Enhanced patient serum immunoreactivity to recombinant Mycobacterium tuberculosis CFP32 produced in the yeast Pichia pastoris compared to Escherichia coli and its potential for serodiagnosis of tuberculosis

Identification of New Mycobacterium bovis antigens and development of a multiplexed serological bead-immunoassay for the diagnosis of bovine tuberculosis in cattle

Serological assays for bovine tuberculosis diagnosis require the use of multiple Mycobacterium bovis specific antigens to ensure the detection of infected animals. In the present study, identification and selection process of antigens, based on data from published proteomic studies and involving the use of bioinformatics tools and an immuno-screening step, was firstly performed for identifying novel antigens that elicit an antibody response in M. bovis infection. Based on this approach, a panel of 10 M. bovis antigens [with known relevance (MPB70, MPB83, MPB70/83, and ESAT6/CFP10) and novel (Mb1961c, Mb1301c, Mb3871, Mb1403, Mb0592, and PE25/PPE41)] were constructed and thenused to develop a new multiplexed serological assay based on Luminex technology. The performance of the Luminex-bTB immunoassay was evaluated using sera from cattle with known tuberculosis status. Among the proteins whose ability to detect bovine tuberculosis was evaluated for the first time, PE25/PPE41 and Mb1403, but not Mb3871, showed good detection capacity. Following multiple antigen combination, the final Luminex-bTB immunoassay included seven antigens (MPB70, MPB83, MPB70/83, ESAT6/CFP10, PE25/PPE41, Mb1403, and Mb0592) and showed better global performance than the immunoassay using the four usual antigens (MPB70, MPB70/83, MPB83 and ESAT6/CFP10). The specificity and sensitivity values were, respectively, of 97.6% and 42.8% when the cut-off of two-positive antigens was used to classify samples as positive. With the use of the more-restrictive criterion of three-positive antigens, the specificity increased to 99.2% but the sensitivity decreased to 23.9%. The analysis of antigen profiles generated with the Luminex-bTB immunoassay showed that mainly serodominant proteins were recognized in samples from infected cattle. The detection of Mb1961c and Mb1301c appeared to be associated with presumed false-positive results. Moreover, sera from cattle originating from bTB-outbreaks but having inconclusive or negative skin test results were identified as positive by the Luminex-bTB immunoassay and showed an antigen pattern associated with M. bovis infection. The Luminex-bTB immunoassay including seven antigens may be useful as adjunct test for the detection of M. bovis-infected herds, and different cut-offs could be applied according to the bovine tuberculosis epidemiological context.

Culture filtrate protein 32 as a potential target to attenuate the heterogeneous antibody response against Mycobacterium tuberculosis Antigens in different endemic settings

Background

We previously reported the development of an enzyme-linked immunosorbent assay for the detection of the immunoglobulin G (IgG) response to Mycobacterium tuberculosis virulence factor - culture filtrate protein 32 (CFP32). The assay achieved high performance in comparing healthy Bacillus Calmette-Guerin-vaccinated controls with active tuberculosis (TB) patients from the Tunisian population. Herein, we aimed to assess the anti-CFP32 IgG response in suspected or confirmed active pulmonary TB individuals in different endemic settings.

Methods

Serum samples were obtained from 224 donors from African and Latin American countries with variable levels of TB endemicity and different ethnical origins. Receiver operating characteristic curve was used to evaluate the performance of the serological assay.

Results

The area under the curve was 0.70. The use of a cutoff level of 0.65 gave 67% and 68% sensitivity and specificity, respectively, regardless of ethnicity and endemicity. Except for the suspected Latin American group, overall multiple comparisons of medians pointed out the stability of the anti-CFP32 IgG response across the different endemic settings. Therefore, endemicity and ethnicity seem not to affect anti-CFP32 IgG response, mainly for detecting confirmed active TB individuals.

Conclusions

These findings suggest that the inclusion of CFP32 epitopes in multi-antigen TB assay could attenuate serological differences related to heterogeneous endemicity and ethnicity. For this purpose, we further identified B-cell epitopes belonging to CFP32 by an in silico analysis.

The epidemiology of concurrent extrapulmonary tuberculosis in inpatients with extrapulmonary tuberculosis lesions in China: a large-scale observational multi-center investigation

AIMS

A high proportion of all tuberculosis (TB) cases present with extrapulmonary tuberculosis (EPTB), including concurrent EPTB involving more than one extrapulmonary lesion site within the body. However, previous reports only characterised lesions of single-site EPTB cases. This study aimed to investigate epidemiological characteristics and association rules of concurrent EPTB cases in China.

METHODS

An observational multi-centre study was carried out in China from Jan 2011 to Dec 2017 that included a total of 208,214 patients with EPTB lesions. Multivariable logistic regression analysis was used to identify associations between gender and age with concurrent EPTB. Association rules were analysed for significance using the Apriori algorithm.

RESULTS

The most prevalent form of EPTB lesion was tuberculous pleurisy (49.8%), followed by bronchial tuberculosis (14.8%) and tuberculous meningitis (7.6%). The most predominant concurrent EPTB case type was tuberculous pleurisy concurrent with tuberculous peritonitis (1.80%). Altogether 22 association rules were identified that included 20 strong association rules, among which highest confidence rates were found for tuberculous myelitis concurrent with tuberculous meningitis and sacral TB concurrent with lumbar vertebral TB. Moreover, association rules of EPTB concurrent with other EPTB types were found to vary with gender and age. The confidence rate of tuberculous myelitis concurrent with tuberculous meningitis was higher in females (83.67%) than males and highest in patients of ages 25-34 years (87.50%).

CONCLUSIONS

Many types of concurrent EPTB were found. Thus, greater awareness of concurrent EPTB disease characteristics is needed to ensure timely clinical diagnosis and treatment of this disease.

N-glycosylation and homodimeric folding significantly enhance the immunoreactivity of Mycobacterium tuberculosis virulence factor CFP32 when produced in the yeast Pichia pastoris

We previously reported that immunoreactivity of recombinant CFP32 (Rv0577), a virulence factor of Mycobacterium tuberculosis, was higher when produced in transformed Pichia pastoris as compared to transformed E. coli. In this study, we show that this difference is partly due to the N-glycosylation of the recombinant CFP32 (rCFP32) by the yeast Pichia pastoris. In addition, SDS-PAGE and western blotting analysis of Mycobacterium bovis BCG and yeast-produced rCFP32 showed the presence of a band corresponding to a homodimeric state of the protein, unlike that of rCFP32 produced in E. coli. Computational modeling indicates that a single cysteine residue at position 193 of each monomer might bond to stabilize the homodimeric state of CFP32. Computational study showed that this residue is buried inside the protein core of E. coli-produced rCFP32 suggesting that rCFP32 may adopt a different folding in P. pastoris and BCG, in which C193 is solvent exposed. Surprisingly, an enzyme-linked immunosorbent assay using a generated monoclonal antibody (14D4) reveals the presence of a differential epitope that appears to be the consequence of the protein dimerization of the yeast- and BCG-, but not E.coli- produced, CFP32 recombinant form. We conclude that, in addition to N-glycosylation, homodimeric folding significantly enhances the immunoreactivity of rCFP32 and may these post-translational modifications may factor into the structure and function of native M. tuberculosis CFP32.

Recombinant O-mannosylated protein production (PstS-1) from Mycobacterium tuberculosis in Pichia pastoris (Komagataella phaffii) as a tool to study tuberculosis infection

Background

Pichia pastoris (syn. Komagataella phaffii) is one of the most highly utilized eukaryotic expression systems for the production of heterologous glycoproteins, being able to perform both N- and O-mannosylation. In this study, we present the expression in P. pastoris of an O-mannosylated recombinant version of the 38 kDa glycolipoprotein PstS-1 from Mycobacterium tuberculosis (Mtb), that is similar in primary structure to the native secreted protein.

Results

The recombinant PstS-1 (rPstS-1) was produced without the native lipidation signal. Glycoprotein expression was under the control of the methanol-inducible promoter pAOX1, with secretion being directed by the α-mating factor secretion signal. Production of rPstS-1 was carried out in baffled shake flasks (BSFs) and controlled bioreactors. A production up to ~ 46 mg/L of the recombinant protein was achieved in both the BSFs and the bioreactors. The recombinant protein was recovered from the supernatant and purified in three steps, achieving a preparation with 98% electrophoretic purity. The primary and secondary structures of the recombinant protein were characterized, as well as its O-mannosylation pattern. Furthermore, a cross-reactivity analysis using serum antibodies from patients with active tuberculosis demonstrated recognition of the recombinant glycoprotein, indirectly indicating the similarity between the recombinant PstS-1 and the native protein from Mtb.

Conclusions

rPstS-1 (98.9% sequence identity, O-mannosylated, and without tags) was produced and secreted by P. pastoris, demonstrating that this yeast is a useful cell factory that could also be used to produce other glycosylated Mtb antigens. The rPstS-1 could be used as a tool for studying the role of this molecule during Mtb infection, and to develop and improve vaccines or kits based on the recombinant protein for serodiagnosis.

Electronic supplementary material

The online version of this article (10.1186/s12934-019-1059-3) contains supplementary material, which is available to authorized users.

High level expression and glycosylation of recombinant Mycobacterium tuberculosis Ala-Pro-rich antigen in Pichia pastoris

The Ala-Pro-rich Antigen (Apa) from Mycobacterium tuberculosis is a mannosylated protein with immunogenic and antigenic properties. The O-mannosylation is essential for its biological function in the process of colonization and invasion of host cells by M. tuberculosis. In this work, the gene encoding Apa was cloned from M. tuberculosis and expressed in Pichia pastoris GS115. In shake-flasks, the recombinant Apa was secreted into the culture media and purified with a yield of 0.6 g/L. Both N- and O-glycans were found in recombinant Apa. In P. pastoris the known M. tuberculosis-derived O-glycosites of Apa were modified with short chains of mannose units, and a few additional glycosylation sites were also observed. Therefore, the recombinant Apa expressed in P. pastoris has similar but not identical O-mannose patterns to the native protein from M. tuberculosis. P. pastoris and mycobacteria share similarities in the protein O-glycosylation pathway. Thus P. pastoris could be a potential powerful expression system to produce mycobacteria-derived glycoproteins.

The Mycobacterium bovis BCG prime-Rv0577 DNA boost vaccination induces a durable Th1 immune response in mice

Tuberculosis remains a major global health problem and effective vaccines are urgently needed. In this study, we used the combined DNA- and protein-based vaccines of immunodominant antigen Rv0577 to boost BCG and evaluated their immunogenicity in BALB/c mice. Our data suggest that the booster vaccine may substantially enhance the immunogenicity of BCG and strengthen both CD4+ T cell-mediated Th1 and CD8+ T cell-mediated cytolytic responses. Compared with the protein-based vaccine, the DNA-based vaccine can induce more durable Th1 immune response, characterized by high levels of antibody response, proliferation response, percentages of CD4+/CD8+ and cytokine secretion in antigen-stimulated splenocyte cultures. In conclusion, we for the first time, developed a protein- and plasmid DNA-based booster vaccine based on Rv0577. Our findings suggest that antigen Rv0577-based DNA vaccine is immunogenic and can efficiently boost BCG, which could be helpful in the design of an efficient vaccination strategy against TB.

Mycobacterium tuberculosis Rv0577, a novel TLR2 agonist, induces maturation of dendritic cells and drives Th1 immune response

Tuberculosis (TB) caused by Mycobacterium tuberculosis constitutes an ongoing threat to global health. An antigen that can induce dendritic cell (DC) maturation and lead to enhanced cellular immunity is crucial to the development of an effective TB vaccine. Here, we investigated the functional roles and the related signaling mechanism of the Rv0577 protein, a M. tuberculosis complex-restricted secreted protein involved in the methylglyoxal detoxification pathway. Rv0577 recognizes Toll-like receptor 2 (TLR2) and functionally induces DC maturation by augmenting the expression of cell surface molecules (CD80, CD86, and MHC class I and II) and proinflammatory cytokine production (TNF-α, IL-1β, IL-6, and IL-12p70) in DCs on MyD88-dependent signaling, mitogen-activated protein kinases, and nuclear factor κB signaling pathways. In addition, Rv0577-treated DCs activated naive T cells, effectively polarized CD4(+) and CD8(+) T cells to secrete IFN-γ and IL-2, and induced T-cell proliferation, indicating that this protein possibly contributes to Th1-polarization of the immune response. More important, unlike LPS, Rv0577-treated DCs specifically induced the proliferation of memory CD4(+)/CD8(+)CD44(high)CD62L(low) T cells in the spleen of M. tuberculosis-infected mice in a TLR2-dependent manner. Taken together, these findings suggest that Rv0577 may regulate innate and adaptive immunity by interacting with TLR2, a finding that could be helpful in the design of new TB vaccines.

Proteomic profile of culture filtrate from the Brazilian vaccine strain Mycobacterium bovis BCG Moreau compared to M. bovis BCG Pasteur

Background

Bacille Calmette-Guerin (BCG) is currently the only available vaccine against tuberculosis (TB) and comprises a heterogeneous family of sub-strains with genotypic and phenotypic differences. The World Health Organization (WHO) affirms that the characterization of BCG sub-strains, both on genomic and proteomic levels, is crucial for a better comprehension of the vaccine. In addition, these studies can contribute in the development of a more efficient vaccine against TB. Here, we combine two-dimensional electrophoresis (2DE) and mass spectrometry to analyse the proteomic profile of culture filtrate proteins (CFPs) from M. bovis BCG Moreau, the Brazilian vaccine strain, comparing it to that of BCG Pasteur. CFPs are considered of great importance given their dominant immunogenicity and role in pathogenesis, being available for interaction with host cells since early infection.

Results

The 2DE proteomic map of M. bovis BCG Moreau CFPs in the pH range 3 - 8 allowed the identification of 158 spots corresponding to 101 different proteins, identified by MS/MS. Comparison to BCG Pasteur highlights the great similarity between these BCG strains. However, quantitative analysis shows a higher expression of immunogenic proteins such as Rv1860 (BCG1896, Apa), Rv1926c (BCG1965c, Mpb63) and Rv1886c (BCG1923c, Ag85B) in BCG Moreau when compared to BCG Pasteur, while some heat shock proteins, such as Rv0440 (BCG0479, GroEL2) and Rv0350 (BCG0389, DnaK), show the opposite pattern.

Conclusions

Here we report the detailed 2DE profile of CFPs from M. bovis BCG Moreau and its comparison to BCG Pasteur, identifying differences that may provide relevant information on vaccine efficacy. These findings contribute to the detailed characterization of the Brazilian vaccine strain against TB, revealing aspects that may lead to a better understanding of the factors leading to BCG's variable protective efficacy against TB.

Serological evaluation of Mycobacterium ulcerans antigens identified by comparative genomics

A specific and sensitive serodiagnostic test for Mycobacterium ulcerans infection would greatly assist the diagnosis of Buruli ulcer and would also facilitate seroepidemiological surveys. By comparative genomics, we identified 45 potential M. ulcerans specific proteins, of which we were able to express and purify 33 in E. coli. Sera from 30 confirmed Buruli ulcer patients, 24 healthy controls from the same endemic region and 30 healthy controls from a non-endemic region in Benin were screened for antibody responses to these specific proteins by ELISA. Serum IgG responses of Buruli ulcer patients were highly variable, however, seven proteins (MUP045, MUP057, MUL_0513, Hsp65, and the polyketide synthase domains ER, AT propionate, and KR A) showed a significant difference between patient and non-endemic control antibody responses. However, when sera from the healthy control subjects living in the same Buruli ulcer endemic area as the patients were examined, none of the proteins were able to discriminate between these two groups. Nevertheless, six of the seven proteins showed an ability to distinguish people living in an endemic area from those in a non-endemic area with an average sensitivity of 69% and specificity of 88%, suggesting exposure to M. ulcerans. Further validation of these six proteins is now underway to assess their suitability for use in Buruli ulcer seroepidemiological studies. Such studies are urgently needed to assist efforts to uncover environmental reservoirs and understand transmission pathways of the M. ulcerans.

Buruli ulcer is a slowly progressive but potentially devastating disease of skin and subcutaneous tissue caused by the bacterium Mycobacterium ulcerans. The disease is widespread throughout West and Central Africa, and some countries in the region have established Buruli ulcer control programs. Buruli ulcer is difficult to distinguish from other chronic skin conditions that require different treatments, and there is an urgent need for an accurate point-of-care diagnostic test. In this study, we have used genomic techniques to identify 45 potential M. ulcerans–specific antigens, 33 of which we have been able to produce and purify. We tested these proteins against sera from patients, healthy people living in the same region as the patients and from individuals living in a region with no cases of Buruli ulcer. We found that seven proteins were able to elicit antibody responses that were significantly different between patients and the control subjects from the non-endemic region but not from the healthy individuals in the same Buruli ulcer endemic region. Further analysis showed that six of these M. ulcerans proteins might be useful as markers of exposure to M. ulcerans and could be developed into tools to uncover environmental reservoirs and understand transmission pathways of the bacterium.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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.