Human TLR-7-, -8-, and -9-mediated induction of IFN-alpha/beta and -lambda Is IRAK-4 dependent and redundant for protective immunity to viruses

IL-1 receptor-associated kinase family proteins: An overview of their role in liver disease

The interleukin-1 receptor-associated kinase (IRAK) family is a group of serine-threonine kinases that regulates various cellular processes via toll-like receptor (TLR)/interleukin-1 receptor (IL1R)-mediated signaling. The IRAK family comprises four members, including IRAK1, IRAK2, IRAK3, and IRAK4, which play an important role in the expression of various inflammatory genes, thereby contributing to the inflammatory response. IRAKs are key proteins in chronic and acute liver diseases, and recent evidence has implicated IRAK family proteins (IRAK1, IRAK3, and IRAK4) in the progression of liver-related disorders, including alcoholic liver disease, non-alcoholic steatohepatitis, hepatitis virus infection, acute liver failure, liver ischemia-reperfusion injury, and hepatocellular carcinoma. In this article, we provide a comprehensive review of the role of IRAK family proteins and their associated inflammatory signaling pathways in the pathogenesis of liver diseases. The purpose of this study is to explore whether IRAK family proteins can serve as the main target for the treatment of liver related diseases.

Effects of toll-like receptor agonists and SARS-CoV-2 antigens on interferon (IFN) expression by peripheral blood CD3+ T cells from COVID-19 patients

BACKGROUND

Signaling by toll-like receptors (TLRs) initiates important immune responses against viral infection. The role of TLRs in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is not well elucidated. Thus, we investigated the interaction of TLRs agonists and SARS-COV-2 antigens with immune cells in vitro.

MATERIAL & METHODS

30 coronavirus disease 2019 (COVID-19) patients (15 severe and 15 moderate) and 10 age and sex-matched healthy control (HC) were enrolled. Peripheral blood mononuclear cells (PBMCs) were isolated and activated with TLR3, 7, 8, and 9 agonists, the spike protein (SP) of SARS-CoV-2, and the receptor binding domain (RBD) of SP. Frequencies of CD3+IFN-β+ T cells, and CD3+IFN-γ+ T cells were evaluated by flow cytometry. Interferon (IFN)-β gene expression was assessed by qRT-PCR.

RESULTS

The frequency of CD3+IFN-β+ T cells was higher in PBMCs from moderate (p < 0.0001) and severe (p = 0.009) patients at baseline in comparison with HCs. The highest increase in the frequency of CD3+IFN-β+ T cells in cell from moderate patients was induced by TLR8 agonist and SP (p < 0.0001 for both) when compared to HC, while, the highest increase of the frequency of CD3+IFN-β+ T cells in sample of severe patients was seen with TLR8 and TLR7 agonists (both p = 0.002). The frequency of CD3+IFN-γ+ T cells was significantly increased upon stimulation with TLR agonists in cell from patients with moderate and severe COVID-19, compared with HC (all p < 0.01), except with TLR7 and TLR8 agonists. The TLR8 agonist did not significantly increase the frequency of CD3+IFN-γ+ T cells in PBMCs of severe patients, but did so in cells from patients with moderate disease (p = 0.01). Moreover, IFN-β gene expression was significantly upregulated in CD3+T cells from moderate (p < 0.0001) and severe (p = 0.002) COVID-19 patients, compared to HC after stimulation with the TLR8 agonist, while, stimulation of T cells with SP, significantly up-regulated IFN-β mRNA expression in cells from patients with moderate (p = 0.0003), but not severe disease.

CONCLUSION

Stimulation of PBMCs from COVID-19 patients, especially patients with moderate disease, with TLR8 agonist and SP increased the frequency of IFN-β-producing T cells and IFN-β gene expression.

The role of plasmacytoid dendritic cells (pDCs) in immunity during viral infections and beyond

Type I and III interferons (IFNs) are essential for antiviral immunity and act through two different but complimentary pathways. First, IFNs activate intracellular antimicrobial programs by triggering the upregulation of a broad repertoire of viral restriction factors. Second, IFNs activate innate and adaptive immunity. Dysregulation of IFN production can lead to severe immune system dysfunction. It is thus crucial to identify and characterize the cellular sources of IFNs, their effects, and their regulation to promote their beneficial effects and limit their detrimental effects, which can depend on the nature of the infected or diseased tissues, as we will discuss. Plasmacytoid dendritic cells (pDCs) can produce large amounts of all IFN subtypes during viral infection. pDCs are resistant to infection by many different viruses, thus inhibiting the immune evasion mechanisms of viruses that target IFN production or their downstream responses. Therefore, pDCs are considered essential for the control of viral infections and the establishment of protective immunity. A thorough bibliographical survey showed that, in most viral infections, despite being major IFN producers, pDCs are actually dispensable for host resistance, which is achieved by multiple IFN sources depending on the tissue. Moreover, primary innate and adaptive antiviral immune responses are only transiently affected in the absence of pDCs. More surprisingly, pDCs and their IFNs can be detrimental in some viral infections or autoimmune diseases. This makes the conservation of pDCs during vertebrate evolution an enigma and thus raises outstanding questions about their role not only in viral infections but also in other diseases and under physiological conditions.

In search of a function for human type III interferons: insights from inherited and acquired deficits

The essential and redundant functions of human type I and II interferons (IFNs) have been delineated over the last three decades by studies of patients with inborn errors of immunity or their autoimmune phenocopies, but much less is known about type III IFNs. Patients with cells that do not respond to type III IFNs due to inherited IL10RB deficiency display no overt viral disease, and their inflammatory disease phenotypes can be explained by defective signaling via other interleukine10RB-dependent pathways. Moreover, patients with inherited deficiencies of interferon-stimulated gene factor 3 (ISGF-3) (STAT1, STAT2, IRF9) present viral diseases also seen in patients with inherited deficiencies of the type I IFN receptor (IFNAR1/2). Finally, patients with autoantibodies neutralizing type III IFNs have no obvious predisposition to viral disease. Current findings thus suggest that type III IFNs are largely redundant in humans. The essential functions of human type III IFNs, particularly in antiviral defenses, remain to be discovered.

Potential role of EBV and Toll-like receptor 9 ligand in patients with systemic lupus erythematosus

SLE is a multisystem autoimmune disease characterized by multiple immunological abnormalities including production of autoantibodies. While the etiology of SLE is largely unknown, it is generally accepted that both genetic and environmental factors contribute to disease risk and immune dysregulation. Production of IFN-α is important for protecting the host against infections; however, over stimulation of innate immune pathways can induce autoimmune disease. Environmental factors, particularly Epstein-Barr virus (EBV), have been proposed to play an important role in SLE disease. Improper engagement of Toll-like receptor (TLR) pathways by endogenous or exogenous ligands may lead to the initiation of autoimmune responses and tissue injury. EBV is shown to be a potent stimulant of IFN-α by TLR signaling cascades. Given the highlighted role of IFN-α in SLE pathogenesis and potential role of EBV infection in this disease, the present study is aimed at exploring the in vitro effects of EBV infection and CPG (either alone or in combination) on IFN-α. We also examined the expression level of CD20 and BDCA-4 and CD123 in PBMCs in 32 SLE patients and 32 healthy controls. Our results showed PBMCs treated with CPG-induced higher levels of IFN-α and TLR-9 gene expression fold change compared to cells treated with either EBV or EBV-CPG. Moreover, PBMCs treated with CPG produced significantly higher IFN-α concentration in supernatant compared to cells treated with EBV but not EBV-CPG. Our results further highlight the potential role of EBV infection and TLRs in SLE patients although more studies are warranted to ascertain the global imprint that EBV infection can have on immune signature in patients with SLE.

Humans with inherited MyD88 and IRAK-4 deficiencies are predisposed to hypoxemic COVID-19 pneumonia

X-linked recessive deficiency of TLR7, a MyD88- and IRAK-4-dependent endosomal ssRNA sensor, impairs SARS-CoV-2 recognition and type I IFN production in plasmacytoid dendritic cells (pDCs), thereby underlying hypoxemic COVID-19 pneumonia with high penetrance. We report 22 unvaccinated patients with autosomal recessive MyD88 or IRAK-4 deficiency infected with SARS-CoV-2 (mean age: 10.9 yr; 2 mo to 24 yr), originating from 17 kindreds from eight countries on three continents. 16 patients were hospitalized: six with moderate, four with severe, and six with critical pneumonia, one of whom died. The risk of hypoxemic pneumonia increased with age. The risk of invasive mechanical ventilation was also much greater than in age-matched controls from the general population (OR: 74.7, 95% CI: 26.8-207.8, P < 0.001). The patients' susceptibility to SARS-CoV-2 can be attributed to impaired TLR7-dependent type I IFN production by pDCs, which do not sense SARS-CoV-2 correctly. Patients with inherited MyD88 or IRAK-4 deficiency were long thought to be selectively vulnerable to pyogenic bacteria, but also have a high risk of hypoxemic COVID-19 pneumonia.

Inherited IRAK-4 Deficiency in Acute Human Herpesvirus-6 Encephalitis

Human herpesvirus-6 (HHV-6) infection can rarely cause life-threatening conditions, such as encephalitis, in otherwise healthy children, with unclear pathogenesis. We studied a child who presented with acute HHV-6 encephalitis at the age of 10 months and who was homozygous for a novel missense mutation in IRAK4, encoding interleukin-1 receptor-associated kinase 4, identified by whole-exome sequencing. We tested the damaging impact of this mutation in silico by molecular dynamics simulations and in vitro by biochemical and functional experiments utilizing cell lines and patient's cells. We found that the mutation is severely hypomorphic, impairing both the expression and function of IRAK-4. Patient's leukocytes had barely detectable levels of IRAK-4 and diminished anti-viral immune responses to various stimuli inducing different Toll-like receptors and cytosolic nucleic acid sensors. Overall, these findings suggest that acute HHV-6 encephalitis can result from inborn errors of immunity to virus. This study represents the first report of isolated acute HHV-6 infection causing encephalitis in an inherited primary immunodeficiency, notably autosomal recessive (AR) partial IRAK-4 deficiency, and the first report of AR IRAK-4 deficiency presenting with a severe viral disease, notably HHV-6 encephalitis upon an acute infection, thereby expanding the clinical spectrum of IRAK-4 deficiency.

Ablation of SigH+ pDCs in B6.Nba2 mice prevents lupus-like disease development only if started before disease is fully established

Systemic lupus erythematosus is characterized by hyper-activation of the immune system, multi-organ inflammation, and end-organ damage. Type I interferons (IFN-I) have been strongly implicated a role in disease etiology as has the main IFN-I-producing cell subset, the plasmacytoid dendritic cell (pDC). The B6.Nba2 mouse model develops a lupus-like disease characterized by elevated IFN-I levels and pDC pathogenicity. We have previously shown that pDC ablation prior to disease development in B6.Nba2 mice effectively prevents disease; however, it remains unclear if a similar protection can be seen if pDC ablation is initiated during later disease stages. This is important as Systemic lupus erythematosus patients are rarely diagnosed until disease is well-established and thus preventative treatment is unlikely to take place. Here we show that ablation of pDCs in the B6.Nba2 mouse model must be initiated early in order to effectively block disease development and that sustained reduction in pDC numbers is necessary for sustained effects. Finally, targeting of pDCs have been hypothesized to affect immunity towards infectious agents, in particular virus and intracellular bacteria. We show here that pDC ablation in B6.Nba2 mice does not affect the anti-viral response to encephalomyocarditic virus or a model T-dependent antigen. In summary, pDC ablation does not affect general immunity, but needs to happen early and be sustained to prevent lupus-like disease development in B6.Nba2 mice.

Sensing of SARS-CoV-2 by pDCs and their subsequent production of IFN-I contribute to macrophage-induced cytokine storm during COVID-19

Lung-infiltrating macrophages create a marked inflammatory milieu in a subset of patients with COVID-19 by producing a cytokine storm, which correlates with increased lethality. However, these macrophages are largely not infected by SARS-CoV-2, so the mechanism underlying their activation in the lung is unclear. Type I interferons (IFN-I) contribute to protecting the host against SARS-CoV-2 but may also have some deleterious effect, and the source of IFN-I in the lungs of infected patients is not well defined. Plasmacytoid dendritic cells (pDCs), a key cell type involved in antiviral responses, can produce IFN-I in response to SARS-CoV-2. We observed the infiltration of pDCs in the lungs of SARS-CoV-2-infected patients, which correlated with strong IFN-I signaling in lung macrophages. In patients with severe COVID-19, lung macrophages expressed a robust inflammatory signature, which correlated with persistent IFN-I signaling at the single-cell level. Hence, we observed the uncoupling in the kinetics of the infiltration of pDCs in the lungs and the associated IFN-I signature, with the cytokine storm in macrophages. We observed that pDCs were the dominant IFN-α-producing cells in response to the virus in the blood, whereas macrophages produced IFN-α only when in physical contact with infected epithelial cells. We also showed that IFN-α produced by pDCs, after the sensing of SARS-CoV-2 by TLR7, mediated changes in macrophages at both transcriptional and epigenetic levels, which favored their hyperactivation by environmental stimuli. Together, these data indicate that the priming of macrophages can result from the response by pDCs to SARS-CoV-2, leading to macrophage activation in patients with severe COVID-19.

Oral IRAK4 inhibitor BAY-1834845 prevents acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a lethal clinical entity that has become an emergency event with the outbreak of COVID-19. However, to date, there are no well-proven pharmacotherapies except dexamethasone. This study is aimed to evaluate IRAK4 inhibitors as a potential treatment for ARDS-cytokine release syndrome (CRS). We applied two IRAK4 inhibitors, BAY-1834845 and PF-06650833 to an inhaled lipopolysaccharide (LPS)-induced ARDS mouse model with control of high dose dexamethasone (10 mg/kg). Unexpectedly, although both compounds had excellent IC₅₀ on IRAK4 kinase activity, only BAY-1834845 but not PF-06650833 or high dose dexamethasone could significantly prevent lung injury according to a blinded pathology scoring. Further, only BAY-1834845 and BAY-1834845 combined with dexamethasone could effectively improve the injury score of pre-existed ARDS. Compared with PF-06650833 and high dose dexamethasone, BAY-1834845 remarkably decreased inflammatory cells infiltrating lung tissue and neutrophil count in BALF. BAY-1834845, DEX, and the combination of the two agents could decrease BALF total T cells, monocyte, and macrophages. In further cell type enrichment analysis based on lung tissue RNA-seq, both BAY-1834845 and dexamethasone decreased signatures of inflammatory cells and effector lymphocytes. Interestingly, unlike the dexamethasone group, BAY-1834845 largely preserved the signatures of naïve lymphocytes and stromal cells such as endothelial cells, chondrocytes, and smooth muscle cells. Differential gene enrichment suggested that BAY-1834845 downregulated genes more efficiently than dexamethasone, especially TNF, IL-17, interferon, and Toll-like receptor signaling.

Virus Infection and Systemic Inflammation: Lessons Learnt from COVID-19 and Beyond

Respiratory infections with newly emerging zoonotic viruses such as SARS-CoV-2, the etiological agent of COVID-19, often lead to the perturbation of the human innate and adaptive immune responses causing severe disease with high mortality. The responsible mechanisms are commonly virus-specific and often include either over-activated or delayed local interferon responses, which facilitate efficient viral replication in the primary target organ, systemic viral spread, and rapid onset of organ-specific and harmful inflammatory responses. Despite the distinct replication strategies, human infections with SARS-CoV-2 and highly pathogenic avian influenza viruses demonstrate remarkable similarities and differences regarding the mechanisms of immune induction, disease dynamics, as well as the long-term sequelae, which will be discussed in this review. In addition, we will highlight some important lessons about the effectiveness of antiviral and immunomodulatory therapeutic strategies that this pandemic has taught us.

Recent advances in treatment Crimean-Congo hemorrhagic fever virus: A concise overview

The Crimean Congo Hemorrhagic Fever Virus (CCHFV) is widespread in Africa, Asia, and Europe, among other places. The disease was initially discovered in the Crimean cities of the Soviet Union and the Congo, and it was given the name Crimean Congo because it induces hemorrhagic fever. According to studies, when the virus enters the body, it settles in immune cells such as macrophages and dendritic cells, causing them to malfunction and secrete inflammatory cytokines such as TNF-alpha, IL1, and IL6, resulting in cytokine storms that induces shock via endothelial activation and vascular leakage, while on the other hand, clots and disseminated intravascular coagulation (DIC) formation causes massive defects in various organs such as the liver and kidneys, as well as fatal bleeding. Disease prevention and treatment are crucial since no other effective vaccination against the disease has yet been developed. Immunotherapy is utilized as a consequence. One of the most effective treatments, when combined with compensatory therapies such as blood and platelet replacement, water, electrolytes, Fresh Frozen Plasma (FFP) replacement, and other compensatory therapies, is one of the most effective treatments. Studies; show that immunotherapy using IVIG and neutralizing and non-neutralizing monoclonal antibodies; cytokine therapy, and anti-inflammatory therapy using corticosteroids are effective ways to treat the disease.

Targeted protein degradation: mechanisms, strategies and application

Traditional drug discovery mainly focuses on direct regulation of protein activity. The development and application of protein activity modulators, particularly inhibitors, has been the mainstream in drug development. In recent years, PROteolysis TArgeting Chimeras (PROTAC) technology has emerged as one of the most promising approaches to remove specific disease-associated proteins by exploiting cells’ own destruction machinery. In addition to PROTAC, many different targeted protein degradation (TPD) strategies including, but not limited to, molecular glue, Lysosome-Targeting Chimaera (LYTAC), and Antibody-based PROTAC (AbTAC), are emerging. These technologies have not only greatly expanded the scope of TPD, but also provided fresh insights into drug discovery. Here, we summarize recent advances of major TPD technologies, discuss their potential applications, and hope to provide a prime for both biologists and chemists who are interested in this vibrant field.

Type I interferons and SARS-CoV-2: from cells to organisms

Type I interferons (IFNs) have broad and potent antiviral activity. We review the interplay between type I IFNs and SARS-CoV-2. Human cells infected with SARS-CoV-2 in vitro produce low levels of type I IFNs, and SARS-CoV-2 proteins can inhibit various steps in type I IFN production and response. Exogenous type I IFNs inhibit viral growth in vitro. In various animal species infected in vivo, type I IFN deficiencies underlie higher viral loads and more severe disease than in control animals. The early administration of exogenous type I IFNs improves infection control. In humans, inborn errors of, and auto-antibodies against type I IFNs underlie life-threatening COVID-19 pneumonia. Overall, type I IFNs are essential for host defense against SARS-CoV-2 in individual cells and whole organisms.

A Review of Human Coronaviruses' Receptors: The Host-Cell Targets for the Crown Bearing Viruses

A novel human coronavirus prompted considerable worry at the end of the year 2019. Now, it represents a significant global health and economic burden. The newly emerged coronavirus disease caused by the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is the primary reason for the COVID-19 global pandemic. According to recent global figures, COVID-19 has caused approximately 243.3 million illnesses and 4.9 million deaths. Several human cell receptors are involved in the virus identification of the host cells and entering them. Hence, understanding how the virus binds to host-cell receptors is crucial for developing antiviral treatments and vaccines. The current work aimed to determine the multiple host-cell receptors that bind with SARS-CoV-2 and other human coronaviruses for the purpose of cell entry. Extensive research is needed using neutralizing antibodies, natural chemicals, and therapeutic peptides to target those host-cell receptors in extremely susceptible individuals. More research is needed to map SARS-CoV-2 cell entry pathways in order to identify potential viral inhibitors.

Innate Immunity

The innate immune response system forms an important line of defense by deploying a limited number of receptors specific for conserved microbial components. This deployment generates a rapid inflammatory response, while activating the adaptive immune system. Improvements in our understanding of the innate immune system have allowed us to explore various therapeutic strategies via modulation of the immune response.

Sex Hormones and Aging Modulate Interferon Lambda 1 Production and Signaling by Human Uterine Epithelial Cells and Fibroblasts

Estradiol (E2) and progesterone (P) have potent effects on immune function in the human uterine endometrium which is essential for creating an environment conducive for successful reproduction. Type III/lambda (λ) interferons (IFN) are implicated in immune defense of the placenta against viral pathogens, which occurs against the backdrop of high E2 and P levels. However, the effect of E2 and P in modulating the expression and function of IFNλ1 in the non-pregnant human uterine endometrium is unknown. We generated purified in vitro cultures of human uterine epithelial cells and stromal fibroblast cells recovered from hysterectomy specimens. Poly (I:C), a viral dsRNA mimic, potently increased secretion of IFNλ1 by both epithelial cells and fibroblasts. The secretion of IFNλ1 by epithelial cells significantly increased with increasing age following poly (I:C) stimulation. Stimulation of either cell type with E2 (5x10-8M) or P (1x10-7M) had no effect on expression or secretion of IFNλ1 either alone or in the presence of poly (I:C). E2 suppressed the IFNλ1-induced upregulation of the antiviral IFN-stimulated genes (ISGs) MxA, OAS2 and ISG15 in epithelial cells, but not fibroblasts. Estrogen receptor alpha (ERα) blockade using Raloxifene indicated that E2 mediated its inhibitory effects on ISG expression via ERα. In contrast to E2, P potentiated the upregulation of ISG15 in response to IFNλ1 but had no effect on MxA and OAS2 in epithelial cells. Our results demonstrate that the effects of E2 and P on IFNλ1-induced ISGs are cell-type specific. E2-mediated suppression, and selective P-mediated stimulation, of IFNλ1-induced ISG expression in uterine epithelial cells suggest that the effects of IFNλ1 varies with menstrual cycle stage, pregnancy, and menopausal status. The suppressive effect of E2 could be a potential mechanism by which ascending pathogens from the lower reproductive tract can infect the pregnant and non-pregnant endometrium.

X-linked recessive TLR7 deficiency in ~1% of men under 60 years old with life-threatening COVID-19

Autosomal inborn errors of type I IFN immunity and autoantibodies against these cytokines underlie at least 10% of critical COVID-19 pneumonia cases. We report very rare, biochemically deleterious X-linked TLR7 variants in 16 unrelated male individuals aged 7 to 71 years (mean: 36.7 years) from a cohort of 1,202 male patients aged 0.5 to 99 years (mean: 52.9 years) with unexplained critical COVID-19 pneumonia. None of the 331 asymptomatically or mildly infected male individuals aged 1.3 to 102 years (mean: 38.7 years) tested carry such TLR7 variants (p = 3.5 × 10-5). The phenotypes of five hemizygous relatives of index cases infected with SARS-CoV-2 include asymptomatic or mild infection (n=2, 5 and 38 years), or moderate (n=1, 5 years), severe (n=1, 27 years), or critical (n=1, 29 years) pneumonia. Two boys (aged 7 and 12 years) from a cohort of 262 male patients with severe COVID-19 pneumonia (mean: 51.0 years) are hemizygous for a deleterious TLR7 variant. The cumulative allele frequency for deleterious TLR7 variants in the male general population is < 6.5x10-4 We also show that blood B cell lines and myeloid cell subsets from the patients do not respond to TLR7 stimulation, a phenotype rescued by wild-type TLR7 The patients' blood plasmacytoid dendritic cells (pDCs) produce low levels of type I IFNs in response to SARS-CoV-2. Overall, X-linked recessive TLR7 deficiency is a highly penetrant genetic etiology of critical COVID-19 pneumonia, in about 1.8% of male patients below the age of 60 years. Human TLR7 and pDCs are essential for protective type I IFN immunity against SARS-CoV-2 in the respiratory tract.

Coxsackievirus B4 Transplacental Infection Severely Disturbs Central Tolerogenic Mechanisms in the Fetal Thymus

Thymus plays a fundamental role in central tolerance establishment, especially during fetal life, through the generation of self-tolerant T cells. This process consists in T cells education by presenting them tissue-restricted autoantigens promiscuously expressed by thymic epithelial cells (TECs), thus preventing autoimmunity. Thymus infection by Coxsackievirus B (CV-B) during fetal life is supposed to disturb thymic functions and, hence, to be an inducing or accelerating factor in the genesis of autoimmunity. To further investigate this hypothesis, in our current study, we analyzed thymic expression of autoantigens, at the transcriptional and protein level, following in utero infection by CV-B4. mRNA expression levels of Igf2 and Myo7, major autoantigens of pancreas and heart, respectively, were analyzed in whole thymus and in enriched TECs together along with both transcription factors, Aire and Fezf2, involved in autoantigens expression in the thymus. Results show that in utero infection by CV-B4 induces a significant decrease in Igf2 and Myo7 expression at both mRNA and protein level in whole thymus and in enriched TECs as well. Moreover, a correlation between viral load and autoantigens expression can be observed in the whole thymus, indicating a direct effect of in utero infection by CV-B4 on autoantigens expression. Together, these results indicate that an in utero infection of the thymus by CV-B4 may interfere with self-tolerance establishment in TECs by decreasing autoantigen expression at both mRNA and protein level and thereby increase the risk of autoimmunity onset.

Depleting plasmacytoid dendritic cells reduces local type I interferon responses and disease activity in patients with cutaneous lupus

Plasmacytoid dendritic cells (pDCs) not only are specialized in their capacity to secrete large amounts of type I interferon (IFN) but also serve to enable both innate and adaptive immune responses through expression of additional proinflammatory cytokines, chemokines, and costimulatory molecules. Persistent activation of pDCs has been demonstrated in a number of autoimmune diseases. To evaluate the potential benefit of depleting pDCs in autoimmunity, a monoclonal antibody targeting the pDC-specific marker immunoglobulin-like transcript 7 was generated. This antibody, known as VIB7734, which was engineered for enhanced effector function, mediated rapid and potent depletion of pDCs through antibody-dependent cellular cytotoxicity. In cynomolgus monkeys, treatment with VIB7734 reduced pDCs in blood below the lower limit of normal by day 1 after the first dose. In two phase 1 studies in patients with autoimmune diseases, VIB7734 demonstrated an acceptable safety profile, comparable to that of placebo. In individuals with cutaneous lupus, VIB7734 profoundly reduced both circulating and tissue-resident pDCs, with a 97.6% median reduction in skin pDCs at study day 85 in VIB7734-treated participants. Reductions in pDCs in the skin correlated with a decrease in local type I IFN activity as well as improvements in clinical disease activity. Biomarker analysis suggests that responsiveness to pDC depletion therapy may be greater among individuals with high baseline type I IFN activity, supporting a central role for pDCs in type I IFN production in autoimmunity and further development of VIB7734 in IFN-associated diseases.

A Review on Inosine Pranobex Immunotherapy for Cervical HPV-Positive Patients

The purpose of this review was to examine and summarize data for inosine pranobex (IP) immunotherapy in cervical HPV-positive patients. Persistent or recurring cervical human papillomavirus (HPV) infection is a major cause of cervical cancer. Self-clearance and blocking of cervical HPV infection depend on the status of the host immune system. Immunotherapy helps accelerate elimination of the infection. Host immunity is involved in the development of HPV infection. Several mechanisms of interaction between the virus and the immune system have been revealed; however, the mechanisms have not been completely elucidated. A properly functioning immune system impedes HPV progress and helps clear the pathogen from the body. IP has antiviral efficacy because it modulates both cellular and humoral immunities. IP has been on the market since 1971. Nevertheless, it has seldom been administered to treat cervical HPV infections. In this review, Google Scholar, PubMed/MEDLINE, Scopus, Cochrane Library, and Research Gate were searched for the period 1971–2021. Prospective controlled trials, observational and retrospective studies, and meta-analysis and reviews on immunotherapy against HPV cervical infection were explored. Prior studies showed strong clinical efficacy of combined and standalone IP therapy in reversing HPV-induced changes in the cervix, preventing disease progression, and clearing the pathogen. IP treatment enhanced host antiviral activity against HPV, delayed or stopped cervical oncogenesis, and rapidly removed HPV from the body.

Herpes Simplex Virus 1 Infection of Neuronal and Non-Neuronal Cells Elicits Specific Innate Immune Responses and Immune Evasion Mechanisms

Alphaherpesviruses (α-HV) are a large family of double-stranded DNA viruses which cause many human and animal diseases. There are three human α-HVs: Herpes Simplex Viruses (HSV-1 and HSV-2) and Varicella Zoster Virus (VZV). All α-HV have evolved multiple strategies to suppress or exploit host cell innate immune signaling pathways to aid in their infections. All α-HVs initially infect epithelial cells (primary site of infection), and later spread to infect innervating sensory neurons. As with all herpesviruses, α-HVs have both a lytic (productive) and latent (dormant) stage of infection. During the lytic stage, the virus rapidly replicates in epithelial cells before it is cleared by the immune system. In contrast, latent infection in host neurons is a life-long infection. Upon infection of mucosal epithelial cells, herpesviruses immediately employ a variety of cellular mechanisms to evade host detection during active replication. Next, infectious viral progeny bud from infected cells and fuse to neuronal axonal terminals. Here, the nucleocapsid is transported via sensory neuron axons to the ganglion cell body, where latency is established until viral reactivation. This review will primarily focus on how HSV-1 induces various innate immune responses, including host cell recognition of viral constituents by pattern-recognition receptors (PRRs), induction of IFN-mediated immune responses involving toll-like receptor (TLR) signaling pathways, and cyclic GMP-AMP synthase stimulator of interferon genes (cGAS-STING). This review focuses on these pathways along with other mechanisms including autophagy and the complement system. We will summarize and discuss recent evidence which has revealed how HSV-1 is able to manipulate and evade host antiviral innate immune responses both in neuronal (sensory neurons of the trigeminal ganglia) and non-neuronal (epithelial) cells. Understanding the innate immune response mechanisms triggered by HSV-1 infection, and the mechanisms of innate immune evasion, will impact the development of future therapeutic treatments.

Modulation of IGF2 Expression in the Murine Thymus and Thymic Epithelial Cells Following Coxsackievirus-B4 Infection

Coxsackievirus B4 (CV-B4) can infect human and murine thymic epithelial cells (TECs). In a murine TEC cell line, CV-B4 can downregulate the transcription of the insulin-like growth factor 2 (Igf2) gene coding for the self-peptide of the insulin family. In this study, we show that CV-B4 infections of a murine TEC cell line decreased Igf2 P3 promoter activity by targeting a region near the transcription start site; however, the stability of Igf2 transcripts remained unchanged, indicating a regulation of Igf2 transcription. Furthermore, CV-B4 infections decreased STAT3 phosphorylation in vitro. We also showed that mice infected with CV-B4 had an altered expression of Igf2 isoforms as detected in TECs, followed by a decrease in the pro-IGF2 precursor in the thymus. Our study sheds new light on the intrathymic regulation of Igf2 transcription during CV-B4 infections and supports the hypothesis that a viral infection can disrupt central self-tolerance to insulin by decreasing Igf2 transcription in the thymic epithelium.

Can SARS-CoV-2 Virus Use Multiple Receptors to Enter Host Cells?

The occurrence of the novel severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), responsible for coronavirus disease 2019 (COVD-19), represents a catastrophic threat to global health. Protruding from the viral surface is a densely glycosylated spike (S) protein, which engages angiotensin-converting enzyme 2 (ACE2) to mediate host cell entry. However, studies have reported viral susceptibility in intra- and extrapulmonary immune and non-immune cells lacking ACE2, suggesting that the S protein may exploit additional receptors for infection. Studies have demonstrated interactions between S protein and innate immune system, including C-lectin type receptors (CLR), toll-like receptors (TLR) and neuropilin-1 (NRP1), and the non-immune receptor glucose regulated protein 78 (GRP78). Recognition of carbohydrate moieties clustered on the surface of the S protein may drive receptor-dependent internalization, accentuate severe immunopathological inflammation, and allow for systemic spread of infection, independent of ACE2. Furthermore, targeting TLRs, CLRs, and other receptors (Ezrin and dipeptidyl peptidase-4) that do not directly engage SARS-CoV-2 S protein, but may contribute to augmented anti-viral immunity and viral clearance, may represent therapeutic targets against COVID-19.

Clinical IRAK4 deficiency caused by homozygosity for the novel IRAK4 (c.1049delG, p.Gly350Glufs*15) variant

The innate immune system allows for rapid recognition of pathogens. Toll-like receptor (TLR) signaling is a key aspect of the innate immune response, and interleukin-1 receptor-associated kinase 4 (IRAK4) plays a vital role in the TLR signaling cascade. Each TLR recognizes a distinct set of pathogen-associated molecular patterns (PAMPs) that encompass conserved microbial components such as lipopolysaccharides and flagellin. Upon binding of PAMPs and TLR activation, TLR intracellular domains initiate the oligomerization of the myeloid differentiation primary response 88 (MyD88), IRAK1, IRAK2, and IRAK4 signaling platform known as the Myddosome complex while also triggering the Toll/IL-1R domain-containing adaptor-inducing IFN-β (TRIF)-dependent pathway. The Myddosome complex initiates signal transduction pathways enabling the activation of NF-κB and mitogen-activated protein kinase (MAPK) transcription factors and the subsequent production of inflammatory cytokines. Human IRAK4 deficiency is an autosomal recessive inborn error of immunity that classically presents with blunted or delayed inflammatory response to infection and susceptibility to a narrow spectrum of pyogenic bacteria, particularly Streptococcus pneumoniae, Staphylococcus aureus, and Pseudomonas aeruginosa. We describe a case of IRAK4 deficiency in an 11-mo-old boy with concurrent S. pneumoniae bacteremia and S. aureus cervical lymphadenitis with a blunted inflammatory response to invasive infection. Although initial clinical immune profiling was unremarkable, a high degree of suspicion for an innate immune defect prompted genetic sequencing. Genetic testing revealed a novel variant in the IRAK4 gene (c.1049delG, p.(Gly350Glufs*15)) predicted to be likely pathogenic. Functional testing showed a loss of IRAK4 protein expression and abolished TLR signaling, confirming the pathogenicity of this novel IRAK4 variant.

Diminished toll-like receptor response in febrile infection-related epilepsy syndrome (FIRES)

Background

Defective human TLR3 signaling causes recurrent and refractory herpes simplex encephalitis/encephalopathy. Children with febrile infection-related epilepsy syndrome with refractory seizures may have defective TLR responses.

Methods

Children with febrile infection-related epilepsy syndrome were enrolled in this study to evaluate TLR1-9 responses (IL-6, IL-8, IL-12p40, INF-α, INF-γ, and TNF-α) in their peripheral blood mononuclear cells (PBMCs) and monocyte-derived dendritic cells (MDDCs), compared to those with febrile seizures and non-refractory epilepsy with/without underlying encephalitis/encephalopathy.

Results

Adenovirus and enterovirus were found in throat cultures of enrolled patients (2–13 years) as well as serologic IgM elevation of mycoplasma pneumonia and herpes simplex virus, although neither detectable pathogens nor anti-neural autoantibodies in the CSF could be noted. Their PBMCs and MDDCs trended to have impaired TLR responses and significantly lower in cytokine profiles of TLR3, TLR4, TLR7/8, and TLR9 responses but not other TLRs despite normal TLR expressions and normal candidate genes for defective TLR3 signaling. They also had decreased naïve T and T regulatory cells, and weakened phagocytosis.

Conclusion

Children with febrile infection-related epilepsy syndrome (FIRES) could have impaired TLR3, TLR4, TLR7/8, and TLR9 responses possibly relating to their weakened phagocytosis and decreased T regulatory cells.

Investigational IRAK-4 inhibitors for the treatment of rheumatoid arthritis

INTRODUCTION

Rheumatoid arthritis (RA) is a chronic inflammatory auto-immune disease that can lead to permanent disability and deformity. Despite current treatment modalities, many patients are still unable to reach remission. Interleukin-1 receptor-associated kinase 4 (IRAK-4) inhibitors are novel agents designed to suppress immune signaling pathways involved in inflammation and joint destruction in RA. Four IRAK-4 inhibitors have entered clinical trials.

AREAS COVERED

This review summarizes the current stage of development of IRAK-4 inhibitors in clinical trials, detailing their chemistry, pharmacokinetics, and therapeutic potential in the treatment of RA. PubMed, Embase and restricted Google searches were conducted using the term 'IRAK-4', and publicly accessible clinical trial databases were reviewed.

EXPERT OPINION

IRAK-4 inhibitors are an exciting therapeutic option in RA management because unlike other targeted disease-modifying agents, they target the innate immune system. The role of IRAK-4 as a key component of Toll/Interleukin-1 receptor signaling and its potential for a low rate of infectious complications is particularly exciting and this may facilitate their use in combination treatment. A key aspect of upcoming clinical trials will be the identification of biomarkers predictive of treatment efficacy, which will help to define if and how they will be used in the clinic.

Manipulation of the Innate Immune Response by Varicella Zoster Virus

Varicella zoster virus (VZV) is the causative agent of chickenpox (varicella) and shingles (herpes zoster). VZV and other members of the herpesvirus family are distinguished by their ability to establish a latent infection, with the potential to reactivate and spread virus to other susceptible individuals. This lifelong relationship continually subjects VZV to the host immune system and as such VZV has evolved a plethora of strategies to evade and manipulate the immune response. This review will focus on our current understanding of the innate anti-viral control mechanisms faced by VZV. We will also discuss the diverse array of strategies employed by VZV to regulate these innate immune responses and highlight new knowledge on the interactions between VZV and human innate immune cells.

Innate Immunity

The innate immune response system forms an important line of defense by deploying a limited number of receptors specific for conserved microbial components. This deployment generates a rapid inflammatory response, while activating the adaptive immune system. Improvements in our understanding of the innate immune system have allowed us to explore various therapeutic strategies via modulation of the immune response.

The Interplay between Host Immunity and Respiratory Viral Infection in Asthma Exacerbation

Asthma is one of the most common and chronic diseases characterized by multidimensional immune responses along with poor prognosis and severity. The heterogeneous nature of asthma may be attributed to a complex interplay between risk factors (either intrinsic or extrinsic) and specific pathogens such as respiratory viruses, and even bacteria. The intrinsic risk factors are highly correlated with asthma exacerbation in host, which may be mediated via genetic polymorphisms, enhanced airway epithelial lysis, apoptosis, and exaggerated viral replication in infected cells, resulting in reduced innate immune response and concomitant reduction of interferon (types I, II, and III) synthesis. The canonical features of allergic asthma include strong Th2-related inflammation, sensitivity to non-steroidal anti-inflammatory drugs (NSAIDs), eosinophilia, enhanced levels of Th2 cytokines, goblet cell hyperplasia, airway hyper-responsiveness, and airway remodeling. However, the NSAID-resistant non-Th2 asthma shows a characteristic neutrophilic influx, Th1/Th17 or even mixed (Th17-Th2) immune response and concurrent cytokine streams. Moreover, inhaled corticosteroid-resistant asthma may be associated with multifactorial innate and adaptive responses. In this review, we will discuss the findings of various in vivo and ex vivo models to establish the critical heterogenic asthmatic etiologies, host-pathogen relationships, humoral and cell-mediated immune responses, and subsequent mechanisms underlying asthma exacerbation triggered by respiratory viral infections.

A pathogenic role of plasmacytoid dendritic cells in autoimmunity and chronic viral infection

Following the discovery of plasmacytoid dendritic cells (pDCs) and of their extraordinary ability to produce type I IFNs (IFN-I) in response to TLR7 and TLR9 stimulation, it is assumed that their main function is to participate in the antiviral response. There is increasing evidence suggesting that pDCs and/or IFN-I can also have a detrimental role in a number of inflammatory and autoimmune diseases, in the context of chronic viral infections and in cancers. Whether these cells should be targeted in patients and how much of their biology is connected to IFN-I production remains unclear and is discussed here.

The Innate Antiviral Response in Animals: An Evolutionary Perspective from Flagellates to Humans

Animal cells have evolved dedicated molecular systems for sensing and delivering a coordinated response to viral threats. Our understanding of these pathways is almost entirely defined by studies in humans or model organisms like mice, fruit flies and worms. However, new genomic and functional data from organisms such as sponges, anemones and mollusks are helping redefine our understanding of these immune systems and their evolution. In this review, we will discuss our current knowledge of the innate immune pathways involved in sensing, signaling and inducing genes to counter viral infections in vertebrate animals. We will then focus on some central conserved players of this response including Toll-like receptors (TLRs), RIG-I-like receptors (RLRs) and cGAS-STING, attempting to put their evolution into perspective. To conclude, we will reflect on the arms race that exists between viruses and their animal hosts, illustrated by the dynamic evolution and diversification of innate immune pathways. These concepts are not only important to understand virus-host interactions in general but may also be relevant for the development of novel curative approaches against human disease.

DNA methylation and hydroxymethylation profiles reveal possible role of highly methylated TLR signaling on Fasciola gigantica excretory/secretory products (FgESPs) modulation of buffalo dendritic cells

BACKGROUND

Excretory/secretory products (ESPs) released by parasites influence the development and functions of host dendritic cells (DCs). However, little is known about changes of DNA (hydroxy)methylation on DC development during Fasciola gigantica infection. The present study aimed to investigate whether F. gigantica ESPs (FgESPs) affects the development and functions of buffalo DCs through altering the DNA (hydroxy)methylation of DCs.

METHODS

Buffalo DCs were prepared from peripheral blood mononuclear cells (PBMCs) and characterized using scanning and transmission electron microscopy (SEM/TEM) and quantitative reverse transcriptional PCR (qRT-RCR). DCs were treated with 200 μg/ml of FgESPs in vitro, following DNA extraction. The DNA methylome and hydroxymethylome were profiled based on (hydroxy)methylated DNA immunoprecipitation sequencing [(h)MeDIP-Seq] and bioinformatics analyses. qRT-RCR was also performed to assess the gene transcription levels of interest.

RESULTS

FgESPs markedly suppressed DC maturation evidenced by morphological changes and downregulated gene expression of CD1a and MHC II. Totals of 5432 and 360 genes with significant changes in the 5-methylcytosine (5-mC) and the 5-hydroxymethylcytosine (5-hmC) levels, respectively, were identified in buffalo DCs in response to FgESPs challenge. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that these differentially expressed genes were highly enriched in pathways associated with immune response. Some cancer-related pathways were also indicated. There were 111 genes demonstrating changes in both 5-mC and 5-hmC levels, 12 of which were interconnected and enriched in 12 pathways. The transcription of hypermethylated genes TLR2, TLR4 and IL-12B were downregulated or in a decreasing trend, while the mRNA level of high-hydroxymethylated TNF gene was upregulated in buffalo DCs post-exposure to FgESPs in vitro.

CONCLUSIONS

To our knowledge, the present study provides for the first time a unique genome-wide profile of DNA (hydroxy)methylation for DCs that interact with FgESPs, and suggests a possible mechanism of FgESPs in suppressing DC maturation and functions that are involved in TLR signaling.

MicroRNA-147 negatively regulates expression of toll-like receptor-7 in rat macrophages and attenuates pristane induced rheumatoid arthritis in rats

Background/Introduction: Aberrant expression of Toll like receptors (TLR) plays a vital role in pathogenesis of rheumatoid arthritis (RA). Micro RNAs (miRs) could play important role in the related signaling pathways. The present study was undertaken to establish the link between miR-147 and TLR-7 in rat macrophages (in vitro) and in pristane (PS) induced arthritic rats.

METHODOLOGY

Dual luciferase assay was done to confirm the interaction between miR-147 and TLR-7. The effect of miR-147 on regulation of TLR-7 was done by RT-qPCR and Immunoblotting studies in rat macrophages (ATCC^® CRL-2192^TM) after treating them with miR-147 mimics and inhibitors. R-848 (Imiquimod) was used as TLR-7 stimulant, the mRNA and protein expression levels of IFN-β and TNF-α were recorded to determine the regulation of TLR-7. The levels of miR-147 and TLR-7 were evaluated during induction of rat bone marrow derived macrophage in the PS induced rat macrophages and spleens of methotrexate exposed rats. The miR-147 mimics was injected intraperitoneal to the PS treated rats and the severity of arthritis was studied.

RESULTS

The study confirmed TLR-7 mRNA as the potential target of miR-147 in rats. Alterations in miR-147 by transfecting mimics or inhibitors in ATCC^® CRL-2192^TM cells exhibited suppression and amelioration of TLR-7 and cytokine expression. The alteration in expression of miR-147 was inversely correlated with expression of TLR-7 during bone marrow derived macrophages induction in PS exposed cells and spleens. The abnormal expression was reversed in spleens of methotrexate treated arthritic rats. The treatment of miR-147 mimic caused suppression in expression of TLR-7 and improved the severity of arthritis in PS induced arthritic rats.

CONCLUSIONS

MiR-147 inversely regulates the TLR-7 signaling by targeting TLR-7 itself both in vivo and in vitro. The study provides a novel approach for conditions involving abnormal TLR-7 expression in arthritis.

HERVs, immunity, and autoimmunity: understanding the connection

Since their discovery in the 1960s, further investigation into endogenous retroviruses (ERVs) has challenged the conventional view of viral sequences as exclusively parasitic elements. Once presumed to be a group of passive genetic relics, it is becoming increasingly clear that this view of ERVs, while generally accurate, is incorrect in many specific cases. Research has identified ERV genes that appear to be co-opted by their mammalian hosts, but the biological function of ERV elements in humans remains a controversial subject. One area that has attracted some attention in this domain is the role of co-opted ERV elements in mammalian immune systems. The relationship between ERVs and human autoimmune diseases has also been investigated, but has historically been treated as a separate topic. This review will summarize the current evidence concerning the phenotypic significance of ERVs, both in the healthy immune system and in manifestations of autoimmunity. Furthermore, it will evaluate the relationship between these fields of study, and propose previously-unexplored molecular mechanisms through which human endogenous retroviruses might contribute to certain autoimmune pathologies. Investigation into these novel mechanisms could further our understanding of the molecular basis of autoimmune disease, and may one day provide new targets for treatment.

Identification and functional characterization of IRAK-4 in grass carp (Ctenopharyngodon idellus)

IL-1R-associated kinase 4 (IRAK4), a central TIR signaling mediator in innate immunity, can initiate a cascade of signaling events and lead to induction of inflammatory target gene expression eventually. In the present study, we cloned and characterized an IRAK4 orthologue from grass carp (Ctenopharyngodon idella). The full length cDNA of CiIRAK4 was 2057 bp with an ORF of 1422 bp encoding a polypeptide of 472 amino acids. Multiple alignments showed that IRAK4s were highly conserved among different species. Phylogenetic tree analysis revealed that CiIRAK4 shared high homologous with zebra fish IRAK4. Expression analysis indicated that CiIRAK4 was widely expressed in all tested tissues. It was significantly up-regulated after treatment with poly I:C, especially obvious in liver and spleen. Also, CiIRAK4 could be induced by poly I:C and LPS in CIK cells. Fluorescence microscopy assays showed that CiIRAK4 localized in the cytoplasm. RNAi-mediated knockdown and overexpression assays indicated that CiIRAK4 might have little effect on NF-kappa B p65 translocation from cytoplasm to nucleus, indicating that CiIRAK4 was dispensable for activation of NF-kappa B p65. In addition, IRAK4 promoted IRF5 nuclear translocation, which has nothing to do with the interaction between IRAK4 and IRF5. It suggested that fish IRAK4 kinase regulated IRF5 activity through indirect ways.

Below the surface: The inner lives of TLR4 and TLR9

TLRs are a class of pattern recognition receptors (PRRs) that detect invading microbes by recognizing pathogen-associated molecular patterns (PAMPs). Upon PAMP engagement, TLRs activate a signaling cascade that leads to the production of inflammatory mediators. The localization of TLRs, either on the plasma membrane or in the endolysosomal compartment, has been considered to be a fundamental aspect to determine to which ligands the receptors bind, and which transduction pathways are induced. However, new observations have challenged this view by identifying complex trafficking events that occur upon TLR-ligand binding. These findings have highlighted the central role that endocytosis and receptor trafficking play in the regulation of the innate immune response. Here, we review the TLR4 and TLR9 transduction pathways and the importance of their different subcellular localization during the inflammatory response. Finally, we discuss the implications of TLR9 subcellular localization in autoimmunity.

Targeting the immunity protein kinases for immuno-oncology

With the rise of immuno-oncology, small-molecule modulators targeting immune system and inflammatory processes are becoming a research hotspot. This work mainly focuses on key kinases acting as central nodes in immune signaling pathways. Although over thirty small-molecule kinase inhibitors have been approved by FDA for the treatment of various cancers, only a few are associated with immuno-oncology. With the going deep of the research work, more and more immunity protein kinase inhibitors are approved for clinical trials to treat solid tumors and hematologic malignancies by FDA, which remain good prospects. Meanwhile, in-depth understanding of biological function of immunity protein kinases in immune system is pushing the field forward. This article focuses on the development of safe and effective small-molecule immunity protein kinase inhibitors and further work needs to keep the promises of these inhibitors for patients' welfare.

Lambda interferons come to light: dual function cytokines mediating antiviral immunity and damage control

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IFNλs are dual function cytokines mediating antiviral activity and damage control.

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IFNλs confer initial antimicrobial protection at anatomical barriers without provoking unnecessary inflammation.

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IFNλs exhibit immune regulatory and host protective actions reminiscent of IL-10.

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IFNλs form novel therapeutics with the beneficial actions of type I IFNs but lacking their pro-inflammatory side effects.

Lambda interferons (IFNλs, type III IFNs or interleukins-28/29) were described fifteen years ago as novel cytokines sharing structural and functional homology with IL-10 and type I IFNs, respectively. IFNλs engage a unique receptor complex comprising IFNLR1 and IL10R2, nevertheless they share signaling cascade and many functions with type I IFNs, questioning their possible non-redundant roles and overall biological importance. Here, we review the latest evidence establishing the primacy of IFNλs in front line protection at anatomical barriers, mediating antiviral immunity before type I IFNs. We also discuss their emerging role in regulating inflammation and limiting host damage, a major difference to type I IFNs. IFNλs come thus to light as dual function cytokines mediating antiviral immunity and damage control.

Human Metapneumovirus Small Hydrophobic Protein Inhibits Interferon Induction in Plasmacytoid Dendritic Cells

Human metapneumovirus (hMPV), a leading cause of respiratory tract infections in infants, encodes a small hydrophobic (SH) protein of unknown function. Here we show that infection of plasmacytoid dendritic cells (pDCs) with a recombinant virus lacking SH expression (rhMPV-ΔSH) enhanced the secretion of type I interferons (IFNs), which required TLR7 and MyD88 expression. HMPV SH protein inhibited TLR7/MyD88/TRAF6 signaling leading to IFN gene transcription, identifying a novel mechanism by which paramyxovirus SH proteins modulate innate immune responses.

Interferon-λs: Front-Line Guardians of Immunity and Homeostasis in the Respiratory Tract

Type III interferons (IFNs), also termed lambda IFNs (IFNλs) or interleukins-28/29, constitute a new addition to the IFN family. They are induced upon infection and are particularly abundant at barrier surfaces, such as the respiratory and gastrointestinal tracts. Although they signal through a unique heterodimeric receptor complex comprising IFNLR1 and IL10RB, they activate a downstream signaling pathway remarkably similar to that of type I IFNs and share many functions with them. Yet, they also have important differences which are only now starting to unfold. Here, we review the current literature implicating type III IFNs in the regulation of immunity and homeostasis in the respiratory tract. We survey the common and unique characteristics of type III IFNs in terms of expression patterns, cellular targets, and biological activities and discuss their emerging role in first line defenses against respiratory viral infections. We further explore their immune modulatory functions and their involvement in the regulation of inflammatory responses during chronic respiratory diseases, such as asthma and chronic obstructive pulmonary disease. Type III IFNs are, therefore, arising as front-line guardians of immune defenses in the respiratory tract, fine tuning inflammation, and as potential novel therapeutics for the treatment of diverse respiratory diseases, including influenza virus infection and asthma.

Molecular cloning, structural modeling, and expression analysis of MyD88 and IRAK4 of golden pompano (Trachinotus ovatus)

MyD88 and IRAK4 are important components of TLR signaling pathways. However, information about MyD88 and IRAK4 is vacant in golden pompano (Trachinotus ovatus), a marine teleost with great commercial value. Thus, in this study the full lengths of trMyD88 and trIRAK4 were cloned from golden pompano using RT-PCR and RACE-PCR methods. trMyD88 was 1213 bp in length, encoding a putative protein of 288 amino acids (aa), consisting of a 99 aa of death domain at its N-terminal and a 137 aa of the TIR domain at its C-terminal. trIRAK4 was 1606 bp in length, encoding a putative protein of 469 aa, including an N-terminal death domain and a central kinase domain, connected by a ProST domain. Other domains or aa residues needed for their functions were also identified in trMyD88 and trIRAK4. Physicochemical features and 3-D structures of trMyD88 and trIRAK4 were also analyzed. Quantitative real-time PCR revealed that the 2 genes were ubiquitously expressed in tissues from healthy pompano, especially highly in the spleen and head kidney, indicating their roles in the immune response. Further, trMyD88 and trIRAK4 were up-regulated at 12 h after the Vibrio alginilyticus and polyI:C challenge and continued to 48 h post challenge. Our results demonstrated that MyD88 and IRAK4 played important roles in the golden pompano innate immune system, providing the basis for further study of the signaling pathways that these 2 genes are involved in.

(-)-Epigallocatechin-3-gallate enhances poly I:C-induced interferon-λ1 production and inhibits hepatitis C virus replication in hepatocytes

AIM

To investigate the effect of (-)-epigallocatechin-3-gallate (EGCG) on polyinosinic-polycytidylic acid (poly I:C)-triggered intracellular innate immunity against hepatitis C virus (HCV) in hepatocytes.

METHODS

A cell culture model of HCV infection was generated by infecting a hepatoma cell line, Huh7, with HCV JFH-1 strain (JFH-1-Huh7). Poly I:C with a high molecular weight and EGCG were used to stimulate the JFH-1-Huh7 cells. Real-time reverse transcription-polymerase chain reaction was used to detect the expression levels of intracellular mRNAs and of intracellular and extracellular HCV RNA. Enzyme-linked immunosorbent assay was used to evaluate the interferon (IFN)-λ1 protein level in the cell culture supernatant. Immunostaining was used to examine HCV core protein expression in Huh7 cells.

RESULTS

Our recent study showed that HCV replication could impair poly I:C-triggered intracellular innate immune responses in hepatocytes. In the current study, we showed that EGCG treatment significantly increased the poly I:C-induced expression of Toll-like receptor 3 (TLR3), retinoic acid-inducible gene I, and IFN-λ1 in JFH-1-Huh7 cells. In addition, supplementation with EGCG increased the poly I:C-mediated antiviral activity in JFH-1-Huh7 cells at the intracellular and extracellular HCV RNA and protein levels. Further investigation of the mechanisms showed that EGCG treatment significantly enhanced the poly I:C-induced expression of IFN-regulatory factor 9 and several antiviral IFN-stimulated genes, including ISG15, ISG56, myxovirus resistance A, and 2'-5'-oligoadenylate synthetase 1, which encode the key antiviral elements in the IFN signaling pathway.

CONCLUSION

Our observations provide experimental evidence that EGCG has the ability to enhance poly I:C-induced intracellular antiviral innate immunity against HCV replication in hepatocytes.

Discovery of Clinical Candidate 1-{[(2S,3S,4S)-3-Ethyl-4-fluoro-5-oxopyrrolidin-2-yl]methoxy}-7-methoxyisoquinoline-6-carboxamide (PF-06650833), a Potent, Selective Inhibitor of Interleukin-1 Receptor Associated Kinase 4 (IRAK4), by Fragment-Based Drug Design

Through fragment-based drug design focused on engaging the active site of IRAK4 and leveraging three-dimensional topology in a ligand-efficient manner, a micromolar hit identified from a screen of a Pfizer fragment library was optimized to afford IRAK4 inhibitors with nanomolar potency in cellular assays. The medicinal chemistry effort featured the judicious placement of lipophilicity, informed by co-crystal structures with IRAK4 and optimization of ADME properties to deliver clinical candidate PF-06650833 (compound 40). This compound displays a 5-unit increase in lipophilic efficiency from the fragment hit, excellent kinase selectivity, and pharmacokinetic properties suitable for oral administration.

EBI2 expression in B lymphocytes is controlled by the Epstein-Barr virus transcription factor, BRRF1 (Na), during viral infection

Epstein-Barr virus-induced gene 2 (EBI2) is an important chemotactic receptor that is involved in proper B-cell T-cell interactions. Epstein-Barr virus (EBV) has been shown to upregulate this gene upon infection of cell lines, but the timing and mechanism of this upregulation, as well as its importance to EBV infection, remain unknown. This work investigated EBV's manipulation of EBI2 expression of primary naive B cells. EBV infection induces EBI2 expression resulting in elevated levels of EBI2 after 24 h until 7 days post-infection, followed by a dramatic decline (P=0.027). Increased EBI2 expression was not found in non-specifically stimulated B cells or when irradiated virus was used. The EBV lytic gene BRRF1 exhibited a similar expression pattern to EBI2 (R2=0.4622). BRRF1-deficient EBV could not induce EBI2. However, B cells transduced with BRRF1 showed elevated expression of EBI2 (P=0.042), a result that was not seen with transduction of a different EBV lytic transfection factor, BRLF1. Based on these results, we conclude that EBI2 expression is directly influenced by EBV infection and that BRRF1 is necessary and sufficient for EBI2 upregulation during infection.

MicroRNA 373 Facilitates the Replication of Porcine Reproductive and Respiratory Syndrome Virus by Its Negative Regulation of Type I Interferon Induction

MicroRNAs (miRNAs) play an important role in the regulation of immune responses. Previous studies have indicated that dysregulating the miRNAs leads to the immunosuppression of porcine reproductive and respiratory syndrome virus (PRRSV). However, it is not clear how PRRSV regulates the expression of host miRNA, which may lead to immune escape or promote the replication of the virus. The present work suggests that PRRSV upregulated the expression of miR-373 through elevating the expression of specificity protein 1 (Sp1) in MARC-145 cells. Furthermore, this work demonstrated that miR-373 promoted the replication of PRRSV, since miR-373 was a novel negative miRNA for the production of beta interferon (IFN-β) by targeting nuclear factor IA (NFIA), NFIB, interleukin-1 receptor-associated kinase 1 (IRAK1), IRAK4, and interferon regulatory factor 1 (IRF1). We also found that both NFIA and NFIB were novel proteins for inducing the production of IFN-β, and both of them could inhibit the replication of PRRSV. In conclusion, PRRSV upregulated the expression of miR-373 by elevating the expression of Sp1 and hijacked the host miR-373 to promote the replication of PRRSV by negatively regulating the production of IFN-β.

IMPORTANCE

PRRSV causes one of the most economically devastating diseases of swine, and there is no effective method for controlling PRRSV. It is not clear how PRRSV inhibits the host's immune response and induces persistent infection. Previous studies have shown that PRRSV inhibited the production of type I IFN, and the treatment of type I IFN could efficiently inhibit the replication of PRRSV, so it will be helpful to design new methods of controlling PRRSV by understanding the molecular mechanism by which PRRSV modulated the production of IFN. The current work shows that miR-373, upregulated by PRRSV, promotes PRRSV replication, since miR-373 impaired the production of IFN-β by targeting NFIA, NFIB, IRAK1, IRAK4, and IRF1, and both NFIA and NFIB were antiviral proteins to PRRSV. In conclusion, this paper revealed a novel mechanism of PRRSV that impaired the production of type I IFN by upregulating miR-373 expression in MARC-145 cells.

Pathogen recognition and Toll-like receptor targeted therapeutics in innate immune cells

The innate immune system deploys a variety of pattern-recognition receptors (PRRs) which include Toll-like receptors (TLRs), RIG-I-like receptors, NOD-like receptors, and C-type lectin receptors to detect the invasion of pathogens and initiate protective responses. The intercellular and intracellular orchestration of signals from different PRRs, their endogenous or microbial ligands and accessory molecules determine the stimulatory or inhibitory responses. Progressing over the last two decades, considerable research on the molecular mechanisms underlying host-pathogen interactions has led to a paradigm shift of our understanding of TLR signaling in the innate immune system. Given that a significant amount of evidence implicates TLRs in the pathogenesis of immune diseases and cancer, and their activation occurs early in the inflammatory cascade, they are attractive targets for novel therapeutic agents. In this review, we discuss the recent advances in TLR signaling cross talks and the mechanism of pathogen recognition with special emphasis on the role of TLRs in tumor immunity and TLR-targeted therapeutics.

Stress and Non-Stress Roles of Inflammatory Signals during HSC Emergence and Maintenance

Hematopoietic stem cells (HSCs) are a rare population that gives rise to almost all cells of the hematopoietic system, including immune cells. Until recently, it was thought that immune cells sense inflammatory signaling and HSCs respond only secondarily to these signals. However, it was later shown that adult HSCs could directly sense and respond to inflammatory signals, resulting in a higher output of immune cells. Recent studies demonstrated that inflammatory signaling is also vital for HSC ontogeny. These signals are thought to arise in the absence of pathogens, are active during development, and indispensable for HSC formation. In contrast, during times of stress and disease, inflammatory responses can be activated and can have devastating effects on HSCs. In this review, we summarize the current knowledge about inflammatory signaling in HSC development and maintenance, as well as the endogenous molecular cues that can trigger inflammatory pathway activation. Finally, we comment of the role of inflammatory signaling in hematopoietic diseases.