Dengue virus selectively induces human mast cell chemokine production

The SARS-CoV-2 antibody-dependent enhancement façade

Antibody-dependent enhancement (ADE) is an immunological paradox whereby sensitization following a primary viral infection results in the subsequent enhancement of a similar secondary infection. This idiosyncratic immune response has been established in dengue virus infections, driven by four antigenically related serotypes co-circulating in endemic regions. Several coronaviruses exhibit antibody-mediated mechanisms of viral entry, which has led to speculation of an ADE capacity for SARS-CoV-2, though in vivo and epidemiological evidence do not currently support this phenomenon. Three distinct antibody-dependent mechanisms for SARS-CoV-2 entry have recently been demonstrated: 1. FcR-dependent, 2. ACE2-FcR-interdependent, and 3. FcR-independent. These mechanisms of viral entry may be dependent on SARS-CoV-2 antibody specificity; antibodies targeting the receptor binding domain (RBD) typically result in Fc-dependent and ACE2-FcR-interdependent entry, whereas antibodies targeting the N-terminal domain can induce a conformational change to the RBD that optimizes ACE2-receptor binding domain interactions independent of Fc receptors. Whether these antibody-dependent entry mechanisms of SARS-CoV-2 result in the generation of infectious progenies and enhancement of infection has not been robustly demonstrated. Furthermore, ADE of SARS-CoV-2 mediated by antigenic seniority remains a theoretical concern, as no evidence suggests that SARS-CoV-2 imprinting blunts a subsequent immune response, contributing to severe COVID-19 disease.

Mast Cells and Basophils in Major Viral Diseases: What Are the Correlations with SARS-CoV-2, Influenza A Viruses, HIV, and Dengue?

The SARS-CoV-2 pandemic has significantly impacted global health and has led the population and the scientific community to live in fear of a future pandemic. Based on viral infectious diseases, innate immunity cells such as mast cells and basophils play a fundamental role in the pathogenesis of viral diseases. Understanding these mechanisms could be essential to better study practical therapeutic approaches not only to COVID-19 but also to other viral infections widely spread worldwide, such as influenza A, HIV, and dengue. In this literature review, we want to study these concepts. Mast cells and basophils intervene as a bridge between innate and acquired immunity and seem to have a role in the damage mechanisms during infection and in the stimulation of humoral and cellular immunity. In some cases, these cells can act as reservoirs and favor the replication and spread of the virus in the body. Understanding these mechanisms can be useful not only in therapeutic but also in diagnostic and prognostic perspectives. The prospects of applying artificial intelligence and machine learning algorithms for the creation of very accurate diagnostic/prognostic tools are interesting.

The Dynamic Relationship between Dengue Virus and the Human Cutaneous Innate Immune Response

Dengue virus (DENV) is a continuing global threat that puts half of the world's population at risk for infection. This mosquito-transmitted virus is endemic in over 100 countries. When a mosquito takes a bloodmeal, virus is deposited into the epidermal and dermal layers of human skin, infecting a variety of permissive cells, including keratinocytes, Langerhans cells, macrophages, dermal dendritic cells, fibroblasts, and mast cells. In response to infection, the skin deploys an array of defense mechanisms to inhibit viral replication and prevent dissemination. Antimicrobial peptides, pattern recognition receptors, and cytokines induce a signaling cascade to increase transcription and translation of pro-inflammatory and antiviral genes. Paradoxically, this inflammatory environment recruits skin-resident mononuclear cells that become infected and migrate out of the skin, spreading virus throughout the host. The details of the viral-host interactions in the cutaneous microenvironment remain unclear, partly due to the limited body of research focusing on DENV in human skin. This review will summarize the functional role of human skin, the cutaneous innate immune response to DENV, the contribution of the arthropod vector, and the models used to study DENV interactions in the cutaneous environment.

Dengue Vaccination: Towards a New Dawn of Curbing Dengue Infection

Dengue is an infectious disease caused by dengue virus (DENV) and is a serious global burden. Antibody-dependent enhancement and the ability of DENV to infect immune cells, along with other factors, lead to fatal Dengue Haemorrhagic Fever and Dengue Shock Syndrome. This necessitates the development of a robust and efficient vaccine but vaccine development faces a number of hurdles. In this review, we look at the epidemiology, genome structure and cellular targets of DENV and elaborate upon the immune responses generated by human immune system against DENV infection. The review further sheds light on various challenges in development of a potent vaccine against DENV which is followed by presenting a current account of different vaccines which are being developed or have been licensed.

Vitamin D Influences the Activity of Mast Cells in Allergic Manifestations and Potentiates Their Effector Functions against Pathogens

Mast cells (MCs) are abundant at sites exposed to the external environment and pathogens. Local activation of these cells, either directly via pathogen recognition or indirectly via interaction with other activated immune cells and results in the release of pre-stored mediators in MC granules. The release of these pre-stored mediators helps to enhance pathogen clearance. While MCs are well known for their protective role against parasites, there is also significant evidence in the literature demonstrating their ability to respond to viral, bacterial, and fungal infections. Vitamin D is a fat-soluble vitamin and hormone that plays a vital role in regulating calcium and phosphorus metabolism to maintain skeletal homeostasis. Emerging evidence suggests that vitamin D also has immunomodulatory properties on both the innate and adaptive immune systems, making it a critical regulator of immune homeostasis. Vitamin D binds to its receptor, called the vitamin D receptor (VDR), which is present in almost all immune system cells. The literature suggests that a vitamin D deficiency can activate MCs, and vitamin D is necessary for MC stabilization. This manuscript explores the potential of vitamin D to regulate MC activity and combat pathogens, with a focus on its ability to fight viruses.

High Heme and Low Heme Oxygenase-1 Are Associated with Mast Cell Activation/Degranulation in HIV-Induced Chronic Widespread Pain

An overwhelming number of people with HIV (PWH) experience chronic widespread pain (CWP) throughout their lifetimes. Previously, we demonstrated that PWH with CWP have increased hemolysis and attenuated heme oxygenase 1 (HO-1) levels. HO-1 degrades reactive, cell-free heme into antioxidants like biliverdin and carbon monoxide (CO). We found that high heme or low HO-1 caused hyperalgesia in animals, likely through multiple mechanisms. In this study, we hypothesized that high heme or low HO-1 caused mast cell activation/degranulation, resulting in the release of pain mediators like histamine and bradykinin. PWH who self-report CWP were recruited from the University of Alabama at Birmingham HIV clinic. Animal models included HO-1-/- mice and hemolytic mice, where C57BL/6 mice were injected intraperitoneally with phenylhydrazine hydrochloride (PHZ). Results demonstrated that plasma histamine and bradykinin were elevated in PWH with CWP. These pain mediators were also high in HO-1-/- mice and in hemolytic mice. Both in vivo and in vitro (RBL-2H3 mast cells), heme-induced mast cell degranulation was inhibited by treatment with CORM-A1, a CO donor. CORM-A1 also attenuated mechanical and thermal (cold) allodynia in hemolytic mice. Together, the data suggest that mast cell activation secondary to high heme or low HO-1 seen in cells and animals correlates with elevated plasma levels of heme, histamine, and bradykinin in PWH with CWP.

Zika Virus Replication in a Mast Cell Model is Augmented by Dengue Virus Antibody-Dependent Enhancement and Features a Selective Immune Mediator Secretory Profile

Antibodies generated against one dengue serotype can enhance infection of another by a phenomenon called antibody-dependent enhancement (ADE). Additionally, antigenic similarities between Zika and dengue viruses can promote Zika virus infection by way of ADE in vitro using these very same anti-dengue antibodies.

Cytosolic Sensing of Intracellular Staphylococcus aureus by Mast Cells Elicits a Type I IFN Response That Enhances Cell-Autonomous Immunity

Strategically located at mucosal sites, mast cells are instrumental in sensing invading pathogens and modulating the quality of the ensuing immune responses depending on the nature of the infecting microbe. It is believed that mast cells produce type I IFN (IFN-I) in response to viruses, but not to bacterial infections, because of the incapacity of bacterial pathogens to internalize within mast cells, where signaling cascades leading to IFN-I production are generated. However, we have previously reported that, in contrast with other bacterial pathogens, Staphylococcus aureus can internalize into mast cells and therefore could trigger a unique response. In this study, we have investigated the molecular cross-talk between internalized S. aureus and the human mast cells HMC-1 using a dual RNA sequencing approach. We found that a proportion of internalized S. aureus underwent profound transcriptional reprogramming within HMC-1 cells to adapt to the nutrients and stress encountered in the intracellular environment and remained viable. HMC-1 cells, in turn, recognized intracellular S. aureus via cGMP-AMP synthase-STING-TANK-binding kinase 1 signaling pathway, leading to the production of IFN-I. Bacterial internalization and viability were crucial for IFN-I induction because inhibition of S. aureus internalization or infection with heat-killed bacteria completely prevented the production of IFN-I by HMC-1 cells. Feeding back in an autocrine manner in S. aureus-harboring HMC-1 cells and in a paracrine manner in noninfected neighboring HMC-1 cells, IFN-I promoted a cell-autonomous antimicrobial state by inducing the transcription of IFN-I-stimulated genes. This study provides unprecedented evidence of the capacity of mast cells to produce IFN-I in response to a bacterial pathogen.

Mast cells: Therapeutic targets for COVID-19 and beyond

Mast cells (MCs) are innate immune cells that widely distribute throughout all tissues and express a variety of cell surface receptors. Upon activation, MCs can rapidly release a diverse array of preformed mediators residing within their secretory granules and newly synthesize a broad spectrum of inflammatory and immunomodulatory mediators. These unique features of MCs enable them to act as sentinels in response to rapid changes within their microenvironment. There is increasing evidence now that MCs play prominent roles in other pathophysiological processes besides allergic inflammation. In this review, we highlight the recent findings on the emerging roles of MCs in the pathogenesis of coronavirus disease-2019 (COVID-19) and discuss the potential of MCs as novel therapeutic targets for COVID-19 and other non-allergic inflammatory diseases.

Basophils and Mast Cells in COVID-19 Pathogenesis

Basophils and mast cells are among the principal inducers of Th2 responses and have a crucial role in allergic and anti-parasitic protective immunity. Basophils can function as antigen-presenting cells that bind antigens on their surface and boost humoral immune responses, inducing Th2 cell differentiation. Their depletion results in lower humoral memory activation and greater infection susceptibility. Basophils seem to have an active role upon immune response to SARS-CoV-2. In fact, a coordinate adaptive immune response to SARS-CoV-2 is magnified by basophils. It has been observed that basophil amount is lower during acute disease with respect to the recovery phase and that the grade of this depletion is an important determinant of the antibody response to the virus. Moreover, mast cells, present in a great quantity in the nasal epithelial and lung cells, participate in the first immune response to SARS-CoV-2. Their activation results in a hyperinflammatory syndrome through the release of inflammatory molecules, participating to the "cytokine storm" and, in a longer period, inducing pulmonary fibrosis. The literature data suggest that basophil counts may be a useful prognostic tool for COVID-19, since their reduction is associated with a worse prognosis. Mast cells, on the other hand, represent a possible therapeutic target for reducing the airway inflammation characteristic of the hyperacute phase of the disease.

Mast Cell Modulation of B Cell Responses: An Under-Appreciated Partnership in Host Defence

Mast cells are well known to be activated via cross-linking of immunoglobulins bound to surface receptors. They are also recognized as key initiators and regulators of both innate and adaptive immune responses against pathogens, especially in the skin and mucosal surfaces. Substantial attention has been given to the role of mast cells in regulating T cell function either directly or indirectly through actions on dendritic cells. In contrast, the ability of mast cells to modify B cell responses has been less explored. Several lines of evidence suggest that mast cells can greatly modify B cell generation and activities. Mast cells co-localise with B cells in many tissue settings and produce substantial amounts of cytokines, such as IL-6, with profound impacts on B cell development, class-switch recombination events, and subsequent antibody production. Mast cells have also been suggested to modulate the development and functions of regulatory B cells. In this review, we discuss the critical impacts of mast cells on B cells using information from both clinical and laboratory studies and consider the implications of these findings on the host response to infections.

Responses of Mast Cells to Pathogens: Beneficial and Detrimental Roles

Mast cells (MCs) are strategically located in tissues close to the external environment, being one of the first immune cells to interact with invading pathogens. They are long living effector cells equipped with different receptors that allow microbial recognition. Once activated, MCs release numerous biologically active mediators in the site of pathogen contact, which induce vascular endothelium modification, inflammation development and extracellular matrix remodeling. Efficient and direct antimicrobial mechanisms of MCs involve phagocytosis with oxidative and non-oxidative microbial destruction, extracellular trap formation, and the release of antimicrobial substances. MCs also contribute to host defense through the attraction and activation of phagocytic and inflammatory cells, shaping the innate and adaptive immune responses. However, as part of their response to pathogens and under an impaired, sustained, or systemic activation, MCs may contribute to tissue damage. This review will focus on the current knowledge about direct and indirect contribution of MCs to pathogen clearance. Antimicrobial mechanisms of MCs are addressed with special attention to signaling pathways involved and molecular weapons implicated. The role of MCs in a dysregulated host response that can increase morbidity and mortality is also reviewed and discussed, highlighting the complexity of MCs biology in the context of host-pathogen interactions.

Mast Cells Modulate Antigen-Specific CD8+ T Cell Activation During LCMV Infection

Mast cells (MCs), strategically localized at mucosal surfaces, provide first-line defense against pathogens and shape innate and adaptive immune responses. Recent studies have shown that MCs are involved in pathogenic responses to several viruses including herpes simplex viruses, dengue virus, vaccinia virus and influenza virus. However, the underlying mechanisms of MCs in the activation of CD8+ T cells during viral infections are not fully understood. Therefore, we investigate the role of MCs in the development of virus-specific CD8+ T cell responses using the well-characterized murine lymphocytic choriomeningitis virus (LCMV) model and the transgenic MasTRECK mice that contain the human diphtheria toxin receptor as an inducible MC-deficient model. Here, we report that MCs are essential for the activation and expansion of virus-specific CD8+ T cells. After MC depletion and subsequent intradermal LCMV infection, the CD8 + T cell effector phenotype and antiviral cytokine production were impaired at the peak of infection (day 8 p.i.). Importantly, MC-deficient mice were unable to control the infection and exhibited significantly higher viral loads in the spleen and in the ear draining lymph nodes compared to that of wild type control mice. In the absence of MCs, dendritic cell (DC) activation was impaired upon LCMV infection. In addition, type-I interferon (IFN) levels in the serum and in the spleen of MC-deficient mice were reduced during the first days of infection. Interestingly, depletion of MCs after intradermal LCMV infection did not impair virus-specific CD8+ T cell expansion, activation or antiviral cytokine production. In summary, our results indicate that MCs play a pivotal role in the activation and antiviral functions of CD8+ T cells through proper DC activation. A better understanding of the impact of MCs on CD8+ T cell responses is mandatory to improve antiviral immune responses.

Potential of brain mast cells for therapeutic application in the immune response to bacterial and viral infections

A wide range of microorganisms can infect the central nervous system (CNS). The immune response of the CNS provides limited protection against microbes penetrating the blood-brain barrier. This results in a neurological deficit and sometimes leads to high morbidity and mortality rates despite advanced therapies. For the last two decades, different studies have expanded our understanding of the molecular basis of human neuroinfectious diseases, especially concerning the contributions of mast cell interactions with other central nervous system compartments. Brain mast cells are multifunctional cells derived from the bone marrow and reside in the brain. Their proximity to blood vessels, their role as "first responders" their unique receptors systems and their ability to rapidly release pathogen responsive mediators enable them to exert a crucial defensive role in the host-defense system. This review describes key biological and physiological functions of mast cells, concerning their ability to recognize pathogens via various receptor systems, followed by a coordinated and selective mediator release upon specific interactions with pathogenic stimulating factors. The goal of this review is to direct attention to the possibilities for therapeutic applications of mast cells against bacterial and viral related infections. We also focus on opportunities for future research activating mast cells via adjuvants.

The impact of TLR7 agonist R848 treatment on mast cell phenotype and activity

Bearing in mind that mast cell contribution to viral clearance is still not fully understood, in this study, we evaluated the effect of Toll-like receptor (TLR)7 viral single-stranded ribonucleic acid (ssRNA) mimic ligand, namely resiquimod (R)848, on mast cell phenotype and activity. We demonstrated that rat peritoneal mast cells exhibit surface and intracellular expression of ssRNA-specific TLR7 molecule, and that mimic ligand switches the self-expression of this receptor. We also detected other proteins associated with the cellular antiviral response: interferon-alpha receptor 1 (IFNAR1), interferon-gamma receptor 1 (IFNGR1), and major histocompatibility complex I (MHC I). Moreover, we showed that R848 caused the decrease of all molecule's expression after prolonged incubation. Interestingly, we found that R848 induced the increase of high-affinity IgE receptor (FcεRI) expression. Finally, we documented that TLR7 ligand-stimulated mast cells synthesize/release interferon (IFN)-α and -β, tumor necrosis factor (TNF), and chemokines CCL3, CXCL8, as well as pro-inflammatory lipid mediators. Our findings confirm that mast cells may respond to TLR7 ligand by altering their phenotype and synthesizing mediators and could serve as active participants in the antiviral immune response.

Current Understanding of the Pathogenesis of Dengue Virus Infection

The pathogenesis of dengue virus infection is attributed to complex interplay between virus, host genes and host immune response. Host factors such as antibody-dependent enhancement (ADE), memory cross-reactive T cells, anti-DENV NS1 antibodies, autoimmunity as well as genetic factors are major determinants of disease susceptibility. NS1 protein and anti-DENV NS1 antibodies were believed to be responsible for pathogenesis of severe dengue. The cytokine response of cross-reactive CD4+ T cells might be altered by the sequential infection with different DENV serotypes, leading to further elevation of pro-inflammatory cytokines contributing a detrimental immune response. Fcγ receptor-mediated antibody-dependent enhancement (ADE) results in release of cytokines from immune cells leading to vascular endothelial cell dysfunction and increased vascular permeability. Genomic variation of dengue virus and subgenomic flavivirus RNA (sfRNA) suppressing host immune response are viral determinants of disease severity. Dengue infection can lead to the generation of autoantibodies against DENV NS1antigen, DENV prM, and E proteins, which can cross-react with several self-antigens such as plasminogen, integrin, and platelet cells. Apart from viral factors, several host genetic factors and gene polymorphisms also have a role to play in pathogenesis of DENV infection. This review article highlights the various factors responsible for the pathogenesis of dengue and also highlights the recent advances in the field related to biomarkers which can be used in future for predicting severe disease outcome.

Type I Interferon α/β Receptor-Mediated Signaling Negatively Regulates Antiviral Cytokine Responses in Murine Bone-Marrow-Derived Mast Cells and Protects the Cells from Virus-Induced Cell Death

Mast cells (MCs) are critical for initiating inflammatory responses to pathogens including viruses. Type I interferons (IFNs) that exert their antiviral functions by interacting with the type I IFN receptor (IFNAR) play a central role in host cellular responses to viruses. Given that virus-induced excessive toxic inflammatory responses are associated with aberrant IFNAR signaling and considering MCs are an early source of inflammatory cytokines during viral infections, we sought to determine whether IFNAR signaling plays a role in antiviral cytokine responses of MCs. IFNAR-intact, IFNAR-blocked, and IFNAR-knockout (IFNAR^−/−) bone-marrow-derived MCs (BMMCs) were treated in vitro with a recombinant vesicular stomatitis virus (rVSVΔm51) to assess cytokine production by these cells. All groups of MCs produced the cytokines interleukin-6 and tumor necrosis factor-α in response to rVSVΔm51. However, production of the cytokines was lowest in IFNAR-intact cells as compared with IFNAR^−/− or IFNAR-blocked cells at 20 h post-stimulation. Surprisingly, rVSVΔm51 was capable of infecting BMMCs, but functional IFNAR signaling was able to protect these cells from virus-induced death. This study showed that BMMCs produced pro-inflammatory cytokines in response to rVSVΔm51 and that IFNAR signaling was required to down-modulate these responses and protect the cells from dying from viral infection.

Mobilization and Activation of the Innate Immune Response to Dengue Virus

Dengue virus is an important human pathogen, infecting an estimated 400 million individuals per year and causing symptomatic disease in a subset of approximately 100 million. Much of the effort to date describing the host response to dengue has focused on the adaptive immune response, in part because of the well-established roles of antibody-dependent enhancement and T cell original sin as drivers of severe dengue upon heterotypic secondary infection. However, the innate immune system is a crucial factor in the host response to dengue, as it both governs the fate and vigor of the adaptive immune response, and mediates the acute inflammatory response in tissues. In this review, we discuss the innate inflammatory response to dengue infection, focusing on the role of evolutionarily conserved innate immune cells, their effector functions, and clinical course.

The Anti-apoptotic Murine Cytomegalovirus Protein vMIA-m38.5 Induces Mast Cell Degranulation

Mast cells (MC) represent “inbetweeners” of the immune system in that they are part of innate immunity by acting as first-line sentinels for environmental antigens but also provide a link to adaptive immunity by secretion of chemokines that recruit CD8 T cells to organ sites of infection. An interrelationship between MC and cytomegalovirus (CMV) has been a blank area in science until recently when the murine model revealed a role for MC in the resolution of pulmonary infection by murine CMV (mCMV). As to the mechanism, MC were identified as a target cell type of mCMV. Infected MC degranulate and synthesize the CC-chemokine ligand-5 (CCL-5), which is released to attract protective virus-specific CD8 T cells to infected host tissue for confining and eventually resolving the productive, cytopathogenic infection. In a step forward in our understanding of how mCMV infection of MC triggers their degranulation, we document here a critical role for the mCMV m38.5 gene product, a mitochondria-localized inhibitor of apoptosis (vMIA). We show an involvement of mCMV vMIA-m38.5 in MC degranulation by two reciprocal approaches: first, by enhanced degranulation after m38.5 gene transfection of bone marrow-derived cell culture-grown MC (BMMC) and, second, by reduced degranulation of MC in peritoneal exudate cell populations infected ex corpore or in corpore with mutant virus mCMV-Δm38.5. These studies thus reveal a so far unknown function of mCMV vMIA-m38.5 and offer a previously unconsidered but biologically relevant cell system for further analyzing functional analogies between vMIAs of different CMV species.

Protective and pathogenic roles for mast cells during viral infections

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At the host-environment interfaces such as skin or mucosae mast cells act as immune sentinels for variety of pathogens including viruses.

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Mast cells initiate cellular immune responses at the infection site by recruitment of various subsets of T cells.

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Systemic activation of mast cells is associated with vascular pathologies during viral infections.

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Targeting of mast cell specific products has a promising therapeutic potential in treating virus induced immune pathologies.

Mast cells (MCs) are long-lived immune cells. They are armed with preformed mediators within granules that can be instantaneously released in response to an invading pathogen, including certain viruses. At the skin and mucosae, they initiate innate immune responses and promote the development of adaptive immune responses, through cellular recruitment or antigen presentation. However, systemic MC activation may promote immune pathologies through their vasoactive proteases and biogenic amines. Recently, MC products were identified to contribute to pathologies associated with viral hemorrhagic fever, such vascular leakage and thrombocytopenia. Similar associations of MCs with disease severity have been noted for certain respiratory viral pathogens. Here we discuss the specific MC responses to viruses and their influences on functional immune outcomes during infection.

Comprehensive Immunoprofiling of Pediatric Zika Reveals Key Role for Monocytes in the Acute Phase and No Effect of Prior Dengue Virus Infection

Zika virus (ZIKV) is an emerging, mosquito-borne flavivirus responsible for recent epidemics across the Americas, and it is closely related to dengue virus (DENV). Here, we study samples from 46 DENV-naive and 43 DENV-immune patients with RT-PCR-confirmed ZIKV infection at early-acute, late-acute, and convalescent time points from our pediatric cohort study in Nicaragua. We analyze the samples via RNA sequencing (RNA-seq), CyTOF, and multiplex cytokine/chemokine Luminex to generate a comprehensive, innate immune profile during ZIKV infection. Immunophenotyping and analysis of cytokines/chemokines reveal that CD14+ monocytes play a key role during ZIKV infection. Further, we identify CD169 (Siglec-1) on CD14+ monocytes as a potential biomarker of acute ZIKV infection. Strikingly distinct transcriptomic and immunophenotypic signatures are observed at all three time points. Interestingly, pre-existing dengue immunity has minimal impact on the innate immune response to Zika. Finally, this comprehensive immune profiling and network analysis of ZIKV infection in children serves as a valuable resource.

IL-33 stimulates human mast cell release of CCL5 and CCL2 via MAPK and NF-κB, inhibited by methoxyluteolin

Mast Cells (MCs) are critical for allergic reactions but also play important roles in inflammation, following stimulation by non-allergic triggers such as cytokines. Upon stimulation, MCs secrete numerous newly synthesized mediators, but the mechanism of the release of chemokines, which are important in the pathogenesis of allergic and inflammatory diseases, remains unknown. IL-33 is an "alarmin", known to augment allergic stimulation of MCs, but its effect on the release of chemokines is not known. The present work investigated the action of IL-33 on the release of the chemokines CCL5 and CCL2 from human MCs, as well as the inhibitory effect of the flavonoid 3',4',5,7-tetramethoxyflavone (methoxyluteolin). Stimulation of cultured human MCs (LAD2) and primary MCs (hCBMCs) by IL-33 (1-100 ng/ml) increased the gene expression and the release of CCL5 (P < 0.0001) and CCL2 (P < 0.01). Stimulation with IL-33 (10 ng/ml) activated MAPK components, as shown by phosphorylation of p38α MAPK, JNK, and c-Jun using Western blot analysis. Inhibition of these responses by known inhibitors confirmed that CCL5 and CCL2 are stimulated by the activation of p38α MAPK, JNK, and IκB-α. The gene expression and the release of CCL5 and CCL2 stimulated by IL-33 were significantly inhibited by 2 h pre-treatment with methoxyluteolin (10, 50, 100  μM). The inhibition by methoxyluteolin (50 μM) was not mediated via MAPK inhibition as phosphorylated p38α MAPK and JNK expression were not affected. In conclusion, IL-33 plays an important role in chemokine release from human MCs and that is by activation of more than one signaling pathway. The inhibitory effect of methoxyluteolin may indicate that it can be developed as a novel treatment for inflammatory diseases.

Mast Cell Responses to Viruses and Pathogen Products

Mast cells are well accepted as important sentinel cells for host defence against selected pathogens. Their location at mucosal surfaces and ability to mobilize multiple aspects of early immune responses makes them critical contributors to effective immunity in several experimental settings. However, the interactions of mast cells with viruses and pathogen products are complex and can have both detrimental and positive impacts. There is substantial evidence for mast cell mobilization and activation of effector cells and mobilization of dendritic cells following viral challenge. These cells are a major and under-appreciated local source of type I and III interferons following viral challenge. However, mast cells have also been implicated in inappropriate inflammatory responses, long term fibrosis, and vascular leakage associated with viral infections. Progress in combating infection and boosting effective immunity requires a better understanding of mast cell responses to viral infection and the pathogen products and receptors we can employ to modify such responses. In this review, we outline some of the key known responses of mast cells to viral infection and their major responses to pathogen products. We have placed an emphasis on data obtained from human mast cells and aim to provide a framework for considering the complex interactions between mast cells and pathogens with a view to exploiting this knowledge therapeutically. Long-lived resident mast cells and their responses to viruses and pathogen products provide excellent opportunities to modify local immune responses that remain to be fully exploited in cancer immunotherapy, vaccination, and treatment of infectious diseases.

Responses of human mast cells and epithelial cells following exposure to influenza A virus

As a part of innate immune defense, the role of mast cells during viral replication has been incompletely understood. In this study, we characterized and compared the responses of the human mast cell line, LAD2, and human lung epithelial cell line, Calu-3, against three influenza A virus strains; A/PR/8/34 (H1N1), A/WS/33 (H1N1) and A/HK/8/68 (H3N2). We found that there were strain-dependent mast cell responses, and different profiles of cytokine, chemokine and antiviral gene expression between the two cell types. All three strains did not induce histamine or β-hexosaminidase release in LAD2. A/HK/8/68 induced release of prostaglandin D2 in LAD2, whereas A/PR/8/34 and A/WS/33 did not. We found that, among those examined, only CCL4 (by A/PR/8/34) was statistically significantly released from LAD2 cells. Furthermore, there was increased mRNA expression of viral recognition receptors (RIG-I and MDA5) and antiviral protein, viperin, but levels and kinetics of the expression were different among the cell types, as well as by the strains examined. Our findings highlight the variability in innate response to different strains of influenza A virus in two human cell types, indicating that further investigation is needed to understand better the role of mast cells and epithelial cells in innate immunity against influenza A viruses.

Dengue virus-elicited tryptase induces endothelial permeability and shock

Dengue virus (DENV) infection causes a characteristic pathology in humans involving dysregulation of the vascular system. In some patients with dengue hemorrhagic fever (DHF), vascular pathology can become severe, resulting in extensive microvascular permeability and plasma leakage into tissues and organs. Mast cells (MCs), which line blood vessels and regulate vascular function, are able to detect DENV in vivo and promote vascular leakage. Here, we identified that a MC-derived protease, tryptase, is consequential for promoting vascular permeability during DENV infection, through inducing breakdown of endothelial cell tight junctions. Injected tryptase alone was sufficient to induce plasma loss from the circulation and hypovolemic shock in animals. A potent tryptase inhibitor, nafamostat mesylate, blocked DENV-induced vascular leakage in vivo. Importantly, in two independent human dengue cohorts, tryptase levels correlated with the grade of DHF severity. This study defines an immune mechanism by which DENV can induce vascular pathology and shock.

Mast Cells in Viral, Bacterial, and Fungal Infection Immunity

Mast cells are granule-rich immune cells that are distributed throughout the body in areas where microorganisms typically reside, such as mucosal tissues and the skin, as well as connective tissues. It is well known that mast cells have significant roles in IgE-mediated conditions, such as anaphylaxis, but, because of their location, it is also thought that mast cells act as innate immune cells against pathogens and initiate defensive immune responses. In this review, we discuss recent studies focused on mast cell interactions with flaviviruses and Candida albicans, and mast cell function in the cecal ligation and puncture model of sepsis. We selected these studies because they are clear examples of how mast cells can either promote host resistance to infection, as previously proposed, or contribute to a dysregulated host response that can increase host morbidity and mortality. Importantly, we can distill from these studies that the contribution of mast cells to infection outcomes depends in part on the infection model, including the genetic approach used to assess the influence of mast cells on host immunity, the species in which mast cells are studied, and the differential contribution of mast cell subtypes to immunity. Accordingly, we think that this review highlights the complexity of mast cell biology in the context of innate immune responses.

Japanese encephalitis virus neuropenetrance is driven by mast cell chymase

Japanese encephalitis virus (JEV) is a leading cause of viral encephalitis. However, the mechanisms of JEV penetration of the blood-brain-barrier (BBB) remain poorly understood. Mast cells (MCs) are granulated innate immune sentinels located perivascularly, including at the BBB. Here we show that JEV activates MCs, leading to the release of granule-associated proteases in vivo. MC-deficient mice display reduced BBB permeability during JEV infection compared to congenic wild-type (WT) mice, indicating that enhanced vascular leakage in the brain during JEV infection is MC-dependent. Moreover, MCs promoted increased JEV infection in the central nervous system (CNS), enhanced neurological deficits, and reduced survival in vivo. Mechanistically, chymase, a MC-specific protease, enhances JEV-induced breakdown of the BBB and cleavage of tight-junction proteins. Chymase inhibition reversed BBB leakage, reduced brain infection and neurological deficits during JEV infection, and prolonged survival, suggesting chymase is a novel therapeutic target to prevent JEV encephalitis.

How Japanese encephalitis virus (JEV) penetrates the blood-brain barrier (BBB) remains unclear. Here, using a genetic mouse model and a virulent JEV strain, the authors show that perivascular mast cells (MC) mediate JEV neuroinvasion and identify the MC-protease chymase as a potential therapeutic target.

The controversial role of mast cells in fibrosis

Fibrosis is a medical condition characterized by an excessive deposition of extracellular matrix compounds such as collagen in tissues. Fibrotic lesions are present in many diseases and can affect all organs. The excessive extracellular matrix accumulation in these conditions can often have serious consequences and in many cases be life-threatening. A typical event seen in many fibrotic conditions is a profound accumulation of mast cells (MCs), suggesting that these cells can contribute to the pathology. Indeed, there is now substantialv evidence pointing to an important role of MCs in fibrotic disease. However, investigations from various clinical settings and different animal models have arrived at partly contradictory conclusions as to how MCs affect fibrosis, with many studies suggesting a detrimental role of MCs whereas others suggest that MCs can be protective. Here, we review the current knowledge of how MCs can affect fibrosis.

Mast cells as sources of cytokines, chemokines, and growth factors

Mast cells are hematopoietic cells that reside in virtually all vascularized tissues and that represent potential sources of a wide variety of biologically active secreted products, including diverse cytokines and growth factors. There is strong evidence for important non-redundant roles of mast cells in many types of innate or adaptive immune responses, including making important contributions to immediate and chronic IgE-associated allergic disorders and enhancing host resistance to certain venoms and parasites. However, mast cells have been proposed to influence many other biological processes, including responses to bacteria and virus, angiogenesis, wound healing, fibrosis, autoimmune and metabolic disorders, and cancer. The potential functions of mast cells in many of these settings is thought to reflect their ability to secrete, upon appropriate activation by a range of immune or non-immune stimuli, a broad spectrum of cytokines (including many chemokines) and growth factors, with potential autocrine, paracrine, local, and systemic effects. In this review, we summarize the evidence indicating which cytokines and growth factors can be produced by various populations of rodent and human mast cells in response to particular immune or non-immune stimuli, and comment on the proven or potential roles of such mast cell products in health and disease.

Mast cells as protectors of health

Mast cells (MCs), which are well known for their effector functions in T_H2-skewed allergic and also autoimmune inflammation, have become increasingly acknowledged for their role in protection of health. It is now clear that they are also key modulators of immune responses at interface organs, such as the skin or gut. MCs can prime tissues for adequate inflammatory responses and cooperate with dendritic cells in T-cell activation. They also regulate harmful immune responses in trauma and help to successfully orchestrate pregnancy. This review focuses on the beneficial effects of MCs on tissue homeostasis and elimination of toxins or venoms. MCs can enhance pathogen clearance in many bacterial, viral, and parasitic infections, such as through Toll-like receptor 2-triggered degranulation, secretion of antimicrobial cathelicidins, neutrophil recruitment, or provision of extracellular DNA traps. The role of MCs in tumors is more ambiguous; however, encouraging new findings show they can change the tumor microenvironment toward antitumor immunity when adequately triggered. Uterine tissue remodeling by α-chymase (mast cell protease [MCP] 5) is crucial for successful embryo implantation. MCP-4 and the tryptase MCP-6 emerge to be protective in central nervous system trauma by reducing inflammatory damage and excessive scar formation, thereby protecting axon growth. Last but not least, proteases, such as carboxypeptidase A, released by FcεRI-activated MCs detoxify an increasing number of venoms and endogenous toxins. A better understanding of the plasticity of MCs will help improve these advantageous effects and hint at ways to cut down detrimental MC actions.

The monocyte-macrophage-mast cell axis in dengue pathogenesis

Dengue virus, the causative agent of dengue disease which may have hemorrhagic complications, poses a global health threat. Among the numerous target cells for dengue virus in humans are monocytes, macrophages and mast cells which are important regulators of vascular integrity and which undergo dramatic cellular responses after infection by dengue virus. The strategic locations of these three cell types, inside blood vessels (monocytes) or outside blood vessels (macrophages and mast cells) allow them to respond to dengue virus infection with the production of both intracellular and secretory factors which affect virus replication, vascular permeability and/or leukocyte extravasation. Moreover, the expression of Fc receptors on the surface of monocytes, macrophages and mast cells makes them important target cells for antibody-enhanced dengue virus infection which is a major risk factor for severe dengue disease, involving hemorrhage. Collectively, these features of monocytes, macrophages and mast cells contribute to both beneficial and harmful responses of importance to understanding and controlling dengue infection and disease.

Mast Cell Activation and KSHV Infection in Kaposi Sarcoma

Purpose: Kaposi sarcoma (KS) is a vascular tumor initiated by infection of endothelial cells (ECs) with KS-associated herpesvirus (KSHV). KS is dependent on sustained proinflammatory signals provided by intralesional leukocytes and continued infection of new ECs. However, the sources of these cytokines and infectious virus within lesions are not fully understood. Here, mast cells (MCs) are identified as proinflammatory cells within KS lesions that are permissive for, and activated by, infection with KSHV.Experimental Design: Three validated MC lines were used to assess permissivity of MCs to infection with KSHV and to evaluate MCs activation following infection. Biopsies from 31 AIDS-KS cases and 11 AIDS controls were evaluated by IHC for the presence of MCs in KS lesions and assessment of MC activation state and infection with KSHV. Plasma samples from 26 AIDS-KS, 13 classic KS, and 13 healthy adults were evaluated for levels of MC granule contents tryptase and histamine.Results: In culture, MCs supported latent and lytic KSHV infection, and infection-induced MC degranulation. Within KS lesions, MCs were closely associated with spindle cells. Furthermore, MC activation was extensive within patients with KS, reflected by elevated circulating levels of tryptase and a histamine metabolite. One patient with clinical signs of extensive MC activation was treated with antagonists of MC proinflammatory mediators, which resulted in a rapid and durable regression of AIDS-KS lesions.Conclusions: Using complimentary in vitro and in vivo studies we identify MCs as a potential long-lived reservoir for KSHV and a source of proinflammatory mediators within the KS lesional microenvironment. In addition, we identify MC antagonists as a promising novel therapeutic approach for KS. Clin Cancer Res; 24(20); 5085-97. ©2018 AACR.

Characterization of Dendritic Cell-Derived Extracellular Vesicles During Dengue Virus Infection

The dengue virus (DENV), transmitted by Aedes spp. mosquitoes, is one of the most important arboviral infections in the world. Dengue begins as a febrile condition, and in certain patients, it can evolve severe clinical outcomes, such as dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). The reasons why certain patients develop DHF or DSS have not been thoroughly elucidated to date, and both patient and viral factors have been implicated. Previous work has shown that a severe immune dysfunction involving dendritic cells and T cells plays a key role in increasing the disease severity, especially in secondary heterologous infections. Extracellular vesicles (EVs) are membranous particles that are secreted by several cell types involved in homeostatic and pathological processes. Secretion of EVs by infected cells can enhance immune responses or favor viral evasion. In this study, we compare the molecular content of EVs that are secreted by human primary dendritic cells under different conditions: uninfected or infected with DENV3 strains isolated from patients with different infection phenotypes (a severe case involving DSS and a mild case). Human monocyte-derived dendritic cells (mdDCs) were infected with the dengue virus strains DENV3 5532 (severe) or DENV3 290 (mild), and the EVs were isolated. The presence of cup-shaped EVs was confirmed by electron microscopy and immunostaining with CD9, CD81, and CD83. The RNA content from the mdDC-infected cells contained several mRNAs and miRNAs related to immune responses compared to the EVs from mock-infected mdDCs. A number of these RNAs were detected exclusively during infection with DENV3 290 or DENV3 5532. This result suggests that the differential immune modulation of mdDCs by dengue strains can be achieved through the EV pathway. Additionally, we observed an association of EVs with DENV-infectious particles that seem to be protected from antibodies targeting the DENV envelope protein. We also showed that EVs derived from cells treated with IFN alpha have a protective effect against DENV infection in other cells. These results suggested that during DENV infection, the EV pathway could be exploited to favor viral viability, although immune mechanisms to counteract viral infection can also involve DC-derived EVs.

The Good, the Bad, and the Shocking: The Multiple Roles of Dengue Virus Nonstructural Protein 1 in Protection and Pathogenesis

Dengue virus (DENV) is the most prevalent medically important mosquito-borne virus in the world. Upon DENV infection of a host cell, DENV nonstructural protein 1 (NS1) can be found intracellularly as a monomer, associated with the cell surface as a dimer, and secreted as a hexamer into the bloodstream. NS1 plays a variety of roles in the viral life cycle, particularly in RNA replication and immune evasion of the complement pathway. Over the past several years, key roles for NS1 in the pathogenesis of severe dengue disease have emerged, including direct action of the protein on the vascular endothelium and triggering release of vasoactive cytokines from immune cells, both of which result in endothelial hyperpermeability and vascular leak. Importantly, the adaptive immune response generates a robust response against NS1, and its potential contribution to dengue vaccines is also discussed.

Which Dengue Vaccine Approach Is the Most Promising, and Should We Be Concerned about Enhanced Disease after Vaccination? Questions Raised by the Development and Implementation of Dengue Vaccines: Example of the Sanofi Pasteur Tetravalent Dengue Vaccine

Dengue is a still-growing public health concern in many tropical and subtropical regions of the world. The development and implementation of an effective dengue vaccine in these regions is a high priority. This insight focuses on the expected characteristics of a safe and efficacious vaccine, referring to the clinical experience obtained during the development of the first tetravalent dengue vaccine from Sanofi Pasteur, now licensed in several endemic countries. Safety and efficacy data from both short- and long-term follow-up of large-scale efficacy studies will be discussed, as well as the next steps following vaccine introduction.

Association between dengue severity and plasma levels of dengue-specific IgE and chymase

There is no definitive predictor of dengue severity, and this has led to a very large number of unnecessary hospitalizations worldwide. Although mast cell mediators are believed to a play role in dengue severity, the lack of precise kinetic data demands further research on early predictors. We enrolled 111 patients with confirmed dengue and 85 with "other febrile illness" (OFI) in a hospital-based prospective study in Vietnam. Dengue patients were classified as level 1, 2, or 3 based on the clinical intervention received. Blood samples were collected from each patient every day (pre- and post-defervescence) and after discharge. Plasma chymase, total IgE, and dengue-specific IgE were measured. Dengue-specific IgE levels showed an increasing trend during the course of illness and remained high even at post-discharge, although no significant difference was observed among severity levels. Total IgE showed no such trend. The specific IgE/total IgE ratio (S/T ratio) remained constantly higher in level 3 patients compared to other levels, with a significant difference at some time points. The S/T ratio of acute phase samples (before defervescence) tended to increase with increasing severity (level 1 < 2 < 3), and was significantly higher in level 3 patients than in level 1 and OFI patients. As an early predictor of severity allowing level 3 patients to be distinguished from other dengue patients, the S/T ratio achieved a sensitivity of 75% and specificity of 68%. We describe the kinetic profiles of IgEs, their ratio, and chymase levels at different severity levels. The S/T ratio was found to be associated with dengue severity, suggesting that it could potentially be used as an early predictor of severity.

Diverse exocytic pathways for mast cell mediators

Mast cells play pivotal roles in innate and adaptive immunities but are also culprits in allergy, autoimmunity, and cardiovascular diseases. Mast cells respond to environmental changes by initiating regulated exocytosis/secretion of various biologically active compounds called mediators (e.g. proteases, amines, and cytokines). Many of these mediators are stored in granules/lysosomes and rely on intricate degranulation processes for release. Mast cell stabilizers (e.g. sodium cromoglicate), which prevent such degranulation processes, have therefore been clinically employed to treat asthma and allergic rhinitis. However, it has become increasingly clear that different mast cell diseases often involve multiple mediators that rely on overlapping but distinct mechanisms for release. This review illustrates existing evidence that highlights the diverse exocytic pathways in mast cells. We also discuss strategies to delineate these pathways so as to identify unique molecular components which could serve as new drug targets for more effective and specific treatments against mast cell-related diseases.

Host genetics and dengue fever

Dengue is a major worldwide problem in tropical and subtropical areas; it is caused by four different viral serotypes, and it can manifest as asymptomatic, mild, or severe. Many factors interact to determine the severity of the disease, including the genetic profile of the infected patient. However, the mechanisms that lead to severe disease and eventually death have not been determined, and a great challenge is the early identification of patients who are more likely to progress to a worse health condition. Studies performed in regions with cyclic outbreaks such as Cuba, Brazil, and Colombia have demonstrated that African ancestry confers protection against severe dengue. Highlighting the host genetics as an important factor in infectious diseases, a large number of association studies between genetic polymorphisms and dengue outcomes have been published in the last two decades. The most widely used approach involves case-control studies with candidate genes, such as the HLA locus and genes for receptors, cytokines, and other immune mediators. Additionally, a Genome-Wide Association Study (GWAS) identified SNPs associated with African ethnicity that had not previously been identified in case-control studies. Despite the increasing number of publications in America, Africa, and Asia, the results are quite controversial, and a meta-analysis is needed to assess the consensus among the studies. SNPs in the MICB, TNF, CD209, FcγRIIA, TPSAB1, CLEC5A, IL10 and PLCE1 genes are associated with the risk or protection of severe dengue, and the findings have been replicated in different populations. A thorough understanding of the viral, human genetic, and immunological mechanisms of dengue and how they interact is essential for effectively preventing dengue, but also managing and treating patients.

Clinical Proteomics and Cytokine Profiling for Dengue Fever Disease Severity Biomarkers

Dengue fever (DF) is a major global health burden with a pathophysiology that is still incompletely understood. Biomarkers that predict and explain susceptibility to DF and its progression to its more severe hemorrhagic form are much needed. DF is endemic in tropical and subtropical regions of the world, with a rapidly increasing incidence of disease severity. We conducted a clinical biomarker discovery study using both a case-control and longitudinal study design. Plasma proteome alterations in patients with DF (n = 12) and dengue hemorrhagic fever (DHF, n = 24) were analyzed in comparison to healthy controls (HCs, n = 16), using the isobaric tags for relative and absolute quantification (iTRAQ)-based quantitative proteomics methodology (false discovery rate of 1%, ≥2 peptides). Several proteins such as the alpha-2 macroglobulin, angiotensinogen, apolipoprotein B-100, serotransferrin, and ceruloplasmin were upregulated (fold change >1.2) in all DHF cases, and downregulated in DF (fold change <0.83), compared with HCs. Plasma cytokine profiling (8 DF, 8 DHF, and 8 HC) on two consecutive time points, at day 0 (day of admission) and days 5-7, found significant elevation in IL-1RA, IL-7, TNF-α, MCP1-MCAF, and MIP-1β levels, but only in the DHF cases, which is the severe disease, and not in DF, compared with HCs (p < 0.05). These new observations on changes in the plasma proteome and cytokine profiles in patients with dengue infection identify several putative molecular leads for future biomarker development and precision medicine in relation to forecasting DF disease severity.

Role of Mast Cells in Dengue Virus Pathogenesis

Dengue is currently regarded as the most common arthropod-borne viral disease in tropical and subtropical areas, with an estimated 50-100 million infections occurring each year. Nearly all patients experience a self-limiting clinical course; however, the illness ranges from undifferentiated fever to severe hemorrhagic fever with or without shock syndrome complications. There are several immune cells associated with the pathogenesis of dengue virus (DENV) infection and systemic spread, including dendritic cells, macrophages, and mast cells (MCs). MCs are widely recognized for their immune functions and as cellular regulators of vascular integrity in human skin. Furthermore, these cells are able to detect DENV, which results in activation and degranulation of potent vasoactive mediators prestored in the granules. These mediators can act directly on vascular endothelium, increasing permeability and inducing vascular leakage. This review is designed to present an insight into the role of MCs during DENV infection and the dual functions in immune protection and contribution to the most severe forms of dengue.

Antibodies against nonstructural protein 1 protect mice from dengue virus-induced mast cell activation

Dengue virus (DENV) infection causes dengue fever, dengue hemorrhagic fever (DHF), and dengue shock syndrome (DSS). DHF/DSS patients have been reported to have increased levels of urinary histamine, chymase, and tryptase, which are major granule-associated mediators from mast cells. Previous studies also showed that DENV-infected human mast cells induce production of proinflammatory cytokines and chemokines, suggesting a role played by mast cells in vascular perturbation as well as leukocyte recruitment. In this study, we show that DENV but not UV-inactivated DENV enhanced degranulation of mast cells and production of chemokines (MCP-1, RANTES, and IP-10) in a mouse model. We have previously shown that antibodies (Abs) against a modified DENV nonstructural protein 1 (NS1), designated DJ NS1, provide protection in mice against DENV challenge. In the present study, we investigate the effects of DJ NS1 Abs on mast cell-associated activities. We showed that administration of anti-DJ NS1 Abs into mice resulted in a reduction of mast cell degranulation and macrophage infiltration at local skin DENV infection sites. The production of DENV-induced chemokines (MCP-1, RANTES, and IP-10) and the percentages of tryptase-positive activated mast cells were also reduced by treatment with anti-DJ NS1 Abs. These results indicate that Abs against NS1 protein provide multiple therapeutic benefits, some of which involve modulating DENV-induced mast cell activation.Laboratory Investigation advance online publication, 27 February 2017; doi:10.1038/labinvest.2017.10.

Induction of Osteopontin by Dengue Virus-3 Infection in THP-1 Cells: Inhibition of the Synthesis by Brefelamide and Its Derivative

Osteopontin (OPN) is a multifunctional matricellular protein produced by a broad range of cells including osteoclasts, macrophages, T cells, endothelial cells, and vascular smooth muscle cells. OPN modulates various physiological and pathological events such as inflammation, wound healing, and bone formation and remodeling. Dengue virus (DENV) infection causes an increase in plasma OPN levels, which is correlated with the severity of symptoms and coagulation abnormalities. DENV infection also induces OPN gene expression in human macrophages. This study investigated the inhibitory effects of brefelamide and its methyl ether derivative on DENV-3 by measuring changes in OPN levels in human THP-1 and 293T cell lines infected at different multiplicities of infection and post-infection time points. OPN mRNA expression and viral RNA were detected by reverse transcriptase quantitative real-time PCR, whereas protein level was determined by enzyme-linked immunosorbent assay. We found that viral copy number was higher in 293T than in THP-1 cells. However, THP-1 constitutively expressed higher levels of OPN mRNA and protein, which were enhanced by DENV-3 infection. Brefelamide and its derivative suppressed OPN production in DENV-3 infected THP-1 cells; the effective doses of these compounds had no effect on uninfected cells, indicating low cytotoxicity. These results suggest that brefelamide and its methyl ether derivative have therapeutic effects in preventing inflammation, coagulopathy, and fibrinolysis caused by OPN upregulation induced by DENV-3 infection.

Mast cells are permissive for rhinovirus replication: potential implications for asthma exacerbations

BACKGROUND

Human rhinoviruses (HRVs) are a major trigger of asthma exacerbations, with the bronchial epithelium being the major site of HRV infection and replication. Mast cells (MCs) play a key role in asthma where their numbers are increased in the bronchial epithelium with increasing disease severity.

OBJECTIVE

In view of the emerging role of MCs in innate immunity and increased localization to the asthmatic bronchial epithelium, we investigated whether HRV infection of MCs generated innate immune responses which were protective against infection.

METHODS

The LAD2 MC line or primary human cord blood-derived MCs (CBMCs) were infected with HRV or UV-irradiated HRV at increasing multiplicities of infection (MOI) without or with IFN-β or IFN-λ. After 24 h, innate immune responses were assessed by RT-qPCR and IFN protein release by ELISA. Viral replication was determined by RT-qPCR and virion release by TCID₅₀ assay.

RESULTS

HRV infection of LAD2 MCs induced expression of IFN-β, IFN-λ and IFN-stimulated genes. However, LAD2 MCs were permissive for HRV replication and release of infectious HRV particles. Similar findings were observed with CBMCs. Neutralization of the type I IFN receptor had minimal effects on viral shedding, suggesting that endogenous type I IFN signalling offered limited protection against HRV. However, augmentation of these responses by exogenous IFN-β, but not IFN-λ, protected MCs against HRV infection.

CONCLUSION AND CLINICAL RELEVANCE

MCs are permissive for the replication and release of HRV, which is prevented by exogenous IFN-β treatment. Taken together, these findings suggest a novel mechanism whereby MCs may contribute to HRV-induced asthma exacerbations.

Progress towards understanding the pathogenesis of dengue hemorrhagic fever

Dengue virus (DENV) is a mosquito-borne virus belonging to the Flaviviridae family. There are 4 serotypes of DENV that cause human disease through transmission by mosquito vectors. DENV infection results in a broad spectrum of clinical symptoms, ranging from mild fever to dengue hemorrhagic fever (DHF), the latter of which can progress to dengue shock syndrome (DSS) and death. Researchers have made unremitting efforts over the last half-century to understand DHF pathogenesis. DHF is probably caused by multiple factors, such as virus-specific antibodies, viral antigens and host immune responses. This review summarizes the current progress of studies on DHF pathogenesis, which may provide important information for achieving effective control of dengue in the future.

A Role for Human Skin Mast Cells in Dengue Virus Infection and Systemic Spread

Dengue virus (DENV) is a mosquito-borne flavivirus that causes serious global human disease and mortality. Skin immune cells are an important component of initial DENV infection and systemic spread. Here, we show that mast cells are a target of DENV in human skin and that DENV infection of skin mast cells induces degranulation and alters cytokine and growth factor expression profiles. Importantly, to our knowledge, we also demonstrate for the first time that DENV localizes within secretory granules in infected skin mast cells. In addition, DENV within extracellular granules was infectious in vitro and in vivo, trafficking through lymph to draining lymph nodes in mice. We demonstrate an important role for human skin mast cells in DENV infection and identify a novel mechanism for systemic spread of DENV infection from the initial peripheral mosquito injection site.

Mast cells in asthma--state of the art

Mast cells (MCs) play a central role in tissue homoeostasis, sensing the local environment through numerous innate cell surface receptors. This enables them to respond rapidly to perceived tissue insults with a view to initiating a co-ordinated programme of inflammation and repair. However, when the tissue insult is chronic, the ongoing release of multiple pro-inflammatory mediators, proteases, cytokines and chemokines leads to tissue damage and remodelling. In asthma, there is strong evidence of ongoing MC activation, and their mediators and cell-cell signals are capable of regulating many facets of asthma pathophysiology. This article reviews the evidence behind this.

Biomarkers of severe dengue disease - a review

Dengue virus infection presents a wide spectrum of manifestations including asymptomatic condition, dengue fever (DF), or severe forms, such as dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS) in affected individuals. The early prediction of severe dengue in patients without any warning signs who may later develop severe DHF is very important to choose appropriate intensive supportive therapy since available vaccines for immunization are yet to be approved. Severe dengue responses include T and B cell activation and apoptosis, cytokine storm, hematologic disorders and complement activation. Cytokines, complement and other unidentified factors may transiently act on the endothelium and alter normal fluid barrier function of the endothelial cells and cause plasma leakage. In this review, the host factors such as activated immune and endothelial cells and their products which can be utilized as biomarkers for severe dengue disease are discussed.