Human humoral responses to antigens of Mycobacterium tuberculosis: immunodominance of high-molecular-mass antigens

Lipoarabinomannan in Active and Passive Protection Against Tuberculosis

Glycolipids of the cell wall of Mycobacterium tuberculosis (Mtb) are important immunomodulators in tuberculosis. In particular, lipoarabinomannan (LAM) has a profound effect on the innate immune response. LAM and its structural variants can be recognized by and activate human CD1b-restricted T cells, and emerging evidence indicates that B cells and antibodies against LAM can modulate the immune response to Mtb. Anti-LAM antibodies are induced during Mtb infection and after bacille Calmette-Guerin (BCG) vaccination, and monoclonal antibodies against LAM have been shown to confer protection by passive administration in mice and guinea pigs. In this review, we describe the immune response against LAM and the potential use of the mannose-capped arabinan moiety of LAM in the construction of vaccine candidates against tuberculosis.

Structural switching electrochemical DNA aptasensor for the rapid diagnosis of tuberculous meningitis

Background

Tuberculous meningitis (TBM) is the most devastating manifestation of extra-pulmonary tuberculosis. About 33% of TBM patients die due to very late diagnosis of the disease. Conventional diagnostic methods based on signs and symptoms, cerebrospinal fluid (CSF) smear microscopy or liquid culture suffer from either poor sensitivity or long turnaround time (up to 8 weeks). Therefore, in order to manage the disease efficiently, there is an urgent and unmet need for a rapid and reliable diagnostic test.

Methods

In the current study, to address the diagnostic challenge of TBM, a highly rapid and sensitive structural switching electrochemical aptasensor was developed by combining the electrochemical property of methylene blue (MB) with the molecular recognition ability of a ssDNA aptamer. To demonstrate the clinical diagnostic utility of the developed aptasensor, a blinded study was performed on 81 archived CSF specimens using differential pulse voltammetry.

Results

The electrochemical aptasensor developed in the current study can detect as low as 10 pg HspX in CSF background and yields a highly discriminatory response (P<0.0001) for TBM and not-TBM categories with ~95% sensitivity and ~97.5% specificity and has the ability to deliver sample-to-answer in ≤30 minutes.

Conclusion

In summary, we demonstrate a new aptamer-based electrochemical biosensing strategy by exploiting the target-induced structural switching of H63 SL-2 M6 aptamer and electroactivity of aptamer-tagged MB for the detection of HspX in CSF samples for the diagnosis of TBM. Further, the clinical utility of this sensor could be extended for the diagnosis of other forms of tuberculosis in the near future.

Immunoscreening of the M. tuberculosis F15/LAM4/KZN secretome library against TB patients' sera identifies unique active- and latent-TB specific biomarkers

Tuberculosis (TB) protein biomarkers are urgently needed for the development of point-of-care diagnostics, new drugs and vaccines. Mycobacterium tuberculosis extracellular and secreted proteins play an important role in host-pathogen interactions. Antibodies produced against M. tuberculosis proteins before the onset of clinical symptoms can be used in proteomic studies to identify their target proteins. In this study, M. tuberculosis F15/LAM4/KZN strain phage secretome library was screened against immobilized polyclonal sera from active TB patients (n = 20), TST positive individuals (n = 15) and M. tuberculosis uninfected individuals (n = 20) to select and identify proteins recognized by patients' antibodies. DNA sequence analysis from randomly selected latent TB and active TB specific phage clones revealed 118 and 96 ORFs, respectively. Proteins essential for growth, virulence and metabolic pathways were identified using different TB databases. The identified active TB specific biomarkers included five proteins, namely, TrpG, Alr, TreY, BfrA and EspR, with no human homologs, whilst latent TB specific biomarkers included NarG, PonA1, PonA2 and HspR. Future studies will assess potential applications of identified protein biomarkers as TB drug or vaccine candidates/targets and diagnostic markers with the ability to discriminate LTBI from active TB.

Biomarkers for tuberculosis: the case for lipoarabinomannan

Tuberculosis (TB) is considered the most onerous of infectious diseases according to recent reports from the World Health Organization. Available tests for TB diagnosis present severe limitations, and a reliable point-of-care (POC) diagnostic test does not exist. Neither is there a test to discern between the different stages of TB, and in particular to predict which patients with Mycobacterium tuberculosis infection and no clinical signs are more at risk of advancing to overt disease. We here review the usefulness of mycobacterial lipoarabinomannan (LAM) as a diagnostic marker for active and latent TB and, also, aspects of the immune response to LAM relevant to such tests. There is a high potential for urinary LAM-based POC tests for the diagnosis of active TB. Some technical challenges to optimised sensitivity of the test will be detailed. A method to quantify LAM in urine or serum should be further explored as a test of treatment effect. Recent data on the immune response to LAM suggest that markers for host response to LAM should be investigated for a prognostic test to recognise individuals at the greatest risk of disease activation.

There is a high potential for a urinary LAM-based point-of-care test to diagnose TB. Markers for host response to LAM should be explored to identify those at highest risk of developing active TB.http://ow.ly/FyCs30n4uFE

Improved Serodiagnostic Sensitivity of Strip Test for Latent Tuberculosis

INTRODUCTION

Diagnosis of Latent Tuberculosis Infection (LTBI) is difficult due to no clinical manifestations. Cases of LTBI are mostly sputum negative. The World Health Organization recommends the Tuberculin Skin Test (TST) as the current diagnostic standard for LTBI. Our previously developed serologic strip test for LTBI detection had suboptimal sensitivity. Additional Mycobacteriumtuberculosis (MTB) latency-associated antigens may improve the detection rate of LTBI.

AIM

The present study aimed to optimize sensitivity of existing strip test.

MATERIALS AND METHODS

A combination of recombinant latency proteins Rv2029c, Rv2031c, Rv2032, Rv2627c, Rv3133c, and Rv3716c was used to prepare the strips and evaluate the performance with the sera of patients in four well-classified categories: LTBI, active pulmonary TB, healthy TB contacts and other non-TB diseases.

RESULTS

A total of 91 serum samples from various clinical categories were screened with the strips. Among clinically diagnosed LTBI patients, strip test yielded a sensitivity of 75.0%. Among clinically diagnosed non-LTBI subjects, strip test yielded 88.1% specificity. The diagnostic positive and negative predictive values for strip test in reference to various clinical contexts were 77.4% and 86.7%, respectively.

CONCLUSION

Addition of the six potential latency proteins could improve the diagnostic performance of existing strip test for LTBI. The use of suitable immunodominant antigens could maximize sensitivity in the diagnosis and differentiate MTB infection status.

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

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

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Transcriptional profiling of Mycobacterium tuberculosis replicating ex vivo in blood from HIV- and HIV+ subjects

Hematogenous dissemination of Mycobacterium tuberculosis (M. tb) occurs during both primary and reactivated tuberculosis (TB). Although hematogenous dissemination occurs in non-HIV TB patients, in ∼80% of these patients, TB manifests exclusively as pulmonary disease. In contrast, extrapulmonary, disseminated, and/or miliary TB is seen in 60–70% of HIV-infected TB patients, suggesting that hematogenous dissemination is likely more common in HIV+ patients. To understand M. tb adaptation to the blood environment during bacteremia, we have studied the transcriptome of M. tb replicating in human whole blood. To investigate if M. tb discriminates between the hematogenous environments of immunocompetent and immunodeficient individuals, we compared the M. tb transcriptional profiles during replication in blood from HIV- and HIV+ donors. Our results demonstrate that M. tb survives and replicates in blood from both HIV- and HIV+ donors and enhances its virulence/pathogenic potential in the hematogenous environment. The M. tb blood-specific transcriptome reflects suppression of dormancy, induction of cell-wall remodeling, alteration in mode of iron acquisition, potential evasion of immune surveillance, and enhanced expression of important virulence factors that drive active M. tb infection and dissemination. These changes are accentuated during bacterial replication in blood from HIV+ patients. Furthermore, the expression of ESAT-6, which participates in dissemination of M. tb from the lungs, is upregulated in M. tb growing in blood, especially during growth in blood from HIV+ patients. Preliminary experiments also demonstrate that ESAT-6 promotes HIV replication in U1 cells. These studies provide evidence, for the first time, that during bacteremia, M. tb can adapt to the blood environment by modifying its transcriptome in a manner indicative of an enhanced-virulence phenotype that favors active infection. Additionally, transcriptional modifications in HIV+ blood may further accentuate M. tb virulence and drive both M. tb and HIV infection.

Interaction of Mycobacterium leprae with human airway epithelial cells: adherence, entry, survival, and identification of potential adhesins by surface proteome analysis

This study examined the in vitro interaction between Mycobacterium leprae, the causative agent of leprosy, and human alveolar and nasal epithelial cells, demonstrating that M. leprae can enter both cell types and that both are capable of sustaining bacterial survival. Moreover, delivery of M. leprae to the nasal septum of mice resulted in macrophage and epithelial cell infection in the lung tissue, sustaining the idea that the airways constitute an important M. leprae entry route into the human body. Since critical aspects in understanding the mechanisms of infection are the identification and characterization of the adhesins involved in pathogen-host cell interaction, the nude mouse-derived M. leprae cell surface-exposed proteome was studied to uncover potentially relevant adhesin candidates. A total of 279 cell surface-exposed proteins were identified based on selective biotinylation, streptavidin-affinity purification, and shotgun mass spectrometry; 11 of those proteins have been previously described as potential adhesins. In vitro assays with the recombinant forms of the histone-like protein (Hlp) and the heparin-binding hemagglutinin (HBHA), considered to be major mycobacterial adhesins, confirmed their capacity to promote bacterial attachment to epithelial cells. Taking our data together, they suggest that the airway epithelium may act as a reservoir and/or portal of entry for M. leprae in humans. Moreover, our report sheds light on the potentially critical adhesins involved in M. leprae-epithelial cell interaction that may be useful in designing more effective tools for leprosy control.

Effect of mycobacterial secretory proteins on the cellular integrity and cytokine profile of type II alveolar epithelial cells

Background:

Pulmonary tuberculosis (TB) is caused by Mycobacterium tuberculosis (M. tb). In lungs, alveolar macrophages and type II alveolar epithelial cells serve as a replicative niche for this pathogen. Secretory proteins released by actively replicating tubercle bacilli are known to interact with host cells at the initial stages of infection. To understand the role of these cells in TB pathogenesis, it is important to identify the mycobacterial components involved in interaction with alveolar epithelial cells.

Materials and Methods:

We fractionated the whole secretory proteome of M. tb H₃₇Rv into 10 narrow molecular mass fractions (A1-A10; <20 kDa to >90 kDa) that were studied for their binding potential with A549; type II alveolar epithelial cell line. We also studied the consequences of this interaction in terms of change in epithelial cell viability by MTT assay and cytokine release by ELISA.

Results:

Our results show that several mycobacterial proteins bind and confer cytolysis in epithelial cells. Amongst all the fractions, proteins ranging from 35-45 kDa (A5) exhibited highest binding to A549 cells with a consequence of cytolysis of these cells. This fraction (A5) also led to release of various cytokines important in anti-mycobacterial immunity.

Conclusion:

Fraction A5 (35-45 kDa) of mycobacterial secretory proteome play an important role in mediating M. tb interaction with type II alveolar epithelial cells with the consequences detrimental for the TB pathogenesis. Further studies are being carried out to identify the candidate proteins from this region.

Mycobacterium tuberculosis Rv1419 encodes a secreted 13 kDa lectin with immunological reactivity during human tuberculosis

In this study, we have identified a secreted 13 kDa lectin from Mtb (Mtb, Mycobacterium tuberculosis; sMTL-13) by homology search of a non-redundant lectin database. Bioinformatic analysis revealed that sMTL-13 belongs to the ricin-type beta-trefoil family of proteins containing a Sec-type signal peptide present in Mtb complex species, but not in non-tuberculous mycobacteria. Following heterologous expression of sMTL-13 and generation of an mAb (clone 276.B7/IgG1kappa), we confirmed that this lectin is present in culture filtrate proteins from Mtb H37Rv, but not in non-tuberculous mycobacteria-derived culture filtrate proteins. In addition, sMTL-13 leads to an increased IFN-gamma production by PBMC from active tuberculosis (ATB) patients. Furthermore, sera from ATB patients displayed high titers of IgG Ab against sMTL-13, a response found to be decreased following successful anti-tuberculosis therapy. Together, our findings reveal a secreted 13 kDa ricin-like lectin from Mtb, which is immunologically recognized during ATB and could serve as a biomarker of disease treatment.

Inhibition of Mycobacterium tuberculosis secretory serine protease blocks bacterial multiplication both in axenic culture and in human macrophages

To study the possible importance of mycobacterial ES-31 serine protease for bacterial cell growth, the effect of serine and metalloprotease inhibitors, anti-tubercular drugs such as isoniazid and anti-ES-31 antibody, was evaluated on mycobacterial ES-31 serine protease in vitro and on bacilli in axenic and macrophage cultures. Serine protease inhibitors such as pefabloc, 3,4 dichloroisocoumarin, phenyl methyl sulfonyl fluoride (PMSF) and metalloprotease inhibitors such as ethylene diamine tetracetic acid (EDTA) and 1,10 phenanthroline inhibited 65-92% serine protease activity in vitro. Isoniazid showed 95% inhibition on mycobacterial ES-31 serine protease. These inhibitors also showed decreased bacterial growth in axenic culture and inhibition was further confirmed by a decreased amount of ES-31 serine protease in culture filtrate. In human macrophage culture, highly inhibitory pefabloc, 1,10 phenanthroline and isoniazid inhibited infectivity of virulent as well as avirulent M. tuberculosis bacilli to macrophages. It was observed that addition of mycobacterial ES-31 serine protease to macrophage culture enhanced the entry of bacilli and their multiplication in human macrophages. However, the addition of anti-ES-31 serine protease antibody strongly inhibited the mycobacterial growth as observed by decreased CFU count, showing the importance of mycobacterial ES-31 serine protease for entry of bacilli and their multiplication.

The malate synthase of Paracoccidioides brasiliensis is a linked surface protein that behaves as an anchorless adhesin

BACKGROUND

The pathogenic fungus Paracoccidioides brasiliensis is the agent of paracoccidioidomycosis (PCM). This is a pulmonary mycosis acquired by inhalation of fungal airborne propagules that can disseminate to several organs and tissues leading to a severe form of the disease. Adhesion and invasion to host cells are essential steps involved in the internalization and dissemination of pathogens. Inside the host, P. brasiliensis may use the glyoxylate cycle for intracellular survival.

RESULTS

Here, we provide evidence that the malate synthase of P. brasiliensis (PbMLS) is located on the fungal cell surface, and is secreted. PbMLS was overexpressed in Escherichia coli, and polyclonal antibody was obtained against this protein. By using Confocal Laser Scanning Microscopy, PbMLS was detected in the cytoplasm and in the cell wall of the mother, but mainly of budding cells of the P. brasiliensis yeast phase. PbMLSr and its respective polyclonal antibody produced against this protein inhibited the interaction of P. brasiliensis with in vitro cultured epithelial cells A549.

CONCLUSION

These observations indicated that cell wall-associated PbMLS could be mediating the binding of fungal cells to the host, thus contributing to the adhesion of fungus to host tissues and to the dissemination of infection, behaving as an anchorless adhesin.

Utility of a combination of RD1 and RD2 antigens as a diagnostic marker for tuberculosis

We evaluated the diagnostic potential of a cocktail of 4 antigens encoded by regions of difference (RD) 1 and 2 of Mycobacterium tuberculosis, that is, early secretory antigenic target-6, culture filtrate protein-10 (CFP-10), CFP-21, and mycobacterial protein from species tuberculosis-64 (MPT-64) on the basis of antigen and antibody detection by enzyme-linked immunosorbent assay. Parallel detection of antigens and antibodies in the serum samples of pulmonary tuberculosis (PTB) patients resulted in higher sensitivity as compared to either of the single tests in both smear-positive (90%) and smear-negative (60%) PTB patients. In addition, combined detection of antigens and antibodies in the fluids of extrapulmonary tuberculosis (EPTB) patients could detect >90% of the patients with high specificity. These results demonstrate the ability of the combination of antigen and antibody detection assays based on the cocktail of RD antigens to diagnose a substantial number of PTB and EPTB cases with high specificity.

Peptides of a novel Mycobacterium tuberculosis-specific cell wall protein for immunodiagnosis of tuberculosis

The sequencing of the Mycobacterium tuberculosis genome revealed the existence of several genes encoding novel proteins with unknown functions, one of which is the proline-threonine repetitive protein (PTRP; Rv0538). Genomic studies of various mycobacterial species and M. tuberculosis clinical isolates demonstrate that ptrp is specific to the M. tuberculosis complex and ubiquitous in clinical isolates. Enzyme-linked immunosorbent assay, Western blot analysis, and electron microscopic evaluation of M. tuberculosis subcellular fractions and intact bacteria confirm that PTRP is a cell wall protein. Antibodies to PTRP are present in serum specimens from human immunodeficiency virus (HIV)-negative, tuberculosis (TB)-positive and HIV-positive, TB-positive patients but not purified protein derivative (PPD)-negative or PPD-positive healthy control subjects, demonstrating its diagnostic potential. Epitope mapping of PTRP delineated 4 peptides that can identify >80% of sputum smear-positive and >50% of smear-negative, HIV-negative, TB-positive patients and >80% of HIV-positive, TB-positive patients. These results demonstrate that immunodominant epitopes of carefully selected M. tuberculosis-specific proteins can be used to devise a simple peptide-based serodiagnostic test for TB.

Biomarkers for tuberculosis disease status and diagnosis

PURPOSE OF REVIEW

Every year, over 8 million people develop tuberculosis and nearly 1.8 million die from it, despite extensive vaccination and drug treatment programmes. It is increasingly recognized that the diagnosis of tuberculosis, which relies heavily on century-old techniques, is one of the weakest links in the chain of tuberculosis control, hampering not just treatment but also the development of new drugs and vaccines. As a result, recent years have seen the initiation of large-scale studies aiming to identify biomarkers of Mycobacterium tuberculosis infection and disease. This review discusses initial results and future prospects for that work.

RECENT FINDINGS

The key finding from recent work has been that no one factor seems able to explain the complex course of Mycobacterium tuberculosis infection. Multifactorial analyses have identified a variety of genes and proteins, mostly involved in bacterial persistence or host responses, that offer promise as biomarkers for different disease stages.

SUMMARY

The challenge now is to validate the suggested biomarkers being described and then reduce them to clinical practice. If this can be done, it offers the possibility of greatly improved clinical management of tuberculosis, allowing segregation of patients and contacts into appropriate treatment regimens.

Peptide-based antibody detection for tuberculosis diagnosis

Tuberculosis (TB) is a major cause of morbidity and mortality, especially in developing countries. Despite significant limitations, microscopy remains the cornerstone of the global TB control strategy. As the TB epidemic escalates, new diagnostic methods that are accurate and also economical and simple to manufacture and deploy are urgently needed. Although several promising antigens have been identified and evaluated in recent years, the reproducible production of high-quality recombinant mycobacterial proteins with minimal batch-to-batch variation is difficult, laborious, and expensive. To determine the feasibility of devising a synthetic peptide-based diagnostic test for TB, we have delineated the immunodominant epitopes of three candidate antigens, Ag85B, BfrB, and TrxC, that were previously identified to be immunogenic in TB patients. The results demonstrate that combinations of carefully selected synthetic peptides derived from highly immunogenic proteins can be the basis for devising an immunodiagnostic test for TB.

Biomarkers for clinical and incipient tuberculosis: performance in a TB-endemic country

Background

Simple biomarkers are required to identify TB in both HIV⁻TB⁺ and HIV⁺TB⁺ patients. Earlier studies have identified the M. tuberculosis Malate Synthase (MS) and MPT51 as immunodominant antigens in TB patients. One goal of these investigations was to evaluate the sensitivity and specificity of anti-MS and –MPT51 antibodies as biomarkers for TB in HIV⁻TB⁺ and HIV⁺TB⁺ patients from a TB-endemic setting. Earlier studies also demonstrated the presence of these biomarkers during incipient subclinical TB. If these biomarkers correlate with incipient TB, their prevalence should be higher in asymptomatic HIV⁺ subjects who are at a high-risk for TB. The second goal was to compare the prevalence of these biomarkers in asymptomatic, CD4⁺ T cell-matched HIV⁺TB⁻ subjects from India who are at high-risk for TB with similar subjects from US who are at low-risk for TB.

Methods and Results

Anti-MS and -MPT51 antibodies were assessed in sera from 480 subjects including PPD⁺ or PPD⁻ healthy subjects, healthy community members, and HIV⁻TB⁺ and HIV⁺TB⁺ patients from India. Results demonstrate high sensitivity (∼80%) of detection of smear-positive HIV⁻TB⁺ and HIV⁺TB⁺ patients, and high specificity (>97%) with PPD⁺ subjects and endemic controls. While ∼45% of the asymptomatic HIV⁺TB⁻ patients at high-risk for TB tested biomarker-positive, >97% of the HIV⁺TB⁻ subjects at low risk for TB tested negative. Although the current studies are hampered by lack of knowledge of the outcome, these results provide strong support for the potential of these biomarkers to detect incipient, subclinical TB in HIV⁺ subjects.

Conclusions

These biomarkers provide high sensitivity and specificity for TB diagnosis in a TB endemic setting. Their performance is not compromised by concurrent HIV infection, site of TB and absence of pulmonary manifestations in HIV⁺TB⁺ patients. Results also demonstrate the potential of these biomarkers for identifying incipient subclinical TB in HIV⁺TB⁻ subjects at high-risk for TB.

Humoral immune responses of tuberculosis patients in Brazil indicate recognition of Mycobacterium tuberculosis MPT-51 and GlcB

The humoral responses to recombinant MPT-51 and GlcB was determined by using an enzyme-linked immunosorbent assay. Levels of immunoglobulin M (IgM) against MPT-51 and IgG against GlcB were higher among tuberculosis (TB) patients than among control individuals. When the MPT-51 and GlcB assays were combined, 90.8% specificity and 75.5% sensitivity were observed. MPT-51 and GlcB were recognized in the humoral responses of Brazilian TB patients.

Mycobacterium tuberculosis-induced gamma interferon production by natural killer cells requires cross talk with antigen-presenting cells involving Toll-like receptors 2 and 4 and the mannose receptor in tuberculous pleurisy

Tuberculous pleurisy allows the study of human cells at the site of active Mycobacterium tuberculosis infection. In this study, we found that among pleural fluid (PF) lymphocytes, natural killer (NK) cells are a major source of early gamma interferon (IFN-gamma) upon M. tuberculosis stimulation, leading us to investigate the mechanisms and molecules involved in this process. We show that the whole bacterium is the best inducer of IFN-gamma, although a high-molecular-weight fraction of culture filtrate proteins from M. tuberculosis H37Rv and the whole-cell lysate also induce its expression. The mannose receptor seems to mediate the inhibitory effect of mannosylated lipoarabinomannan, and Toll-like receptor 2 and 4 agonists activate NK cells but do not induce IFN-gamma like M. tuberculosis does. Antigen-presenting cells (APC) and NK cells bind M. tuberculosis, and although interleukin-12 is required, it is not sufficient to induce IFN-gamma expression, indicating that NK cell-APC contact takes place. Indeed, major histocompatibility complex class I, adhesion, and costimulatory molecules as well as NK receptors regulate IFN-gamma induction. The signaling pathway is partially inhibited by dexamethasone and sensitive to Ca2+ flux and cyclosporine. Inhibition of p38 and extracellular-regulated kinase mitogen-activated protein kinase pathways reduces the number of IFN-gamma+ NK cells. Phosphorylated p38 (p-p38) is detected in ex vivo PF-NK cells, and M. tuberculosis triggers p-p38 in PF-NK cells at the same time that binding between NK and M. tuberculosis reaches its maximum value. Thus, interplay between M. tuberculosis and NK cells/APC triggering IFN-gamma would be expected to play a beneficial role in tuberculous pleurisy by helping to maintain a type 1 profile.

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.

Disease State Differentiation and Identification of Tuberculosis Biomarkers via Native Antigen Array Profiling

A critical element of tuberculosis control is early and sensitive diagnosis of infection and disease. Our laboratories recently showed that different stages of disease were distinguishable via two-dimensional Western blot analyses of Mycobacterium tuberculosis culture filtrate proteins. However, this methodology is not suitable for high throughput testing. Advances in protein microarray technology provide a realistic mechanism to screen a large number of serum samples against thousands of proteins to identify biomarkers of disease states. Techniques were established for separation of native M. tuberculosis cytosol and culture filtrate proteins, resulting in 960 unique protein fractions that were used to generate protein microarrays. Evaluation of serological reactivity from 42 patients in three tuberculosis disease states and healthy purified protein derivative-positive individuals demonstrated that human immunodeficiency virus (HIV)-negative cavitary and noncavitary tuberculosis (TB) patients' sera recognized 126 and 59 fractions, respectively. Sera from HIV patients coinfected with TB recognized 20 fractions of which five overlapped with those recognized by non-HIV TB patients' sera and 15 were unique to the HIV+TB+ disease state. Identification of antigens within the reactive fractions yielded 11 products recognized by both cavitary and noncavitary TB patients' sera and four proteins (HspX, MPT64, PstS1, and TrxC) specific to cavitary TB patients. Moreover four novel B cell antigens (BfrB, LppZ, SodC, and TrxC) of human tuberculosis were identified.

Mycobacterium tuberculosis malate synthase is a laminin-binding adhesin

Mycobacterium tuberculosis (M. tb) uses the glyoxalate bypass for intracellular survival in vivo. These studies provide evidence that the M. tb malate synthase (MS) has adapted to function as an adhesin which binds to laminin and fibronectin. This binding is achieved via the unique C-terminal region of the M. tb MS. The ability to function as an adhesin necessitates extracellular localization. We provide evidence that despite the absence of a Sec-translocation signal sequence the M. tb MS is secreted/excreted, and is anchored on the cell wall by an undefined mechanism. The MS of Mycobacterium smegmatis is cytoplasmic but the M. tb MS expressed in M. smegmatis localizes to the cell wall and enhances the adherence of the bacteria to lung epithelial A549 cells. Antibodies to the C-terminal laminin/fibronectin-binding domain interfere with the binding of the M. tb MS to laminin and fibronectin and reduce the adherence of M. tb to A549 cells. Coupled to the earlier evidence of in vivo expression of M. tb MS during active but not latent infection in humans, these studies show that a housekeeping enzyme of M. tb contributes to its armamentarium of virulence promoting factors.

Immunogenicity of the Mycobacterium tuberculosis PPE55 (Rv3347c) protein during incipient and clinical tuberculosis

Clinical tuberculosis (TB), whether noncavitary or cavitary, is the late stage of a chronic disease process, since Mycobacterium tuberculosis is a slowly growing organism. Our studies have shown that the profiles of antigenic proteins expressed by the in vivo bacteria that elicit antibodies differ in cavitary and noncavitary TB. To gain insight into antigenic proteins expressed during incipient, subclinical TB, an expression library of M. tuberculosis genomic DNA was screened with sera obtained during subclinical TB from guinea pigs infected with aerosols of M. tuberculosis H37Rv. One of the proteins recognized by antibodies elicited during subclinical TB infection of guinea pigs is the 309-kDa PPE55 (Rv3347c) protein. Genomic hybridization studies suggest that the PPE55 gene is specific to the M. tuberculosis complex and is present in a majority of clinical isolates tested. Antibodies to the C-terminal, approximately 100-kDa fragment of PPE55 (PPE-C) were detectable in sera from 29/30 (97%) human immunodeficiency virus-negative/TB-positive (HIV(-) TB(+)) patients and 17/24 (71%) HIV(+) TB(+) patients tested but not in sera from purified-protein derivative-positive healthy controls, suggesting that the in vivo expression of PPE55 protein correlates with active M. tuberculosis infection. Anti-PPE-C antibodies were also detected in retrospective sera obtained months prior to manifestation of clinical TB from 17/21 (81%) HIV(+) TB(+) individuals tested, providing evidence that the protein is expressed during incipient, subclinical TB in HIV-infected humans. Thus, PPE55 is a highly immunogenic protein that may be useful for differentiating between latent TB and incipient, subclinical TB.

Antigens of Mycobacterium tuberculosis recognized by antibodies during incipient, subclinical tuberculosis

Serum samples obtained from human immunodeficiency virus (HIV)-infected tuberculosis (TB) patients months prior to clinical TB were used to delineate the profile of Mycobacterium tuberculosis culture filtrate proteins recognized during subclinical TB. A subset of approximately 12 antigens was recognized by antibodies in these serum samples. Antibodies to two of these antigens (81 [88]-kDa malate synthase [GlcB] and MPT51) were present in serum samples obtained during incipient subclinical TB in 19 (approximately 90%) of the 21 HIV-infected TB patients tested. These antigens will be useful for devising diagnostic tests that can identify HIV-positive individuals who are at a high risk for developing clinical TB.

Peripheral blood and pleural fluid mononuclear cell responses to low-molecular-mass secretory polypeptides of Mycobacterium tuberculosis in human models of immunity to tuberculosis

A total of 104 polypeptides were purified from the low-molecular-mass secretory proteome of Mycobacterium tuberculosis H(37)Rv using a combination of anion exchange column chromatography and high resolution preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by electroelution. The goal of this study was to identify polypeptides from a low-molecular-mass secretory proteome recognized by human subjects infected with M. tuberculosis and to ascertain the differences in specificity of antigen recognition by the peripheral blood mononuclear cells (PBMCs) and pleural fluid mononuclear cells (PFMCs) of these individuals. The study identified CFP-8 (Rv0496), CFP-11 (Rv2433c), CFP-14.5 (Rv2445c), and CFP-31 (Rv0831c) as novel T-cell antigens apart from previously characterized ESAT-6, TB10.4, CFP10, GroES, MTSP14, MTSP17, CFP21, MPT64, Ag85A, and Ag85B on the basis of recognition by PBMCs of tuberculosis contacts and treated tuberculosis patients. Further, polypeptides prominently recognized by PFMCs of tuberculous pleurisy patients were the same as those recognized by PBMCs of healthy contacts and treated tuberculosis patients. The results of our study indicate the homogeneity of antigenic target recognition by lymphocytes at the site of infection and at the periphery in the human subjects studied and the need to evaluate these antigenic targets as components of future antituberculous vaccines.

Humoral response to low molecular weight antigens of Mycobacterium tuberculosis by tuberculosis patients and contacts

Much effort has been devoted to the identification of immunologically important antigens of Mycobacterium tuberculosis and to the combination of target antigens to which antibodies from serum of tuberculous patients could react specifically. We searched for IgG antibodies specific for antigens of 45 to 6 kDa obtained after sonication of the well-characterized wild M. tuberculosis strain in order to detect differences in the antibody response to low molecular weight antigens from M. tuberculosis between patients with pulmonary tuberculosis and contacts. Specific IgG antibodies for these antigens were detected by Western blot analysis of 153 serum samples collected from 51 patients with confirmed pulmonary tuberculosis. Three samples were collected from each patient: before therapy, and after 2 and 6 months of treatment. We also analyzed 25 samples obtained from contacts, as well as 30 samples from healthy individuals with known tuberculin status, 50 samples from patients with other lung diseases and 200 samples from healthy blood donors. The positive predictive value for associated IgG reactivity against the 6-kDa and 16-kDa antigens, 6 and 38 kDa, and 16 and 38 kDa was 100% since simultaneous reactivity for these antigens was absent in healthy individuals and individuals with other lung diseases. This association was observed in 67% of the patients, but in only 8% of the contacts. The humoral response against antigens of 16 and 6 kDa seems to be important for the detection of latent tuberculosis since the associated reactivity to these antigens is mainly present in individuals with active disease.

Pulmonary tuberculosis: evaluation of interferon-gamma levels as an immunological healing marker based on the response to the Bacillus Calmette-Guerin

Tuberculosis (TB) is a disease caused by Mycobacterium tuberculosis whose interaction with the host may lead to a cell-mediated protective immune response. The presence of interferon gamma (IFN-gamma) is related to this response. With the purpose of understanding the immunological mechanisms involved in this protection, the lymphoproliferative response, IFN-gamma and other cytokines like interleukin (IL-5, IL-10), and tumor necrosis factor alpha (TNF-alpha) were evaluated before and after the use of anti-TB drugs on 30 patients with active TB disease, 24 healthy household contacts of active TB patients, with positive purified protein derivative (PPD) skin tests (induration > 10 mm), and 34 asymptomatic individuals with negative PPD skin test results (induration < 5 mm). The positive lymphoproliferative response among peripheral blood mononuclear cells of patients showed high levels of IFN-gamma, TNF-alpha, and IL-10. No significant levels of IL-5 were detected. After treatment with rifampicina, isoniazida, and pirazinamida, only the levels of IFN-gamma increased significantly (p < 0.01). These results highlight the need for further evaluation of IFN-gamma production as a healing prognostic of patients treated.

Comparison of antibody responses to a potential combination of specific glycolipids and proteins for test sensitivity improvement in tuberculosis serodiagnosis

The humoral response to different proteinaceous antigens of Mycobacterium tuberculosis is heterogeneous among patients with active disease, and this has originated in the proposal to use a combination of several specific antigens to find an efficient serodiagnostic test for tuberculosis (TB). However, to date, comparisons of antibody responses to several antigens in the same population have been carried out without consideration of antigenic cell wall glycolipids. In the present study the presence of immunoglobulin G (IgG), IgM, and IgA antibodies to M. tuberculosis glycolipids (sulfolipid I, diacyltrehaloses, triacyltrehaloses, and cord factor) was compared with the response to four commercially available tests based on the 38-kDa protein mixed with the 16-kDa protein or lipoarabinomannan. Fifty-two serum samples from TB patients and 83 serum samples from control individuals (48 healthy individuals and 35 non-TB pneumonia patients) were studied. Three relevant results were obtained. (i) Smear-negative TB patients presented low humoral responses, but the sera which did react principally showed IgA antibodies to some glycolipidic antigens. (ii) TB patients exhibit heterogeneous humoral responses against glycolipidic antigens. (iii) Finally, test sensitivity is improved (from 23 to 62%) when IgG and IgA antibodies are detected together in tests based on different antigens (proteins and glycolipids). We conclude that it is possible to include glycolipidic antigens in a cocktail of specific antigens from M. tuberculosis to develop a serodiagnostic test.

PPE antigen Rv2430c of Mycobacterium tuberculosis induces a strong B-cell response

The variation in sequence and length in the C-terminal region among members of the unique PE (Pro-Glu) and PPE (Pro-Pro-Glu) protein families of Mycobacterium tuberculosis is a likely source of antigenic variation, giving rise to the speculation that these protein families could be immunologically important. Based on in silico analysis, we selected a hypothetical open reading frame (ORF) encoding a protein belonging to the PPE family and having epitopes with predictably higher antigenic indexes. Reverse transcriptase PCR using total RNA extracted from in vitro-cultured M. tuberculosis H37Rv generated an mRNA product corresponding to this gene, indicating the expression of this ORF (Rv2430c) at the mRNA level. Recombinant protein expressed in Escherichia coli was used to screen the sera of M. tuberculosis-infected patients, as well as those of clinically healthy controls (n = 10), by enzyme-linked immunosorbent assay. The panel of patient sera comprised sera from fresh infection cases (category 1; n = 32), patients with relapsed tuberculosis (category 2; n = 30), and extrapulmonary cases (category 3; n = 30). Category 2 and 3 sera had strong antibody responses to the PPE antigen, equal to or higher than those to other well-known antigens, such as Hsp10 or purified protein derivative (PPD). However, a higher percentage of patients belonging to category 1, as opposed to clinically healthy controls, showed stronger antibody response against the PPE protein when probed with anti-immunoglobulin M (IgM) (71 versus 37.5%) or anti-IgG (62.5 versus 28.12%). Our results reveal that this PPE ORF induces a strong B-cell response compared to that generated by M. tuberculosis Hsp10 or PPD, pointing to the immunodominant nature of the protein.

Proteomics of bacterial pathogens

The rapid growth of proteomics that has been built upon the available bacterial genome sequences has opened provided new approaches to the analysis of bacterial functional genomics. In the study of pathogenic bacteria the combined technologies of genomics, proteomics and bioinformatics has provided valuable tools for the study of complex phenomena determined by the action of multiple gene sets. The review considers some of the recent developments in the establishment of proteomic databases as well as attempts to define pathogenic determinants at the level of the proteome for some of the major human pathogens. Proteomics can also provide practical applications through the identification of immunogenic proteins that may be potential vaccine targets as well as in extending our understanding of antibiotic action. There is little doubt that proteomics has provided us with new and valuable information on bacterial pathogens and will continue to be an important source of information in the coming years.

Serodiagnosis of tuberculosis: comparison of immunoglobulin A (IgA) response to sulfolipid I with IgG and IgM responses to 2,3-diacyltrehalose, 2,3,6-triacyltrehalose, and cord factor antigens

Nonpeptidic antigens from the Mycobacterium tuberculosis cell wall are the focus of extensive studies to determine their potential role as protective antigens or serological markers of tuberculous disease. Regarding this latter role and using an enzyme-linked immunosorbent assay, we have made a comparative study of the immunoglobulin G (IgG), IgM, and IgA antibody responses to four trehalose-containing glycolipids purified from M. tuberculosis: diacyltrehaloses, triacyltrehaloses, cord factor, and sulfolipid I (SL-I). Sera from 92 tuberculosis patients (taken before starting antituberculosis treatment) and a wide group of control individuals (84 sera from healthy donors, including purified protein derivative-negative, -positive, healed, and vaccinated individuals, and 52 sera from nontuberculous pneumonia patients), all from Spain, were studied. The results indicated a significantly elevated IgG and IgA antibody response in tuberculosis patients, compared with controls, with all the antigens used. SL-I was the best antigen studied, showing test sensitivities and specificities for IgG of 81 and 77.6%, respectively, and of 66 and 87.5% for IgA. Using this antigen and combining IgA and IgG antibody detection, high test specificity was achieved (93.7%) with a sensitivity of 67.5%. Currently, it is widely accepted that it is not possible to achieve sensitivities above 80% in tuberculosis serodiagnosis when using one antigen alone. Thus, we conclude that SL-I, in combination with other antigenic molecules, could be a useful antigen for tuberculosis serodiagnosis.

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.

Identification, molecular cloning, and evaluation of potential use of isocitrate dehydrogenase II of Mycobacterium bovis BCG in serodiagnosis of tuberculosis

Diagnosis of tuberculosis is time-consuming and requires infrastructures which are often not available in countries with high incidences of the disease. In the present study, an 82-kDa protein antigen was isolated by affinity chromatography and was identified by peptide mass fingerprinting as isocitrate dehydrogenase II, which is encoded by the icd2 gene of Mycobacterium bovis BCG. The icd2 gene of BCG was cloned by PCR, and the product of recombinant gene expression was purified and analyzed by two-dimensional polyacrylamide gel electrophoresis. The recombinant protein, named rICD2, was tested for its recognition by immunoglobulin G (IgG) antibodies from the sera of 16 patients with tuberculosis (TB) and 23 healthy individuals by Western blotting. The results showed that rICD2 is recognized by IgG antibodies from the sera of all TB patients tested at serum dilutions of > or = 1:640. At a serum dilution of 1:1,280, the sensitivity was 50% and the specificity was 86.9%. These results indicate that rICD2 might represent a candidate for use in a new assay for the serodiagnosis of TB.

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.

Homogeneity of antibody responses in tuberculosis patients

The goals of the present study were twofold: (i) to compare the repertoires of antigens in culture filtrates of in vitro-grown Mycobacterium tuberculosis that are recognized by antibodies from noncavitary and cavitary tuberculosis (TB) patients and (ii) to determine the extent of variation that exists between the antigen profiles recognized by individual TB patients. Lipoarabinomannan-free culture filtrate proteins of M. tuberculosis were fractionated by one-dimensional (1-D) and 2-D polyacrylamide gel electrophoresis, and the Western blots were probed with sera from non-human immunodeficiency virus (non-HIV)-infected cavitary and noncavitary TB patients and from HIV-infected, noncavitary TB patients. In contrast to earlier studies based on recombinant antigens of M. tuberculosis which suggested that antibody responses in TB patients were heterogeneous (K. Lyashchenko et al., 1998, Infect. Immun. 66:3936-3940, 1998), our studies with native culture filtrate proteins show that the antibody responses in TB patients show significant homogeneity in being directed against a well-defined subset of antigens. Thus, there is a well-defined subset of culture filtrate antigens that elicits antibodies during noncavitary and cavitary disease. In addition, another set of antigens is recognized primarily by cavitary TB patients. The mapping with individual patient sera presented here suggests that serodiagnostic tests based on the subset of antigens recognized during both noncavitary and cavitary TB will enhance the sensitivity of antibody detection in TB patients, especially in difficult-to-diagnose, smear-negative, noncavitary TB patients.

Immune responses in tuberculosis: antibodies and CD4-CD8 lymphocytes with vascular adhesion molecules and cytokines (chemokines) cause a rapid antigen-specific cell infiltration at sites of bacillus Calmette-Guérin reinfection

Rabbit primary dermal bacillus Calmette-Guérin (BCG) lesions were compared with reinfection BCG lesions in order to gain insight into how immune responses protect against clinical tuberculosis. As early as 3 hr, a marked infiltration of macrophages and lymphocytes occurred in the reinfection group, while very little cell infiltration occurred in the primary group. It seems that only an antigen-antibody reaction could produce such an immediate pronounced antigen-specific chemotactic effect, because very few lymphocytes are normally present in the skin. Therefore, antibodies hasten the accumulation of an expanded antigen-specific T-lymphocyte population (memory cells) at sites of bacillary lodgement. By 1-2 days, the primary and reinfection BCG lesions differed 400- to 500-fold in size. By 4-5 days, the size of the reinfection lesions had declined, while the size of the primary lesions had increased, so that, grossly, both types of lesion were similar. At 8 days in reinfection lesions and at 12 days in primary lesions, small secondary peaks in size occurred, which were probably caused by cell-mediated immune responses. In rabbits with primary BCG lesions, skin tests with Old Tuberculin were positive at 9 days, accompanied by a rise in the levels of antibodies to the secreted antigen, phosphate-specific transport protein 1, but the levels of antibodies to the constitutive antigens, purified protein derivative and heat-shock protein 65, did not increase appreciably until some time after 23 days. In tissue sections of reinfection BCG lesions, the percentage of mononuclear cells labelled, by in situ hybridization techniques, for the mRNA of monocyte chemoattractant protein 1 (MCP-1), a chemokine, peaked at 3 hr and then was down-regulated, whereas in primary lesions, this percentage was down-regulated only after 2 days. [The percentage in the tissue sections for the mRNAs of interleukins 1beta and 8, as well as the proteins of MCP-1 and tumor necrosis factor alpha (TNF-alpha), followed a somewhat similar time-course to that of MCP-1 mRNA.] A high percentage of mononuclear cells containing the MCP-1 mRNA 'factory' would favour enlargement of the lesions and a low percentage would favour their regression. At 5 days, the percentage of CD4 and CD8 lymphocytes, stained by immunohistochemical techniques, and the amount of microvasculature stained similarly for vascular cell adhesion molecule 1 were higher in the reinfection group, indicating that prior immunization caused a more rapid (antigen-dependent) up-regulation of these factors. Tuberculin reactions resembled early reinfection BCG lesions in almost every factor evaluated herein. In brief, the production of chemokines began soon after BCG reinfection, peaked within a few hours and was markedly down-regulated by 24 hr, a time at which the lesions of reinfection were of maximal size. Therefore, the amount of cell infiltration was tightly controlled, probably by the variety of mechanisms listed herein.

Cell-mediated immune response to tuberculosis antigens: comparison of skin testing and measurement of in vitro gamma interferon production in whole-blood culture

Although delayed-type hypersensitivity skin testing with tuberculin purified protein derivative (PPD) is the standard for tuberculosis screening, its variability suggests the need for a more sensitive, noninvasive test. An in vitro whole-blood assay has been proposed as an alternative. Using health care worker volunteers, we confirmed the correlation between PPD skin test (PPD-ST) results (positive, induration of >15 mm) and a standardized gamma interferon (IFN-gamma) assay, QuantiFERON-TB (Q-IFN), manufactured by CSL Biosciences in Australia, and we evaluated Mycobacterium tuberculosis culture subfractions as potential substitutes for PPD. Twenty healthy volunteers with positive PPD-ST results and 20 PPD-ST-negative controls were enrolled. Whole blood was cultured with human PPD antigens (HuPPD), Mycobacterium avium complex (MAC) PPD, phytohemagglutinin (PHA), and four M. tuberculosis culture subfractions: low-molecular-weight culture, filtrate, culture filtrate without lipoarabinomannan, soluble cell wall proteins, and cytosolic proteins, all developed from M. tuberculosis strain H(37)RV. Secretion of IFN-gamma (expressed as international units per milliliter) was measured by an enzyme immunoassay. The PPD or subculture fraction response as a percentage of the PHA response was used to determine positivity. Sixteen of 20 PPD-ST-positive individuals were classified as M. tuberculosis positive by Q-IFN, and 1 was classified as MAC positive. Sixteen of 20 PPD-ST-negative individuals were M. tuberculosis negative by Q-IFN, 2 were MAC positive, and 2 were M. tuberculosis positive. The tuberculosis culture subfractions stimulated IFN-gamma production in PPD-ST-positive volunteers, and significant differences could be seen between the two PPD-ST groups with all subfractions except soluble cell wall protein; however, the response was variable and no better than the Q-IFN PPD. The agreement between the Q-IFN test and the PPD-ST was good (Cohen's kappa = 0.73). The Q-IFN assay can be a useful tool in further studies of immune responses to M. tuberculosis antigens.

Mycobacterium tuberculosis-secreted protein antigens: immunogenicity in baboons

The effective control of tuberculosis (TB) requires the development of improved vaccines. It is now well established that Mycobacterium tuberculosis-secreted antigens represent promising candidates to be included in subunit vaccine preparations. It also is accepted that studies in nonhuman primate models will be required to further develop these vaccine preparations. As a necessary step in this direction, we have assessed the immunogenicity of M. tuberculosis-secreted antigens in baboons. Animals received a total of three intramuscular injections consisting of M. tuberculosis culture filtrate proteins resuspended in an adjuvant formulation (MPL-SE) and were tested for development of specific antibody and cellular responses. All animals produced antibody and cellular proliferative responses in the absence of detectable delayed-type hypersensitivity reactions. Production of gamma-interferon following stimulation of peripheral blood lymphocytes with culture filtrate proteins was either absent or present at low levels. Results from this study show that, although M. tuberculosis-secreted protein antigens are relatively safe and immunogenic in baboons, alternative immunization approaches must be identified for the induction of T-helper type 1 responses.

Serodiagnostic potential of culture filtrate antigens of Mycobacterium tuberculosis

Our studies of the humoral responses of tuberculosis (TB) patients have defined the repertoire of culture filtrate antigens of Mycobacterium tuberculosis that are recognized by antibodies from cavitary and noncavitary TB patients and demonstrated that the profile of antigens recognized changes with disease progression (K. Samanich et al., J. Infect. Dis. 178:1534-1538, 1998). We have identified several antigens with strong serodiagnostic potential. In the present study we have evaluated the reactivity of cohorts of human immunodeficiency virus (HIV)-negative, smear-positive; HIV-negative, smear-negative; and HIV-infected TB patients, with three of the candidate antigens, an 88-kDa protein, antigen (Ag) 85C, and MPT32, and compared the reactivity of the same patient cohort with the 38-kDa antigen and Ag 85A. We have also compared the reactivity of native Ag 85C and MPT32 with their recombinant counterparts. The evaluation of the reactivity was done by a modified enzyme-linked immunosorbent assay described earlier (S. Laal et al., Clin. Diag. Lab. Immunol. 4:49-56, 1997), in which all sera are preadsorbed against Escherichia coli lysates to reduce the levels of cross-reactive antibodies. Our results demonstrate that (i) antigens identified on the basis of their reactivity with TB patients' sera provide high sensitivities for serodiagnosis, (ii) recombinant Ag 85C and MPT32, expressed in E. coli, show reduced reactivity with human TB sera, and (iii) of the panel of antigens tested, the 88-kDa protein is the most promising candidate for serodiagnosis of TB in HIV-infected individuals. Moreover, these results reaffirm that both the extent of the disease and the bacterial load may play a role in determining the antigen profile recognized by antibodies.

Mass spectrometric identification of mtb81, a novel serological marker for tuberculosis

We have used serological proteome analysis in conjunction with tandem mass spectrometry to identify and sequence a novel protein, Mtb81, which may be useful for the diagnosis of tuberculosis (TB), especially for patients coinfected with human immunodeficiency virus (HIV). Recombinant Mtb81 was tested by an enzyme-linked immunosorbent assay to detect antibodies in 25 of 27 TB patients (92%) seropositive for HIV as well as in 38 of 67 individuals (57%) who were TB positive alone. No reactivity was observed in 11 of 11 individuals (100%) who were HIV seropositive alone. In addition, neither sera from purified protein derivative (PPD)-negative (0 of 29) nor sera from healthy (0 of 45) blood donors tested positive with Mtb81. Only 2 of 57 of PPD-positive individuals tested positive with Mtb81. Sera from individuals with smear-positive TB and seropositive for HIV but who had tested negative for TB in the 38-kDa antigen immunodiagnostic assay were also tested for reactivity against Mtb81, as were sera from individuals with lung cancer and pneumonia. Mtb81 reacted with 26 of 37 HIV(+) TB(+) sera (70%) in this group, compared to 2 of 37 (5%) that reacted with the 38-kDa antigen. Together, these results demonstrate that Mtb81 may be a promising complementary antigen for the serodiagnosis of TB.

Proteomics in medical microbiology

The techniques of proteomics (high resolution two-dimensional electrophoresis and protein characterisation) are widely used for microbiological research to analyse global protein synthesis as an indicator of gene expression. The rapid progress in microbial proteomics has been achieved through the wide availability of whole genome sequences for a number of bacterial groups. Beyond providing a basic understanding of microbial gene expression, proteomics has also played a role in medical areas of microbiology. Progress has been made in the use of the techniques for investigating the epidemiology and taxonomy of human microbial pathogens, the identification of novel pathogenic mechanisms and the analysis of drug resistance. In each of these areas, proteomics has provided new insights that complement genomic-based investigations. This review describes the current progress in these research fields and highlights some of the technical challenges existing for the application of proteomics in medical microbiology. The latter concern the analysis of genetically heterogeneous bacterial populations and the integration of the proteomic and genomic data for these bacteria. The characterisation of the proteomes of bacterial pathogens growing in their natural hosts remains a future challenge.

Generation of a recombinant bacteriophage antibody library to mycobacterium tuberculosis

Monoclonal antibodies to Mycobacterium tuberculosis (Mtb) may be useful for laboratory diagnosis, antigenic characterization, and studying the immune response to infection and vaccination. To investigate the potential of the recombinant phage antibody technique for the isolation of single-chain fragments (ScFv) reactive with Mtb culture proteins, we generated a bacteriophage antibody library from splenic tissue of mice immunized with heat-killed Mtb. Heavy- and light-chain immunoglobulin genes were isolated and amplified by the polymerase chain reaction (PCR), and the products were assembled into ScFv gene fragments and cloned into the pCANTAB5-E phagemid. Phagemids were introduced into E. coli TG1 by electrotransformation, followed by rescue of antibody-expressing phage using M13K07 helper-phage superinfection. Immunoselection of the Mtb phage library against Mtb cell wall extract or culture filtrate proteins selected antigen-specific and cross-reactive phage antibodies, none of which demonstrated reactivity to the immunodominant 65-kDa Mtb antigen. These results suggest that the phage antibody system has the potential to generate a diverse population of the reactive phage that may prove useful for investigating the immune response to Mtb infection and vaccination.

Definition of Mycobacterium tuberculosis culture filtrate proteins by two-dimensional polyacrylamide gel electrophoresis, N-terminal amino acid sequencing, and electrospray mass spectrometry

A number of the culture filtrate proteins secreted by Mycobacterium tuberculosis are known to contribute to the immunology of tuberculosis and to possess enzymatic activities associated with pathogenicity. However, a complete analysis of the protein composition of this fraction has been lacking. By using two-dimensional polyacrylamide gel electrophoresis, detailed maps of the culture filtrate proteins of M. tuberculosis H37Rv were generated. In total, 205 protein spots were observed. The coupling of this electrophoretic technique with Western blot analysis allowed the identification and mapping of 32 proteins. Further molecular characterization of abundant proteins within this fraction was achieved by N-terminal amino acid sequencing and liquid chromatography-mass spectrometry. Eighteen proteins were subjected to N-group analysis; of these, only 10 could be sequenced by Edman degradation. Among the most interesting were a novel 52-kDa protein demonstrating significant homology to an alpha-hydroxysteroid dehydrogenase of Eubacterium sp. strain VPI 12708, a 25-kDa protein corresponding to open reading frame 28 of the M. tuberculosis cosmid MTCY1A11, and a 31-kDa protein exhibiting an amino acid sequence identical to that of antigen 85A and 85B. This latter product migrated with an isoelectric point between those of antigen 85A and 85C but did not react with the antibody specific for this complex, suggesting that there is a fourth member of the antigen 85 complex. Novel N-terminal amino acid sequences were obtained for three additional culture filtrate proteins; however, these did not yield significant homology to known protein sequences. A protein cluster of 85 to 88 kDa, recognized by the monoclonal antibodies IT-57 and IT-42 and known to react with sera from a large proportion of tuberculosis patients, was refractory to N-group analysis. Nevertheless, mass spectrometry of peptides obtained from one member of this complex identified it as the M. tuberculosis KatG catalase/peroxidase. Thus, the detailed mapping of M. tuberculosis proteins, combined with state-of-the-art analytical techniques such as mass spectrometry, provides a basis for further analysis and rapid identification of biologically relevant molecules.