PPE57 induces activation of macrophages and drives Th1-type immune responses through TLR2

Molecular characteristics of drug-susceptible Mycobacterium tuberculosis clinical isolates based on treatment duration

BACKGROUND

In this study, we performed comparative genomic and transcriptomic analysis of clinical isolates of Mycobacterium tuberculosis collected from patients with drug-susceptible tuberculosis (DS-TB). The clinical isolates were categorized based on treatment duration: standard 6 months or >6 months.

METHODS

Study participants were recruited from a 2016 to 2018 tuberculosis cohort, and clinical M. tuberculosis isolates were collected from the sputum of patients with tuberculosis. We analyzed the genome and transcriptome of the isolated M. tuberculosis.

RESULTS

Genomic analysis revealed a specific non-synonymous single-nucleotide polymorphism in pe_pgrs9 and ppe34, exclusive to the group treated for >6 months. Transcriptomic analysis revealed increased expression of various virulence-associated protein family genes and decreased expression of ribosomal protein genes and ppe38 genes in the group treated for >6 months.

CONCLUSION

The identified genetic variation and gene expression patterns may influence treatment outcomes by modulating host immune responses, increasing virulence, and potentially contributing to persister cell formation in M. tuberculosis. This study provides insights into the genetic and transcriptomic factors associated with prolonged DS-TB treatment. However, our study identified molecular characteristics using a small sample size, and further detailed studies are warranted.

Role of PE/PPE proteins of Mycobacterium tuberculosis in triad of host mitochondria, oxidative stress and cell death

The PE and PPE family proteins of Mycobacterium tuberculosis (Mtb) is exclusively found in pathogenic Mycobacterium species, comprising approximately 8-10 % of the Mtb genome. These emerging virulent factors have been observed to play pivotal roles in Mtb pathogenesis and immune evasion through various strategies. These immunogenic proteins are known to modulate the host immune response and cell-death pathways by targeting the powerhouse of the cell, the mitochondria to support Mtb survival. In this article, we are focused on how PE/PPE family proteins target host mitochondria to induce mitochondrial perturbations, modulate the levels of cellular ROS (Reactive oxygen species) and control cell death pathways. We observed that the time of expression of these proteins at different stages of infection is crucial for elucidating their impact on the cell death pathways and eventually on the outcome of infection. This article focuses on understanding the contributions of the PE/PPE proteins by unravelling the triad of host mitochondria, oxidative stress and cell death pathways that facilitate the Mtb persistence. Understanding the role of these proteins in host cellular pathways and the intricate mechanisms paves the way for the development of novel therapeutic strategies to combat TB infections.

Identification of positively selected genes in Mycobacterium tuberculosis from southern Xinjiang Uygur autonomous region of China

Background

Tuberculosis (TB), mainly caused by Mycobacterium tuberculosis (Mtb), remains a serious public health problem. Increasing evidence supports that selective evolution is an important force affecting genomic determinants of Mtb phenotypes. It is necessary to further understand the Mtb selective evolution and identify the positively selected genes that probably drive the phenotype of Mtb.

Methods

This study mainly focused on the positive selection of 807 Mtb strains from Southern Xinjiang of China using whole genome sequencing (WGS). PAML software was used for identifying the genes and sites under positive selection in 807 Mtb strains.

Results

Lineage 2 (62.70%) strains were the dominant strains in this area, followed by lineage 3 (19.45%) and lineage 4 (17.84%) strains. There were 239 codons in 47 genes under positive selection, and the genes were majorly associated with the functions of transcription, defense mechanisms, and cell wall/membrane/envelope biogenesis. There were 28 codons (43 mutations) in eight genes (gyrA, rpoB, rpoC, katG, pncA, embB, gid, and cut1) under positive selection in multi-drug resistance (MDR) strains but not in drug-susceptible (DS) strains, in which 27 mutations were drug-resistant loci, 9 mutations were non-drug-resistant loci but were in drug-resistant genes, 2 mutations were compensatory mutations, and 5 mutations were in unknown drug-resistant gene of cut1. There was a codon in Rv0336 under positive selection in L3 strains but not in L2 and L4 strains. The epitopes of T and B cells were both hyper-conserved, particularly in the T-cell epitopes.

Conclusion

This study revealed the ongoing selective evolution of Mtb. We found some special genes and sites under positive selection which may contribute to the advantage of MDR and L3 strains. It is necessary to further study these mutations to understand their impact on phenotypes for providing more useful information to develop new TB interventions.

PE12 interaction with TLR4 promotes intracellular survival of Mycobacterium tuberculosis by suppressing inflammatory response

Macrophages serve as the primary immune cells responsible for the innate immune defense against Mycobacterium tuberculosis (MTB) infection within the host. Specifically, NLRP3, a member of the NLRs family, plays a significant role in conferring resistance against MTB infection. Conversely, MTB evades innate immune killing by impeding the activation of the NLRP3 inflammasome, although the precise mechanism remains uncertain. In this study, we have identified PE12 (Rv1172c), a member of the PE/PPE family proteins, as an extracellular protein of MTB. PE12 interacts with Toll like receptor 4 (TLR4) in macrophages, forming the PE12-TLR4 complex which subsequently inhibits the transcription and expression of NLRP3. As a result, the transcription and secretion of IL-1β are reduced through the PE12-TLR4-NLRP3-IL-1β immune pathway. In vitro and in vivo experiments using a PE12-deficient strain (H37RvΔPE12) demonstrate a weakening of the suppression of the inflammatory response to MTB infection. Our findings highlight the role of the PE12 protein in not only inhibiting the transcription and release of inflammatory cytokines but also mediating the killing of MTB escape macrophages through TLR4 and inducing lung injury in MTB-infected mice. These results provide evidence that PE12 plays a significant role in the inhibition of the host immune response by MTB.

Pathogenicity and virulence of Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) is the causative agent of tuberculosis, an infectious disease with one of the highest morbidity and mortality rates worldwide. Leveraging its highly evolved repertoire of non-protein and protein virulence factors, Mtb invades through the airway, subverts host immunity, establishes its survival niche, and ultimately escapes in the setting of active disease to initiate another round of infection in a naive host. In this review, we will provide a concise synopsis of the infectious life cycle of Mtb and its clinical and epidemiologic significance. We will also take stock of its virulence factors and pathogenic mechanisms that modulate host immunity and facilitate its spread. Developing a greater understanding of the interface between Mtb virulence factors and host defences will enable progress toward improved vaccines and therapeutics to prevent and treat tuberculosis.

Role of pattern recognition receptors in sensing Mycobacterium tuberculosis

Mycobacterium tuberculosis is one of the major invasive intracellular pathogens causing most deaths by a single infectious agent. The interaction between host immune cells and this pathogen is the focal point of the disease, Tuberculosis. Host immune cells not only mount the protective action against this pathogen but also serve as the primary niche for growth. Thus, recognition of this pathogen by host immune cells and following signaling cascades are key dictators of the disease state. Immune cells, mainly belonging to myeloid cell lineage, recognize a wide variety of Mycobacterium tuberculosis ligands ranging from carbohydrate and lipids to proteins to nucleic acids by different membrane-bound and soluble pattern recognition receptors. Simultaneous interaction between different host receptors and pathogen ligands leads to immune-inflammatory response as well as contributes to virulence. This review summarizes the contribution of pattern recognition receptors of host immune cells in recognizing Mycobacterium tuberculosis and subsequent initiation of signaling pathways to provide the molecular insight of the specific Mtb ligands interacting with specific PRR, key adaptor molecules of the downstream signaling pathways and the resultant effector functions which will aid in identifying novel drug targets, and developing novel drugs and adjuvants.

Immunological effects of the PE/PPE family proteins of Mycobacterium tuberculosis and related vaccines

Tuberculosis (TB) is a chronic infectious disease caused by Mycobacterium tuberculosis (Mtb), and its incidence and mortality are increasing. The BCG vaccine was developed in the early 20th century. As the most widely administered vaccine in the world, approximately 100 million newborns are vaccinated with BCG every year, which has saved tens of millions of lives. However, due to differences in region and race, the average protective rate of BCG in preventing tuberculosis in children is still not high in some areas. Moreover, because the immune memory induced by BCG will weaken with the increase of age, it is slightly inferior in preventing adult tuberculosis, and BCG revaccination cannot reduce the incidence of tuberculosis again. Research on the mechanism of Mtb and the development of new vaccines against TB are the main strategies for preventing and treating TB. In recent years, Pro-Glu motif-containing (PE) and Pro-Pro-Glu motif-containing (PPE) family proteins have been found to have an increasingly important role in the pathogenesis and chronic protracted infection observed in TB. The development and clinical trials of vaccines based on Mtb antigens are in progress. Herein, we review the immunological effects of PE/PPE proteins and the development of common PE/PPE vaccines.

Vaccines against Tuberculosis: Where Are We Now?

Tuberculosis (TB) is among the top 10 leading causes of death in low-income countries. Statistically, TB kills more than 30,000 people each week and leads to more deaths than any other infectious disease, such as acquired immunodeficiency syndrome (AIDS) and malaria. TB treatment is largely dependent on BCG vaccination and impacted by the inefficacy of drugs, absence of advanced vaccines, misdiagnosis improper treatment, and social stigma. The BCG vaccine provides partial effectiveness in demographically distinct populations and the prevalence of multidrug-resistant (MDR) and extensively drug-resistant (XDR) TB incidences demands the design of novel TB vaccines. Various strategies have been employed to design vaccines against TB, such as: (a) The protein subunit vaccine; (b) The viral vector vaccine; (c) The inactivation of whole-cell vaccine, using related mycobacteria, (d) Recombinant BCG (rBCG) expressing Mycobacterium tuberculosis (M.tb) protein or some non-essential gene deleted BCG. There are, approximately, 19 vaccine candidates in different phases of clinical trials. In this article, we review the development of TB vaccines, their status and potential in the treatment of TB. Heterologous immune responses generated by advanced vaccines will contribute to long-lasting immunity and might protect us from both drug-sensitive and drug-resistant TB. Therefore, advanced vaccine candidates need to be identified and developed to boost the human immune system against TB.

Role of MHC class I pathways in Mycobacterium tuberculosis antigen presentation

MHC class I antigen processing is an underappreciated area of nonviral host–pathogen interactions, bridging both immunology and cell biology, where the pathogen’s natural life cycle involves little presence in the cytoplasm. The effective response to MHC-I foreign antigen presentation is not only cell death but also phenotypic changes in other cells and stimulation of the memory cells ready for the next antigen reoccurrence. This review looks at the MHC-I antigen processing pathway and potential alternative sources of the antigens, focusing on Mycobacterium tuberculosis (Mtb) as an intracellular pathogen that co-evolved with humans and developed an array of decoy strategies to survive in a hostile environment by manipulating host immunity to its own advantage. As that happens via the selective antigen presentation process, reinforcement of the effective antigen recognition on MHC-I molecules may stimulate subsets of effector cells that act earlier and more locally. Vaccines against tuberculosis (TB) could potentially eliminate this disease, yet their development has been slow, and success is limited in the context of this global disease’s spread. This review’s conclusions set out potential directions for MHC-I-focused approaches for the next generation of vaccines.

The PE-PPE Family of Mycobacterium tuberculosis: Proteins in Disguise

Mycobacterium tuberculosis has thrived in parallel with humans for millennia, and despite our efforts, M. tuberculosis continues to plague us, currently infecting a third of the world's population. The success of M. tuberculosis has recently been attributed, in part, to the PE-PPE family; a unique collection of 168 proteins fundamentally involved in the pathogenesis of M. tuberculosis. The PE-PPE family proteins have been at the forefront of intense research efforts since their discovery in 1998 and whilst our knowledge and understanding has significantly advanced over the last two decades, many important questions remain to be elucidated. This review consolidates and examines the vast body of existing literature regarding the PE-PPE family proteins, with respect to the latest developments in elucidating their evolution, structure, subcellular localisation, function, and immunogenicity. This review also highlights significant inconsistencies and contradictions within the field. Additionally, possible explanations for these knowledge gaps are explored. Lastly, this review poses many important questions, which need to be addressed to complete our understanding of the PE-PPE family, as well as highlighting the challenges associated with studying this enigmatic family of proteins. Further research into the PE-PPE family, together with technological advancements in genomics and proteomics, will undoubtedly improve our understanding of the pathogenesis of M. tuberculosis, as well as identify key targets/candidates for the development of novel drugs, diagnostics, and vaccines.

Mycobacterium tuberculosis PPE7 Enhances Intracellular Survival of Mycobacterium smegmatis and Manipulates Host Cell Cytokine Secretion Through Nuclear Factor Kappa B and Mitogen-Activated Protein Kinase Signaling

The PE/PPE family proteins of Mycobacterium tuberculosis have been associated with its virulence and interaction with the host immune system. The highly virulent modern lineage of M. tuberculosis possesses a lineage-specific PPE gene (PPE7), which arises from an ancestral mutation and is rarely studied. Here we examined the role of PPE7 in mycobacterial pathogenicity and survival by expressing M. tuberculosis PPE7 in Mycobacterium smegmatis. We show that, PPE7 activates host inflammation by increasing expression of pro-inflammatory cytokines including tumor necrosis factor-alpha (TNF-α), interleukin (IL)-1β, and IL-6, while suppressing the expression of anti-inflammatory cytokines such as IL-10, possibly through the nuclear factor kappa B, ERK1/2, and p38 mitogen-activated protein kinase pathways. Overexpressing PPE7 in M. smegmatis could enhance bacterial intracellular survival of infected macrophages. Furthermore, higher level of bacterial persistence, higher levels of TNF-α, IL-1β, and IL-6 cytokines, and more injury in the lung, liver, and spleen tissues of infected mice has been discovered. In conclusion, PPE7 could manipulate host immune response and increase bacterial persistence.

The Gene and Regulatory Network Involved in Ethambutol Resistance in Mycobacterium tuberculosis

Ethambutol (EMB) is used in combination with isoniazid and rifampicin for the treatment of tuberculosis caused by Mycobacterium tuberculosis. However, the incidence of EMB resistance is alarming. The EMB targets the cell wall arabinan biosynthesis. It is important to comprehensively understand the molecular basis of EMB to slow down the drug resistance rate of EMB. This study summarized the genes implicated in EMB resistance, regulatory network and the pharmacoproteomic effect of EMB in M. tuberculosis. Many of the genes related to EMB are implicated in membrane components, drug efflux, lipid metabolism, ribosome, and detoxification. The differential response model may help to design a novel anti-tuberculosis antibiotic.

Mycobacterium tuberculosis PPE51 Inhibits Autophagy by Suppressing Toll-Like Receptor 2-Dependent Signaling

Autophagy is an ubiquitous homeostatic pathway in mammalian cells and plays a significant role in host immunity. Substantial evidence indicates that the ability of Mycobacterium tuberculosis (Mtb) to successfully evade immune responses is partially due to inhibition of autophagic pathways. Our previous screening of Mtb transposon mutants identified the PPE51 protein as an important autophagy-inhibiting effector. We found that expression of PPE51, either by infecting bacteria or by direct expression in host cells, suppressed responses to potent autophagy-inducing stimuli and interfered with bacterial phagocytosis. This phenotype was associated with reduced activation of extracellular signal-regulated kinase 1/2 (ERK1/2), a key component of signaling pathways that stimulate autophagy. Multiple lines of evidence demonstrated that the effects of PPE51 are attributable to signal blocking by Toll-like receptor 2 (TLR2), a receptor with known involvement of activation of ERK1/2 and autophagy. Consistent with these results, mice with intact TLR2 signaling showed striking virulence attenuation for an Mtb ppe51 deletion mutant (Δ51) compared to wild-type Mtb, whereas infection of TLR2-deficient mice showed no such attenuation. Mice infected with Δ51 also displayed increased T cell responses to Mtb antigens and increased autophagy in infected lung tissues. Together, these results suggest that TLR2 activates relevant host immune functions during mycobacterial infection, which Mtb then evades through suppression of TLR2 signaling by PPE51. In addition to its previously identified function transporting substrates across the bacterial cell wall, our results demonstrate a direct role of PPE51 for evasion of both innate and adaptive immunity to Mtb.

Mycobacterial PPE36 Modulates Host Inflammation by Promoting E3 Ligase Smurf1-Mediated MyD88 Degradation

Mycobacterium tuberculosis (Mtb) PPE36, a cell-wall-associated protein, is highly specific and conserved for the Mtb complex group. Although PPE36 has been proven essential for iron utilization, little is known about it in regulating host immune responses. Here we exhibited that PPE36 was preferentially enriched in Mtb virulent strains and could efficiently inhibit host inflammatory responses and increase bacterial loads in infected macrophages and mice. In exploring the underlying mechanisms, we found that PPE36 could robustly inhibit the activation of inflammatory NF-κB and MAPK (Erk, p38, and Jnk) pathways by promoting E3 ligase Smurf1-mediated ubiquitination and proteasomal degradation of MyD88 protein. Our research revealed a previously unknown function of PPE36 on modulating host immune responses and provided some clues to the development of novel tuberculosis treatment strategies based on immune regulation.

Potential of Mycobacterium tuberculosis chorismate mutase (Rv1885c) as a novel TLR4-mediated adjuvant for dendritic cell-based cancer immunotherapy

For clinical application by dendritic cell (DC)-based cancer immunotherapy, a proper adjuvant system to elicit a strong anticancer immune response is needed. Here, we investigated the potential of chorismate mutase (TBCM, Rv1885c), a putative Mycobacterium tuberculosis (TB) virulence factor, as an immunoadjuvant in DC-based tumor immunotherapy. First, we found that TBCM functionally activated DCs by upregulating costimulatory molecules, increasing the secretion of proinflammatory cytokines, enhancing migration and inducing the Th1-type immune response in a dose-dependent manner via TLR4-mediated signaling. In addition, subcutaneous injection of TBCM-activated DCs loaded with cell lysates led to reduced tumor mass, enhanced mouse survival and lowered tumor incidence in lung carcinoma (LLC) cell-bearing mice. This is mainly mediated by functional cytotoxic T lymphocyte-mediated oncolytic activity and inhibition of cancer proliferation- and metastasis-related genes. Moreover, TBCM-induced DCs can also generate memory CD4 T cells and exert long-term tumor prevention effects. In conclusion, our findings suggest that TBCM (Rv1885c), a novel TLR4 agonist, could be used as an immunoadjuvant for DC-based cancer immunotherapy.

The Mycobacterium tuberculosis PE_PGRS Protein Family Acts as an Immunological Decoy to Subvert Host Immune Response

Mycobacterium tuberculosis (M.tb) is a successful pathogen that can reside within the alveolar macrophages of the host and can survive in a latent stage. The pathogen has evolved and developed multiple strategies to resist the host immune responses. M.tb escapes from host macrophage through evasion or subversion of immune effector functions. M.tb genome codes for PE/PPE/PE_PGRS proteins, which are intrinsically disordered, redundant and antigenic in nature. These proteins perform multiple functions that intensify the virulence competence of M.tb majorly by modulating immune responses, thereby affecting immune mediated clearance of the pathogen. The highly repetitive, redundant and antigenic nature of PE/PPE/PE_PGRS proteins provide a critical edge over other M.tb proteins in terms of imparting a higher level of virulence and also as a decoy molecule that masks the effect of effector molecules, thereby modulating immuno-surveillance. An understanding of how these proteins subvert the host immunological machinery may add to the current knowledge about M.tb virulence and pathogenesis. This can help in redirecting our strategies for tackling M.tb infections.

Proline-Glutamate/Proline-Proline-Glutamate (PE/PPE) proteins of Mycobacterium tuberculosis: The multifaceted immune-modulators

The PE/PPE proteins encoded by seven percent (7%) of Mycobacterium tuberculosis (Mtb) genome are the chief constituents to pathogen's virulence reservoir. The fact that these genes have evolved along ESX secretory system in pathogenic Mtb strains make their investigation very intriguing. There is lot of speculation about the prominent role of these proteins at host pathogen interface and in disease pathogenesis. Nevertheless, the exact function of PE/PPE proteins still remains a mystery which calls for further research targeting these proteins. This article is an effort to document all the facts known so far with regard to these unique proteins which involves their origin, evolution, transcriptional control, and most important their role as host immune-modulators. Our understanding strongly points towards the versatile nature of these PE/PPE proteins as Mtb's host immune sensors and as decisive factors in shaping the outcome of infection. Further investigation on these proteins will surely pave way for newer and effective vaccines and therapeutics to control Tuberculosis (TB).

Transcriptional Profiling of Human Peripheral Blood Mononuclear Cells Stimulated by Mycobacterium tuberculosis PPE57 Identifies Characteristic Genes Associated With Type I Interferon Signaling

Proline-glutamic acid (PE)- and proline-proline-glutamic acid (PPE)-containing proteins are exclusive to Mycobacterium tuberculosis (MTB), the leading cause of tuberculosis (TB). In this study, we performed global transcriptome sequencing (RNA-Seq) on PPE57-stimulated peripheral blood mononuclear cells (PBMCs) and control samples to quantitatively measure the expression level of key transcripts of interest. A total of 1367 differentially expressed genes (DEGs) were observed in response to a 6 h exposure to PPE57, with 685 being up-regulated and 682 down-regulated. Immune-related gene functions and pathways associated with these genes were evaluated, revealing that the type I IFN signaling pathway was the most significantly enriched pathway in our RNA-seq dataset, with 14 DEGs identified therein including ISG15, MX2, IRF9, IFIT3, IFIT2, OAS3, IFIT1, IFI6, OAS2, OASL, RSAD2, OAS1, IRF7, and MX1. These PPE57-related transcriptomic profiles have implications for a better understanding of host global immune mechanisms underlying MTB infection outcomes. However, more studies regarding these DEGs and type I IFN signaling in this infectious context are necessary to more fully clarify the underlying mechanisms that arise in response to PPE57 during MTB infection.

Mycobacterium tuberculosis Rv2145c Promotes Intracellular Survival by STAT3 and IL-10 Receptor Signaling

Although Mycobacterium tuberculosis (Mtb) is an intracellular pathogen in phagocytic cells, the factors and mechanisms by which they invade and persist in host cells are still not well understood. Characterization of the bacterial proteins modulating macrophage function is essential for understanding tuberculosis pathogenesis and bacterial virulence. Here we investigated the pathogenic role of the Rv2145c protein in stimulating IL-10 production. We first found that recombinant Rv2145c stimulated bone marrow-derived macrophages (BMDMs) to secrete IL-10, IL-6 and TNF-α but not IL-12p70 and to increase the expression of surface molecules through the MAPK, NF-κB, and TLR4 pathways and enhanced STAT3 activation and the expression of IL-10 receptor in Mtb-infected BMDMs. Rv2145c significantly enhanced intracellular Mtb growth in BMDMs compared with that in untreated cells, which was abrogated by STAT3 inhibition and IL-10 receptor (IL-10R) blockade. Expression of Rv2145c in Mycobacterium smegmatis (M. smegmatis) led to STAT3-dependent IL-10 production and enhancement of intracellular growth in BMDMs. Furthermore, the clearance of Rv2145c-expressing M. smegmatis in the lungs and spleens of mice was delayed, and these effects were abrogated by administration of anti-IL-10R antibodies. Finally, all mice infected with Rv2145c-expressing M. smegmatis died, but those infected with the vector control strain did not. Our data suggest that Rv2145c plays a role in creating a favorable environment for bacterial survival by modulating host signals.

Role of the PE/PPE Family in Host-Pathogen Interactions and Prospects for Anti-Tuberculosis Vaccine and Diagnostic Tool Design

The pe/ppe genes are found in pathogenic, slow-growing Mycobacterium tuberculosis and other M. tuberculosis complex (MTBC) species. These genes are considered key factors in host-pathogen interactions. Although the function of most PE/PPE family proteins remains unclear, accumulating evidence suggests that this family is involved in M. tuberculosis infection. Here, we review the role of PE/PPE proteins, which are believed to be linked to the ESX system function. Further, we highlight the reported functions of PE/PPE proteins, including their roles in host cell interaction, immune response regulation, and cell fate determination during complex host-pathogen processes. Finally, we propose future directions for PE/PPE protein research and consider how the current knowledge might be applied to design more specific diagnostics and effective vaccines for global tuberculosis control.

Homoplastic single nucleotide polymorphisms contributed to phenotypic diversity in Mycobacterium tuberculosis

Homoplastic mutations are mutations independently occurring in different clades of an organism. The homoplastic changes may be a result of convergence evolution due to selective pressures. Reports on the analysis of homoplastic mutations in Mycobacterium tuberculosis have been limited. Here we characterized the distribution of homoplastic single nucleotide polymorphisms (SNPs) among genomes of 1,170 clinical M. tuberculosis isolates. They were present in all functional categories of genes, with pe/ppe gene family having the highest ratio of homoplastic SNPs compared to the total SNPs identified in the same functional category. Among the pe/ppe genes, the homoplastic SNPs were common in a relatively small number of homologous genes, including ppe18, the protein of which is a component of a promising candidate vaccine, M72/AS01E. The homoplastic SNPs in ppe18 were particularly common among M. tuberculosis Lineage 1 isolates, suggesting the need for caution in extrapolating the results of the vaccine trial to the population where L1 is endemic in Asia. As expected, homoplastic SNPs strongly associated with drug resistance. Most of these mutations are already well known. However, a number of novel mutations associated with streptomycin resistance were identified, which warrants further investigation. A SNP in the intergenic region upstream of Rv0079 (DATIN) was experimentally shown to increase transcriptional activity of the downstream gene, suggesting that intergenic homoplastic SNPs should have effects on the physiology of the bacterial cells. Our study highlights the potential of homoplastic mutations to produce phenotypic changes. Under selective pressure and during interaction with the host, homoplastic mutations may confer advantages to M. tuberculosis and deserve further characterization.

Transcriptome sequencing analysis of porcine MDM response to FSL-1 stimulation

Mycoplasma infection can cause many diseases in pigs, resulting in great economic losses in pork production. Innate immune responses are thought to play critical roles in the pathogenesis of mycoplasma disease. However, the molecular events involved in immune responses remain to be determined. Hence, the object of this study was to use RNA-Seq to investigate the gene expression profiles of the innate immune response mediated by FSL-1 in pig monocyte-derived macrophages (MDMs). The results revealed that 1442 genes were differentially expressed in the FSL-1 group compared with the control groups, of which 777 genes were upregulated and 665 genes were downregulated. KEGG pathway analysis showed that the upregulated genes were mainly involved in innate immune-related pathways including the TNF signaling pathway, cytokine-cytokine receptor interaction, Toll-like receptor signaling pathway, Jak-STAT signaling pathway, chemokine signaling pathway, NOD-like receptor signaling pathway and NF-kappa B signaling pathway. The downregulated genes were only involved in the cGMP-PKG signaling pathway and glycerophospholipid metabolism. Our results showed that FSL-1 stimulation activated the TLR2 signaling pathway and resulted in diverse inflammatory responses. FSL-1 induced the transcription of numerous protein-coding genes involved in a complex network of innate immune-related pathways. We speculate that TNF, IL1B, IL6, NFKB1, NFKBIA, CXCL2, CXCL8, CXCL10, CCL2, CCL4 and CCL5 were the most likely hub genes that play important roles in the above pathways. This study identified the differentially expressed genes and their related signaling pathways, contributing to the comprehensive understanding of the mechanisms underlying host-pathogen interactions during mycoplasma infection and providing a reference model for further studies.

Molecular Basis Underlying Host Immunity Subversion by Mycobacterium tuberculosis PE/PPE Family Molecules

Mycobacterium tuberculosis proline-glutamic acid (PE)/proline-proline-glutamic acid (PPE) family proteins, with >160 members, are crucial for virulence, cell wall, host cell fate, host Th1/Th2 balance, and CD8⁺ T cell recognition. Ca²⁺ signaling is involved in PE/PPE protein-mediated host-pathogen interaction. PE/PPE proteins also function in heme utilization and nitric oxide production. PE/PPE family proteins are intensively pursued as diagnosis biomarkers and vaccine components.

PPE39 of the Mycobacterium tuberculosis strain Beijing/K induces Th1-cell polarization through dendritic cell maturation

In a previous study, we have identified MTBK_24820, the complete protein form of PPE39 in the hypervirulent Mycobacterium tuberculosis (Mtb) strain Beijing/K by using comparative genomic analysis. PPE39 exhibited vaccine potential against Mtb challenge in a murine model. Thus, in this present study, we characterize PPE39-induced immunological features by investigating the interaction of PPE39 with dendritic cells (DCs). PPE39-treated DCs display reduced dextran uptake and enhanced MHC-I, MHC-II, CD80 and CD86 expression, indicating that this PPE protein induces phenotypic DC maturation. In addition, PPE39-treated DCs produce TNF-α, IL-6 and IL-12p70 to a similar and/or greater extent than lipopolysaccharide-treated DCs in a dose-dependent manner. The activating effect of PPE39 on DCs was mediated by TLR4 through downstream MAPK and NF-κB signaling pathways. Moreover, PPE39-treated DCs promoted naïve CD4⁺ T-cell proliferation accompanied by remarkable increases of IFN-γ and IL-2 secretion levels, and an increase in the Th1-related transcription factor T-bet but not in Th2-associated expression of GATA-3, suggesting that PPE39 induces Th1-type T-cell responses through DC activation. Collectively, the results indicate that the complete form of PPE39 is a so-far-unknown TLR4 agonist that induces Th1-cell biased immune responses by interacting with DCs.This article has an associated First Person interview with the first author of the paper.

Mycobacterium tuberculosis Rv3463 induces mycobactericidal activity in macrophages by enhancing phagolysosomal fusion and exhibits therapeutic potential

Macrophages are responsible for innate and adaptive immune response activation necessary for eliminating infections. Optimal activation of macrophages to phagocytize Mycobacterium tuberculosis is critical in anti-mycobacterial defense. Here, we identified a novel Rv3463 hypothetical protein that induces macrophage activation in Mtb culture filtrate. Recombinant Rv3463 activated mouse bone marrow-derived macrophages to induce the expression of surface molecules and secrete pro-inflammatory cytokines via the TLR2 and TLR4 pathways. Mitogen activated protein kinase, phospatidylinositol-4,5-bisphosphate 3-kinases, and the NF-κB signaling pathways are involved in Rv3463-mediated macrophage activation. Furthermore, Rv3463 induced bactericidal effects in Mtb-infected macrophages through phagosome maturation and phagolysosomal fusion enhanced by phospatidylinositol-4,5-bisphosphate 3-kinases and Ca²⁺ signaling pathways and exhibited therapeutic effects in a short-term Mtb-infection mouse model. Overexpression of Rv3463 in M. smegmatis caused rapid clearance of bacteria in macrophages and mice. Our study suggests that Rv3463 is a promising target for the development of post-exposure tuberculosis vaccines or adjunct immune-therapy.

Vaccine efficacy of a Mycobacterium tuberculosis Beijing-specific proline-glutamic acid (PE) antigen against highly virulent outbreak isolates

Bacillus Calmette-Guerin vaccine confers insufficient pulmonary protection against tuberculosis (TB), particularly the Mycobacterium tuberculosis (Mtb) Beijing strain infection. Identification of vaccine antigens (Ags) by considering Mtb genetic diversity is crucial for the development of improved TB vaccine. MTBK_20640, a new Beijing genotype-specific proline-glutamic acid-family Ag, was identified by comparative genomic analysis. Its immunologic features were characterized by evaluating interactions with dendritic cells (DCs), and immunogenicity and vaccine efficacy were determined against highly virulent Mtb Beijing outbreak Korean Beijing (K) strain and HN878 strain in murine infection model. MTBK_20640 induced DCs via TLR2 and downstream MAPK and NF-κB signaling pathways, effectively promoting naive CD4-positive (CD4⁺) T-cell proliferation and IFN-γ production. Different IFN-γ response was observed in mice infected with Mtb K or reference H37Rv strain. Significant induction of T helper type 1 cell-polarized Ag-specific multifunctional CD4⁺ T cells and a marked Ag-specific IgG2c response were observed in mice immunized with MTBK_20640/glucopyranosyl lipid adjuvant-stable emulsion. The immunization conferred long-term protection against 2 Mtb Beijing outbreak strains, as evidenced by a significant reduction in colony-forming units in the lung and spleen and reduced lung inflammation. MTBK_20640 vaccination conferred long-term protection against highly virulent Mtb Beijing strains. MTBK_20640 may be developed into a novel Ag component in multisubunit TB vaccines in the future.-Kwon, K. W., Choi, H.-H., Han, S. J., Kim, J.-S., Kim, W. S., Kim, H., Kim, L.-H., Kang, S. M., Park, J., Shin, S. J. Vaccine efficacy of a Mycobacterium tuberculosis Beijing-specific proline-glutamic acid (PE) antigen against highly virulent outbreak isolates.

Regulation of host cell pyroptosis and cytokines production by Mycobacterium tuberculosis effector PPE60 requires LUBAC mediated NF-κB signaling

Tuberculosis, caused by Mycobacterium tuberculosis infection, remains a global public health threat. The success of M. tuberculosis largely contributes to its manipulation of host cell fate. The role of M. tuberculosis PE/PPE family effectors in the host destiny was intensively explored. In this study, the role of PPE60 (Rv3478) was characterized by using Rv3478 recombinant M. smegmatis. PPE60 can promote host cell pyroptosis via caspases/NLRP3/gasdermin. The production of pro-inflammatory cytokines, such as IL-1β, IL-6, IL-12p40 and TNF-α was altered by PPE60. We found that LUBAC was involved in PPE60-elicited NF-κB signaling by using Linear Ubiquitin Chain Assembly Complex (LUBAC)-specific inhibitor gliotoxin. The PPE60 recombinant M. smegmatis survival rate within macrophages is increased, as well as elevated resistance to stresses such as low pH, surface stresses and antibiotics exposure. For a first time it is firstly reported that M. tuberculosis effector PPE60 can modulate the host cell fate via LUBAC-mediated NF-κB signaling.

PPE11 of Mycobacterium tuberculosis can alter host inflammatory response and trigger cell death

Tuberculosis (TB), which is caused by Mycobacterium tuberculosis (Mtb), remains a serious global health problem. The PE/PPE family, featuring unique sequences, structures and expression in Mtb, is reported to interfere with the macrophage response to the pathogen and facilitate its infection. PPE11 (Rv0453) existed in pathogenic mycobacteria and was persistently expressed in the infected guinea pig lungs. However, the role it played in the pathogenesis remains unclear. Here, to investigate the interaction and potential mechanism of PPE11 between pathogens and hosts, we heterologously expressed PPE11 in non-pathogenic, rapidly growing Mycobacterium smegmatis strains. We found that the overexpression of the cell wall-associated protein, PPE11, can improve the viability of bacteria in the presence of lysozyme, hydrogen peroxide and acid stress. Expression of PPE11 enhanced the early survival of M. smegmatis in macrophages and sustained a higher bacterial load in mouse tissues that showed exacerbated organ pathology. Macrophages infected with recombinant M. smegmatis produced significantly greater amounts of interleukin (IL)-1β, IL-6, tumour necrosis factor (TNF)-α and an early decrease in IL-10 along with higher levels of host cell death. Similar cytokines changes were observed in the sera of infected mice. Accordingly, PPE11 protein causes histopathological changes by disrupting the dynamic balance of the inflammatory factors and promoting host-cell death, indicating a potential role in the virulence of Mtb.

Specific T cell induction using iron oxide based nanoparticles as subunit vaccine adjuvant

Metal-based nanoparticles (NPs) stimulate innate immunity; however, they have never been demonstrated to be capable of aiding the generation of specific cellular immune responses. Therefore, our objective was to evaluate whether iron oxide-based NPs have adjuvant properties in generating cellular Th1, Th17 and TCD8 (Tc1) immune responses. For this purpose, a fusion protein (CMX) composed of Mycobacterium tuberculosis antigens was used as a subunit vaccine. Citrate-coated MnFe₂O₄ NPs were synthesized by co-precipitation and evaluated by transmission electron microscopy. The vaccine was formulated by homogenizing NPs with the recombinant protein, and protein corona formation was determined by dynamic light scattering and field-emission scanning electron microscopy. The vaccine was evaluated for the best immunization route and strategy using subcutaneous and intranasal routes with 21-day intervals between immunizations. When administered subcutaneously, the vaccine generated specific CD4⁺IFN-γ⁺ (Th1) and CD8⁺IFN-γ⁺ responses. Intranasal vaccination induced specific Th1, Th17 (CD4⁺IL-17⁺) and Tc1 responses, mainly in the lungs. Finally, a mixed vaccination strategy (2 subcutaneous injections followed by one intranasal vaccination) induced a Th1 (in the spleen and lungs) and splenic Tc1 response but was not capable of inducing a Th17 response in the lungs. This study shows for the first time a subunit vaccine with iron oxide based NPs as an adjuvant that generated cellular immune responses (Th1, Th17 and TCD8), thereby exhibiting good adjuvant qualities. Additionally, the immune response generated by the subcutaneous administration of the vaccine diminished the bacterial load of Mtb challenged animals, showing the potential for further improvement as a vaccine against tuberculosis.

Mycobacterium tuberculosis PPE60 antigen drives Th1/Th17 responses via Toll-like receptor 2-dependent maturation of dendritic cells

Targeting of Mycobacterium tuberculosis (MTB) PE/PPE antigens that induce type 1 helper T cell (Th1) and Th17 responses represents a crucial strategy for the development of tuberculosis (TB) vaccines. However, only a few PE/PPE antigens induce these responses. Here, we sought to determine how the cell wall-associated antigen PPE60 (Rv3478) activates dendritic cell (DC) maturation and T-cell differentiation. We observed that PPE60 induces DC maturation by augmenting the protein expression of cluster of differentiation 80 (CD80) and CD86 and major histocompatibility complex (MHC) class I and MHC class II on the cell surface. PPE60 also stimulated the production of tumor necrosis factor-α (TNFα), interleukin (IL)-1β, IL-6, IL-12p70, and IL-23p19 but not IL-10. This induction was mediated by Toll-like receptor 2 (TLR2) and followed by activation of p38, c-Jun N-terminal kinase (JNK), and NF-κB signaling. PPE60 enhanced MHC-II expression and promoted antigen processing by DCs in a TLR2-dependent manner. Moreover, PPE60-stimulated DCs directed naïve CD4⁺ T cells to produce IFN-γ, IL-2, and IL-17A, expanding the Th1 and Th17 responses, along with activation of T-bet and RAR-related orphan receptor C (RORγt) but not GATA-3. Moreover, PPE60 activated the NLRP3 inflammasome followed by caspase-1-dependent IL-1β and IL-18 synthesis in DCs. Of note, pharmacological inhibition of NLRP3 activation specifically attenuated IFN-γ and IL-17A secretion into the supernatant from CD4⁺ T cells cocultured with PPE60-activated DCs. These findings indicate that PPE60 induces Th1 and Th17 immune responses by activating DCs in a TLR2-dependent manner, suggesting PPE60's potential for use in MTB vaccine development.

Innate immunity in tuberculosis: host defense vs pathogen evasion

The major innate immune cell types involved in tuberculosis (TB) infection are macrophages, dendritic cells (DCs), neutrophils and natural killer (NK) cells. These immune cells recognize the TB-causing pathogen Mycobacterium tuberculosis (Mtb) through various pattern recognition receptors (PRRs), including but not limited to Toll-like receptors (TLRs), Nod-like receptors (NLRs) and C-type lectin receptors (CLRs). Upon infection by Mtb, the host orchestrates multiple signaling cascades via the PRRs to launch a variety of innate immune defense functions such as phagocytosis, autophagy, apoptosis and inflammasome activation. In contrast, Mtb utilizes numerous exquisite strategies to evade or circumvent host innate immunity. Here we discuss recent research on major host innate immune cells, PRR signaling, and the cellular functions involved in Mtb infection, with a specific focus on the host's innate immune defense and Mtb immune evasion. A better understanding of the molecular mechanisms underlying host-pathogen interactions could provide a rational basis for the development of effective anti-TB therapeutics.

Mycobacterium tuberculosis Latent Antigen Rv2029c from the Multistage DNA Vaccine A39 Drives TH1 Responses via TLR-mediated Macrophage Activation

Targeting of Mycobacterium tuberculosis (MTB) latent antigens comprises a crucial strategy for the development of alternative tuberculosis (TB) vaccine(s) that protects against TB reactivation. Here, we generated a multistage DNA vaccine, A39, containing the early antigens Ag85A and Rv3425 as well as the latency-associated protein Rv2029c, which conferred protective immunity in a pre-exposure mouse model. Moreover, administration of the A39 vaccination after MTB exposure inhibited reactivation and resulted in significantly lower bacterial loads in the lungs and spleen of mice, compared to those in the control population. Subsequently, we investigated the effect of Rv2029c on innate immunity and characterized the molecular details of the interaction of this protein with the host via iTRAQ proteomic and biochemical assay analyses. Rv2029c activated macrophages, triggered the production of pro-inflammatory cytokines, and promoted toll-like receptor/mitogen-activated protein kinase (TLR/MAPK)-dependent macrophage apoptosis. Furthermore, Rv2029c treatment enhanced the ability of Mycobacterium bovis Bacillus Calmette-Guérin (BCG)-infected macrophages to present antigens to CD4⁺ T cells in vitro, which correlated with an increase in MHC-II expression. Lastly, Rv2029c-treated macrophages activated T cells, effectively polarized CD4⁺ and CD8⁺ T cells to secrete IFN-γ and IL-2, and specifically expanded a population of CD44^highCD62L^lowCD4⁺/CD8⁺ effector/memory cells, indicating that Rv2029c, as a specific recall antigen, contributes to Th1 polarization in T cell immunity. These results suggest that Rv2029c and A39 comprise promising targets for the development of next-generation clinical TB therapeutic vaccines.

New findings of Toll-like receptors involved in Mycobacterium tuberculosis infection

Tuberculosis (TB), an important issue in the present age, affects millions of people each year. The infectious agent of TB, Mycobacterium tuberculosis (Mtb), interacts with the immune system which prevents the development of this bacterium as much as possible. In fact, the receptors on the surface of immune cells identify the bacteria, one of which is Toll-like receptors (TLRs). Different TLRs including 2, 4, 9 and 8 play critical roles in tuberculosis infection. In this paper, we focused on the role of TLRs which interact with different components of Mtb and, consequently, prevent the entrance and influence of bacteria on the body.

Mycobacterium tuberculosis MymA is a TLR2 agonist that activate macrophages and a TH1 response

Cell wall of Mycobacterium tuberculosis (M.tb) is a major source of immunogenic proteins that can be tested as vaccine candidates. MymA (Rv3083), a 55 kDa M.tb flavin containing monooxygenase, is involved in modification of mycolic acids during acidic shock following M.tb internalization in macrophage. In this study, we have investigated the role of this cell wall associated protein in activation of macrophages by toll like receptor (TLRs) engagement and subsequent signaling. Our results showed that MymA stimulation of THP1 cells and human monocyte derived macrophages (MDM) lead to upregulation of TLR2 and co-stimulatory molecules CD40, CD80, CD86 and HLA-DR. This upregulation is partially reduced by TLR2 blocking antibodies. The activation of macrophage following MymA stimulation also resulted in release of proinflammatory cytokines, TNF-α and IL-12. Moreover, MymA also polarized the immune response towards T_H1 as shown by an increased IFN-γ level in the supernatant of stimulated peripheral blood mononuclear cells (PBMC). In consensus with the TLR2 signaling involving MyD88 and NF-κB, we also observed several fold increase in mRNA for TLR2, MyD88 and NF-κB on MymA induction of THP-1 and MDM by qRT-PCR. The increased production of NF-κB following recognition of MymA by TLR2 was further confirmed by HEK-TLR2 reporter cell line colorimetric assay. In conclusion, immunological evaluation revealed that MymA is a TLR2 agonist that upregulates signaling via MyD88 and NF-κB in macrophages to stimulate the release of proinflammatory cytokines. The MymA protein should be investigated further for expression in recombinant BCG as a pre-exposure vaccine or as a post-exposure subunit vaccine candidate.

Modulation of Macrophage Responses by CMX, a Fusion Protein Composed of Ag85c, MPT51, and HspX from Mycobacterium tuberculosis

Mycobacterium bovis Bacillus Calmette–Guérin (BCG) is a vaccine used to prevent tuberculosis (TB). Due to the poor protection conferred by BCG in adults, new, more effective formulations have been developed. A recombinant BCG vaccine expressing the CMX fusion protein Ag85c_MPT51_HspX (rBCG-CMX) induced Th1 and Th17 responses and provided better protection than BCG. It has been shown that Mycobacterium smegmatis expressing CMX also induces better protection than BCG and is a strong macrophage activator. The aim of the present study was to evaluate macrophage activation by the recombinant CMX fusion protein and by rBCG-CMX and to evaluate their ability to generate vaccine-specific immune responses. The results demonstrate that rCMX protein expressed by BCG (rBCG-CMX) activates pulmonary macrophages; increases the expression of activation molecules, cytokines, and MHC-II. The interaction with rCMX activates the transcription factor NF-κB and induces the production of the cytokines TGF-β, TNF-α, and IL-6. The in vitro stimulation of bone marrow-derived macrophages (BMMs) from TLR-4 or TLR-2 KO mice showed that in the absence of TLR-4, IL-6 was not produced. rBCG-CMX was unable to induce CMX-specific Th1 and Th17 cells in TLR-4 and TLR-2 KO mice, suggesting that these receptors participate in their induction. We concluded that both the rBCG-CMX vaccine and the rCMX protein can activate macrophages and favor the specific immune response necessary for this vaccine.

Mycobacterium avium MAV2052 protein induces apoptosis in murine macrophage cells through Toll-like receptor 4

Mycobacterium avium and its sonic extracts induce apoptosis in macrophages. However, little is known about the M. avium components regulating macrophage apoptosis. In this study, using multidimensional fractionation, we identified MAV2052 protein, which induced macrophage apoptosis in M. avium culture filtrates. The recombinant MAV2052 induced macrophage apoptosis in a caspase-dependent manner. The loss of mitochondrial transmembrane potential (ΔΨm), mitochondrial translocation of Bax, and release of cytochrome c from mitochondria were observed in macrophages treated with MAV2052. Further, reactive oxygen species (ROS) production was required for the apoptosis induced by MAV2052. In addition, ROS and mitogen-activated protein kinases were involved in MAV2052-mediated TNF-α and IL-6 production. ROS-mediated activation of apoptosis signal-regulating kinase 1 (ASK1)-JNK pathway was a major signaling pathway for MAV2052-induced apoptosis. Moreover, MAV2052 bound to Toll-like receptor (TLR) 4 molecule and MAV2052-induced ROS production, ΔΨm loss, and apoptosis were all significantly reduced in TLR4(-/-) macrophages. Altogether, our results suggest that MAV2052 induces apoptotic cell death through TLR4 dependent ROS production and JNK pathway in murine macrophages.

Recombinant Lipoprotein Rv1016c Derived from Mycobacterium tuberculosis Is a TLR-2 Ligand that Induces Macrophages Apoptosis and Inhibits MHC II Antigen Processing

TLR2-dependent cellular signaling in Mycobacterium tuberculosis-infected macrophages causes apoptosis and inhibits class II major histocompatibility complex (MHC-II) molecules antigen processing, leading to evasion of surveillance. Mycobacterium tuberculosis (MTB) lipoproteins are an important class of Toll-like receptor (TLR) ligand, and identified as specific components that mediate these effects. In this study, we identified and characterized MTB lipoprotein Rv1016c (lpqT) as a cell wall associated-protein that was exposed on the cell surface and enhanced the survival of recombinants M. smegmatis_Rv1016c under stress conditions. We found that Rv1016c lipoprotein was a novel TLR2 ligand and able to induce macrophage apoptosis in a both dose- and time-dependent manner. Additionally, apoptosis induced by Rv1016c was reserved in THP-1 cells blocked with anti-TLR-2 Abs or in TLR2^−/− mouse macrophages, indicating that Rv1016c-induced apoptosis is dependent on TLR2. Moreover, we demonstrated that Rv1016c lipoprotein inhibited IFN-γ-induced MHC-II expression and processing of soluble antigens in a TLR2 dependent manner. Class II transactivator (CIITA) regulates MHC II expression. In this context, Rv1016c lipoprotein diminished IFN-γ-induced expression of CIITA IV through TLR2 and MAPK Signaling. TLR2-dependent apoptosis and inhibition of MHC-II Ag processing induced by Rv1016c during mycobacteria infection may promote the release of residual bacilli from apoptotic cells and decrease recognition by CD4⁺ T cells. These mechanisms may allow intracellular MTB to evade immune surveillance and maintain chronic infection.

PPE26 induces TLR2-dependent activation of macrophages and drives Th1-type T-cell immunity by triggering the cross-talk of multiple pathways involved in the host response

The pathophysiological functions and the underlying molecular basis of PE /PPE proteins of M. tuberculosis remain largely unknown. In this study, we focused on the link between PPE26 and host response. We demonstrated that PPE26 can induce extensive inflammatory responses in macrophages through triggering the cross-talk of multiple pathways involved in the host response, as revealed by iTRAQ-based subcellular quantitative proteomics. We observed that PPE26 is able to specifically bind to TLR2 leading to the subsequent activation of MAPKs and NF-κB signaling. PPE26 functionally stimulates macrophage activation by augmenting pro-inflammatory cytokine production (TNF-α, IL-6 and IL-12 p40) and the expression of cell surface markers (CD80, CD86, MHC class I and II). We observed that PPE26-treated macrophages effectively polarizes naïve CD4⁺ T cells to up-regulate CXCR3 expression, and to secrete IFN-γ and IL-2, indicating PPE26 contributes to the Th1 polarization during the immune response. Importantly, rBCG::PPE26 induces stronger antigen-specific TNF-α and IFN-γ activity, and higher levels of the Th1 cytokines TNF-α and IFN-γ comparable to BCG. Moreover, PPE26 effectively induces the reciprocal expansion of effector/memory CD4⁺/CD8⁺ CD44^highCD62L^low T cells in the spleens of mice immunized with this strain. These results suggest that PPE26 may be a TLR2 agonist that stimulates innate immunity and adaptive immunity, indicating that PPE26 is a potential antigen for the rational design of an efficient vaccine against M. tuberculosis.

Immunogencity of antigens from Mycobacterium tuberculosis self-assembled as particulate vaccines

Traditional approaches to vaccine development have failed to identify better vaccines to replace or supplement BCG for the control of tuberculosis (TB). Subunit vaccines offer a safer and more reproducible alternative for the prevention of diseases. In this study, the immunogenicity of bacterially derived polyester beads displaying three different Rv antigens of Mycobacterium tuberculosis was evaluated. Polyester beads displaying the antigens Rv1626, Rv2032, Rv1789, respectively, were produced in an endotoxin-free Escherichia coli strain. Beads were formulated with the adjuvant DDA and subcutaneously administered to C57BL/6 mice. Cytokine responses were evaluated by CBA and antibody responses by ELISA. Specificity of the IgG response was assessed by immunoblotting cell lysates of the vaccine production strains using sera from the vaccinated mice. Mice vaccinated with beads displaying Rv1626 had significantly greater IgG1 responses compared to mice vaccinated with Rv1789 beads and greater IgG2 responses than the group vaccinated with Rv2032 beads (p<0.05). Immunoblotting of antisera from these mice indicated the antibody responses were Rv1626 antigen-specific and there was no detectable immune response to the polyester component of the vaccine. Overall, this study suggested that selected TB antigens derived from reverse vaccinology approaches can be displayed on polyester beads to produce antigen-specific immune responses potentially relevant to the prevention of TB.

Mycobacterium tuberculosis Rv2882c Protein Induces Activation of Macrophages through TLR4 and Exhibits Vaccine Potential

Macrophages constitute the first line of defense against Mycobacterium tuberculosis and are critical in linking innate and adaptive immunity. Therefore, the identification and characterization of mycobacterial proteins that modulate macrophage function are essential for understanding tuberculosis pathogenesis. In this study, we identified the novel macrophage-activating protein, Rv2882c, from M. tuberculosis culture filtrate proteins. Recombinant Rv2882c protein activated macrophages to secrete pro-inflammatory cytokines and express co-stimulatory and major histocompatibility complex molecules via Toll-like receptor 4, myeloid differentiation primary response protein 88, and Toll/IL-1 receptor-domain-containing adaptor inducing IFN-beta. Mitogen-activated protein kinases and NF-κB signaling pathways were involved in Rv2882c-induced macrophage activation. Further, Rv2882c-treated macrophages induced expansion of the effector/memory T cell population and Th1 immune responses. In addition, boosting Bacillus Calmette-Guerin vaccination with Rv2882c improved protective efficacy against M. tuberculosis in our model system. These results suggest that Rv2882c is an antigen that could be used for tuberculosis vaccine development.

Induction of Unconventional T Cells by a Mutant Mycobacterium bovis BCG Strain Formulated in Cationic Liposomes Correlates with Protection against Mycobacterium tuberculosis Infections of Immunocompromised Mice

Earlier studies aimed at defining protective immunity induced by Mycobacterium bovis BCG immunization have largely focused on the induction of antituberculosis CD4(+) and CD8(+) T cell responses. Here we describe a vaccine consisting of a BCGΔmmaA4 deletion mutant formulated in dimethyl dioctadecyl-ammonium bromide (DDA) with d-(+)-trehalose 6,6'-dibehenate (TDB) (DDA/TDB) adjuvant (A4/Adj) that protected TCRδ(-/-) mice depleted of CD4(+), CD8(+), and NK1.1(+) T cells against an aerosol challenge with M. tuberculosis These mice were significantly protected relative to mice immunized with a nonadjuvanted BCGΔmmaA4 (BCG-A4) mutant and nonvaccinated controls at 2 months and 9 months postvaccination. In the absence of all T cells following treatment with anti-Thy1.2 antibody, the immunized mice lost the ability to control the infection. These results indicate that an unconventional T cell population was mediating protection in the absence of CD4(+), CD8(+), NK1.1(+), and TCRγδ T cells and could exhibit memory. Focusing on CD4(-) CD8(-) double-negative (DN) T cells, we found that these cells accumulated in the lungs postchallenge significantly more in A4/Adj-immunized mice and induced significantly greater frequencies of pulmonary gamma interferon (IFN-γ)-producing cells than were seen in the nonvaccinated or nonadjuvanted BCG control groups. Moreover, pulmonary DN T cells from the A4/Adj group exhibited significantly higher IFN-γ integrated median fluorescence intensity (iMFI) values than were seen in the control groups. We also showed that enriched DN T cells from mice immunized with A4/Adj could control mycobacterial growth in vitro significantly better than naive whole-spleen cells. These results suggest that formulating BCG in DDA/TDB adjuvant confers superior protection in immunocompromised mice and likely involves the induction of long-lived memory DN T cells.

Mycobacterium tuberculosis PE27 activates dendritic cells and contributes to Th1-polarized memory immune responses during in vivo infection

A gradual understanding of the proline-glutamate (PE) and proline-proline-glutamate (PPE) families, which compromise 10% of the coding regions in the Mycobacterium tuberculosis (Mtb) genome, has uncovered unique roles in host-pathogen interactions. However, the immunological function of PE27 (Rv2769c), the largest PE member, remains unclear. Here, we explored the functional roles and related signaling mechanisms of PE27 in the interaction with dendritic cells (DCs) to shape the T cell response. PE27 phenotypically and functionally induces DC maturation by up-regulating CD80, CD86, MHC class I and MHC class II expression on the DC surface to promote the production of TNF-α, IL-1β, IL-6, and IL-12p70 but not IL-10. Additionally, we found that PE27-mediated DC activation requires the participation of mitogen-activated protein kinases (MAPKs) and nuclear factor κB (NF-κB) signaling pathways. Interestingly, PE27-treated DCs directed naïve CD4(+) T cells to secrete IFN-γ and activate T-bet but not GATA-3. PE27 also induced IFN-γ-producing memory T cell responses in Mtb-infected mice, indicating that PE27 contributes to Th1-polarization. Taken together, these findings suggest that PE27 possesses Th1-polarizing potential through DC maturation and could be useful in the design of TB vaccines.

Synthetic Long Peptide Derived from Mycobacterium tuberculosis Latency Antigen Rv1733c Protects against Tuberculosis

Responsible for 9 million new cases of active disease and nearly 2 million deaths each year, tuberculosis (TB) remains a global health threat of overwhelming dimensions. Mycobacterium bovis BCG, the only licensed vaccine available, fails to confer lifelong protection and to prevent reactivation of latent infection. Although 15 new vaccine candidates are now in clinical trials, an effective vaccine against TB remains elusive, and new strategies for vaccination are vital. BCG vaccination fails to induce immunity against Mycobacterium tuberculosis latency antigens. Synthetic long peptides (SLPs) combined with adjuvants have been studied mostly for therapeutic cancer vaccines, yet not for TB, and proved to induce efficient antitumor immunity. This study investigated an SLP derived from Rv1733c, a major M. tuberculosis latency antigen which is highly expressed by "dormant" M. tuberculosis and well recognized by T cells from latently M. tuberculosis-infected individuals. In order to assess its in vivo immunogenicity and protective capacity, Rv1733c SLP in CpG was administered to HLA-DR3 transgenic mice. Immunization with Rv1733c SLP elicited gamma interferon-positive/tumor necrosis factor-positive (IFN-γ(+)/TNF(+)) and IFN-γ(+) CD4(+) T cells and Rv1733c-specific antibodies and led to a significant reduction in the bacterial load in the lungs of M. tuberculosis-challenged mice. This was observed both in a pre- and in a post-M. tuberculosis challenge setting. Moreover, Rv1733c SLP immunization significantly boosted the protective efficacy of BCG, demonstrating the potential of M. tuberculosis latency antigens to improve BCG efficacy. These data suggest a promising role for M. tuberculosis latency antigen Rv1733c-derived SLPs as a novel TB vaccine approach, both in a prophylactic and in a postinfection setting.