Delayed-type hypersensitivity responses to ESAT-6 and MPT64 from Mycobacterium tuberculosis in the guinea pig

Bacterial Strain-Dependent Dissociation of Cell Recruitment and Cell-to-Cell Spread in Early M. tuberculosis Infection

In the initial stage of respiratory infection, Mycobacterium tuberculosis traverses from alveolar macrophages to phenotypically diverse monocyte-derived phagocytes and neutrophils in the lung parenchyma. Here, we compare the in vivo kinetics of early bacterial growth and cell-to-cell spread of two strains of M. tuberculosis: a lineage 2 strain, 4334, and the widely studied lineage 4 strain H37Rv. Using flow cytometry, live cell sorting of phenotypic subsets, and quantitation of bacteria in cells of the distinct subsets, we found that 4334 induces less leukocyte influx into the lungs but demonstrates earlier population expansion and cell-to-cell spread. The earlier spread of 4334 to recruited cells, including monocyte-derived dendritic cells, is accompanied by earlier and greater magnitude of CD4+ T cell activation. The results provide evidence that strain-specific differences in interactions with lung leukocytes can shape adaptive immune responses in vivo. IMPORTANCE Tuberculosis is a leading infectious disease killer worldwide and is caused by Mycobacterium tuberculosis. After exposure to M. tuberculosis, outcomes range from apparent elimination to active disease. Early innate immune responses may contribute to differences in outcomes, yet it is not known how bacterial strains alter the early dynamics of innate immune and T cell responses. We infected mice with distinct strains of M. tuberculosis and discovered striking differences in innate cellular recruitment, cell-to-cell spread of bacteria in the lungs, and kinetics of initiation of antigen-specific CD4 T cell responses. We also found that M. tuberculosis can spread beyond alveolar macrophages even before a large influx of inflammatory cells. These results provide evidence that distinct strains of M. tuberculosis can exhibit differential kinetics in cell-to-cell spread which is not directly linked to early recruitment of phagocytes but is subsequently linked to adaptive immune responses.

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.

Silver Nanoparticles for the Therapy of Tuberculosis

Rapid emergence of aggressive, multidrug-resistant Mycobacteria strain represents the main cause of the current antimycobacterial-drug crisis and status of tuberculosis (TB) as a major global health problem. The relatively low-output of newly approved antibiotics contributes to the current orientation of research towards alternative antibacterial molecules such as advanced materials. Nanotechnology and nanoparticle research offers several exciting new-concepts and strategies which may prove to be valuable tools in improving the TB therapy. A new paradigm in antituberculous therapy using silver nanoparticles has the potential to overcome the medical limitations imposed in TB treatment by the drug resistance which is commonly reported for most of the current organic antibiotics. There is no doubt that AgNPs are promising future therapeutics for the medication of mycobacterial-induced diseases but the viability of this complementary strategy depends on overcoming several critical therapeutic issues as, poor delivery, variable intramacrophagic antimycobacterial efficiency, and residual toxicity. In this paper, we provide an overview of the pathology of mycobacterial-induced diseases, andhighlight the advantages and limitations of silver nanoparticles (AgNPs) in TB treatment.

Diagnosis of extrapulmonary tuberculosis using the MPT64 antigen detection test in a high-income low tuberculosis prevalence setting

BACKGROUND

Extrapulmonary tuberculosis (EPTB) poses diagnostic challenges due to the paucibacillary nature of the disease. The immunochemistry-based MPT64 antigen detection test (MPT64 test) has shown promising results for diagnosing EPTB in previous studies performed in low-resource settings, with higher sensitivity than microscopy and culture. The aim of this study was to investigate the performance of the MPT64 test in a routine clinical setting in a high-income low TB prevalence country.

METHODS

Extrapulmonary samples sent for TB diagnostics to microbiology and pathology laboratories at three regional tertiary care hospitals in Norway in a one-year period were included and subjected to the MPT64 test in parallel to the routine TB diagnostic tests.

RESULTS

Samples from 288 patients were included and categorised as confirmed TB cases (n = 26), clinically diagnosed TB cases (n = 5), non-TB cases (n = 243) and uncategorised (n = 14), using a composite reference standard (CRS). In formalin-fixed biopsies, the sensitivity (95% CI) of the MPT64 test, microscopy, PCR-based tests pooled, and culture was 37% (16-62), 20% (4-48), 37% (16-62) and 50% (23-77), respectively, against the CRS. The MPT64 test showed a good positive predictive value (88%) and an excellent specificity (99, 95% CI 92-100) in formalin-fixed biopsies. In fine-needle aspirates, pus and fluid samples, the test performance was lower.

CONCLUSIONS

The MPT64 test was implementable in pathology laboratories as part of routine diagnostics, and although the sensitivity of the MPT64 test was not better than culture in this setting, the test supplements other rapid diagnostic methods, including microscopy and PCR-based tests, and can contribute to strengthen the diagnosis of EPTB in formalin-fixed biopsies in the absence of culture confirmation.

Application of transdermal patches with new skin test reagents for detection of latent tuberculosis

Introduction. Current intradermal tuberculin skin tests for latent tuberculosis infection (LTBI) based on purified protein derivative (PPD) have poor specificity.Aims. Developing a better skin test antigen as well as a simple skin patch test may improve and facilitate diagnostic performance.Methodology. Defined recombinant antigens that were unique to Mycobacterium tuberculosis (MTB), including two potential latency-associated antigens (ESAT-6 and Rv2653c) and five DosR-encoded latency proteins (Rv1996, Rv2031c, Rv2032, DevR and Rv3716c), were used as diagnostic skin test reagents in comparison with a standard PPD. The performance of the skin tests based on the detection of delayed-type hypersensitivity (DTH) reaction in guinea pigs sensitized to MTB and M. bovis bacille Calmette-Guérin (BCG) vaccine was evaluated.Results. The latency antigens Rv1996, Rv2031c, Rv2032 and Rv2653c and the ESAT-6 protein elicited less reactive DTH skin responses in MTB-sensitized guinea pigs than those resulting from PPD, but elicited no response in BCG-vaccinated guinea pigs. The remaining two latency antigens (DevR and Rv3716c) elicited DTH responses in both groups of animals, as did PPD. The reactivity of PPD in BCG-vaccinated guinea pigs was greater than that of any of the selected skin test reagents. Using stronger concentrations of selected skin test reagents in the patch test led to increased DTH responses that were comparable to those elicited by PPD in guinea pigs sensitized with MTB.Conclusion. Transdermal application of defined purified antigens might be a promising method for LTBI screening.

Augmentation of DTH reaction of mycobacterial antigenic cocktail using synthetic mycobacterial 19-kDa lipoprotein as a TLR-stimulant

The current study proposed that previously characterized individual antigenic proteins could represent potential replacement for conventional purified protein derivative (PPD) in tuberculosis skin testing when used in cocktails triggered by suitable TLR-stimulants that would provide the missing pro-inflammatory stimulus. Three different cocktails of previously selected antigens, including C1 (ESAT-6/CPF-10/MPB-83); C2 (ESAT-6/MPB-64/MPB-83); and C3 (CPF-10/MPB-64/MPB-83), were evaluated in vitro using lymphocytic proliferation and IFN-γ production assays, as well as mRNA and protein expression levels of TNF-α, IL-12p40, and IL-2 as pro-inflammatory molecules. C1 showed the highest significant induction of pro-inflammatory molecules as compared to other cocktails, yet still significantly lower than that induced by conventional PPD. Interestingly, inclusion of the synthetic Mycobacterium tuberculosis 19-kDa lipoprotein (Pam3Cys-SSNKSTTGSGETTTA) as a TLR-stimulant resulted in obvious augmentation of C1-induced pro-inflammatory molecules to levels comparable to that of PPD. In addition, skin testing using sensitized guinea pig model revealed comparable significant reaction to that of conventional PPD. ESAT-6/CPF-10/MPB-83 cocktail is suggested as a potential alternative skin-testing reagent when used in combination with the M. tuberculosis 19-kDa lipoprotein as a TLR-stimulant.

MPT64 antigen detection test improves routine diagnosis of extrapulmonary tuberculosis in a low-resource setting: A study from the tertiary care hospital in Zanzibar

BACKGROUND

Extrapulmonary tuberculosis (EPTB) is a diagnostic challenge. An immunochemistry-based MPT64 antigen detection test (MPT64 test) has reported higher sensitivity in the diagnosis of EPTB compared with conventional methods. The objective of this study was to implement and evaluate the MPT64 test in routine diagnostics in a low-resource setting.

METHODS

Patients with presumptive EPTB were prospectively enrolled at Mnazi Mmoja Hospital, Zanzibar, and followed to the end of treatment. Specimens collected were subjected to routine diagnostics, GeneXpert® MTB/RIF assay and the MPT64 test. The performance of the MPT64 test was assessed using a composite reference standard, defining the patients as tuberculosis (TB) cases or non-TB cases.

RESULTS

Patients (n = 132) were classified as confirmed TB (n = 12), probable TB (n = 34), possible TB (n = 18), non-TB (n = 62) and uncategorized (n = 6) cases. Overall, in comparison to the composite reference standard for diagnosis, the sensitivity, specificity, positive predictive value, negative predictive value and accuracy of the MPT64 test was 69%, 95%, 94%, 75% and 82%, respectively. The MPT64 test performance was best in TB lymphadenitis cases (n = 67, sensitivity 79%, specificity 97%) and in paediatric TB (n = 41, sensitivity 100%, specificity 96%).

CONCLUSIONS

We show that the MPT64 test can be implemented in routine diagnostics in a low-resource setting and improves the diagnosis of EPTB, especially in TB lymphadenitis and in children.

Mycobacterial ESX-1 secretion system mediates host cell lysis through bacterium contact-dependent gross membrane disruptions

Mycobacterium tuberculosis and Mycobacterium marinum are thought to exert virulence, in part, through their ability to lyse host cell membranes. The type VII secretion system ESX-1 [6-kDa early secretory antigenic target (ESAT-6) secretion system 1] is required for both virulence and host cell membrane lysis. Both activities are attributed to the pore-forming activity of the ESX-1-secreted substrate ESAT-6 because multiple studies have reported that recombinant ESAT-6 lyses eukaryotic membranes. We too find ESX-1 of M. tuberculosis and M. marinum lyses host cell membranes. However, we find that recombinant ESAT-6 does not lyse cell membranes. The lytic activity previously attributed to ESAT-6 is due to residual detergent in the preparations. We report here that ESX-1-dependent cell membrane lysis is contact dependent and accompanied by gross membrane disruptions rather than discrete pores. ESX-1-mediated lysis is also morphologically distinct from the contact-dependent lysis of other bacterial secretion systems. Our findings suggest redirection of research to understand the mechanism of ESX-1-mediated lysis.

Dynamic evolution and immunoreactivity of aptamers binding to polyclonal antibodies against MPT64 antigen of Mycobacterium tuberculosis

Antibody responses can be useful markers of tuberculosis infection. However, the established immunoassay diagnostic method is limited by antigenic variability. Replacing the recombinant proteins with aptamers may overcome these antigenic challenges. In this study, we systematically monitored the selection process of aptamers against anti-MPT64 antibodies of Mycobacterium tuberculosis to obtain more aptamers for developing a multisite system to increase the sensitivity of TB serological diagnosis. Twelve high-affinity aptamers with distinctive secondary structures were obtained by analyzing the dynamic evolution of aptamers against anti-MPT64 antibodies in the process of system evolution of ligands by exponential enrichment (SELEX). Pocket and stem-loops were found to be the basis of these aptamers binding to antibodies. Point mutations of highly conserved nucleotides in the pocket and stem-loop structures resulted in decreased affinity of aptamers to targets. To test the potential of these aptamers for future use in a serological diagnostic tool, three high-affinity aptamers with different epitope specificities were applied as capture aptamer in an enzyme-linked immunosorbent assay (ELISA) with sera of TB patients. The results showed that three aptamers all effectively bound anti-MPT64 antibodies from TB patients and had high specificity and sensitivity. These aptamers with high immunoreactivity in human sera may represent an efficient and promising analogue of MPT64 and have potential to substitute MPT64 as a nucleic acid antigen in the serological diagnosis of TB. Moreover, these aptamers with different epitope specificities may facilitate the development of a sandwich assay platform or a multisite system to effectively capture more targets in sera.

Tuberculosis vaccine with high predicted population coverage and compatibility with modern diagnostics

A central goal in vaccine research is the identification of relevant antigens. The Mycobacterium tuberculosis chromosome encodes 23 early secretory antigenic target (ESAT-6) family members that mostly are localized as gene pairs. In proximity to five of the gene pairs are ESX secretion systems involved in the secretion of the ESAT-6 family proteins. Here, we performed a detailed and systematic investigation of the vaccine potential of five possible Esx dimer substrates, one for each of the five ESX systems. On the basis of gene transcription during infection, immunogenicity, and protective capacity in a mouse aerosol challenge model, we identified the ESX dimer substrates EsxD-EsxC, ExsG-EsxH, and ExsW-EsxV as the most promising vaccine candidates and combined them in a fusion protein, H65. Vaccination with H65 gave protection at the level of bacillus Calmette-Guérin, and the fusion protein exhibited high predicted population coverage in high endemic regions. H65 thus constitutes a promising vaccine candidate devoid of antigen 85 and fully compatible with current ESAT-6 and culture filtrate protein 10-based diagnostics.

Comparative genomic and proteomic anatomy of Mycobacterium ubiquitous Esx family proteins: implications in pathogenicity and virulence

Secreted proteins are among the most important molecules involved in host-pathogen interaction of Mycobacterium tuberculosis, the etiological agent of human tuberculosis (TB). M. tuberculosis encodes five types of VII secretion systems (ESX-1 to ESX-5) responsible for the exportation of many proteins. This system mediated substrates including members of the Esx family implicated in tuberculosis pathogenesis and survival within host cells. However, the distribution and evolution of this family remain elusive. To explore the evolution and distribution of Esx family proteins, we analyzed all available Mycobacteria genomes. Interestingly, amino mutations among M. tuberculosis esx family proteins may relate to their functions. We further analyzed the differences between pathogenic Mycobacteria, the attenuated Mycobacteria and non-pathogenic Mycobacteria. The stability, the globular domains and the phosphorylation of serine/threonine residues of M. tuberculosis esx proteins with their homologies among other Mycoabcteria were analyzed. Our comparative genomic and proteomic analysis found that the change of stability, gain or loss of globular domains and phosphorylation of serine/threonine might be responsible for the difference between the pathogenesis and virulence of the esx proteins and its homolog widespread among Mycobacteria and related species, which may provide clues for novel anti-tuberculosis drug targets.

Interferon Gamma Response to Combinations 38 kDa/CFP-10, 38 kDa/MPT-64, ESAT-6/MPT-64 and ESAT-6/CFP-10, Each Related to a Single Recombinant Protein ofMycobacterium tuberculosisin Individuals from Tuberculosis Endemic Areas

Several antigens of Mycobacterium tuberculosis have been identified and specificity to one or multiple antigens could determine the distinction between protective and pathogenic host reaction. Therefore T cell immune response to combinations 38 kDa/CFP-10, 38 kDa/MPT-64, ESAT-6/MPT-64 and ESAT-6/CFP-10 (each related to a single protein of Mycobacterium tuberculosis) in individuals from tuberculosis endemic areas have been examined. ELISA was used to detect IFN-gamma production in PBMC priming with single proteins and combinations in a panel of 105 individuals: 38 tuberculosis patients (6 untreated and 32 treated) and 67 healthy controls with tuberculin skin test positive or negative (TST). Brazilian TB patients highly recognized ESAT-6 (66%), but combinations improved response in the following order: ESAT-6/MPT-64 (89%) > ESAT-6/CFP-10 (73%) > 38 kDa/CFP-10 (70%), the last combination showing the highest specificity (TST(/) = 42% and TST(-) = 83%). Average IFN-gamma production in TB patients was signifi-cantly higher for 38 kDa/CFP-10 (P = 0.012) and 38 kDa/MPT-64 (P <0.035), when compared to single antigens. None of the combinations was able to discriminate TB patients from TST(+) controls; however, 38 kDa/CFP-10 displayed a borderline significance (P = 0.053). Similar to the ESAT-6/CFP-10 combination, IFN-gamma response to 38 kDa/CFP-10 showed an increased tendency in treated patients, although not signifi-cant (P = 0.16). We demonstrated for the first time that 38 kDa/CFP-10 had prediction sensitivity for TB patients similar to the ESAT-6/CFP-10 combination and also significant response improvement related to the single proteins with more selective reactivity among TST-positive individuals, which could be of potential interest for diagnostic evaluation for tuberculosis infection.

Proteomic analysis of purified protein derivative of Mycobacterium tuberculosis

Background

Purified protein derivative (PPD) has been used for more than half a century as an antigen for the diagnosis of tuberculosis infection based on delayed type hypersensitivity. Although designated as “purified,” in reality, the composition of PPD is highly complex and remains ill-defined. In this report, high resolution mass spectrometry was applied to understand the complexity of its constituent components. A comparative proteomic analysis of various PPD preparations and their functional characterization is likely to help in short-listing the relevant antigens required to prepare a less complex and more potent reagent for diagnostic purposes.

Results

Proteomic analysis of Connaught Tuberculin 68 (PPD-CT68), a tuberculin preparation generated from M. tuberculosis, was carried out in this study. PPD-CT68 is the protein component of a commercially available tuberculin preparation, Tubersol, which is used for tuberculin skin testing. Using a high resolution LTQ-Orbitrap Velos mass spectrometer, we identified 265 different proteins. The identified proteins were compared with those identified from PPD M. bovis, PPD M. avium and PPD-S2 from previous mass spectrometry-based studies. In all, 142 proteins were found to be shared between PPD-CT68 and PPD-S2 preparations. Out of the 354 proteins from M. tuberculosis–derived PPDs (i.e. proteins in either PPD-CT68 or PPD-S2), 37 proteins were found to be shared with M. avium PPD and 80 were shared with M. bovis PPD. Alignment of PPD-CT68 proteins with proteins encoded by 24 lung infecting bacteria revealed a number of similar proteins (206 bacterial proteins shared epitopes with 47 PPD-CT68 proteins), which could potentially be involved in causing cross-reactivity. The data have been deposited to the ProteomeXchange with identifier PXD000377.

Conclusions

Proteomic and bioinformatics analysis of different PPD preparations revealed commonly and differentially represented proteins. This information could help in delineating the relevant antigens represented in various PPDs, which could further lead to development of a lesser complex and better defined skin test antigen with a higher specificity and sensitivity.

In silico analysis and experimental validation of Mycobacterium tuberculosis -specific proteins and peptides of Mycobacterium tuberculosis for immunological diagnosis and vaccine development

Comparative analyses of the Mycobacterium tuberculosis genome with the genomes of other mycobacteria have led to the identification of several genomic regions of difference (RDs) between M. tuberculosis and M. bovis BCG. The identification of immunodominant and HLA-promiscuous antigens and peptides encoded by these RDs could be useful for diagnosis and the development of new vaccines against tuberculosis. The analysis of RD proteins and peptides by in silico methods (using computational programs to predict major and HLA-promiscuous antigenic proteins and peptides) and experimental validations (using peripheral blood mononuclear cells and sera from tuberculosis patients and BCG-vaccinated healthy subjects to assess antigen-specific cellular and humoral immune responses in vitro) identified several major antigens and peptides. To evaluate the in vivo potentials, the genes of immunodominant antigens were cloned and expressed in DNA vaccine vectors. Immunizations of experimental animals with the recombinant constructs induced antigen-specific cellular responses. Further experiments showed that each of these proteins had several T and B cell epitopes scattered throughout their sequence, which confirmed their strong immunogenicity. In conclusion, the bioinformatics-based in silico identification of promiscuous antigens and peptides of M. tuberculosis is a useful approach to identify new candidates important for diagnosis and vaccine applications.

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.

Purified protein derivatives of tuberculin--past, present, and future

The tuberculin skin test, which involves monitoring the immune reaction to an injection of purified protein derivative (PPD), has been the most widely used method for detecting infection with Mycobacterium tuberculosis since its development in 1930s. Until recently, the molecular composition of PPD was unknown. This thwarted the discovery of improved skin testing reagents and drastically hindered efforts to define the mechanism of action. Proteomic evaluation of PPD combined with a detailed analysis in the guinea pig model of tuberculosis led to further definition of the molecular composition of PPD. This communication reviews the history and current status of PPD, in addition to describing candidate next-generation PPD reagents, based on the use of an individual protein or protein cocktails.

Comparative genomics of Esx genes from clinical isolates of Mycobacterium tuberculosis provides evidence for gene conversion and epitope variation

The 23-membered Esx protein family is involved in the host-pathogen interactions of Mycobacterium tuberculosis. These secreted proteins are among the most immunodominant antigens recognized by the human immune system and have thus been used to develop vaccines and immunodiagnostic tests for tuberculosis (TB). Gene pairs for 10 Esx proteins are contained in the ESX-1 to ESX-5 loci, encoding type VII secretion systems. A subset of Esx proteins can be further classified into the Mtb9.9, QILSS, and TB10.4 subfamilies. To survey genetic diversity in the Esx family and its potential for antigenic variation, we sequenced all esx genes from 108 clinical isolates of M. tuberculosis from different clades by using a targeted approach. A total of 109 unique single nucleotide polymorphisms (SNPs) were observed, and 59 of these were nonsynonymous. Some of the resultant amino acid substitutions affect known Esx epitopes, including two in the EsxB (CFP-10) and EsxH (TB10.4) antigens. Assessment of the SNP distribution across the Esx proteins revealed high genetic variability, especially in the Mtb9.9 and QILSS subfamilies, and more conservation in the ESX-1 to ESX-4 loci. Comparison of the DNA sequences of variable esx genes provided clear evidence for recombination events between different genes in the same strain, some of which are predicted to truncate the corresponding protein. Many of these polymorphisms escape detection by ultrahigh-throughput sequencing using short sequence reads, as such approaches cannot distinguish between closely related genes. The esx gene family is dynamic, and sequence changes likely lead to immune variation.

Selection and application of peptide mimotopes of MPT64 protein in Mycobacterium tuberculosis

Antibody responses can be useful markers of tuberculosis (TB) infection, especially in the screening of extra-pulmonary TB. MPT64 is an important antigen in Mycobacterium tuberculosis (MTB) infection and is used in serological diagnosis. However, large variability in the diagnostic accuracy of MPT64 as a serological tool has limited its application. Phage-displayed random peptide libraries have emerged as a powerful technique to select peptides (epitopes) or mimotopes that may serve as surrogate diagnostic markers in serological tests. In the present study, this method was employed to identify mimotopes of the MPT64 protein of MTB by screening a linear heptapeptide library with rabbit antibodies raised against MPT64 protein. Two antigenic mimotopes (M2 and M6) resembling B-cell epitopes of MPT64 were identified that bound the affinity purified anti-MPT64 polyclonal antibodies and competed with MPT64 for antibody binding. From the results of sequence alignment and a structure modelling figure of MPT64, the sequence of the 2nd to 5th amino acids (DSML) of M2 was totally consistent with the sequence of the 224th to 227th amino acids of MPT64 and the peptide is located on the surface of the space structure of MPT64, suggesting that it might be a linear epitope of MPT64. The recognition of both phage-displayed and synthetic peptides of M2 by the anti-MPT64 polyclonal antibodies also supported this. Although no recurring sequence and no analogue to MPT64 of M6 were found for sequence alignment, the recognition of both phage-displayed and synthetic peptides of M6 by the anti-MPT64 polyclonal antibodies indicated that it might be a mimotope of a conformational epitope of MPT64. According to the results of the reactivity of human sera with synthetic M2 and M6 peptides and MPT64, M2 showed a significantly higher AUC and sensitivity than M6 and MPT64, especially for the sera from sputum-negative TB patients, suggesting that the M2 mimotope may be useful in serological diagnostic testing for TB.

Divergence of immunologic and protective responses of different BCG strains in a murine model

The ongoing evolution of BCG after its introduction in 1921 resulted in strains that differ genetically and phenotypically. Based on a genomic deletion (Region of Difference 2 or RD2) that occurred between 1927 and 1931, BCG strains can be sub-classified by the presence or absence of RD2. The existence of other mutations that distinguish BCG strains precludes simple comparison of RD2-positive and RD2-negative BCG strains to determine the importance, if any, of RD2 for vaccine protection. In this study, we have compared the RD2-containing BCG Russia, BCG Pasteur (which is a natural mutant for RD2), and BCG Pasteur complemented with RD2-genes Rv1979c-Rv1982 through various in vitro and in vivo assays of immunogenicity and protection. We determined that the presence of RD2 did not affect vaccine persistence, but lead to increased immunogenicity, as measured by ELISpot. Additionally, T-cells from animals immunized with BCG Russia and BCG Pasteur::Rv1979c-82 were more effective at killing Mycobacterium tuberculosis in macrophages than T-cells from animals immunized with BCG Pasteur. In a mouse vaccine-challenge model, the presence of RD2 had no effect on pulmonary TB, as measured by M. tuberculosis burden and degree of histopathology, at 4, 8 or 12 weeks post-infection. The presence of RD2 was however associated with decreased dissemination of M. tuberculosis to the spleen. Together, our data demonstrated that the loss of RD2 resulted in decreased immunogenicity but did not affect protection against pulmonary TB, indicating a dissociation between these phenotypes associated with BCG vaccination.

Three protein cocktails mediate delayed-type hypersensitivity responses indistinguishable from that elicited by purified protein derivative in the guinea pig model of Mycobacterium tuberculosis infection

Purified protein derivative (PPD) is a widely used reagent for the diagnosis of Mycobacterium tuberculosis infection. Recently, the molecular composition of PPD was defined, with hundreds of mycobacterial protein representatives making up PPD. Which, if any, of these specific products drive the potency of PPD remains in question. In this study, two proteins (DnaK and GroEL2) previously identified as dominant proteins in PPD were tested for the capacity to induce delayed-type hypersensitivity (DTH) responses in H37Rv-infected or BCG-vaccinated guinea pigs. These two proteins were used in pull-down assays to identify interacting PPD products. Six proteins were identified as interacting partners with DnaK and GroEL2, i.e., Rv0009, Rv0475, Rv0569, Rv0685, Rv2626c, and Rv2632c. These six proteins were tested alone and in combination with DnaK and GroEL2 for the capacity to induce a DTH response in the guinea pig model. From these studies, two cocktails, DnaK/GroEL2/Rv0009 and DnaK/GroEL2/Rv0685, were found to induce DTH responses in H37Rv-infected or BCG-vaccinated guinea pigs that were indistinguishable from DTH responses driven by a PPD injection. The mechanism by which DTH responses were induced was elucidated by histologic examination, analysis of activated CD4(+)/CD8(+) T cells, and cytokine mRNA expression at the site of the DTH response. PPD and the protein cocktails tested induced strong DTH responses in H37Rv-infected guinea pigs. Ex vivo phenotyping of T cells at the DTH site indicated that this response is mediated by activated CD4(+) and CD8(+) T cells, with increases in gamma interferon and tumor necrosis factor alpha, but not interleukin-10, at the site of the DTH response. Our results demonstrate for the first time that the PPD response can be mimicked at the molecular level with defined protein cocktails. The use of this defined product will allow a more thorough understanding of the DTH response and may provide a platform for more rapid and sensitive second-generation skin test reagents for the diagnosis of M. tuberculosis infection.

Contrasting transcriptional responses of a virulent and an attenuated strain of Mycobacterium tuberculosis infecting macrophages

Background

H37Rv and H37Ra are well-described laboratory strains of Mycobacterium tuberculosis derived from the same parental strain, H37, that show dramatically different pathogenic phenotypes.

Methodology/Principal Findings

In this study, the transcriptomes of the two strains during axenic growth in broth and during intracellular growth within murine bone-marrow macrophages were compared by whole genome expression profiling. We identified and compared adaptations of either strain upon encountering an intracellular environment, and also contrasted the transcriptomes of the two strains while inside macrophages. In the former comparison, both strains induced genes that would facilitate intracellular survival including those involved in mycobactin synthesis and fatty acid metabolism. However, this response was stronger and more extensive for H37Rv than for H37Ra. This was manifested as the differential expression of a greater number of genes and an increased magnitude of expression for these genes in H37Rv. In comparing intracellular transcriptional signatures, fifty genes were found to be differentially expressed between the strains. Of these fifty, twelve were under control of the PhoPR regulon. Further differences between strains included genes whose products were members of the ESAT-6 family of proteins, or were associated with their secretion.

Conclusions/Significance

Along with the recent identification of single nucleotide polymorphisms in H37Ra when compared to H37Rv, our demonstration of differential expression of PhoP-regulated and ESX-1 region-related genes during macrophage infection further highlights the significance of these genes in the attenuation of H37Ra.

Biomarkers of disease activity, cure, and relapse in tuberculosis

The changing face of tuberculosis, with epidemics fueled by HIV and urbanization in much of the world and a relative increase in the importance of latent tuberculosis as a source of cases in the more economically developed countries, has led to a demand for more robust, clinically applicable diagnostic tools. As a result, research aiming to identify biomarkers of Mycobacterium tuberculosis infection and disease has flourished. This article discusses the most recent findings of that work.

Screening of predicted secreted antigens from Mycobacterium bovis reveals the immunodominance of the ESAT-6 protein family

Results of previous studies utilizing bioinformatic approaches in antigen-mining experiments revealed that secreted proteins are among the most frequently recognized antigens from Mycobacterium bovis. Thus, we hypothesized that the analysis of secreted proteins is likely to reveal additional immunogenic antigens that can be used to increase the specificity of diagnostic tests or be suitable vaccination candidates for mycobacterial infections. To test this hypothesis, 382 pools of overlapping peptides spanning 119 M. bovis secreted and potentially secreted proteins were screened for the ability to stimulate a gamma interferon response in vitro using whole blood from tuberculin-positive reactor (TB reactor) cattle. Of the 119 proteins screened, 70 (59%) induced positive responses in the TB reactor animals to various degrees. Strikingly, all but one of the 15 ESAT-6 proteins tested were recognized by at least 30% of the TB reactor animals, with 12 of the 22 most commonly recognized antigens belonging to this protein family. Further analysis of these data demonstrated that there was no significant difference in immunogenicity between the ESAT-6 proteins that were components of potentially intact ESX secretory systems and those corresponding to additional partial esx loci. Importantly for vaccine design, antigenic epitopes in some highly conserved regions shared by numerous ESAT-6 proteins were identified. However, despite this considerable homology, peptide-mapping experiments also revealed that immunodominant peptides were located in regions of amino acid variability.

The selection and application of ssDNA aptamers against MPT64 protein in Mycobacterium tuberculosis

BACKGROUND

Tuberculosis (TB) remains a major health problem affecting millions of people worldwide. One-third of the world's population is infected with Mycobacterium tuberculosis, the etiologic agent of TB. A simple and rapid method to diagnose TB is urgently needed to be developed. The procedure of systematic evolution of ligands by exponential enrichment (SELEX) is a method in which single-stranded oligonucleotides (called aptamers) are selected from a wide variety of sequences, based on their interaction with a target molecule. Aptamers have been used in numerous investigations as therapeutic or diagnostic tools.

METHODS

In this study, we apply a SELEX method to develop aptamers against MPT64 protein from M. tuberculosis. On this basis, a sandwich assay scheme with the complex of aptamer-MPT64 was designed and tested the feasibility of detecting M. tuberculosis by detecting MPT64 protein levels in the culture filtrates of 77 samples including M. tuberculosis and other Mycobacterium species.

RESULTS

There was a highly significant difference (p<0.01) between group A (non-TB Mycobacterium, bacille Calmette-Guérin) and group B (M. tuberculosis, M. bovis), when they were diagnosed with the sandwich assay scheme based on aptamer-protein complex to detect MPT64 protein levels in the culture filtrates of samples. When the cut-off point was at the optical density value of 0.58 (95%=0.764-0.946; Z=6.130, p=0.0001), the sandwich assay scheme based on aptamer-protein complex had a high sensitivity (negative ration, 24/27, 86.3%) and specificity (positive ration, 46/52, 88.5%).

CONCLUSIONS

Aptamer of MPT64 as a new detection tool, to a certain extent, is feasible to diagnose Mycobacterium tuberculosis.

An improved whole-blood gamma interferon assay based on the CFP21-MPT64 fusion protein

Differentiation of latent tuberculosis infection (LTBI) from a healthy, unexposed population plays a vital role in the strategy of controlling and eliminating tuberculosis (TB). Both CFP21 and MPT64, antigens encoded by the RD2 region which are restricted in the Mycobacterium tuberculosis complex, are TB-specific diagnostic candidate antigens. In this study, we designed a fusion protein by linking both CFP21 and MPT64 with a 15-amino-acid peptide, (G(4)S(1))(3), and overexpressed the fusion protein in Escherichia coli. A new whole-blood gamma interferon assay based on the recombinant fusion protein, CFP21-MPT64 (rCM-WBIA), was developed and compared with the tuberculin skin test (TST) for screening of LTBI in household contacts of patients with sputum-positive TB. rCM-WBIA had a slightly higher sensitivity (66.7%; 24/36 contacts) than that of the TST (61.1%; 22/36 contacts) for household contacts. We found that rCM-WBIA had a very high sensitivity (90.9%) and specificity (71.4%) for LTBI detection compared with TST. The overall agreement between rCM-WBIA and TST was 83.3% (k = 0.64); rCM-WBIA positivity was associated with a larger TST induration. These results suggest that rCM-WBIA, based on the recombinant fusion protein CFP21-MPT64, is a promising alternative diagnostic tool for detection of LTBI.

Clinical evaluation of the recombinant 38 kDa protein of Mycobacterium tuberculosis

The diagnosis of tuberculosis remains among public health concerns due to shortcomings of the purified protein derivative (PPD). Recombinant truncated 38 kDa protein (rTPA38) of Mycobacterium tuberculosis was evaluated to screen new tuberculosis-specific tuberculin. 539 patients, 1133 healthy controls, and 55 guinea pigs were recruited to assess their sensitivity and specificity to rTPA38; 221 healthy controls, with negative responses to rTPA38 and PPD, were vaccinated with M. bovis BCG to determine their cross-reactions with M. bovis BCG. The Mantoux technique was adopted to perform skin tests. No difference in the sensitivity of skin tests was detected between rTPA38 and PPD (78.2% vs 83.4%), but there was a significant difference in the specificity of skin tests between rTPA38 and PPD (75.2% vs 47.0%). Compared to PPD, rTPA38 elicited low positive responses for those recruitments vaccinated with M. bovis BCG. The rTPA38 had significant skin reactions in M. tuberculosis-sensitized guinea pigs, and the opposite was true for both M. fortuitum- and M. kansasii-sensitized guinea pigs. These findings indicate that rTPA38 may have potential as a tuberculosis-specific skin test antigen.

Construction of an encapsulated ESAT-6-based anti-TB DNA vaccine and evaluation of its immunogenic properties

Experimental preparations based on a DNA vaccine encoding the ESAT-6 antigen ofMycobacterium tuberculosishave been obtained (KpONE6) and studied for immunogenic effects in the murine model. The core of the preparation contains DNA of the recombinant plasmid pONE6 encapsulated within a spermidine-polyglucin conjugate, thereby protecting the DNA vaccine from degradation. KpONE6 induces a proliferative T-cell immune response in mice upon intramuscular immunization.

Recombinant early secreted antigen target 6 protein as a skin test antigen for the specific detection of Mycobacterium tuberculosis infection

Although the delayed-type hypersensitivity skin test reaction to tuberculin purified protein derivative (PPD) is used worldwide for tuberculosis (TB) detection, it is incapable of distinguishing Mycobacterium tuberculosis (MTB) infection from bacille Calmette-Guérin (BCG) vaccination or infection with non-tuberculous Mycobacteria. As a result, there is an urgent need for a more specific diagnostic tool for TB. This study reports the skin reactions of guinea pigs and human volunteers to recombinant early secreted antigen target 6 (rESAT6), a secretory protein found only in MTB, M. bovis and few other mycobacterial species. These volunteers had varying histories of BCG vaccination and exposure to MTB, allowing us to determine the specificity of their response to TB exposure. Our results show that 1.0 microg of the purified MTB rESAT6 antigen elicited a positive skin response in both animals and humans exposed to MTB, as well as in animals exposed to M. bovis and M. marinum, all species of Mycobacteria that contain the gene for early secreted antigen target 6 (ESAT6). ESAT6 appears to be more specific to MTB infection than PPD, as demonstrated by the fact that we saw no skin responses in the BCG-vaccinated volunteers, nor in the guinea pigs sensitized with BCG vaccine, or with Mycobacteria that do not contain the gene encoding ESAT6. We believe that this is the first report of the use of a rESAT6 protein in a skin test in human volunteers, and that these data support its use in the specific detection of MTB infection.

Immune response to Nocardia brasiliensis extracellular antigens in patients with mycetoma

The ability of culture-filtrate proteins to induce a cellular immune response in infected mice and humans was investigated. A crude extract culture filtrate of Nocardia brasiliensis (CFA) and five semi-purified CFA fractions (P1, P2, P3, P4, P5) were used to stimulate BALB/c mice spleen-cell cultures. The animals were divided into three groups: the first group was infected with 1 x 10(7) CFU of N. brasiliensis in the footpad, the second group was immunized with heat-killed bacteria, and the third was injected with sterile saline. IFN-gamma, IL-1alpha, and IL-4 concentrations were determined in culture supernatants. Protein fractions eliciting IFN-gamma production in mice, as well as the CFA, were used to stimulate IFN-gamma production and in vitro cell proliferation assays with peripheral blood mononuclear cells of patients with actinomycetoma by N. brasiliensis, individuals with pulmonary tuberculosis, and healthy controls. In mice, CFA and three of the protein fractions (P3, P4 and P5) induced significant IFN-gamma production in the infected group. In humans, only the CFA-induced IFN-gamma production and cell proliferation in the group of patients with actinomycetoma. There was no stimulation in tuberculosis patients nor healthy controls. These results suggest that some culture-filtrate antigens are recognized by patients with active actinomycetoma and do not cross-react with M. tuberculosis antigens, being therefore potential candidates to develop a diagnostic test.

Differential expression of mycobacterial antigen MPT64, apoptosis and inflammatory markers in multinucleated giant cells and epithelioid cells in granulomas caused by Mycobacterium tuberculosis

The development of granulomas is a major histopathological feature of tuberculosis. Very little information is available concerning the physiology and functions of different cell types in the tuberculous granulomas. The aim of this study was to compare the epithelioid cells (ECs) and multinucleated giant cells (MGCs) in the granulomas caused by Mycobacterium tuberculosis complex organisms. Lymph node biopsies from 30 cases of lymphadenitis were studied for expression of the secreted mycobacterial protein MPT64, caspase 3 as a marker of apoptosis, apoptosis-related proteins (Fas Ligand, Fas and Bax) and inflammatory cytokines (interleukin-10, transforming growth factor-β (TGF-β), tumour necrosis factor-α and interferon-γ) by immunohistochemistry. MGCs more often contained M. tuberculosis secretory antigen MPT64 (p < 0.001) and expressed more TGF-β (p = 0.004) than ECs. The total number of apoptotic MGCs was higher than the number of apoptotic ECs (p = 0.04). Interestingly, there was a significant negative correlation between apoptosis and MPT64 expression in MGCs (r = −0.569, p = 0.003), but not in ECs, implying that the heavy antigen load would lead to inhibition of apoptosis in these cells. When compared with ECs, higher percentage of MGCs expressed Fas Ligand and Fas (p < 0.004). The role of MGCs may thus be different from surrounding ECs and these cells by virtue of higher mycobacterial antigen load, more TGF-β and reduced apoptosis may contribute towards persistence of infection.

Reduced apoptosis and increased inflammatory cytokines in granulomas caused by tuberculous compared to non-tuberculous mycobacteria: role of MPT64 antigen in apoptosis and immune response

Inhibition of apoptosis of infected macrophages by pathogenic mycobacteria is suggested to be an important virulence mechanism, but little is known about the mycobacterial proteins involved in the inhibition of apoptosis. In this study we investigated differences in apoptosis and immune response and their correlation with the expression of Mycobacterium tuberculosis complex-specific secretory protein MPT64 in lesions caused by tuberculous or non-tuberculous mycobacteria by analysing the in situ expression of apoptosis-related proteins (FasL, Fas, Bax, Bcl-2), apoptotic cells, inflammatory cytokines [tumour necrosis factor (TNF)-alpha, interleukin (IL)-10, transforming growth factor (TGF)-beta, interferon (IFN)-gamma] and MPT64 antigen. The discrimination of mycobacteria was made by nested polymerase chain reaction (PCR) amplification of IS6110, which is specific for M. tuberculosis complex organisms. Forty-seven cases of lymphadenitis with necrotic granulomas were evaluated. With nested PCR, 30/47 cases were positive for M. tuberculosis. MPT64 antigen was detected specifically in the PCR-positive cases. Granulomas caused by tuberculous mycobacteria had fewer apoptotic cells, higher numbers of cells expressing TNF-alpha and TGF-beta and less extensive necrosis than granulomas caused by non-tuberculous mycobacteria. There was a significant negative correlation between apoptotic cells and the number of cells expressing MPT64 antigens, suggesting a role for MPT64 protein in the inhibition of apoptosis. Granulomas with higher amounts of MPT64 also showed a greater number of cells expressing TGF-beta than those with lower amounts of MPT64. In conclusion, this study supports the hypothesis that inhibition of apoptosis is a virulence mechanism for tuberculous mycobacteria. Correlation of MPT64 antigen with expression of macrophage deactivating cytokines and reduced apoptosis suggests its role in pathogenesis and bacillary persistence.

Effects of pre-culture holding time and temperature on interferon-γ responses in whole blood cultures from Mycobacterium bovis-infected cattle

The Bovigam assay is approved for use within the United States as a complementary tuberculosis test. Prior to whole blood culture and the ensuing ELISA to detect interferon-(IFN)-gamma, samples are subjected to various holding time/temperature combinations due, in part, to practical constraints associated with shipment of samples to approved laboratories. To evaluate these effects, 5-month-old Holstein calves (n = 7) received 10(3) cfu Mycobacterium bovis by aerosol. Heparinized blood was collected 2 months after challenge and held at 4 or 22 degrees C for 0, 8 or 24 h prior to culture with mycobacterial antigens or pokeweed mitogen (PWM). Responses of samples held for 8 or 24 h were comparable and lower than responses of cultures prepared immediately after collection, regardless of holding temperature. Differences in responses of samples held at 4 degrees C versus 22 degrees C were also minimal. A subset of samples was held for 2 h at 37 degrees C at the beginning of the holding period. This subset of samples had diminished responses to all stimulants and increased holding times (i.e., 24 h versus 8 h) negatively impacted the response. Pre-processing conditions, particularly delays in set-up and initial high sample temperatures, reduces IFN-gamma responses of cells from infected cattle increasing the risk of false negatives in this assay of regulatory importance.

Immunohistochemistry using a Mycobacterium tuberculosis complex specific antibody for improved diagnosis of tuberculous lymphadenitis

The clinical and histological criteria used to diagnose lymphadenitis caused by Mycobacterium tuberculosis complex organisms have poor specificity. Acid-fast staining and culture has low sensitivity and specificity. We report a novel method for diagnosis of tuberculosis that uses immunohistochemistry to detect the secreted mycobacterial antigen MPT64 on formalin-fixed tissue biopsies. This antigen has not been detected in non-tuberculous mycobacteria. Polymerase chain reaction (PCR) for amplification of IS6110 from DNA obtained from the biopsies was used as a gold standard. Fifty-five cases of granulomatous lymphadenitis with histologically suspected tuberculosis obtained from Norway and Tanzania were evaluated. Four known tuberculosis cases were used as positive controls, and 16 biopsies (12 foreign body granulomas and four other non-granulomatous cases) as negative controls. With immunohistochemistry, 64% (35/55) and with PCR, 60% (33/55) of granulomatous lymphadenitis cases were positive. Using PCR as the gold standard, the classical tuberculosis histology had sensitivity, specificity, positive and negative predictive values of 92, 37, 60, and 81%, respectively, and immunohistochemistry had sensitivity, specificity, positive and negative predictive values of 90, 83, 86, and 88%, respectively. The observed agreement between PCR and immunohistochemistry was 87% (kappa = 0.73). Immunohistochemistry with anti-MPT64 antiserum is a rapid, sensitive, and specific method for establishing an etiological diagnosis of tuberculosis in histologic specimens. Immunohistochemistry has the advantages over PCR of being robust and cheap, and it can easily be used in a routine laboratory.

Safety of ESAT-6

A recombinant dimer of the Mycobacterium tuberculosis (MTb) 6 kDa early secreted antigenic target (ESAT-6) was produced in Lactococcus lactis. Pharmacodynamic and safety studies were carried out in guinea pigs, rats, mice and dogs with intradermal (id), subcutaneous (sc) and intravenous (iv) administration of the antigen. In contrast to tuberculin purified protein derivative (PPD) the recombinant dimer (rdESAT-6) was able to discriminate MTb infection from BCG vaccination in vivo. In guinea pigs sensitized by infection with MTb, 1 microg rdESAT-6 gave a mean delayed-type hypersensitivity (DTH) response of 22 mm, a significantly stronger reaction than in animals sensitised by the environmental mycobacteria M. kansasii, M. szulgai and M. marinum. rdESAT-6 proved to be a safe tuberculin reagent in a dose range of 1-1000 microg with no or only minor local reactions.

Expression and purification of the Mycobacterium tuberculosis complex-restricted antigen CFP21 to study its immunoprophylactic potential in mouse model

Secreted proteins encoded by different regions of difference (RDs) from the genome of Mycobacterium tuberculosis have been considered as attractive candidates for vaccination against tuberculosis owing to their absence in most BCG strains. In this study, the structural gene for the RD2 locus encoding protein CFP21 was PCR amplified and expressed as a fusion protein with hexahistidine residues in Escherichia coli. Expression of CFP21 in E. coli under transcriptional regulation of the T7 promoter yielded a protein located within inclusion bodies. The inclusion bodies were solubilized in the presence of 8M urea and the protein was purified to homogeneity under denaturing conditions at low pH using nitrilotriacetic acid (Ni-NTA) affinity chromatography. The denatured protein was renatured by gradient dialysis against a decreasing concentration of urea. The purified protein was shown to have esterase activity. CFP21 protein was evaluated for immunogenicity in C57BL/6J mice. We observed an elevated T cell proliferative response and production of IFN-gamma and IL-12 (p40). CFP21 also induced an optimum level of cytotoxic T cell activity and induced a strong humoral response as indicated by higher levels of specific IgG1 and IgG2a antibody isotypes. In addition, a moderate level of protection was observed against experimental tuberculosis. This is the first report describing esterase activity of the M. tuberculosis complex-restricted protein CFP21 and its protective potential against experimental tuberculosis.

Impaired Generation of Reactive Oxygen Species during Differentiation of Dendritic Cells (DCs) byMycobacterium tuberculosisSecretory Antigen (MTSA) and Subsequent Activation of MTSA-DCs by Mycobacteria Results in Increased Intracellular Survival

We investigated the role of reactive oxygen species (ROS) in dendritic cell (DC) differentiation by 10-kDa Mycobacterium tuberculosis secretory Ag (MTSA) and survival of mycobacteria therein. Compared with GM-CSF, MTSA induced lower ROS production during DC differentiation from precursors. This result correlated with higher superoxide dismutase 1 expression in MTSA stimulated precursors as compared with GM-CSF stimulation. Furthermore, a negative regulation of protein kinase C (PKC) activation by ROS was observed during DC differentiation. ROS inhibited the rapid and increased phosphorylation of PKCalpha observed during DC differentiation by MTSA. In contrast, ROS inhibition increased the weak and delayed PKCalpha phosphorylation by GM-CSF. Similar to DC differentiation, upon activation with either M. tuberculosis cell extract (CE) or live Mycobacterium bovis bacillus Calmette-Guérin (BCG), DCs differentiated with MTSA (MTSA-DCs) generated lower ROS levels when compared with DCs differentiated with GM-CSF (GM-CSF-DCs). Likewise, a negative regulation of PKCalpha phosphorylation by ROS was once again observed in DCs activated with either M. tuberculosis CE or live M. bovis BCG. However, a reciprocal positive regulation between ROS and calcium was observed. Compared with MTSA-DCs, stimulation of GM-CSF-DCs with M. tuberculosis CE induced a 2-fold higher ROS-dependent calcium influx. However, pretreatment of MTSA-DCs with H(2)O(2) increased calcium mobilization. Finally, lower ROS levels in MTSA-DCs correlated with increased intracellular survival of M. bovis BCG when compared with survival in GM-CSF-DCs. Although inhibiting ROS in GM-CSF-DCs increased M. bovis BCG survival, H(2)O(2) treatment of MTSA-DCs decreased survival of M. bovis BCG. Overall our results suggest that DCs differentiated with Ags such as MTSA may provide a niche for survival and/or growth of mycobacteria following sequestration of ROS.

Diagnostic implications of antigen-induced gamma interferon production by blood leukocytes from Mycobacterium bovis-infected reindeer (Rangifer tarandus)

The only approved method of tuberculosis (TB) surveillance of reindeer within the United States is tuberculin skin testing; however, skin testing has an apparent lack of specificity, since numerous reindeer are classified as reactors, yet Mycobacterium bovis is not isolated from tissues upon necropsy. The objective of this study was to evaluate the ability of an in vitro assay (the Cervigam assay) to detect gamma interferon (IFN-gamma) produced by blood leukocytes in response to mycobacterial antigens from M. bovis-infected reindeer. Thirteen male reindeer approximately 9 months of age were inoculated with 10(5) CFU M. bovis in their tonsillar crypts. Stimulation of whole-blood cultures with a mitogen resulted in significant production of IFN-gamma compared to that by nonstimulated samples. Responses by infected reindeer to M. bovis purified protein derivative (PPD) were as much as 3.5-fold higher than those by noninfected reindeer (n = 4). Despite differences in responses to PPD by the two groups, reindeer within the noninfected group had responses of >0.1 change in optical density (DeltaOD) (a level generally considered positive) to PPD. Mean responses by infected reindeer to a rESAT-6-CFP-10 fusion protein (Mycobacterium tuberculosis complex specific) were as much as 20-fold higher than respective responses by noninfected reindeer at all time points. Additionally, responses by 3/4 noninfected reindeer were <0.1 DeltaOD (considered negative) at each time point. To further evaluate the specificity of the assay, samples were collected from reindeer in a TB-free herd. All reindeer had responses to mitogen; however, only 1 of 38 had a response to PPD, and none of the reindeer responded to rESAT-6-CFP-10. Together, these findings indicate that IFN-gamma-based tests may prove useful for TB surveillance of reindeer.

Regulation of immune responses to Mycobacterium tuberculosis secretory antigens by dendritic cells

Towards elucidating the immune responses induced by antigens from the Mycobacterium tuberculosis (M. tb) RD-1 region, we have been characterizing their interactions with dendritic cells (DCs) and their precursors. We have shown that incubation of bone marrow DC precursors with M. tb antigens induces the differentiation of DC precursors and also the maturation of various DC subsets. While MTSA differentiated DCs were immature, MTSA matured DCs were terminally mature. However, regardless of their maturation status M. tb secretory antigen-activated DCs down-regulated pro-inflammatory T helper cell responses to a subsequent challenge with M. tb cell extract (CE) while increasing regulatory responses. Investigations into the underlying mechanisms showed that stimulation with M. tb CE changed the polarization of antigen-activated DCs from DC1 to DC2. This resulted in secretion of high levels of IL-10 and TGF-beta together with increased surface expression of CD86. Blocking either IL-10 or TGF-beta or CD86 restored Th1 responses to CE antigens. Conversely, treatment of antigen-activated DCs with IL-12 and/or IFN-gamma fully restored Th1 responses of CE antigens. These results indicate that M. tb strategically secretes antigens from infected macrophages to down-regulate pro-inflammatory immune responses at sites of infection.

The diagnosis of tuberculosis

Diagnostic testing for tuberculosis has remained unchanged for nearly a century, but newer technologies hold the promise of a true revolution in tuberculosis diagnostics. New tests may well supplant the tuberculin skin test in diagnosing latent tuberculosis infection in much of the world. Tests such as the nucleic acid amplification assays allow more rapid and accurate diagnosing of pulmonary and extrapulmonary tuberculosis. The appropriate and affordable use of any of these tests depends on the setting in which they are employed.

Mycobacterium tuberculosis 6kDa early secreted antigenic target stimulates activation of J774 macrophages

The influence of the 6 kDa early-secreted antigenic target (ESAT-6) of Mycobacterium tuberculosis on macrophage activation was investigated using J774 macrophage cell line. While without effect if applied alone, ESAT-6 in a dose-dependent manner enhanced nitric oxide (NO) release by IFN-gamma-stimulated J774 cells. However, it completely failed to modulate NO production in J774 cells activated with E. coli lipopolysaccharide. The effect of ESAT-6 on NO synthesis in IFN-gamma-activated J774 cells was accompanied by up-regulated expression of inducible NO synthase (iNOS), an enzyme that catalyzes NO formation. ESAT-6-mediated enhancement of macrophage NO release was markedly suppressed by pharmacological agents that selectively inhibit iNOS enzymatic activity or protein tyrosine kinase and mitogen-activated protein kinase activation. Finally, treatment of J774 macrophages with ESAT-6 also enhanced IFN-gamma-induced expression of the surface molecules B7.1, MHC-II, and ICAM-1. Collectively, these data suggest that ESAT-6 might contribute to macrophage activation in tuberculosis.