Cytokines in response to proteins predicted in genomic regions of difference of Mycobacterium tuberculosis

Chemical and Biological Characterization of Mycobacterium Tuberculosis-Specific ESAT6-Like Proteins and their Potentials in the Prevention of Tuberculosis and Asthma

Early Secreted Antigenic Target 6 kDa (ESAT6) is a potent immunogenic protein secreted by the bacteria causing tuberculosis, i.e., Mycobacterium tuberculosis. Another highly immunogenic culture filtrate protein whose gene is linked to ESAT6/ESXA is known as CFP10/ESXB. Because of their high immunogenicity and specificity to M. tuberculosis, these proteins have been proposed as a vaccine to prevent tuberculosis and diagnose the active/latent disease. However, the same proteins cannot be used for prevention and diagnosis because immunized but healthy people will also show a positive response and be falsely reported as diseased. Therefore, in this review article, the search was made to identify if any other ESAT6-like proteins exist in the M. tuberculosis genome. The search identified 21 additional ESAT-like proteins, i.e., ESXC to ESXW. Immunological characterization has shown that some of them (especially ESXV) were able to induce immune responses in vitro with cells obtained from tuberculosis patients and healthy donors. When the protein ESXV was tested in different recombinant forms (expressed in Escherichia coli, mycobacterial vectors, and DNA plasmids) and injected in mice, immune responses were induced to multiple epitopes of the protein. Furthermore, immunization of mice with ESXV protected them from infection with M. tuberculosis. The same protein was also able to protect mice against the induction of asthma. These results suggest that ESXV has the potential to protect against two major diseases of the world, i.e., tuberculosis and asthma, and hence may be used as a common vaccine for both diseases.

Cytokine upsurge among drug-resistant tuberculosis endorse the signatures of hyper inflammation and disease severity

Tuberculosis (TB) elimination is possible with the discovery of accurate biomarkers that define the stages of infection. Drug-resistant TB impair the current treatment strategies and worsen the unfavourable outcomes. The knowledge on host immune responses between drug-sensitive and drug-resistant infection is inadequate to understand the pathophysiological differences and disease severity. The secreted proteins, cytokines display versatile behaviour upon infection with Mycobacterium tuberculosis (MTB) and their imbalances often tend to assist disease pathology than protection. Therefore, studying these soluble proteins across TB infection spectrum (drug-resistant TB, drug-sensitive TB, and latent TB) may unveil the disease mediated responses and unique stage specific cytokine signatures. Thus, we sought to determine the plasma cytokine levels from healthy, latently infected, drug-sensitive, and drug-resistant TB individuals. Our study revealed top 8 cytokines (IL-17, IL-1α, IL-2, IL-10, IL-5, IFN-γ, TNF-α and IL-6) and their biomarker abilities to discriminate different stages of infection.

Immunological Characterization of Proteins Expressed by Genes Located in Mycobacterium tuberculosis-Specific Genomic Regions Encoding the ESAT6-like Proteins

The 6 kDa early secreted antigen target (ESAT6) is a low molecular weight and highly immunogenic protein of Mycobacterium tuberculosis with relevance in the diagnosis of tuberculosis and subunit vaccine development. The gene encoding the ESAT6 protein is located in the M. tuberculosis-specific genomic region known as the region of difference (RD)1. There are 11 M. tuberculosis-specific RDs absent in all of the vaccine strains of BCG, and three of them (RD1, RD7, and RD9) encode immunodominant proteins. Each of these RDs has genes for a pair of ESAT6-like proteins. The immunological characterizations of all the possible proteins encoded by genes in RD1, RD7 and RD9 have shown that, besides ESAT-6 like proteins, several other proteins are major antigens useful for the development of subunit vaccines to substitute or supplement BCG. Furthermore, some of these proteins may replace the purified protein derivative of M. tuberculosis in the specific diagnosis of tuberculosis by using interferon-gamma release assays and/or tuberculin-type skin tests. At least three subunit vaccine candidates containing ESAT6-like proteins as antigen components of multimeric proteins have shown efficacy in phase 1 and phase II clinical trials in humans.

The effect of adjuvants and delivery systems on Th1, Th2, Th17 and Treg cytokine responses in mice immunized with Mycobacterium tuberculosis-specific proteins

Tuberculosis (TB) is a major health problem of global concern. The control of this disease requires appropriate preventive measures, including vaccines. In TB, T helper (Th)1 cytokines provide protection whereas Th2 and T regulatory (Treg) cytokines contribute to the pathogenesis and Th17 cytokines play a role in both protection and pathogenesis. Previous studies with Mycobacterium tuberculosis-specific proteins have identified seven low molecular weight proteins, PE35, ESXA, ESXB, Rv2346c, Rv2347c, Rv3619c, and Rv3620c, as immunodominant antigens inducing Th1-cell responses in humans following natural infection with M. tuberculosis. The aim of this study was to characterize the cytokine responses induced in mice immunized with these proteins, using various adjuvants and delivery systems, i.e. chemical adjuvants (Alum and IFA), non-pathogenic mycobacteria (M. smegmatis and M. vaccae) and a DNA vaccine plasmid (pUMVC6). The immune responses were monitored by quantifying the marker cytokines secreted by Th1 (IFN-ɣ), Th2 (IL-5), Treg (IL-10), and Th17 (IL-17A) cells. DNA corresponding to pe35, esxa, esxb, rv2346c, rv2347c, rv3619c, and rv3620c genes were cloned into the expression vectors pGES-TH-1, pDE22 and pUMVC6 for expression in Escherichia coli, mycobacteria and eukaryotic cells, respectively. Mice were immunized with the recombinants using different adjuvants and delivery systems, and spleen cells were stimulated in vitro with peptides of immunizing proteins to investigate antigen-specific secretion of Th1 (IFN-ɣ), Th2 (IL-5), Treg (IL-10), and Th17 (IL-17A) cytokines. The results showed that spleen cells, from mice immunized with all antigens, secreted the protective Th1 cytokine IFN-ɣ, except ESXB, with one or more adjuvants and delivery systems. However, only Rv3619c consistently induced Th1-biased responses, without the secretion of significant concentrations of Th2, Th17 and Treg cytokines, with all adjuvants and delivery systems. Rv3619c also induced antigen-specific IgG antibodies in immunized mice.

Vaccine Potential of Mycobacterial Antigens against Asthma

Asthma is a cause of substantial burden of disease in the world, including both premature deaths and reduced quality of life. A leading hypothesis to explain the worldwide increase of asthma is the "hygiene hypothesis," which suggests that the increase in the prevalence of asthma is due to the reduction in exposure to infections/microbial antigens. In allergic asthma, the most common type of asthma, antigen-specific T helper (Th)2 and Th17 cells and their cytokines are primary mediators of the pathological consequences. In contrast, Th1 and T regulatory (Treg) cells and their cytokines play a protective role. This article aims to review the information on the effect of mycobacteria and their antigens in modulating Th2/Th17 responses towards Th1/Treg responses and protection against asthma in humans and animal models.

Assessing and screening for T-cell epitopes from Mycobacterium tuberculosis RD2 proteins for the diagnosis of active tuberculosis

The Region of D eletion 2 (RD2) of Mycobacterium tuberculosis encodes reserved antigens that contribute to bacterial virulence. Among these antigens, Rv1983, Rv1986, Rv1987, and Rv1989c have been shown to be immunodominant in infected cattle; however, their diagnostic utility has not been evaluated in humans.

In this study, we screened 87 overlapping synthetic peptides encoded by five RD2 proteins for diagnosing tuberculosis epitopes in 50 active tuberculosis (TB) cases, 31 non-tuberculosis patients and 36 healthy individuals. A pool of promising epitopes was then assessed for their diagnostic value in 233 suspected TB patients using a whole blood IFN-γ release assay.

Only 10 peptides were recognized by more than 10% of active tuberculosis patients. The IFN-γ release responses to Rv1986-P9, P15, P16, Rv1988-P4, P11, and Rv1987-P11 were significantly higher in the active TB group than in the control groups (p < 0.05). The whole blood IFN-γ release assay based on these epitopes yielded a sensitivity of 51% and a specificity of 85% in diagnosing active tuberculosis, and the corresponding results using the T-SPOT.TB assay were 76% and 75%, respectively.

In conclusion, these results suggest that the six epitopes from the RD2 of M. tuberculosis have potential diagnostic value in TB.

Vaccine research and development: tuberculosis as a global health threat

One of the aims of the World Health Organisation (WHO) Millennium Development Goals (MDG) is to reduce the number of cases of tuberculosis (TB) infection by the year 2015. However, 9 million new cases were reported in 2013, with an estimated 480,000 new cases of multi-drug resistant tuberculosis (MDR-TB) globally. Bacille Calmette-Guérin (BCG) is the most available and currently used candidate vaccine against tuberculosis; it prevents childhood TB, but its effectiveness against pulmonary TB in adults and adolescents is disputed. To achieve the goal of the WHO MDG, the need for a new improved vaccine is of primary importance. This review highlights several articles that have reported vaccine development. There are about 16 TB vaccines in different phases of clinical trials at the time of writing, which include recombinant peptide/protein, live-attenuated and recombinant live-attenuated, protein/adjuvant, viral-vectored, and immunotherapeutic vaccine. Further studies in reverse vaccinology and massive campaigns on vaccination are needed in order to achieve the target for TB eradication by 2050.

Mycobacterium tuberculosis Rv1987 induces Th2 immune responses and enhances Mycobacterium smegmatis survival in mice

Mycobacterium tuberculosis can interfere with host immune response and escape clearance through its specific antigens. M. tuberculosis Rv1987 encoded by region of difference (RD)-2 gene is a secretory protein with immunogenic potency. Here, we investigated the impact of Rv1987 on host cytokine responses and T cell polarization in mouse aerosol model. A recombinant M. smegmatis mc²155 strain that overexpressed Rv1987 protein (named MS1987) was constructed and used to infect C57BL/6 mice. The mc²155 harbored the empty vector (named MSVec) was as a control. The results showed that MS1987 challenged mice promoted Th2-biased cytokine responses with lower secretion of IFN-γ but higher production of IL-4 and Rv1987-specific IgG antibody compared to MSVec infected mice. Neutrophilic inflammation and high bacterial burden were observed in the lung tissues of MS1987 infected mice probably own to the failed Th1 cell immunity. Besides, subcutaneous injection of Rv1987 protein could mediate the Th1 cytokine responses caused by M. bovis BCG in mice. These results indicated that M. tuberculosis Rv1987 protein could modulate host immune response towards Th2 profile, which probably contributed to the immune evasion of bacteria from host elimination.

Synergistic effect of high-mobility group box-1 and lipopolysaccharide on cytokine induction in bovine peripheral blood mononuclear cells

High-mobility group box 1 (HMGB1) is one of the potent endogenous adjuvants released by necrotic and activated innate immune cells. HMGB1 modulates innate and adaptive immune responses in humans and mice by mediating immune cells crosstalk. However, the immuno-modulatory effects of HMGB1 in the bovine immune system are not clearly known. In this study, the effect of bovine HMGB1 alone or in combination with LPS on the expression kinetics of cytokines upon in vitro stimulation of bovine peripheral blood mononuclear cells (PBMCs) was investigated by quantitative PCR assay. The biological activity of bovine HMGB1 expressed in this prokaryotic expression system was confirmed by its ability to induce nitric oxide secretion in RAW 264.7 cells. The present results indicate that HMGB1 induces a more delayed TNF-α response than does LPS in stimulated PBMCs. However, IFN-γ, IFN-β and IL-12 mRNA transcription peaked at 6 hr post stimulation after both treatments. Further, HMGB1 and LPS heterocomplex up-regulated TNF-α, IFN-γ and IL-12 mRNA expression significantly than did individual TLR4 agonists. The heterocomplex also enhanced the expression of TLR4 on bovine PBMCs. In conclusion, the data indicate that HMGB1 and LPS act synergistically and enhance proinflammatory cytokines, thereby eliciting Th1 responses in bovine PBMCs. These results suggest that HMGB1 can act as an adjuvant in modulating the bovine immune system and thus lays a foundation for using HMGB1 as an adjuvant in various bovine vaccine preparations.

The assessment of cytokines in Quantiferon supernatants for the diagnosis of latent TB infection in a tribal population of Melghat, India

The tuberculin skin test (TST) and interferon-gamma release assays (IGRA), namely, the QuantiFERON-TB Gold test (QFT), remain the standard immunological diagnostic tools for latent tuberculosis (TB) infection (LTBI). However, the sub-optimal detection rates of both of these tests are major impediments in recognizing the population at risk. This study was aimed at evaluating additional cytokines besides interferon-gamma (IFN-γ) as biomarkers for improving LTBI diagnosis in the tribal population of Melghat, India. Seventy-four close TB contacts were stratified by QFT and TST results into: (i) QFT+/TST+ (n = 26), (ii) QFT+/TST- (n = 12), (iii) QFT-/TST- (n = 35) and (iv) QFT-/TST+ (n = 1) groups. A panel of cytokines (IL-6, IL-10, TNF-α and IL-2R) was then evaluated in antigen-stimulated QFT cell-free culture supernatants using IMMULITE-1000, an automated immunoassay analyzer. Cytokine estimation showed significantly higher levels of IL-6 in the QFT+/TST+ group, while significantly higher levels of IL-10 were found in the QFT-/TST- group. Correlation analysis identified a positive correlation between IL-6 and the QFT response (r = 0.6723, P < 0.0001), while a negative correlation was seen between QFT and IL-10 expression (r = -0.3271, P = 0.0044). Similarly, IL-6 was positively correlated with TST levels (r = 0.6631, P <0 .0001), and conversely, a negative correlation was found between TST and IL-10 expression (r = -0.5698, P < 0.0001). The positive and negative predictive values of IL-6 were found to be 92.59 and 93.33%, respectively, and the positive and negative predictive values of IL-10 were 96.55 and 91.18%, respectively. No significant impact of the demographic characteristics on cytokine positivity was observed. Our preliminary results suggest that the evaluation of additional cytokines in QFT cell-free culture supernatants may be valuable for the identification of LTBI. Combining IL-6 and IL-10 with QFT and/or TST could markedly improve the detection accuracy of LTBI. Our observations require investigation in larger well-characterized cohorts along with follow-up studies to further confirm the study outcome.

ELISA in the multiplex era: potentials and pitfalls

Multiplex immunoassays confer several advantages over widely adopted singleplex immunoassays including increased efficiency at a reduced expense, greater output per sample volume ratios and higher throughput predicating more resolute, detailed diagnostics and facilitating personalised medicine. Nonetheless, to date, relatively few protein multiplex immunoassays have been validated for in vitro diagnostics in clinical/point-of-care settings. This review article will outline the challenges, which must be ameliorated prior to the widespread integration of multiplex immunoassays in clinical settings: (i) biomarker validation; (ii) standardisation of immunoassay design and quality control (calibration and quantification); (iii) availability, stability, specificity and cross-reactivity of reagents; (iv) assay automation and the use of validated algorithms for transformation of raw data into diagnostic results. A compendium of multiplex immunoassays applicable to in vitro diagnostics and a summary of the diagnostic products currently available commercially are included, along with an analysis of the relative states of development for each format (namely planar slide based, suspension and planar/microtitre plate based) with respect to the aforementioned issues.

Characterization of a cross-reactive, immunodominant and HLA-promiscuous epitope of Mycobacterium tuberculosis-specific major antigenic protein PPE68

PPE68 (Rv3873), a major antignic protein encoded by Mycobacteriun tuberculosis-specific genomic region of difference (RD)1, is a strong stimulator of peripheral blood mononuclear cells (PBMCs) obtained from tuberculosis patients and Mycobacterium bovis bacillus Calmette Guerin (BCG)-vaccianted healthy subjects in T helper (Th)1 cell assays, i.e. antigen-induced proliferation and interferon-gamma (IFN-γ) secretion. To confirm the antigen-specific recognition of PPE68 by T cells in IFN-γ assays, antigen-induced human T-cell lines were established from PBMCs of M. Bovis BCG-vaccinated and HLA-heterogeneous healthy subjects and tested with peptide pools of RD1 proteins. The results showed that PPE68 was recognized by antigen-specific T-cell lines from HLA-heteregeneous subjects. To further identify the immunodominant and HLA-promiscuous Th1-1 cell epitopes present in PPE68, 24 synthetic peptides covering the sequence of PPE68 were indivdually analyzed for HLA-DR binding prediction analysis and tested with PBMCs from M. bovis BCG-vaccinated and HLA-heterogeuous healthy subjects in IFN-γ assays. The results identified the peptide P9, i.e. aa 121-VLTATNFFGINTIPIALTEMDYFIR-145, as an immunodominant and HLA-DR promiscuous peptide of PPE68. Furthermore, by using deletion peptides, the immunodominant and HLA-DR promiscuous core sequence was mapped to aa 127-FFGINTIPIA-136. Interestingly, the core sequence is present in several PPE proteins of M. tuberculosis, and conserved in all sequenced strains/species of M. tuberculosis and M. tuberculosis complex, and several other pathogenic mycobacterial species, including M. leprae and M. avium-intracellulalae complex. These results suggest that the peptide aa 121-145 may be exploited as a peptide-based vaccine candidate against tuberculosis and other mycobacterial diseases.

The 30-kDa and 38-kDa antigens from Mycobacterium tuberculosis induce partial maturation of human dendritic cells shifting CD4(+) T cell responses towards IL-4 production

BACKGROUND

Mycobacterium tuberculosis (Mtb) infections are still a major cause of death among all infectious diseases. Although 99% of individuals infected with Mtb develop a CD4(+) Th1 and CD8(+) T cell mediated immunity as measured by tuberculin skin test, this results only in partial protection and Mtb vaccines are not effective. Deviation of immune responses by pathogens towards a Th2 profile is a common mechanism of immune evasion, typically leading to the persistence of the microbes.

RESULTS

Here we tested the stimulatory capacity of selective Mtb antigens on human monocyte-derived dendritic cell (DC) maturation and cytokine production. DC maturation markers CD80, CD86 and CD83 were readily upregulated by H37Ra- and H37Rv-associated antigens, the 30-kDa (from Ag85 B complex) and 38-KDa Mtb antigens only partially induced these markers. All Mtb antigens induced variable levels of IL-6 and low levels of IL-10, there was no release of IL-12p70 detectable. Substantial IL-12p40 production was restricted to LPS or H37Ra and H37Rv preparations. Although the proliferation levels of primary T cell responses were comparable using all the differentially stimulated DC, the 30-kDa and 38-kDa antigens showed a bias towards IL-4 secretion of polarized CD4(+) T cells after secondary stimulation as compared to H37Ra and H37Rv preparations.

CONCLUSION

Together our data indicate that 30-kDa and 38-kDa Mtb antigens induced only partial DC maturation shifting immune responses towards a Th2 profile.

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

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

Analysis of immune responses against a wide range of Mycobacterium tuberculosis antigens in patients with active pulmonary tuberculosis

Characterizing host immune responses to molecular targets of Mycobacterium tuberculosis is essential to develop effective immunodiagnostics and better vaccines. We investigated the immune response against a large series of M. tuberculosis antigens, including 5 classical and 64 nonclassical (39 DosR regulon-encoded, 4 resuscitation-promoting factor [RPF], and 21 reactivation-associated) antigens in active-pulmonary-tuberculosis (TB) patients. Whole blood from TB patients (n = 34) was stimulated in vitro with M. tuberculosis antigens. Gamma interferon (IFN-γ) was measured after 7 days of stimulation, using an enzyme-linked immunosorbent assay (ELISA). The majority of the study participants responded to the classical M. tuberculosis antigens TB10.4 (84.8%), early secreted antigenic target-6 kDa (ESAT-6)/CFP-10 (70.6%), and purified protein derivative (PPD) (55.9%). However, only 26.5% and 24.2% responded to HSP65 and Ag85A/B, respectively. Of the 64 nonclassical antigens, 23 (33.3%) were immunogenic (IFN-γ levels, >62 pg/ml) and 8 were strong inducers of IFN-γ (IFN-γ levels, ≥100 pg/ml). The RPF antigens were the most immunogenic. In addition, we observed distinct cytokine expression profiles in response to several M. tuberculosis antigens by multiplex immunoassay. Tumor necrosis factor alpha (TNF-α), interleukin 10 (IL-10), and IL-6 were commonly detected at high levels after stimulation with 4/15 latency antigens (Rv0081, Rv2006, Rv2629, and Rv1733c) and were found especially in supernatants of the three strong IFN-γ inducers (Rv2629, Rv1009, and Rv2389c). IL-8, IL-6, and IL-17 were exclusively detected after stimulation with Rv0574c, Rv2630, Rv1998, Rv054c, and Rv2028c. In conclusion, in active-pulmonary-TB patients, we identified 23 new immunogenic M. tuberculosis antigens. The distinct expression levels of IFN-γ, TNF-α, IL-6, and IL-10 in response to specific subsets of M. tuberculosis antigens may be promising for the development of immunodiagnostics.

Comparative evaluation of MPT83 (Rv2873) for T helper-1 cell reactivity and identification of HLA-promiscuous peptides in Mycobacterium bovis BCG-vaccinated healthy subjects

MPT83 (Rv2873), a surface lipoprotein excreted in the culture of Mycobacterium tuberculosis, is immunoreactive in antibody assays in humans and animals and provides protection as a combined DNA vaccine in mice and cattle. This study was undertaken to determine the reactivity of MPT83 in T helper 1 (Th1)-cell assays, i.e., antigen-induced proliferation and gamma interferon (IFN-γ) secretion, using peripheral blood mononuclear cells (PBMCs) obtained from Mycobacterium bovis bacillus Calmette-Guérin (BCG)-vaccinated and/or M. tuberculosis-infected healthy subjects. PBMCs were tested with complex mycobacterial antigens and pools of synthetic peptides corresponding to MPT63, MPT83, MPB70, LppX, PPE68, CFP10, and ESAT-6. The results showed that MPT83 is among the strongest Th1 cell antigens of M. tuberculosis, and it was recognized equally strongly by BCG-vaccinated and by BCG-vaccinated and M. tuberculosis-infected healthy subjects. Furthermore, HLA heterogeneity of the responding donors suggested that MPT83 was presented to Th1 cells by several HLA-DR molecules. The analysis of the mature MPT83 sequence (amino acids [aa] 1 to 220) and its 14 overlapping synthetic peptides for binding prediction to HLA class II molecules and actual recognition of the peptides by PBMCs from HLA-DR-typed subjects in antigen-induced proliferation and IFN-γ assays suggested that Th1 cell epitopes were scattered throughout the sequence of MPT83. In addition, the HLA-promiscuous nature of at least three peptides, i.e., P11 (aa 151 to 175), P12 (aa 166 to 190), and P14 (aa 196 to 220), was suggested by HLA-DR binding predictions and recognition by HLA-DR heterogeneous donors in Th1 cell assays. These results support the inclusion of MPT83 in an antigen cocktail to develop a new antituberculosis vaccine.