Chlamydia psittaci-Infected Dendritic Cells Communicate with NK Cells via Exosomes To Activate Antibacterial Immunity

Emerging role of extracellular vesicles in veterinary practice: novel opportunities and potential challenges

Extracellular vesicles are nanoscale vesicles that transport signals between cells, mediating both physiological and pathological processes. EVs facilitate conserved intercellular communication. By transferring bioactive molecules between cells, EVs coordinate systemic responses, regulating homeostasis, immunity, and disease progression. Given their biological importance and involvement in pathogenesis, EVs show promise as biomarkers for veterinary diagnosis, and candidates for vaccine production, and treatment agents. Additionally, different treatment or engineering methods could be used to boost the capability of extracellular vesicles. Despite the emerging veterinary interest, EV research has been predominantly human-based. Critical knowledge gaps remain regarding isolation protocols, cargo loading mechanisms, in vivo biodistribution, and species-specific functions. Standardized methods for veterinary EV characterization and validation are lacking. Regulatory uncertainties impede veterinary clinical translation. Advances in fundamental EV biology and technology are needed to propel the veterinary field forward. This review introduces EVs from a veterinary perspective by introducing the latest studies, highlighting their potential while analyzing challenges to motivate expanded veterinary investigation and translation.

Extracellular Vesicles and Infection: From Hijacked Machinery to Therapeutic Tools

Extracellular vesicles (EVs) comprise a broad range of secreted cell-derived membrane vesicles. Beyond their more well-characterized role in cell communication, in recent years, EVs have also been shown to play important roles during infection. Viruses can hijack the biogenesis of exosomes (which are small EVs) to promote viral spreading. Additionally, these exosomes are also important mediators in inflammation and immune responses during both bacterial and viral infections. This review summarizes these mechanisms while also describing the impact of bacterial EVs in regulating immune responses. Finally, the review also focuses on the potential and challenges of using EVs, in particular, to tackle infectious diseases.

The emerging roles of long non-coding RNA in host immune response and intracellular bacterial infections

The long non-coding RNAs (lncRNAs) are evolutionarily conserved classes of non-coding regulatory transcripts of > 200 nucleotides in length. They modulate several transcriptional and post-transcriptional events in the organism. Depending on their cellular localization and interactions, they regulate chromatin function and assembly; and alter the stability and translation of cytoplasmic mRNAs. Although their proposed range of functionality remains controversial, there is increasing research evidence that lncRNAs play a regulatory role in the activation, differentiation and development of immune signaling cascades; microbiome development; and in diseases such as neuronal and cardiovascular disorders; cancer; and pathogenic infections. This review discusses the functional roles of different lncRNAs in regulation of host immune responses, signaling pathways during host-microbe interaction and infection caused by obligate intracellular bacterial pathogens. The study of lncRNAs is assuming significance as it could be exploited for development of alternative therapeutic strategies for the treatment of severe and chronic pathogenic infections caused by Mycobacterium, Chlamydia and Rickettsia infections, as well as commensal colonization. Finally, this review summarizes the translational potential of lncRNA research in development of diagnostic and prognostic tools for human diseases.

Natural killer (NK) cell-derived extracellular-vesicle shuttled microRNAs control T cell responses

Natural killer (NK) cells recognise and kill target cells undergoing different types of stress. NK cells are also capable of modulating immune responses. In particular, they regulate T cell functions. Small RNA next-generation sequencing of resting and activated human NK cells and their secreted EVs led to the identification of a specific repertoire of NK-EV-associated microRNAs and their post-transcriptional modifications signature. Several microRNAs of NK-EVs, namely miR-10b-5p, miR-92a-3p and miR-155-5p, specifically target molecules involved in Th1 responses. NK-EVs promote the downregulation of GATA3 mRNA in CD4⁺ T cells and subsequent TBX21 de-repression that leads to Th1 polarization and IFN-γ and IL-2 production. NK-EVs also have an effect on monocyte and moDCs function, driving their activation and increased presentation and co-stimulatory functions. Nanoparticle-delivered NK-EV microRNAs partially recapitulate NK-EV effects in mice. Our results provide new insights on the immunomodulatory roles of NK-EVs that may help to improve their use as immunotherapeutic tools.

Immune Cell-Derived Extracellular Vesicles in the Face of Pathogenic Infections

Extracellular Vesicles (EVs) are a collection of vesicles released from cells that play an important role in intercellular communication. Microbial infections are known as one of the major problems in the medical field. Considering the increasing resistance of strains to routine drug treatments, the need for new therapies seems to be more than ever. Recent studies have shown that the EVs released from immune cells during microbial infections had anti-microbial effects or were able to induce neighbouring cells to display anti-microbial effects. This mini-review aimed to explore the latest studies on immune cell-derived EVs in viral, bacterial, fungal, and parasitic infections. Review of the literature demonstrated that specific cargos in EVs were involved in the fight against pathogenic infections. Additionally, the transport of appropriate bioactive molecules including miRNAs, mRNAs, and proteins via EVs could mediate the anti-microbial process. Thus, it could be a proof-of-principle that therapeutic approaches based on EVs derived from immune cells could offer a promising path forward, which is still in early stages and needs further assessments.

Exogenous and Endogenous Dendritic Cell-Derived Exosomes: Lessons Learned for Immunotherapy and Disease Pathogenesis

Immune therapeutic exosomes, derived exogenously from dendritic cells (DCs), the 'directors' of the immune response, are receiving favorable safety and tolerance profiles in phase I and II clinical trials for a growing number of inflammatory and neoplastic diseases. DC-derived exosomes (EXO), the focus of this review, can be custom tailored with immunoregulatory or immunostimulatory molecules for specific immune cell targeting. Moreover, the relative stability, small size and rapid uptake of EXO by recipient immune cells offer intriguing options for therapeutic purposes. This necessitates an in-depth understanding of mechanisms of EXO biogenesis, uptake and routing by recipient immune cells, as well as their in vivo biodistribution. Against this backdrop is recognition of endogenous exosomes, secreted by all cells, the molecular content of which is reflective of the metabolic state of these cells. In this regard, exosome biogenesis and secretion is regulated by cell stressors of chronic inflammation and tumorigenesis, including dysbiotic microbes, reactive oxygen species and DNA damage. Such cell stressors can promote premature senescence in young cells through the senescence associated secretory phenotype (SASP). Pathological exosomes of the SASP amplify inflammatory signaling in stressed cells in an autocrine fashion or promote inflammatory signaling to normal neighboring cells in paracrine, without the requirement of cell-to-cell contact. In summary, we review relevant lessons learned from the use of exogenous DC exosomes for immune therapy, as well as the pathogenic potential of endogenous DC exosomes.

Gift bags from the sentinel cells of the immune system: The diverse role of dendritic cell-derived extracellular vesicles

Dendritic cells (DCs) are professional APCs of the immune system that continuously sample their environment and function to stimulate an adaptive immune response by initiating Ag-specific immunity or tolerance. Extracellular vesicles (EVs), small membrane-bound structures, are released from DCs and have been discovered to harbor functional peptide-MHC complexes, T cell costimulatory molecules, and other molecules essential for Ag presentation, immune cell regulation, and stimulating immune responses. As such, DC-derived EVs are being explored as potential immunotherapeutic agents. DC-derived EVs have also been implicated to function as a trafficking mechanism of infectious particles aiding viral propagation. This review will explore the unique features that enable DC-derived EVs to regulate immune responses and interact with recipient cells, their roles within Ag-presentation and disease settings, as well as speculating on a potential immunological role of apoptotic DC-derived EVs.

Insights Into Host Cell Cytokines in Chlamydia Infection

Chlamydial infection causes a number of clinically relevant diseases and induces significant morbidity in humans. Immune and inflammatory responses contribute to both the clearance of Chlamydia infection and pathology in host tissues. Chlamydia infection stimulates host cells to produce a large number of cytokines that trigger and regulate host immune responses against Chlamydia. However, inappropriate responses can occur with excessive production of cytokines, resulting in overreactive inflammatory responses and alterations in host or Chlamydia metabolism. As a result, Chlamydia persists and causes wound healing delays, leading to more severe tissue damage and triggering long-lasting fibrotic sequelae. Here, we summarize the roles of cytokines in Chlamydia infection and pathogenesis, thus advancing our understanding chlamydial infection biology and the pathogenic mechanisms involved.

Cytokine response following perturbation of the cervicovaginal milieu during HPV genital infection

Human papillomaviruses (HPVs) are oncogenic viruses causing most cervical cancers. Highly prevalent in young, sexually active women, only a minority of HPV infections persist. To better characterize the immuno-modulatory impact of early HPV infections, we measured changes in a panel of 20 cytokines in cervicovaginal samples collected from young women who were tested for HPV and self-reported for genital inflammation and infection symptoms. Multi-factor statistical analyses revealed that increased IL-1Alpha and IL-12/IL-23p40 concentrations were associated with HPV infection and that macrophage inflammatory proteins were associated in particular with high-risk HPV infections. ClinicalTrials.gov identifier NCT02946346.

Exosomes derived from Fusobacterium nucleatum-infected colorectal cancer cells facilitate tumour metastasis by selectively carrying miR-1246/92b-3p/27a-3p and CXCL16

OBJECTIVE

Exosomes released from tumour cells are packed with unique RNA and protein cargo, and they are emerging as an important mediator in the communication network that promotes tumour progression. The facultative intracellular bacterium Fusobacterium nucleatum (Fn) is an important colorectal cancer (CRC)-associated bacterium. To date, the function of exosomes from Fn-infected CRC cells has not been explored.

DESIGN

Exosomes were isolated by sequential differential centrifugation and verified by transmission electron microscopy, NanoSight analysis and Western blotting. Given that exosomes have been shown to transport miRNAs and proteins to alter cellular functions, we performed miRNA sequencing and proteome analysis of exosomes from Fn-infected and non-infected cells. The biological role and mechanism of exosomes from Fn-infected cells in CRC tumour growth and liver metastasis were determined in vitro and in vivo.

RESULTS

We demonstrated that exosomes delivered miR-1246/92b-3p/27a-3p and CXCL16/RhoA/IL-8 from Fn-infected cells into non-infected cells to increase cell migration ability in vitro and promote tumour metastasis in vivo. Finally, both circulating exosomal miR-1246/92b-3p/27a-3p and CXCL16 levels were closely associated with Fn abundance and tumour stage in patients with CRC.

CONCLUSION

This study suggests that Fn infection may stimulate tumour cells to generate miR-1246/92b-3p/27a-3p-rich and CXCL16/RhoA/IL-8 exosomes that are delivered to uninfected cells to promote prometastatic behaviours.

[Inhibition of CD96 enhances interferon-γ secretion by natural killer cells to alleviate lung injury in mice with pulmonary Chlamydia muridarum infection]

OBJECTIVE

To assess the effect of neutralizing CD96 on natural killer (NK) cell functions in mice with pulmonary Chlamydia muridarum infection and explore the possible mechanism.

METHODS

Male BALB/c mice were randomly divided into infection group (Cm group), anti-CD96 treatment group (anti-CD96 group) and control group (n=5). In the former two groups, C. muridarum was inoculated via intranasal administration to establish mouse models of pulmonary C. muridarum infection, and the mice in the control group received intranasal administration of the inhalation buffer. In anti-CD96 group, the mice were injected with anti-CD96 antibody intraperitoneally at the dose of 250 μg every 3 days after the infection; the mice in Cm group received intraperitoneal injections of saline. The body weight of the mice was recorded daily. The mice were sacrificed 5 days after C. muridarum infection, and CD96 expression was detected by quantitative real-time PCR and Western blotting. HE staining and pathological scores were used to evaluate pneumonia of the mice. The inclusion body forming units (IFUs) were detected in the lung tissue homogenates to assess lung tissue chlamydia load. Flow cytometry and ELISA were used to assess the capacity of the lung NK cells to produce interferon-γ (IFN-γ) and regulate macrophages and Th1 cells.

RESULTS

C. muridarum infection inhibited CD96 expression in NK cells of the mice. Compared with those in Cm group, the mice in antiCD96 mice showed significantly milder lung inflammation (P < 0.05) and reduced chlamydia load in the lung tissue (P < 0.05). Neutralizing CD96 with anti-CD96 significantly enhanced IFN-γ secretion by the NK cells (P < 0.05) and augmented the immunoregulatory effect of the NK cells shown by enhanced responses of the lung macrophages (P < 0.05) and Th1 cells (P < 0.05).

CONCLUSIONS

Inhibition of CD96 alleviates pneumonia in C. muridarum-infected mice possibly by enhancing IFN-γ secretion by NK cells and augmenting the immunoregulatory effect of the NK cells on innate and adaptive immunity.

Development of a Plasmid Shuttle Vector System for Genetic Manipulation of Chlamydia psittaci

The obligate intracellular bacterium Chlamydia psittaci is a known avian pathogen causing psittacosis in birds and is capable of zoonotic transmission. In human pulmonary infections, C. psittaci can cause pneumonia associated with significant mortality if inadequately diagnosed and treated. Although intracellular C. psittaci manipulates host cell organelles for its replication and survival, it has been difficult to demonstrate host-pathogen interactions in C. psittaci infection due to the lack of easy-to-handle genetic manipulation tools. Here, we show the genetic transformation of C. psittaci using a plasmid shuttle vector that contains a controllable gene induction system. The 7,553-bp plasmid p01DC12 was prepared from the nonavian C. psittaci strain 01DC12. We constructed the shuttle vector pCps-Tet-mCherry using the full sequence of p01DC12 and the 4,449-bp fragment of Chlamydia trachomatis shuttle vector pBOMB4-Tet-mCherry. pCps-Tet-mCherry includes genes encoding the green fluorescent protein (GFP), mCherry, and ampicillin resistance (AmpR). Target genes can be inserted at a multiple cloning site (MCS). Importantly, these genes can be regulated by a tetracycline-inducible (tet) promoter. Using the pCps-Tet-mCherry plasmid shuttle vector, we show the expression of GFP, as well as the induction of mCherry expression, in C. psittaci strain 02DC15, which belongs to the avian C. psittaci 6BC clade. Furthermore, we demonstrated that pCps-Tet-mCherry was stably retained in C. psittaci transformants. Thus, our C. psittaci plasmid shuttle vector system represents a novel targeted approach that enables the elucidation of host-pathogen interactions.IMPORTANCE Psittacosis, caused by avian C. psittaci, has a major economic impact in the poultry industry worldwide and represents a significant risk for zoonotic transmission to humans. In the past decade, the tools of genetic manipulation have been improved for chlamydial molecular studies. While several genetic tools have been mainly developed in Chlamydia trachomatis, a stable gene-inducible shuttle vector system has not to date been available for C. psittaci In this study, we adapted a C. trachomatis plasmid shuttle vector system to C. psittaci We constructed a C. psittaci plasmid backbone shuttle vector called pCps-Tet-mCherry. The construct expresses GFP in C. psittaci Importantly, exogeneous genes can be inserted at an MCS and are regulated by a tet promoter. The application of the pCps-Tet-mCherry shuttle vector system enables a promising new approach to investigate unknown gene functions of this pathogen.

Production of IFN-γ by splenic dendritic cells during innate immune responses against Francisella tularensis LVS depends on MyD88, but not TLR2, TLR4, or TLR9

Production of IFN-γ is a key innate immune mechanism that limits replication of intracellular bacteria such as Francisella tularensis (Ft) until adaptive immune responses develop. Previously, we demonstrated that the host cell types responsible for IFN-γ production in response to murine Francisella infection include not only natural killer (NK) and T cells, but also a variety of myeloid cells. However, production of IFN-γ by mouse dendritic cells (DC) is controversial. Here, we directly demonstrated substantial production of IFN-γ by DC, as well as hybrid NK-DC, from LVS-infected wild type C57BL/6 or Rag1 knockout mice. We demonstrated that the numbers of conventional DC producing IFN-γ increased progressively over the course of 8 days of LVS infection. In contrast, the numbers of conventional NK cells producing IFN-γ, which represented about 40% of non-B/T IFN-γ-producing cells, peaked at day 4 after LVS infection and declined thereafter. This pattern was similar to that of hybrid NK-DC. To further confirm IFN-γ production by infected cells, DC and neutrophils were sorted from naïve and LVS-infected mice and analyzed for gene expression. Quantification of LVS by PCR revealed the presence of Ft DNA not only in macrophages, but also in highly purified, IFN-γ producing DC and neutrophils. Finally, production of IFN-γ by infected DC was confirmed by immunohistochemistry and confocal microscopy. Notably, IFN-γ production patterns similar to those in wild type mice were observed in cells derived from LVS-infected TLR2, TLR4, and TLR2xTLR9 knockout (KO) mice, but not from MyD88 KO mice. Taken together, these studies demonstrate the pivotal roles of DC and MyD88 in IFN-γ production and in initiating innate immune responses to this intracellular bacterium.

Role of bacterial infections in extracellular vesicles release and impact on immune response

Extracellular vesicle (EV) biology involves understanding the cellular and molecular mechanisms of cell communication. Studies conducted so far with various bacterial infection models demonstrate the release of various types of EVs that include exosomes and microvesicles. Depending upon the infection and cell type, EV cargo composition changes and ultimately might impact the host immune response and bacterial growth. The mechanisms behind the EVs release, cargo composition, and impact on the immune system have not been fully investigated. Future research needs to include in vivo models to understand the relevance of EVs in host immune function during bacterial infection, and to determine aspects that are shared or species-specific in the host. This would aid in the development of EVs as therapeutics or as markers of disease.