Elicitation of epithelial cell-derived immune effectors by outer membrane vesicles of nontypeable Haemophilus influenzae

Bacteria extracellular vesicle as nanopharmaceuticals for versatile biomedical potential

Bacteria extracellular vesicles (BEVs), characterized as the lipid bilayer membrane-surrounded nanoparticles filled with molecular cargo from parent cells, play fundamental roles in the bacteria growth and pathogenesis, as well as facilitating essential interaction between bacteria and host systems. Notably, benefiting from their unique biological functions, BEVs hold great promise as novel nanopharmaceuticals for diverse biomedical potential, attracting significant interest from both industry and academia. Typically, BEVs are evaluated as promising drug delivery platforms, on account of their intrinsic cell-targeting capability, ease of versatile cargo engineering, and capability to penetrate physiological barriers. Moreover, attributing to considerable intrinsic immunogenicity, BEVs are able to interact with the host immune system to boost immunotherapy as the novel nanovaccine against a wide range of diseases. Towards these significant directions, in this review, we elucidate the nature of BEVs and their role in activating host immune response for a better understanding of BEV-based nanopharmaceuticals' development. Additionally, we also systematically summarize recent advances in BEVs for achieving the target delivery of genetic material, therapeutic agents, and functional materials. Furthermore, vaccination strategies using BEVs are carefully covered, illustrating their flexible therapeutic potential in combating bacterial infections, viral infections, and cancer. Finally, the current hurdles and further outlook of these BEV-based nanopharmaceuticals will also be provided.

The Role of Bacterial Extracellular Vesicles in the Immune Response to Pathogens, and Therapeutic Opportunities

Pathogenic bacteria have several mechanisms to evade the host's immune response and achieve an efficient infection. Bacterial extracellular vesicles (EVs) are a relevant cellular communication mechanism, since they can interact with other bacterial cells and with host cells. In this review, we focus on the EVs produced by some World Health Organization (WHO) priority Gram-negative and Gram-positive pathogenic bacteria; by spore-producing bacteria; by Mycobacterium tuberculosis (a bacteria with a complex cell wall); and by Treponema pallidum (a bacteria without lipopolysaccharide). We describe the classification and the general properties of bacterial EVs, their role during bacterial infections and their effects on the host immune response. Bacterial EVs contain pathogen-associated molecular patterns that activate innate immune receptors, which leads to cytokine production and inflammation, but they also contain antigens that induce the activation of B and T cell responses. Understanding the many effects of bacterial EVs on the host's immune response can yield new insights on the pathogenesis of clinically important infections, but it can also lead to the development of EV-based diagnostic and therapeutic strategies. In addition, since EVs are efficient activators of both the innate and the adaptive immune responses, they constitute a promising platform for vaccine development.

The effect of site-specific recombinases XerCD on the removal of over-replicated chromosomal DNA through outer membrane vesicles in bacteria

Outer membrane vesicles (OMVs) are universally produced by Gram-negative bacteria and play important roles in symbiotic and pathogenic interactions. The DNA from the lumen of OMVs from the Alphaproteobacterium Dinoroseobacter shibae was previously shown to be enriched for the region around the terminus of replication ter and specifically for the recognition sequence dif of the two site-specific recombinases XerCD. These enzymes are highly conserved in bacteria and play an important role in the last phase of cell division. Here, we show that a similar enrichment of ter and dif is found in the DNA inside OMVs from Prochlorococcus marinus, Pseudomonas aeruginosa, Vibrio cholerae, and Escherichia coli. The deletion of xerC or xerD in E. coli reduced the enrichment peak directly at the dif sequence, while the enriched DNA region around ter became broader, demonstrating that either enzyme influences the DNA content inside the lumen of OMVs. We propose that the intra-vesicle DNA originated from over-replication repair and the XerCD enzymes might play a role in this process, providing them with a new function in addition to resolving chromosome dimers.IMPORTANCEImprecise termination of replication can lead to over-replicated parts of bacterial chromosomes that have to be excised and removed from the dividing cell. The underlying mechanism is poorly understood. Our data show that outer membrane vesicles (OMVs) from diverse Gram-negative bacteria are enriched for DNA around the terminus of replication ter and the site-specific XerCD recombinases influence this enrichment. Clearing the divisome from over-replicated parts of the bacterial chromosome might be a so far unrecognized and conserved function of OMVs.

Bacterial membrane vesicles in the pathogenesis and treatment of inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic and debilitating condition of relapsing and remitting inflammation in the gastrointestinal tract. Conventional therapeutic approaches for IBD have shown limited efficacy and detrimental side effects, leading to the quest for novel and effective treatment options for the disease. Bacterial membrane vesicles (MVs) are nanosized lipid particles secreted by lysis or blebbing processes from both Gram-negative and Gram-positive bacteria. These vesicles, known to carry bioactive components, are facsimiles of the parent bacterium and have been implicated in the onset and progression, as well as in the amelioration of IBD. This review discusses the overview of MVs and their impact in the pathogenesis, diagnosis, and treatment of IBD. We further discuss the technical challenges facing this research area and possible research questions addressing these challenges. We summarize recent advances in the diverse relationship between IBD and MVs, and the application of this knowledge as a viable and potent therapeutic strategy for IBD.

Screening for Genes Involved in Outer Membrane Vesicle Biogenesis in Bacteroides thetaiotaomicron

Bacteroides spp. are prominent gut commensals that are believed to modulate the intestinal environment, in part, by producing outer membrane vesicles (OMVs). Bacteroides OMVs have been ascribed many functions in vitro, but the genetic underpinnings behind OMV biogenesis and regulation are unclear. Understanding the mechanism of OMV biogenesis is required to determine the importance of Bacteroides OMVs in vivo. Here, we describe our methodology for screening Bacteroides thetaiotaomicron VPI-5482 to identify genes required for OMV biogenesis and regulation in a high-throughput format. This protocol is easily adaptable and can potentially be employed to further our knowledge of OMV biogenesis in other bacteria.

Bacterial Outer Membrane Vesicles: Role in Pathogenesis and Host-Cell Interactions

Outer membrane vesicles (OMVs) are small, spherical structures released from the outer membranes of Gram-negative bacteria into the surrounding environment. Investigations into OMVs range from their biogenesis and cargo composition to their ability to transfer virulence factors and modulate host immune responses. This emerging understanding of OMVs has unveiled their pivotal role in the pathogenicity of infectious diseases, shedding light on their interactions with host cells, their contributions to inflammation, their potential involvement in antimicrobial resistance, and their promising use for the development of novel treatments and therapies. Numerous studies have associated the OMVs of pathogenic bacteria with the exacerbation of inflammatory diseases, underlining the significance of understanding the mechanisms associated with these vesicles to find alternatives for combating these conditions. Additionally, OMVs possess the ability to act as decoys, absorbing and neutralizing antibiotics, which significantly diminishes the efficacy of a broad spectrum of antimicrobial agents. Another subtopic of interest is OMVs produced by commensal microbiota. These vesicles are increasingly acknowledged for their mutualistic functions, significantly influencing their host's physiology and immune responses. Consequently, OMVs play a crucial role in maintaining a balanced gut microbiota by fostering symbiotic relationships that significantly contribute to the overall health and well-being of the host. This comprehensive review aims to provide an up-to-date review of OMVs derived from Gram-negative bacteria, summarizing current research findings, and elucidating the multifaceted role of these vesicles in diverse biological contexts.

Extracellular vesicles as a novel mediator of interkingdom communication

Extracellular vesicles (EVs) are nanosized lipid bilayer-delimited particles secreted from almost all types of cells including bacteria, mammals and plants, and are presumed to be mediators of intercellular communication. Bacterial extracellular vesicles (BEVs) are nanoparticles with diverse diameters, ranging from 20 to 400 nm. BEVs are composed of soluble microbial metabolites, including nucleic acid, proteins, lipoglycans, and short-chain fatty acids (SCFAs). In addition, EVs may contain quorum sensing peptides that are endowed with the ability to protect bacteria against bacteriophages, form and maintain bacterial communities, and modulate the host immune system. BEVs are potentially promising therapeutic modalities for use in vaccine development, cancer immunotherapy regimens, and drug delivery cargos. Plant-derived EVs (PEVs), such as EVs derived from herbal medicines, can be absorbed by the gut microbiota and influence the composition and homeostasis of gut microbiota. This review highlights the roles of BEVs and PEVs in bacterial and plant physiology and discusses crosstalk among gut bacteria, host metabolism and herbal medicine. In summary, EVs represent crucial communication messengers in the gut microbiota, with potential therapeutic value in the delivery of herbal medicines.

Bacterial Membrane Vesicles: Physiological Roles, Infection Immunology, and Applications

Bacterial or fungal membrane vesicles, traditionally considered as microbial metabolic wastes, are secreted mainly from the outer membrane or cell membrane of microorganisms. However, recent studies have shown that these vesicles play essential roles in direct or indirect communications among microorganisms and between microorganisms and hosts. This review aims to provide an updated understanding of the physiological functions and emerging applications of bacterial membrane vesicles, with a focus on their biogenesis, mechanisms of adsorption and invasion into host cells, immune stimulatory effects, and roles in the much-concerned problem of bacterial resistance. Additionally, the potential applications of these vesicles as biomarkers, vaccine candidates, and drug delivery platforms are discussed.

Aerosolization inhalation of non-typeable Haemophilus influenzae outer membrane vesicles contributing to neutrophilic asthma

Background

Neutrophilic asthma is poorly responsive to corticosteroids, and the mechanism underlying its pathogenesis remains unclear. Non-typeable Haemophilus influenzae (NTHi) is the most common bacterium found in induced sputum from patients with neutrophilic asthma. NTHi can release outer membrane vesicles (OMVs), which transfer biomolecules to host cells and the external environment. However, the role and mechanisms of NTHi OMVs in the pathogenesis of neutrophilic asthma remain unclear.

Methods

We conducted assays to investigate whether NTHi OMVs can induce neutrophilic asthma when inhaled. We isolated and purified NTHi OMVs and administered them via a nebulizer to ovalbumin (OVA)-sensitized mice. We collected and sequenced serum, blood, bronchoalveolar lavage fluid, and lung tissue from each group and gathered lung function data.

Results

Inhaled NTHi OMVs-induced neutrophilic asthma in OVA-sensitized mice. High-throughput sequencing revealed that NTHi OMV inhalation in OVA-sensitized mice significantly enriched inflammatory and immune-related signaling pathways. We found increased transcription and secretion of interleukin (IL)-1β and IL-17, which may contribute to neutrophilic asthma. Furthermore, we discovered that airway epithelium is the first receptor cell of NTHi OMVs and releases IL-1β. These findings suggest that NTHi OMVs could be a potential target for neutrophilic asthma therapy.

Correlation between bacterial extracellular vesicles and antibiotics: A potentially antibacterial strategy

Bacterial extracellular vesicles (BEVs) are proteoliposome nanoparticles that are secreted by both Gram-negative (G^-) and Gram-positive (G⁺) bacteria. BEVs have significant roles in various physiological processes of bacteria, including driving inflammatory responses, regulating bacterial pathogenesis, and promoting bacterial survival in diverse environments. Recently, there has been increasing interest in the use of BEVs as a potential solution to antibiotic resistance. BEVs have shown great promise as a new approach to antibiotics, as well as a drug-delivery tool in antimicrobial strategies. In this review, we provide a summary of recent scientific advances in BEVs and antibiotics, including BEV biogenesis, ability to kill bacteria, potential for delivering antibiotics, and their role in the development of vaccines or as immune adjuvants. We propose that BEVs provide a novel antimicrobial strategy that would be beneficial against the increasing threat of antibiotic resistance.

A Robust Protocol to Isolate Outer Membrane Vesicles from Nontypeable Haemophilus influenzae

Outer membrane vesicles (OMVs) are lipid structures containing various biomolecules in their native environment and are spontaneously shed by gram-negative bacteria. OMVs perform several biological functions critical to both bacterial physiology and pathogenicity. Scientific research on OMV function and biogenesis requires a standardized and robust method of isolating these vesicles from bacterial cultures that reliably provide high-purity OMVs. Herein, we describe an optimized protocol to isolate OMVs from overnight cultures of three different strains of nontypeable Haemophilus influenzae (NTHi) for use in different downstream applications. Involving mainly differential centrifugation of the culture supernatant, the procedure described is relatively simple, efficient, and generates high-quality OMV preparations from each strain tested with sufficient yields, while preserving the native outer membrane composition.

Outer Membrane Vesicles: Biogenesis, Functions, and Issues

This review focuses on nonlytic outer membrane vesicles (OMVs), a subtype of bacterial extracellular vesicles (BEVs) produced by Gram-negative organisms focusing on the mechanisms of their biogenesis, cargo, and function. Throughout, we highlight issues concerning the characterization of OMVs and distinguishing them from other types of BEVs. We also highlight the shortcomings of commonly used methodologies for the study of BEVs that impact the interpretation of their functionality and suggest solutions to standardize protocols for OMV studies.

Involvement of Bacterial Extracellular Membrane Nanovesicles in Infectious Diseases and Their Application in Medicine

Bacterial extracellular membrane nanovesicles (EMNs) are attracting the attention of scientists more and more every year. These formations are involved in the pathogenesis of numerous diseases, among which, of course, the leading role is occupied by infectious diseases, the causative agents of which are a range of Gram-positive and Gram-negative bacteria. A separate field for the study of the role of EMN is cancer. Extracellular membrane nanovesicles nowadays have a practical application as vaccine carriers for immunization against many infectious diseases. At present, the most essential point is their role in stimulating immune response to bacterial infections and tumor cells. The possibility of nanovesicles' practical use in several disease treatments is being evaluated. In our review, we listed diseases, focusing on their multitude and diversity, for which EMNs are essential, and also considered in detail the possibilities of using EMNs in the therapy and prevention of various pathologies.

Protein domain-dependent vesiculation of Lipoprotein A, a protein that is important in cell wall synthesis and fitness of the human respiratory pathogen Haemophilus influenzae

The human pathogen Haemophilus influenzae causes respiratory tract infections and is commonly associated with prolonged carriage in patients with chronic obstructive pulmonary disease. Production of outer membrane vesicles (OMVs) is a ubiquitous phenomenon observed in Gram-negative bacteria including H. influenzae. OMVs play an important role in various interactions with the human host; from neutralization of antibodies and complement activation to spread of antimicrobial resistance. Upon vesiculation certain proteins are found in OMVs and some proteins are retained at the cell membrane. The mechanism for this phenomenon is not fully elucidated. We employed mass spectrometry to study vesiculation and the fate of proteins in the outer membrane. Functional groups of proteins were differentially distributed on the cell surface and in OMVs. Despite its supposedly periplasmic and outer membrane location, we found that the peptidoglycan synthase-activator Lipoprotein A (LpoA) was accumulated in OMVs relative to membrane fractions. A mutant devoid of LpoA lost its fitness as revealed by growth and electron microscopy. Furthermore, high-pressure liquid chromatography disclosed a lower concentration (55%) of peptidoglycan in the LpoA-deficient H. influenzae compared to the parent wild type bacterium. Using an LpoA-mNeonGreen fusion protein and fluorescence microscopy, we observed that LpoA was enriched in “foci” in the cell envelope, and further located in the septum during cell division. To define the fate of LpoA, C-terminally truncated LpoA-variants were constructed, and we found that the LpoA C-terminal domain promoted optimal transportation to the OMVs as revealed by flow cytometry. Taken together, our study highlights the importance of LpoA for H. influenzae peptidoglycan biogenesis and provides novel insights into cell wall integrity and OMV production.

Bacterial outer membrane vesicles as a candidate tumor vaccine platform

Cancer represents a serious concern for human life and health. Due to drug resistance and the easy metastasis of tumors, there is urgent need to develop new cancer treatment methods beyond the traditional radiotherapy, chemotherapy, and surgery. Bacterial outer membrane vesicles (OMVs) are a type of double-membrane vesicle secreted by Gram-negative bacteria in the process of growth and life, and play extremely important roles in the survival and invasion of those bacteria. In particular, OMVs contain a large number of immunogenic components associated with their parent bacterium, which can be used as vaccines, adjuvants, and vectors to treat diseases, especially in presenting tumor antigens or targeted therapy with small-molecule drugs. Some OMV-based vaccines are already on the market and have demonstrated good therapeutic effect on the corresponding diseases. OMV-based vaccines for cancer are also being studied, and some are already in clinical trials. This paper reviews bacterial outer membrane vesicles, their interaction with host cells, and their applications in tumor vaccines.

Outer membrane vesicles as biomimetic vaccine carriers against infections and cancers

In the last decade, nanoparticle-based therapeutic modalities have emerged as promising treatment options for cancer and infectious diseases. To improve prognosis, chemotherapeutic and antimicrobial drugs must be delivered selectively to the target sites. Researchers have increasingly focused their efforts on improving drug delivery, with a particular emphasis on cancer and infectious diseases. When drugs are administered systemically, they become diluted and can diffuse to all tissues but only until the immune system intervenes and quickly removes them from circulation. To enhance and prolong the systemic circulation of drugs, nanocarriers have been explored and used; however, nanocarriers have a major drawback in that they can trigger immune responses. Numerous nanocarriers for optimal drug delivery have been developed using innovative and effective biointerface technologies. Autologous cell-derived drug carriers, such as outer membrane vesicles (OMVs), have demonstrated improved bioavailability and reduced toxicity. Thus, this study investigates the use of biomimetic OMVs as biomimetic vaccine carriers against infections and cancers to improve our understanding in the field of nanotechnology. In addition, discussion on the advantages, disadvantages, and future prospects of OMVs will also be explored. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.

Emerging Roles of Extracellular Vesicles in Pneumococcal Infections: Immunomodulators to Potential Novel Vaccine Candidates

The Gram-positive bacterial pathogen, Streptococcus pneumoniae is a major global health threat that kills over one million people worldwide. The pneumococcus commonly colonizes the nasopharynx asymptomatically as a commensal, but is also capable of causing a wide range of life-threatening diseases such as pneumonia, meningitis and septicemia upon migration into the lower respiratory tract and spread to internal organs. Emergence of antibiotic resistant strains and non-vaccine serotypes has led to the classification of pneumococcal bacteria as a priority pathogen by the World Health Organization that needs urgent research into bacterial pathogenesis and development of novel vaccine strategies. Extracellular vesicles are spherical membrane bound structures that are released by both pathogen and host cells, and influence bacterial pathogenesis as well as the immune response. Recent studies have found that while bacterial vesicles shuttle virulence factors and toxins into host cells and regulate inflammatory responses, vesicles released from the infected host cells contain both bacterial and host proteins that are antigenic and immunomodulatory. Bacterial membrane vesicles have great potential to be developed as cell-free vaccine candidates in the future due to their immunogenicity and biostability. Host-derived vesicles isolated from patient biofluids such as blood and bronchoalveolar lavage could be used to identify potential diagnostic biomarkers as well as engineered to deliver desired payloads to specific target cells for immunotherapy. In this review, we summarize the recent developments on the role of bacterial and host vesicles in pneumococcal infections and future prospects in developing novel therapeutics and diagnostics for control of invasive pneumococcal diseases.

The Role of Extracellular Vesicles as a Shared Disease Mechanism Contributing to Multimorbidity in Patients With COPD

Chronic obstructive pulmonary disease (COPD) is one of the leading causes of death worldwide. Individuals with COPD typically experience a progressive, debilitating decline in lung function as well as systemic manifestations of the disease. Multimorbidity, is common in COPD patients and increases the risk of hospitalisation and mortality. Central to the genesis of multimorbidity in COPD patients is a self-perpetuating, abnormal immune and inflammatory response driven by factors including ageing, pollutant inhalation (including smoking) and infection. As many patients with COPD have multiple concurrent chronic conditions, which require an integrative management approach, there is a need to greater understand the shared disease mechanisms contributing to multimorbidity. The intercellular transfer of extracellular vesicles (EVs) has recently been proposed as an important method of local and distal cell-to-cell communication mediating both homeostatic and pathological conditions. EVs have been identified in many biological fluids and provide a stable capsule for the transfer of cargo including proteins, lipids and nucleic acids. Of these cargo, microRNAs (miRNAs), which are short 17-24 nucleotide non-coding RNA molecules, have been amongst the most extensively studied. There is evidence to support that miRNA are selectively packaged into EVs and can regulate recipient cell gene expression including major pathways involved in inflammation, apoptosis and fibrosis. Furthermore changes in EV cargo including miRNA have been reported in many chronic diseases and in response to risk factors including respiratory infections, noxious stimuli and ageing. In this review, we discuss the potential of EVs and EV-associated miRNA to modulate shared pathological processes in chronic diseases. Further delineating these may lead to the identification of novel biomarkers and therapeutic targets for patients with COPD and multimorbidities.

Application of Stem Cell-Derived Extracellular Vesicles as an Innovative Theranostics in Microbial Diseases

Extracellular vesicles (EVs), as nano-/micro-scale vehicles, are membranous particles containing various cargoes including peptides, proteins, different types of RNAs and other nucleic acids, and lipids. These vesicles are produced by all cell types, in which stem cells are a potent source for them. Stem cell-derived EVs could be promising platforms for treatment of infectious diseases and early diagnosis. Infectious diseases are responsible for more than 11 million deaths annually. Highly transmissible nature of some microbes, such as newly emerged severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), drives researcher's interest to set up different strategies to develop novel therapeutic strategies. Recently, EVs-based diagnostic and therapeutic approaches have been launched and gaining momentum very fast. The efficiency of stem cell-derived EVs on treatment of clinical complications of different viruses and bacteria, such as SARS-CoV-2, hepatitis B virus (HBV), hepatitis C virus (HCV), human immunodeficiency virus (HIV), Staphylococcus aureus, Escherichia coli has been demonstrated. On the other hand, microbial pathogens are able to incorporate their components into their EVs. The microbe-derived EVs have different physiological and pathological impacts on the other organisms. In this review, we briefly discussed biogenesis and the fate of EVs. Then, EV-based therapy was described and recent developments in understanding the potential application of stem cell-derived EVs on pathogenic microorganisms were recapitulated. Furthermore, the mechanisms by which EVs were exploited to fight against infectious diseases were highlighted. Finally, the deriver challenges in translation of stem cell-derived EVs into the clinical arena were explored.

Bacterial membrane vesicle functions, laboratory methods, and applications

Bacterial membrane vesicles are cupped-shaped structures formed by bacteria in response to environmental stress, genetic alteration, antibiotic exposure, and others. Due to the structural similarities shared with the producer organism, they can retain certain characteristics like stimulating immune responses. They are also able to carry molecules for long distances, without changes in the concentration and integrity of the molecule. Bacteria originally secrete membrane vesicles for gene transfer, excretion, cell to cell interaction, pathogenesis, and protection against phages. These functions are unique and have several innovative applications in the pharmaceutical industry that have attracted both scientific and commercial interest.This led to the development of efficient methods to artificially stimulate vesicle production, purification, and manipulation in the lab at nanoscales. Also, for specific applications, engineering methods to impart pathogen antigens against specific diseases or customization as cargo vehicles to deliver payloads to specific cells have been reported. Many applications of bacteria membrane vesicles are in cancer drugs, vaccines, and adjuvant development with several candidates in clinical trials showing promising results. Despite this, applications in therapy and commercialization stay timid probably due to some challenges one of which is the poor understanding of biogenesis mechanisms. Nevertheless, so far, bacterial membrane vesicles seem to be a reliable and cost-efficient technology with several therapeutic applications. Research toward characterizing more membrane vesicles, genetic engineering, and nanotechnology will enable the scope of applications to widen. This might include solutions to other currently faced medical and healthcare-related challenges.

The clinical role of host and bacterial-derived extracellular vesicles in pneumonia

Pneumonia is among the leading causes of morbidity and mortality worldwide. Due to constant evolution of respiratory bacteria and viruses, development of drug resistance and emerging pathogens, it constitutes a considerable health care threat. To enable development of novel strategies to control pneumonia, a better understanding of the complex mechanisms of interaction between host cells and infecting pathogens is vital. Here, we review the roles of host cell and bacterial-derived extracellular vesicles (EVs) in these interactions. We discuss clinical and experimental as well as pathogen-overarching and pathogen-specific evidence for common viral and bacterial elicitors of community- and hospital-acquired pneumonia. Finally, we highlight the potential of EVs for improved management of pneumonia patients and discuss the translational steps to be taken before they can be safely exploited as novel vaccines, biomarkers, or therapeutics in clinical practice.

The Role of Non-Typeable Haemophilus influenzae Biofilms in Chronic Obstructive Pulmonary Disease

Non-typeable Haemophilus influenzae (NTHi) is an ubiquitous commensal-turned-pathogen that colonises the respiratory mucosa in airways diseases including Chronic Obstructive Pulmonary Disease (COPD). COPD is a progressive inflammatory syndrome of the lungs, encompassing chronic bronchitis that is characterised by mucus hypersecretion and impaired mucociliary clearance and creates a static, protective, humid, and nutrient-rich environment, with dysregulated mucosal immunity; a favourable environment for NTHi colonisation. Several recent large COPD cohort studies have reported NTHi as a significant and recurrent aetiological pathogen in acute exacerbations of COPD. NTHi proliferation has been associated with increased hospitalisation, disease severity, morbidity and significant lung microbiome shifts. However, some cohorts with patients at different severities of COPD do not report that NTHi is a significant aetiological pathogen in their COPD patients, indicating other obligate pathogens including Moraxella catarrhalis, Streptococcus pneumoniae and Pseudomonas aeruginosa as the cause. NTHi is an ubiquitous organism across healthy non-smokers, healthy smokers and COPD patients from childhood to adulthood, but it currently remains unclear why NTHi becomes pathogenic in only some cohorts of COPD patients, and what behaviours, interactions and adaptations are driving this susceptibility. There is emerging evidence that biofilm-phase NTHi may play a significant role in COPD. NTHi displays many hallmarks of the biofilm lifestyle and expresses key biofilm formation-promoting genes. These include the autoinducer-mediated quorum sensing system, epithelial- and mucus-binding adhesins and expression of a protective, self-produced polymeric substance matrix. These NTHi biofilms exhibit extreme tolerance to antimicrobial treatments and the immune system as well as expressing synergistic interspecific interactions with other lung pathogens including S. pneumoniae and M. catarrhalis. Whilst the majority of our understanding surrounding NTHi as a biofilm arises from otitis media or in-vitro bacterial monoculture models, the role of NTHi biofilms in the COPD lung is now being studied. This review explores the evidence for the existence of NTHi biofilms and their impact in the COPD lung. Understanding the nature of chronic and recurrent NTHi infections in acute exacerbations of COPD could have important implications for clinical treatment and identification of novel bactericidal targets.

Extracellular Vesicles and Host-Pathogen Interactions: A Review of Inter-Kingdom Signaling by Small Noncoding RNA

The focus of this brief review is to describe the role of noncoding regulatory RNAs, including short RNAs (sRNA), transfer RNA (tRNA) fragments and microRNAs (miRNA) secreted in extracellular vesicles (EVs), in inter-kingdom communication between bacteria and mammalian (human) host cells. Bacteria secrete vesicles that contain noncoding regulatory RNAs, and recent studies have shown that the bacterial vesicles fuse with and deliver regulatory RNAs to host cells, and similar to eukaryotic miRNAs, regulatory RNAs modulate the host immune response to infection. Recent studies have also demonstrated that mammalian cells secrete EVs containing miRNAs that regulate the gut microbiome, biofilm formation and the bacterial response to antibiotics. Thus, as evidence accumulates it is becoming clear that the secretion of noncoding regulatory RNAs and miRNAs in extracellular vesicles is an important mechanism of bidirectional communication between bacteria and mammalian (human) host cells. However, additional research is necessary to elucidate how noncoding regulatory RNAs and miRNA secreted in extracellular vesicles mediate inter-kingdom communication.

The complex, bidirectional role of extracellular vesicles in infection

Cells from all domains of life release extracellular vesicles (EVs), packages that carry a cargo of molecules that participate in communication, co-ordination of population behaviours, virulence and immune response mechanisms. Mammalian EVs play an increasingly recognised role to fight infection, yet may also be commandeered to disseminate pathogens and enhance infection. EVs released by bacterial pathogens may deliver toxins to host cells, signalling molecules and new DNA to other bacteria, and act as decoys, protecting infecting bacteria from immune killing. In this review, we explore the role of EVs in infection from the perspective of both the pathogen and host, and highlight their importance in the host/pathogen relationship. We highlight proposed strategies for EVs in therapeutics, and call attention to areas where existing knowledge and evidence is lacking.

Bacterial Extracellular Vesicles and the Gut-Microbiota Brain Axis: Emerging Roles in Communication and Potential as Therapeutics

Bacterial extracellular vesicles (BEVs) have emerged as candidate signaling vectors for long-distance interkingdom communication within the gut-microbiota brain axis. Most bacteria release these nanosized vesicles, capable of signaling to the brain via their abundant protein and small RNA cargo, possibly directly via crossing the blood-brain barrier. BEVs have been shown to regulate brain gene expression and induce pathology at most stages of neuroinflammation and neurodegeneration, and thus they may play a causal role in diseases such as Alzheimer's, Parkinson's, and depression/anxiety. On the other hand, BEVs have intrinsic therapeutic properties that may be relevant to probiotic therapy and can also be engineered to function as drug delivery vehicles and vaccines. Thus, BEVs may be both a cause of and solution to neuropathological conditions. In this review, current knowledge of the physiological roles of BEVs as well as state of the art pertaining to the development of therapeutic BEVs in the context of the microbiome-gut-brain axis are summarized.

Sphingolipid-Containing Outer Membrane Vesicles Serve as a Delivery Vehicle To Limit Macrophage Immune Response to Porphyromonas gingivalis

Sphingolipids (SLs) are essential structural components of mammalian cell membranes. Our group recently determined that the oral anaerobe Porphyromonas gingivalis delivers its SLs to host cells and that the ability of P. gingivalis to synthesize SLs limits the elicited host inflammatory response during cellular infection.

Sphingolipids (SLs) are essential structural components of mammalian cell membranes. Our group recently determined that the oral anaerobe Porphyromonas gingivalis delivers its SLs to host cells and that the ability of P. gingivalis to synthesize SLs limits the elicited host inflammatory response during cellular infection. As P. gingivalis robustly produces outer membrane vesicles (OMVs), we hypothesized that OMVs serve as a delivery vehicle for SLs, that the SL status of the OMVs may impact cargo loading to OMVs, and that SL-containing OMVs limit elicited host inflammation similar to that observed by direct bacterial challenge. Transwell cell culture experiments determined that in comparison to the parent strain W83, the SL-null mutant elicited a hyperinflammatory immune response from THP-1 macrophage-like cells with elevated tumor necrosis factor alpha (TNF-α), interleukin 1β (IL-1β), and IL-6. Targeted assessment of Toll-like receptors (TLRs) identified elevated expression of TLR2, unchanged TLR4, and elevated expression of the adaptor molecules MyD88 and TRIF (Toll/IL-1 receptor domain-containing adaptor-inducing beta interferon) by SL-null P. gingivalis. No significant differences in gingipain activity were observed in our infection models, and both strains produced OMVs of similar sizes. Using comparative two-dimensional gel electrophoresis, we identified differences in the protein cargo of the OMVs between parent and SL-null strain. Importantly, use of purified OMVs recapitulated the cellular inflammatory response observed in the transwell system with whole bacteria. These findings provide new insights into the role of SLs in P. gingivalis OMV cargo assembly and expand our understanding of SL-OMVs as bacterial structures that modulate the host inflammatory response.

Immunomodulatory roles and novel applications of bacterial membrane vesicles

Bacteria release extracellular vesicles (EVs) known as bacterial membrane vesicles (BMVs) during their normal growth. Gram-negative bacteria produce BMVs termed outer membrane vesicles (OMVs) that are composed of a range of biological cargo and facilitate numerous bacterial functions, including promoting pathogenesis and mediating disease in the host. By contrast, less is understood about BMVs produced by Gram-positive bacteria, which are referred to as membrane vesicles (MVs), however their contribution to mediating bacterial pathogenesis has recently become evident. In this review, we summarise the mechanisms whereby BMVs released by Gram-negative and Gram-positive bacteria are produced, in addition to discussing their key functions in promoting bacterial survival, mediating pathogenesis and modulating host immune responses. Furthermore, we discuss the mechanisms whereby BMVs produced by both commensal and pathogenic organisms can enter host cells and interact with innate immune receptors, in addition to how they modulate host innate and adaptive immunity to promote immunotolerance or drive the onset and progression of disease. Finally, we highlight current and emerging applications of BMVs in vaccine design, biotechnology and cancer therapeutics.

Evaluation of immunological responses against outer membrane vesicles (OMV) of nontypeable Haemophilus influenzae using MPLA-CpG adjuvant as a vaccine candidate

Background and Objectives

Nontypeable Haemophilus influenzae (NTHi) are major causes of non-invasive infections, including otitis media and sinusitis and it can also contribute to respiratory infections of all ages. Currently, there is no licensed vaccine against NTHi commercially available. Many studies have been conducted on the use of OMV as a vaccine against NTHi. The purpose of this study is to achieve an immunogenic vaccine against NTHi.

Materials and Methods

In this study, standard OMV Haemophilus (ATCC49766) with adjuncts CpG and MPLA was used and after infusion into BALB/c mice, the levels of antibodies and cytokines were measured on serum of immunized mice.

Results

The results showed that total IgG antibody and IgG1 and IgG2a isotypes in OMV immunized mice with mixture of CpG-MPLA adjuvant had a significant increase. Also, the results of cytokines (IL-10, IL-4 and IFN-γ) showed that IL-4 had the highest rate.

Conclusion

These findings indicate that OMVs derived from NTHi strains have a high potential to act as a vaccine against NTHi infections.

Detection of Bacterial Membrane Vesicles by NOD-Like Receptors

Bacterial membrane vesicles (BMVs) are nanoparticles produced by both Gram-negative and Gram-positive bacteria that can function to modulate immunity in the host. Both outer membrane vesicles (OMVs) and membrane vesicles (MVs), which are released by Gram-negative and Gram-positive bacteria, respectively, contain cargo derived from their parent bacterium, including immune stimulating molecules such as proteins, lipids and nucleic acids. Of these, peptidoglycan (PG) and lipopolysaccharide (LPS) are able to activate host innate immune pattern recognition receptors (PRRs), known as NOD-like receptors (NLRs), such as nucleotide-binding oligomerisation domain-containing protein (NOD) 1, NOD2 and NLRP3. NLR activation is a key driver of inflammation in the host, and BMVs derived from both pathogenic and commensal bacteria have been shown to package PG and LPS in order to modulate the host immune response using NLR-dependent mechanisms. Here, we discuss the packaging of immunostimulatory cargo within OMVs and MVs, their detection by NLRs and the cytokines produced by host cells in response to their detection. Additionally, commensal derived BMVs are thought to shape immunity and contribute to homeostasis in the gut, therefore we also highlight the interactions of commensal derived BMVs with NLRs and their roles in limiting inflammatory diseases.

Caveolae as Potential Hijackable Gates in Cell Communication

Caveolae are membrane microdomains described in many cell types involved in endocytocis, transcytosis, cell signaling, mechanotransduction, and aging. They are found at the interface with the extracellular environment and are structured by caveolin and cavin proteins. Caveolae and caveolins mediate transduction of chemical messages via signaling pathways, as well as non-chemical messages, such as stretching or shear stress. Various pathogens or signals can hijack these gates, leading to infectious, oncogenic and even caveolin-related diseases named caveolinopathies. By contrast, preclinical and clinical research have fallen behind in their attempts to hijack caveolae and caveolins for therapeutic purposes. Caveolae involvement in human disease is not yet fully explored or understood and, of all their scaffold proteins, only caveolin-1 is being considered in clinical trials as a possible biomarker of disease. This review briefly summarizes current knowledge about caveolae cell signaling and raises the hypothesis whether these microdomains could serve as hijackable “gatekeepers” or “gateways” in cell communication. Furthermore, because cell signaling is one of the most dynamic domains in translating data from basic to clinical research, we pay special attention to translation of caveolae, caveolin, and cavin research into clinical practice.

Host-microbe cross-talk in the lung microenvironment: implications for understanding and treating chronic lung disease

Chronic respiratory diseases are highly prevalent worldwide and will continue to rise in the foreseeable future. Despite intensive efforts over recent decades, the development of novel and effective therapeutic approaches has been slow. However, there is new and increasing evidence that communities of micro-organisms in our body, the human microbiome, are crucially involved in the development and progression of chronic respiratory diseases. Understanding the detailed mechanisms underlying this cross-talk between host and microbiota is critical for development of microbiome- or host-targeted therapeutics and prevention strategies. Here we review and discuss the most recent knowledge on the continuous reciprocal interaction between the host and microbes in health and respiratory disease. Furthermore, we highlight promising developments in microbiome-based therapies and discuss the need to employ more holistic approaches of restoring both the pulmonary niche and the microbial community.

The reciprocal interaction between microbes and host in the lung is increasingly recognised as an important determinant of health. The complexity of this cross-talk needs to be taken into account when studying diseases and developing future new therapies.https://bit.ly/2VKYUfT

Data on proteomic profiling of extracellular vesicles of Acholeplasma laidlawii strains with increased resistance to antibiotics of different classes - ciprofloxacin and tetracycline

To elucidate the regularities of adaptation of the representatives of class Mollicutes to antimicrobials and to identify the promising targets for eradication of mycoplasma infections and contaminations the comparative analysis of the molecular basis of bacterial resistance to antibiotics of different classes is needed. Previously, we presented the data on the whole-genome sequences of Acholeplasma laidlawii strains with different susceptibility to ciprofloxacin (GenBank: LXYB00000000.1), tetracycline (GenBank: NELO00000000.2) and melittin (GenBank: NELN00000000.2) as well as the data on cell and extracellular vesicle proteomes of melittin-resistant A. laidlawii strain [1]. The lists of extracellular vesicle proteins secreted by A. laidlawii strains with the increased resistance to ciprofloxacin (PG8R₁₀) and tetracycline (PG8R_Tet) are presented here. The vesicle proteome profiles were obtained by 1D SDS-PAGE and liquid chromatography-mass spectrometry.

Outer Membrane Lipid Secretion and the Innate Immune Response to Gram-Negative Bacteria

The outer membrane (OM) of Gram-negative bacteria is an asymmetric lipid bilayer that consists of inner leaflet phospholipids and outer leaflet lipopolysaccharides (LPS). The asymmetric character and unique biochemistry of LPS molecules contribute to the OM's ability to function as a molecular permeability barrier that protects the bacterium against hazards in the environment. Assembly and regulation of the OM have been extensively studied for understanding mechanisms of antibiotic resistance and bacterial defense against host immunity; however, there is little knowledge on how Gram-negative bacteria release their OMs into their environment to manipulate their hosts. Discoveries in bacterial lipid trafficking, OM lipid homeostasis, and host recognition of microbial patterns have shed new light on how microbes secrete OM vesicles (OMVs) to influence inflammation, cell death, and disease pathogenesis. Pathogens release OMVs that contain phospholipids, like cardiolipins, and components of LPS molecules, like lipid A endotoxins. These multiacylated lipid amphiphiles are molecular patterns that are differentially detected by host receptors like the Toll-like receptor 4/myeloid differentiation factor 2 complex (TLR4/MD-2), mouse caspase-11, and human caspases 4 and 5. We discuss how lipid ligands on OMVs engage these pattern recognition receptors on the membranes and in the cytosol of mammalian cells. We then detail how bacteria regulate OM lipid asymmetry, negative membrane curvature, and the phospholipid-to-LPS ratio to control OMV formation. The goal is to highlight intersections between OM lipid regulation and host immunity and to provide working models for how bacterial lipids influence vesicle formation.

The Contribution of Membrane Vesicles to Bacterial Pathogenicity in Cystic Fibrosis Infections and Healthcare Associated Pneumonia

Almost all bacteria secrete spherical membranous nanoparticles, also referred to as membrane vesicles (MVs). A variety of MV types exist, ranging from 20 to 400 nm in diameter, each with their own formation routes. The most well-known vesicles are the outer membrane vesicles (OMVs) which are formed by budding from the outer membrane in Gram-negative bacteria. Recently, other types of MVs have been discovered and described, including outer-inner membrane vesicles (OIMVs) and cytoplasmic membrane vesicles (CMVs). The former are mainly formed by a process termed endolysin-triggered cell lysis in Gram-negative bacteria, the latter are formed by Gram-positive bacteria. MVs carry a wide range of cargo, such as nucleic acids, virulence factors and antibiotic resistance components. Moreover, they are involved in a multitude of biological processes that increase bacterial pathogenicity. In this review, we discuss the functional aspects of MVs secreted by bacteria associated with cystic fibrosis and nosocomial pneumonia. We mainly focus on how MVs are involved in virulence, antibiotic resistance, biofilm development and inflammation that consequently aid these bacterial infections.

Bacterial Membrane Vesicles as Mediators of Microbe - Microbe and Microbe - Host Community Interactions

Bacterial membrane vesicles are proteoliposomal nanoparticles produced by both Gram-negative and Gram-positive bacteria. As they originate from the outer surface of the bacteria, their composition and content is generally similar to the parent bacterium’s membrane and cytoplasm. However, there is ample evidence that preferential packaging of proteins, metabolites, and toxins into vesicles does occur. Incorporation into vesicles imparts a number of benefits to the cargo, including protection from degradation by other bacteria, the host organism, or environmental factors, maintenance of a favorable microenvironment for enzymatic activity, and increased potential for long-distance movement. This enables vesicles to serve specialized functions tailored to changing or challenging environments, particularly in regard to microbial community interactions including quorum sensing, biofilm formation, antibiotic resistance, antimicrobial peptide expression and deployment, and nutrient acquisition. Additionally, based on their contents, vesicles play crucial roles in host-microbe interactions as carriers of virulence factors and other modulators of host cell function. Here, we discuss recent advances in our understanding of how vesicles function as signals both within microbial communities and between pathogenic or commensal microbes and their mammalian hosts. We also highlight a few areas that are currently ripe for additional research, including the mechanisms of selective cargo packaging into membrane vesicles and of cargo processing once it enters mammalian host cells, the function of vesicles in transfer of nucleic acids among bacteria, and the possibility of engineering commensal bacteria to deliver cargo of interest to mammalian hosts in a controlled manner.

Metabolic analyses reveal common adaptations in two invasive Haemophilus influenzae strains

Non-typeable Haemophilus influenzae (NTHi) is a major pathogen in upper and lower respiratory tract infections in humans, and is increasingly also associated with invasive disease. We have examined two unrelated NTHi invasive disease isolates, R2866 and C188, in order to identify metabolic and physiological properties that distinguish them from respiratory tract disease isolates such as Hi2019. While the general use of the Hi metabolic network was similar across all three strains, the two invasive isolates secreted increased amounts of succinate, which can have anti-inflammatory properties. In addition, they showed a common shift in their carbon source utilization patterns, with strongly enhanced metabolism of nucleoside substrates, glucose and sialic acid. The latter two are major compounds present in blood and cerebrospinal fluid (CSF). Interestingly, C188 and R2866 also shared a reduced ability to invade or survive intracellularly in 16HBE14 bronchial epithelial cells relative to Hi2019 (4-fold (4 h), 25-fold (24 h) reduction). Altered metabolic properties, such as the ones observed here, could arise from genomic adaptations that NTHi undergo during infection. Together these data indicate that shifts in substrate preferences in otherwise conserved metabolic pathways may underlie strain niche specificity and thus have the potential to alter the outcomes of host-NTHi interactions.

Detection and Quantification of eDNA-Associated Bacterial Membrane Vesicles by Flow Cytometry

Bacteria generate membrane vesicles, which are structures known as extracellular vesicles (EVs), reported to be involved in different pathogenic mechanisms, as it has been demonstrated that EVs participate in biofilm formation, cell-to-cell communication, bacteria–host interactions, and nutrients supply. EVs deliver nucleic acids, proteins, and polysaccharides. It has been reported that Helicobacter pylori (H. pylori) and Lactobacillus reuteri (L. reuteri), of both planktonic and biofilm phenotypes, produce EVs carrying extracellular DNA (eDNA). Here, we used polychromatic flow cytometry (PFC) to identify, enumerate, and characterize EVs as well as the eDNA-delivering EV compartment in the biofilm and planktonic phenotypes of H.pylori ATCC 43629 and L. reuteri DSM 17938. Biofilm formation was demonstrated and analyzed by fluorescence microscopy, using a classical live/dead staining protocol. The enumeration of EVs and the detection of eDNA-associated EVs were performed by PFC, analyzing both whole samples (cells plus vesicles) and EVs isolated by ultracentrifugation confirm EVs isolated by ultracentrifugation. PFC analysis was performed relying on a known-size beaded system and a mix of three different fluorescent tracers. In detail, the whole EV compartment was stained by a lipophilic cationic dye (LCD), which was combined to PKH26 and PicoGreen that selectively stain lipids and DNA, respectively. Fluorescence microscopy results displayed that both H. pylori and L. reuteri produced well-structured biofilms. PFC data highlighted that, in both detected bacterial species, biofilms produced higher EVs counts when paralleled to the related planktonic phenotypes. Furthermore, the staining with PicoGreen showed that most of the generated vesicles were associated with eDNA. These data suggest that the use of PFC, set according to the parameters here described, allows for the study of the production of eDNA-associated EVs in different microbial species in the same or several phases of growth, thus opening new perspectives in the study of microbial derived EVs in clinical samples.

The Diverse Functional Roles of Elongation Factor Tu (EF-Tu) in Microbial Pathogenesis

Elongation factor thermal unstable Tu (EF-Tu) is a G protein that catalyzes the binding of aminoacyl-tRNA to the A-site of the ribosome inside living cells. Structural and biochemical studies have described the complex interactions needed to effect canonical function. However, EF-Tu has evolved the capacity to execute diverse functions on the extracellular surface of both eukaryote and prokaryote cells. EF-Tu can traffic to, and is retained on, cell surfaces where can interact with membrane receptors and with extracellular matrix on the surface of plant and animal cells. Our structural studies indicate that short linear motifs (SLiMs) in surface exposed, non-conserved regions of the molecule may play a key role in the moonlighting functions ascribed to this ancient, highly abundant protein. Here we explore the diverse moonlighting functions relating to pathogenesis of EF-Tu in bacteria and examine putative SLiMs on surface-exposed regions of the molecule.

Natural and engineered bacterial outer membrane vesicles

Bacterial outer membrane vesicle (OMV) is a kind of spherical lipid bilayer nanostructure naturally secreted by bacteria, which has diverse functions such as intracellular and extracellular communication, horizontal gene transfer, transfer of contents to host cells, and eliciting an immune response in host cells. In this review, several methods including ultracentrifugation and precipitation for isolating OMVs were summarized. The latest progresses of OMVs in biomedical fields, especially in vaccine development, cancer treatment, infection control, and bioimaging and detection were also summarized in this review. We highlighted the importance of genetic engineering for the safe and effective application and in facilitating the rapid development of OMVs. Finally, we discussed the bottleneck problems about OMVs in preparation and application at present and put forward our own suggestions about them. Some perspectives of OMVs in biomedical field were also provided.

Design of Outer Membrane Vesicles as Cancer Vaccines: A New Toolkit for Cancer Therapy

Cancer vaccines have been extensively studied in recent years and have contributed to exceptional achievements in cancer treatment. They are some of the most newly developed vaccines, although only two are currently approved for use, Provenge and Talimogene laherparepvec (T-VEC). Despite the approval of these two vaccines, most vaccines have been terminated at the clinical trial stage, which indicates that although they are effective in theory, concerns still exist, including low antigenicity of targeting antigens and tumor heterogeneity. In recent years, with new understanding of the biological function and vaccine potential of outer membrane vesicles (OMVs), their potential application in cancer vaccine design deserves our attention. Therefore, this review focuses on the mechanisms, advantages, and prospects of OMVs as antigen-carrier vaccines in cancer vaccine development. We believe that OMV-based vaccines present a safe and effective cancer therapeutic option with broad application prospects.

The Contribution of Geogenic Particulate Matter to Lung Disease in Indigenous Children

Indigenous children have much higher rates of ear and lung disease than non-Indigenous children, which may be related to exposure to high levels of geogenic (earth-derived) particulate matter (PM). The aim of this study was to assess the relationship between dust levels and health in Indigenous children in Western Australia (W.A.). Data were from a population-based sample of 1077 Indigenous children living in 66 remote communities of W.A. (>2,000,000 km²), with information on health outcomes derived from carer reports and hospitalisation records. Associations between dust levels and health outcomes were assessed by multivariate logistic regression in a multi-level framework. We assessed the effect of exposure to community sampled PM on epithelial cell (NuLi-1) responses to non-typeable Haemophilus influenzae (NTHi) in vitro. High dust levels were associated with increased odds of hospitalisation for upper (OR 1.77 95% CI [1.02–3.06]) and lower (OR 1.99 95% CI [1.08–3.68]) respiratory tract infections and ear disease (OR 3.06 95% CI [1.20–7.80]). Exposure to PM enhanced NTHi adhesion and invasion of epithelial cells and impaired IL-8 production. Exposure to geogenic PM may be contributing to the poor respiratory health of disadvantaged communities in arid environments where geogenic PM levels are high.

Bacterial Outer Membrane Vesicles Induce Vitronectin Release Into the Bronchoalveolar Space Conferring Protection From Complement-Mediated Killing

Pathogens causing pneumonia utilize the complement regulator vitronectin to evade complement-mediated killing. Although vitronectin is associated with several chronic lung diseases, the role of bronchoalveolar vitronectin in pneumonia has not been studied. This study sought to reveal the involvement of vitronectin in the bronchoalveolar space during pneumonia, to assess the effect of outer membrane vesicles and endotoxin on vitronectin release, and to determine whether bacterial pathogens utilize pulmonary vitronectin for evasion. Vitronectin was analyzed in cell-free bronchoalveolar lavage fluid harvested from patients with pneumonia (n = 8) and from healthy volunteers after subsegmental endotoxin instillation (n = 13). Vitronectin binding by Pseudomonas aeruginosa and Haemophilus influenzae was analyzed, and subsequent complement evasion was assessed by serum challenge. The effects of outer membrane vesicles on vitronectin production in mouse lungs and human type II alveolar epithelial cells (A549) were determined. We detected increased vitronectin concentrations in lavage fluid during pneumonia (p = 0.0063) and after bronchial endotoxin challenge (p = 0.016). The capture of vitronectin by bacteria significantly reduced complement-mediated lysis. Following challenge with vesicles, vitronectin was detected in mouse bronchoalveolar space, and mouse alveolar epithelial cells in vivo as well as A549 cells in vitro contained increased levels of vitronectin. Taken together, outer membrane vesicles and endotoxin from Gram-negative bacteria induce vitronectin, which is released into the bronchoalveolar space, and used for evasion of complement-mediated clearance.

Association of Vibrio cholerae 569B outer membrane vesicles with host cells occurs in a GM1-independent manner

The primary virulence factor of Vibrio cholerae, cholera toxin (CT), initiates a pathway in epithelial cells that leads to the severe diarrhoea characteristic of cholera. Secreted CT binds to GM1 on the surface of host cells to facilitate internalisation. Many bacterial toxins, including CT, have been shown to be additionally delivered via outer membrane vesicles (OMVs). A fraction of the closely related heat labile toxin produced by enterotoxigenic Escherichia coli has been demonstrated to reside on the surface of OMVs, where it binds GM1 to facilitate OMV internalisation by host cells. In this work, we investigated whether OMV-associated CT is likewise trafficked to host cells in a GM1-dependent mechanism. We demonstrated that a majority of CT is secreted in its OMV-associated form and is located exclusively inside the vesicle. Therefore, the toxin is unable to bind GM1 on the host cell surface, and the OMVs are trafficked to the host cells in a GM1-independent mechanism. These findings point to a secondary, noncompeting mechanism for secretion and delivery of CT, beyond its well-studied secretion via a Type II secretion system and underscore the importance of focusing future studies on understanding this GM1-independent delivery mechanism to fully understand Vibrio cholerae pathogenesis.

Drivers of persistent infection: pathogen-induced extracellular vesicles

Extracellular vesicles (EVs) are produced by invading pathogens and also by host cells in response to infection. The origin, composition, and function of EVs made during infection are diverse and provide effective vehicles for localized and broad dissimilation of effector molecules in the infected host. Extracellular pathogens use EVs to communicate with each other by sensing the host environment contributing to social motility, tissue tropism, and persistence of infection. Pathogen-derived EVs can also interact with host cells to influence the adhesive properties of host membranes and to alter immune recognition and response. Intracellular pathogens can affect both the protein and RNA content of EVs produced by infected host cells. Release of pathogen-induced host EVs can affect host immune responses to infection. In this review, we will describe both the biogenesis and content of EVs produced by a number of diverse pathogens. In addition, we will examine the pathogen-induced changes to EVs produced by infected host cells.

Bacterial outer membrane vesicles: New insights and applications

Outer membrane vesicles (OMVs) (∼50-250 nm in diameter) are produced by both pathogenic and nonpathogenic bacteria as a canonical end product of secretion. In this review, we focus on the OMVs produced by gram-negative bacteria. We provide an overview of the OMV structure, various factors regulating their production, and their role in modulating host immune response using a few representative examples. In light of the importance of the diverse cargoes carried by OMVs, we discuss the different modes of their entry into the host cell and advances in the high-throughput detection of these OMVs. A conspicuous application of OMVs lies in the field of vaccination; we discuss its success in immunization against human diseases such as pertussis, meningitis, shigellosis and aqua-farming endangering diseases like edwardsiellosis.

Highlights of the São Paulo ISEV workshop on extracellular vesicles in cross-kingdom communication

In the past years, extracellular vesicles (EVs) have become an important field of research since EVs have been found to play a central role in biological processes. In pathogens, EVs are involved in several events during the host–pathogen interaction, including invasion, immunomodulation, and pathology as well as parasite–parasite communication. In this report, we summarised the role of EVs in infections caused by viruses, bacteria, fungi, protozoa, and helminths based on the talks and discussions carried out during the International Society for Extracellular Vesicles (ISEV) workshop held in São Paulo (November, 2016), Brazil, entitled Cross-organism Communication by Extracellular Vesicles: Hosts, Microbes and Parasites.

Immunomodulatory role for membrane vesicles released by THP-1 macrophages and respiratory pathogens during macrophage infection

Background

During infection, inflammation is partially driven by the release of mediators which facilitate intercellular communication. Amongst these mediators are small membrane vesicles (MVs) that can be released by both host cells and Gram-negative and -positive bacteria. Bacterial membrane vesicles are known to exert immuno-modulatory and -stimulatory actions. Moreover, it has been proposed that host cell-derived vesicles, released during infection, also have immunostimulatory properties. In this study, we assessed the release and activity of host cell-derived and bacterial MVs during the first hours following infection of THP-1 macrophages with the common respiratory pathogens non-typeable Haemophilus influenzae, Moraxella catarrhalis, Streptococcus pneumoniae, and Pseudomonas aeruginosa.

Results

Using a combination of flow cytometry, tunable resistive pulse sensing (TRPS)-based analysis and electron microscopy, we demonstrated that the release of MVs occurs by both host cells and bacteria during infection. MVs released during infection and bacterial culture were found to induce a strong pro-inflammatory response by naive THP-1 macrophages. Yet, these MVs were also found to induce tolerance of host cells to secondary immunogenic stimuli and to enhance bacterial adherence and the number of intracellular bacteria.

Conclusions

Bacterial MVs may play a dual role during infection, as they can both trigger and dampen immune responses thereby contributing to immune defence and bacterial survival.

Immunogenicity of Nontypeable Haemophilus influenzae Outer Membrane Vesicles and Protective Ability in the Chinchilla Model of Otitis Media

Outer membrane vesicles (OMVs) produced by Gram-negative bacteria are enriched in several outer membrane components, including major and minor outer membrane proteins and lipooligosaccharide. We assessed the functional activity of nontypeable Haemophilus influenzae (NTHi) OMV-specific antisera and the protective ability of NTHi OMVs as vaccine antigens in the chinchilla otitis media model. OMVs were purified from three HMW1/HMW2-expressing NTHi strains, two of which were also engineered to overexpress Hia proteins. OMV-specific antisera raised in guinea pigs were assessed for their ability to mediate killing of representative NTHi in an opsonophagocytic assay. The three OMV-specific antisera mediated killing of 18 of 65, 24 of 65, and 30 of 65 unrelated HMW1/HMW2-expressing NTHi strains. Overall, they mediated killing of 39 of 65 HMW1/HMW2-expressing strains. The two Hia-expressing OMV-specific antisera mediated killing of 17 of 25 and 14 of 25 unrelated Hia-expressing NTHi strains. Overall, they mediated killing of 20 of 25 Hia-expressing strains. OMVs from prototype NTHi strain 12 were used to immunize chinchillas and the course of middle ear infection was monitored following intrabullar challenge with the homologous strain. All control animals developed culture-positive otitis media, as did two of three HMW1/HMW2-immunized animals. All OMV-immunized animals, with or without supplemental HMW1/HMW2 immunization, were completely protected against otitis media. NTHi OMVs are the first immunogens examined in this model that provided complete protection with sterile immunity after NTHi strain 12 challenge. These data suggest that NTHi OMVs hold significant potential as components of protective NTHi vaccines, possibly in combination with HMW1/HMW2 proteins.

Outer Membrane Vesicles Prime and Activate Macrophage Inflammasomes and Cytokine Secretion In Vitro and In Vivo

Outer membrane vesicles (OMVs) are proteoliposomes blebbed from the surface of Gram-negative bacteria. Chronic periodontitis is associated with an increase in subgingival plaque of Gram-negative bacteria, Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia. In this study, we investigated the immune-modulatory effects of P. gingivalis, T. denticola, and T. forsythia OMVs on monocytes and differentiated macrophages. All of the bacterial OMVs were phagocytosed by monocytes, M(naïve) and M(IFNγ) macrophages in a dose-dependent manner. They also induced NF-κB activation and increased TNFα, IL-8, and IL-1β cytokine secretion. P. gingivalis OMVs were also found to induce anti-inflammatory IL-10 secretion. Although unprimed monocytes and macrophages were resistant to OMV-induced cell death, lipopolysaccharide or OMV priming resulted in a significantly reduced cell viability. P. gingivalis, T. denticola, and T. forsythia OMVs all activated inflammasome complexes, as monitored by IL-1β secretion and ASC speck formation. ASC was critical for OMV-induced inflammasome formation, while AIM2-/- and Caspase-1-/- cells had significantly reduced inflammasome formation and NLRP3-/- cells exhibited a slight reduction. OMVs were also found to provide both priming and activation of the inflammasome complex. High-resolution microscopy and flow cytometry showed that P. gingivalis OMVs primed and activated macrophage inflammasomes in vivo with 80% of macrophages exhibiting inflammasome complex formation. In conclusion, periodontal pathogen OMVs were found to have significant immunomodulatory effects upon monocytes and macrophages and should therefore influence pro-inflammatory host responses associated with disease.