacterial culture. The aim of this study was to determine the diagnostic accuracy of a novel enzyme linked immunosorbent assay for immunoglobulin G against Mycobacterium avium complex, which could help stratify patients according to risk.

METHODS

A retrospective cross sectional analysis of serum samples from the Copenhagen Cystic Fibrosis Center was performed. Corresponding clinical data were reviewed and patients with cystic fibrosis were assigned to one of four groups based on their mycobacterial culture results. In addition, anti-Mycobacterium avium complex immunoglobulin G levels were measured longitudinally before and after first positive culture in the period 1984-2015.

RESULTS

Three-hundred and five patients with cystic fibrosis were included with a median of five nontuberculous mycobacterial cultures. Four individuals had Mycobacterium avium complex pulmonary disease at the time of cross sectional testing and their median antibody level was 22-fold higher than patients with no history of infection (1820 vs. 80 IgG units; p < 0.001). Test sensitivity was 100% (95% CI 40-100) and specificity 77% (95% CI 72-81). Longitudinal kinetics showed rising antibodies prior to first positive culture suggesting diagnostic delay.

CONCLUSIONS

Antibody screening for Mycobacterium avium complex may be used as a supplement to culture. Although confirmation in a larger cohort is needed, our findings suggest that stratifying a cystic fibrosis population into high- and low-risk groups based on antibody levels may help clinicians identify patients in need of more frequent culture.

Handheld Raman Spectrometer Instrumentation for Quantitative Tuberculosis Biomarker Detection: A Performance Assessment for Point-of-Need Infectious Disease Diagnostics

Techniques for the detection of disease biomarkers are key components in the protection of human health. While work over the last few decades has redefined the low-level measurement of disease biomarkers, the translation of these capabilities from the formal clinical setting to point-of-need (PON) usage has been much more limited. This paper presents the results of experiments designed to examine the potential utility of a handheld Raman spectrometer as a PON electronic reader for a sandwich immunoassay based on surface-enhanced Raman scattering (SERS). In so doing, the study herein used a recently developed procedure for the SERS detection of phospho-myo-inositol-capped lipoarabinomannan (PILAM) as a means to compare the performance of laboratory-grade and handheld instrumentation and, therefore, gauge the utility of the handheld instrument for PON deployment. Phospho-myo-inositol-capped lipoarabinomannan is a non-pathogenic simulant for mannose-capped lipoarabinomannan (ManLAM), which is an antigenic marker found in serum and other body fluids of individuals infected with tuberculosis (TB). The results of the measurements with the field-portable spectrometer were then compared to those obtained for the same samples when using a much more sensitive benchtop Raman spectrometer. The results, albeit under different operational settings for the two spectrometers (e.g., signal integration time), are promising in that the limit of detection found for PILAM spiked in human serum when using the handheld system (0.18 ng/mL) approached that of the benchtop instrument (0.032 ng/mL). This work also: (1) identified potential adaptations (e.g., optimization of the plasmonically enhanced response for measurement by the handheld unit through a change in the excitation wavelength) to tighten the gap in performance; and (2) briefly examined the next steps and potential processes required to move this immunoassay platform closer to PON utility.

Identification of new diagnostic biomarkers for Mycobacterium tuberculosis and the potential application in the serodiagnosis of human tuberculosis

Mycobacterium tuberculosis (M. tuberculosis) regions of difference (RD) encode proteins which are potentially useful as diagnostic reagents for tuberculosis (TB). In this study, 75 genes from M. tuberculosis RD1‐RD16 were successfully cloned from which 68 proteins were expressed and purified. Three serum pools from patients with pulmonary TB (PTB), extra‐pulmonary tuberculosis (EPTB) and healthy controls (HC) were used to preliminarily screen individual RD proteins. The OD₆₃₀ ratio of the PTB or EPTB to the HC group ≥ 2‐fold was positive. As a result, 29 proteins were obtained. The serological response to the identified antigens was further verified using 58 PTB samples with 38 sera from smear‐positive PTB (PTB‐SP) patients and 20 sera from smear‐negative PTB (PTB‐SN) patients, 16 EPTB samples, 42 latent M. tuberculosis infection samples and 40 HCs by indirect ELISA. With respect to the PTB diagnosis, receiver operating characteristic analysis showed that Rv0222 [area under the curve (AUC), 0.8129; 95% confidence interval (CI), 0.7280–0.8979] and Rv3403c (AUC, 0.8537; 95% CI, 0.7779–0.9294) performed better than ESAT6/CFP10 (AUC, 0.7435; 95% CI, 0.6465–0.8406). Rv0222 and Rv3403c demonstrated the highest diagnostic ability in the PTB‐SP group (sensitivity, 86.8%; specificity, 80%), while Rv3403c demonstrated the highest diagnostic ability in the PTB‐SN group (sensitivity, 70%; specificity, 80%). With respect to the EPTB diagnosis, Rv0222 exhibited the highest diagnostic value (AUC, 0.7523; sensitivity, 68.8%; specificity, 87.5%). In addition, the combination of Rv0222 and Rv3403c improved the test for PTB‐SN. These results indicate that Rv0222 and Rv3403c would be potential diagnostic biomarkers for active TB serodiagnosis. Mouse experiments demonstrated that Rv0222 and Rv3403c elicited specific cellular and humoral responses which were characterized by production of IFN‐γ, IgG1, and IgG2a, but a higher level of IgG1 than IgG2a.

Mathematical Modeling of Bioassays

The high affinity and specificity of biological receptors determine the demand for and the intensive development of analytical systems based on use of these receptors. Therefore, theoretical concepts of the mechanisms of these systems, quantitative parameters of their reactions, and relationships between their characteristics and ligand-receptor interactions have become extremely important. Many mathematical models describing different bioassay formats have been proposed. However, there is almost no information on the comparative characteristics of these models, their assumptions, and predictive insights. In this review we suggested a set of criteria to classify various bioassays and reviewed classical and contemporary publications on these bioassays with special emphasis on immunochemical analysis systems as the most common and in-demand techniques. The possibilities of analytical and numerical modeling are discussed, as well as estimations of the minimum concentrations that may be detected in bioassays and recommendations for the choice of assay conditions.

Evaluation of Mycobacterium tuberculosis-specific antibody responses for the discrimination of active and latent tuberculosis infection

OBJECTIVES

The serological antibody detection tests offer several advantages for the rapid diagnosis of tuberculosis (TB). The Mycobacterium tuberculosis-specific antibody responses associated with different stages of TB infection remain to be investigated.

METHODS

The Pathozyme-Myco IgG (Myco G), Pathozyme TB Complex Plus (TB Complex), IBL M. tuberculosis IgG ELISA (IBL), Anda Biologicals TB IgG (Anda-TB), and T-SPOT.TB (T-SPOT) tests were performed for 133 active TB patients (ATB group), 131 controls (CON group), and 95 subjects with latent TB infection (LTBI group).

RESULTS

The four serological tests all showed relatively low sensitivity in the ATB group but high specificity in the LTBI and CON groups. The antibody levels of the four serological tests were significantly higher in the ATB group than in the LTBI group. The same trend was observed between the LTBI and CON groups. The four serological tests demonstrated potential diagnostic value in discriminating ATB from LTBI. A combination of the Anda-TB and TB Complex tests exhibited the best diagnostic potential in discriminating ATB from LTBI, with a sensitivity of 89.4% and a specificity of 94.7%. Further, the diagnostic value of Anda-TB and TB Complex were validated in a prospective cohort including 106 patients with suspected ATB. Combined with the T-SPOT test, the tests showed a sensitivity of 87.2% and a specificity of 92.5% for discriminating ATB patients from all ATB suspected cases in the validation group.

CONCLUSIONS

The antibody responses of the serological tests all showed significant differences between the ATB and LTBI groups. A combination of Anda-TB and the TB Complex test demonstrated high diagnostic potential in discriminating ATB from LTBI and may be an additional diagnostic tool in the diagnosis of M. tuberculosis infection.

Detection of the tuberculosis antigenic marker mannose-capped lipoarabinomannan in pretreated serum by surface-enhanced Raman scattering

The ability to detect tuberculosis (TB) continues to be a global health care priority. This paper describes the development and preliminary assessment of the clinical accuracy of a heterogeneous immunoassay that integrates a serum pretreatment process with readout by surface-enhanced Raman scattering (SERS) for the low-level detection of mannose-capped lipoarabinomannan (ManLAM). ManLAM is a major virulence factor in the infectious pathology of Mycobacterium tuberculosis (Mtb) that has been found in the serum and other body fluids of infected patients. The effectiveness of ManLAM as a TB diagnostic marker, however, remains unproven for reasons not yet well understood. As reported herein, we have found that (1) ManLAM complexes with proteins and possibly other components in serum; (2) these complexes have a strongly detrimental impact on the ability to detect ManLAM using an immunoassay; (3) a simple pretreatment step can disrupt this complexation; and (4) disruption by pretreatment improves detection by 250×. We also describe the results from a preliminary assessment on the utility of serum pretreatment by running immunoassays on archived specimens from 24 TB-positive patients and 10 healthy controls. ManLAM was measurable in 21 of the 24 TB-positive specimens, but not in any of the 10 control specimens. These findings, albeit for a very small specimen set, translate to a clinical sensitivity of 87.5% and a clinical specificity of 100%. Together, these results both provide much needed evidence for the clinical utility of ManLAM as a TB marker, and demonstrate the potential utility of our overall approach to serve as a new strategy for the development of diagnostic tests for this disease.

IFN-γ against the 38-kDa antigen of Mycobacterium tuberculosis discriminates pulmonary tuberculosis from infection and infection from exposure: evidence from a study of human population in a high endemic setting

Mycobacterium tuberculosis (Mtb) 38-kDa antigen is an immunogenic lipoprotein that induces strong T-cell responses in experimental animals. However, there is limited information on the role of this antigen in human population. In this article, we present the dynamics of pro-inflammatory (IFN-γ and TNF-α) and anti-inflammatory cytokine (IL-10) against the 38 kDa in cohorts of pulmonary TB (PTB) patients, household contacts (HHCs), and community controls (CCs) in a high endemic setting. Whole blood assay was used to determine the levels of cytokines in 149 patients, 149 HHCs, and 68 CCs at baseline, 6 months, and 12 months. At baseline, the level of IFN-γ was significantly (p < 0.0001) higher in CCs and HHCs than in untreated patients. CCs had significantly (p < 0.05) higher level of IFN-γ than HHCs. There was no significant difference between treated and untreated patients, and there was no significant change in HHCs over 12 months. At baseline, the levels of IL-10 and TNF-α were significantly (p < 0.0001) higher in patients than in HHCs and CCs. No significant change was observed between treated patients and untreated patients and HHCs over time. The study shows that IFN-γ against the 38 kDa discriminates clinical TB from infection and infection from exposure, suggesting its potential for immune protection and diagnosis.

Immuno-PCR, a new technique for the serodiagnosis of tuberculosis

Rapid and accurate diagnosis of tuberculosis (TB) is essential to control the disease. The conventional microbiological tests have limitations and there is an urgent need to devise a simple, rapid and reliable point-of-care (POC) test. The failure of TB diagnostic tests based on antibody detection due to inconsistent and imprecise results has stimulated renewed interest in the development of rapid antigen detection methods. However, the World Health Organization (WHO) has emphasized to continue research for designing new antibody-based detection tests with improved accuracy. Immuno-polymerase chain reaction (I-PCR) combines the simplicity and versatility of enzyme-linked immunosorbent assay (ELISA) with the exponential amplification capacity and sensitivity of PCR thus leading to several-fold increase in sensitivity in comparison to analogous ELISA. In this review, we have described the serodiagnostic potential of I-PCR assays for an early diagnosis of TB based on the detection of potential mycobacterial antigens and circulating antibodies in body fluids of TB patients.

Field evaluation of a blood based test for active tuberculosis in endemic settings

Over 9 million new active tuberculosis (TB) cases emerge each year from an enormous pool of 2 billion individuals latently infected with Mycobacterium tuberculosis (M. tb.) worldwide. About 3 million new TB cases per year are unaccounted for, and 1.5 million die. TB, however, is generally curable if diagnosed correctly and in a timely manner. The current diagnostic methods for TB, including state-of-the-art molecular tests, have failed in delivering the capacity needed in endemic countries to curtail this ongoing pandemic. Efficient, cost effective and scalable diagnostic approaches are critically needed. We report a multiplex TB serology panel using microbead suspension array containing a combination of 11 M.tb. antigens that demonstrated overall sensitivity of 91% in serum/plasma samples from TB patients confirmed by culture. Group wise sensitivities for sputum smear positive and negative patients were 95%, and 88%, respectively. Specificity of the test was 96% in untreated COPD patients and 91% in general healthy population. The sensitivity of this test is superior to that of the frontline sputum smear test with a comparable specificity (30–70%, and 93–99%, respectively). The multiplex serology test can be performed with scalability from 1 to 360 patients per day, and is amenable to automation for higher (1000s per day) throughput, thus enabling a scalable clinical work flow model for TB endemic countries. Taken together, the above results suggest that well defined antibody profiles in blood, analyzed by an appropriate technology platform, offer a valuable approach to TB diagnostics in endemic countries.

Evaluation of 5 Novel protein biomarkers for the rapid diagnosis of pulmonary and extra-pulmonary tuberculosis: preliminary results

Improved methods are required for the early and accurate diagnosis of tuberculosis, especially in the patients with smear-negative disease. Several biomarkers have been tried but most have shown poor sensitivity or specificity. In present study we aimed to evaluate the diagnostic utility of five novel antigens identified earlier by us. This is an initial study conducted on 250 subjects. The five recombinant antigens, named as rSS1 (Rv2145c), rSS2 (Rv0164), rSS3 (Rv1437), rSS4 (Rv1827) and rSS5 (Rv2970c), were expressed in pQE-30 expression vector, purified and their sero-diagnostic efficacy was evaluated in an unblinded manner using dot-blot and ELISA methods. The sensitivity and specificity of these novel antigens were compared with commercially available standard esat6 and 38 kDa antigens. Bacteriologically confirmed TB patients, non-TB disease controls and healthy individuals were included. which are based on novel antigen or novel technology, Area under curve (AUC) of the selected antigens were 0.98 (0.98-0.99) for rSS1, 0.88 (0.84-0.92) for rSS2, 0.88 (0.84-0.92) for rSS3, 0.95 (0.93-0.98) for rSS4 and 0.99 (0.98-1.0) for rSS5. Receiver operative characteristic (ROC) curve showed highly significant difference between TB and healthy subjects (p = <0.001). These initial findings, show that the recombinant antigens rSS1, rSS4 and rSS5 could be used as highly potential biomarkers for the serological diagnosis of active TB.

Mass spectrometry applied to the identification of Mycobacterium tuberculosis and biomarker discovery

An adequate and effective tuberculosis (TB) diagnosis system has been identified by the World Health Organization as a priority in the fight against this disease. Over the years, several methods have been developed to identify the bacillus, but bacterial culture remains one of the most affordable methods for most countries. For rapid and accurate identification, however, it is more feasible to implement molecular techniques, taking advantage of the availability of public databases containing protein sequences. Mass spectrometry (MS) has become an interesting technique for the identification of TB. Here, we review some of the most widely employed methods for identifying Mycobacterium tuberculosis and present an update on MS applied for the identification of mycobacterial species.

Evaluation of a bovine antibody test for diagnosing Mycobacterium avium complex in patients with cystic fibrosis

INTRODUCTION

The aim of this study was to test a commercial bovine enzyme-linked immunosorbent assay for investigating antibody activity against Mycobacterium avium complex.

METHODS

All patients at the Copenhagen Cystic Fibrosis (CF) Center who had culture for nontuberculous mycobacteria performed were included. A commercially available antibody test used in veterinary medicine, was adjusted for human use, and applied to patient sera in a cross sectional test. The test positivity threshold was determined using a receiver operating curve (ROC). A longitudinal analysis of antibody kinetics before and after culture conversion was performed in case patients.

RESULTS

Out of 286 included subjects, six had clinical M. avium complex pulmonary disease at the time of sera sampling. These patients presented with higher antibody test values (P-value <0.01). A test cut point of 0.78 was chosen, corresponding to a sensitivity of 100% (54-100), specificity of 66% (60-72), a positive predictive value of 6% (2-13), and negative predictive value of 100% (98-100).

CONCLUSION

While not suited for direct diagnosis of M. avium complex due to a high number of false positive subjects, the assay proved useful at ruling out pulmonary disease. Screening sera from patients with CF could guide clinicians to focus attention on patients at higher risk of M. avium complex pulmonary disease. Pediatr Pulmonol. 2017;52:34-40. © 2016 Wiley Periodicals, Inc.

Calibrant-Free Analyte Quantitation via a Variable Velocity Flow Cell

In this paper, we describe a novel method for analyte quantitation that does not rely on calibrants, internal standards, or calibration curves but, rather, leverages the relationship between disparate and predictable surface-directed analyte flux to an array of sensing addresses and a measured resultant signal. To reduce this concept to practice, we fabricated two flow cells such that the mean linear fluid velocity, U, was varied systematically over an array of electrodes positioned along the flow axis. This resulted in a predictable variation of the address-directed flux of a redox analyte, ferrocenedimethanol (FDM). The resultant limiting currents measured at a series of these electrodes, and accurately described by a convective-diffusive transport model, provided a means to calculate an "unknown" concentration without the use of calibrants, internal standards, or a calibration curve. Furthermore, the experiment and concentration calculation only takes minutes to perform. Deviation in calculated FDM concentrations from true values was minimized to less than 0.5% when empirically derived values of U were employed.

Development of real-time immuno-PCR for the quantitative detection of mycobacterial PstS1 in tuberculosis patients

A novel indirect real-time immuno-polymerase chain reaction (RT-I-PCR) assay, an evolution of I-PCR, was developed for the quantitative detection of Mycobacterium tuberculosis PstS1 (Rv0934) with a wide dynamic range of 10ng/mL to 1pg/mL in body fluids of tuberculosis (TB) patients, which may monitor the dynamics of disease.

Fusion Molecules of Heat Shock Protein HSPX with Other Antigens of Mycobacterium tuberculosis Show High Potential in Serodiagnosis of Tuberculosis

Variable individual response against the antigens of Mycobacterium tuberculosis necessitates detection of multiple antibodies for enhancing reliability of serodiagnosis of tuberculosis. Fusion molecules consisting of two or more antigens showing high sensitivity would be helpful in achieving this objective. Antigens of M. tuberculosis HSPX and PE35 were expressed in a soluble form whereas tnPstS1 and FbpC1 were expressed as inclusion bodies at 37°C. Heat shock protein HSPX when attached to the N-termini of the antigens PE35, tnPstS1 and FbpC1, all the fusion molecules were expressed at high levels in E. coli in a soluble form. ELISA analysis of the plasma samples of TB patients against HSPX-tnPstS1 showed 57.7% sensitivity which is nearly the same as the expected combined value obtained after deducting the number of plasma samples (32) containing the antibodies against both the individual antigens. Likewise, the 54.4% sensitivity of HSPX-PE35 was nearly the same as that expected from the combined values of the contributing antigens. Structural analysis of all the fusion molecules by CD spectroscopy showed that α-helical and β-sheet contents were found close to those obtained through molecular modeling. Molecular modeling studies of HSPX-tnPstS1 and HSPX-PE35 support the analytical results as most of the epitopes of the contributing antigens were found to be available for binding to the corresponding antibodies. Using these fusion molecules in combination with other antigenic molecules should reduce the number of antigenic proteins required for a more reliable and economical serodiagnosis of tuberculosis. Also, HSPX seems to have potential application in soluble expression of heterologous proteins in E. coli.

Detection of Tuberculosis in HIV Co-infected Individuals: Use of Multiple ELISA Responses to 38kDa, Lipoarabinomannan and ESAT- 6 of M. tuberculosis

INTRODUCTION

There is a constant search for more sensitive and specific laboratory markers for tuberculosis (TB) infection. The early detection of TB in HIV co infected individuals is a diagnostic challenge. This is further compounded in those harbouring extrapulmonary disease.

AIM

To evaluate the use of multiple Enzyme Linked Immunosorbent Assays (ELISA) quantifying antibody responses to 38kDa, LAM and ESAT-6 M.tb antigens in detection of TB in patients with TB and HIV-TB co-infection.

MATERIALS AND METHODS

This is a cross-sectional study carried out in Hyderabad, India. Patient groups included 124 HIV-TB {62 with pulmonary TB (PTB) and 62 with extrapulmonary TB (ETB)}, 39 TB, 56 HIV and 57 healthy subjects (HS). A combination of anti 38kDa and LAM ELISAs measuring IgG, IgM and IgA levels and another ELISA measuring anti ESAT-6 combined antibody levels of IgG, IgM and IgA were evaluated. One-way ANOVA was performed to compare antibody responses among groups. To assess the efficacy of multiple ELISAs in detecting TB, concomitant seropositivity of an individual for all four ELISAs were evaluated for sensitivity and specificity.

RESULTS

A single ELISA carried out to detect TB in HIV patients showed a sensitivity ranging from 39% to 72%. The sensitivities of concomitant evaluation of multiple ELISAs were 92% for any single, 72% for any two, 44% for any three and 14% for any four. Based on the specificities, a simple algorithm for TB detection can be deduced. When four ELISAs are positive (specificity 100%) in a patient-confirmed TB; when three ELISAs are positive (specificity 98%) - probably TB; when two ELISAs are positive (specificity 95%) - possibly TB; and when one ELISA is positive (specificity 70%) - suspicion of TB.

CONCLUSION

The present study establishes the value of combining two or more M.tb antigen based ELISAs to enhance the sensitivity and specificity of TB detection in patients with tuberculosis as well as in those co-infected with HIV.

Naturally produced opsonizing antibodies restrict the survival of Mycobacterium tuberculosis in human macrophages by augmenting phagosome maturation

This study investigated the hypothesis that serum antibodies against Mycobacterium tuberculosis present in naturally infected healthy subjects of a tuberculosis (TB) endemic area could create and/or sustain the latent form of infection. All five apparently healthy Indian donors showed high titres of serum antibodies against M. tuberculosis cell membrane antigens, including lipoarabinomannan and alpha crystallin. Uptake and killing of bacilli by the donor macrophages was significantly enhanced following their opsonization with antibody-rich, heat-inactivated autologous sera. However, the capability to opsonize was apparent for antibodies against some and not other antigens. High-content cell imaging of infected macrophages revealed significantly enhanced colocalization of the phagosome maturation marker LAMP-1, though not of calmodulin, with antibody-opsonized compared with unopsonized M. tuberculosis. Key enablers of macrophage microbicidal action--proinflammatory cytokines (IFN-γ and IL-6), phagosome acidification, inducible NO synthase and nitric oxide--were also significantly enhanced following antibody opsonization. Interestingly, heat-killed M. tuberculosis also elevated these mediators to the levels comparable to, if not higher than, opsonized M. tuberculosis. Results of the study support the emerging view that an efficacious vaccine against TB should, apart from targeting cell-mediated immunity, also generate 'protective' antibodies.

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.

Performance of a Tuberculosis Serologic Assay in Various Patient Populations

OBJECTIVES

Detection of the humoral response to diagnose active tuberculosis has had varied success. We sought to further characterize the performance of a commercial serologic assay (Active TBDetect IgG ELISA; InBios International, Seattle, WA), which had demonstrated promising results in prior studies.

METHODS

Blood specimens from patients with mycobacterial infections, autoimmune disorders, and documented nonmycobacterial infections were prospectively collected for testing by the Active TBDetect IgG ELISA. Pertinent medical records were reviewed.

RESULTS

The sensitivity of the InBios IgG ELISA for active tuberculosis cases was 54.1% (20/37). Reactivity occurred in 24.1% (14/58) of nontuberculous mycobacterium cases, 10.4% (7/67) of nonmycobacterial infections, 10.5% (11/105) of autoimmune disorder cases, 8.7% (8/92) of noninfected patients, 14.3% (1/7) of patients with latent tuberculosis, and 10.7% (3/28) of control pediatric cases. Overall specificity was 87.5% (288/329). Receiver operator curve analysis demonstrated an area under the curve of 0.74. Reactivity with nontuberculous mycobacterium infection occurred with Mycobacterium avium-intracellulare complex, Mycobacterium chelonae/abscessus complex, Mycobacterium simiae, and Mycobacterium gordonae and was positively associated with having a positive acid-fast bacilli smear.

CONCLUSIONS

This study confirmed the limitations of serodiagnosis for active tuberculosis, including poor sensitivity and increased reactivity with nontuberculous mycobacterium-positive patients.

Fusion of selected regions of mycobacterial antigens for enhancing sensitivity in serodiagnosis of tuberculosis

Serodiagnosis of tuberculosis requires detection of antibodies against multiple antigens of Mycobacterium tuberculosis, because antibody profiles differ among the patients. Using fusion proteins with epitopes from two or more antigens would facilitate in the detection of multiple antibodies. Fusion constructs tn1FbpC1-tnPstS1 and tn2FbpC1-tnPstS1 were produced by linking truncated regions of variable lengths from FbpC1 to the N-terminus of the truncated PstS1. Similarly a truncated fragment of HSP was linked to the N-terminus of a truncated fragment from FbpC1 to produce tnHSP-tn1FbpC1. ELISA analysis of the plasma samples of TB patients against tn2FbpC1-tnPstS1 showed 72.2% sensitivity which is nearly the same as the expected combined value for the two individual antigens. However, the sensitivity of tn1FbpC1-tnPstS1 was lowered to 60%. tnHSP-tn1FbpC1 showed 67.7% sensitivity which is slightly less than the expected combined value for the two individual antigens, but still significantly higher than that of each of the individual antigen. Data for secondary structure analysis by CD spectrometry was in reasonable agreement with the X-ray crystallographic data of the native proteins and the predicted structure of the fusion proteins. Comparative molecular modeling suggests that the epitopes of the constituent proteins are better exposed in tn2FbpC1-tnPstS1 as compared to those in tn1FbpC1-tnPstS1. Therefore, removal of the N-terminal non-epitopic region of FbpC1 from 34-96 amino acids seems to have unmasked at least some of the epitopes, resulting in greater sensitivity. The high level of sensitivity of tn2FbpC1-tnPstS1 and tnHSP-tn1FbpC1, not reported before, shows that these fusion proteins have great potential for use in serodiagnosis of tuberculosis.

Serodiagnosis of Mycobacterium abscessus complex infection in cystic fibrosis

Early signs of pulmonary disease with Mycobacterium abscessus complex (MABSC) can be missed in patients with cystic fibrosis (CF). A serological method could help stratify patients according to risk. The objective of this study was to test the diagnostic accuracy of a novel method for investigating IgG activity against MABSC.A prospective study of all patients attending the Copenhagen CF Centre was conducted by culturing for MABSC during a 22-month period and then screening patients with an anti-MABSC IgG ELISA. Culture-positive patients had stored serum examined for antibody kinetics before and after culture conversion.307 patients had 3480 respiratory samples cultured and were then tested with the anti-MABSC IgG ELISA. Patients with MABSC pulmonary disease had median anti-MABSC IgG levels six-fold higher than patients with no history of infection (434 versus 64 ELISA units; p<0.001). The test sensitivity was 95% (95% CI 74-99%) and the specificity was 73% (95% CI 67-78%). A diagnostic algorithm was constructed to stratify patients according to risk.The test accurately identified patients with pulmonary disease caused by MABSC and was suited to be used as a complement to mycobacterial culture.

Evaluation of antigen-specific immunoglobulin g responses in pulmonary tuberculosis patients and contacts

This study aimed to evaluate the serodiagnostic potential of immunoglobulin G (IgG) responses to Mycobacterium tuberculosis antigens in pulmonary tuberculosis (TB) patients, recent TB contacts with latent TB infection (LTBI), and healthy subjects. Infections were assessed using tuberculin skin tests, QuantiFERON-TB Gold In-Tube tests, drug susceptibility testing, and molecular genotyping of clinical isolates. Serum IgG responses to selective M. tuberculosis antigens, including the 38-kDa and 16-kDa antigens, lipoarabinomannan (LAM), and recombinant early secreted antigen target 6 kDa (ESAT-6) and culture filtrate protein 10 kDa (CFP-10), were determined. We found that the serum IgG responses to all antigens might differentiate between active TB and LTBI, with LAM having the highest diagnostic value (area under the curve [AUC] of 0.7756, P < 0.001). Recurrent TB cases showed significantly higher IgG responses to 38 kDa, CFP-10 (P < 0.01), and LAM (P < 0.05) than new cases, and male patients had higher levels of antigen-specific IgG than females (P < 0.05). Conversely, drug resistance and patient body mass index did not affect IgG responses (P > 0.05). LAM-specific IgG responses differentiated between acid-fast bacillus (AFB) smear-positive and -negative patients (P < 0.01), whereas antigen-specific IgG responses did not vary with the M. tuberculosis genotype (P > 0.05). Significantly higher IgG responses to 38 kDa and 16 kDa were observed in AFB smear-negative patients than in controls. These results suggest that assessment of serum IgG responses to selective purified M. tuberculosis antigens may help improve the diagnosis of active TB, particularly for sputum smear-negative patients or recurrent cases, and these may also help to differentiate between active TB and LTBI.

Differential in vivo expression of mycobacterial antigens in Mycobacterium tuberculosis infected lungs and lymph node tissues

Background

The clinical course of tuberculosis (TB) infection, bacterial load and the morphology of lesions vary between pulmonary and extrapulmonary TB. Antigens expressed in abundance during infection could represent relevant antigens in the development of diagnostic tools, but little is known about the in vivo expression of various M. tuberculosis antigens in different clinical manifestations. The aim of this study was to study the differences in the presence of major secreted as well as somatic mycobacterial antigens in host tissues during advanced rapidly progressing and fatal pulmonary disease with mainly pneumonic infiltrates and high bacterial load, and to compare this to the presence of the same antigens in TB lymphadenitis cases, which is mainly chronic and self-limiting disease with organised granulomas and lower bacterial load.

Methods

Human pulmonary (n = 3) and lymph node (n = 17) TB biopsies, and non-TB controls (n = 12) were studied. Ziehl-Neelsen stain, nested PCR 1S6110 and immunohistochemistry were performed. Major secreted (MPT32, MPT44, MPT46, MPT51, MPT53, MPT59, MPT63, and MPT64) and somatic mycobacterial antigens (Mce1A, Hsp65, and MPT57) were detected by using rabbit polyclonal antibodies.

Results

Plenty of bacilli were detectable with Ziehl-Neelsen stain in the lung biopsies while no bacilli were detected in the lymph node biopsies. All the cases were shown to be positive by PCR. Both secretory and somatic antigens were expressed in abundance in pulmonary infiltrates, while primarily somatic antigens were detected in the lymphadenitis cases. Of the secreted antigens, only MPT64 was consistently detected in both cases, indicating a preferential accumulation of this antigen within the inflammatory cells, even if the cells of the granuloma can efficiently restrict bacterial growth and clear away the secreted antigens.

Conclusions

This study shows that major secreted mycobacterial antigens were found in high amounts in advanced pulmonary lesions without proper granuloma formation, while their level of staining was very low, or absent, in the lymph node TB lesions with organised granulomas and very low bacillary load, with one exception of MPT64, suggesting its role in the persistence of chronic infection. These findings have implication for development of new diagnostic tools.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2334-14-535) contains supplementary material, which is available to authorized users.

Mycobacterium tuberculosis adhesins: potential biomarkers as anti-tuberculosis therapeutic and diagnostic targets

Adhesion to host cells is a precursor to host colonization and evasion of the host immune response. Conversely, it triggers the induction of the immune response, a process vital to the host’s defence against infection. Adhesins are microbial cell surface molecules or structures that mediate the attachment of the microbe to host cells and thus the host–pathogen interaction. They also play a crucial role in bacterial aggregation and biofilm formation. In this review, we discuss the role of adhesins in the pathogenesis of the aetiological agent of tuberculosis, Mycobacterium tuberculosis. We also provide insight into the structure and characteristics of some of the characterized and putative M. tuberculosis adhesins. Finally, we examine the potential of adhesins as targets for the development of tuberculosis control strategies.

Serologic diagnosis of tuberculosis by combining Ig classes against selected mycobacterial targets

INTRODUCTION

Accurate, simple and cost-effective diagnostic tests are needed for diagnosis of active tuberculosis (TB). Serodiagnosis is attractive as it can be harnessed for point-of-care tests.

METHODS

We evaluated, in a blinded fashion, the sensitivity and specificity of serologic immunoglobulin (Ig)G, IgA and/or IgM responses to Apa, heat shock protein (HSP) 16.3, HSP20, PE35, probable thiol peroxidase Tpx and lipoarabinomannan (LAM) in 42 HIV-negative South African pulmonary TB patients and 67 control individuals. The status of latent Mycobacterium tuberculosis infection (LTBI) among controls was defined through the TST and IFN-γ release assays (IGRAs). We evaluated 47 definite LTBI (IGRA(+)/LTBI), 8 putative LTBI (IGRA(-)/TST(+)) and 12 TB-uninfected (non-LTBI) subjects.

RESULTS

In contrast to anti-PE35 IgA, anti-PE35 IgG and particularly anti-Apa IgA, performances of anti-LAM IgG and selected anti-protein antibodies were less affected by inclusion of LTBI participants into the analysis. Anti-LAM IgG showed with a sensitivity/specificity of 71.4%/86.6% (p < 0.001) the best discrimination between TB and non-TB subjects. Selected five-antibody-combinations (including anti-LAM IgG, anti-LAM IgA and anti-Tpx IgG) further improved this performance to an accuracy exceeding 86%.

CONCLUSIONS

Antibody responses to some Mycobacterium tuberculosis antigens often also reflect latent infection explaining the poor performance of antibody-based tests for active TB in TB-endemic settings. Our results suggest that rather a combination of serological responses against selected protein and non-protein antigens and different Ig classes should be investigated for TB serodiagnostics.