Toll like receptor 3 and viral infections of nervous system

Intratracheal instillation of graphene oxide with different diameters suppressed toll-like receptor 3-mediated lipid droplet biogenesis in lungs and livers of mice

Recent advances have established lipid droplets as dynamic innate immune hubs coordinating cellular metabolism and defense mechanisms. While previous studies primarily focused on nanomaterials (NMs) altering lipid metabolism to influence lipid droplet dynamics, this study pioneers the investigation of NM-induced immune modulation via Toll-like receptor (TLR) pathways as a novel regulatory axis for lipid droplets. Building on our prior findings that graphene oxide (GO) impaired TLR3-mediated lipid signaling, we systematically explored the role of GO's diameter in modulating this process. Mice were subjected to daily intratracheal instillation of three GO variants (50-200 nm, <500 nm or > 500 nm) at 1 mg/kg for 7 days. Although no significant change in body weight or organ coefficient was observed, all GO exposure suppressed lipid staining in mouse lungs and livers, correlating with altered co-localization of TLR3 and perilipin 2 (PLIN2), critical regulators of lipid droplet biogenesis. Down-regulation of TLR3 signaling components, namely interferon induced protein with tetratricopeptide repeats 1 (IFIT1), radical S-adenosyl methionine domain containing 2 (RSAD2), and PLIN2, occurred in a diameter-dependent manner, with GO 50-200 nm showing the most pronounced effects, likely attributable to the smallest hydrodynamic size and polydispersity index in suspension. This work provides evidence that NM geometry governs TLR-mediated lipid droplet regulation, bridging the knowledge gap between nanotoxicology and immunometabolic cross-talking, a paradigm distinct from conventional lipid metabolism-focused nanotoxicological studies.

Varicellovirus bovinealpha (BoAHV) 1 and 5 activate distinct toll-like receptors signaling pathways in neural cells

Varicellovirus bovinealpha (BoAHV) types 5 and 1 are closely-related, neurotropic alphaherpesviruses. BoAHV-5 is the etiological agent of non-suppurative meningoencephalitis in calves, whereas BoAHV-1 is responsible for several syndromes in cattle, including respiratory and reproductive diseases. The innate immune response mediated by TLR3 and TLR7 is crucial in controlling infection and modulating pro-inflammatory cytokines, such as IFNs. In this study, it was evaluated whether TLR3 and TLR7 agonists affect BoAHV replication and whether TLR stimulation has an effect on the IFN-λ3 response in neural cells. TLR3 and TLR7 expression in neural cells was induced by the TLR agonists, Poly I:C and Imiquimod, respectively. The antiviral effect of the agonists varied with the virus strain. TLR7 was suppressed early after BoAHV-5 infection and it was upregulated during BoAHV-1 infection. Imiquimod pre-treatment of neural cells induced higher levels of TLR7 mRNA and reduced the replication of the natural BoAHV-5/1 recombinant. In this study, TLR3 expression was completely inhibited during infection with BoAHV-5 and there was a marked up-regulation of TLR3 mRNA during BoAHV-1 infection. Poly I:C treatment up-regulated TLR3 expression in infected cells but a detrimental effect on BoAHV-5 replication was not observed. Infection of neural cells with the recombinant virus A665 stimulated TLR3 expression late in the infectious cycle. Steady levels of BoAHV-1 replication were maintained in the presence of IFN-λ3 and this cytokine was unable to slow the replication of BoAHV-5. For BoAHV-5/1 A663 strain there was a consistent induction of IFN-λ3 throughout the infection period and maximum A663 titers at advanced stages of the replication cycle were in agreement with a decrease in expression levels. The study emphasizes the importance of strain-specific factors, the infection phase and the cell type involved in virus- and agonist-induced TLR and IFN-λ3 expression. Furthermore, these results evidenced that a deeper analysis on the role and activity of TLR agonists on BoAHV infection should be conducted to evaluate their potential as preventive or therapeutic molecules.

A Comprehensive Review of poly(I: C) as a Tool for Investigating Astrocytic TLR3 Signaling

Astrocytes play a crucial role in regulating the structure, function, and interactions between the synaptic and vascular compartments in the brain. Toll-like receptor 3 (TLR3) is expressed in astrocytes and recognizes double-stranded RNA (dsRNA), a pathogen-associated molecular pattern (PAMP). This review examines the current understanding of TLR3 signaling, with a focus on its specific role in astrocytes, and the use of the viral mimetic polyinosinic: polycytidylic acid (poly(I: C)) to model the effects of viral infections in both in vitro and in vivo studies. Poly(I: C) is a useful tool for studying neuro-immune communication and has significantly added to our knowledge of how the brain responds to immune challenges. Upon poly(I: C) exposure, TLR3 activation in astrocytes triggers inflammatory signaling pathways, leading to both antiviral responses and neuroinflammation. However, further research is required to investigate the cell-specific impacts of TLR3 activation, along with the influence of developmental stages, brain regions, and sex-specific responses, to gain a comprehensive understanding of how immune activation shapes the development and function of the central nervous system (CNS).

Genetic causes of infection induced encephalitis

INTRODUCTION

Patients with encephalitis following a viral infection are often thought to have a para infectious, inflammatory, or autoimmune cause for their presentation. These diagnoses usually result in treatments with immunosuppressant therapies which can have side effects. However, there is an increasing body of evidence demonstrating that patients can have a direct genetic cause mediating viral infection triggered encephalitis, where inflammation is a secondary response. These patients may benefit not from immunosuppressive therapies, but from protection from infection through dedicated immunisation programs and early antiviral therapies at times of infection.

METHODS

A small case series of paediatric neurology patients (n = 2) from a single institution with infection induced encephalitis and an underlying genetic cause, is presented. Patients with a confirmed genetic cause of infection induced encephalitis were identified and consented by their treating neurologist for inclusion in this case series. Ethics approval was gained for this case series and review of the surrounding literature.

CONCLUSION

A case of both DBR1 and NUP214 genetic changes resulting in infection induced encephalitis is presented. This case series raises awareness of this rare group of disorders and provides clues to their identification. Features to prompt clinician consideration of such genetic conditions are also highlighted. Although rare, identification of these patients is important due to implications on treatment, prognosis, and family planning.

Modulation of immune responses in the central nervous system by Zika virus, West Nile virus, and dengue virus

Arthropod-borne viruses (arboviruses) pose significant threats to global public health by causing a spectrum of diseases ranging from mild febrile illnesses to severe neurological complications. Understanding the intricate interplay between arboviruses and the immune system within the central nervous system is crucial for developing effective strategies to combat these infections and mitigate their neurological sequelae. This review comprehensively explores the mechanisms by which arboviruses such as Zika virus, West Nile virus, and Dengue virus manipulate immune responses within the CNS, leading to diverse clinical manifestations.

Generation of porcine PK-15 cells lacking the Ifnar1 or Stat2 gene to optimize the efficiency of viral isolation

Because pigs are intermediate or amplifying hosts for several zoonotic viruses, the pig-derived PK-15 cell line is an indispensable tool for studying viral pathogenicity and developing treatments, vaccines, and preventive measures to mitigate the risk of disease outbreaks. However, we must consider the possibility of contamination by type I interferons (IFNs), such as IFNα and IFNβ, or IFN-inducing substances, such as virus-derived double-stranded RNA or bacterial lipopolysaccharides, in clinical samples, leading to lower rates of viral isolation. In this study, we aimed to generate a PK-15 cell line that can be used to isolate viruses from clinical samples carrying a risk of contamination by IFN-inducing substances. To this end, we depleted the IFN alpha and beta receptor subunit 1 (Ifnar1) gene or signal transducer and activator of transcription 2 (Stat2) gene in PK-15 cells using the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 method. Treatment of PK-15 cells lacking Ifnar1 or Stat2 with IFNβ or poly (I:C) resulted in no inhibitory effects on viral infection by a lentiviral vector, influenza virus, and Akabane virus. These results demonstrate that PK-15 cells lacking Ifnar1 or Stat2 could represent a valuable and promising tool for viral isolation, vaccine production, and virological investigations.

Coding and noncoding RNA profile of human heterotopic ossifications - Risk factors and biomarkers

Heterotopic ossification (HO) means the formation of bone in muscles and soft tissues, such as ligaments or tendons. HO could have a genetic history or develop after a traumatic event, as a result of muscle injury, fractures, burns, surgery, or neurological disorders. Many lines of evidence suggest that the formation of HO is related to the pathological differentiation of stem or progenitor cells present within soft tissues or mobilized from the bone marrow. The cells responsible for the initiation and progression of HO are generally called HO precursor cells. The exact mechanisms behind the development of HO are not fully understood. However, several factors have been identified as potential contributors. For example, local tissue injury and inflammation disturb soft tissue homeostasis. Inflammatory cells release growth factors and cytokines that promote osteogenic or chondrogenic differentiation of HO precursor cells. The bone morphogenetic protein (BMP) is one of the main factors involved in the development of HO. In this study, next-generation sequencing (NGS) and RT-qPCR were performed to analyze the differences in mRNA, miRNA, and lncRNA expression profiles between muscles, control bone samples, and HO samples coming from patients who underwent total hip replacement (THR). As a result, crucial changes in the level of gene expression between HO and healthy tissues were identified. The bioinformatic analysis allowed to describe the processes most severely impacted, as well as genes which level differed the most significantly between HO and control samples. Our analysis showed that the level of transcripts involved in leukocyte migration, differentiation, and activation, as well as markers of chronic inflammatory diseases, that is, miR-148, increased in HO, as compared to muscle. Furthermore, the levels of miR-195 and miR-143, which are involved in angiogenesis, were up-regulated in HO, as compared to bone. Thus, we suggested that inflammation and angiogenesis play an important role in HO formation. Importantly, we noticed that HO is characterized by a higher level of TLR3 expression, compared to muscle and bone. Thus, we suggest that infection may also be a risk factor in HO development. Furthermore, an increased level of transcripts coding proteins involved in osteogenesis and signaling pathways, such as ALPL, SP7, BGLAP, BMP8A, BMP8B, SMPD3 was noticed in HO, as compared to muscles. Interestingly, miR-99b, miR-146, miR-204, and LINC00320 were up-regulated in HO, comparing to muscles and bone. Therefore, we suggested that these molecules could be important biomarkers of HO formation and a potential target for therapies.

Investigation of the impact of AXL, TLR3, and STAT2 in congenital Zika syndrome through genetic polymorphisms and protein-protein interaction network analyses

INTRODUCTION

Zika virus (ZIKV) is a human teratogen that causes congenital Zika syndrome (CZS). AXL, TLR3, and STAT2 are proteins involved in the ZIKV's entry into cells (AXL) and host's immune response (TLR3 and STAT2). In this study, we evaluated the role of genetic polymorphisms in these three genes as risk factors to CZS, and highlighted which proteins that interact with them could be important for ZIKV infection and teratogenesis.

MATERIALS AND METHODS

We evaluate eighty-eight children exposed to ZIKV during the pregnancy, 40 with CZS and 48 without congenital anomalies. The evaluated polymorphisms in AXL (rs1051008), TLR3 (rs3775291), and STAT2 (rs2066811) were genotyped using TaqMan® Genotyping Assays. A protein-protein interaction network was created in STRING database and analyzed in Cytoscape software.

RESULTS

We did not find any statistical significant association among the polymorphisms and the occurrence of CZS. Through the analyses of the network composed by AXL, TLR3, STAT2 and their interactions targets, we found that EGFR and SRC could be important proteins for the ZIKV infection and its teratogenesis.

CONCLUSION

In summary, our results demonstrated that the evaluated polymorphisms do not seem to represent risk factors for CZS; however, EGFR and SRC appear to be important proteins that should be investigated in future studies.

TRIM3 attenuates cytokine storm caused by Dabie bandavirus via promoting Toll-like receptor 3 degradation

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease that was caused by the Dabie bandavirus (DBV), and it has become a global public health threat. Cytokine storm is considered to be an important pathogenesis of critical SFTS. Tripartite motif-containing 3 (TRIM3), as a member of the TRIM protein family, may contribute to the regulation of the immune and inflammatory responses after viral infection. However, whether TRIM3 plays a major role in the pathogenesis of SFTS has not yet been investigated.

Methods

TRIM3 mRNA levels were detected in PBMCs between 29 SFTS patients and 29 healthy controls by qRT-PCR. We established the pathogenic IFNAR^-/- SFTS mouse model successfully by inoculating subcutaneously with DBV and testing the expression levels of TRIM3 mRNA and protein by qRT-PCR and immunofluorescence in the livers, spleens, lungs, and kidneys. TRIM3^OE THP-1 cells and peritoneal macrophages extracted from TRIM3^-/- mice were infected with DBV. The effect of TRIM3 on cytokines was detected by qRT-PCR and ELISA. Then we examined Toll-like receptor 3 (TLR3) and protein phosphorylation in the MAPK pathway after DBV infection using Western blot. Flow cytometry was used to verify TLR3 expression on peripheral blood monocytes in SFTS patients. We further explored the interaction between TRIM3 and TLR3 using CO-IP and Western blot.

Results

Compared to healthy controls, TRIM3 mRNA expression in PBMCs is decreased in SFTS patients, especially in severe cases. TRIM3 mRNA and protein were synchronously reduced in the livers, spleens, lungs, and kidney tissues of the IFNAR^-/- SFTS mice model. In the DBV-infected cell model, TRIM3 overexpression can inhibit the DBV-induced release of IL-1β, IL-6, and TNF-α, the expression of TLR3, and protein phosphorylation in the MAPK pathway, which plays an anti-inflammatory role, while TRIM3 deficiency exacerbates the pro-inflammatory effects. We further found that TRIM3 can promote TLR3 degradation through K48-linked ubiquitination.

Conclusion

TRIM3 can inhibit the production of cytokines by regulating the degradation of TLR3 through K48-linked ubiquitination, which can be a therapeutic target for improving the prognosis of SFTS.

Graphene oxide links alterations of anti-viral signaling pathways with lipid metabolism via suppressing TLR3 in vascular smooth muscle cells

Vascular smooth muscle cells (VSMCs), the main cells constructing blood vessels, are important in the regulation of the pathophysiology of vascular systems; however, relatively few studies have investigated the influence of nanomaterials (NMs) on VSMCs. In this study, we found that the interaction between graphene oxide and human VSMCs led to the cytotoxicity and morphological changes of cells. Because transcriptomic data suggested that graphene oxide decreased anti-viral signaling pathways via decreasing Toll-like receptor 3 (TLR3), we further verified that graphene oxide decreased interferon induced protein with tetratricopeptide repeats 1 (IFIT1) and the radical S-adenosyl methionine domain containing 2 (RSAD2), and TLR3-downstream genes involved in anti-viral responses. Due to the involvement of RSAD2 in lipid dysfunction, we also verified that graphene oxide disrupted lipid homeostasis and increased adipose triglyceride lipase (ATGL). Adding TLR3 agonist polyinosinic:polycytidylic acid (Poly IC) partially increased TLR3-downstream protein interleukin-8 (IL-8) and some lipid classes, particularly lysophosphatidylcholine (LPC) and lysophosphatidylethanolamine (LPE), in graphene oxide-exposed VSMCs. In mice receiving repeated intravenous injection of graphene oxide, significantly decreased TLR3, IFIT1 and RSAD2 but increased ATGL proteins were observed in aortas. We conclude that graphene oxide altered anti-viral signaling pathways and lipid metabolism via decreasing TLR3 in VSMCs.

Deciphering the TLR transcriptome and downstream signaling pathway in cerebrospinal fluid in pediatric meningitis

OBJECTIVE/DESIGN

Pediatric meningitis is characterized by a colossal inflammatory response to the pathogen in the central nervous system (CNS). This unabated inflammatory response persists even after the removal of the pathogen by antibiotics/steroids causing collateral damage to CNS tissue. Toll-like receptors (TLRs) are the key players in the recognition and elicitation of innate-immune response against bacterial/viral components in cerebrospinal fluid (CSF). Till date, the precise understanding of TLR-triggered inflammatory response in pediatric meningitis is lacking. The present study was designed to delineate the role of TLR transcriptome and downstream signaling pathways in CSF of pediatric meningitis.

METHODS

Children in the age group of > 3 months to 12 years with pediatric meningitis were included. A total of 249 cases of pediatric meningitis (bacterial = 89, viral = 160) were included. In addition, 71 children who tested negative to the pathogen in CSF tap and did not have signs of infection clinically constituted the controls. RNA was extracted from the CSF samples of both cases and controls. The relative gene expression profile of 42 TLR signaling pathway genes was performed. For the analysis of secretory cytokines and chemokines in CSF, Luminex assay was performed.

RESULTS

We report global upregulation of TLR genes in patients with acute bacterial meningitis (ABM). The downstream signaling molecules were upregulated as well. The CSF of pediatric ABM patients revealed a predominant pro-inflammatory milieu marked by increased levels of pro-inflammatory cytokines. A significant correlation between poor clinical outcomes of patients and an increased expression of TLR/pro-inflammatory cytokine genes was observed.

CONCLUSION

Our findings provide support for future studies exploring TLR-based adjunct therapy to limit the neurological sequelae, owing to persistent inflammation in pediatric ABM patients.

TLR3 Mediates Senescence and Immunosurveillance of Hepatic Stellate Cells

Background: Activation of hepatic stellate cells (HSCs) is an important driver of liver fibrosis, which is a health problem of global concern, and there is no effective solution for it at the present. Senescent activated HSCs are preferentially killed by natural killer cells (NK cells) to promote the regression of hepatic fibrosis. Objectives: The purpose of this study was to investigate the effect of polyinosinic-polycytidylic acid (poly I:C) on HSCs’ senescence, a trigger for NK cell-induced cytotoxicity. Methods: The senescence of HSCs was assessed by western blot, qRT-PCR, and flow cytometry, and NK cell cytotoxicity was assessed in a co-culture of NK cells with poly I:C-treated HSCs by measuring CD107a expression. Results: The expression of p16, p21, SA-β-gal, MICA/MICB, and ULBP2 increased in poly I:C-treated HSCs, rendering them significantly susceptible to NK cell cytotoxicity. Conclusions: Poly I:C induces cellular senescence in HSCs and triggers NK cell immunosurveillance, suggesting that the role of poly I:C in HSC senescence may promote fibrosis regression.

Human host genetics and susceptibility to ZIKV infection

Managing emerging infectious diseases is a current challenge in the fields of microbiology and epidemiology. Indeed, among other environmental and human-related factors, climate change and global warming favor the emergence of new pathogens. The recent Zika virus (ZIKV) epidemic, of which the large and rapid spread surprised the scientific community, is a reminder of the importance to study viruses currently responsible for sporadic infections. Increasing our knowledge of key factors involved in emerging infections is essential to implement specific monitoring that can be oriented according to the pathogen, targeted population, or at-risk environment. Recent technological developments, such as high-throughput sequencing, genome-wide association studies and CRISPR screenings have allowed the identification of human single nucleotide polymorphisms (SNPs) involved in infectious disease outcome. This review focuses on the human genetic host factors that have been identified and shown to be associated with the pathogenesis of ZIKV infection and candidate SNP targets.

TLR2- and TLR3-activated microglia induce different levels of neuronal network dysfunction in a context-dependent manner

Recognition of pathogen- or damage-associated molecular patterns (PAMPs, DAMPs) by innate Toll-like receptors (TLRs) is central to the activation of microglia (brain macrophages) in many CNS diseases. Notably, TLR-mediated microglial activation is complex and modulated by additional exogenous and endogenous immunological signals. The impact of different microglial reactive phenotypes on electrical activity and neurotransmission is widely unknown, however. We explored the effects of TLR ligands on microglia and neuronal network function in rat organotypic hippocampal slice cultures (in situ), i.e., postnatal cortical tissue lacking adaptive immunity. Single exposure of slice cultures to TLR2 or TLR3 ligands [PGN, poly(I:C)] for 2-3 days induced moderate microglial activation featuring IL-6 and TNF-α release and only mild alterations of fast neuronal gamma band oscillations (30-70 Hz) that are fundamental to higher cognitive functions, such as perception, memory and behavior. Paired exposure to TLR3/TLR2 or TLR3/TLR4 ligands (LPS) induced nitric oxide (NO) release, enhanced TNF-α release, and associated with advanced network dysfunction, including slowing to the beta frequency band (12-30 Hz) and neural bursts (hyperexcitability). Paired exposure to a TLR ligand and the leukocyte cytokine IFN-γ enhanced NO release and associated with severe network dysfunction, albeit sensitive parvalbumin- and somatostatin-positive inhibitory interneurons were preserved. Notably, the neuronal disturbance was prevented by either microglial depletion or pharmacological inhibition of oxidant-producing enzymes, inducible NO synthase (iNOS) and NADPH oxidase. In conclusion, TLR-activated microglia can induce different levels of neuronal network dysfunction, in which severe dysfunction is mainly caused by reactive oxygen and nitrogen species rather than proinflammatory cytokines. Our findings provide a mechanistic insight into microglial activation and functional neuronal network impairment, with relevance to neuroinflammation and neurodegeneration observed in, e.g., meningoencephalitis, multiple sclerosis and Alzheimer's disease.

Genetic variations of toll-like receptors: Impact on susceptibility, severity and prognosis of bacterial meningitis

Bacterial meningitis (BM) is a serious infectious disease of the central nervous system，which is mainly caused by Streptococcus pneumoniae, Neisseria meningitidis, Haemophilus influenzae, Group B Streptococcus and Listeria monocytogenes. Throughout the world, BM has become one of the most lethal diseases that commonly occurs in children. Toll like receptors (TLRs) are one of the most important immune defense lines in infectious diseases, and play an essential role in host defense. Accumulating evidence shows that genetic variations in TLRs are associated with host responses in BM. This review aims to summarize the role of different TLRs and their genetic variations in the susceptibility, severity and prognosis of BM and discuss the identified risk factors for better treatment and improvement of the course and outcome of BM.

Chronic ethanol exposure induces neuroinflammation in H4 cells through TLR3 / NF-κB pathway and anxiety-like behavior in male C57BL/6 mice

Chronic alcoholism has become a major public health problem. Long-term and excessive drinking can lead to a variety of diseases. Chronic ethanol exposure can induce neuroinflammation and anxiety-like behavior, and this may be induced through the Toll-like receptor 3/nuclear factor-κB (TLR3/NF-κB) pathway. Animal experiments were performed using healthy adult male C57BL/6 N mice given 10 % (m/V) or 20 % ethanol solution as the only choice of drinkable fluid for 60, 90 or 180 d. In cell culture experiments, H4 human glioma cells were treated with 100 mM ethanol for 2 d, with the TLR3 gene silenced by RNAi and NF-κB inhibited by ammonium pyrrolidine dithiocarbamate (PDTC, 10 μM). After treatment with ethanol solution for a specific time, the anxiety-like behavior of the mice was tested using the open field test and the elevated plus maze test. Western blotting was used to detect the expression of TLR3, TLR4, NF-κB, IL-1β, IL-6, and TNF-α in the mouse hippocampus and H4 cells. The expression of IL-1β, IL-6 and TNF-α in the supernatant of cell culture medium was detected by ELISA. The open field test showed a decrease in time spent in the central area, and the elevated plus maze test showed a decrease in activity time in the open arm region. These behavioral tests indicated that ethanol caused anxiety-like behavior in mice. The expression levels of TLR3, TLR4, NF-κB, IL-1β, IL-6, and TNF-α increased after ethanol exposure in both the hippocampus of mice and H4 cells. Silencing of the TLR3 gene by RNAi or inhibition of NF-κB by PDTC attenuated the ethanol-induced increase in the expression of inflammatory factors in H4 cells. These findings indicated that chronic ethanol exposure increases the expression of TLR3 and NF-κB and produces neuroinflammation and anxiety-like behavior in male C57BL/6 mice and that ethanol-induced neuroinflammation can be caused through the TLR3/NF-κB pathway.

Toll-like receptor-mediated innate immunity against herpesviridae infection: a current perspective on viral infection signaling pathways

Background

In the past decades, researchers have demonstrated the critical role of Toll-like receptors (TLRs) in the innate immune system. They recognize viral components and trigger immune signal cascades to subsequently promote the activation of the immune system.

Main body

Herpesviridae family members trigger TLRs to elicit cytokines in the process of infection to activate antiviral innate immune responses in host cells. This review aims to clarify the role of TLRs in the innate immunity defense against herpesviridae, and systematically describes the processes of TLR actions and herpesviridae recognition as well as the signal transduction pathways involved.

Conclusions

Future studies of the interactions between TLRs and herpesviridae infections, especially the subsequent signaling pathways, will not only contribute to the planning of effective antiviral therapies but also provide new molecular targets for the development of antiviral drugs.

Modulation of the Innate Immune Response by Targeting Toll-like Receptors: A Perspective on Their Agonists and Antagonists

Toll-like receptors (TLRs) are a class of proteins that recognize pathogen-associated molecular patterns (PAMPs) and damaged-associated molecular patterns (DAMPs), and they are involved in the regulation of innate immune system. These transmembrane receptors, localized at the cellular or endosomal membrane, trigger inflammatory processes through either myeloid differentiation primary response 88 (MyD88) or TIR-domain-containing adapter-inducing interferon-β (TRIF) signaling pathways. In the last decades, extensive research has been performed on TLR modulators and their therapeutic implication under several pathological conditions, spanning from infections to cancer, from metabolic disorders to neurodegeneration and autoimmune diseases. This Perspective will highlight the recent discoveries in this field, emphasizing the role of TLRs in different diseases and the therapeutic effect of their natural and synthetic modulators, and it will discuss insights for the future exploitation of TLR modulators in human health.

Transcriptome Analysis Reveals the Neuro-Immune Interactions in Duck Tembusu Virus-Infected Brain

The duck Tembusu virus (DTMUV) is a mosquito-borne flavivirus. It causes severe symptoms of egg-drop, as well as neurological symptoms and brain damage in ducks. However, the specific molecular mechanisms of DTMUV-induced neurovirulence and host responses in the brain remain obscure. To better understand the host-pathogen and neuro-immune interactions of DTMUV infection, we conducted high-throughput RNA-sequencing to reveal the transcriptome profiles of DTMUV-infected duck brain. Totals of 117, 212, and 150 differentially expressed genes (DEGs) were identified at 12, 24, and 48 h post infection (hpi). Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses uncovered genes and pathways related to the nervous system and immune responses in duck brain. Neuro-related genes, including WNT3A, GATA3, and CHRNA6, were found to be significantly downregulated. RIG-I-like receptors (DHX58, IFIH1) and Toll-like receptors (TLR2 and TLR3) were activated, inducing the expression of 22 interferon stimulated genes (ISGs) and antigen-processing and -presenting genes (TAP1 and TAP2) in the brain. Our research provides comprehensive information for the molecular mechanisms of neuro-immune and host-pathogen interactions of DTMUV.

Inflammatory Role of TLR-MyD88 Signaling in Multiple Sclerosis

Multiple sclerosis (MS) is a neuro-autoimmune and neurodegenerative disorder leading to chronic inflammation, demyelination, axonal, and neuronal loss in the central nervous system (CNS). Despite intense research efforts, the pathogenesis of MS still remains unclear. Toll-like receptors (TLRs) are a family of type I transmembrane receptors that play a crucial role in the innate immune response. Myeloid differentiation factor 88 (MyD88) is the adaptor of major TLRs. It has been widely considered that the TLR-MyD88 signaling pathway plays an important role in the occurrence and development of autoimmune disease. Data have revealed that the TLR-MyD88 signaling may be involved in the pathogenesis of MS and experimental autoimmune encephalomyelitis (EAE), an animal model for MS, by regulating the antigen presentation of dendritic cells, the integrity of blood-brain barrier (BBB), and the activation of T cells and B cells. Here, we summarize the role of TLRs and MyD88 in MS and discuss the possible therapies that are based on these molecules.

TLR3 preconditioning induces anti-inflammatory and anti-ictogenic effects in mice mediated by the IRF3/IFN-β axis

Activation of Toll-like receptor 3 (TLR3) was previously shown to contribute to the generation of epileptic seizures in rodents by evoking a proinflammatory response in the forebrain. This suggests that TLR3 blockade may provide therapeutic effects in epilepsy. We report that brain activation of TLR3 using the synthetic receptor ligand Poly I:C may also result in remarkable dose- and time-dependent inhibitory effects on acute seizures in mice without inducing inflammation. These inhibitory effects are associated with reduced neuronal excitability in the hippocampus as shown by a decrease in the population spike amplitude of CA1 pyramidal neurons following Schaffer collaterals stimulation. TLR3 activation which results in seizure inhibition does not evoke NF-kB-dependent inflammatory molecules or morphological activation of glia, however, it induces the alternative interferon (IFN) regulatory factor (IRF)-3/IFN-β signaling pathway. IFN-β reproduced the inhibitory effects of Poly I:C on neuronal excitability in hippocampal slices. Seizure inhibition attained with activation the TLR3-IRF3/IFN-β axis should be carefully considered when TLR3 are targeted for therapeutic purposes.

Systemic IL-1β production as a consequence of corneal HSV-1 infection-contribution to the development of herpes simplex keratitis

This study sought to identify potential therapeutic targets in herpes simplex keratitis (HSK) patients with active and inactive infection by investigating peripheral cytokine production. Peripheral blood mononuclear cells (PBMCs) and serum were prepared from healthy controls and HSK patients during active infection or following treatment (inactive infection). Serum antibody titres were determined by ELISA. Protein expression levels were analysed by Western blot. Cytokine levels were determined by multiplex ELISA. Active corneal herpes simplex virus type 1 (HSV-1) infection resulted in significantly elevated peripheral levels of IL-1β in HSK patients compared to healthy controls, and remained significantly increased following treatment. Elevated production of IL-1β in inactive patients was associated with significantly increased levels of IRF3 and STAT1, key proteins involved in promoting anti-viral immune responses. Our data suggest that inflammation persists beyond the period that it is clinically evident and that enhanced peripheral production of IL-1β may have implications for HSV-1 viral clearance in active and inactive HSK patients.

The zinc-finger protein ZFYVE1 modulates TLR3-mediated signaling by facilitating TLR3 ligand binding

Recognition of viral dsRNA by Toll-like receptor 3 (TLR3) leads to the induction of downstream antiviral effectors and the innate antiviral immune response. Here, we identified the zinc-finger FYVE domain-containing protein ZFYVE1, a guanylate-binding protein (GBP), as a positive regulator of TLR3-mediated signaling. Overexpression of ZFYVE1 promoted the transcription of downstream antiviral genes upon stimulation with the synthetic TLR3 ligand poly(I:C). Conversely, ZFYVE1 deficiency had the opposite effect. Zfyve1^-/- mice were less susceptible than wild-type mice to inflammatory death induced by poly(I:C) but not LPS. ZFYVE1 was associated with TLR3, and the FYVE domain of ZFYVE1 and the ectodomain of TLR3 were shown to be responsible for their interaction. ZFYVE1 was bound to poly(I:C) and increased the binding affinity of TLR3 to poly(I:C). These findings suggest that ZFYVE1 plays an important role in the TLR3-mediated innate immune and inflammatory responses by promoting the ligand binding of TLR3.

Human Interleukin-34 facilitates microglia-like cell differentiation and persistent HIV-1 infection in humanized mice

Background

Microglia are the principal innate immune defense cells of the centeral nervous system (CNS) and the target of the human immunodeficiency virus type one (HIV-1). A complete understanding of human microglial biology and function requires the cell’s presence in a brain microenvironment. Lack of relevant animal models thus far has also precluded studies of HIV-1 infection. Productive viral infection in brain occurs only in human myeloid linage microglia and perivascular macrophages and requires cells present throughout the brain. Once infected, however, microglia become immune competent serving as sources of cellular neurotoxic factors leading to disrupted brain homeostasis and neurodegeneration.

Methods

Herein, we created a humanized bone-marrow chimera producing human “microglia like” cells in NOD.Cg-Prkdc^scidIl2rg^tm1SugTg(CMV-IL34)1/Jic mice. Newborn mice were engrafted intrahepatically with umbilical cord blood derived CD34+ hematopoietic stem progenitor cells (HSPC). After 3 months of stable engraftment, animals were infected with HIV-1_ADA, a myeloid-specific tropic viral isolate. Virologic, immune and brain immunohistology were performed on blood, peripheral lymphoid tissues, and brain.

Results

Human interleukin-34 under the control of the cytomegalovirus promoter inserted in NSG mouse strain drove brain reconstitution of HSPC derived peripheral macrophages into microglial-like cells. These human cells expressed canonical human microglial cell markers that included CD14, CD68, CD163, CD11b, ITGB2, CX3CR1, CSFR1, TREM2 and P2RY12. Prior restriction to HIV-1 infection in the rodent brain rested on an inability to reconstitute human microglia. Thus, the natural emergence of these cells from ingressed peripheral macrophages to the brain could allow, for the first time, the study of a CNS viral reservoir. To this end we monitored HIV-1 infection in a rodent brain. Viral RNA and HIV-1p24 antigens were readily observed in infected brain tissues. Deep RNA sequencing of these infected mice and differential expression analysis revealed human-specific molecular signatures representative of antiviral and neuroinflammatory responses.

Conclusions

This humanized microglia mouse reflected human HIV-1 infection in its known principal reservoir and showed the development of disease-specific innate immune inflammatory and neurotoxic responses mirroring what can occur in an infected human brain.

Electronic supplementary material

The online version of this article (10.1186/s13024-019-0311-y) contains supplementary material, which is available to authorized users.

Microglial Activation and Psychotic Disorders: Evidence from Pre-clinical and Clinical Studies

Clinical and pre-clinical studies have demonstrated an important role of neuroinflammation in the etiology of schizophrenia. While the underlying mechanisms remain poorly understood, there are some studies demonstrating an association between maternal immune activation and behavioral changes in adult offspring and identifying early life infection as a trigger for schizophrenia; in addition, inflammatory markers were found to be increased in the schizophrenic post-mortem brain. During maternal immune activation, pro-inflammatory mediators such as cytokines, chemokines, antibodies, and acute-phase proteins are released in the maternal bloodstream, thus increasing the permeability of the placental barrier and the fetal blood-brain barrier, allowing the inflammatory mediators to enter the fetal brain. In the central nervous system (CNS), these pro-inflammatory mediators are able to activate microglial cells that can release pro-inflammatory cytokines such as tumor necrosis factor alpha (TNF-α), interleukin (IL)-1β, and IL-6. As a consequence, circulating immune cells may infiltrate the brain, increasing cytokine levels and releasing antibodies that aggravate the neuroinflammation. Neuroinflammation may affect processes that are pivotal for normal brain maturation such as myelination, synaptic pruning, and neuronal remodeling. Microglial cell activation and pro-inflammatory mediators have been extensively studied in schizophrenic post-mortem brain samples. Some results of these investigations demonstrated an increase in microglial activation markers, cytokines, and chemokines in post-mortem brain samples from individuals with schizophrenia. In contrast, there are studies that have demonstrated low levels of microglial activation makers in the schizophrenic post-mortem brain. Thus, based on the important role of neuroinflammation as a trigger in the development of schizophrenia, this chapter aims (1) to enumerate evidence of neuroinflammation and microglial activation from pre-clinical schizophrenia models, (2) to show links between schizophrenia and neuroinflammation in clinical studies, and (3) to identify mechanisms by which microglial activation may influence in the development of schizophrenia.

Skeletal muscle cells actively shape (auto)immune responses

Histopathological analyses of muscle specimens from myositis patients indicate that skeletal muscle cells play an active role in the interaction with immune cells. Research over the last few decades has shown that skeletal muscle cells exhibit immunobiological properties that perfectly define them as non-professional antigen presenting cells. They are able to present antigens via major histocompatibility complex molecules, exhibit costimulatory molecules and secrete soluble molecules that actively shape the immune response in an either pro- or anti-inflammatory manner. Skeletal muscle cells regulate both innate and adaptive immune responses and are essentially involved in the pathophysiological processes of idiopathic inflammatory myopathies. Understanding the role of skeletal muscle cells might help to identify new therapeutic targets for these devastating diseases. This review summarizes the immunobiological features of skeletal muscle cells, especially in the context of idiopathic inflammatory myopathies, and discusses shortcomings and limitations in skeletal muscle related research providing potential perspectives to overcome them in the future.

A comprehensive study on cellular RNA editing activity in response to infections with different subtypes of influenza a viruses

Background

RNA editing is an important mechanism that expands the diversity and complexity of genetic codes. The conversions of adenosine (A) to inosine (I) and cytosine (C) to uridine (U) are two prominent types of RNA editing in animals. The roles of RNA editing events have been implicated in important biological pathways. Cellular RNA editing activity in response to influenza A virus infection has not been fully characterized in human and avian hosts. This study was designed as a big data analysis to investigate the role and response of RNA editing in epithelial cells during the course of infection with various subtypes of influenza A viruses.

Results

Using a bioinformatics pipeline modified from our previous study, we characterized the profiles of A-to-I and C-to-U RNA editing events in human epithelial cells during the course of influenza A virus infection. Our results revealed a striking diversity of A-to-I RNA editing activities in human epithelial cells in responses to different subtypes of influenza A viruses. The infection of H1N1 and H3N2 significantly up-regulated normalized A-to-I RNA editing levels in human epithelial cells, whereas that of H5N1 did not change it and H7N9 infection significantly down-regulated normalized A-to-I editing level in A549 cells. Next, the expression levels of ADAR and APOBEC enzymes responsible for A-to-I and C-to-U RNA editing during the course of virus infection were examined. The increase of A-to-I RNA editing activities in infections with some influenza A viruses (H1N1 and H3N2) is linked to the up-regulation of ADAR1 but not ADAR2. Further, the pattern recognition receptors of human epithelial cells infected with H1N1, H3N2, H5N1 and H7N9 were examined. Variable responsive changes in gene expression were observed with RIG-I like receptors and Toll like receptors. Finally, the effect of influenza A virus infection on cellular RNA editing activity was also analyzed in avian hosts.

Conclusion

This work represents the first comprehensive study of cellular RNA editing activity in response to different influenza A virus infections in human and avian hosts, highlighting the critical role of RNA editing in innate immune response and the pathogenicity of different subtypes of influenza A viruses.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4330-1) contains supplementary material, which is available to authorized users.

The Significance of Type-I Interferons in the Pathogenesis and Therapy of Human Immunodeficiency Virus 1 Infection

Type-I interferons (IFN-I) are a widely expressed family that could promote antivirus immunity in the process of pathogens invasion. In a human immunodeficiency virus 1 (HIV-1)-infected individual, the production of IFN-I can be detected as early as the acute phase and will persist throughout the course of infection. However, sustained stimulation of immune system by IFN-I also contributes greatly to host-mediated immunopathology and diseases progression. Although the protective effects of IFN-I in the acute phase of HIV-1 infection have been observed, more studies recently focus on their detrimental role in the chronic stage. Inhibition of IFN-I signaling may reverse HIV-1-induced immune hyperactivation and furthermore reduce HIV-1 reservoirs, which suggest this strategy may provide a potential way to enhance the therapeutic effect of antiretroviral therapy. Therefore, we review the role of IFN-I in HIV-1 progression, their effects on different immunocytes, and therapeutic prospects targeting the IFN-I system.

Expression of CCL5 is induced by polyinosinic : polycytidylic acid in cultured hCMEC/D3 human brain microvascular endothelial cells

Objective

Brain microvascular endothelial cells are one of the cell types that form the blood–brain barrier, and play an important role in the defense system of the brain. Toll‐like receptor 3 (TLR3) is a pattern‐recognition receptor against double‐stranded RNA, and TLR3 signaling is important in antiviral innate immune reactions. However, TLR3 signaling in brain microvascular endothelial cells is not well understood. We aimed to investigate the role of TLR3 signaling in chemokine CCL5 production in human brain microvascular endothelial cells.

Methods

The hCMEC/D3 human brain microvascular endothelial cells were cultured, and treated with an authentic TLR3 agonist polyinosinic : polycytidylic acid. The expression of CCL5 was examined using quantitative real‐time reverse transcription polymerase chain reaction and enzyme‐linked immunosorbent assay. Involvement of TLR3, interferon (IFN)‐β, or IFN‐λ1, IFN‐regulatory factor 3 or nuclear factor‐κB p65 in this reaction was examined using RNA interference. Translocation of p65 into the nucleus was examined using immunofluorescence staining.

Results

Treatment of cells with polyinosinic : polycytidylic acid induced the expression of CCL5, IFN‐β and IFN‐λ1, and also the translocation of p65 into the nucleus. Knockdown of TLR3, IFN‐regulatory factor 3 or p65 inhibited the induction of these molecules, while knockdown of neither IFN‐β nor IFN‐λ1 affected the expression of CCL5.

Conclusions

TLR3 activation by polyinosinic : polycytidylic acid induces the expression of CCL5 in cultured hCMEC/D3 cells, and IFN‐regulatory factor 3 and p65 are involved in this reaction. CCL5 induced by TLR3 signaling in brain microvascular endothelial cells might contribute to antiviral protective reactions and/or detrimental responses associated with viral infection in the brain.

Elevated expression of EBV and TLRs in the brain is associated with Rasmussen's encephalitis

Rasmussen's encephalitis (RE) is a rare pediatric neurological disorder, the etiology of which remains unclear. It has been speculated that the immunopathogenesis of RE involves damage to neurons, which eventually leads to the occurrence of RE. Viral infection may be a critical factor in triggering RE immunopathogenesis. In this study, we analyzed the expression of Epstein-Barr virus (EBV) antigens as well as of Toll-like receptor 3 (TLR3), TLR9, and downstream adapter TIRdomain-containing adapter-inducing interferon-β (TRIF) in the brain tissues of 26 patients with RE and 16 control individuals using immunohistochemistry (IHC). In the RE group, EBV antigens were detected in 53% of individuals at various expression levels. In contrast, there was no detectable EBV antigen expression in control brain tissues. Moreover, we found marked increases in the expression of TLR3, TLR9, and TRIF in the brain tissues of RE patients compared with levels in the control group. Furthermore, among RE cases, EBV expression and high TLR3 expression were associated with more severe brain atrophy. Our results suggest that the elevated expression of EBV and TLRs may be involved in RE occurrence through the activation of downstream molecules.

Effect of feeding frequency on growth, body composition, antioxidant status and mRNA expression of immunodependent genes before or after ammonia-N stress in juvenile oriental river prawn, Macrobrachium nipponense

Feeding frequency is important for the improvement of growth performance and immunity of aquatic animals. In this study, the effect of feeding frequency on growth, body composition, antioxidant status and mRNA expression of immunodependent genes before or after ammonia-N stress was examined in Macrobrachium nipponense. Prawns were randomly assigned to one of five feeding frequencies (1, 2, 3, 4 and 6 times/day) following the same ration size over an 8-week growth trial. After the feeding trial, prawns were challenged by ammonia-N. The weight gain of prawns fed with 3-6 times/day was significantly higher than that of prawns fed with 1 time/day. The best feed conversion ratio was obtained from prawns fed with 3-6 times/day. Body crude lipid with feeding frequency of 3, 4 or 6 times/day was quite lower than that with 1 time/day. High feeding frequency (6 times/day) induced significantly elevated hepatopancreas super oxide dismutase and catalase activities. The malondialdehyde level in prawns fed with 6 times/day was also significantly increased, which was higher than that of prawns fed with other feeding frequency. mRNA expression of toll like receptor 3 and myeloid differentiation primary response protein MyD88 was promoted by feeding frequency from 3 to 4 time/day but inhibited by high or low feeding frequency. Similar mRNA expression variation trends of the two genes were observed in prawns after ammonia-N stress. After ammonia-N challenge, the highest cumulative mortality was observed in prawns fed with 6 times/day, which was significantly higher than that of prawns fed with 2-4 times/day. These findings demonstrate that (1) too high feeding frequency induced oxidative stress and malondialdehyde accumulation, negatively affecting the health status of prawns and reduced its resistance to ammonia-N stress; (2) the optimal feeding frequency to improve growth and immune response of this species at juvenile stage is 3-4 times/day; (3) considering costs of labour, a feeding frequency of 3 times/day is recommended for this prawn.

Expression of miR-155 associated with Toll-like receptors 3, 7, and 9 transcription in the olfactory bulbs of cattle naturally infected with BHV5

Bovine herpesvirus 5 (BHV5) infection of young cattle is frequently associated with fatal neurological disease and, as such, represents an attractive model for studying the pathogenesis of viral-induced meningoencephalitis. Following replication in the nasal mucosa, BHV5 invades the central nervous system (CNS) mainly through the olfactory pathway. The innate immune response triggered by the host face to virus replication through the olfactory route is poorly understood. Recently, an upregulation of conserved pathogen-associated molecular pattern, as Toll-like receptors (TLRs), has been demonstrated in the CNS of BHV5 experimentally infected cows. A new perspective to understand host-pathogen interactions has emerged elucidating microRNAs (miRNAs) network that interact with innate immune response during neurotropic viral infections. In this study, we demonstrated a link between the expression of TLRs 3, 7, and 9 and miR-155 transcription in the olfactory bulbs (OB) of 16 cows suffering from acute BHV5-induced neurological disease. The OBs were analyzed for viral antigens and genome, miR-155 and TLR 3, 7, and 9 expression considering three major regions: olfactory receptor neurons (ORNs), glomerular layer (GL), and mitral cell layer (ML). BHV5 antigens and viral genomes, corresponding to glycol-C gene, were detected in all OBs regions by fluorescent antibody assay (FA) and PCR, respectively. TLR 3, 7, and 9 transcripts were upregulated in ORNs and ML, yet only ORN layers revealed a positive correlation between TLR3 and miR-155 transcription. In ML, miR-155 correlated positively with all TLRs studied. Herein, our results evidence miR-155 transcription in BHV5 infected OB tissue associated to TLRs expression specifically ORNs which may be a new window for further studies.

RNA sensors of the innate immune system and their detection of pathogens

The innate immune system plays a critical role in pathogen recognition and initiation of protective immune response through the recognition of pathogen associated molecular patterns (PAMPs) by its pattern recognition receptors (PRRs). Nucleic acids including RNA and DNA have been recognized as very important PAMPs of pathogens especially for viruses. RNA are the major PAMPs of RNA viruses, to which most severe disease causing viruses belong thus posing a tougher challenge to human and animal health. Therefore, the understanding of the immune biology of RNA PRRs is critical for control of pathogen infections especially for RNA virus infections. RNA PRRs are comprised of TLR3, TLR7, TLR8, RIG-I, MDA5, NLRP3, NOD2, and some other minorities. This review introduces these RNA PRRs by describing the cellular localizations, ligand recognitions, activation mechanisms, cell signaling pathways, and recognition of pathogens; the cross-talks between various RNA PRRs are also reviewed. The deep insights of these RNA PRRs can be utilized to improve anti-viral immune response. © 2017 IUBMB Life, 69(5):297-304, 2017.