Local not systemic modulation of dendritic cell S1P receptors in lung blunts virus-specific immune responses to influenza

The discovery and development of the sphingosine 1-phosphate receptor modulator ozanimod in ulcerative colitis

Sphingosine-1 phosphate (S1P) modulators have received recent FDA-approval for the treatment of moderate-to-severe ulcerative colitis, including agents ozanimod, approved in 2021, and etrasimod, approved in 2023. These oral drugs are uniquely efficacious in UC as they have multimodal mechanisms contributing to their beneficial immunomodulatory effects, while preserving host response to pathogens and attenuating toxicities observed with less specific agents. In this review, the discovery and development of the first approved S1P modulator, ozanimod, is described in detail: from design of initial screens to discover unique binding agents, to extensive chemical modifications to improve pharmacokinetic and safety profiles, and through preclinical and clinical studies validating mechanism and establishing safety and efficacy. Ultimately, this review will not only inform the reader of the unique path to development of a clinical S1P modulator for UC, but will also highlight advances made and gaps remaining to individualize therapeutic approaches for inflammatory bowel disease.

Ozanimod Therapy in Patients With COVID-19 Requiring Oxygen Support: A Randomized Open-Label Pilot Trial

BACKGROUND

Sphingosine-1-phosphate receptor ligands (SRLs) dampen immunopathologic damages in models of viral pneumonia.

RESEARCH QUESTION

Is it feasible to administer an SRL therapy, here ozanimod (OZA), to acutely ill patients infected with SARS-CoV-2?

STUDY DESIGN AND METHODS

The prospective randomized open-label COVID-19 Ozanimod Intervention (COZI) pilot trial was conducted in three Canadian hospitals. Patients admitted for COVID-19 requiring oxygen were eligible. Randomization was stratified for risk factors of poor outcome and oxygen needs at inclusion. Participants were allocated to standard of care or to standard of care plus OZA. OZA (oral, once daily, incremental dosage) was administered for a maximum of 14 days. Primary end point investigated for size effect and variance over time was the assessment of safety and efficacy, evaluated by the daily score on the World Health Organization-adapted six-point ordinal scale for clinical improvement analyzed under the intention-to-treat principle.

RESULTS

Twenty-three patients were randomized to the standard of care arm, and 20 were randomized to the OZA arm from September 2020 to February 2022. Evaluation of efficacy showed nonsignificant reductions of median (interquartile range) duration of respiratory support (6 [3-10] vs 9 [4-12] days; P = .34), median duration of hospitalization (9 [6-12] vs 10 [6-18] days; P = .20), and median time to clinical improvement (4 [3-7] vs 7 [3-11] days; P = .12) for OZA compared with standard of care, respectively. Heart rate was significantly lower with OZA (65 [ 63-67] vs 71 [69-72] beats/min; P < .0001). However, QT and PR intervals were not affected. No severe adverse drug reaction was reported.

INTERPRETATION

To our knowledge, SRL utility in severe pneumonia has never been tested in patients. This study shows for the first time that this new pharmacologic agent may safely be administered to patients hospitalized for viral pneumonia, with potential clinical benefits. Bradycardia was frequent but well tolerated.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov; No.: NCT04405102; URL: www.

CLINICALTRIALS

gov.

CD200Fc limits dendritic cell and B-cell activation during chronic allergen exposures

Allergic asthma is a chronic inflammatory disease characterized by Th2, conventional dendritic cell, and B-cell activation. In addition to excessive inflammation, asthma pathogenesis includes dysregulation of anti-inflammatory pathways, such as the CD200/CD200R pathway. Thus, we investigated whether a CD200R agonist, CD200Fc, could disrupt the inflammatory cascade in chronic allergic asthma pathogenesis using a mice model of experimental asthma. Mice were exposed to house dust mites for 5 wk, and CD200Fc treatment was initiated after chronic inflammation was established (starting on week 4). We demonstrate that chronic house dust mite exposure altered CD200 and CD200R expression on lung immune cell populations, including upregulation of CD200 on alveolar macrophages and reduced expression of CD200 on conventional dendritic cells. CD200Fc treatment does not change bronchoalveolar cellular infiltration, but it attenuates B-cell activation and skews the circulating immunoglobulin profile toward IgG2a. This is accompanied by reduced activation of conventional dendritic cells, including lower expression of CD40, especially on conventional dendritic cell subset 2 CD200R+. Furthermore, we confirm that CD200Fc can directly modulate conventional dendritic cell activation in vitro using bone marrow-derived dendritic cells. Thus, the CD200/CD200R pathway is dysregulated during chronic asthma pathogenesis, and the CD200R agonist modulates B-cell and dendritic cell activation but, in our chronic model, is not sufficient to alter inflammation measured in bronchoalveolar lavage.

PET Study of Sphingosine-1-phosphate Receptor 1 Expression in Response to S. aureus Infection

Sphingosine-1-phosphate receptor 1 (S1PR1) plays a crucial role in infectious diseases. Targeting S1PR1 provides protection against pathogens, such as influenza viruses. This study is aimed at investigating S1PR1 in response to bacterial infection by assessing S1PR1 expression in S. aureus-infected mice. A rodent local muscle bacterial infection model was developed by injecting S. aureus to the lower hind limb of Balb/c mice. The changes of S1PR1 expression in response to bacterial infection and blocking treatment were assessed using ex vivo biodistribution and in vivo positron emission tomography (PET) after intravenous injection of an S1PR1-specific radiotracer [18F]TZ4877. The specificity of [18F]TZ4877 was assessed using S1PR1-specific antagonist, NIBR-0213, and S1PR1-specific DsiRNA pretreated the animals. Immunohistochemical studies were performed to confirm the increase of S1PR1 expression in response to infection. Ex vivo biodistribution data showed that the uptake of [18F]TZ4877 was increased 30.6%, 54.3%, 74.3%, and 115.3% in the liver, kidney, pancreas, and thymus of the infected mice, respectively, compared to that in normal control mice, indicating that S1PR1 is involved in the early immune response to bacterial infection. NIBR-0213 or S1PR1-specific DsiRNA pretreatment reduced the tissue uptake of [18F]TZ4877, suggesting that uptake of [18F]TZ4877 is specific. Our PET/CT study data also confirmed that infected mice have increased [18F]TZ4877 uptake in several organs comparing to that in normal control mice. Particularly, compared to control mice, a 39% increase of [18F]TZ4877 uptake was observed in the infected muscle of S. aureus mice, indicating that S1PR1 expression was directly involved in the inflammatory response to infection. Overall, our study suggested that S1PR1 plays an important role in the early immune response to bacterial infection. The uptake of [18F]TZ4877 is tightly correlated with the S1R1 expression in response to S. aureus infection. PET with S1PR1-specific radiotracer [18F]TZ4877 could provide a noninvasive tool for detecting the early S1PR1 immune response to infectious diseases.

Structures of signaling complexes of lipid receptors S1PR1 and S1PR5 reveal mechanisms of activation and drug recognition

Sphingosine-1-phosphate (S1P) is an important bioactive lipid molecule in cell membrane metabolism and binds to G protein-coupled S1P receptors (S1PRs) to regulate embryonic development, physiological homeostasis, and pathogenic processes in various organs. S1PRs are lipid-sensing receptors and are therapeutic targets for drug development, including potential treatment of COVID-19. Herein, we present five cryo-electron microscopy structures of S1PRs bound to diverse drug agonists and the heterotrimeric Gi protein. Our structural and functional assays demonstrate the different binding modes of chemically distinct agonists of S1PRs, reveal the mechanical switch that activates these receptors, and provide a framework for understanding ligand selectivity and G protein coupling.

Sphingosine kinase 2 restricts T cell immunopathology but permits viral persistence

Chronic viral infections are often established by the exploitation of immune-regulatory mechanisms that result in nonfunctional T cell responses. Viruses that establish persistent infections remain a serious threat to human health. Sphingosine kinase 2 (SphK2) generates sphingosine 1-phosphate, which is a molecule known to regulate multiple cellular processes. However, little is known about SphK2's role during the host immune responses to viral infection. Here, we demonstrate that SphK2 functions during lymphocytic choriomeningitis virus Cl 13 (LCMV Cl 13) infection to limit T cell immune pathology, which subsequently aids in the establishment of virus-induced immunosuppression and the resultant viral persistence. The infection of Sphk2-deficient (Sphk2-/-) mice with LCMV Cl 13 led to the development of nephropathy and mortality via T cell-mediated immunopathology. Following LCMV infection, Sphk2-/- CD4+ T cells displayed increased activity and proliferation, and these cells promoted overactive LCMV Cl 13-specific CD8+ T cell responses. Notably, oral instillation of an SphK2-selective inhibitor promoted protective T cell responses and accelerated the termination of LCMV Cl 13 persistence in mice. Thus, SphK2 is indicated as an immunotherapeutic target for the control of persistent viral infections.

Behavioral strategies to prevent and mitigate COVID-19 infection

The single stranded RNA virus SARS-CoV-2 has caused a massive addition to the already leading global cause of mortality, viral respiratory tract infections. Characterized by and associated with early and deleteriously enhanced production of pro-inflammatory cytokines by respiratory epithelial cells, severe COVID-19 illness has the potential to inflict acute respiratory distress syndrome and even death. Due to the fast spreading nature of COVID-19 and the current lack of a vaccine or specific pharmaceutical treatments, understanding of viral pathogenesis, behavioral prophylaxis, and mitigation tactics are of great public health concern. This review article outlines the immune response to viral pathogens, and due to the novelty of COVID-19 and the large body of evidence suggesting the respiratory and immune benefits from regular moderate intensity exercise, provides observational and mechanistic evidence from research on other viral infections that suggests strategically planned exercise regimens may help reduce susceptibility to infection, while also mitigating severe immune responses to infection commonly associated with poor COVID-19 prognosis. We propose that regular moderate intensity exercise should be considered as part of a combinatorial approach including widespread hygiene initiatives, properly planned and well-executed social distancing policies, and use of efficacious facial coverings like N95 respirators. Studies discerning COVID-19 pathogenesis mechanisms, transfer dynamics, and individual responses to pharmaceutical and adjunct treatments are needed to reduce viral transmission and bring an end to the COVID-19 pandemic.

Emerging Connections of S1P-Metabolizing Enzymes with Host Defense and Immunity During Virus Infections

The sphingosine 1-phosphate (S1P) metabolic pathway is a dynamic regulator of multiple cellular and disease processes. Identification of the immune regulatory role of the sphingosine analog FTY720 led to the development of the first oral therapy for the treatment of an autoimmune disease, multiple sclerosis. Furthermore, inhibitors of sphingosine kinase (SphK), which mediate S1P synthesis, are being evaluated as a therapeutic option for the treatment of cancer. In conjunction with these captivating discoveries, S1P and S1P-metabolizing enzymes have been revealed to display vital functions during virus infections. For example, S1P lyase, which is known for metabolizing S1P, inhibits influenza virus replication by promoting antiviral type I interferon innate immune responses. In addition, both isoforms of sphingosine kinase have been shown to regulate the replication or pathogenicity of many viruses. Pro- or antiviral activities of S1P-metabolizing enzymes appear to be dependent on diverse virus–host interactions and viral pathogenesis. This review places an emphasis on summarizing the functions of S1P-metabolizing enzymes during virus infections and discusses the opportunities for designing pioneering antiviral drugs by targeting these host enzymes.

Sphingosine-1-Phosphate: A Potential Biomarker and Therapeutic Target for Endothelial Dysfunction and Sepsis?

Sepsis is an acute life-threatening multiple organ failure caused by a dysregulated host response to infection. Endothelial dysfunction, particularly barrier disruption leading to increased vascular permeability, edema, and insufficient tissue oxygenation, is critical to sepsis pathogenesis. Sphingosine-1-phosphate (S1P) is a signaling lipid that regulates important pathophysiological processes including vascular endothelial cell permeability, inflammation, and coagulation. It is present at high concentrations in blood and lymph and at very low concentrations in tissues due to the activity of the S1P-degrading enzyme S1P-lyase in tissue cells. Recently, four preclinical observational studies determined S1P levels in serum or plasma of sepsis patients, and all found reduced S1P levels associated with the disease. Based on these findings, this review summarizes S1P-regulated processes pertaining to endothelial functions, discusses the possible use of S1P as a marker and possibilities how to manipulate S1P levels and S1P receptor activation to restore endothelial integrity, dampens the inflammatory host response, and improves organ function in sepsis.

Sphingolipids role in the regulation of inflammatory response: From leukocyte biology to bacterial infection

Sphingolipids (SLs) are amphiphilic molecules mainly associated with the external leaflet of eukaryotic plasma membrane, and are structural membrane components with key signaling properties. Since the beginning of the last century, a large number of papers described the involvement of these molecules in several aspects of cell physiology and pathology. Several lines of evidence support the critical role of SLs in inflammatory diseases, by acting as anti- or pro-inflammatory mediators. They are involved in control of leukocyte activation and migration, and are recognized as essential players in host response to pathogenic infection. We propose here a critical overview of current knowledge on involvement of different classes of SLs in inflammation, focusing on the role of simple and complex SLs in pathogen-mediated inflammatory response.

Sphingosine 1-Phosphate Lyase Enhances the Activation of IKKε To Promote Type I IFN-Mediated Innate Immune Responses to Influenza A Virus Infection

Sphingosine 1-phosphate (S1P) lyase (SPL) is an intracellular enzyme that mediates the irreversible degradation of the bioactive lipid S1P. We have previously reported that overexpressed SPL displays anti-influenza viral activity; however, the underlying mechanism is incompletely understood. In this study, we demonstrate that SPL functions as a positive regulator of IKKε to propel type I IFN-mediated innate immune responses against viral infection. Exogenous SPL expression inhibited influenza A virus replication, which correlated with an increase in type I IFN production and IFN-stimulated gene accumulation upon infection. In contrast, the lack of SPL expression led to an elevated cellular susceptibility to influenza A virus infection. In support of this, SPL-deficient cells were defective in mounting an effective IFN response when stimulated by influenza viral RNAs. SPL augmented the activation status of IKKε and enhanced the kinase-induced phosphorylation of IRF3 and the synthesis of type I IFNs. However, the S1P degradation-incompetent form of SPL also enhanced IFN responses, suggesting that SPL's pro-IFN function is independent of S1P. Biochemical analyses revealed that SPL, as well as the mutant form of SPL, interacts with IKKε. Importantly, when endogenous IKKε was downregulated using a small interfering RNA approach, SPL's anti-influenza viral activity was markedly suppressed. This indicates that IKKε is crucial for SPL-mediated inhibition of influenza virus replication. Thus, the results illustrate the functional significance of the SPL-IKKε-IFN axis during host innate immunity against viral infection.

Reduction of Pertussis Inflammatory Pathology by Therapeutic Treatment With Sphingosine-1-Phosphate Receptor Ligands by a Pertussis Toxin-Insensitive Mechanism

Recent data have demonstrated the potential of sphingosine 1-phosphate (S1P) receptor (S1PR) agonism in the treatment of infectious diseases. A previous study used a murine model of Bordetella pertussis infection to demonstrate that treatment with the S1PR agonist AAL-R reduces pulmonary inflammation during infection. In the current study, we showed that this effect is mediated via the S1PR1 on LysM+ (myeloid) cells. Signaling via this receptor results in reduced lung inflammation and cellular recruitment as well as reduced morbidity and mortality in a neonatal mouse model of disease. Despite the fact that S1PRs are pertussis toxin-sensitive G protein-coupled receptors, the effects of AAL-R were pertussis toxin insensitive in our model. Furthermore, our data demonstrate that S1PR agonist administration may be effective at therapeutic time points. These results indicate a role for S1P signaling in B. pertussis-mediated pathology and highlight the possibility of host-targeted therapy for pertussis.

Modulators of Sphingosine-1-phosphate Pathway Biology: Recent Advances of Sphingosine-1-phosphate Receptor 1 (S1P1) Agonists and Future Perspectives

The sphingoid base derived class of lipids (sphingolipids) is a family of interconverting molecules that play key roles in numerous structural and signaling processes. The biosynthetic pathway of the sphingolipids affords many opportunities for therapeutic intervention: targeting the ligands directly, targeting the various proteins involved in the interconversion of the ligands, or targeting the receptors that respond to the ligands. The focus of this article is on the most advanced of the sphingosine-related therapeutics, agonists of sphingosine-1-phosphate receptor 1 (S1P₁). The diverse structural classes of S1P₁ agonists will be discussed and the status of compounds of clinical relevance will be detailed. An examination of how potential safety concerns are being navigated with compounds currently under clinical evaluation is followed by a discussion of the novel methods being explored to identify next-generation S1P₁ agonists with improved safety profiles. Finally, therapeutic opportunities for sphingosine-related targets outside of S1P₁ are touched upon.

Combinations of L-NG-monomethyl-arginine and oseltamivir against pandemic influenza A virus infections in mice

L-N^G-monomethyl-arginine (L-NMMA) is an experimental compound that suppresses nitric oxide production in animals. The compound was combined with oseltamivir to treat lethal influenza A/California/04/2009 (H1N1) pandemic virus infections in mice. Treatments were given twice a day for five days starting 4 h (oseltamivir, by oral gavage) or three days (L-NMMA, by intraperitoneal route; corresponding to the time previously reported for nitric oxide induction in the animals) after infection. Low doses of oseltamivir were used in order to demonstrate synergy or antagonism. Oseltamivir monotherapy protected 70% of mice from death at 1 mg/kg/day. L-NMMA (40 and 80 mg/kg/day) was ineffective alone in preventing mortality. Compared to oseltamivir treatment alone, L-NMMA combined with oseltamivir was synergistically effective (as evaluated by three-dimensional MacSynergy analysis), resulting in survival increases from 20 to 70% when 40 or 80 mg/kg/day of L-NMMA was combined with 0.3 mg/kg/day of oseltamivir, and from 70 to 100% survival increases when these doses were combined with 1 mg/kg/day of oseltamivir. These data demonstrate that a nitric oxide inhibitor such as L-NMMA has the potential to be beneficial when combined with oseltamivir in treating influenza virus infections.

FTY720 promotes pulmonary fibrosis when administered during the remodelling phase following a bleomycin-induced lung injury

Fibrosis complicates numerous pathologies including interstitial lung diseases. Sphingosine analogs such as FTY720 can alleviate lung injury-induced fibrosis in murine models. Contradictorily, FTY720 also promotes in vitro processes normally leading to fibrosis and high doses in vivo foster lung fibrosis by enhancing vascular leakage into the lung. The goal of this study was to determine the effect of low doses of FTY720 on lung fibrosis triggered by an acute injury in mice. We first defined the time-boundaries delimiting the inflammatory and remodelling phases of an injury elicited by bleomycin based on neutrophil counts, total lung capacity and lung stiffness. Thereafter, FTY720 (0.1 mg/kg) was delivered during either the inflammatory or the remodelling phases of bleomycin-induced injury. While FTY720 decreased fibrosis by 60% and lung stiffness by 28% when administered during the inflammatory phase, it increased fibrosis (2.1-fold) and lung stiffness (1.7-fold) when administered during the remodelling phase. FTY720-induced worsening of fibrosis was associated with an increased expression of connective tissue growth factor, but not with vascular leakage into the lung. Thus, the timing of FTY720 delivery following a bleomycin-induced lung injury determines pro-vs anti-fibrotic outcomes.

A Phosphorylatable Sphingosine Analog Induces Airway Smooth Muscle Cytostasis and Reverses Airway Hyperresponsiveness in Experimental Asthma

In asthma, excessive bronchial narrowing associated with thickening of the airway smooth muscle (ASM) causes respiratory distress. Numerous pharmacological agents prevent experimental airway hyperresponsiveness (AHR) when delivered prophylactically. However, most fail to resolve this feature after disease is instated. Although sphingosine analogs are primarily perceived as immune modulators with the ability to prevent experimental asthma, they also influence processes associated with tissue atrophy, supporting the hypothesis that they could interfere with mechanisms sustaining pre-established AHR. We thus assessed the ability of a sphingosine analog (AAL-R) to reverse AHR in a chronic model of asthma. We dissected the pharmacological mechanism of this class of agents using the non-phosphorylatable chiral isomer AAL-S and the pre-phosphorylated form of AAL-R (AFD-R) in vivo and in human ASM cells. We found that a therapeutic course of AAL-R reversed experimental AHR in the methacholine challenge test, which was not replicated by dexamethasone or the non-phosphorylatable isomer AAL-S. AAL-R efficiently interfered with ASM cell proliferation in vitro, supporting the concept that immunomodulation is not necessary to interfere with cellular mechanisms sustaining AHR. Moreover, the sphingosine-1-phosphate lyase inhibitor SM4 and the sphingosine-1-phosphate receptor antagonist VPC23019 failed to inhibit proliferation, indicating that intracellular accumulation of sphingosine-1-phosphate or interference with cell surface S1P₁/S1P₃ activation, are not sufficient to induce cytostasis. Potent AAL-R-induced cytostasis specifically related to its ability to induce intracellular AFD-R accumulation. Thus, a sphingosine analog that possesses the ability to be phosphorylated in situ interferes with cellular mechanisms that beget AHR.

Networks of Host Factors that Interact with NS1 Protein of Influenza A Virus

Pigs are an important host of influenza A viruses due to their ability to generate reassortant viruses with pandemic potential. NS1 protein of influenza A viruses is a key virulence factor and a major antagonist of innate immune responses. It is also involved in enhancing viral mRNA translation and regulation of virus replication. Being a protein with pleiotropic functions, NS1 has a variety of cellular interaction partners. Hence, studies on swine influenza viruses (SIV) and identification of swine influenza NS1-interacting host proteins is of great interest. Here, we constructed a recombinant SIV carrying a Strep-tag in the NS1 protein and infected primary swine respiratory epithelial cells (SRECs) with this virus. The Strep-tag sequence in the NS1 protein enabled us to purify intact, the NS1 protein and its interacting protein complex specifically. We identified cellular proteins present in the purified complex by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and generated a dataset of these proteins. 445 proteins were identified by LC-MS/MS and among them 192 proteins were selected by setting up a threshold based on MS parameters. The selected proteins were analyzed by bioinformatics and were categorized as belonging to different functional groups including translation, RNA processing, cytoskeleton, innate immunity, and apoptosis. Protein interaction networks were derived using these data and the NS1 interactions with some of the specific host factors were verified by immunoprecipitation. The novel proteins and the networks revealed in our study will be the potential candidates for targeted study of the molecular interaction of NS1 with host proteins, which will provide insights into the identification of new therapeutic targets to control influenza infection and disease pathogenesis.

Sphingosine-1-phosphate signaling: unraveling its role as a drug target against infectious diseases

Sphingosine-1-phosphate (S1P) signaling is reported in variety of cell types, including immune, endothelial and cancerous cells. It is emerging as a crucial regulator of cellular processes, such as apoptosis, cell proliferation, migration, differentiation and so on. This signaling pathway is initiated by the intracellular production and secretion of S1P through a cascade of enzymatic reactions. Binding of S1P to different S1P receptors (S1PRs) activates different downstream signaling pathways that regulate the cellular functions differentially depending upon the cell type. An accumulating body of evidence suggests that S1P metabolism and signaling is often impaired during infectious diseases; thus, its manipulation might be helpful in the treatment of such diseases. In this review, we summarize recent advances in our understanding of the S1P signaling pathway and its candidature as a novel drug target against infectious diseases.

Modulating the Innate Immune Response to Influenza A Virus: Potential Therapeutic Use of Anti-Inflammatory Drugs

Infection by influenza A viruses (IAV) is frequently characterized by robust inflammation that is usually more pronounced in the case of avian influenza. It is becoming clearer that the morbidity and pathogenesis caused by IAV are consequences of this inflammatory response, with several components of the innate immune system acting as the main players. It has been postulated that using a therapeutic approach to limit the innate immune response in combination with antiviral drugs has the potential to diminish symptoms and tissue damage caused by IAV infection. Indeed, some anti-inflammatory agents have been shown to be effective in animal models in reducing IAV pathology as a proof of principle. The main challenge in developing such therapies is to selectively modulate signaling pathways that contribute to lung injury while maintaining the ability of the host cells to mount an antiviral response to control virus replication. However, the dissection of those pathways is very complex given the numerous components regulated by the same factors (i.e., NF kappa B transcription factors) and the large number of players involved in this regulation, some of which may be undescribed or unknown. This article provides a comprehensive review of the current knowledge regarding the innate immune responses associated with tissue damage by IAV infection, the understanding of which is essential for the development of effective immunomodulatory drugs. Furthermore, we summarize the recent advances on the development and evaluation of such drugs as well as the lessons learned from those studies.

A ceramide analogue stimulates dendritic cells to promote T cell responses upon virus infections

The ceramide family of lipids plays important roles in both cell structure and signaling in a diverse array of cell types, including immune cells. However, very little is known regarding how ceramide affects the activation of dendritic cells (DCs) in response to viral infection. In this study, we demonstrate that a synthetic ceramide analog (C8) stimulates DCs to increase the expansion of virus-specific T cells upon virus infection. Exogenously supplied C8 ceramide elevated the expression of DC maturation markers such as MHC class I and costimulatory molecules following infection with the clone 13 strain of lymphocytic choriomeningitis virus (LCMV) or influenza virus. Importantly, ceramide-conditioned, LCMV-infected DCs displayed an increased ability to promote expansion of virus-specific CD8(+) T cells when compared with virus-infected DCs. Furthermore, a locally instilled ceramide analog significantly increased virus-reactive T cell responses in vivo to both LCMV and influenza virus infections. Collectively, these findings provide new insights into ceramide-mediated regulation of DC responses against virus infection and help us establish a foundation for novel immune-stimulatory therapeutics.

Treatment with a sphingosine analog after the inception of house dust mite-induced airway inflammation alleviates key features of experimental asthma

Background

In vivo phosphorylation of sphingosine analogs with their ensuing binding and activation of their cell-surface sphingosine-1-phosphate receptors is regarded as the main immunomodulatory mechanism of this new class of drugs. Prophylactic treatment with sphingosine analogs interferes with experimental asthma by impeding the migration of dendritic cells to draining lymph nodes. However, whether these drugs can also alleviate allergic airway inflammation after its onset remains to be determined. Herein, we investigated to which extent and by which mechanisms the sphingosine analog AAL-R interferes with key features of asthma in a murine model during ongoing allergic inflammation induced by Dermatophagoides pteronyssinus.

Methods

BALB/c mice were exposed to either D. pteronyssinus or saline, intranasally, once-daily for 10 consecutive days. Mice were treated intratracheally with either AAL-R, its pre-phosphorylated form AFD-R, or the vehicle before every allergen challenge over the last four days, i.e. after the onset of allergic airway inflammation. On day 11, airway responsiveness to methacholine was measured; inflammatory cells and cytokines were quantified in the airways; and the numbers and/or viability of T cells, B cells and dendritic cells were assessed in the lungs and draining lymph nodes.

Results

AAL-R decreased airway hyperresponsiveness induced by D. pteronyssinus by nearly 70%. This was associated with a strong reduction of IL-5 and IL-13 levels in the airways and with a decreased eosinophilic response. Notably, the lung CD4⁺ T cells were almost entirely eliminated by AAL-R, which concurred with enhanced apoptosis/necrosis in that cell population. This inhibition occurred in the absence of dendritic cell number modulation in draining lymph nodes. On the other hand, the pre-phosphorylated form AFD-R, which preferentially acts on cell-surface sphingosine-1-phosphate receptors, was relatively impotent at enhancing cell death, which led to a less efficient control of T cell and eosinophil responses in the lungs.

Conclusion

Airway delivery of the non-phosphorylated sphingosine analog, but not its pre-phosphorylated counterpart, is highly efficient at controlling the local T cell response after the onset of allergic airway inflammation. The mechanism appears to involve local induction of lymphocyte apoptosis/necrosis, while mildly affecting dendritic cell and T cell accumulation in draining lymph nodes.

The transforming growth factor beta signaling pathway is critical for the formation of CD4 T follicular helper cells and isotype-switched antibody responses in the lung mucosa

T follicular helper cells (Tfh) are crucial for the initiation and maintenance of germinal center (GC) reactions and high affinity, isotype-switched antibody responses. In this study, we demonstrate that direct TGF-β signaling to CD4 T cells is important for the formation of influenza-specific Tfh cells, GC reactions, and development of isotype-switched, flu-specific antibody responses. Early during infection, TGF-β signaling suppressed the expression of the high affinity IL-2 receptor α chain (CD25) on virus-specific CD4 T cells, which tempered IL-2 signaling and STAT5 and mammalian target of rapamycin (mTOR) activation in Tfh precursor CD4 T cells. Inhibition of mTOR allowed for the differentiation of Tfh cells in the absence of TGF-βR signaling, suggesting that TGF-β insulates Tfh progenitor cells from IL-2-delivered mTOR signals, thereby promoting Tfh differentiation during acute viral infection. These findings identify a new pathway critical for the generation of Tfh cells and humoral responses during respiratory viral infections.

DOI:http://dx.doi.org/10.7554/eLife.04851.001

The influenza virus is thought to cause illness in up to 10% of adults and 30% of children each year worldwide. Most of these cases resolve on their own and don’t require treatment, but three to five million people are hospitalized and up to half a million people die each year.

Unfortunately, the vaccines currently available to protect against influenza only target particular varieties or “strains” of the virus. The strains that circulate vary from year-to-year so it is necessary to develop new influenza vaccines every year. However, it is difficult to correctly predict which strains will circulate, so a more effective solution would be to develop a new vaccine that can help the body defend itself against many, or ideally any influenza strain.

During a viral infection, a type of immune cell in the host can specialize into two different types of cells to help fight the virus: T helper 1 cells and CD4 T follicular helper cells. T helper 1 cells help to kill host cells that have become infected. CD4 T follicular helper cells promote the production of proteins called antibodies, which identify and neutralize the virus.

Here, Marshall et al. studied how T helper 1 cells and CD4 T follicular helper cells form in mice suffering from a lung infection similar to influenza. It was already known that a protein called transforming growth factor beta (TGF-β) helps the immune response to mount an effective defense against an infection without causing too much harm to the host. Marshall et al. show that TGF-β increases the number of CD4 T follicular helper cells in the mice by suppressing the production of another protein—called IL-2—on the surface of CD4 T cells. Treating mice lacking the ability to detect TGF-β with a drug that blocks a protein controlled by IL-2 also allows more CD4 T follicular helper cells to be produced.

Marshall et al.’s findings reveal that TGF-β is involved in controlling the balance of T helper 1 cells and CD4 T follicular helper cells produced during viral infections of the respiratory tract. Since TGF-β also has other roles in immune responses against viruses, it is now an attractive target for the development of a vaccine that may protect us against all strains of the influenza virus.

DOI:http://dx.doi.org/10.7554/eLife.04851.002

CD8+ T cells control Ross River virus infection in musculoskeletal tissues of infected mice

Ross River virus (RRV), chikungunya virus, and related alphaviruses cause debilitating polyarthralgia and myalgia. Mouse models of RRV and chikungunya virus have demonstrated a role for the adaptive immune response in the control of these infections. However, questions remain regarding the role for T cells in viral control, including the magnitude, location, and dynamics of CD8(+) T cell responses. To address these questions, we generated a recombinant RRV expressing the H-2(b)-restricted glycoprotein 33 (gp33) determinant derived from the glycoprotein of lymphocytic choriomeningitis virus. Using tetramers, we tracked gp33-specific CD8(+) T cells during RRV-lymphocytic choriomeningitis virus infection. We found that acute RRV infection induces activation of CD8(+) T cell responses in lymphoid and musculoskeletal tissues that peak from 10-14 d postinoculation, suggesting that CD8(+) T cells contribute to control of acute RRV infection. Mice genetically deficient for CD8(+) T cells or wild-type mice depleted of CD8(+) T cells had elevated RRV loads in skeletal muscle tissue, but not joint-associated tissues, at 14 d postinoculation, suggesting that the ability of CD8(+) T cells to control RRV infection is tissue dependent. Finally, adoptively transferred T cells were capable of reducing RRV loads in skeletal muscle tissue of Rag1(-/-) mice, indicating that T cells can contribute to the control of RRV infection in the absence of B cells and Ab. Collectively, these data demonstrate a role for T cells in the control of RRV infection and suggest that the antiviral capacity of T cells is controlled in a tissue-specific manner.

S1P signaling: new therapies and opportunities

Development of sphingosine-1-phosphate receptor 1 (S1P1) modulators to dampen inflammation and its sequelae is becoming increasingly promising for treating medical conditions characterized by significant immunopathology. As shown by the non-selective S1P receptor modulator FTY720 (fingolimod [Gilenya(®)]) in the treatment of relapsing-remitting multiple sclerosis (MS), the ability to use S1P1 modulation to precisely block immune cell traffic-immunomodulation-while maintaining immunosurveillance, has opened therapeutic opportunities in various other immune-derived chronic pathologies, including inflammatory bowel disease (IBD), lupus, psoriasis, as well as, potentially, in early acute viral respiratory infection. Proof-of-concept studies across validated animal models with S1P receptor modulators highly selective for S1P1, such as BAF-312 (Siponimod), KRP-203, ONO-4641 (Ceralifimod), ponesimod and RPC-1063, and emerging clinical trials for safety and efficacy in humans, particularly in MS, ulcerative colitis (UC) and psoriasis, have set the stage for us to consider additional testing in various other autoimmune diseases.

Sphingosine analog AAL-R promotes activation of LCMV-infected dendritic cells

Sphingosine analogs display diverse immunoregulatory activities with curative potential in autoimmune diseases and viral infections. Recently, the sphingosine analog AAL-R was shown to increase DC activation upon TLR7 stimulation. Here, we investigated the effect of AAL-R on activation of dendritic cells (DCs) infected by lymphocytic choriomeningitis virus (LCMV). Concomitant treatment of LCMV-infected DCs with AAL-R enhanced DC maturation and DC ability to stimulate and expand antiviral CD8(+) T cells. Importantly, AAL-R's stimulatory activity was abrogated in type I interferon (IFN) receptor-deficient DCs following LCMV infection. In support of this observation, AAL-R increased type I IFN production from DCs infected with LCMV. Taken together, the sphingosine analog could directly act on DCs to promote defensive host DC responses to the viral invasion via type I IFN signaling.

Chemical and genetic tools to explore S1P biology

The zwitterionic lysophospholipid Sphingosine 1-Phosphate (S1P) is a pleiotropic mediator of physiology and pathology. The synthesis, transport, and degradation of S1P are tightly regulated to ensure that S1P is present in the proper concentrations in the proper location. The binding of S1P to five G protein-coupled S1P receptors regulates many physiological systems, particularly the immune and vascular systems. Our understanding of the functions of S1P has been aided by the tractability of the system to both chemical and genetic manipulation. Chemical modulators have been generated to affect most of the known components of S1P biology, including agonists of S1P receptors and inhibitors of enzymes regulating S1P production and degradation. Genetic knockouts and manipulations have been similarly engineered to disrupt the functions of individual S1P receptors or enzymes involved in S1P metabolism. This chapter will focus on the development and utilization of these chemical and genetic tools to explore the complex biology surrounding S1P and its receptors, with particular attention paid to the in vivo findings that these tools have allowed for.

Animal model of respiratory syncytial virus: CD8+ T cells cause a cytokine storm that is chemically tractable by sphingosine-1-phosphate 1 receptor agonist therapy

The cytokine storm is an intensified, dysregulated, tissue-injurious inflammatory response driven by cytokine and immune cell components. The cytokine storm during influenza virus infection, whereby the amplified innate immune response is primarily responsible for pulmonary damage, has been well characterized. Now we describe a novel event where virus-specific T cells induce a cytokine storm. The paramyxovirus pneumonia virus of mice (PVM) is a model of human respiratory syncytial virus (hRSV). Unexpectedly, when C57BL/6 mice were infected with PVM, the innate inflammatory response was undetectable until day 5 postinfection, at which time CD8(+) T cells infiltrated into the lung, initiating a cytokine storm by their production of gamma interferon (IFN-γ) and tumor necrosis factor alpha (TNF-α). Administration of an immunomodulatory sphingosine-1-phosphate (S1P) receptor 1 (S1P1R) agonist significantly inhibited PVM-elicited cytokine storm by blunting the PVM-specific CD8(+) T cell response, resulting in diminished pulmonary disease and enhanced survival.

IMPORTANCE

A dysregulated overly exuberant immune response, termed a "cytokine storm," accompanies virus-induced acute respiratory diseases (VARV), is primarily responsible for the accompanying high morbidity and mortality, and can be controlled therapeutically in influenza virus infection of mice and ferrets by administration of sphingosine-1-phosphate 1 receptor (S1P1R) agonists. Here, two novel findings are recorded. First, in contrast to influenza infection, where the cytokine storm is initiated early by the innate immune system, for pneumonia virus of mice (PVM), a model of RSV, the cytokine storm is initiated late in infection by the adaptive immune response: specifically, by virus-specific CD8 T cells via their release of IFN-γ and TNF-α. Blockading these cytokines with neutralizing antibodies blunts the cytokine storm and protects the host. Second, PVM infection is controlled by administration of an S1P1R agonist.

Influenza viral manipulation of sphingolipid metabolism and signaling to modulate host defense system

Viruses attempt to create a distinctive cellular environment to favor viral replication and spread. Recent studies uncovered new functions of the sphingolipid signaling/metabolism during pathogenic virus infections. While sphingolipids such as sphingomyelin and ceramide were reported to influence the entry step of several viruses, sphingolipid-metabolizing enzymes could directly alter viral replication processes. Influenza virus was shown to increase the level of sphingosine kinase (SK) 1 to promote virus propagation. The mechanism involves regulation of intracellular signaling pathways, leading to the amplification of influenza viral RNA synthesis and nuclear export of viral ribonucleoprotein (RNP) complex. However, bovine viral diarrhea virus inhibits SK1 to enhance the efficacy of virus replication, demonstrating the presence of virus-specific strategies for modulation of the sphingolipid system. Therefore, investigating the sphingolipid metabolism and signaling in the context of virus replication could help us design innovative therapeutic approaches to improve human health.

The organization of the sphingosine 1-phosphate signaling system

The understanding of the role of the sphingosine 1-phosphate signaling system in immunology and host defense has deepened exponentially over the past 12 years since the discovery that lymphocyte egress was reversibly modulated by sphingosine 1-phosphate receptors, and with the development of fingolimod, a prodrug of a nonselective S1P receptor agonist, for therapeutic use in the treatment of relapsing, remitting multiple sclerosis. Innovative genetic and chemical approaches, together with structural biology, now provide a more detailed molecular understanding of a regulated lysophospholipid ligand with a variety of autocrine, paracrine, and systemic effects in physiology and pathology, based upon selective interactions with a high affinity and selective evolutionary cluster of G-protein-coupled receptors.

The role of cytokine responses during influenza virus pathogenesis and potential therapeutic options

Aberrant pulmonary immune responses are linked to the pathogenesis of multiple human respiratory viral infections. Elevated cytokine and chemokine production "cytokine storm" has been continuously associated with poor clinical outcome and pathogenesis during influenza virus infection in humans and animal models. Initial trials using global immune suppression with corticosteroids or targeted neutralization of single inflammatory mediators proved ineffective to ameliorate pathology during pathogenic influenza virus infection. Thus, it was believed that cytokine storm was either chemically intractable or not causal in the pathology observed. During this review, we will discuss the history of research assessing the roles various cytokines, chemokines, and innate immune cells play in promoting pathology or protection during influenza virus infection. Several promising new strategies modulating lipid signaling have been recently uncovered for global blunting, but not ablation, of innate immune responses following influenza virus infection. Importantly, modulating lipid signaling through various means has proven effective at curbing morbidity and mortality in animal models and may be useful for curbing influenza virus induced pathology in humans. Finally, we highlight future research directions for mechanistically dissecting how modulation of lipid signaling pathways results in favorable outcomes following influenza virus infection.

Cytokine storm plays a direct role in the morbidity and mortality from influenza virus infection and is chemically treatable with a single sphingosine-1-phosphate agonist molecule

Cytokine storm defines a dysregulation of and an excessively exaggerated immune response most often accompanying selected viral infections and several autoimmune diseases. Newly emerging and re-emerging infections of the respiratory tract, especially influenza, SARS, and hantavirus post considerable medical problems. Their morbidities and mortalities are often a direct result of cytokine storm. This chapter visits primarily influenza virus infection and resultant cytokine storm. It provides the compelling evidence that illuminates cytokine storm in influenza pathogenesis and the clear findings that cytokine storm is chemically tractable by therapy directed toward sphingosine-1-phosphate receptor (S1PR) modulation, specifically S1P1R agonist therapy. The mechanism(s) of how S1P1R signaling works and the pathways involved are subjects of this review.

Antigen-activated dendritic cells ameliorate influenza A infections

Influenza A viruses cause significant morbidity and mortality worldwide. There is a need for alternative or adjunct therapies, as resistance to currently used antiviral drugs is emerging rapidly. We tested ligand epitope antigen presentation system (LEAPS) technology as a new immune-based treatment for influenza virus infection in a mouse model. Influenza-J-LEAPS peptides were synthesized by conjugating the binding ligand derived from the β2-microglobulin chain of the human MHC class I molecule (J-LEAPS) with 15 to 30 amino acid-long peptides derived from influenza virus NP, M, or HA proteins. DCs were stimulated with influenza-J-LEAPS peptides (influenza-J-LEAPS) and injected intravenously into infected mice. Antigen-specific LEAPS-stimulated DCs were effective in reducing influenza virus replication in the lungs and enhancing survival of infected animals. Additionally, they augmented influenza-specific T cell responses in the lungs and reduced the severity of disease by limiting excessive cytokine responses, which are known to contribute to morbidity and mortality following influenza virus infection. Our data demonstrate that influenza-J-LEAPS-pulsed DCs reduce virus replication in the lungs, enhance survival, and modulate the protective immune responses that eliminate the virus while preventing excessive cytokines that could injure the host. This approach shows promise as an adjunct to antiviral treatment of influenza virus infections.

Sphingosine 1-phosphate receptor agonists: a patent review (2010-2012)

INTRODUCTION

The sphingosine-1-phosphate (S1P)-driven signaling regulates fundamental biological functions, including cell proliferation, angiogenesis, endothelial cell chemotaxis, immune cell trafficking and mitogenesis. A large body of research has been focusing on the development of immunosuppressive S1P1 receptor (S1P1-R) agonist molecules. The S1P(1,3-5)-R pan-agonist fingolimod (FTY720) has been approved by the FDA for the treatment of relapsing-remitting multiple sclerosis. However, FTY720 is now contraindicated in patients with compromised cardiac function. Although the main adverse effect bradycardia has been linked to the S1P3-R activation, cardiovascular liabilities persist with more selective S1P1-R agonists that have entered clinical trials. In contrast to the S1P1-R, the therapeutic application of the S1P(2-5)-Rs remains poorly explored.

AREAS COVERED

This review provides the patent literature from 2010 to date on S1P-R agonist molecules and their relevant biological properties.

EXPERT OPINION

Limited progress has been made on agonists at S1P(4,5)-R subtypes, with some families of S1P5-R agonists showing promising results in animal models of age-related cognitive disorders. A discrete number of reviewed molecules are S1P1-R agonists with a promising clinical outlook in transplantation, inflammation, cancer and autoimmune settings. Further preclinical and clinical studies will determine whether the new developed S1P1-R agonists do indeed improve the safety profile of FTY720.

Three phases of CD8 T cell response in the lung following H1N1 influenza infection and sphingosine 1 phosphate agonist therapy

Influenza-induced lung edema and inflammation are exacerbated by a positive feedback loop of cytokine and chemokine production termed a 'cytokine storm', a hallmark of increased influenza-related morbidity and mortality. Upon infection, an immune response is rapidly initiated in the lungs and draining lymph node, leading to expansion of virus-specific effector cells. Using two-photon microscopy, we imaged the dynamics of dendritic cells (DC) and virus-specific eGFP(+)CD8(+) T cells in the lungs and draining mediastinal lymph nodes during the first two weeks following influenza infection. Three distinct phases of T cell and CD11c(+) DC behavior were revealed: 1) Priming, facilitated by the arrival of lung DCs in the lymph node and characterized by antigen recognition and expansion of antigen-specific CD8(+) T cells; asymmetric T cell division in contact with DCs was frequently observed. 2) Clearance, during which DCs re-populate the lung and T cells leave the draining lymph node and re-enter the lung tissue where enlarged, motile T cells come into contact with DCs and form long-lived interactions. 3) Maintenance, characterized by T-cell scanning of the lung tissue and dissociation from local antigen presenting cells; the T cells spend less time in association with DCs and migrate rapidly on collagen. A single dose of a sphingosine-1-phosphate receptor agonist, AAL-R, sufficient to suppress influenza-induced cytokine-storm, altered T cell and DC behavior during influenza clearance, delaying T cell division, cellular infiltration in the lung, and suppressing T-DC interactions in the lung. Our results provide a detailed description of T cell and DC choreography and dynamics in the lymph node and the lung during influenza infection. In addition, we suggest that phase lags in T cell and DC dynamics induced by targeting S1P receptors in vivo may attenuate the intensity of the immune response and can be manipulated for therapeutic benefit.

Sphingosine-1-phosphate and its receptors: structure, signaling, and influence

The sphingosine-1-phosphate (S1P) receptor signaling system has biological and medical importance and is the first lipid G protein-coupled receptor (GPCR) structure to be solved to 2.8-Å resolution. S1P binds to five high-affinity GPCRs generating multiple downstream signals that play essential roles in vascular development and endothelial integrity, control of cardiac rhythm, and routine oral treatment of multiple sclerosis. Genetics, chemistry, and now structural biology have advanced this integrated biochemical system. The S1P receptors have a novel N-terminal fold that occludes access to the binding pocket from the extracellular environment as well as orthosteric and bitopic ligands with very different physicochemical properties. S1P receptors and metabolizing enzymes have been deleted, inducibly deleted, and knocked in as tagged or altered receptors in mice. An array of genetic models allows analysis of integrated receptor function in vivo. We can now directly understand causal relationships among protein expression, signal, and control points in physiology and pathology.

Lessons learned and concepts formed from study of the pathogenesis of the two negative-strand viruses lymphocytic choriomeningitis and influenza

Viruses have unique lifestyles. To describe the pathogenesis and significance of viral infection in terms of host responses, resultant injury, and therapy, we focused on two RNA viruses: lymphocytic choriomeningitis (LCMV) and influenza (Flu). Many of the currently established concepts and consequences about viruses and immunologic tolerance, virus-induced immunosuppression, virus-induced autoimmunity, immune complex disease, and virus-lymphocyte and virus-dendritic cell interactions evolved through studies of LCMV in its natural murine host. Similarly, the mechanisms, aftermath, and treatment of persistent RNA viruses emerged, in large part, from research on LCMV. Analysis of acute influenza virus infections uncovered the prominent direct role that cytokine storm plays in the pathogenesis, morbidity, and mortality from this disease. Cytokine storm of influenza virus infection is initiated via a pulmonary endothelial cell amplification loop involving IFN-producing cells and virus-infected pulmonary epithelial cells. Importantly, the cytokine storm is chemically treatable with specific agonist therapy directed to the sphingosphine 1 phosphate receptor 1, which is located on pulmonary endothelial cells, pointing to the endothelial cells as the gatekeepers of this hyperaggressive host immune response.

Targeting the host or the virus: current and novel concepts for antiviral approaches against influenza virus infection

Influenza epidemics and pandemics are constant threats to human health. The application of antiviral drugs provides an immediate and direct control of influenza virus infection. At present, the major strategy for managing patients with influenza is through targeting conserved viral proteins critical for viral replication. Two classes of conventional antiviral drugs, the M2 ion channel blockers and the neuraminidase inhibitors, are frequently used. In recent years, increasing levels of resistance to both drug classes has become a major public health concern, highlighting the urgent need for the development of alternative treatments. Novel classes of antiviral compounds or biomolecules targeting viral replication mechanism are under development, using approaches including high-throughput small-molecule screening platforms and structure-based designs. In response to influenza virus infection, host cellular mechanisms are triggered to defend against the invaders. At the same time, viruses as obligate intracellular pathogens have evolved to exploit cellular responses in support of their efficient replication, including antagonizing the host type I interferon response as well as activation of specific cellular pathways at different stages of the replication cycle. Numerous studies have highlighted the possibility of targeting virus-host interactions and host cellular mechanisms to develop new treatment regimens. This review aims to give an overview of current and novel concepts targeting the virus and the host for managing influenza.

Effect of statin treatments on highly pathogenic avian influenza H5N1, seasonal and H1N1pdm09 virus infections in BALB/c mice

Statins are used to control elevated cholesterol or hypercholesterolemia, but have previously been reported to have antiviral properties. AIMS: To show efficacy of statins in various influenza virus mouse models. MATERIALS & METHODS: BALB/c mice were treated intraperitoneally or orally with several types of statins (simvastatin, lovastatin, mevastatin, pitavastatin, atorvastatin or rosuvastatin) at various concentrations before or after infection with either influenza A/Duck/ MN/1525/81 H5N1 virus, influenza A/Vietnam/1203/2004 H5N1 virus, influenza A/ Victoria/3/75 H3N2 virus, influenza A/NWS/33 H1N1 virus or influenza A/CA/04/09 H1N1pdm09 virus. RESULTS: The statins administered intraperitoneally or orally at any dose did not significantly enhance the total survivors relative to untreated controls. In addition, infected mice receiving any concentration of statin were not protected against weight loss due to the infection. None of the statins significantly increased the mean day of death relative to mice in the placebo treatment group. Furthermore, the statins had relatively few ameliorative effects on lung pathology or lung weights at day 3 and 6 after virus exposure, although mice treated with simvastatin did have improved lung function as measured by arterial saturated oxygen levels in one experiment. CONCLUSION: Statins showed relatively little efficacy in any mouse model used by any parameter tested.

Sphingosine analogue AAL-R increases TLR7-mediated dendritic cell responses via p38 and type I IFN signaling pathways

Sphingosine analogues display immunosuppressive activities and thus have therapeutic potential in the treatment of autoimmune diseases. In this study, we investigated the effects of the sphingosine analogue AAL-R (FTY720 derivative) on dendritic cell (DC) response upon TLR stimulation. Unlike its known immunosuppressive activity, AAL-R increased TLR7-mediated DC responses by elevating the levels of MHC class I and costimulatory molecules and type I IFN expression and by enhancing the capacity of DCs to induce CD8(+) T cell proliferation. Importantly, the stimulatory activity of AAL-R was dependent on type I IFN signaling, as type I IFN receptor-deficient DCs failed to respond to AAL-R. Also, AAL-R activated p38 MAPK to increase type I IFN synthesis and TLR7-mediated DC maturation. These findings enhance our understanding of sphingosine regulation of the host immune system, in particular upon pathogenic infections.

Regulating the adaptive immune response to respiratory virus infection

The respiratory tract is a major portal of entry for viruses into the body. Infection of the respiratory tract can, if severe, induce life-threatening damage to the lungs. Various strategies to control virus replication and to limit immune-mediated inflammation and tissue injury have evolved in the respiratory tract.

Multiple innate immune cell types, particularly dendritic cells (DCs), within the pulmonary interstitium and between airway epithelial cells are strategically poised to recognize and sample airway particulates, such as viruses.

In response to respiratory virus infection, several distinct DC subsets are stimulated to migrate from the site of infection in the lungs to the draining lymph nodes. Here, these migrant DCs have a crucial role in initiating the antivirus adaptive immune response to the invading viruses.

After entering the infected lungs, effector T cells that were generated in the lymph nodes undergo further modifications that are shaped by the inflammatory milieu.

Co-stimulatory receptor–ligand interactions between effector T cells and various cell types presenting viral antigens in the infected lungs modulate the host adaptive immune response in situ.

Effector T cells that produce pro-inflammatory mediators are also the major producers of regulatory (anti-inflammatory) cytokines, providing a fine-tuning mechanism of self-control by effector T cells responding to viruses in the inflamed tissue.

The immune mechanisms that control virus replication and/or excessive inflammation in the virus-infected lungs can also predispose the individual recovering from a virus infection to bacterial superinfection. Therapeutic strategies should consider balancing the need to inhibit virus replication and excessive inflammation with the need to optimize the antibacterial functions of innate immune phagocytes, which are crucial for clearing the bacteria from the lungs.

This article reviews the interplay between innate and adaptive immune cells in the response to viral infection of the lower respiratory tract and describes the fine-tuning mechanisms that control antiviral T cells in the lungs but that can also predispose an individual to subsequent pulmonary bacterial infections.

Recent years have seen several advances in our understanding of immunity to virus infection of the lower respiratory tract, including to influenza virus infection. Here, we review the cellular targets of viruses and the features of the host immune response that are unique to the lungs. We describe the interplay between innate and adaptive immune cells in the induction, expression and control of antiviral immunity, and discuss the impact of the infected lung milieu on moulding the response of antiviral effector T cells. Recent findings on the mechanisms that underlie the increased frequency of severe pulmonary bacterial infections following respiratory virus infection are also discussed.

Quelling the storm: utilization of sphingosine-1-phosphate receptor signaling to ameliorate influenza virus-induced cytokine storm

Initial and early tissue injury associated with severe influenza virus infection is the result of both virus-mediated lysis of infected pulmonary cells coupled with an exuberant immune response generated against the virus. The excessive host immune response associated with influenza virus infection has been termed "cytokine storm." Therapies that target virus replication are available; however, the selective pressure by such antiviral drugs on the virus often results in mutation and the escape of virus progeny now resistant to the antiviral regimen, thereby rendering such treatments ineffective. This event highlights the necessity for developing novel methods to combat morbidity and mortality caused by influenza virus infection. One potential method is restricting the host's immune response. However, prior treatment regimens employing drugs like corticosteroids that globally suppress the host's immune response were found unsatisfactory in large part because they disrupted the host's ability to control virus replication. Here, we discuss a novel therapy that utilizes sphingosine-1-phosphate (S1P) receptor signaling that has the ability to significantly limit immunopathologic injury caused by the host's innate and adaptive immune response, thereby significantly aborting morbidity and mortality associated with influenza virus infection. Moreover, S1P analog therapy allows for sufficient anti-influenza T cell and antibody formation to control infection. We review the anti-inflammatory effects of S1P signaling pathways and how modulation of these pathways during influenza virus infection restricts immunopathology. Finally, we discuss that combinatorial administration of S1P simultaneously with a current antiviral enhances the treatment efficacy for virulent influenza virus infections above that of either drug treatment alone. Interestingly, the scope of S1P receptor therapy reported here is likely to extend beyond influenza virus infection and could prove useful for the treatment of multiple maladies like other viral infections and autoimmune diseases where the host's inflammatory response is a major component in the disease process.

Endothelial cells are central orchestrators of cytokine amplification during influenza virus infection

Cytokine storm during viral infection is a prospective predictor of morbidity and mortality, yet the cellular sources remain undefined. Here, using genetic and chemical tools to probe functions of the S1P₁ receptor, we elucidate cellular and signaling mechanisms that are important in initiating cytokine storm. Whereas S1P₁ receptor is expressed on endothelial cells and lymphocytes within lung tissue, S1P₁ agonism suppresses cytokines and innate immune cell recruitment in wild-type and lymphocyte-deficient mice, identifying endothelial cells as central regulators of cytokine storm. Furthermore, our data reveal immune cell infiltration and cytokine production as distinct events that are both orchestrated by endothelial cells. Moreover, we demonstrate that suppression of early innate immune responses through S1P₁ signaling results in reduced mortality during infection with a human pathogenic strain of influenza virus. Modulation of endothelium with a specific agonist suggests that diseases in which amplification of cytokine storm is a significant pathological component could be chemically tractable.

A new shield for a cytokine storm

Highly virulent influenza virus infection results in excessive cytokine production, recruitment of leukocytes, and immune-mediated pulmonary injury. Teijaro et al. (2011) now demonstrate that sphingosine-1-phosphate receptor 1 ligands suppress all features of flu-inflicted pathological inflammation and place the endothelium at the center of this regulatory network.

Discovery, design and synthesis of novel potent and selective sphingosine-1-phosphate 4 receptor (S1P₄-R) agonists

High affinity and selective small molecule agonists of the S1P(4) receptor (S1P(4)-R) may have significant therapeutic utility in diverse disease areas including autoimmune diseases, viral infections and thrombocytopenia. A high-throughput screening (HTS) of the Molecular Libraries-Small Molecule Repository library identified 3-(2-(2,4-dichlorophenoxy)ethoxy)-6-methyl-2-nitropyridine as a moderately potent and selective S1P(4)-R hit agonist. Design, synthesis and systematic structure-activity relationships study of the HTS-derived hit led to the development of novel potent S1P(4)-R agonists exquisitely selective over the remaining S1P(1-3,5)-Rs family members. Remarkably, the molecules herein reported provide novel pharmacological tools to decipher the biological function and assess the therapeutic utility of the S1P(4)-R.

Discovery, synthesis and SAR analysis of novel selective small molecule S1P4-R agonists based on a (2Z,5Z)-5-((pyrrol-3-yl)methylene)-3-alkyl-2-(alkylimino)thiazolidin-4-one chemotype

High affinity and selective S1P(4) receptor (S1P(4)-R) small molecule agonists may be important proof-of-principle tools used to clarify the receptor biological function and effects to assess the therapeutic potential of the S1P(4)-R in diverse disease areas including treatment of viral infections and thrombocytopenia. A high-throughput screening campaign of the Molecular Libraries-Small Molecule Repository was carried out by our laboratories and identified (2Z,5Z)-5-((1-(2-fluorophenyl)-2,5-dimethyl-1H-pyrrol-3-yl)methylene)-3-methyl-2-(methylimino) thiazolidin-4-one as a promising S1P(4)-R agonist hit distinct from literature S1P(4)-R modulators. Rational chemical modifications of the hit allowed the identification of a promising lead molecule with low nanomolar S1P(4)-R agonist activity and exquisite selectivity over the other S1P(1-3,5)-Rs family members. The lead molecule herein disclosed constitutes a valuable pharmacological tool to explore the effects of the S1P(4)-R signaling cascade and elucidate the molecular basis of the receptor function.

SAR analysis of innovative selective small molecule antagonists of sphingosine-1-phosphate 4 (S1P₄) receptor

Recent evidence suggests an innovative application of chemical modulators targeting the S1P(4) receptor as novel mechanism-based drugs for the treatment of influenza virus infection. Modulation of the S1P(4) receptor may also represent an alternative therapeutic approach for clinical conditions where reactive thrombocytosis is an undesired effect or increased megakaryopoiesis is required. With the exception of our recent research program disclosure, we are not aware of any selective S1P(4) antagonists reported in the literature to date. Herein, we describe complementary structure-activity relationships (SAR) of the high-throughput screening (HTS)-derived hit 5-(2,5-dichlorophenyl)-N-(2,6-dimethylphenyl)furan-2-carboxamide and its 2,5-dimethylphenyl analog. Systematic structural modifications of the furan ring showed that both steric and electronic factors in this region have a significant impact on the potency. The furan moiety was successfully replaced with a thiophene or phenyl ring maintaining potency in the low nanomolar range and high selectivity against the other S1P receptor subtypes. By expanding the molecular diversity within the hit-derived class, our SAR study provides innovative small molecule potent and selective S1P(4) antagonists suitable for in vivo pharmacological validation of the target receptor.

Suppression of cytokine storm with a sphingosine analog provides protection against pathogenic influenza virus

Human pandemic H1N1 2009 influenza virus rapidly infected millions worldwide and was associated with significant mortality. Antiviral drugs that inhibit influenza virus replication are the primary therapy used to diminish disease; however, there are two significant limitations to their effective use: (i) antiviral drugs exert selective pressure on the virus, resulting in the generation of more fit viral progeny that are resistant to treatment; and (ii) antiviral drugs do not directly inhibit immune-mediated pulmonary injury that is a significant component of disease. Here we show that dampening the host's immune response against influenza virus using an immunomodulatory drug, AAL-R, provides significant protection from mortality (82%) over that of the neuraminidase inhibitor oseltamivir alone (50%). AAL-R combined with oseltamivir provided maximum protection against a lethal challenge of influenza virus (96%). Mechanistically, AAL-R inhibits cellular and cytokine/chemokine responses to limit immunopathologic damage, while maintaining host control of virus replication. With cytokine storm playing a role in the pathogenesis of a wide assortment of viral, bacterial, and immunologic diseases, a therapeutic approach using sphingosine analogs is of particular interest.

Discovery, design and synthesis of the first reported potent and selective sphingosine-1-phosphate 4 (S1P4) receptor antagonists

Selective S1P(4) receptor antagonists could be novel therapeutic agents for the treatment of influenza infection in addition to serving as a useful tool for understanding S1P(4) receptor biological functions. 5-(2,5-Dichlorophenyl)-N-(2,6-dimethylphenyl)furan-2-carboxamide was identified from screening the Molecular Libraries-Small Molecule Repository (MLSMR) collection and selected as a promising S1P(4) antagonist hit with moderate in vitro potency and high selectivity against the other family receptor subtypes (S1P(1-3,5)). Rational chemical modifications of the hit allowed the disclosure of the first reported highly selective S1P(4) antagonists with low nanomolar activity and adequate physicochemical properties suitable for further lead-optimization studies.

Actions of a picomolar short-acting S1P₁ agonist in S1P₁-eGFP knock-in mice

Sphingosine 1-phosphate receptor 1 (S1P(1)) is critical for lymphocyte recirculation and is a clinical target for treatment of multiple sclerosis. By generating a short-duration S1P(1) agonist and mice in which fluorescently tagged S1P(1) replaces wild-type receptor, we elucidate physiological and agonist-perturbed changes in expression of S1P(1) at a subcellular level in vivo. We demonstrate differential downregulation of S1P(1) on lymphocytes and endothelia after agonist treatment.