Aggravated infection in mice co-administered with Mycobacterium tuberculosis and the 27-kDa lipoprotein

Proteomic profiling of membrane vesicles from Mycobacterium avium subsp. paratuberculosis: Navigating towards an insilico design of a multi-epitope vaccine targeting membrane vesicle proteins

Bacteria typically produce membrane vesicles (MVs) at varying levels depending on the surrounding environments. Gram-negative bacterial outer membrane vesicles (OMVs) have been extensively studied for over 30 years, but MVs from Gram-positive bacteria only recently have been a focus of research. In the present study, we isolated MVs from Mycobacterium avium subsp. paratuberculosis (MAP) and analyzed their protein composition using LC-MS/MS. A total of 316 overlapping proteins from two independent preparations were identified in our study, and topology prediction showed these cargo proteins have different subcellular localization patterns. When MVs were administered to bovine-derived macrophages, significant up-regulation of pro-inflammatory cytokines was observed via qRT-PCR. Proteome functional annotation revealed that many of these proteins are involved in the cellular protein metabolic process, tRNA aminoacylation, and ATP synthesis. Secretory proteins with high antigenicity and adhesion capability were mapped for B-cell and T-cell epitopes. Antigenic, Immunogenic and IFN-γ inducing B-cell, MHC-I, and MHC-II epitopes were stitched together through linkers to form multi-epitope vaccine (MEV) construct against MAP. Strong binding energy was observed during the docking of the 3D structure of the MEV with the bovine TLR2, suggesting that the putative MEV may be a promising vaccine candidate against MAP. However, in vitro and in vivo analysis is required to prove the immunogenic concept of the MEV which we will follow in our future studies. SIGNIFICANCE: Johne's disease is a chronic infection caused by Mycobacterium avium subsp. paratuberculosis that has a potential link to Crohn's disease in humans. The disease is characterized by persistent diarrhea and enteritis, resulting in significant economic losses due to reduced milk yield and premature culling of infected animals. The dairy industry in the United States alone experiences losses of approximately USD 250 million due to Johne's disease. The current vaccine against Johne's disease is limited by several factors, including variable efficacy, limited duration of protection, interference with diagnostic tests, inability to prevent infection, and logistical and cost-related challenges. Nevertheless, a multiepitope vaccine design approach targeting M. avium subsp. paratuberculosis has the potential to overcome these challenges and offer improved protection against Johne's disease.

An update on Mycobacterium tuberculosis lipoproteins

Almost 3% of the proteins of Mycobacterium tuberculosis (M. tuberculosis), the main causative agent of human tuberculosis, are lipoproteins. These lipoproteins are characteristic of the mycobacterial cell envelope and participate in many mechanisms involved in the pathogenesis of M. tuberculosis. In this review, the authors provide an updated analysis of M. tuberculosis lipoproteins and categorize them according to their demonstrated or predicted functions, including transport of compounds to and from the cytoplasm, biosynthesis of the mycobacterial cell envelope, defense and resistance mechanisms, enzymatic activities and signaling pathways. In addition, this updated analysis revealed that at least 40% of M. tuberculosis lipoproteins are glycosylated.

Effect of the deletion of lprG and p55 genes in the K10 strain of Mycobacterium avium subspecies paratuberculosis

The lprG-p55 operon of Mycobacterium tuberculosis, M. bovis and M. avium strain D4ER has been identified as a virulence factor involved in the transport of toxic compounds. LprG is a lipoprotein that modulates the host immune response against mycobacteria, whereas P55 is an efflux pump that provides resistance to several drugs. In the present study we search for, and characterize, lprg and p55, putative virulence genes in Mycobacterium avium subsp. paratuberculosis (MAP) to generate a live-attenuated strain of MAP that may be useful in the future as live-attenuated vaccine. For this purpose, we generated and evaluated two mutants of MAP strain K10: one mutant lacking the lprG gene (ΔlprG) and the other lacking both genes lprG and p55 (ΔlprG-p55). None of the mutant strains showed altered susceptibility to first-line and second-line antituberculosis drugs or ethidium bromide, only the double mutant had two-fold increase in clarithromycin susceptibility compared with the wild-type strain. The deletion of lprG and of lprG-p55 reduced the replication of MAP in bovine macrophages; however, only the mutant in lprG-p55 grew faster in liquid media and showed reduced viability in macrophages and in a mouse model. Considering that the deletion of both genes lprG-p55, but not that of lprG alone, showed a reduced replication in vivo, we can speculate that p55 contributes to the survival of MAP in this animal model.

Rhodococcus erythropolis as a host for expression, secretion and glycosylation of Mycobacterium tuberculosis proteins

Background

Glycosylation is one of the most abundant posttranslational polypeptide chain modification in nature. Although carbohydrate modification of protein antigens from many microbial pathogens constitutes important components of B cell epitopes, the role in T cell immunity is not completely understood. There is growing evidence about the importance of these modifications in host bacteria interactions in tuberculosis. It is known, that the sugars present in some Mycobacterium tuberculosis glycoproteins play an important role in both humoral and cellular immune response against the pathogen. Since this modification is lost in the recombinant proteins expressed in Escherichia coli, it is fundamental to search for host bacteria with the capacity to modify the foreign proteins. Amongst the bacteria that are likely to have this possibility are some members of Rhodococcus genus which are Gram-positive bacteria, with high GC-content and genetically very close related to M. tuberculosis.

Results

In this work, apa, pstS1 and lprG genes that coding for M. tuberculosis glycoproteins were cloned and expressed in Rhodococcus erythropolis. All recombinant proteins were mannosylated as demonstrated by their interaction with mannose binding lectin Concanavalin A. In addition, as native proteins recombinants Apa and PstS1 were secreted to the culture medium in contrast with LprG that was retained in the cell wall.

Conclusions

Together these results, point out R. erythropolis, as a new host for expression of M. tuberculosis glycoproteins.

Mycobacterium tuberculosis effectors involved in host-pathogen interaction revealed by a multiple scales integrative pipeline

BACKGROUND

Mycobacterium tuberculosis (Mtb) has evolved multiple strategies to counter host immunity. Proteins are one important player in the host-pathogen interaction. A comprehensive list of such proteins will benefit our understanding of pathogenesis of Mtb.

METHODS

A genome-scale dataset was created from different sources of published data: global gene expression studies in disease models; genome-wide insertional mutagenesis defining gene essentiality under different conditions; genes lost in clinical isolates; subcellular localization analysis and non-homology analysis. Using data mining and meta-analysis, expressed proteins critical for intracellular survival of Mtb are first identified, followed by subcellular localization analysis, finally filtering a series of subtractive channel of analysis to find out promising drug target candidates.

RESULTS

The analysis found 54 potential candidates essential for the intracellular survival of the pathogen and non-homologous to host or gut flora, and might be promising drug targets.

CONCLUSION

Based on our meta-analysis and bioinformatics analysis, 54 hits were found from Mtb around 4000 open reading frames. These hits can be good candidates for further experimental investigation.

Proteomic analysis of purified protein derivative of Mycobacterium tuberculosis

Background

Purified protein derivative (PPD) has been used for more than half a century as an antigen for the diagnosis of tuberculosis infection based on delayed type hypersensitivity. Although designated as “purified,” in reality, the composition of PPD is highly complex and remains ill-defined. In this report, high resolution mass spectrometry was applied to understand the complexity of its constituent components. A comparative proteomic analysis of various PPD preparations and their functional characterization is likely to help in short-listing the relevant antigens required to prepare a less complex and more potent reagent for diagnostic purposes.

Results

Proteomic analysis of Connaught Tuberculin 68 (PPD-CT68), a tuberculin preparation generated from M. tuberculosis, was carried out in this study. PPD-CT68 is the protein component of a commercially available tuberculin preparation, Tubersol, which is used for tuberculin skin testing. Using a high resolution LTQ-Orbitrap Velos mass spectrometer, we identified 265 different proteins. The identified proteins were compared with those identified from PPD M. bovis, PPD M. avium and PPD-S2 from previous mass spectrometry-based studies. In all, 142 proteins were found to be shared between PPD-CT68 and PPD-S2 preparations. Out of the 354 proteins from M. tuberculosis–derived PPDs (i.e. proteins in either PPD-CT68 or PPD-S2), 37 proteins were found to be shared with M. avium PPD and 80 were shared with M. bovis PPD. Alignment of PPD-CT68 proteins with proteins encoded by 24 lung infecting bacteria revealed a number of similar proteins (206 bacterial proteins shared epitopes with 47 PPD-CT68 proteins), which could potentially be involved in causing cross-reactivity. The data have been deposited to the ProteomeXchange with identifier PXD000377.

Conclusions

Proteomic and bioinformatics analysis of different PPD preparations revealed commonly and differentially represented proteins. This information could help in delineating the relevant antigens represented in various PPDs, which could further lead to development of a lesser complex and better defined skin test antigen with a higher specificity and sensitivity.

Virulence factors of the Mycobacterium tuberculosis complex

The Mycobacterium tuberculosis complex (MTBC) consists of closely related species that cause tuberculosis in both humans and animals. This illness, still today, remains to be one of the leading causes of morbidity and mortality throughout the world. The mycobacteria enter the host by air, and, once in the lungs, are phagocytated by macrophages. This may lead to the rapid elimination of the bacillus or to the triggering of an active tuberculosis infection. A large number of different virulence factors have evolved in MTBC members as a response to the host immune reaction. The aim of this review is to describe the bacterial genes/proteins that are essential for the virulence of MTBC species, and that have been demonstrated in an in vivo model of infection. Knowledge of MTBC virulence factors is essential for the development of new vaccines and drugs to help manage the disease toward an increasingly more tuberculosis-free world.

Ultra-low dose of Mycobacterium tuberculosis aerosol creates partial infection in mice

A murine low dose (LD) aerosol model is commonly used to test tuberculosis vaccines. Doses of 50-400 CFU (24h lung CFU) infect 100% of exposed mice. The LD model measures progression from infection to disease based on organ CFU at defined time points. To mimic natural exposure, we exposed mice to an ultra-low dose (ULD) aerosol. We estimated the presented dose by sampling the aerosol. Female C57BL/6 mice were exposed to Mycobacterium tuberculosis H37Rv aerosol at 1.0, 1.1, 1.6, 5.4, and 11 CFU presented dose, infecting 27%, 36%, 36%, 100%, and 95% of mice, respectively. These data are compatible with a stochastic infection event (Poisson distribution, weighted R(2)=0.97) or with a dose-response relationship (sigmoid distribution, weighted R(2)=0.97). Based on the later assumption, the ID50 was 1.6CFU presented dose (95% confidence interval, 1.2-2.1). We compared organ CFU after ULD and LD aerosols (5.4 vs. 395CFU presented dose). Lung burden was 30-fold lower in the ULD model at 4 weeks (3.4 vs. 4.8 logs, p<0.001) and 18 weeks (≤3.6 vs. 5.0 logs, p=0.01). Mice exposed to ULD aerosols as compared to LD aerosols had greater within-group CFU variability. Exposure to ULD aerosols leads to infection in a subset of mice, and to persistently low organ CFU. The ULD aerosol model may resemble human pulmonary tuberculosis more closely than the standard LD model, and may be used to identify host or bacterial factors that modulate the initial infection event.

Direct and indirect impairment of human dendritic cell function by virulent Francisella tularensis Schu S4

The gram-negative, facultative intracellular bacterium Francisella tularensis causes acute, lethal pneumonic disease following infection with only 10 CFU. The mechanisms used by the bacterium to accomplish this in humans are unknown. Here, we demonstrate that virulent, type A F. tularensis strain Schu S4 efficiently infects and replicates in human myeloid dendritic cells (DCs). Despite exponential replication over time, Schu S4 failed to stimulate transforming growth factor beta, interleukin-10 (IL-10), IL-6, IL-1beta, IL-12, tumor necrosis factor alpha, alpha interferon (IFN-alpha), and IFN-beta throughout the course of infection. Schu S4 also suppressed the ability of directly infected DCs to respond to different Toll-like receptor agonists. Furthermore, we also observed functional inhibition of uninfected bystander cells. This inhibition was mediated, in part, by a heat-stable bacterial component. Lipopolysaccharide (LPS) from Schu S4 was present in Schu S4-conditioned medium. However, Schu S4 LPS was weakly inflammatory and failed to induce suppression of DCs at concentrations below 10 microg/ml, and depletion of Schu S4 LPS did not significantly alleviate the inhibitory effect of Schu S4-conditioned medium in uninfected human DCs. Together, these data show that type A F. tularensis interferes with the ability of a central cell type of the immune system, DCs, to alert the host of infection both intra- and extracellularly. This suggests that immune dysregulation by F. tularensis operates on a broader and more comprehensive scale than previously appreciated.

Mycobacterial lipopeptides elicit CD4+ CTLs in Mycobacterium tuberculosis-infected humans

In searching for immunogenic molecules with the potential to induce protective immune responses against tuberculosis, we developed an ex vivo model to study frequency, phenotype, and effector functions of human T lymphocytes recognizing hydrophobic Ags of Mycobacterium tuberculosis (M.Tb). To obtain unbiased results, we characterized T lymphocytes responding to a crude cell wall extract (chloroform methanol extract of M.Tb (M.Tb-CME)) containing a broad spectrum of mycobacterial glycolipids and lipopeptides. A significant proportion of T lymphocytes recognized M.Tb-CME (290 IFN-gamma+ T cells/10(5) PBMCs) and developed to effector memory cells as determined by the expression of CD45RO and the chemokine receptors CXCR3 and CCR5. Expanded lymphocytes fulfilled all criteria required for an efficient immune response against tuberculosis: 1) release of macrophage-activating Th1 cytokines and chemokines required for the spatial organization of local immune responses, 2) cytolytic activity against Ag-pulsed macrophages, and 3) recognition of infected macrophages and killing of the intracellular bacteria. Phenotypically, M.Tb-CME-expanded cells were CD4+ and MHC class II restricted, challenging current concepts that cytotoxic and antimicrobial effector cells are restricted to the CD8+ T cell subset. Pretreatment of M.Tb-CME with protease or chemical delipidation abrogated the biological activity, suggesting that responses were directed toward mycobacterial lipopeptides. These findings suggest that lipidated peptides are presented by M.Tb-infected macrophages and elicit CD4+ cytolytic and antimicrobial T lymphocytes. Our data support an emerging concept to include hydrophobic microbial Ags in vaccines against tuberculosis.

A Toll-like receptor-2-directed fusion protein vaccine against tuberculosis

A fusion protein designated CSU-F36 was constructed that consisted of acylated Rv1411, a potent Toll-like receptor-2 agonist, fused to ESAT-6, a well-characterized immunogenic protein from Mycobacterium tuberculosis. The CSU-F36 fusion protein strongly induced interleukin 12 secretion from macrophages and induced the increased accumulation of CD4 T cells capable of secreting gamma interferon in the lungs of infected mice. These mice were significantly protected from low-dose aerosol challenge with M. tuberculosis, even with CSU-F36 delivered in a simple depot material. This "natural adjuvant"-containing system could potentially bypass the need for more expensive TH1-inducing adjuvants and could be applied to many mycobacterial proteins to provide effective and cheap new vaccines against tuberculosis.