Immunoproteomic identification of human T cell antigens of Mycobacterium tuberculosis that differentiate healthy contacts from tuberculosis patients

Relevance of antigen-induced IL-6 and mitogen-induced or spontaneous IFN-γ secretions in whole blood cultures for detection of Mycobacterium tuberculosis infection and disease

For an effective control of tuberculosis (TB), there is a persistent need for biomarkers that can report true estimates of TB infection (TBI) and predict its progression towards active TB disease. We investigated whether the cell-mediated immune responses to Mycobacterium tuberculosis (Mtb) antigens could provide such biomarkers. The study subjects (n = 174) comprised a cohort of smear-positive, drug-sensitive, HIV-negative pulmonary TB patients (n = 54) and their household contacts (HC, n = 120). Whole blood cultures, in the presence or absence of Mtb antigens- membrane (MtM), purified protein derivative (PPD) and alpha-crystallin (Acr), or the mitogen PHA were subjected to determinations, by flow cytometry, for T cell proliferative and, by ELISA, for IFN-γ, TNF-α, and IL-6 cytokine responses. Additionally, serum levels of the three cytokines were also estimated. The strongest cell-proliferative and cytokine responses were induced by MtM and IL-6 was the most abundantly produced cytokine. While none of the responses induced by Mtb antigens or the serum cytokines levels could discriminate between TB and HC, the ex vivo cytokine responses induced by PHA or 'spontaneously' could apparently do so. The concentrations of IFN-γ induced by PHA in TB blood cultures were significantly lower than in HC cultures (AUC = 0.72). Conversely, the spontaneous IFN-γ or TNF-α secretions in TB cultures were significantly higher than in HC cultures (AUC = 0.66). Our results suggest that IL-6 responses to MtM could be a sensitive indicator of TBI, and low levels of PHA-induced or high levels of spontaneous IFN-γ secretions in HC blood cultures may indicate a progressive infection.

Comparison of cytokine profile of IFN-γ, IL-5 and IL-10 in cutaneous leishmaniasis using PBMC vs. whole blood

BACKGROUND AND OBJECTIVES

The surrogate marker (s) of cure and protection in intracellular pathogens is not yet well defined. The aim of this study was to compare the cytokine profile using whole blood cells (WBC) vs. peripheral blood mononuclear cells (PBMC) in healthy and cutaneous leishmaniasis (CL) volunteers.

MATERIALS AND METHODS

In this study, WBC and PBMC of the volunteers with history of CL (HCL), Active lesion (ACL) and healthy volunteers were collected. The WBC and PBMC were cultured and stimulated with either PHA or soluble Leishmania antigens (SLA), after 72 hours, the supernatants were collected and the levels of IFN-γ, IL-5 and IL-10 were titrated using ELISA method.

RESULTS

The mean ± SD of cytokines using WBC and PBMC in cutaneous leishmaniasis volunteers stimulated with phytohemagglutin (PHA) or SLA are as follow, PHA, IFN-γ=2295±995 vs. 2339±1115, IL-10=853±309 vs. 1330±966, and IL-5=299±136 vs. 352+156, SLA, IFN-γ, 931±824 vs. 825±532, IL-10, 233±78 vs. 408±381, and IL-5, 185±59 vs. 217±76, respectively. There was no significant difference between the IFN-γ, IL-5 and IL-10 levels using WBC vs. PBMC. There was a strong correlation between the cytokine profiles using WBC and PBMC in cutaneous leishmaniasis volunteers.

CONCLUSION

There was no significant difference between IFN-γ, IL-10, IL-5 levels in whole blood and PBMC of volunteers with active lesion or history of CL. Whole-blood culture which is easier, cheaper and more convenient could be used instead of PBMC to evaluate the cytokine profile in field conditions.

Altered expression of antigen-specific memory and regulatory T-cell subsets differentiate latent and active tuberculosis

Although one-third of the world population is infected with Mycobacterium tuberculosis, only 5-10% of the infected individuals will develop active tuberculosis (TB) disease and the rest will remain infected with no symptoms, known as latent TB infection (LTBI). Identifying biomarkers that differentiate latent and active TB disease enables effective TB control, as early detection, treatment of active TB and preventive treatment of individuals with LTBI are crucial steps involved in TB control. Here, we have evaluated the frequency of antigen-specific memory and regulatory T (Treg) cells in 15 healthy household contacts (HHC) and 15 pulmonary TB patients (PTB) to identify biomarkers for differential diagnosis of LTBI and active TB. Among all the antigens tested in the present study, early secretory antigenic target-6 (ESAT-6) -specific CD4⁺ and CD8⁺ central memory (Tcm) cells showed 93% positivity in HHC and 20% positivity in PTB. The novel test antigens Rv0753c and Rv0009 both displayed 80% and 20% positivity in HHC and PTB, respectively. In contrast to Tcm cells, effector memory T (Tem) cells showed a higher response in PTB than HHC; both ESAT-6 and Rv0009 showed similar positivity of 80% in PTB and 33% in HHC. PTB patients have a higher proportion of circulating antigen-reactive Treg cells (CD4⁺  CD25⁺  FoxP3⁺ ) than LTBI. Rv2204c-specific Treg cells showed maximum positivity of 73% in PTB and 20% in HHC. Collectively, our data conclude that ESAT-6-specific Tcm cells and Rv2204c-specific Treg cells might be useful biomarkers to discriminate LTBI from active TB.

Influence of HLA-DRB1 Alleles on the Variations of Antibody Response to Tuberculosis Serodiagnostic Antigens in Active Tuberculosis Patients

Serology-based tests for tuberculosis (TB) diagnosis, though rapid, efficient and easily implemented, have so far shown unsatisfactory levels of sensitivity and specificity, probably due to variations of the antibody response in TB patients. The number and types of seropositive antigens vary from individual to individual. The person-to-person variations of antigen recognition may be linked to genetic polymorphisms of the human leukocyte antigen (HLA) class II alleles. In the present study, we find that there is a significant increase in the frequency of HLA-DRB1*14 (P = 2.5×10⁻⁴) among subjects with high antibody response levels compared to those with low antibody levels. HLA-DRB1*15, the most frequent allelic group in the studied active TB population, positively correlates with subjects with low antibody response levels rather than subjects with high antibody response levels (P = 0.005), which indicates the loss of relevant antigens for screening of patients with this allelic group. The potential association between HLA-DRB1 allelic group and individual antigens implies that TB diagnostic yield could be improved by the addition of antigens screened at the proteome scale in infected subjects from the HLA-DRB1*15 allelic group.

Proteomics Analysis of Three Different Strains of Mycobacterium tuberculosis under In vitro Hypoxia and Evaluation of Hypoxia Associated Antigen's Specific Memory T Cells in Healthy Household Contacts

In vitro mimicking conditions are thought to reflect the environment experienced by Mycobacterium tuberculosis inside the host granuloma. The majority of in vitro dormancy experimental models use laboratory-adapted strains H37Rv or Erdman instead of prevalent clinical strains involved during disease outbreaks. Thus, we included the most prevalent clinical strains (S7 and S10) of M. tuberculosis from south India in addition to H37Rv for our in vitro oxygen depletion (hypoxia) experimental model. Cytosolic proteins were prepared from hypoxic cultures, resolved by two-dimensional electrophoresis and protein spots were characterized by mass spectrometry. In total, 49 spots were characterized as over-expressed or newly emergent between the three strains. Two antigens (ESAT-6, Lpd) out of the 49 characterized spots were readily available in recombinant form in our lab. Hence, these two genes were overexpressed, purified and used for in vitro stimulation of whole blood collected from healthy household contacts (HHC) and active pulmonary tuberculosis patients (PTB). Multicolor flow cytometry analysis showed high levels of antigen specific CD4(+) central memory T cells in the circulation of HHC compared to PTB (p < 0.005 for ESAT-6 and p < 0.0005 for Lpd). This shows proteins that are predicted to be up regulated during in vitro hypoxia in most prevalent clinical strains would indicate possible potential immunogens. In vitro hypoxia experiments with most prevalent clinical strains would also elucidate the probable true representative antigens involved in adaptive mechanisms.

Dynamic IgG antibody response to immunodominant antigens of M. tuberculosis for active TB diagnosis in high endemic settings

BACKGROUND

Even though various techniques have been developed for rapid diagnosis of tuberculosis (TB), still there is an immense need for a simple, cost effective, highly sensitive and specific test. Hence, one of the possibilities is identification of Mycobacterium tuberculosis specific antibodies in infected serum by using specific antigens.

METHODS

We tested 10 recombinant M. tuberculosis antigens to evaluate IgG levels among Healthy control subjects (HCS), Healthy household contacts (HHC) and pulmonary TB patients (PTB) by ELISA.

RESULTS

The median IgG levels specific to all the antigens are higher in PTB than HHC and HCS. Amongst single antigens, 38-kDa antigen has showed maximum sensitivity of 50% than any other antigens at 95.5% specificity. Among the two antigen combination, 38-kDa+Rv1860 has showed maximum sensitivity of 66.6% with specificity of 92.2%. The same antigen combination (38-kDa and Rv1860) predominantly identifies smear negative and culture positive TB patients with 68% sensitivity and 92.2% specificity. Most of the antigens have exhibited higher antibody titre in cavitary TB than non cavitary. With regard to latent TB infection (LTBI) identification, Rv1860 has exhibited maximum sensitivity of 53.3% with 95% specificity.

CONCLUSIONS

IgG response to combination of recombinant mycobacterial antigens (38-kDa, Rv1860, Rv2204c and Rv0753c) presents good specificity with acceptable level of sensitivity for TB diagnosis.

Identification of HLA-A*11:01-restricted Mycobacterium tuberculosis CD8(+) T cell epitopes

New vaccines are needed to combat Mycobacterium tuberculosis (MTB) infections. The currently employed Bacillus Calmette‐Guérin vaccine is becoming ineffective, due in part to the emergence of multidrug‐resistant tuberculosis (MDR‐TB) strains and the reduced immune capacity in cases of HIV coinfection. CD8⁺ T cells play an important role in the protective immunity against MTB infections, and the identification of immunogenic CD8⁺ T cell epitopes specific for MTB is essential for the design of peptide‐based vaccines. To identify CD8⁺ T cell epitopes of MTB proteins, we screened a set of 94 MTB antigens for HLA class I A*11:01‐binding motifs. HLA‐A*11:01 is one of the most prevalent HLA molecules in Southeast Asians, and definition of T cell epitopes it can restrict would provide significant coverage for the Asian population. Peptides that bound with high affinity to purified HLA molecules were subsequently evaluated in functional assays to detect interferon‐γ release and CD8⁺ T cell proliferation in active pulmonary TB patients. We identified six novel epitopes, each derived from a unique MTB antigen, which were recognized by CD8⁺ T cells from active pulmonary TB patients. In addition, a significant level of epitope‐specific T cells could be detected ex vivo in peripheral blood mononuclear cells from active TB patients by an HLA‐A*11:01 dextramer carrying the peptide Rv3130c_194‐204 (from the MTB triacylglycerol synthase Tgs1), which was the most frequently recognized epitope in our peptide library. In conclusion, this study identified six dominant CD8⁺ T cell epitopes that may be considered potential targets for subunit vaccines or diagnostic strategies against TB.

Mycobacterium tuberculosis MmsA, a novel immunostimulatory antigen, induces dendritic cell activation and promotes Th1 cell-type immune responses

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis, is an outstanding pathogen that modulates the host immune response. This inconvenient truth drives the continual identification of antigens that generate protective immunity, including Th1-type T cell immunity. Here, the contribution of methylmalonate semialdehyde dehydrogenase (MmsA, Rv0753c) of Mtb to immune responses was examined in the context of dendritic cell (DC) activation and T cell immunity both in vitro and in vivo. The results showed that MmsA induced DC activation by activating the MAPK and NF-κB signaling pathways. Additionally, MmsA-treated DCs activated naïve T cells, effectively polarized CD4(+) and CD8(+) T cells to secrete IFN-γ and IL-2, and induced T cell proliferation. These results indicate that MmsA is a novel DC maturation-inducing antigen that drives the Th1 immune response. Thus, MmsA was found to potentially regulate immune responses via DC activation toward Th1-type T cell immunity, enhancing our understanding of Mtb pathogenesis.

PpiA antigen specific immune response is a potential biomarker for latent tuberculosis infection

One third of the world's population is estimated to harbour latent tuberculosis infection (LTBI). Around 10% of them have the life time risk of developing active tuberculosis (PTB). Currently there is no gold standard test for identifying LTBI. Therefore identification of specific markers for LTBI will help as to develop a test specific for LTBI. Earlier, in our immunoproteomic analysis, we found that peptidyl-prolyl cis-trans isomerase A (PpiA) protein-containing fractions induced significantly higher interferon-gamma (IFN-γ) response in LTBI than in PTB. Immunological characterisation of recombinant PpiA protein was carried out in the current study. We have studied 10 cytokines and 2 chemokine responses against PpiA and standard antigens such as early secretory antigenic target-6 (ESAT-6) and culture filtrate antigen-10 (CFP-10). In healthy household contacts (HHC), all the tested antigens induced significantly higher levels of IFN-γ and Interlukin-8 (IL-8) compared with those in PTB. PpiA-specific IL-12p40 response was significantly increased in HHC compared with that in PTB. PpiA antigen-specific IFN-γ and IL-12p40 both showed 86% positivity in HHC, whereas in PTB, they showed 20% and 38% positivity, respectively. In terms of IFN-γ/TNF-α ratio, PpiA displayed 86% (30/35) positivity in HHC and 18% (7/39) positivity in PTB. In summary we found that PpiA-specific IFN-γ and IFN-γ/TNF-α ratio response were specific biomarkers for LTBI identification.

Assessing humoral immune response of 4 recombinant antigens for serodiagnosis of tuberculosis

Serodiagnostic potential of four recombinant proteins (38 kDa[Rv0934], MPT64[Rv1980c], Adk[Rv0733], and BfrB[Rv3874]) was evaluated in Healthy control subjects (HCS), Healthy household contacts (HHC), Pulmonary tuberculosis patients (PTB), and Human immuno deficiency virus & Tuberculosis co-infected patients (HIV-TB). All the antigens tested individually for the detection of serum IgG by indirect ELISA. All the four antigens have a significantly higher antibody response in PTB compared to healthy controls (P < 0.05). The sensitivity of individual antigens ranged from 20% to 52.5% for the prefixed specificity of 95%. When results of all 4 antigens were combined the sensitivity was increased to 75% and specificity was reduced 89% in HCS. In smear- and culture-positive (S+C+) PTB, four antigen combination gives maximum sensitivity (89.6%) with 89% specificity. In smear negative culture negative (S-C+) PTB, three antigen combination (38 kDa with MPT64 and BfrB) gives maximum sensitivity (69.5%) and specificity (91.6%). In HIV-TB, 4 antigen combinations give the maximum sensitivity of 51.2% with 89% specificity. Combining serology (Four antigen combination) with smear was able to increase the sensitivity from 70% to 92.5% in culture positive PTB. So, we propose that this serology test can be used as adjunct test along with smear for rapid diagnosis of PTB.

IFN-γ/TNF-α ratio in response to immuno proteomically identified human T-cell antigens of Mycobacterium tuberculosis - The most suitable surrogate biomarker for latent TB infection

The enormous reservoir of latent TB infection (LTBI) poses a major hurdle for global TB control. The existing Tuberculin skin test (TST) and IFN-γ release assays (IGRAs) are found to be suboptimal for LTBI diagnosis. Previously we had taken an immunoproteomic approach and identified 10 protein fractions (contains 16 proteins), which are solely recognized by LTBI. In a cohort of 40 pulmonary TB patients (PTB) and 35 healthy household contacts (HHC), IFN-γ and TNF-α response were measured against 16 antigens by using 1:10 diluted whole blood assay. Among all the antigens, IFN-γ response to Rv2626c has shown positivity of 88.57% in HHC and 7.5% in PTB group. IFN-γ response to combination of Rv2626c + Rv3716c has demonstrated 100% positivity in HHC and 17.5% positivity in PTB respectively. Compared to individual cytokines (i.e. IFN-γ and TNF-α), ratio of IFN-γ/TNF-α has shown promising results for diagnosis of LTBI. IFN-γ/TNF-α ratio against Rv3716c and TrxC has exhibited a positivity of 94.29% in HHC and 5% in PTB group. Accession of Rv2626c and Rv3716c may improve the diagnostic performance of existing QFT-GIT. Independent of QFT-GIT assay, ratio of IFN-γ/TNF-α in response to either Rv3716c or TrxC may acts as suitable surrogate biomarker for LTBI.

Fractionation and analysis of mycobacterial proteins

The extraction and isolation of native bacterial proteins continue to be valuable technical pursuits in order to understand bacterial physiology, screen for virulence determinants, and describe antigens. In this chapter, methods for the manipulation of whole mycobacterial cells are described in detail. Specifically, the concentration of spent culture filtrate media is described in order to permit separation of soluble, secreted proteins; several discrete separation techniques, including precipitation of protein mixtures with ammonium sulfate and separation of proteins by hydrophobic chromatography are also provided. Similarly, the generation of whole cell lysate and facile separation of lysate into subcellular fractions to afford cell wall, cell membrane, and cytosol enriched proteins is described. Due to the hydrophobic nature of cell wall and cell membrane proteins, several extraction protocols to resolve protein subsets (such as extraction with urea and SDS) are also provided, as well as a separation technique (isoelectric focusing) that can be applied to separate hydrophobic proteins. Lastly, two commonly used analytical techniques, in-gel digestion of proteins for LC-MS and analysis of intact proteins by MALDI-ToF MS, are provided for rapid analysis of discrete proteins within subcellular or chromatographic fractions. While these methods were optimized for the manipulation of Mycobacterium tuberculosis cells, they have been successfully applied to extract and isolate Mycobacterium leprae, Mycobacterium ulcerans, and Mycobacterium avium proteins. In addition, a number of these methods may be applied to extract and analyze mycobacterial proteins from cell lines and host derived samples.

Antigens for CD4 and CD8 T cells in tuberculosis

Tuberculosis (TB), caused by infection with Mycobacterium tuberculosis (MTB), represents an important cause of morbidity and mortality worldwide for which an improved vaccine and immunodiagnostics are urgently needed. CD4(+) and CD8(+) T cells play an important role in host defense to TB. Definition of the antigens recognized by these T cells is critical for improved understanding of the immunobiology of TB and for development of vaccines and diagnostics. Herein, the antigens and epitopes recognized by classically HLA class I- and II-restricted CD4(+) and CD8(+) T cells in humans infected with MTB are reviewed. Immunodominant antigens and epitopes have been defined using approaches targeting particular TB proteins or classes of proteins and by genome-wide discovery approaches. Antigens and epitopes recognized by classically restricted CD4(+) and CD8(+) T cells show extensive breadth and diversity in MTB-infected humans.

Identification of immunogenic proteins of Candida parapsilosis by serological proteome analysis

AIMS

Systemic candidiasis is the leading fungal bloodstream infection, and its incidence has been on the rise. Recently, Candida parapsilosis has emerged as an increasingly prevalent fungal pathogen, but little is known about its antigenic profile. Hence, the current work was performed to discover immunogenic proteins of C. parapsilosis using serological proteome analysis.

METHODS AND RESULTS

Cell wall proteins extracted from C. parapsilosis were resolved by two-dimensional electrophoresis followed by immunoblotting using antisera from experimentally infected mice. Mass spectrometry analysis of the 32 immunoreactive protein spots resulted in the identification of 12 distinct proteins. Among them, 11 proteins were known antigens of Candida albicans, whereas Idh2p was identified for the first time as an immunogenic protein of Candida species. Recombinant Idh2p was expressed in Escherichia coli, and its antigenicity was verified by immunoblot analysis.

CONCLUSIONS

An immunoproteomic approach was successfully applied to identify immunogenic proteins of C. parapsilosis, with Idh2p as a novel candidate antigen. The identified antigens may serve as potential biomarkers for development of diagnostic assay and/or vaccine for C. parapsilosis.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work represents the first immunoproteomic analysis of C. parapsilosis, which provides new insights into host-pathogen interactions and pathogenesis of C. parapsilosis. The immunogenic proteins could be studied as biomarker candidates for C. parapsilosis.

Exosomes carrying mycobacterial antigens can protect mice against Mycobacterium tuberculosis infection

Approximately 2 billion people are infected with Mycobacterium tuberculosis, the etiological agent of tuberculosis (TB), and an estimated 1.5 million individuals die annually from TB. Presently, Mycobacterium bovis BCG remains the only licensed TB vaccine; however, previous studies suggest its protective efficacy wanes over time and fails in preventing pulmonary TB. Therefore, a safe and effective vaccine is urgently required to replace BCG or boost BCG immunizations. Our previous studies revealed that mycobacterial proteins are released via exosomes from macrophages infected with M. tuberculosis or pulsed with M. tuberculosis culture filtrate proteins (CFP). In the present study, exosomes purified from macrophages treated with M. tuberculosis CFP were found to induce antigen-specific IFN-γ and IL-2-expressing CD4(+) and CD8(+) T cells. In exosome-vaccinated mice, there was a similar TH1 immune response but a more limited TH2 response compared to BCG-vaccinated mice. Using a low-dose M. tuberculosis mouse aerosol infection model, exosomes from CFP-treated macrophages were found to both prime a protective immune response as well as boost prior BCG immunization. The protection was equal to or superior to BCG. In conclusion, our findings suggest that exosomes might serve as a novel cell-free vaccine against an M. tuberculosis infection.

Comparison of whole blood and PBMC assays for T-cell functional analysis

Background

Tuberculosis remains the foremost cause of morbidity and mortality, more than any other single infectious disease in the world. Cell mediated immune response plays a crucial role in the control of tuberculosis. Therefore, measuring cell mediated immune response against the antigens is having a vital role in understanding the pathogenesis of tuberculosis, which will also help in the diagnosis of and vaccination for tuberculosis.

Findings

The aim of the present study was to compare and optimize the assay conditions to measure the cell mediated immune response against M. tuberculosis specific antigens. Because the conventional PBMC assays (due to requirement of large volume of blood sample) are unable to screen more number of antigens within the same blood sample. So, here we have compared 6 days culture supernatants of 1:5 and 1:10 diluted blood and PBMCs from healthy laboratory volunteers, to assess the proliferative response of T lymphocytes and secreted IFN-γ levels against purified recombinant antigen of M. tuberculosis (MPT51, Rv3803c), crude antigens of M. tuberculosis (PPD) and mitogen (PHA).

Conclusions

We have observed good correlation between each assay and also the mean difference of these assays did not reach the statistical significance (p > 0.05). From these results, we conclude that 1:10 diluted whole-blood cultures can be well-suited as an alternative assay to measure cytokine production and lymphocyte proliferation in comparison to the conventional PBMC assays. Moreover, 1:10 diluted blood assays require less volume of blood when compared to PBMC assays which will be useful particularly in paediatric and field studies in endemic countries, where blood volume is a limiting factor.

Identification and elimination of an immunodominant T-cell epitope in recombinant immunotoxins based on Pseudomonas exotoxin A

Recombinant immunotoxins (RITs) are chimeric proteins that are being developed for cancer treatment. We have produced RITs that contain PE38, a portion of the bacterial protein Pseudomonas exotoxin A. Because the toxin is bacterial, it often induces neutralizing antibodies, which limit the number of treatment cycles and the effectiveness of the therapy. Because T cells are essential for antibody responses to proteins, we adopted an assay to map the CD4(+) T-cell epitopes in PE38. We incubated peripheral blood mononuclear cells with an immunotoxin to stimulate T-cell expansion, followed by exposure to overlapping peptide fragments of PE38 and an IL-2 ELISpot assay to measure responses. Our observation of T-cell responses in 50 of 50 individuals correlates with the frequency of antibody formation in patients with normal immune systems. We found a single, highly immunodominant epitope in 46% (23/50) of the donors. The immunodominant epitope is DRB1-restricted and was observed in subjects with different HLA alleles, indicating promiscuity. We identified two amino acids that, when deleted or mutated to alanine, eliminated the immunodominant epitope, and we used this information to construct mutant RITs that are highly cytotoxic and do not stimulate T-cell responses in many donors.

Exploring serological classification tree model of active pulmonary tuberculosis by magnetic beads pretreatment and MALDI-TOF MS analysis

Pulmonary tuberculosis (TB) is an infectious disease disturbing status of public health, and accurate diagnosis of TB would effectively help control the disturbance. Our study tried to establish a classification tree model that distinguished active TB from non-TB individuals. We used matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) combined with weak cationic exchange (WCX) magnetic beads to analyse 178 serum samples containing 75 patients with active TB and 103 non-TB individuals (43 patients with common pulmonary diseases and 60 healthy controls). Samples were randomly divided into a training set and a test set. Statistical softwares were applied to construct this model. An amount of 48 differential expressed peaks (P < 0.05) were identified by the training set, and our model was set up by three of them, m/z 7626, 8561 and 8608. This model can discriminate patients with active TB from patients with non-TB with a sensitivity of 98.3% and a specificity of 84.4%. The test set was used to verify the performance, which demonstrated good sensitivity and specificity: 85.7% and 83.3%, respectively. Differential expressed peaks between smear-positive and smear-negative active TB also have been analysed. It came out that m/z 8561 and 8608 not only acted as vital factors in the pathogenesis of active TB but also played an important role in regulating different active TB status. In conclusion, MALDI-TOF MS combined with WCX magnetic beads was a powerful technology for constructing classification tree model, and the model we built could serve as a potential diagnostic tool for active TB.