Release of vasoactive cytokines by antibody-enhanced dengue virus infection of a human mast cell/basophil line

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.

Viremia and Inflammatory Cytokines in Dengue: Interleukin-2 as a Biomarker of Infection, and Interferon-α and -γ as Markers of Primary versus Secondary Infection

The pathogenesis of Dengue virus (DENV) infection is complex and involves viral replication that may trigger an inflammatory response leading to severe disease. Here, we investigated the correlation between viremia and cytokine levels in the serum of DENV-infected patients. Between 2013 and 2014, 138 patients with a diagnosis of acute-phase DENV infection and 22 patients with a non-dengue acute febrile illness (AFI) were enrolled. Through a focus-forming assay (FFU), we determined the viremia levels in DENV-infected patients and observed a peak in the first two days after the onset of symptoms. A higher level of viremia was observed in primary versus secondary DENV-infected patients. Furthermore, no correlation was observed between viremia and inflammatory cytokine levels in DENV-infected patients. Receiver operating characteristic (ROC) curve analysis revealed that IL-2 has the potential to act as a marker to distinguish dengue from other febrile illnesses and is positively correlated with Th1 cytokines. IFN-α and IFN-γ appear to be potential markers of primary versus secondary infection in DENV-infected patients, respectively. The results also indicate that viremia levels are not the main driving force behind inflammation in dengue and that cytokines could be used as infection biomarkers and for differentiation between primary versus secondary infection.

The Current Landscape of Bioactive Molecules against DENV: A Systematic Review

With a 30-fold increase in incidence over the previous 50 years, dengue fever is now the most widespread viral disease transmitted by mosquitoes in the world. The intricate interaction of the human defense system, hereditary predisposition, and specific bitterness elements is more likely to be the pathogenesis of dengue. There are presently no viable treatments for dengue. Synthetic drugs which are used against this ailment also show major side effects. There must be a deeper understanding of the underlying mechanism generating severe symptoms to develop auguring markers, cutting-edge diagnostics, and treatments and finally a well-rounded and secure antiserum. Hence, the aim is to search for safer and more potent drugs derived from plants. Plants or herbs are mainly targeting replication or its enzyme or specific stereotypes, though an exact mechanism of phytoconstituents interfering with the viral replication is still undiscovered. The present attempt provided the update with the objective to bringing up forward pathophysiological eventualities involved in dengue virus along with the naturally derived treatment relevant to provide the impregnable therapy by evading the noxious symptoms for dengue fever. Governor's plum, Cryptocarya chartacea, magnolia berry, and Chinese ginger are such plants exhibiting many effective phytoconstituents against DENV and can be further explored for novel drug discovery by medicinal scientists.

Host immune response against DENV and ZIKV infections

Dengue is a major public health concern, affecting almost 400 million people worldwide, with about 70% of the global burden of disease in Asia. Despite revised clinical classifications of dengue infections by the World Health Organization, the wide spectrum of the manifestations of dengue illness continues to pose challenges in diagnosis and patient management for clinicians. When the Zika epidemic spread through the American continent and then later to Africa and Asia in 2015, researchers compared the characteristics of the Zika infection to Dengue, considering both these viruses were transmitted primarily through the same vector, the Aedes aegypti female mosquitoes. An important difference to note, however, was that the Zika epidemic diffused in a shorter time span compared to the persisting feature of Dengue infections, which is endemic in many Asian countries. As the pathogenesis of viral illnesses is affected by host immune responses, various immune modulators have been proposed as biomarkers to predict the risk of the disease progression to a severe form, at a much earlier stage of the illness. However, the findings for most biomarkers are highly discrepant between studies. Meanwhile, the cross-reactivity of CD8+ and CD4+ T cells response to Dengue and Zika viruses provide important clues for further development of potential treatments. This review discusses similarities between Dengue and Zika infections, comparing their disease transmissions and vectors involved, and both the innate and adaptive immune responses in these infections. Consideration of the genetic identity of both the Dengue and Zika flaviviruses as well as the cross-reactivity of relevant T cells along with the actions of CD4+ cytotoxic cells in these infections are also presented. Finally, a summary of the immune biomarkers that have been reported for dengue and Zika viral infections are discussed which may be useful indicators for future anti-viral targets or predictors for disease severity. Together, this information appraises the current understanding of both Zika and Dengue infections, providing insights for future vaccine design approaches against both viruses.

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.

Rescue therapy with intravenous immunoglobulin in severe refractory dengue: A pilot study

Background

Severe dengue causes more than 22,000 deaths annually worldwide. Complicated dengue has high mortality of 44-72%. Disordered immune system with capillary leak and thrombocytopenia are hallmark of complicated dengue. Intravenous immunoglobulin (IV Ig) therapy has shown to be effective in complicated dengue in pediatric age group with refractory shock, but studies in adults are lacking. Its immunoresuscitative role is not yet fully explored in critically ill patients with severe dengue.

Methods

This is retrospective observational study of patients with complicated dengue fever who were administered IV Ig therapy in a tertiary care hospital of southern India from 01 Jan 2018 to 31 Dec 2019.

Results

A total of 999 patients with dengue were admitted; 754 (75.47%) were males, and 245 (24.53%) were females. A total of 402 (40.24%) patients presented with warning signs. Bleeding was seen in 121 patients (12.11%); 102 (10.21%) had shock; 29 (2.90%) had acute kidney injury and 24 (2.40%) had adult respiratory distress syndrome. Overall, four people died (mortality rate: 0.40%). IV Ig in the dose of 0.4 g/kg for 5 days was used in 13 critically ill patients where standard therapy failed, 9 patients with refractory shock (which included three with myocarditis with refractory shock), 2 with encephalitis, 2 in hemophagocytic lymphohistiocytosis. Two patients died, one with myocarditis with refractory shock and another with refractory shock.

Conclusion

IV Ig therapy in critically ill patients with complicated dengue can be used as a rescue therapy.

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.

Morphological Aspects and Viremia Analysis of BALB/c Murine Model Experimentally Infected with Dengue Virus Serotype 4

Ever since its brief introduction in the Brazilian territory in 1981, dengue virus serotype 4 (DENV-4) remained absent from the national epidemiological scenario for almost 25 years. The emergence of DENV-4 in 2010 resulted in epidemics in most Brazilian states. DENV-4, however, remains one of the least studied among the four DENV serotypes. Despite being known as a mild serotype, DENV-4 is associated with severe cases and deaths and deserves to be investigated; however, the lack of suitable experimental animal models is a limiting factor for pathogenesis studies. Here, we aimed to investigate the susceptibility and potential tropism of DENV-4 for liver, lung and heart of an immunocompetent mice model, and to evaluate and investigate the resulting morphological and ultrastructural alterations upon viral infection. BALB/c mice were inoculated intravenously with non-neuroadapted doses of DENV-4 isolated from a human case. The histopathological analysis of liver revealed typical alterations of DENV, such as microsteatosis, edema and vascular congestion, while in lung, widespread areas of hemorrhage and interstitial pneumonia were observed. While milder alterations were present in heart, characterized by limited hemorrhage and discrete presence of inflammatory infiltrate, the disorganization of the structure of the intercalated disc is of particular interest. DENV-4 RNA was detected in liver, lung, heart and serum of BALB/c mice through qRT-PCR, while the NS3 viral protein was observed in all of the aforementioned organs through immunohistochemistry. These findings indicate the susceptibility of the model to the serotype and further reinforce the usefulness of BALB/c mice in studying the many alterations caused by DENV.

Ross River Virus Immune Evasion Strategies and the Relevance to Post-viral Fatigue, and Myalgic Encephalomyelitis Onset

Ross River virus (RRV) is an endemic Australian arbovirus, and member of the Alphavirus family that also includes Chikungunya virus (CHIK). RRV is responsible for the highest prevalence of human disease cases associated with mosquito-borne transmission in Australia, and has long been a leading suspect in cases of post-viral fatigue syndromes, with extrapolation of this link to Myalgic Encephalomyelitis (ME). Research into RRV pathogenesis has revealed a number of immune evasion strategies, impressive for a virus with a genome size of 12 kb (plus strand RNA), which resonate with insights into viral pathogenesis broadly. Drawing from observations on RRV immune evasion, mechanisms of relevance to long term idiopathic fatigue are featured as a perspective on infection and eventual ME symptoms, which include considerations of; (1) selective pro-inflammatory gene suppression post antibody-dependent enhancement (ADE) of RRV infection, (2) Evidence from other virus families of immune disruption and evasion post-ADE, and (3) how virally-driven immune evasion may impact on mitochondrial function via target of rapamycin (TOR) complexes. In light of these RRV measures to counter the host immune - inflammatory responses, links to recent discoveries explaining cellular, immune and metabolomic markers of ME will be explored and discussed, with the implications for long-COVID post SARS-CoV-2 also considered. Compelling issues on the connections between virally-induced alterations in cytokine expression, for example, will be of particular interest in light of energy pathways, and how these perturbations manifest clinically.

Mast Cell and Astrocyte Hemichannels and Their Role in Alzheimer's Disease, ALS, and Harmful Stress Conditions

Considered relevant during allergy responses, numerous observations have also identified mast cells (MCs) as critical effectors during the progression and modulation of several neuroinflammatory conditions, including Alzheimer’s disease (AD) and amyotrophic lateral sclerosis (ALS). MC granules contain a plethora of constituents, including growth factors, cytokines, chemokines, and mitogen factors. The release of these bioactive substances from MCs occurs through distinct pathways that are initiated by the activation of specific plasma membrane receptors/channels. Here, we focus on hemichannels (HCs) formed by connexins (Cxs) and pannexins (Panxs) proteins, and we described their contribution to MC degranulation in AD, ALS, and harmful stress conditions. Cx/Panx HCs are also expressed by astrocytes and are likely involved in the release of critical toxic amounts of soluble factors—such as glutamate, adenosine triphosphate (ATP), complement component 3 derivate C3a, tumor necrosis factor (TNFα), apoliprotein E (ApoE), and certain miRNAs—known to play a role in the pathogenesis of AD, ALS, and other neurodegenerative disorders. We propose that blocking HCs on MCs and glial cells offers a promising novel strategy for ameliorating the progression of neurodegenerative diseases by reducing the release of cytokines and other pro-inflammatory compounds.

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.

John AL. Th1-Polarized, Dengue Virus-Activated Human Mast Cells Induce Endothelial Transcriptional Activation and Permeability

Dengue virus (DENV), an arbovirus, strongly activates mast cells (MCs), which are key immune cells for pathogen immune surveillance. In animal models, MCs promote clearance of local peripheral DENV infections but, conversely, also promote pathological vascular leakage when widely activated during systemic DENV infection. Since DENV is a human pathogen, we sought to ascertain whether a similar phenomenon could occur in humans by characterizing the products released by human MCs (huMCs) upon direct (antibody-independent) DENV exposure, using the phenotypically mature huMC line, ROSA. DENV did not productively infect huMCs but prompted huMC release of proteases and eicosanoids and induced a Th1-polarized transcriptional profile. In co-culture and trans-well systems, huMC products activated human microvascular endothelial cells, involving transcription of vasoactive mediators and increased monolayer permeability. This permeability was blocked by MC-stabilizing drugs, or limited by drugs targeting certain MC products. Thus, MC stabilizers are a viable strategy to limit MC-promoted vascular leakage during DENV infection in humans.

Safety, Immunogenicity, and Effectiveness of Defective Viral Particles Arising in Mast Cells Against Influenza in Mice

Mast cells play pivotal roles in the pathogenesis of influenza A virus (IAV) infections. Defective viral particles (DPs) often arise during IAV replication, which can interfere with the replication of infectious viruses and stimulate the antiviral response of host cells. Therefore, DPs are expected to have immune-protective functions in clinic. However, the potent immunogenicity and effectiveness of DPs arising in mast cells during IAV replication have not been reported. In the present study, we showed that DPs generated in the human mastocytoma cell line HMC-1 following H1N1 infection were safe to mice after vaccination. Compared with lung adenocarcinoma cells, A549, DPs generated in infected mast cells had much better immunostimulatory activity, enhancing both humoral and cellular immunity of hosts. Notably, they could significantly increase the expression of immune-associated cytokines, especially the IFN-γ. Due to the robust immunogenicity, thus DPs generated in infected mast cells could stimulate the robust protective immune reaction effectively to fight against lethal IAV re-challenge after vaccination, which result in the high survival, decreased lung injury as well as inhibition of viral replication and inflammatory response in lungs. This study is the first to illustrate and explore the safety, immunogenicity, and effectiveness of DPs arising in mast cells against influenza as favorable potential vaccination. The results provide insight into the advances of new prophylactic strategies to fight influenza by focusing on DPs generated in mast cells.

Defective Viral Particles Produced in Mast Cells Can Effectively Fight Against Lethal Influenza A Virus

Mast cells play an important role in the pathogenesis of highly pathogenic H5N1 avian influenza virus (H5N1-HPAIV) infection. Defective viral particles (DPs) can interfere with the replication of infectious viruses and stimulate the innate immune response of host cells. However, DPs arising from mast cells during HPAIV replication and their potent antiviral actions has not been reported. Here, we showed that the human mastocytoma cell line, HMC-1, allowed for the productive replication of the H5N1-HPAIV. Compared with alveolar cell line A549, DPs were propagated preferentially and abundantly in mast cells following IAV infection, which can be attributed to the wide existence of Argonaute 2 (AGO2) in HMC-1 cells. In addition, DPs generated in H5N1-infected cells could provide great therapeutic protection on mice to fight against various influenza A viruses, which included not only homologous H5N1-HPAIV, but also heterologous H1N1, H3N2, H7N2, and H9N2. Importantly, DPs generated in H5N1-infected HMC-1 cells could diminish viral virulence in vivo and in vitro by triggering a robust antiviral response through type II interferon signaling pathways. This study is the first to illustrate the arising of DPs in H5N1-HPAIV infected mast cells and explore their favorable ability to protect mice from influenza A viruses infection, which provides a novel insight and valuable information for the progress of new strategies to fight influenza A viruses infection, especially highly pathogenic avian influenza virus infection by focusing on the DPs generated in mast cells.

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.

What the physicians should know about mast cells, dendritic cells, urticaria, and omalizumab during COVID-19 or asymptomatic infections due to SARS-CoV-2?

Coronavirus disease (COVID-19) pandemic presents several dermatological manifestations described in the present indexed literature, with around 700 cases reported until May 2020, some described as urticaria or urticarial rashes. Urticaria is constituted by evanescent erythematous-edematous lesions (wheals and flare), which does not persist in the same site for more than 24 to 48 hours and appears in other topographic localization, resolving without residual hyper pigmentation. During the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, some cytokines are synthesized, including Interferon (IFN) type I, TNF-α, and chemokines which may induce mast cells (MCs) and basophils degranulation by mechanisms similar to the autoinflammatory monogenic or polygenic diseases. In this article, we discuss the spectrum of the urticaria and urticarial-like lesions in the COVID-19's era, besides other aspects related to innate and adaptative immune response to viral infections, interactions between dermal dendritic cells and MCs, and degranulation of MCs by different stimuli. Plasmacytoid dendritic cells share, in allergic patients, expression of the high-affinity IgE receptors on cell membranes and demonstrated a low pattern of type I IFN secretion in viral infections. We discuss the previous descriptions of the effects of omalizumab, a monoclonal antibody directed to IgE and high-affinity IgE receptors, to improve the IFN responses and enhance their antiviral effects.

Insight into the Tropism of Dengue Virus in Humans

In tropical and subtropical zones, arboviruses are among the major threats to human life, affecting a large number of populations with serious diseases. Worldwide, over three hundred million people are infected with dengue virus (DENV) every year as per the World Health Organization (WHO). DENV-mediated disease severity ranges from a mild fever to hemorrhagic fever and shock syndrome. Patients suffering from severe infection might experience multi-organ failure, cardiomyopathy and even encephalopathy, further complicating the disease pathogenesis. In life-threatening cases, DENV has been reported to affect almost all organs of the human body. In this review, we discuss the organ tropism of DENV in humans in depth as detected in various autopsy studies. Keeping in mind the fact that there is currently no DENV-specific antiviral, it is of utmost importance to achieve a vivid picture of the susceptible cells in humans which might help in designing antivirals against DENV, especially targeting those tissues in which infection might lead to life-threatening conditions.

Hijacking the Host Immune Cells by Dengue Virus: Molecular Interplay of Receptors and Dengue Virus Envelope

Dengue virus (DENV) is one of the lethal pathogens in the hot climatic regions of the world and has been extensively studied to decipher its mechanism of pathogenesis and the missing links of its life cycle. With respect to the entry of DENV, multiple receptors have been recognized in different cells of the human body. However, scientists still argue whether these identified receptors are the exclusive entry mediators for the virus. Adding to the complexity, DENV has been reported to be infecting multiple organ types in its human host. Also, more than one receptor in a particular cell has been discerned to take part in mediating the ingress of DENV. In this review, we aim to discuss the different cells of the human immune system that support DENV infection and their corresponding receptors that DENV deploy to gain access to the cells.

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.

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.

Immune responses to dengue virus in the skin

Dengue virus (DENV) causes infection in humans and current estimates place 40% of the world population at risk for contracting disease. There are four DENV serotypes that induce a febrile illness, which can develop into a severe and life-threatening disease in some cases, characterized primarily by vascular dysregulation. As a mosquito-borne infection, the skin is the initial site of DENV inoculation and also where primary host immune responses are initiated. This review discusses the early immune response to DENV in the skin by both infection target cells such as dendritic cells and by immune sentinels such as mast cells. We provide an overview of the mechanisms of immune sensing and functional immune responses that have been shown to aid clearance of DENV in vivo. Finally, we discuss factors that can influence the immune response to DENV in the skin, such as mosquito saliva, which is co-injected with virus during natural route infection, and pre-existing immunity to other DENV serotypes or to related flaviviruses.

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.

Activation of mast cells in skin abscess induced by Staphylococcus aureus (S. aureus) infection in mice

The skin abscess is a common inflammatory disease that occurs following the ubiquitous S. aureus infection. In our study, a skin abscess murine model was established and the dynamics of mast cells chemotaxing was evaluated. In the S. aureus-infected mice, severe infiltration of inflammatory cells in the dermis were observed, and mast cells were markedly accumulated in the skins. Besides, tryptase, the marker for mast cells activation, has a positive correlation with mast cell activity. The mast cells identified in the tissues were likely to be activated since they were associated with cell degranulation and the presence of tryptase. Our results suggested that mast cells and its mediator tryptase contribute to the inflammation of skin abscess induced by S. aureus infection.

Skin microbiome and mast cells

Microbiotas in the skin have high levels of diversity at the species level, but low phylum-level diversity. The human skin microbiota is composed predominantly of Gram-positive bacteria especially Actinobacteria, which are the dominant bacterial phylum on the skin. Lipoteichoic acid (LTA) is a major constituent of the cell wall of Gram-positive bacteria and is therefore abundant in the skin microbiome. Recent studies have shown that LTA, and other bacterial products, permeates the whole skin and comes into contact with epidermal and dermal cells, including mast cells (MCs), with the potential of stimulating MC toll-like receptors (TLRs). MCs express a variety of pattern recognition receptors, including TLRs, on their cell surface in order to detect bacteria. Recent publications suggest that the skin microbiome has influence on MC migration, localization and maturation in the skin. Germ free (no microbiome) animals possess an underdeveloped immune system and immature MCs. Despite much research done on skin microbiota and many papers describing skin interaction with "the good microbiota", there is still controversy regarding how mast cells, communicate with surface bacteria. The present review intends to quell the controversy by illuminating the communication mechanism between bacteria and MCs.

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.

Isoquercitrin suppresses the expression of histamine and pro-inflammatory cytokines by inhibiting the activation of MAP Kinases and NF-κB in human KU812 cells

Mast cells and basophils are multifunctional effector cells that contain abundant secretory granules in their cytoplasm. Both cell types are involved in a variety of inflammatory and immune events, producing an array of inflammatory mediators, such as cytokines. The aim of the study was to examine whether isoquercitrin modulates allergic and inflammatory reactions in the human basophilic KU812 cells and to elucidate its influence on the phosphorylation of mitogen-activated protein kinase (MAPK) and nuclear factor (NF)-κB activation. The KU812 cells were stimulated with phorbol-12-myristate 13-acetate plus the calcium ionophore A23187 (PMACI). The inhibitory effects of isoquercitrin on the productions of histamine and pro-inflammatory cytokines in the stimulated KU812 cells were measured using cytokine-specific enzyme-linked immunosorbent (ELISA) assays. Western blotting analysis was used to assess the effects of isoquercitrin on the MAPKs and NF-κB protein levels. Our results indicated that the isoquercitrin treatment of PMACI-stimulated KU812 cells significantly reduced the production of histamine and the pro-inflammatory cytokines, such as interleukin (IL)-6, IL-8, IL-1β, and tumor necrosis factor (TNF)-α. The treated cells exhibited decreased phosphorylation of extracellular signal-regulated kinase (ERK), revealing the role of ERK MAPK in isoquercitrin-mediated allergy inhibition. Furthermore, isoquercitrin suppressed the PMACI-mediated activation of NF-κB in the human basophil cells. In conclusion, the results from the present study provide insights into the potential therapeutic use of isoquercitrin for the treatment of inflammatory and allergic reactions.

Influenza A Viruses Replicate Productively in Mouse Mastocytoma Cells (P815) and Trigger Pro-inflammatory Cytokine and Chemokine Production through TLR3 Signaling Pathway

The influenza A viruses (IAVs) cause acute respiratory infection in both humans and animals. As a member of the initial lines of host defense system, the role of mast cells during IAV infection has been poorly understood. Here, we characterized for the first time that both avian-like (α-2, 3-linked) and human-like (α-2, 6- linked) sialic acid (SA) receptors were expressed by the mouse mastocytoma cell line (P815). The P815 cells did support the productive replication of H1N1 (A/WSN/33), H5N1 (A/chicken/ Henan/1/04) and H7N2 (A/chicken/Hebei/2/02) in vitro while the in vivo infection of H5N1 in mast cells was confirmed by the specific staining of nasal mucosa and lung tissue from mice. All the three viruses triggered the infected P815 cells to produce pro-inflammatory cytokines and chemokines including IL-6, IFN-γ, TNF-α, CCL-2, CCL-5, and IP-10, but not the antiviral type I interferon. It was further confirmed that TLR3 pathway was involved in P815 cell response to IAV-infection. Our findings highlight the remarkable tropism and infectivity of IAV to P815 cells, indicating that mast cells may be unneglectable player in the development of IAV infection.

The therapeutic effects of sodium cromoglycate against influenza A virus H5N1 in mice

Objectives

To identify the protective role of sodium cromoglycate in mice during influenza virus infection.

Design

H5N1 virus‐infected mice were treated with the mast cell stabilizer sodium cromoglycate (SCG) to investigate its therapeutic effect.

Sample

The nose, trachea and lungs from mice were collected.

Main outcome measures

Virus replication and host responses were determined by plaque assay, quantitative PCR, immunohistochemistry, and histology.

Results

SCG‐treated mice survived better than did PBS‐treated mice after H5N1 virus infection. Mild pathological changes with fewer inflammatory cell infiltration and fewer virus antigens were observed in the nose, trachea, and lungs of SCG‐treated mice on days 3 and 5 post‐infection. However, no significant changes in viral load in the lungs were detected between SCG‐ and PBS‐treated mice. Furthermore, significantly decreased expression of interleukin‐6, tumor necrosis factor‐a, Toll‐like receptor 3, and TIR‐domain‐containing adapter‐inducing interferon‐b was detected in the lungs of SCG‐treated mice, and no higher expression of interferon‐c was detected.

Conclusion

These results suggest that SCG has therapeutic roles in H5N1 virus‐infected mice by alleviating the inflammatory response rather than inhibition of viral replication in the lungs.

Mast cell-macrophage dynamics in modulation of dengue virus infection in skin

Dengue virus (DENV) infection causes dengue fever, dengue haemorrhagic fever, or dengue shock syndrome. Mast cells have been speculated to play a role in DENV disease although their precise roles are unclear. In this study, we used mast cell-deficient Kit(W-sh/W-sh) mice to investigate the involvement of mast cells after intradermal DENV infection. An approximately two- to three-fold higher level of DENV NS3 antigen was detected at the skin inoculation site in DENV-infected Kit(W-sh/W-sh) mice than in DENV-infected wild-type (WT) mice (using a dose of 1 × 10(9) plaque-forming units/mouse). Moreover, as an indicator of heightened pathogenesis, a more prolonged bleeding time was observed in DENV-infected Kit(W-sh/W-sh) mice than in WT mice. Monocytes/macrophages are considered to be important targets for DENV infection, so we investigated the susceptibility and chemokine response of DENV-infected peritoneal macrophages from Kit(W-sh/W-sh) and WT mice both ex vivo and in vivo. There was a tendency for higher DENV infection and higher secretion of CCL2 (MCP-1) from peritoneal macrophages isolated from Kit(W-sh/W-sh) mice than those from WT mice. In vivo studies using intradermal inoculation of DENV showed about twofold higher levels of infiltrating macrophages and CCL2 (MCP-1) at the inoculation site in both mock control and DENV-inoculated Kit(W-sh/W-sh) mice than in corresponding WT mice. In summary, compared with WT mice, Kit(W-sh/W-sh) mice show enhanced DENV infection and macrophage infiltration at the skin inoculation site as well as increased DENV-associated bleeding time. The results indicate an intriguing interplay between mast cells and tissue macrophages to restrict DENV replication in the skin.

Dengue vascular leakage is augmented by mast cell degranulation mediated by immunoglobulin Fcγ receptors

Dengue virus (DENV) is the most significant human arboviral pathogen and causes ∼400 million infections in humans each year. In previous work, we observed that mast cells (MC) mediate vascular leakage during DENV infection in mice and that levels of MC activation are correlated with disease severity in human DENV patients (St John et al., 2013b). A major risk factor for developing severe dengue is secondary infection with a heterologous serotype. The dominant theory explaining increased severity during secondary DENV infection is that cross-reactive but non-neutralizing antibodies promote uptake of virus and allow enhanced replication. Here, we define another mechanism, dependent on FcγR-mediated enhanced degranulation responses by MCs. Antibody-dependent mast cell activation constitutes a novel mechanism to explain enhanced vascular leakage during secondary DENV infection.

Human mast cell activation with viruses and pathogen products

Mast cells have been demonstrated to have critical roles in host defense against a number of types of pathogens. In order to better understand how mast cells participate in effective immune responses, it is important to evaluate their ability to respond directly to pathogens and their products. In the current chapter we provide a methodology to evaluate human mast cell responses to a number of bacterial and fungal pathogen products and to mammalian reovirus as a model of acute viral infection. These methods should provide key information necessary to aid in the effective design of experiments to evaluate human mast cell responses to a number of other organisms. However, it is important to carefully consider the biology of the mast cell subsets and pathogens involved and the optimal experimental conditions necessary to evaluate mediators of interest.

Endothelial dysfunction in dengue virus pathology

Dengue virus (DENV) is a leading cause of illness and death, mainly in the (sub)tropics, where it causes dengue fever and/or the more serious diseases dengue hemorrhagic fever and dengue shock syndrome that are associated with changes in vascular permeability. Despite extensive research, the pathogenesis of DENV is still poorly understood and, although endothelial cells represent the primary fluid barrier of the blood vessels, the extent to which these cells contribute to DENV pathology is still under debate. The primary target cells for DENV are dendritic cells and monocytes/macrophages that release various chemokines and cytokines upon infection, which can activate the endothelium and are thought to play a major role in DENV-induced vascular permeability. However, recent studies indicate that DENV also replicates in endothelial cells and that DENV-infected endothelial cells may directly contribute to viremia, immune activation, vascular permeability and immune targeting of the endothelium. Also, the viral non-structural protein-1 and antibodies directed against this secreted protein have been reported to be involved in endothelial cell dysfunction. This review provides an extensive overview of the effects of DENV infection on endothelial cell physiology and barrier function.

Mast cell mediators: their differential release and the secretory pathways involved

Mast cells (MC) are widely distributed throughout the body and are common at mucosal surfaces, a major host-environment interface. MC are functionally and phenotypically heterogeneous depending on the microenvironment in which they mature. Although MC have been classically viewed as effector cells of IgE-mediated allergic diseases, they are also recognized as important in host defense, innate and acquired immunity, homeostatic responses, and immunoregulation. MC activation can induce release of pre-formed mediators such as histamine from their granules, as well as release of de novo synthesized lipid mediators, cytokines, and chemokines that play diverse roles, not only in allergic reactions but also in numerous physiological and pathophysiological responses. Indeed, MC release their mediators in a discriminating and chronological manner, depending upon the stimuli involved and their signaling cascades (e.g., IgE-mediated or Toll-like receptor-mediated). However, the precise mechanisms underlying differential mediator release in response to these stimuli are poorly known. This review summarizes our knowledge of MC mediators and will focus on what is known about the discriminatory release of these mediators dependent upon diverse stimuli, MC phenotypes, and species of origin, as well as on the intracellular synthesis, storage, and secretory processes involved.

Autophagy facilitates antibody-enhanced dengue virus infection in human pre-basophil/mast cells

BACKGROUND

Dengue virus (DENV) infection can cause severe hemorrhagic disease in humans. Although the pathogenic mechanisms underlying severe DENV disease remain unclear, one of the possible contributing factors is antibody-dependent enhancement (ADE) which occurs when sub-neutralizing antibodies derived from a previous DENV infection enhance viral infection through interaction between virus-antibody complexes and FcR-bearing cells, such as macrophages and basophil/mast cells. Although recent reports showed that DENV induces autophagy, the relationship between antibody-enhanced DENV infection and autophagy is not clear.

METHODOLOGY/PRINCIPAL FINDINGS

We showed that sub-neutralizing antibodies derived from dengue patient sera enhanced DENV infection and autophagy in the KU812 pre-basophil-like cell line as well as the HMC-1 immature mast cell line. Antibody-enhanced DENV infection of KU812 cells increased the number of autophagosome vesicles, LC3 punctation, LC3-II accumulation, and p62 degradation over that seen in cells infected with DENV alone. The percentages of DENV envelope (E) protein-positive cells and LC3 puncta following antibody-enhanced DENV infection of KU812 cells were reduced by the autophagy inhibitor 3-MA. Antibody-enhanced DENV infection of HMC-1 cells showed co-localization of DENV E protein and dsRNA with autophagosomes, which was inhibited by 3-MA treatment. Furthermore, DENV infection and replication were reduced when KU812 cells were transfected with the autophagy-inhibiting Atg4BC74A mutant.

CONCLUSIONS/SIGNIFICANCE

Our results demonstrate a significant induction of autophagy in antibody-enhanced DENV infection of pre-basophil-like KU812 and immature mast cell-like HMC-1 cells. Also, autophagy plays an important role in DENV infection and replication in these cells. Given the importance of ADE and FcR-bearing cells such as monocytes, macrophages and basophil/mast cells in dengue disease, the results provide insights into dengue pathogenesis and therapeutic means of control.

Modulation of inflammation and pathology during dengue virus infection by p38 MAPK inhibitor SB203580

Dengue virus (DENV) infection could lead to dengue fever (DF), dengue hemorrhagic fever (DHF) or dengue shock syndrome (DSS). The disease outcome is controlled by both viral and host factors. Inflammation mediators from DENV-infected cells could contribute to increased vascular permeability, leading to severe DHF/DSS. Therefore, suppression of inflammation could be a potential therapeutic approach for treatment of dengue patients. In this context, p38 MAPK (mitogen-activated protein kinase) is a key enzyme that modulates the initiation of stress and inflammatory responses. Here we show that SB203580, a p38 MAPK inhibitor, suppressed the over production of DENV-induced pro-inflammatory mediators such as TNF-α, IL-8, and RANTES from human PBMCs, monocytic THP-1, and granulocyte KU812 cell lines. Oral administration of SB203580 in DENV-infected AG129 mice prevented hematocrit rise and lymphopenia, limited the development of inflammation and pathology (including intestine leakage), and significantly improved survival. These results, for the first time, have provided experimental evidence to imply that a short term inhibition of p38 MAPK may be beneficial to reduce disease symptoms in dengue patients.

Mast cell mediator responses and their suppression by pathogenic and commensal microorganisms

Mast cells (MCs) are selectively found at the host environment interface and are capable of secreting a wide array of pharmacologically active mediators, many of which are prepackaged in granules. Over the past two decades, it has become clear that these cells have the capacity to recognize a range of infectious agents allowing them to play a key role in initiating and modulating early immune responses to infectious agents. However, a number of pathogenic and commensal microbes appear to have evolved distinct mechanisms to suppress MC mediator release to avoid elimination in the host. Understanding how these microbes suppress MC functions may have significant therapeutic value to relieve inflammatory disorders mediated by MCs.

Salmonella typhimurium impedes innate immunity with a mast-cell-suppressing protein tyrosine phosphatase, SptP

The virulence of Salmonella is linked to its invasive capacity and suppression of adaptive immunity. This does not explain, however, the rapid dissemination of the pathogen after it breaches the gut. In our study, S. Typhimurium suppressed degranulation of local mast cells (MCs), resulting in limited neutrophil recruitment and restricting outflow of vascular contents into infection sites, thus facilitating bacterial spread. MC suppression was mediated by secreted effector protein (SptP), which shares structural homology with Yersinia YopH. SptP functioned by dephosphorylating the vesicle fusion protein N-ethylmalemide-sensitive factor and by blocking phosphorylation of Syk. Without SptP, orally challenged S. Typhimurium failed to suppress MC degranulation and exhibited limited colonization of the mesenteric lymph nodes. Administration of SptP to sites of E. coli infection markedly enhanced its virulence. Thus, SptP-mediated inactivation of local MCs is a powerful mechanism utilized by S. Typhimurium to impede early innate immunity.

Limited replication of influenza A virus in human mast cells

Mast cells are important in innate immunity and protective against certain bacterial infections. However, there is limited evidence that mast cells respond to viruses. As mast cells are abundant in mucosal tissues of the lung, they are in a prime location to detect and respond to influenza virus. In this study, we characterized for the first time the replication cycle of influenza A virus in human mast cells by measuring influenza A virus transcription, RNA replication, protein synthesis, and formation of infectious virus as compared to the replication cycle in epithelial cells. We detected the presence of influenza A viral genomic RNA transcription, replication, and protein synthesis in human mast cells and epithelial cells. However, there was no significant release of infectious influenza A virus from mast cells, whereas epithelial cells produce ~100-fold virus compared with the inoculating dose. We confirmed that influenza A virus infects human mast cells, begins to replicate, but the production of new virus is aborted. Thus, mast cells may lack critical factors essential for productive infection or there are intrinsic or inducible anti-influenza A mechanisms in mast cells.

Unmasking the role of mast cells in dengue

Immune cells called mast cells can hinder rather than help the body's response to dengue virus, which suggests that mast cell products could be used as biomarkers to identify severe forms of the disease.

Role and relevance of mast cells in fungal infections

In addition to their detrimental role in allergic diseases, mast cells (MCs) are well known to be important cells of the innate immune system. In the last decade, they have been shown to contribute significantly to optimal host defense against numerous pathogens including parasites, bacteria, and viruses. The contribution of MCs to the immune responses in fungal infections, however, is largely unknown. In this review, we first discuss key features of mast cell responses to pathogens in general and then summarize the current knowledge on the function of MCs in the defense against fungal pathogens. We especially focus on the potential and proven mechanisms by which MCs can detect fungal infections and on possible MC effector mechanisms in protecting from fungal infections.

RNA sensors enable human mast cell anti-viral chemokine production and IFN-mediated protection in response to antibody-enhanced dengue virus infection

Dengue hemorrhagic fever and/or dengue shock syndrome represent the most serious pathophysiological manifestations of human dengue virus infection. Despite intensive research, the mechanisms and important cellular players that contribute to dengue disease are unclear. Mast cells are tissue-resident innate immune cells that play a sentinel cell role in host protection against infectious agents via pathogen-recognition receptors by producing potent mediators that modulate inflammation, cell recruitment and normal vascular homeostasis. Most importantly, mast cells are susceptible to antibody-enhanced dengue virus infection and respond with selective cytokine and chemokine responses. In order to obtain a global view of dengue virus-induced gene regulation in mast cells, primary human cord blood-derived mast cells (CBMCs) and the KU812 and HMC-1 mast cell lines were infected with dengue virus in the presence of dengue-immune sera and their responses were evaluated at the mRNA and protein levels. Mast cells responded to antibody-enhanced dengue virus infection or polyinosiniċpolycytidylic acid treatment with the production of type I interferons and the rapid and potent production of chemokines including CCL4, CCL5 and CXCL10. Multiple interferon-stimulated genes were also upregulated as well as mRNA and protein for the RNA sensors PKR, RIG-I and MDA5. Dengue virus-induced chemokine production by KU812 cells was significantly modulated by siRNA knockdown of RIG-I and PKR, in a negative and positive manner, respectively. Pretreatment of fresh KU812 cells with supernatants from dengue virus-infected mast cells provided protection from subsequent infection with dengue virus in a type I interferon-dependent manner. These findings support a role for tissue-resident mast cells in the early detection of antibody-enhanced dengue virus infection via RNA sensors, the protection of neighbouring cells through interferon production and the potential recruitment of leukocytes via chemokine production.

Association of mast cell-derived VEGF and proteases in Dengue shock syndrome

BACKGROUND

Recent in-vitro studies have suggested that mast cells are involved in Dengue virus infection. To clarify the role of mast cells in the development of clinical Dengue fever, we compared the plasma levels of several mast cell-derived mediators (vascular endothelial cell growth factor [VEGF], soluble VEGF receptors [sVEGFRs], tryptase, and chymase) and -related cytokines (IL-4, -9, and -17) between patients with differing severity of Dengue fever and healthy controls.

METHODOLOGY/PRINCIPAL FINDINGS

The study was performed at Children's Hospital No. 2, Ho Chi Minh City, and Vinh Long Province Hospital, Vietnam from 2002 to 2005. Study patients included 103 with Dengue fever (DF), Dengue hemorrhagic fever (DHF), and Dengue shock syndrome (DSS), as diagnosed by the World Health Organization criteria. There were 189 healthy subjects, and 19 febrile illness patients of the same Kinh ethnicity. The levels of mast cell-derived mediators and -related cytokines in plasma were measured by ELISA. VEGF and sVEGFR-1 levels were significantly increased in DHF and DSS compared with those of DF and controls, whereas sVEGFR-2 levels were significantly decreased in DHF and DSS. Significant increases in tryptase and chymase levels, which were accompanied by high IL-9 and -17 concentrations, were detected in DHF and DSS patients. By day 4 of admission, VEGF, sVEGFRs, and proteases levels had returned to similar levels as DF and controls. In-vitro VEGF production by mast cells was examined in KU812 and HMC-1 cells, and was found to be highest when the cells were inoculated with Dengue virus and human Dengue virus-immune serum in the presence of IL-9.

CONCLUSIONS

As mast cells are an important source of VEGF, tryptase, and chymase, our findings suggest that mast cell activation and mast cell-derived mediators participate in the development of DHF. The two proteases, particularly chymase, might serve as good predictive markers of Dengue disease severity.