Molecular cloning, expression, and immunogenicity of MTB12, a novel low-molecular-weight antigen secreted by Mycobacterium tuberculosis

Novel structure of secreted small molecular weight antigen Mtb12 from Mycobacterium tuberculosis

Mtb12, a small protein secreted by Mycobacterium tuberculosis, is known to elicit immune responses in individuals infected with the pathogen. It serves as an antigen recognized by the host's immune system. Due to its immunogenic properties and pivotal role in tuberculosis (TB) pathogenesis, Mtb12 is considered a promising candidate for TB diagnosis and vaccine development. However, the structural and functional properties of Mtb12 are largely unexplored, representing a significant gap in our understanding of M. tuberculosis biology. In this study, we present the first structure of Mtb12, which features a unique tertiary configuration consisting of four beta strands and four alpha helices. Structural analysis reveals that Mtb12 has a surface adorned with a negatively charged pocket adjacent to a central cavity. The features of these structural elements and their potential effects on the function of Mtb12 warrant further exploration. These findings offer valuable insights for vaccine design and the development of diagnostic tools.

Proteome characterization of the culture supernatant of Mycobacterium bovis in different growth stages

This study aimed to identify proteins secreted by Mycobacterium bovis into culture medium at different stages of bacterial growth. A field strain of M. bovis was grown in Middlebrook 7H9 media and culture supernatant was collected at three-time points representing three different phases of growth (early exponential, late exponential, and stationary phases). Supernatants were double filtered, digested by trypsin and analyzed by LC-MS/MS. The study found 15, 21, and 16 proteins in early, mid and late growth phases, respectively. In total, 22 proteins were identified, 18 of which were reported or predicted to have a cell wall or extracellular localization. To our knowledge, this is the first study to identify proteins secreted into the culture medium by a field strain of M. bovis in three different stages of growth. The dataset generated here provides candidate proteins with the potential for the development of serological diagnostic reagents or vaccine for bovine tuberculosis. Data are available via ProteomeXchange with identifier PXD017817.

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Identifying extracellular proteins produced by M. bovis using mass spectrometry.

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Culture supernatant proteins secreted in three different stages of bacterial growth.

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Proteins were secreted from live bacteria and heat-killing was omitted.

Biofilm formation in the lung contributes to virulence and drug tolerance of Mycobacterium tuberculosis

Tuberculosis is a chronic disease that displays several features commonly associated with biofilm-associated infections: immune system evasion, antibiotic treatment failures, and recurrence of infection. However, although Mycobacterium tuberculosis (Mtb) can form cellulose-containing biofilms in vitro, it remains unclear whether biofilms are formed during infection in vivo. Here, we demonstrate the formation of Mtb biofilms in animal models of infection and in patients, and that biofilm formation can contribute to drug tolerance. First, we show that cellulose is also a structural component of the extracellular matrix of in vitro biofilms of fast and slow-growing nontuberculous mycobacteria. Then, we use cellulose as a biomarker to detect Mtb biofilms in the lungs of experimentally infected mice and non-human primates, as well as in lung tissue sections obtained from patients with tuberculosis. Mtb strains defective in biofilm formation are attenuated for survival in mice, suggesting that biofilms protect bacilli from the host immune system. Furthermore, the administration of nebulized cellulase enhances the antimycobacterial activity of isoniazid and rifampicin in infected mice, supporting a role for biofilms in phenotypic drug tolerance. Our findings thus indicate that Mtb biofilms are relevant to human tuberculosis.

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

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

Evaluation of cellular immunogenicity of recombinant cytochrome p450 cyp141 protein of Mycobacterium tuberculosis in human and mouse model

Mycobacterium tuberculosis (Mtb) is still considered one of the unsolved problems for the World Health Organization Identifying and selecting an immunogenic antigen capable of generating specific immune responses is generally the goal of all studies being carried out in to designing new vaccines. Accordingly, the present study was conducted to evaluate the immunogenicity of a M. tuberculosis recombinant protein which exist in the regions of the bacterium genome and may be an immunogenic protein. Immunogenicity of purified proteins was measured by PBMC and mouse spleen lymphocytes culturing methods using ELISA after an appropriate amount of time of incubation with Recombinant cytochrome P450 CYP141 protein. Cellular immune responses were determined and compared by measuring IFN-γ and IL4 in human, and mouse groups. The results revealed a high level of IFN-γ in PPD + individuals and the mice immunized with protein and adjuvant. Recombinant cytochrome P450 CYP141 protein proved capable of generating an immune response in mice and people with a history of previous encounters with Mycobacterium tuberculosis bacteria. It, could be considered a tuberculosis vaccine candidate in order to induce a specific effective immune response in both mice and humans.

FurA contributes to the oxidative stress response regulation of Mycobacterium avium ssp. paratuberculosis

The ferric uptake regulator A (FurA) is known to be involved in iron homeostasis and stress response in many bacteria. In mycobacteria the precise role of FurA is still unclear. In the presented study, we addressed the functional role of FurA in the ruminant pathogen Mycobacterium avium ssp. paratuberculosis (MAP) by construction of a furA deletion strain (MAPΔfurA). RNA deep sequencing revealed that the FurA regulon consists of repressed and activated genes associated to stress response or intracellular survival. Not a single gene related to metal homeostasis was affected by furA deletion. A decisive role of FurA during intracellular survival in macrophages was shown by significantly enhanced survival of MAPΔfurA compared to the wildtype, indicating that a principal task of mycobacterial FurA is oxidative stress response regulation in macrophages. This resistance was not associated with altered survival of mice after long term infection with MAP. Our results demonstrate for the first time, that mycobacterial FurA is not involved in the regulation of iron homeostasis. However, they provide strong evidence that FurA contributes to intracellular survival as an oxidative stress sensing regulator.

Recombinant protein truncation strategy for inducing bactericidal antibodies to the macrophage infectivity potentiator protein of Neisseria meningitidis and circumventing potential cross-reactivity with human FK506-binding proteins

A recombinant macrophage infectivity potentiator (rMIP) protein of Neisseria meningitidis induces significant serum bactericidal antibody production in mice and is a candidate meningococcal vaccine antigen. However, bioinformatics analysis of MIP showed some amino acid sequence similarity to human FK506-binding proteins (FKBPs) in residues 166 to 252 located in the globular domain of the protein. To circumvent the potential concern over generating antibodies that could recognize human proteins, we immunized mice with recombinant truncated type I rMIP proteins that lacked the globular domain and the signal leader peptide (LP) signal sequence (amino acids 1 to 22) and contained the His purification tag at either the N or C terminus (C-term). The immunogenicity of truncated rMIP proteins was compared to that of full (i.e., full-length) rMIP proteins (containing the globular domain) with either an N- or C-terminal His tag and with or without the LP sequence. By comparing the functional murine antibody responses to these various constructs, we determined that C-term His truncated rMIP (-LP) delivered in liposomes induced high levels of antibodies that bound to the surface of wild-type but not Δmip mutant meningococci and showed bactericidal activity against homologous type I MIP (median titers of 128 to 256) and heterologous type II and III (median titers of 256 to 512) strains, thereby providing at least 82% serogroup B strain coverage. In contrast, in constructs lacking the LP, placement of the His tag at the N terminus appeared to abrogate bactericidal activity. The strategy used in this study would obviate any potential concerns regarding the use of MIP antigens for inclusion in bacterial vaccines.

Analysis of the secretome and identification of novel constituents from culture filtrate of bacillus Calmette-Guerin using high-resolution mass spectrometry

Tuberculosis (TB) is an infectious bacterial disease that causes morbidity and mortality, especially in developing countries. Although its efficacy against TB has displayed a high degree of variability (0%-80%) in different trials, Mycobacterium bovis bacillus Calmette-Guérin (BCG) has been recognized as an important weapon for preventing TB worldwide for over 80 years. Because secreted proteins often play vital roles in the interaction between bacteria and host cells, the secretome of mycobacteria is considered to be an attractive reservoir of potential candidate antigens for the development of novel vaccines and diagnostic reagents. In this study, we performed a proteomic analysis of BCG culture filtrate proteins using SDS-PAGE and high-resolution Fourier transform mass spectrometry. In total, 239 proteins (1555 unique peptides) were identified, including 185 secreted proteins or lipoproteins. Furthermore, 17 novel protein products not annotated in the BCG database were detected and validated by means of RT-PCR at the transcriptional level. Additionally, the translational start sites of 52 proteins were confirmed, and 22 proteins were validated through extension of the translational start sites based on N-terminus-derived peptides. There are 103 secreted proteins that have not been reported in previous studies on BCG [corrected] secretome and are unique to our study. The physicochemical characteristics of the secreted proteins were determined. Major components from the culture supernatant, including low-molecular-weight antigens, lipoproteins, Pro-Glu and Pro-Pro-Glu family proteins, and Mce family proteins, are discussed; some components represent potential predominant antigens in the humoral and cellular immune responses.

Screening and assessing 11 Mycobacterium tuberculosis proteins as potential serodiagnostical markers for discriminating TB patients from BCG vaccinees

Purified protein derivative (PPD) skin tests often yield poor specificity, so that to develop new serological antigens for distinguishing between Mycobacterium tuberculosis infection and Bacille Calmette-Guerin (BCG) vaccination is a priority, especially for developing countries like China. We predicted the antigenicity for selected open reading frames (ORFs) based on the genome sequences of M. tuberculosis H37Rv and M. bovis BCG, as well as their functions and differences of expression under different stimulus. The candidate ORFs were cloned from H37Rv sequences and expressed as recombinant proteins in Escherichia coli. We studied the serodiagnostic potential of 11 purified recombinants by using enzyme-linked immunosorbent assay (ELISA) and involving a cohort composed of 58 TB patients (34 males and 24 females), 8 healthy volunteers and 50 PPD-negative individuals before and after BCG vaccination. For all the 11 antigens, the median OD values for the sera from TB patients were statistically significantly higher than those for PPD-negative individuals before or after BCG vaccination (P<0.01). They had at least 92% specificity in healthy controls and six seroantigens (Rv0251c, Rv1973, Rv2376c, Rv2537c, Rv2785c and Rv3873A) were never reported with seroantigenicities previously. Thus the approach combining comparative genomics, bioinformatics and ELISA techniques can be employed to identify new seroantigens distinguishing M. tuberculosis infection from BCG vaccination.

Differential cytokine levels and immunoreactivities against Mycobacterium tuberculosis antigens between tuberculous and malignant effusions

Much effort has been devoted to the identification of immunologically important factors in tuberculous pleurisy (TBP) and malignant pleurisy (MP) to improve the differential diagnosis of the two major causes of lymphocyte-dominant pleurisy. This study evaluated the immunoreactivity and potential diagnostic utility of both host (cytokines and chemokines) and pathogen (mycobacterial proteins) factors in pleural effusions. Effusion samples were collected from 41 patients with MP caused by lung cancer and from 81 patients with TBP. The concentrations of nine cytokines and chemokines (interleukin (IL)-12 p40, interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, IL-6, IL-10, CXCL8/IL-8, CXCL10/IP-10, CCL3/MIP-1alpha, and CCL4/MIP-1beta) and antibody responses (IgG, IgM, and IgA) against five Mycobacterium tuberculosis antigens (early secreted antigenic target (ESAT)-6, 30-kDa, MTB12, 38-kDa, and a heparin-binding hemagglutinin (HBHA)) were determined in pleural fluids using enzyme-linked immunosorbent assays (ELISA). In the logistic regression, IFN-gamma (odds ratio, 7.178; 95% confidence interval (CI), 2.258-22.817; p=0.001), IL-12 p40 (odds ratio, 11.037; 95% CI, 3.38-36.037; p<0.001), and IL-6 (odds ratio, 3.295; 95% CI, 1.147-9.463; p=0.027) were found to be statistically significant cytokines predicting tuberculous from malignant effusions. Although IgG responses to all of the M. tuberculosis antigens tested were significantly higher in effusions from TBP (p<0.001) compared with those from MP, the logistic regression showed IgG levels for ESAT-6 and MTB12 to be statistically significant for differentiation of TBP from MP. HBHA showed the highest sensitivity of IgM antibody responses in TBP in comparison with other antigens. These data indicate that selected mycobacterial antigens (ESAT-6 and MTB12) and cytokine markers (IFN-gamma, IL-12p40, and IL-6) provide useful information for differentiating tuberculous and malignant effusions in clinical practice.

Tuberculosis subunit vaccine development: Impact of physicochemical properties of mycobacterial test antigens

Tuberculosis caused by Mycobacterium tuberculosis continues to be one of the major public health problems in the world. The eventual control of this disease will require the development of a safe and effective vaccine. One of the approaches receiving a great deal of attention recently is subunit vaccination. An efficacious antituberculous subunit vaccine requires the identification and isolation of key components of the pathogen that are capable of inducing a protective immune response. Clues to identify promising subunit vaccine candidates may be found in their physicochemical and immunobiological properties. In this article, we review the evidence that the physicochemical properties of mycobacterial components can greatly impact the induction of either protective or deleterious immune response and consequently influence the potential utility as an antituberculous subunit vaccine.

Development of bioprocess for the production of purified protein derivative with Brazilian strains of Mycobacterium tuberculosis for diagnosis use

Tuberculin, a purified protein derivative (PPD), when diluted in adequate concentration it is utilized for an early detection and to control tuberculosis. In Brazil, the PPD is imported and distributed by the Health System in all Brazilian regions. This, in addition to eventual delay in delivery caused by the legal import process, makes difficult the access of the product to poor communities from distant places as Brazil is a geographically a large country. Thus, indigenous production of PPD would be very beneficial for the society. This work was undertaken with a view to initiate studies towards the development of an indigenous technology for PPD production, using the strains of Mycobacterium tuberculosis isolated from patients during the course of disease from several regions of Brazil. The strain selection criteria for PPD production were the sequencing of three immunodominant proteins and the genetic differentiation by DNA fingerprinting and grouped by UPGMA program, the capacity of protein production in liquid medium, and finally the intradermal injection tests used on animal model. Compared to gold standard, the PPD showed similar indurations when tested individually, and better results were obtained when products were combined in pool. These strategies are discussed in detail in this research.

Ex VivoResponses for Interferon-gamma and Proinflammatory Cytokine Secretion to Low-Molecular-Weight Antigen MTB12 ofMycobacterium tuberculosisduring Human Tuberculosis

MTB12 protein, also called CFP-2, is a major and early secreted component of Mycobacterium tuberculosis. However, its role during mycobacterial infection has been poorly characterized. In this study, we purified the native MTB12 protein and investigated the profile of MTB12-induced cytokines [interferon (IFN)-gamma, tumour necrosis factor (TNF)-alpha and interleukin (IL)-6], in early tuberculosis (TB) patients (n = 20) and healthy controls (n = 35). The cytokine profiles were compared with those induced by the 30-kDa antigen (Ag). In healthy controls, MTB12-induced IFN-gamma production was markedly decreased in peripheral blood mononuclear cells compared with 30-kDa Ag-induced IFN-gamma. In TB patients, the mean IFN-gamma level induced by MTB12 was lower than that induced by the 30-kDa Ag, albeit the difference was not significant. After 2 months of anti-TB therapy, both the MTB12- and 30-kDa-induced IFN-gamma levels were significantly increased in TB patients. MTB12-induced TNF-alpha and IL-6 levels were prominently upregulated in monocyte-derived macrophages from TB patients, but they were not significantly different from those induced by the 30-kDa Ag. Further, the activation of p38 mitogen-activated protein kinase and extracellular signal-regulated kinase was required for the induction of TNF-alpha and IL-6 by MTB12, as well as by the 30-kDa Ag. Collectively, these data suggest that the MTB12 protein plays an essential role for proinflammatory responses through the MAPK pathway during the early stages of human TB, even though its T-cell immunoreactivity is weaker than that of the 30-kDa Ag.

TB subunit vaccines—putting the pieces together

The search for a new and improved vaccine against tuberculosis (TB) is currently a very active field of research, which in the last 10 years has benefited tremendously from the completed Mycobacterium tuberculosis genome and the progress in molecular biology and computer science. In this review, we discuss how Genomics, Proteomics and Transcriptomics have accelerated the pace of antigen discovery and vaccine development and have changed this field completely, resulting in the identification of a large number of antigens with potential in TB vaccines. The next phase of this work has now started--putting the most relevant molecules back together as fusion molecules and cocktails. This requires carefully monitoring aspects as immunodominance, recognition in different populations as well as vaccine manufacturing.

Lipoproteins ofMycobacterium tuberculosis: an abundant and functionally diverse class of cell envelope components

Mycobacterium tuberculosis remains the predominant bacterial scourge of mankind. Understanding of its biology and pathogenicity has been greatly advanced by the determination of whole genome sequences for this organism. Bacterial lipoproteins are a functionally diverse class of membrane-anchored proteins. The signal peptides of these proteins direct their export and post-translational lipid modification. These signal peptides are amenable to bioinformatic analysis, allowing the lipoproteins encoded in whole genomes to be catalogued. This review applies bioinformatic methods to the identification and functional characterisation of the lipoproteins encoded in the M. tuberculosis genomes. Ninety nine putative lipoproteins were identified and so this family of proteins represents ca. 2.5% of the M. tuberculosis predicted proteome. Thus, lipoproteins represent an important class of cell envelope proteins that may contribute to the virulence of this major pathogen.

Differential Immune Responses and Protective Efficacy Induced by Components of a Tuberculosis Polyprotein Vaccine, Mtb72F, Delivered as Naked DNA or Recombinant Protein

Key Ags of Mycobacterium tuberculosis initially identified in the context of host responses in healthy purified protein derivative-positive donors and infected C57BL/6 mice were prioritized for the development of a subunit vaccine against tuberculosis. Our lead construct, Mtb72F, codes for a 72-kDa polyprotein genetically linked in tandem in the linear order Mtb32(C)-Mtb39-Mtb32(N). Immunization of C57BL/6 mice with Mtb72F DNA resulted in the generation of IFN-gamma responses directed against the first two components of the polyprotein and a strong CD8(+) T cell response directed exclusively against Mtb32(C). In contrast, immunization of mice with Mtb72F protein formulated in the adjuvant AS02A resulted in the elicitation of a moderate IFN-gamma response and a weak CD8(+) T cell response to Mtb32c. However, immunization with a formulation of Mtb72F protein in AS01B adjuvant generated a comprehensive and robust immune response, resulting in the elicitation of strong IFN-gamma and Ab responses encompassing all three components of the polyprotein vaccine and a strong CD8(+) response directed against the same Mtb32(C) epitope identified by DNA immunization. All three forms of Mtb72F immunization resulted in the protection of C57BL/6 mice against aerosol challenge with a virulent strain of M. tuberculosis. Most importantly, immunization of guinea pigs with Mtb72F, delivered either as DNA or as a rAg-based vaccine, resulted in prolonged survival (>1 year) after aerosol challenge with virulent M. tuberculosis comparable to bacillus Calmette-Guérin immunization. Mtb72F in AS02A formulation is currently in phase I clinical trial, making it the first recombinant tuberculosis vaccine to be tested in humans.

Immune responses to mycobacterial antigens in the Gambian population: implications for vaccines and immunodiagnostic test design

Recombinant immunodominant mycobacterial antigens are needed for the development of new vaccines and immunodiagnostic tools for use against tuberculosis. Ubiquitous exposure to mycobacteria in tropical countries could influence vaccine-induced immunity and the specificity of tuberculosis immunodiagnosis. For this study conducted in The Gambia, cellular immune responses to recombinant mycobacterial antigens were characterized in Mycobacterium bovis BCG-vaccinated and nonvaccinated infants, adult community controls, household contacts, health care workers, and tuberculosis patients. Neonatal BCG vaccination induced gamma interferon (IFN-gamma) responses to Mtb8.4, Mtb32-C, Mtb39A, Mtb9.9A, and Mtb32-N, but not CFP-10 (Mtb11) and alpha-crystallin (Mtb16). Exposure to Mycobacterium tuberculosis in household contacts and health care workers was associated with high responses to CFP-10 and alpha-crystallin. Generally, low IFN-gamma responses were found in tuberculosis patients. These results suggest that Mtb8.4, Mtb32-C, Mtb39A, Mtb9.9A, and Mtb32-N may be used in a subunit vaccine to boost BCG-induced immunity. While CFP-10 and alpha-crystallin are promising candidates for the immunodiagnosis of M. tuberculosis infection or for vaccine use, disease-associated immunosuppression may prevent IFN-gamma immunodiagnosis of more advanced tuberculosis.

Epitope mapping of the immunodominant antigen TB10.4 and the two homologous proteins TB10.3 and TB12.9, which constitute a subfamily of the esat-6 gene family

The human T-cell recognition of the low-molecular-mass culture filtrate antigen TB10.4 was evaluated in detail. The molecule was strongly recognized by T cells isolated from tuberculosis (TB) patients and from BCG-vaccinated donors. The epitopes on TB10.4 were mapped with overlapping peptides and found to be distributed throughout the molecule. The broadest response was found in TB patients, whereas the response in BCG-vaccinated donors was focused mainly toward a dominant epitope located in the N terminus (amino acids 1 to 18). The gene encoding TB10.4 was found to belong to a subfamily within the esat-6 family that consists of the three highly homologous proteins TB10.4, TB10.3, and TB12.9 (Rv0288, Rv3019c, and Rv3017c, respectively). Southern blot analysis combined with database searches revealed that the three members of the TB10.4 family were present only in strains of the Mycobacterium tuberculosis complex, including BCG, and M. kansasii, whereas other atypical mycobacteria had either one (M. avium, M. intracellulare, and M. marinum) or none (M. scrofulaceum, M. fortuitum, and M. szulgai) of the genes. The fine specificity of the T-cell response to the three closely related esat-6 family members was markedly different, with only a few epitopes shared between the molecules. Minimal differences in the amino acid sequence translated into large differences in recognition by T cells and secretion of gamma interferon. In general, the peptides from TB10.4 stimulated the largest responses, but epitopes unique to both TB10.3 and TB12.9 were found. The relevance of the findings for TB vaccine development and as a potential mechanism for immune evasion is discussed.

Use of multiepitope polyproteins in serodiagnosis of active tuberculosis

Screening of genomic expression libraries from Mycobacterium tuberculosis with sera from tuberculosis (TB) patients or rabbit antiserum to M. tuberculosis led to the identification of novel antigens capable of detecting specific antibodies to M. tuberculosis. Three antigens, Mtb11 (also known as CFP-10), Mtb8, and Mtb48, were tested together with the previously reported 38-kDa protein, in an enzyme-linked immunosorbent assay (ELISA) to detect antibodies in TB patients. These four proteins were also produced as a genetically fused polyprotein, which was tested with two additional antigens, DPEP (also known as MPT32) and Mtb81. Sera from individuals with pulmonary and extrapulmonary TB, human immunodeficiency virus (HIV)-TB coinfections, and purified protein derivative (PPD)-positive and PPD-negative status with no evidence of disease were tested. In samples from HIV-negative individuals, the ELISA detected antibodies in >80% of smear-positive individuals and >60% smear-negative individuals, with a specificity of approximately 98%. For this group, smears detected 81.6% but a combination of smear and ELISA had a sensitivity of approximately 93%. The antigen combination detected a significant number of HIV-TB coinfections as well as antibodies in patients with extrapulmonary infections. Improved reactivity in the HIV-TB group was observed by including the antigen Mtb81 that was identified by proteomics. The data indicate that the use of multiple antigens, some of which are in a single polyprotein, can be used to facilitate the development of a highly sensitive test for M. tuberculosis antibody detection.

Purification, biochemical characterization and immunogenicity of SA5K, a secretion antigen of Mycobacterium tuberculosis

Mycobacterium tuberculosis (MTB) secretory proteins are generally considered important antigens for immune protection against tuberculosis (TB). An 8.3-kDa secretory antigen of MTB and Mycobacterium bovis bacillus Calmette-Guérin (BCG), called SA5K, was recently identified and cloned in our laboratory. In this report, recombinant SA5K containing a histidine hexamer was expressed in Escherichia coli and purified to investigate its biochemical structure and to establish whether it was immunogenic for healthy sensitized and nonsensitized human donors and for patients infected with MTB. The protein nucleotide sequence was shown to be identical in BCG and in MTB. SA5K revealed an abnormal electrophoretic mobility in SDS-PAGE that made it look lighter than it is in Western blotting. While recombinant SA5K was poorly recognized by T lymphocytes from patients with pulmonary TB, it elicited proliferation of CD4+ T lymphocytes in the vast majority of healthy individuals sensitized to mycobacterial antigens by BCG vaccination. At a serum dilution of 1 : 80, antibodies reacting against recombinant SA5K were found in 67% of sera from TB patients and in 73% of sera from healthy subjects. The percentage of positive subjects dropped at higher serum dilutions, but no significant difference in the recognition rate was observed between TB patients and healthy donors and between healthy vaccinated and nonvaccinated subjects. Owing to the high percentage of sera from healthy subjects who recognized SA5K in Western blotting, the antigen seems to exhibit, at least in the present form, a poor specificity for an employment for a serodiagnosis of TB.

Antigen discovery and tuberculosis vaccine development in the post-genomic era

For a number of years, a major effort has been put into the identification of candidate molecules for inclusion in a novel vaccine against tuberculosis. Various techniques have been exploited and have resulted in the identification of immunologically important antigens such as the immunodominant antigens ESAT-6 and antigen 85A/B. Today, the availability of the total nucleotide sequence of the Mycobacterium tuberculosis genome enables a post-genomic antigen discovery approach based on denotation and screening of complete protein families containing immunodominant molecules. One group of genes sharing properties with ESAT-6 constitute what has been called the esat-6 gene family. The genes have 10-35% homology to esat-6, are approximately the same size and share genomic organization. The data accumulated so far demonstrate that these molecules are immunodominant antigens strongly recognized in human TB patients and with the potential for a novel TB vaccine.

DNA vaccine combinations expressing either tissue plasminogen activator signal sequence fusion proteins or ubiquitin-conjugated antigens induce sustained protective immunity in a mouse model of pulmonary tuberculosis

DNA vaccination has emerged as a powerful approach in the search for a more efficacious vaccine against tuberculosis. In this study, we evaluated the effectiveness of immunizing with combinations of 10 different tuberculosis DNA vaccines that expressed mycobacterial proteins fused at the N terminus to eukaryotic intracellular targeting sequences. In one vaccine combination, the genes were fused to the tissue plasminogen activator signal sequence (TPA), while in a second combination the same 10 genes were expressed as ubiquitin (Ub)-conjugated proteins. In ex vivo studies in which the secretion of gamma interferon was measured, cellular immune responses were detected in mice vaccinated with either the TPA DNA vaccine combination or the Ub DNA vaccine combination at 7 and 14 days following a low-dose Mycobacterium tuberculosis challenge. Moreover, mice vaccinated with the TPA combination, the Ub combination, and Mycobacterium bovis BCG were able to limit the growth of tubercle bacilli in the lung and spleen after a virulent tuberculous aerosol challenge. Histopathological analyses also showed that mice immunized with the DNA vaccine combinations had substantially improved postinfection lung pathology relative to the naïve controls. Finally, in three different long-term experiments, the survival periods following aerogenic challenge were extended as much as sevenfold for vaccinated mice compared to naïve controls. Interestingly, in all three experiments, no significant differences were detected in the mean times to death for mice immunized with the TPA combination or the Ub combination relative to the BCG controls. In conclusion, these studies demonstrate the effectiveness of immunization with DNA vaccine combinations against tuberculosis and suggest that further testing of these plasmid cocktails is warranted.

Protection of mice with a tuberculosis subunit vaccine based on a fusion protein of antigen 85b and esat-6

In this study, we investigated the potential of a tuberculosis subunit vaccine based on fusion proteins of the immunodominant antigens ESAT-6 and antigen 85B. When the fusion proteins were administered to mice in the adjuvant combination dimethyl dioctadecylammonium bromide-monophosphoryl lipid A, a strong dose-dependent immune response was induced to both single components as well as to the fusion proteins. The immune response induced was accompanied by high levels of protective immunity and reached the level of Mycobacterium bovis BCG-induced protection over a broad dose range. The vaccine induced efficient immunological memory, which remained stable 30 weeks postvaccination.

Antigenic role of the endosymbionts of filarial nematodes: IgG response against the Wolbachia surface protein in cats infected with Dirofilaria immitis

Filarial nematodes harbour intracellular endosymbiotic bacteria, which have been assigned to the genus Wolbachia. These bacteria appear to play an important role in the pathogenesis of filarial diseases through their lipopolysaccharides. In view of the presence of Wolbachia endosymbionts in the body of filarial nematodes, one might also expect that proteins from these bacteria play an antigenic role in humans and animals affected by filariases. To test this hypothesis, we produced in recombinant form the surface protein WSP and a portion of the cell-cycle protein FTSZ from the Wolbachia of Dirofilaria immitis. Western immunoblot assays were then performed using cat sera to test the immunogenicity of these proteins. Sera were collected from owners' cats, which were either sero-negative or sero-positive for D. immitis and from cats before and after experimental infection with D. immitis. FTSZ was recognized in Western blots by sera from both positive and negative cats and from both uninfected and experimentally infected cats. WSP was recognized only by sera from positive cats and from cats experimentally infected with D. immitis; this protein was not recognized by sera from negative cats and from cats before experimental infection with D. immitis. The results of Western blot assays on WSP thus support the hypothesis that infection with filarial nematodes induces the production of antibodies against Wolbachia proteins.

T cell expression cloning of a Mycobacterium tuberculosis gene encoding a protective antigen associated with the early control of infection

Infection of C57BL/6 mice with Mycobacterium tuberculosis results in the development of a progressive disease during the first 2 wk after challenge. Thereafter, the disease is controlled by the emergence of protective T cells. We have used this infection model in conjunction with direct T cell expression cloning to identify Ags involved with the early control of the disease. A protective M. tuberculosis-specific CD4 T cell line derived from mice at 3 wk postchallenge was used to directly screen an M. tuberculosis genomic expression library. This screen resulted in the identification of a genomic clone comprising two putative adjacent genes with predicted open reading frames of 10 and 41 kDa, MTB10 and MTB41, respectively (the products of Rv0916c and Rv0915c, respectively, in the TubercuList H37Rv database). MTB10 and MTB41 belong to the PE and PPE family of proteins recently identified to comprise 10% of the M. tuberculosis genome. Evaluation of the recombinant proteins revealed that MTB41, but not MTB10, is the Ag recognized by the cell line and by M. tuberculosis-sensitized human PBMC. Moreover, C57BL/6 mice immunized with MTB41 DNA developed both CD4- (predominantly Th1) and CD8-specific T cell responses to rMTB41 protein. More importantly, immunization of C57BL/6 mice with MTB41 DNA induced protection against infection with M. tuberculosis comparable to that induced by bacillus Calmette-Guérin. Thus, the use of a proven protective T cell line in conjunction with the T cell expression cloning approach resulted in the identification of a candidate Ag for a subunit vaccine against tuberculosis.

Extracytoplasmic proteins of Mycobacterium tuberculosis - mature secreted proteins often start with aspartic acid and proline

A surrogate expression system, based on fusions to the phoA bacterial reporter gene, was used to identify Mycobacterium tuberculosis genes that encode exported proteins and the promoter regions required for their expression in the heterologous host Mycobacterium smegmatis. To assess these results in the context of the complete M. tuberculosis genome sequence, the corresponding genes were identified and computational algorithms were employed to identify signal peptide (SP), transmembrane domain and membrane lipoprotein attachment motifs. This information was used to predict the subset of M. tuberculosis genes that encode exported proteins. Of the 34 genes identified by the phoA method, 22 were classified to encode potential soluble secreted proteins. Among these, 14 genes may encode novel secreted proteins. Six of the remaining 12 genes were predicted to encode membrane lipoproteins and an additional six to encode integral membrane proteins. Published observations of proteins proven to be secreted into M. tuberculosis culture filtrates were reviewed to further characterize the mycobacterial SP motif. It was concluded that mycobacterial SPs are comparable in size to Gram-positive SPs, but certain features are different. In particular, arginine was the predominant N-terminally positively charged amino acid in contrast to lysine in the Gram-positives. The hydrophobic transmembrane segment of the SP was dominated by alanine, in contrast to leucine. At the C-terminal end of the SPs, the (-3, -1) rule (AXA motif) holds, with alanine as the dominant amino acid in both positions, being most dominant in the (-1) position. A high proportion of mature sequences start with aspartic acid in the (+1) position and proline in the (+2) position - the DP motif. The authors propose that the DP sequence serves as a sorting signal, following translocation and cleavage by signal peptidase I. Alternatively, the DP motif may be part of the recognition site for the signal peptidase.

Isolation, purification and immunological characterization of novel low molecular weight protein antigen CFP 6 from culture filtrate of M. tuberculosis

A novel immunogenic antigen, CFP 6 was purified from culture filtrate of M. tuberculosis by a preparatory 2-D electrophoresis method. The protein focused at pI of 4.0 during isoelectric focusing. Molecular weight of the purified protein by ES MS was found to be 11.61 kD. N-terminal amino acid sequence of CFP 6 could be aligned to the deduced amino acid sequence from ORF Rv3004 and was found to be a novel protein with 112 aa residues. Single N-terminal sequence showed that the purified protein was essentially free from contaminants and the amino acid analysis of the antigen was in good agreement with the DNA sequence deduced amino acid composition. Purified CFP 6 was studied for its ability to induce proliferative responses of peripheral blood lymphocytes from five categories of human subjects. These were: untreated, active pulmonary tuberculosis patients; patients after 2-3 months of chemotherapy; vaccinated professional contacts; vaccinated/nonvaccinated healthy controls. CFP 6 elicited high proliferative responses in healthy contacts and patients recovering from the disease. This protein also induced the release of a significantly high amount of IFN-gamma in cell culture supernatant of healthy contacts as compared to other categories of subjects. This protein was further evaluated and compared with PPD and total CS for its DTH inducing ability in guinea pigs immunised with BCG or M. tuberculosis H(37)Rv. CFP 6 elicited a powerful immune response in vitro and in vivo animal model, hence seems to be an immunologically important protein.

DNA vaccination against tuberculosis: expression of a ubiquitin-conjugated tuberculosis protein enhances antimycobacterial immunity

Genetic immunization is a promising new technology for developing vaccines against tuberculosis that are more effective. In the present study, we evaluated the effects of intracellular turnover of antigens expressed by DNA vaccines on the immune response induced by these vaccines in a mouse model of pulmonary tuberculosis. The mycobacterial culture filtrate protein MPT64 was expressed as a chimeric protein fused to one of three variants of the ubiquitin protein (UbG, UbA, and UbGR) known to differentially affect the intracellular processing of the coexpressed antigens. Immunoblot analysis of cell lysates of in vitro-transfected cells showed substantial differences in the degradation rate of ubiquinated MPT64 (i.e., UbG64 < UbA64 < UbGR64). The specific immune response generated in mice correlated with the stability of the ubiquitin-conjugated antigen. The UbA64 DNA vaccine induced a weak humoral response compared to UbG64, and a mixed population of interleukin-4 (IL-4)- and gamma interferon (IFN-gamma)-secreting cells. Vaccination with the UbGR64 plasmid generated a strong Th1 cell response (high IFN-gamma, low IL-4) in the absence of a detectable humoral response. Aerogenic challenge of vaccinated mice with Mycobacterium tuberculosis indicated that immunization with both the UbA64- and UbGR64-expressing plasmids evoked an enhanced protective response compared to the vector control. The expression of mycobacterial antigens from DNA vaccines as fusion proteins with a destabilizing ubiquitin molecule (UbA or UbGR) shifted the host response toward a stronger Th1-type immunity which was characterized by low specific antibody levels, high numbers of IFN-gamma-secreting cells, and significant resistance to a tuberculous challenge.

Identification of secreted proteins of Mycobacterium tuberculosis by a bioinformatic approach

Proteins secreted by Mycobacterium tuberculosis are usually targets of immune responses in the infected host. Here we describe a search for secreted proteins that combined the use of bioinformatics and phoA' fusion technology. The 3,924 proteins deduced from the M. tuberculosis genome were analyzed with several computer programs. We identified 52 proteins carrying an NH(2)-terminal secretory signal peptide but lacking additional membrane-anchoring moieties. Of these 52 proteins-the TM1 subgroup-only 7 had been previously reported to be secreted proteins. Our predictions were confirmed in 9 of 10 TM1 genes that were fused to Escherichia coli phoA', a marker of subcellular localization. These findings demonstrate that the systematic computer search described in this work identified secreted proteins of M. tuberculosis with high efficiency and 90% accuracy.

Mapping and identification of Mycobacterium tuberculosis proteins by two-dimensional gel electrophoresis, microsequencing and immunodetection

Mycobacterium tuberculosis is the infectious agent giving rise to human tuberculosis. The entire genome of M. tuberculosis, comprising approximately 4000 open reading frames, has been sequenced. The huge amount of information released from this project has facilitated proteome analysis of M. tuberculosis. Two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) was applied to fractions derived from M. tuberculosis culture filtrate, cell wall, and cytosol, resulting in the resolution of 376, 413, and 395 spots, respectively, in silver-stained gels. By microsequencing and immunodetection, 38 culture filtrate proteins were identified and mapped, of which 12 were identified for the first time. In the same manner, 23 cell wall proteins and 19 cytosol proteins were identified and mapped, with 9 and 10, respectively, being novel proteins. One of the novel proteins was not predicted in the genome project, and for four of the identified proteins alternative start codons were suggested. Fourteen of the culture filtrate proteins were proposed to possess signal sequences. Seven of these proteins were microsequenced and the N-terminal sequences obtained confirmed the prediction. The data presented here are an important complement to the genetic information, and the established 2-D PAGE maps (also available at: www.ssi.dk/publichealth/tbimmun) provide a basis for comparative studies of protein expression.

Comparative evaluation of low-molecular-mass proteins from Mycobacterium tuberculosis identifies members of the ESAT-6 family as immunodominant T-cell antigens

Culture filtrate from Mycobacterium tuberculosis contains protective antigens of relevance for the generation of a new antituberculosis vaccine. We have identified two previously uncharacterized M. tuberculosis proteins (TB7.3 and TB10.4) from the highly active low-mass fraction of culture filtrate. The molecules were characterized, mapped in a two-dimensional electrophoresis reference map of short-term culture filtrate, and compared with another recently identified low-mass protein, CFP10 (F. X. Berthet, P. B. Rasmussen, I. Rosenkrands, P. Andersen, and B. Gicquel. Microbiology 144:3195-3203, 1998), and the well-described ESAT-6 antigen. Genetic analyses demonstrated that TB10.4 as well as CFP10 belongs to the ESAT-6 family of low-mass proteins, whereas TB7.3 is a low-molecular-mass protein outside this family. The proteins were expressed in Escherichia coli, and their immunogenicity was tested in cultures of peripheral blood mononuclear cells from human tuberculosis (TB) patients, Mycobacterium bovis BCG-vaccinated donors, and nonvaccinated donors. The two ESAT-6 family members, TB10.4 and CFP10, were very strongly recognized and induced gamma interferon release at the same level (CFP10) as or at an even higher level (TB10.4) than ESAT-6. The non-ESAT-6 family member, TB7.3, for comparison, was recognized at a much lower level. CFP10 was found to distinguish TB patients from BCG-vaccinated donors and is, together with ESAT-6, an interesting candidate for the diagnosis of TB. The striking immunodominance of antigens within the ESAT-6 family is discussed, and hypotheses are presented to explain this targeting of the immune response during TB infection.

Cloning, characterization and serological evaluation of K9 and K26: two related hydrophilic antigens of Leishmania chagasi

We report here the molecular cloning and characterization of two related hydrophilic antigens of Leishmania chagasi. These two antigens have predicted molecular weights of approximately 9 and 26 kDa and detect antibodies in sera of patients with kala-azar (k). Thus, to maintain consistency with nomenclature of the previously described 39 kDa diagnostic antigen of L. chagasi (k39 [1]), these antigens are being referred to as k9 and k26. A significant difference between k9 and k26 is the presence of 11 copies of a 14 amino acid repeat in the open reading frame of k26. The region flanking the repeats of k26 shares a 69% identity with the open reading frame of k9. The recombinant proteins encoded by both antigens are very hydrophilic and show aberrant migration on SDS PAGE. Results of Southern blot analysis reveal that k9 and k26 are conserved to varying degrees among various Leishmania species. Interestingly, the repeat region of k26 is specific to L. chagasi and L. donovani while the flanking region is conserved among several other species. Transcript levels of k26 are significantly upregulated in the amastigote stage of the parasite. Our results show that recombinant K26 is specific in detecting antibodies in infection sera from visceral leishmaniasis (VL) patients. Thus rK26 may complement rK39 in a more accurate diagnosis of VL in the old and the new world.

Cloning, expression, and immunological evaluation of two putative secreted serine protease antigens of Mycobacterium tuberculosis

Culture filtrate proteins (CFP) of Mycobacterium tuberculosis have been shown to contain immunogenic components that elicit at least partial protective immunity against Mycobacterium infection. To clone genes encoding some of the immunogenic proteins, we made a high-titer rabbit anti-CFP serum and used it to screen an M. tuberculosis genomic expression library in Escherichia coli. In this paper, we describe the molecular cloning of two new protein components of CFP and identified them as members of the serine protease gene family. Their open reading frames contain N-terminal hydrophobic secretory signals consistent with their detection in CFP. The predicted molecular masses of the mature, fully processed forms of both antigens are approximately 32 kDa, in agreement with their observed sizes on immunoblots of CFP probed with polyclonal rabbit antisera made to the recombinant proteins. Thus, these proteins have been designated MTB32A and MTB32B. Interestingly, and despite 66% amino acid sequence homology between the two proteins, polyclonal rabbit antisera made to each of the recombinant proteins were found to be specific for the respective immunizing antigens. The recombinant proteins were also evaluated in in vitro assays with donor peripheral blood mononuclear cells (PBMC) from healthy purified protein derivative (PPD)-positive individuals of diverse ethnic backgrounds. MTB32A but not MTB32B stimulated PBMC from healthy PPD-positive donors but not from PPD-negative donors to proliferate and secrete gamma interferon. MTB32A is encoded by a single-copy gene which is present in both virulent and avirulent strains of the M. tuberculosis complex and the BCG strain of Mycobacterium bovis but absent in the environmental mycobacterial species tested. In addition, nucleotide sequence comparison of mtb32a of the avirulent H37Ra strain and the virulent Erdman strain, as well as with the corresponding sequences (identified in the databases) of strain H37Rv and the clinical isolate CSU93, revealed 100% identity. MTB32A, therefore, represents a candidate for inclusion in subunit vaccine development. Finally, the possible role of MTB32 serine proteases as a virulence factor(s) during Mycobacterium spp. infection is discussed.