Serodiagnostic efficacy of Mycobacterium tuberculosis 30/32-kDa mycolyl transferase complex, ESAT-6, and CFP-10 in patients with active tuberculosis

Ag85B-ENO146-82 therapeutic vaccines enhance anti-tumor immunity by inducing CD8+ T cells and remodeling tumor microenvironment

Lung cancer is the leading cause of cancer-related morbidity and mortality in China. However, the effect of traditional cancer treatment is limited. Herein, we designed a therapeutic cancer vaccine based on the tumor-associated antigen mENO1, which can prevent lung cancer growth in vivo, and explored the underlying mechanism of Ag85B-ENO146-82 therapy. Lewis lung carcinoma (LLC) tumor-bearing immunocompetent C57BL/6 mice that received Ag85B-ENO146-82 treatment showed antitumor effect. Further, we detected CD8+ T, CD4+ T in LLC-bearing C57BL/6 mice to understand the impact of Ag85B-ENO146-82 therapy on antitumor capacity. The Ag85B-ENO146-82 therapy induced intensive infiltration of CD4+ and CD8+ T cells in tumors, increased tumor-specific IFN-γ and TNF-α secretion by CD8+ T cells and promoted macrophage polarization toward M1 phenotype. Flow cytometric analysis revealed that CD8+ T effector memory (TEM) cells and central memory (TCM) cells were upregulated. qPCR and ELISA analysis showed that the expression of IFN-γ and TNF-α were upregulated, whereas of IL1β, IL6 and IL10 were downregulated. This study demonstrated that Ag85B-ENO146-82 vaccine augmented antitumor efficacy, which was CD8+ T cells dependent. Our findings paved the way for therapeutic tumor-associated antigen peptide vaccines to enhance anti-tumor immunotherapy for treatment of cancer.

Changing paradigms in the treatment of tuberculosis

Tuberculosis, caused by Mycobacterium tuberculosis, is a disease long dealt with, but still remains the second leading cause of death world-wide. The current anti-tubercular chemotherapy primarily targets the microbial pathogenesis, which however, is failing due to the development of drug resistance. Moreover, with fewer new drugs reaching the market, there is a need to focus on alternate treatment approaches that could be used as stand-alone or adjunct therapy and the existing drugs, referred to as Track II chemotherapy. This article is an attempt to review the changing global patterns of tuberculosis and its treatment. Further, newer drug delivery approaches like multi-particulate drug carriers which increase the therapeutic efficacy and bring down the systemic toxicity associated with drugs have also been discussed. There is also a need to use interventions which can be used as Track II therapy. Host-directed therapeutics (HDT) is an emerging area concept in which host cell functions and hence the response to pathogens can be modulated, which can help manage TB. HDT decreases damage induced due to inflammation and necrosis in the lungs and other parts of the body due to the disease. Various immuno-modulatory pathways have been discussed in this review which could be explored further to treat TB. An in-depth understanding of multi-particulate drug carriers and HDT could help in dealing with tuberculosis; however, there is still a long way to go.

Recent advances in airborne pathogen detection using optical and electrochemical biosensors

The world is currently facing an adverse condition due to the pandemic of airborne pathogen SARS-CoV-2. Prevention is better than cure; thus, the rapid detection of airborne pathogens is necessary because it can reduce outbreaks and save many lives. Considering the immense role of diverse detection techniques for airborne pathogens, proper summarization of these techniques would be beneficial for humans. Hence, this review explores and summarizes emerging techniques, such as optical and electrochemical biosensors used for detecting airborne bacteria (Bacillus anthracis, Mycobacterium tuberculosis, Staphylococcus aureus, and Streptococcus pneumoniae) and viruses (Influenza A, Avian influenza, Norovirus, and SARS-CoV-2). Significantly, the first section briefly focuses on various diagnostic modalities applied toward airborne pathogen detection. Next, the fabricated optical biosensors using various transducer materials involved in colorimetric and fluorescence strategies for infectious pathogen detection are extensively discussed. The third section is well documented based on electrochemical biosensors for airborne pathogen detection by differential pulse voltammetry, cyclic voltammetry, square-wave voltammetry, amperometry, and impedance spectroscopy. The unique pros and cons of these modalities and their future perspectives are addressed in the fourth and fifth sections. Overall, this review inspected 171 research articles published in the last decade and persuaded the importance of optical and electrochemical biosensors for airborne pathogen detection.

Defining Discriminatory Antibody Fingerprints in Active and Latent Tuberculosis

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

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.

Novel T7 Phage Display Library Detects Classifiers for Active Mycobacterium Tuberculosis Infection

Tuberculosis (TB) is caused by Mycobacterium tuberculosis (MTB) and transmitted through inhalation of aerosolized droplets. Eighty-five percent of new TB cases occur in resource-limited countries in Asia and Africa and fewer than 40% of TB cases are diagnosed due to the lack of accurate and easy-to-use diagnostic assays. Currently, diagnosis relies on the demonstration of the bacterium in clinical specimens by serial sputum smear microscopy and culture. These methods lack sensitivity, are time consuming, expensive, and require trained personnel. An alternative approach is to develop an efficient immunoassay to detect antibodies reactive to MTB antigens in bodily fluids, such as serum. Sarcoidosis and TB have clinical and pathological similarities and sarcoidosis tissue has yielded MTB components. Using sarcoidosis tissue, we developed a T7 phage cDNA library and constructed a microarray platform. We immunoscreened our microarray platform with sera from healthy (n = 45), smear positive TB (n = 24), and sarcoidosis (n = 107) subjects. Using a student t-test, we identified 192 clones significantly differentially expressed between the three groups at a False Discovery Rate (FDR) <0.01. Among those clones, we selected the top ten most significant clones and validated them on independent test set. The area under receiver operating characteristics (ROC) for the top 10 significant clones was 1 with a sensitivity of 1 and a specificity of 1. Sequence analyses of informative phage inserts recognized as antigens by active TB sera may identify immunogenic antigens that could be used to develop therapeutic or prophylactic vaccines, as well as identify molecular targets for therapy.

Antigen 85B peptidomic analysis allows species-specific mycobacterial identification

BACKGROUND

Nontuberculous mycobacteria (NTM)-mediated infections are a growing cause of worldwide morbidity, but lack of rapid diagnostics for specific NTM species can delay the initiation of appropriate treatment regimens. We thus examined whether mass spectrometry analysis of an abundantly secreted mycobacterial antigen could identify specific NTM species.

METHODS

We analyzed predicted tryptic peptides of the major mycobacterial antigen Ag85B for their capacity to distinguish Mycobacterium tuberculosis and three NTM species responsible for the majority of pulmonary infections caused by slow-growing mycobacterial species. Next, we analyzed trypsin-digested culture supernatants of these four mycobacterial species by liquid chromatography-tandem mass spectrometry (LC-MS/MS) to detect candidate species-specific Ag85B peptides, the identity of which were validated by LC-MS/MS performed in parallel reaction monitoring mode.

RESULTS

Theoretical tryptic digests of the Ag85B proteins of four common mycobacterial species produced peptides with distinct sequences, including two peptides that could each identify the species origin of each Ag85B protein. LC-MS/MS analysis of trypsinized culture supernatants of these four species detected one of these species-specific signature peptides in each sample. Subsequent LC-MS/MS analyses confirmed these results by targeting these species-specific Ag85B peptides.

CONCLUSIONS

LC-MS/MS analysis of Ag85B peptides from trypsin-digested mycobacterial culture supernatants can rapidly detect and identify common mycobacteria responsible for most pulmonary infections caused by slow-growing mycobacteria, and has the potential to rapidly diagnose pulmonary infections caused by these mycobacteria through direct analysis of clinical specimens.

In silicoevaluation of the interactions among two selected single chain variable fragments (scFvs) and ESAT-6 antigen ofMycobacterium tuberculosis

Nowadays antibody engineering is an important approach in the design and manufacture of therapeutic and diagnostic antibodies. The study of interactions between antibodies and antigens is the critical step in the design of antibodies with desirable properties. Computational docking is a useful tool for structural characterization of bimolecular interactions. Docking is the process of predicting bound conformations and binding enthalpy of antibody–antigen complexes. In this study, the three-dimensional structures of two ribosome displayed-selected scFv antibodies were constructed by Kotai Antibody Builder. By using ClusPro 2.0 web server, the ESAT-6 antigen (a tuberculosis-specific antigen) structure was docked to both scFv models to obtain the structures of the binding complexes and molecular dynamics (MD) simulations were performed using GROMACS 4.5.3 package. By analyzing of the ESAT-scFv complexes, important amino acids involved in antigen–antibody interactions were identified which were Asn164 in VL3, Ser164 in VL7 and Asn55 in VH7. All three amino acids belonged to the CDRs. In conclusion, results achieved from this bioinformatics study can help in the design and development of novel antibodies with improved affinities for tuberculosis diagnosis.

Antigen 85 complex as a powerful Mycobacterium tuberculosis immunogene: Biology, immune-pathogenicity, applications in diagnosis, and vaccine design

Mycobacterium tuberculosis (Mtb) is one of the most life-threatening mycobacterial species which is increasing the death rate due to emerging multi-drug resistant (MDR) strains. Concerned health authorities worldwide are interested in developing an effective vaccine to prevent the spread of Mtb. After years of research, including successful identification of many Mtb immunogenic molecules, effective therapeutic agents or a vaccine have yet to be found. However, among the identified Mtb immunogenes, antigen 85 (Ag85) complex (Ag85A, Ag85B, and Ag85C) is receiving attention from scientists as it allows bacteria to evade the host immune response by preventing formation of phagolysosomes for eradication of infection. Due to their importance, A85 molecules are being utilized as tools in diagnostic methods and in the construction of new vaccines, such as recombinant attenuated vaccines, DNA vaccines, and subunit vaccines. This paper represents a comprehensive review of studies on Mtb molecules examining pathogenicity, biochemistry, immunology, and the role of Mtb in therapeutic or vaccine research.

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.

Recombinant Bacillus subtilis spores for the delivery of Mycobacterium tuberculosis Ag85B-CFP10 secretory antigens

Tuberculosis continues to be a great cause of morbidity and mortality in different parts of the world. Unfortunately, the current BCG vaccine being administered is not fully protective against tuberculosis; therefore, there is a great need for alternate vaccines. With an aim to develop such vaccines, we have analyzed the utility of Bacillus subtilis spores for the expression of two major immunodominant antigens of Mycobacterium tuberculosis, Ag85B and CFP10. We created three recombinant B. subtilis strains to express a truncated fusion of Ag85B_191-325 and CFP10_1-70 antigens (T85BCFP), either on the spore coat (MTAG1 strain) or in the cytosol of B. subtilis (MTAG 2 and MTAG 3 strains). Examination of spores isolated from these strains revealed successful expression of T85BCFP antigens on the spore coat of MTAG1 as well as in the cytosol of vegetatively grown cells of MTAG2 and MTAG3, indicating that spores can indeed express M. tuberculosis antigens. In vitro antigen presentation assays with spore-infected mouse bone marrow derived macrophages (BMDM) showed that all three recombinant spores could deliver these antigens to antigen presenting cells (APCs). Mice immunized with recombinant spores displayed significantly higher levels of Ag85B specific IFN-γ producing cells in the spleen than in mice immunized with wild-type (non-recombinant) spores. In addition, these mice showed relatively higher levels of Ag85B specific IgG antibodies in the serum in comparison to mice immunized with non-recombinant spores, thus providing additional evidence that recombinant spores can deliver these antigens in vivo. These results suggest that B. subtilis spores are ideal vehicles for antigen delivery and have great potential in the development of primary and booster vaccines against tuberculosis.

Diagnosis of tuberculosis based on the detection of a cocktail of mycobacterial antigen 85B, ESAT-6 and cord factor by immuno-PCR

Attempts were made to enhance the sensitivity of immuno-PCR assay based on the detection of cocktail of mycobacterial antigen 85B (Rv1886c), ESAT-6 (Rv3875) and cord factor (trehalose 6,6'-dimycolate) in pulmonary and extrapulmonary TB patients. Detection of Ag85B was found to be superior to the detection of cocktail in TB patients.

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.

The Mycobacterium tuberculosis PPE protein Rv1168c induces stronger B cell response than Rv0256c in active TB patients

Tuberculosis (TB) caused by Mycobacterium tuberculosis is a serious global health problem and is responsible for millions of deaths every year. For effective control of this dreadful disease, it is necessary to diagnose TB cases at the initial stages of infection. The serodiagnosis of disease represents simple, rapid and inexpensive method that can be used at the primary health care levels. In this study we have compared sensitivity of two PPE proteins of M. tuberculosis, i.e., Rv0256c and Rv1168c for their use as serodiagnostic markers in active tuberculosis patients. Employing a standardized enzyme immunoassay with these PPE proteins as candidate antigens we were able to successfully discriminate the TB patients' sera from the BCG-vaccinated healthy controls. Further, we observed that Rv1168c displayed higher sensitivity in detecting extrapulmonary and smear negative pulmonary TB cases which are difficult to diagnose by available diagnostic methods. Overall the study highlights that Rv1168c can be used as a potential serodiagnostic marker for the diagnosis of active tuberculosis disease.

Enhancement of antimycobacterial Th1-cell responses by a Mycobacterium bovis BCG prime-protein boost vaccination strategy

Tuberculosis is a major global health problem, and the only available vaccine Bacille Calmette-Guérin (BCG) is not sufficiently effective against the disease. It is extremely urgent to develop novel vaccine approaches. Previous research demonstrated that there were several Regions of Difference (RD1-16) between the substrains of BCG and Mycobacterium tuberculosis or Mycobacterium bovis. The ORFs Rv1769 and Rv1772 are located in the RD14 deletions and have not been major targets of study. However, some studies have demonstrated that the two genes (Rv1769 and Rv1772) are excellent T cell antigens, which might induce an immune response. What kind of role these ORFs might play in anti-mycobacterial immunity, however, is still unknown. In our research we used the BCG prime-protein boost strategy to immunize BALB/c mice and evaluated its immunogenicity. Our data suggest that our novel BCG-P+PRO69 vaccine could elicit the most long-lasting and strongest Th1 type cellular immune responses. This response is characterized by a strong antibody response, the proliferation rate of splenocytes, a high percentage of CD4+ and CD8+ T cells and high levels of IFN-γ in antigen-stimulated splenocyte cultures. These results indicate that prime-boost is a potent strategy and the protein of gene Rv1769 is a potential antigen or subunit vaccine to TB for further study.

Construction of eukaryotic expression vectors encoding CFP-10 and ESAT-6 genes and their potential in lymphocyte proliferation

BACKGROUND

Mycobacterium (M.) bovis is the agent of bovine tuberculosis (TB) in a range of animal species, including humans. Recent advances in immunology and the molecular biology of Mycobacterium have allowed identification of a large number of antigens with the potential for the development of a new TB vaccine. The ESAT-6 and CFP-10 proteins of M. bovis are important structural and functional proteins known to be important immunogens.

METHODS

In the current study, the DNAs encoding these genes were utilized in the construction of pcDNA 3.1+/ESAT-6 and pcDNA3.1+/CFP-10 plasmids. After intramuscular injection of BALB/c mice with these plasmids, ESAT-6 and CFP-10 mRNA expression was assessed by RT-PCR. Mice were inoculated and boosted with the plasmids to evaluate their effects on lymphocyte proliferation.

RESULTS

Our results indicate the plasmids are expressed at the RNA level and can induce lymphocyte proliferation.

CONCLUSION

Further study is needed to characterize the effect of these antigens on the immune system and determine whether they are effective vaccine candidates against M. bovis.

Laboratory investigations on the diagnosis of tuberculosis in the malnourished tribal population of melghat, India

BACKGROUND

Malnutrition is a major risk factor for the development of tuberculosis (TB). In India, Melghat is among the tribal regions which consist of highest number of malnutrition cases. Because of the paucity of TB data from these malnourished areas there is an urgent need for the development and evaluation of improved TB diagnostic tests. In the present study, three in house developed diagnostic tests namely TB-Ag(antigen) ELISA, Adenosine deaminase (ADA) estimation and IS6110 polymerase chain reaction (PCR) assay were investigated for the detection of Mycobacterium tuberculosis (M. tb.) infection.

METHODS

For investigation, blood samples were collected from 128 study subjects from six villages of Melghat tribal area and evaluated using three in house developed assays, namely TB-Ag ELISA, ADA estimation and IS6110 PCR.

RESULTS

The TB-Ag ELISA method yielded 83% sensitivity and 94% specificity. The ADA and PCR assay gave a sensitivity of 61% and 49% and specificity of 62% and 98% respectively. A considerable good agreement of 82.81% (k=0.472) between TB-Ag ELISA and PCR was observed. The overall sensitivity of TB-Ag ELISA was significantly higher (p<0.05) than the ADA and PCR while PCR yielded highest specificity among all the three evaluated tests.

CONCLUSIONS

We concluded that the routine use of TB-Ag ELISA can be useful for screening of suspected TB patients in the malnourished population where sophisticated laboratory set up is difficult.

Generation of Mycobacterium tuberculosis-specific recombinant antigens and evaluation of the clinical value of antibody detection for serological diagnosis of pulmonary tuberculosis

Rapid diagnosis of pulmonary tuberculosis (TB) infection is critical in clinical practice. To establish an effective serological diagnostic technique, we generated the several Mycobacterium tuberculosis (MTB)-specific immunogenic antigens and evaluated the clinical benefits of detection of immunoglobulin G (IgG) and IgM antibodies raised against these target antigens for the diagnosis of patients with active TB. The genes encoding the MTB-specific antigens 6-kDa early secretory antigenic target of MTB (ESAT-6), 10-kDa culture filtrate protein (CFP-10), ESX-1 substrate protein C (ESPC), 14KD/38KD and ESAT-6/14KD/38KD, were amplified from the MTB genome by PCR. Prokaryotic vectors were constructed for the expression of the individual MTB antigens. The target recombinant protein was expressed in Escherichia coli (BL21/DE3) and purified using immobilized metal affinity chromatography (IMAC). An ELISA based immunoassay was set up using these target antigens for the diagnosis of active TB. The detection samples included 98 patients with active TB and 102 healthy control volunteers. The cutoff OD value for IgG and IgM antibodies was selected according to a receiver operating characteristic (ROC) analysis. The sensitivity, specificity and positive likelihood ratio were also determined. We successfully cloned, expressed and purified the ESAT-6, CFP-10, ESPC, 14KD/38KD and ESAT‑6/14KD/38KD recombinant antigens of MTB. The mean levels of IgG antibodies were significantly higher in patients with pulmonary TB compared with control groups. The target MTB-specific antigens can distinguish a TB infection from a non-TB infection, showing significant difference in statistics (P<0.001). The sensitivity of the IgG test ranged from 69.4% (ESAT-6) to 77.6% (ESAT-6/14KD/38KD) in the active TB patients; the specificity of assays varied from 78.4% (CFP-10) to 90.2% (14KD+38KD) in the healthy control groups. The IgM antibody test can not distinguish a TB infection from a non-TB healthy control. In conclusion, clinical use of the ESAT-6, CFP-10, ESPC, 14KD/38KD and ESAT-6/14KD/38KD antigens based on serodiagnostic IgG assay is of significant value for the rapid diagnosis of TB and for the discrimination between active TB patients and healthy controls.

A novel B-cell epitope identified within Mycobacterium tuberculosis CFP10/ESAT-6 protein

Background

The 10-kDa culture filtrate protein (CFP10) and 6-kDa early-secreted target antigen (ESAT-6) play important roles in mycobacterial virulence and pathogenesis through a 1∶1 complex formation (CFP10/ESAT-6 protein, CE protein), which have been used in discriminating TB patients from BCG-vaccinated individuals. The B-cell epitopes of CFP10 and ESAT-6 separately have been analyzed before, however, the epitopes of the CE protein are unclear and the precise epitope in the positions 40 to 62 of ESAT-6 is still unknown.

Methods

In the present study, we searched for the B-cell epitopes of CE protein by using phage-display library biopanning with the anti-CE polyclonal antibodies. The epitopes were identified by sequence alignment, binding affinity and specificity detection, generation of polyclonal mouse sera and detection of TB patient sera.

Results

One linear B-cell epitope (KWDAT) consistent with the 162^nd–166^th sequence of CE and the 57^th–61^st sequence of ESAT-6 protein was selected and identified. Significantly higher titers of E5 peptide-binding antibodies were found in the sera of TB patients compared with those of healthy individuals.

Conclusion

There was a B-cell epitope for CE and ESAT-6 protein in the position 40 to 62 of ESAT-6. E5 peptide may be useful in the serodiagnosis of tuberculosis, which need to be further confirmed by more sera samples.

Use of recombinant purified protein derivative (PPD) antigens as specific skin test for tuberculosis

BACKGROUND & OBJECTIVES

Purified protein derivative (PPD) is currently the only available skin test reagent used worldwide for the diagnosis of tuberculosis (TB). The aim of this study was to develop a Mycobacterium tuberculosis specific skin test reagent, without false positive results due to Bacillus Calmette-Guerin (BCG) vaccination using recombinant antigens.

METHODS

Proteins in PPD IC-65 were analyzed by tandem mass spectrometry and compared to proteins in M. tuberculosis culture filtrate; 54 proteins were found in common. Top candidates MPT64, ESAT 6, and CFP 10 were overexpressed in Escherichia coli expression strains and purified as recombinant proteins. To formulate optimal immunodiagnostic PPD cocktails, the antigens were evaluated by skin testing guinea pigs sensitized with M. tuberculosis H37Rv and BCG.

RESULTS

For single antigens and a cocktail mixture of these antigens, best results were obtained using 3 μg/0.1 ml, equivalent to 105 TU (tuberculin units). Each animal was simultaneously tested with PPD IC-65, 2 TU/0.1 ml, as reference. Reactivity of the multi-antigen cocktail was greater than that of any single antigen. The skin test results were between 34.3 and 76.6 per cent the level of reactivity compared to that of the reference when single antigens were tested and 124 per cent the level of reactivity compared to the reference for the multi-antigen cocktail.

INTERPRETATION & CONCLUSIONS

Our results showed that this specific cocktail could represent a potential candidate for a new skin diagnostic test for TB.

Serodiagnosis efficacy and immunogenicity of the fusion protein of Mycobacterium tuberculosis composed of the 10-kilodalton culture filtrate protein, ESAT-6, and the extracellular domain fragment of PPE68

In order to identify immunodominant antigens of Mycobacterium tuberculosis that may be used in the serodiagnosis of active tuberculosis (TB), we designed an M. tuberculosis fusion protein consisting of CFP-10 (10-kDa culture filtrate protein), ESAT-6 (6-kDa early secreted antigenic target), and the extracellular domain fragment of PPE68 (PPE68'). Then, the coding sequences of the three proteins were inserted into a prokaryotic expression vector, pET-32a(+). To enhance the immunological response, the proteins were linked together. The fusion proteins with a 6 × His tag were successfully overexpressed in Escherichia coli BL21 and purified. The purified proteins were applied for detection of the total IgG titer by using an enzyme-linked immunosorbent assay (ELISA) with human sera from well-characterized TB cases and the control cases, and results were compared to those with purified protein derivative tuberculin (PPD). The ELISA results showed that among 140 cases of confirmed active TB and 70 control cases, CFP-10-ESAT-6-PPE68' had a sensitivity of 73.3% and specificity of 94.3%, compared to a sensitivity of 66.7% and specificity of 74.3% for PPD and a sensitivity of 65% and specificity of 91.4% for CFP-10-ESAT-6. In addition, the fusion protein CFP-10-ESAT-6-PPE68' stimulated a higher level of antigen-specific gamma interferon (IFN-γ) release for active-TB patients than PPD and CFP-10-ESAT-6. After immunization of C57BL/6 mice, the findings indicated that the total IgG titers and the concentrations of IFN-γ in mice immunized by CFP-10-ESAT-6-PPE68' were high and induced strong, long-term humoral immunity compared to results with PPD and CFP-10-ESAT-6. Thus, our study indicates that the fusion protein CFP-10-ESAT-6-PPE68' may be useful as an immunodominant antigen for the serodiagnosis of active TB.

Assessment of five antigens from Mycobacterium tuberculosis for serodiagnosis of tuberculosis

Tuberculosis (TB), caused by Mycobacterium tuberculosis, is a major public health issue, particularly in developing countries, and thus effective diagnostic methods for TB remain a central theme in basic and clinical research. To evaluate five antigens (38-kDa protein [38kDa], Rv3621c, Rv3618, 38kDa-ESAT-6 [38E6], and Ag85B-HBHA [AH]) in serological tests for TB patients, we recruited 288 patients and 201 healthy controls. The median IgG reactivity to 38kDa, 38E6, and AH was higher than that to Rv3618 and Rv3621c in pulmonary TB. 38kDa and 38E6 provided high sensitivities in pulmonary TB but low sensitivities in extrapulmonary TB (EPTB). The specificities achieved by 38kDa and 38E6 ranged from 82.0% to 93.9% in patients with non-TB respiratory disease (PD) and in controls. 38kDa and 38E6 exhibited lower sensitivities and higher specificities than their combinations with Rv3618. These findings provide useful information on the relative importance of the above five antigens and suggest that combinations of Rv3618 with 38kDa and 38E6 can increase their sensitivities, but their specificities need to be further increased.