Defense against HSV-1 in a murine model is mediated by iNOS and orchestrated by the activation of TLR2 and TLR9 in trigeminal ganglia

Toll-like receptors as a missing link in Notch signaling cascade during neurodevelopment

Neurodevelopment encompasses a complex series of molecular events occuring at defined time points distinguishable by the specific genetic readout and active protein machinery. Due to immense intricacy of intertwined molecular pathways, extracting and describing all the components of a single pathway is a demanding task. In other words, there is always a risk of leaving potential transient molecular partners unnoticed while investigating signaling cascades with core functions-and the very neglected ones could be the turning point in understanding the context and regulation of the signaling events. For example, signaling pathways of Notch and Toll-like receptors (TLRs) have been so far unrelated in the vast body of knowledge about neurodevelopment, however evidence from available literature points to their remarkable overlap in influence on identical molecular processes and reveals their potential functional links. Based on data demonstrating Notch and TLR structural engagement and functions during neurodevelopment, along with our description of novel molecular binding models, here we hypothesize that TLR proteins act as likely crucial components in the Notch signaling cascade. We advocate for the hypothesized role of TLRs in Notch signaling by: elaborating components and features of their pathways; reviewing their effects on fates of neural progenitor cells during neurodevelopment; proposing molecular and functional aspects of the hypothesis, along with venues for testing it. Finally, we discuss substantial indications of environmental influence on the proposed Notch-TLR system and its impact on neurodevelopmental outcomes.

Transplacental infection by bovine alphaherpesvirus type 1 induces protein expression of COX-2, iNOS and inflammatory cytokines in fetal lungs and placentas

Bovine alphaherpesvirus type 1 (BoAHV-1) is associated with respiratory and reproductive syndromes. Until present the immunologic mechanisms involved in BoAHV-1 abortion are partially known. We studied key elements of the innate immune response in the placentas and fetal lungs from cattle experimentally-inoculated with BoAHV-1. These tissues were analyzed by histopathology. Furthermore, virus identification was performed by qPCR and the expression of the inflammatory cytokines such as tumor necrosis factor-alpha, interleukin 1-alpha and inflammatory mediators like inducible nitric oxide synthase and cyclooxeganse-2 was evaluated by immunohistochemistry. The viral transplacental infection was confirmed by the detection of BoAHV-1 by qPCR in the placenta and fetal organs, which revealed mild inflammatory lesions. Inducible nitric oxide synthase immunolabelling was high in the lungs of infected fetuses and placentas, as well as for tumor necrosis factor-alpha in the pulmonary parenchyma and cyclooxeganse-2 in fetal annexes. However, the expression of interleukin 1-alpha was weak in these organs. To our knowledge, this is the first study that provides strong evidence of an early immune response to BoAHV-1 infection in the conceptus. Advances in the knowledge of the complex immunological interactions at the feto-maternal unit during BoAHV-1 infection are needed to clarify the pathogenesis of abortion.

Free Radical and Viral Infection: A Review from the Perspective of Ferroptosis

Free radicals, including reactive oxygen species (ROS) and reactive nitrogen species (RNS), play critical roles in various physiological activities such as cell differentiation, apoptosis, and vascular tension when existing in cells at low levels. However, excessive amounts of free radicals are harmful, causing DNA damage, lipid peroxidation, protein degeneration, and abnormal cell death. Certain viral infections induce cells to produce excessive free radicals, which in multiple ways help the virus to replicate, mature, and exit. Iron is a necessary element for many intracellular enzymes, involved in both cellular activities and viral replication. Ferroptosis, a programmed cell death mode distinct from apoptosis, necrosis, and pyroptosis, is characterized by lipid peroxide accumulation and damage to the antioxidant system, affecting many cellular processes. Viral infection commonly manifests as decreased glutathione (GSH) content and down-regulated glutathione peroxidase 4 (GPX4) activity, similar to ferroptosis. Recent studies have suggested a possible relationship among free radicals, viral infections and ferroptosis. This review aims to elucidate the molecular mechanism linking free radicals and ferroptosis during viral infections and provide a new theoretical basis for studying viral pathogenesis and control.

Role of Microglia in Herpesvirus-Related Neuroinflammation and Neurodegeneration

Neuroinflammation is defined as an inflammatory state within the central nervous system (CNS). Microglia conprise the resident tissue macrophages of the neuronal tissue. Upon viral infection of the CNS, microglia become activated and start to produce inflammatory mediators important for clearance of the virus, but an excessive neuroinflammation can harm nearby neuronal cells. Herpesviruses express several molecular mechanisms, which can modulate apoptosis of infected neurons, astrocytes and microglia but also divert immune response initiated by the infected cells. In this review we also describe the link between virus-related neuroinflammation, and development of neurodegenerative diseases.

Differential expression profile and in-silico functional analysis of long noncoding RNA and mRNA in duck embryo fibroblasts infected with duck plague virus

Background

Duck plague virus (DPV), belonging to herpesviruses, is a linear double-stranded DNA virus. There are many reports about the outbreak of the duck plague in a variety of countries, which caused huge economic losses. Recently, increasing reports revealed that multiple long non-coding RNAs (lncRNAs) can possess great potential in the regulation of host antiviral immune response. Furthermore, it remains to be determined which specific molecular mechanisms are responsible for the DPV-host interaction in host immunity. Here, lncRNAs and mRNAs in DPV infected duck embryonic fibroblast (DEF) cells were identified by high-throughput RNA-sequencing (RNA-seq). And we predicted target genes of differentially expressed genes (DEGs) and formed a complex regulatory network depending on in-silico analysis and prediction.

Result

RNA-seq analysis results showed that 2921 lncRNAs were found at 30 h post-infection (hpi). In our study, 218 DE lncRNAs and 2840 DE mRNAs were obtained in DEF after DPV infection. Among these DEGs and target genes, some have been authenticated as immune-related molecules, such as a Macrophage mannose receptor (MR), Anas platyrhynchos toll-like receptor 2 (TLR2), leukocyte differentiation antigen, interleukin family, and their related regulatory factors. Furthermore, according to the Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) enrichment analysis, we found that the target genes may have important effects on biological development, biosynthesis, signal transduction, cell biological regulation, and cell process. Also, we obtained, the potential targeting relationship existing in DEF cells between host lncRNAs and DPV-encoded miRNAs by software.

Conclusions

This study revealed not only expression changes, but also the possible biological regulatory relationship of lncRNAs and mRNAs in DPV infected DEF cells. Together, these data and analyses provide additional insight into the role of lncRNAs and mRNAs in the host's immune response to DPV infection.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08739-7.

Children with sickle cell disease and severe COVID-19 presenting single nucleotide polymorphisms in innate immune response genes - A case report

Here we report three clinical cases of children with sickle cell disease (SCD) and severe COVID-19 who evolved with complications during hospitalization or after discharge. They present single nucleotide polymorphisms in tlr-7 and tirap genes, identified from 37 patients under 16 years old hospitalized from September 2020 to May 2021 in the Hospital João Paulo II, Belo Horizonte, Brazil. They presented significant complications of SCD as acute chest syndrome, splenic sequestration, and pain crisis during hospitalization or up to 2 months after SARS-CoV-2 infection. They all required transfusion of concentrated red blood cells and hospitalization in a reference hospital to care for children with SCD.

Microglia Reduce Herpes Simplex Virus 1 Lethality of Mice with Decreased T Cell and Interferon Responses in Brains

Herpes simplex virus 1 (HSV-1) infects the majority of the human population and can induce encephalitis, which is the most common cause of sporadic, fatal encephalitis. An increase of microglia is detected in the brains of encephalitis patients. The issues regarding whether and how microglia protect the host and neurons from HSV-1 infection remain elusive. Using a murine infection model, we showed that HSV-1 infection on corneas increased the number of microglia to outnumber those of infiltrating leukocytes (macrophages, neutrophils, and T cells) and enhanced microglia activation in brains. HSV-1 antigens were detected in brain neurons, which were surrounded by microglia. Microglia depletion increased HSV-1 lethality of mice with elevated brain levels of viral loads, infected neurons, neuron loss, CD4 T cells, CD8 T cells, neutrophils, interferon (IFN)-β, and IFN-γ. In vitro studies demonstrated that microglia from infected mice reduced virus infectivity. Moreover, microglia induced IFN-β and the signaling pathway of signal transducer and activator of transcription (STAT) 1 to inhibit viral replication and damage of neurons. Our study reveals how microglia protect the host and neurons from HSV-1 infection.

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.

Brain-derived neurotrophic factor is down regulated after bovine alpha-herpesvirus 5 infection in both wild-type and TLR3/7/9 deficient mice

Neurotrophic factors have been implicated in the control of neuronal survival and plasticity in different brain diseases. Meningoencephalitis caused by bovine alpha-herpesvirus 5 (BoHV-5) infection is a frequent neurological disease of young cattle, being the involvement of apoptosis in the development of neuropathological changes frequently discussed in the literature. It's well known that Toll-like receptors (TLRs) can activate neuroinflammatory response and consequently lead to neuronal loss. However, there are no studies evaluating the expression of neurotrophic factors and their association with brain pathology and TLRs during the infection by BoHV-5. The current study aimed to analyze brain levels of neurotrophic factors along with neuropathological changes during acute infection by BoHV-5 in wild-type (WT) and TLR3/7/9 (TLR3/7/9-/-) deficiency mice. The infection was induced by intracranial inoculation of 1 × 104 TCID50 of BoHV-5. Infected animals presented similar degrees of clinical signs and neuropathological changes. Both infected groups had meningoencephalitis and neuronal damage in CA regions from hippocampus. BoHV-5 infection promoted the proliferation of Iba-1 positive cells throughout the neuropil, mainly located in the frontal cortex. Moreover, significant lower levels of brain-derived neurotrophic factor (BDNF) were detected in both BoHV-5 infected WT and TLR3/7/9 deficient mice, compared with non-infected animals. Our study showed that BDNF down regulation was associated with brain inflammation, reactive microgliosis and neuronal loss after bovine alpha-herpesvirus 5 infection in mice. Moreover, we demonstrated that combined TLR3/7/9 deficiency does not alter those parameters.

Perforin and granzymes in neurological infections: From humans to cattle

Perforin and granzymes are essential components of the cytotoxic granules present in cytotoxic T lymphocytes and natural killer cells. These proteins play a crucial role in a variety of conditions, including viral infections, tumor immune surveillance, and tissue rejection. Besides their beneficial effect in most of these situations, perforin and granzymes have also been associated with tissue damage and immune diseases. Moreover, it has been reported that perforin and granzymes released during viral infections could contribute to the pathogenesis of diseases. In this review, we summarize the information available on human perforin and granzymes and their relationship with neurological infections and immune disorders. Furthermore, we compare this information with that available for bovine and present data on perforin and granzymes expression in cattle infected with bovine alphaherpesvirus types1 and -5. To our knowledge, this is the first review analyzing the impact of perforin and granzymes on neurological infections caused by bovine herpesviruses.

Transcriptomic Analysis of Interferon Response in Toll-Like Receptor 2 Ligand-Treated and Herpes Simplex Virus 1-Infected Neurons and Astrocytes

Herpes simplex virus (HSV)-1 infection causes cold sores and keratitis. Upon infection, it forms lesions at the epithelium and enters neurons where it establishes a latent infection. Host innate immune receptor Toll-like receptor (TLR)2 recognizes HSV by sensing its glycoproteins and induces an innate immune response. Upon activation, TLR2 forms a dimer with TLR1, TLR2, or TLR6 and signals inducing cytokines and interferons (IFNs). In this study, we checked the effect of differential activation of TLR2 by using different TLR2 dimer-specific ligands on the anti-HSV-1 innate immune response. We found that TLR2/2 ligand-induced IFN-β in neurons, while IFN-α in astrocytes and these IFNs subsequently induce the expression of IFN stimulatory genes like viperin, Ch25H, OAS2, latent RNase (RNase L), protein kinase R (PKR), and interferon-induced proteins with tetratricopeptide repeats (IFIT) 1. These are the genes with antiviral functions such as blocking viral attachment, protein synthesis, and egress.

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.

Anti-HSV-1 effect of dihydromyricetin from Ampelopsis grossedentata via the TLR9-dependent anti-inflammatory pathway

OBJECTIVES

Herpes simplex virus 1 (HSV-1) is one of the most prevalent viruses in humans worldwide. Owing to limited therapeutic options mainly with acyclovir (ACV) and analogues and the emergence of ACV-resistant strains, new drugs with different modes of action and low toxicity are required. The aim of this study was to determine the anti-HSV-1 effect and mechanism of action of the flavonoid compound dihydromyricetin (DHM) from Ampelopsis grossedentata.

METHODS

The HSV-1 inhibitory effect of DHM was evaluated by measuring plaque formation and generation of progeny virus as well as expression of HSV-1-related genes in Vero cells. The molecular mechanism of the antiviral activity of DHM against HSV-1 was explored by real-time quantitative PCR and ELISA.

RESULTS

DHM presented a significant inhibitory effect on HSV-1 plaque formation and generation of progeny virus, with an EC₅₀ (50% effective concentration) of 12.56 μM in Vero cells. Furthermore, expression of HSV-1 immediate-early genes (ICP4 and ICP22), early genes (ICP8 and UL42) and late genes (gB, VP1/2) was decreased by DHM at concentrations of 16 μM and 32 μM. DHM specifically suppressed mRNA levels of Toll-like receptor 9 (TLR9), leading to inhibition of the inflammatory transcriptional factor NFκB and a decrease in TNFα.

CONCLUSION

These findings indicate that the effective inhibitory activity of DHM was achieved by suppressing TNFα production in a TLR9-dependent manner. Although further studies are needed to better characterise the activity of DHM in vivo, the results suggest this extract as a promising new anti-HSV-1 agent.

Insights into the toll-like receptors in sexually transmitted infections

Toll-like receptors (TLRs) are like soldiers of an innate immune system, which protects vital biological processes against invading pathogens. TLR signalling pathways help in the removal of pathogens and mediate well-established inflammatory processes. However, these processes may also aid in the development or augmentation of an infection or an autoimmune disease. Recent studies have delineated TLR polymorphism's role in the loss of function, making hosts more resistant or vulnerable to the development of an infection. In this review, we have discussed the association of TLRs with sexually transmitted infections (STIs), especially to the pathogen-specific ligands. We have also assessed the impact on TLR downstream signalling and the maintenance of cellular homeostasis during immune responses. Besides, we have discussed the role of TLRs single nucleotide polymorphisms in various STIs. Since TLRs are known to play a part in defence mechanisms and in aiding infections therefore, a thorough understanding of TLRs structure and molecular mechanisms is required to explain how they can influence the outcome of an STI. Such a strategy may lead to the development of novel and useful immunotherapeutic approaches to control pathogen progression and prevent transmission.

Cervical cancer in low and middle-income countries

Cervical cancer is a malignant tumour that occurs in the cervix and is classified into two histological types, adenocarcinoma and squamous cell carcinoma (SCC); SCC is more common and accounts for 70% of all cases. In 2018 there were ~569,000 new cases of cervical cancer diagnosed worldwide and ~311,000 deaths were attributed to cervical cancer. Of these, between 84 and 90% occurred in low- and middle-income countries (LMICs) such as South Africa, India, China and Brazil. The most common cause of cervical cancer is persistent infection caused by the sexually transmitted human papilloma virus. Other factors that contribute to the incidence of cervical cancer include geography, traditional practices and beliefs, the screening levels, socioeconomic status, healthcare access, public awareness, use of oral contraceptives, smoking and co-infection with HIV. An estimated 11 million women from LMICs will be diagnosed with cervical cancer in the next 10-20 years. The aim of this review was to explore various types of genetic and epigenetic factors that influence the development, progression or suppression of cervical cancer.

Nitric oxide in cellular adaptation and disease

Nitric oxide synthases are the major sources of nitric oxide, a critical signaling molecule involved in a wide range of cellular and physiological processes. These enzymes comprise a family of genes that are highly conserved across all eukaryotes. The three family members found in mammals are important for inter- and intra-cellular signaling in tissues that include the nervous system, the vasculature, the gut, skeletal muscle, and the immune system, among others. We summarize major advances in the understanding of biochemical and tissue-specific roles of nitric oxide synthases, with a focus on how these mechanisms enable tissue adaptation and health or dysfunction and disease. We highlight the unique mechanisms and processes of neuronal nitric oxide synthase, or NOS1. This was the first of these enzymes discovered in mammals, and yet much remains to be understood about this highly conserved and complex gene. We provide examples of two areas that will likely be of increasing importance in nitric oxide biology. These include the mechanisms by which these critical enzymes promote adaptation or disease by 1) coordinating communication by diverse cell types within a tissue and 2) directing cellular differentiation/activation decisions processes.

Sendai virus V protein decreases nitric oxide production by inhibiting RIG-I signaling in infected RAW264.7 macrophages

Sendai virus V protein is a known antagonist of RIG-I-like receptors (RLRs) RIG-I and MDA5, which activate transcription factors IRF3, leading to activation of ISGF3 and NF-κB. These transcription factors are known activators of inducible NO synthase (iNOS) and increase the production of nitric oxide (NO). By inhibiting ISGF3 and NF-κB, the V protein acts as an indirect negative regulator of iNOS and NO. Here we report that the V gene knockout Sendai virus [SeV V(-)] markedly enhanced iNOS expression and subsequent NO production in infected macrophages compared to wild-type SeV. The knockout of RIG-I in cells inhibited SeV V(-)-induced iNOS expression and subsequent NO production. To understand the underlying mechanism of the V protein-mediated negative regulation of iNOS activation, we transfected HEK293T cells with RIG-I and the RIG-I regulatory protein TRIM25. Our results demonstrated that the V protein inhibited iNOS activation via the RIG-I/TRIM25 pathway. Moreover, the V protein inhibited TRIM25-mediated K63-linked ubiquitination of RIG-I, as well as its CARD-dependent interaction with mitochondrial antiviral signaling (MAVS) molecules. These results suggest that the V protein downregulates iNOS activation and inhibits NO production by preventing the RIG-I-MAVS interaction, possibly through its effect on the ubiquitination status of RIG-I.

Herpes Simplex Virus Type 1 Engages Toll Like Receptor 2 to Recruit Macrophages During Infection of Enteric Neurons

Herpes simplex virus type 1 (HSV-1) is a widespread neurotropic pathogen responsible for a range of clinical manifestations. Inflammatory cell infiltrate is a common feature of HSV-1 infections and has been implicated in neurodegeneration. Therefore, viral recognition by innate immune receptors (i.e., TLR2) and the subsequent inflammatory response are now deemed key players in HSV-1 pathogenesis. In this study we infected with HSV-1 the enteric nervous system (ENS) of wild-type (WT) and TLR2 knock-out (TLR2ko) mice to investigate whether and how TLR2 participates in HSV-1 induced neuromuscular dysfunction. Our findings demonstrated viral specific transcripts suggestive of abortive replication in the ENS of both WT and TLR2ko mice. Moreover, HSV-1 triggered TLR2-MyD88 depend signaling in myenteric neurons and induced structural and functional alterations of the ENS. Gastrointestinal dysmotility was, however, less pronounced in TLR2ko as compared with WT mice. Interesting, HSV-1 caused up-regulation of monocyte chemoattractant protein-1 (CCL2) and recruitment of CD11b+ macrophages in the myenteric ganglia of WT but not TLR2ko mice. At the opposite, the myenteric plexuses of TLR2ko mice were surrounded by a dense infiltration of HSV-1 reactive CD3+CD8+INFγ+ lymphocytes. Indeed, depletion CD3+CD8+ cells by means of administration of anti-CD8 monoclonal antibody reduced neuromuscular dysfunction in TLR2ko mice infected with HSV-1. During HSV-1 infection, the engagement of TLR2 mediates production of CCL2 in infected neurons and coordinates macrophage recruitment. Bearing in mind these observations, blockage of TLR2 signaling could provide novel therapeutic strategies to support protective and specific T-cell responses and to improve neuromuscular dysfunction in pathogen-mediated alterations of the ENS.

Insights into the pathogenesis of herpes simplex encephalitis from mouse models

A majority of the world population is infected with herpes simplex viruses (HSV; human herpesvirus types 1 and 2). These viruses, perhaps best known for their manifestation in the genital or oral mucosa, can also cause herpes simplex encephalitis, a severe and often fatal disease of the central nervous system. Antiviral therapies for HSV are only partially effective since the virus can establish latent infections in neurons, and severe pathological sequelae in the brain are common. A better understanding of disease pathogenesis is required to develop new strategies against herpes simplex encephalitis, including the precise viral and host genetic determinants that promote virus invasion into the central nervous system and its associated immunopathology. Here we review the current understanding of herpes simplex encephalitis from the host genome perspective, which has been illuminated by groundbreaking work on rare herpes simplex encephalitis patients together with mechanistic insight from single-gene mouse models of disease. A complex picture has emerged, whereby innate type I interferon-mediated antiviral signaling is a central pathway to control viral replication, and the regulation of immunopathology and the balance between apoptosis and autophagy are critical to disease severity in the central nervous system. The lessons learned from mouse studies inform us on fundamental defense mechanisms at the interface of host–pathogen interactions within the central nervous system, as well as possible rationales for intervention against infections from severe neuropathogenic viruses.

TLR2 signal influences the iNOS/NO responses and worm development in C57BL/6J mice infected with Clonorchis sinensis

BACKGROUND

Although the responses of inducible nitric oxide synthase (iNOS) and associated cytokine after Clonorchis sinensis infection have been studied recently, their mechanisms remain incompletely understood. In this study, we investigated the effects of toll-like receptor 2 (TLR2) signals on iNOS/nitric oxide (NO) responses after C. sinensis infection. We also evaluated the correlations between iNOS responses and worm development, which are possibly regulated by TLR2 signal.

METHODS

TLR2 wild-type and mutant C57BL/6 J mice were infected with 60 C. sinensis metacercariae, and the samples were collected at 30, 60, 90 and 120 days post-infection (dpi). The total serum NO levels were detected using Griess reagent after nitrate was reduced to nitrite. Hepatic tissue samples from the infected mice were sliced and stained with hematoxylin and eosin (HE) to observe worm development in the intrahepatic bile ducts. The iNOS mRNA transcripts in the splenocytes were examined by real time reverse transcriptase polymerase chain reaction (qRT-PCR), and iNOS expression was detected by immunohistochemistry.

RESULTS

Developing C. sinensis juvenile worms were more abundant in the intrahepatic bile ducts of TLR2 mutant mice than those of TLR2 wild-type mice. However, no eggs were found in the faeces of both mice samples. The serum levels of total NO significantly increased in TLR2 mutant mice infected with C. sinensis at 30 (t (5) = 2.595, P = 0.049), 60 (t (5) = 7.838, P = 0.001) and 90 dpi (t (5) = 3.032, P = 0.029). Meanwhile, no changes occurred in TLR2 wild-type mice compared with uninfected controls during the experiment. The iNOS expression in splenocytes showed unexpected higher background levels in TLR2 mutant mice than those in TLR2 wild-type mice. Furthermore, the iNOS mRNA transcripts in splenocytes were significantly increased in the TLR2 wild-type mice infected with C. sinensis at 30 (t (5) = 5.139, P = 0.004), 60 (t (5) = 6.138, P = 0.002) and 90 dpi (t (5) = 6.332, P = 0.001). However, the rising of iNOS transcripts dropped under the uninfected control level in the TLR2 mutant mice at 120 dpi (t (5) = -9.082, P < 0.0001). Both total NO and iNOS transcripts were significantly higher in the TLR2 mutant mice than those in the TLR2 wild-type mice at 30 (t (5) = 3.091/2.933, P = 0.027/0.033) and 60 dpi (t (5) = 2.667/6.331, P = 0.044/0.001), respectively. In addition, the remarkable increase of iNOS expressions was immunohistochemically detected in the splenic serial sections of TLR2 wild-type mice at 30 and 60 dpi. However, the expressions of iNOS were remarkably decreased in the splenocytes of both TLR2 wild-type and mutant mice at 120 dpi.

CONCLUSIONS

These results demonstrate that TLR2 signal plays an important role in the regulation of iNOS expression after C. sinensis infection. TLR2 signal is also beneficial to limiting worm growth and development and contributing to the susceptibility to C. sinensis in which the iNOS/NO reactions possibly participate.

Satellite glial cells in human trigeminal ganglia have a broad expression of functional Toll-like receptors

Toll-like receptors (TLRs) orchestrate immune responses to a wide variety of danger- and pathogen-associated molecular patterns. Compared to the central nervous system (CNS), expression profile and function of TLRs in the human peripheral nervous system (PNS) are ill-defined. We analyzed TLR expression of satellite glial cells (SGCs) and microglia, glial cells predominantly involved in local immune responses in ganglia of the human PNS and normal-appearing white matter (NAWM) of the CNS, respectively. Ex vivo flow cytometry analysis of cell suspensions obtained from human cadaveric trigeminal ganglia (TG) and NAWM showed that both SGCs and microglia expressed TLR1-5, TLR7, and TLR9, although expression levels varied between these cell types. Immunohistochemistry confirmed expression of TLR1-TLR4 and TLR9 by SGCs in situ. Stimulation of TG- and NAWM-derived cell suspensions with ligands of TLR1-TLR6, but not TLR7 and TLR9, induced interleukin 6 (IL-6) secretion. We identified CD45^LOW CD14^POS SGCs and microglia, but not CD45^HIGH leukocytes and CD45^NEG cells as the main source of IL-6 and TNF-α upon stimulation with TLR3 and TLR5 ligands. In conclusion, human TG-resident SGCs express a broad panel of functional TLRs, suggesting their role in initiating and orchestrating inflammation to pathogens in human sensory ganglia.

Dendritic cells, macrophages, NK and CD8+ T lymphocytes play pivotal roles in controlling HSV-1 in the trigeminal ganglia by producing IL1-beta, iNOS and granzyme B

Background

Herpes simplex virus type 1 (HSV-1) cause not only mild symptoms but also blindness and encephalitis. It was previously shown that the immune response against HSV-1 occurs mainly in the trigeminal ganglia (TG) and that Toll-like receptors 2 and 9 (TLR2/9) are important in mediating this response. It was also demonstrated that iNOS (nitric oxide synthase) and interleukin 1 beta (IL-1β) play an essential role in the defense against HSV-1 infection. Importantly, the present work aimed to identify the primary cells responsible for iNOS and IL-1β production and search for other important molecules and cells that might or might not depend on TLR2/9 receptors to mediate the immune response against HSV-1.

Methods

C57BL/6 (wild type, WT) and TLR2/9^−/− mice were infected by the intranasal route with HSV-1 (1 × 10⁶ p.f.u.). Cells were obtained from the TG and spleen tissues and the profile of immune cells was determined by flow cytometry in infected and mock infected WT and knockout mice. The percentage of cells producing iNOS, IL-1β, granzyme B and perforin was also determined by flow cytometry. Chemokine monocyte chemoattractant protein-1 (MCP1) was measured by Cytometric Bead Array (CBA) in the TG, spleen and lung. Expression of type I interferons (IFNs), interleukins (IL) 5 and 10, IL-1β and granzyme B were quantified by real time PCR.

Results

The results indicate that dendritic cells (DCs) and monocytes/macrophages (Mo/Mϕ) were the main sources of IL-1β and iNOS, respectively, which, together with type I IFNs, were essential for the immune response against HSV-1. Additionally, we showed that granzyme B produced by CD8⁺ T and NK lymphocytes and MCP-1 were also important for this immune response. Moreover, our data indicate that the robust production of MCP-1 and granzyme B is either TLR-independent or down regulated by TLRs and occurs in the TG of TLR2/9^−/− infected mice.

Conclusion

Taken together, our data provide strong evidence that the responses mediated by DCs, Mo/Mϕ, NK and CD8⁺ T lymphocytes through IL-1β, iNOS and granzyme B production, respectively, together with the production of type I IFN early in the infection, are crucial to host defense against HSV-1.

Electronic supplementary material

The online version of this article (doi:10.1186/s12985-017-0692-x) contains supplementary material, which is available to authorized users.

Innate recognition of alphaherpesvirus DNA

Alphaherpesviruses include human and animal pathogens, such as herpes simplex virus type 1, which establish life-long latent infections with episodes of recurrence. The immunocompetence of the infected host is an important determinant for the outcome of infections with alphaherpesviruses. Recognition of pathogen-associated molecular patterns by pattern recognition receptors is an essential, early step in the innate immune response to pathogens. In recent years, it has been discovered that herpesvirus DNA is a strong inducer of the innate immune system. The viral genome can be recognized in endosomes by TLR9, as well as intracellularly by a variety of DNA sensors, the best documented being cGAS, RNA Pol III, IFI16, and AIM2. These DNA sensors use converging signaling pathways to activate transcription factors, such as IRF3 and NF-κB, which induce the expression of type I interferons and other inflammatory cytokines and activate the inflammasome. This review summarizes the recent literature on the innate sensing of alphaherpesvirus DNA, the mechanisms of activation of the different sensors, their mechanisms of signal transduction, their physiological role in defense against herpesvirus infection, and how alphaherpesviruses seek to evade these responses to allow establishment and maintenance of infection.

The role of myeloid cell activation and arginine metabolism in the pathogenesis of virus-induced diseases

When an antiviral immune response is generated, a balance must be reached between two opposing pathways: the production of proinflammatory and cytotoxic effectors that drive a robust antiviral immune response to control the infection and regulators that function to limit or blunt an excessive immune response to minimize immune-mediated pathology and repair tissue damage. Myeloid cells, including monocytes and macrophages, play an important role in this balance, particularly through the activities of the arginine-hydrolyzing enzymes nitric oxide synthase 2 (Nos2; iNOS) and arginase 1 (Arg1). Nitric oxide (NO) production by iNOS is an important proinflammatory mediator, whereas Arg1-expressing macrophages contribute to the resolution of inflammation and wound repair. In the context of viral infections, expression of these enzymes can result in a variety of outcomes for the host. NO has direct antiviral properties against some viruses, whereas during other virus infections NO can mediate immunopathology and/or inhibit the antiviral immune response to promote chronic infection. Arg1 activity not only has important wound healing functions but can also inhibit the antiviral immune response during some viral infections. Thus, depending on the specific virus and the tissue(s) involved, the activity of both of these arginine-hydrolyzing enzymes can either exacerbate or limit the severity of virus-induced disease. In this review, we will discuss a variety of viral infections, including HIV, SARS-CoV, LCMV, HCV, RSV, and others, where myeloid cells influence the control and clearance of the virus from the host, as well as the severity and resolution of tissue damage, via the activities of iNOS and/or Arg1. Clearly, monocyte/macrophage activation and arginine metabolism will continue to be important areas of investigation in the context of viral infections.

Prophylactic and therapeutic modulation of innate and adaptive immunity against mucosal infection of herpes simplex virus

Herpes simplex virus types 1 and 2 (HSV-1 and HSV-2) are the most common cause of genital ulceration in humans worldwide. Typically, HSV-1 and 2 infections via mucosal route result in a lifelong latent infection after peripheral replication in mucosal tissues, thereby providing potential transmission to neighbor hosts in response to reactivation. To break the transmission cycle, immunoprophylactics and therapeutic strategies must be focused on prevention of infection or reduction of infectivity at mucosal sites. Currently, our understanding of the immune responses against mucosal infection of HSV remains intricate and involves a balance between innate signaling pathways and the adaptive immune responses. Numerous studies have demonstrated that HSV mucosal infection induces type I interferons (IFN) via recognition of Toll-like receptors (TLRs) and activates multiple immune cell populations, including NK cells, conventional dendritic cells (DCs), and plasmacytoid DCs. This innate immune response is required not only for the early control of viral replication at mucosal sites, but also for establishing adaptive immune responses against HSV antigens. Although the contribution of humoral immune response is controversial, CD4(+) Th1 T cells producing IFN-γ are believed to play an important role in eradicating virus from the hosts. In addition, the recent experimental successes of immunoprophylactic and therapeutic compounds that enhance resistance and/or reduce viral burden at mucosal sites have accumulated. This review focuses on attempts to modulate innate and adaptive immunity against HSV mucosal infection for the development of prophylactic and therapeutic strategies. Notably, cells involved in innate immune regulations appear to shape adaptive immune responses. Thus, we summarized the current evidence of various immune mediators in response to mucosal HSV infection, focusing on the importance of innate immune responses.