Endosomal Toll-Like Receptors 7 and 9 Cooperate in Detection of Murine Gammaherpesvirus 68 Infection

Murine gammaherpesvirus 68 (MHV68) is a small-animal model suitable for study of the human pathogens Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus. Here, we have characterized the roles of the endosomal Toll-like receptor (TLR) escort protein UNC93B, endosomal TLR7, -9, and -13, and cell surface TLR2 in MHV68 detection. We found that the alpha interferon (IFN-α) response of plasmacytoid dendritic cells (pDC) to MHV68 was reduced in Tlr9 ^-/- cells compared to levels in wild type (WT) cells but not completely lost. Tlr7 ^-/- pDC responded similarly to WT. However, we found that in Unc93b ^-/- pDC, as well as in Tlr7 ^-/- Tlr9 ^-/- double-knockout pDC, the IFN-α response to MHV68 was completely abolished. Thus, the only pattern recognition receptors contributing to the IFN-α response to MHV68 in pDC are TLR7 and TLR9, but the contribution of TLR7 is masked by the presence of TLR9. To address the role of UNC93B and TLR for MHV68 infection in vivo, we infected mice with MHV68. Lytic replication of MHV68 after intravenous infection was enhanced in the lungs, spleen, and liver of UNC93B-deficient mice, in the spleen of TLR9-deficient mice, and in the liver and spleen of Tlr7 ^-/- Tlr9 ^-/- mice. The absence of TLR2 or TLR13 did not affect lytic viral titers. We then compared reactivation of MHV68 from latently infected WT, Unc93b ^-/-, Tlr7 ^-/- Tlr9 ^-/-, Tlr7 ^-/-, and Tlr9 ^-/- splenocytes. We observed enhanced reactivation and latent viral loads, particularly from Tlr7 ^-/- Tlr9 ^-/- splenocytes compared to levels in the WT. Our data show that UNC93B-dependent TLR7 and TLR9 cooperate in and contribute to detection and control of MHV68 infection.IMPORTANCE The two human gammaherpesviruses, Epstein-Barr virus (EBV) and Kaposi's sarcoma-associated herpesvirus (KSHV), can cause aggressive forms of cancer. These herpesviruses are strictly host specific, and therefore the homolog murine gammaherpesvirus 68 (MHV68) is a widely used model to obtain in vivo insights into the interaction between these two gammaherpesviruses and their host. Like EBV and KSHV, MHV68 establishes lifelong latency in B cells. The innate immune system serves as one of the first lines of host defense, with pattern recognition receptors such as the Toll-like receptors playing a crucial role in mounting a potent antiviral immune response to various pathogens. Here, we shed light on a yet unanticipated role of Toll-like receptor 7 in the recognition of MHV68 in a subset of immune cells called plasmacytoid dendritic cells, as well as on the control of this virus in its host.

A Plant Immune Receptor Degraded by Selective Autophagy

Plants recycle non-activated immune receptors to maintain a functional immune system. The Arabidopsis immune receptor kinase FLAGELLIN-SENSING 2 (FLS2) recognizes bacterial flagellin. However, the molecular mechanisms by which non-activated FLS2 and other non-activated plant PRRs are recycled remain not well understood. Here, we provide evidence showing that Arabidopsis orosomucoid (ORM) proteins, which have been known to be negative regulators of sphingolipid biosynthesis, act as selective autophagy receptors to mediate the degradation of FLS2. Arabidopsis plants overexpressing ORM1 or ORM2 have undetectable or greatly diminished FLS2 accumulation, nearly lack FLS2 signaling, and are more susceptible to the bacterial pathogen Pseudomonas syringae. On the other hand, ORM1/2 RNAi plants and orm1 or orm2 mutants generated by the CRISPR/Cas9-mediated gene editing have increased FLS2 accumulation and enhanced FLS2 signaling, and are more resistant to P. syringae. ORM proteins interact with FLS2 and the autophagy-related protein ATG8. Interestingly, overexpression of ORM1 or ORM2 in autophagy-defective mutants showed FLS2 abundance that is comparable to that in wild-type plants. Moreover, FLS2 levels were not decreased in Arabidopsis plants overexpressing ORM1/2 derivatives that do not interact with ATG8. Taken together, these results suggest that selective autophagy functions in maintaining the homeostasis of a plant immune receptor and that beyond sphingolipid metabolic regulation ORM proteins can also act as selective autophagy receptors.

Dendritic cell subpopulations in nasopharyngeal cancer

Nasopharyngeal cancer (NPC) is associated with Epstein-Barr virus (EBV) and EBV antigen may be utilized for therapeutic purposes, including targeting of dendritic cells (DCs). Although DCs may be present in NPC, the information is limited and not up-to-date with current knowledge on DC subsets. In the present study, biopsies from untreated NPC were obtained and subjected to multicolor flow-cytometry focusing on DC subtype markers: CD123 for plasmacytoid DCs (pDCs); and CD1c and CD141 for myeloid DCs (mDCs). Furthermore, subset-specific expression of the C-lectin receptor (CLR) CD207 (also termed langerin) was assessed. pDCs and mDCs were detected in the NPC lesions, contributing to a frequency mean average of 0.78% of CD45⁺ leukocytes in situ. Different subpopulations, previously not described in NPC, were observed, including: CD123⁺ pDCs; CD1c⁺ mDCs; CD141⁺ mDCs; and CD1c^-CD141^- mDCs. A high frequency of CD1c⁺ mDCs expressing CD207 was observed, compared with other subsets. In conclusion, different DC subsets are present in NPC lesions. The CLR CD207, a selective endocytic marker on CD1c⁺ mDCs, may be targeted for therapeutic purposes to facilitate cross-presentation of antigens and aid cell-mediated antitumor effects.

Visualization of Double-Stranded RNA Colocalizing With Pattern Recognition Receptors in Arenavirus Infected Cells

An important step in the initiation of the innate immune response to virus infection is the recognition of non-self, viral RNA, including double-stranded RNA (dsRNA), by cytoplasmic pattern recognition receptors (PRRs). For many positive-sense RNA viruses and DNA viruses, the production of viral dsRNA, and the interaction of viral dsRNA and PRRs are well characterized. However, for negative-sense RNA viruses, viral dsRNA was thought to be produced at low to undetectable levels and PRR recognition of viral dsRNA is still largely unclear. In the case of arenaviruses, the nucleocaspid protein (NP) has been identified to contain an exoribonuclease activity that preferentially degrades dsRNA in biochemical studies. Nevertheless, pathogenic New World (NW) arenavirus infections readily induce an interferon (IFN) response in a RIG-I dependent manner, and also activate the dsRNA-dependent Protein Kinase R (PKR). To better understand the innate immune response to pathogenic arenavirus infection, we used a newly identified dsRNA-specific antibody that efficiently detects viral dsRNA in negative-sense RNA virus infected cells. dsRNA was detected in NW arenavirus infected cells colocalizing with virus NP in immunofluorescence assay. Importantly, the dsRNA signals also colocalized with cytoplasmic PRRs, namely, PKR, RIG-I and MDA-5, as well as with the phosphorylated, activated form of PKR in infected cells. Our data clearly demonstrate the PRR recognition of dsRNA and their activation in NW arenavirus infected cells. These findings provide new insights into the interaction between NW arenaviruses and the host innate immune response.

Disease Resistance Mechanisms in Plants

Plants have developed a complex defense system against diverse pests and pathogens. Once pathogens overcome mechanical barriers to infection, plant receptors initiate signaling pathways driving the expression of defense response genes. Plant immune systems rely on their ability to recognize enemy molecules, carry out signal transduction, and respond defensively through pathways involving many genes and their products. Pathogens actively attempt to evade and interfere with response pathways, selecting for a decentralized, multicomponent immune system. Recent advances in molecular techniques have greatly expanded our understanding of plant immunity, largely driven by potential application to agricultural systems. Here, we review the major plant immune system components, state of the art knowledge, and future direction of research on plant⁻pathogen interactions. In our review, we will discuss how the decentralization of plant immune systems have provided both increased evolutionary opportunity for pathogen resistance, as well as additional mechanisms for pathogen inhibition of such defense responses. We conclude that the rapid advances in bioinformatics and molecular biology are driving an explosion of information that will advance agricultural production and illustrate how complex molecular interactions evolve.

The Interaction of Human Pathogenic Fungi With C-Type Lectin Receptors

Fungi, usually present as commensals, are a major cause of opportunistic infections in immunocompromised patients. Such infections, if not diagnosed or treated properly, can prove fatal. However, in most cases healthy individuals are able to avert the fungal attacks by mounting proper antifungal immune responses. Among the pattern recognition receptors (PRRs), C-type lectin receptors (CLRs) are the major players in antifungal immunity. CLRs can recognize carbohydrate ligands, such as β-glucans and mannans, which are mainly found on fungal cell surfaces. They induce proinflammatory immune reactions, including phagocytosis, oxidative burst, cytokine, and chemokine production from innate effector cells, as well as activation of adaptive immunity via Th17 responses. CLRs such as Dectin-1, Dectin-2, Mincle, mannose receptor (MR), and DC-SIGN can recognize many disease-causing fungi and also collaborate with each other as well as other PRRs in mounting a fungi-specific immune response. Mutations in these receptors affect the host response and have been linked to a higher risk in contracting fungal infections. This review focuses on how CLRs on various immune cells orchestrate the antifungal response and on the contribution of single nucleotide polymorphisms in these receptors toward the risk of developing such infections.

Polyglutamine binding protein 1 (PQBP1) inhibits innate immune responses to cytosolic DNA

Recent studies have highlighted the importance of immune sensing of cytosolic DNA of both pathogen and host origin. We aimed to examine the role of DNA sensors interferon-γ-inducible protein 16 (IFI16) and cyclic GMP-AMP synthase (cGAS) in responding to cytosolic DNA. We show IFI16 and cGAS can synergistically induce IFNb transcriptional activity in response to cytoplasmic DNA. We also examined the role of polyglutamine binding protein 1 (PQBP1), a protein predominantly expressed in lymphoid and myeloid cells that has been shown to lead to type I interferon production in response to retroviral infection. We show PQBP1 associates with cGAS and IFI16 in THP-1 cells. Unexpectedly, knockout of PQBP1 in THP-1 cells causes significantly increased type I IFN production in response to transfected cytosolic nucleic acids or DNA damage, unlike what is seen in response to retroviral infection. Overexpression of PQBP1 in HEK293 T cells impairs IFI16/cGAS-induced IFNb transcriptional activity. In human cancer patients, low expression of PQBP1 is correlated with improved survival, the opposite correlation of that seen with cGAS or IFI16 expression. Our findings suggest that PQBP1 inhibits IFI16/cGAS-induced signaling in response to cytosolic DNA, in contrast to the role of this protein in response to retroviral infection.

Pathogen-Derived Carbohydrate Recognition in Molluscs Immune Defense

Self-nonself discrimination is a common theme for all of the organisms in different evolutionary branches, which is also the most fundamental step for host immune protection. Plenty of pattern recognition receptors (PRRs) with great diversity have been identified from different organisms to recognize various pathogen-associated molecular patterns (PAMPs) in the last two decades, depicting a complicated scene of host-pathogen interaction. However, the detailed mechanism of the complicate PAMPs–PRRs interactions at the contacting interface between pathogens and hosts is still not well understood. All of the cells are coated by glycosylation complex and thick carbohydrates layer. The different polysaccharides in extracellular matrix of pathogen-host are important for nonself recognition of most organisms. Coincidentally, massive expansion of PRRs, majority of which contain recognition domains of Ig, leucine-rich repeat (LRR), C-type lectin (CTL), C1q and scavenger receptor (SR), have been annotated and identified in invertebrates by screening the available genomic sequence. The phylum Mollusca is one of the largest groups in the animal kingdom with abundant biodiversity providing plenty of solutions about pathogen recognition and immune protection, which might offer a suitable model to figure out the common rules of immune recognition mechanism. The present review summarizes the diverse PRRs and common elements of various PAMPs, especially focusing on the structural and functional characteristics of canonical carbohydrate recognition proteins and some novel proteins functioning in molluscan immune defense system, with the objective to provide new ideas about the immune recognition mechanisms.

Probiotic Bacteria Alter Pattern-Recognition Receptor Expression and Cytokine Profile in a Human Macrophage Model Challenged with Candida albicans and Lipopolysaccharide

Probiotics are live microorganisms that confer benefits to the host health. The infection rate of potentially pathogenic organisms such as Candida albicans, the most common agent associated with mucosal candidiasis, can be reduced by probiotics. However, the mechanisms by which the probiotics interfere with the immune system are largely unknown. We evaluated the effect of probiotic bacteria on C. albicans challenged human macrophages. Macrophages were pretreated with lactobacilli alone (Lactobacillus rhamnosus LR32, Lactobacillus casei L324m, or Lactobacillus acidophilus NCFM) or associated with Escherichia coli lipopolysaccharide (LPS), followed by the challenge with C. albicans or LPS in a co-culture assay. The expression of pattern-recognition receptors genes (CLE7A, TLR2, and TLR4) was determined by RT-qPCR, and dectin-1 reduced levels were confirmed by flow cytometry. The cytokine profile was determined by ELISA using the macrophage cell supernatant. Overall probiotic lactobacilli down-regulated the transcription of CLEC7A (p < 0.05), resulting in the decreased expression of dectin-1 on probiotic pretreated macrophages. The tested Lactobacillus species down-regulated TLR4, and increased TLR2 mRNA levels in macrophages challenged with C. albicans. The cytokines profile of macrophages challenged with C. albicans or LPS were altered by the probiotics, which generally led to increased levels of IL-10 and IL-1β, and reduction of IL-12 production by macrophages (p < 0.05). Our data suggest that probiotic lactobacilli impair the recognition of PAMPs by macrophages, and alter the production of pro/anti-inflammatory cytokines, thus modulating inflammation.

DM9 Domain Containing Protein Functions As a Pattern Recognition Receptor with Broad Microbial Recognition Spectrum

DM9 domain was first identified in Drosophila melanogaster, and it was subsequently found to integrate with or without other protein domains across a wide range of invertebrates and vertebrates. In the present study, a member of DM9 domain containing protein (DM9CP) family from marine invertebrate Crassostrea gigas (designated CgDM9CP-1), which was only composed of two DM9 domains, was taken as a protein model to study the biological functions of DM9 domain and its molecular determinants. CgDM9CP-1 was found to exhibit high binding specificity and avidity toward d-mannose residue. It served as a pattern recognition receptor (PRR) with a broad range of recognition spectrum to various pathogen-associated molecular patterns, including lipopolysaccharide, peptidylglycan, mannan, and β-1, 3-glucan in a d-mannose-dependent manner, as well as bacteria and fungi. In order to reveal the molecular mechanism underlying its pattern recognition activity, the crystal structures of wild-type and loss-of-function mutants were solved, and Asp22 and Lys43 were found to be the critical residues for ligand recognition. Moreover, CgDM9CP-1 protein was found to mainly distribute on the surface of C. gigas hemocytes, and it could be translocated into cytoplasm and colocalized with the engulfed microbes during hemocyte phagocytosis. The present result clearly indicated that CgDM9CP-1 was a PRR, and it provided an important clue for the better understanding of DM9CP function.

Hop/Sti1 - A Two-Faced Cochaperone Involved in Pattern Recognition Receptor Maturation and Viral Infection

Perception of pathogens by host pattern recognition receptors (PRRs) or R proteins is a prerequisite to promote successful immune responses. The Hsp70/Hsp90 organizing protein Hop/Sti1, a multifunctional cochaperone, has been implicated in the maturation of a receptor-like kinase (RLK) necessary for chitin sensing. However, it remains unknown whether Hop/Sti1 is generally participating in PRR genesis. Using RNA-interference (RNAi), we silenced Hop/Sti1 expression in Nicotiana tabacum to gain further insight into the role of the cochaperone in plant defense responses. As expected, transgenic plants do not respond to chitin treatment anymore. In contrast to this, trafficking and functionality of the flagellin PRR FLS2 were unaltered, suggesting a selective involvement of Hop/Sti1 during PRR maturation. Furthermore, Hop/Sti1 was identified as a cellular determinant of Potato virus Y (PVY) symptom development in tobacco, since PVY was able to accumulate to near wild-type level without provoking the usual veinal necrosis phenotype. In addition, typical antiviral host defense responses were suppressed in the transgenic plants. These data suggest that perception of PVY is dependent on Hop/Sti1-mediated receptor maturation, while viral symptoms represent a failing attempt to restrict PVY spread. In addition, Hop/Sti1 colocalized with virus-induced membrane aggregates in wild-type plants. The retention of Hop/Sti1 in potential viral replication complexes suggests a role during viral translation/replication, explaining why RNAi-lines do not exhibit increased susceptibility to PVY. This study provides evidence for a dual role of Hop/Sti1 in PRR maturation and pathogen perception as well as in promoting viral proliferation.

Mycobacterium tuberculosis inhibits human innate immune responses via the production of TLR2 antagonist glycolipids

Mycobacterium tuberculosis is a major human pathogen that is able to survive inside host cells and resist immune clearance. Most particularly, it inhibits several arms of the innate immune response, including phagosome maturation or cytokine production. To better understand the molecular mechanisms by which M. tuberculosis circumvents host immune defenses, we used a transposon mutant library generated in a virulent clinical isolate of M. tuberculosis of the W/Beijing family to infect human macrophages, utilizing a cell line derivative of THP-1 cells expressing a reporter system for activation of the transcription factor NF-κB, a key regulator of innate immunity. We identified several M. tuberculosis mutants inducing a NF-κB activation stronger than that of the wild-type strain. One of these mutants was found to be deficient for the synthesis of cell envelope glycolipids, namely sulfoglycolipids, suggesting that the latter can interfere with innate immune responses. Using natural and synthetic molecular variants, we determined that sulfoglycolipids inhibit NF-κB activation and subsequent cytokine production or costimulatory molecule expression by acting as competitive antagonists of Toll-like receptor 2, thereby inhibiting the recognition of M. tuberculosis by this receptor. Our study reveals that producing glycolipid antagonists of pattern recognition receptors is a strategy used by M. tuberculosis to undermine innate immune defense. Sulfoglycolipids are major and specific lipids of M. tuberculosis, considered for decades as virulence factors of the bacilli. Our study uncovers a mechanism by which they may contribute to M. tuberculosis virulence.

Enhanced Bacterial Wilt Resistance in Potato Through Expression of Arabidopsis EFR and Introgression of Quantitative Resistance from Solanum commersonii

Bacterial wilt (BW) caused by Ralstonia solanacearum is responsible for substantial losses in cultivated potato (Solanum tuberosum) crops worldwide. Resistance genes have been identified in wild species; however, introduction of these through classical breeding has achieved only partial resistance, which has been linked to poor agronomic performance. The Arabidopsis thaliana (At) pattern recognition receptor elongation factor-Tu (EF-Tu) receptor (EFR) recognizes the bacterial pathogen-associated molecular pattern EF-Tu (and its derived peptide elf18) to confer anti-bacterial immunity. Previous work has shown that transfer of AtEFR into tomato confers increased resistance to R. solanacearum. Here, we evaluated whether the transgenic expression of AtEFR would similarly increase BW resistance in a commercial potato line (INIA Iporá), as well as in a breeding potato line (09509.6) in which quantitative resistance has been introgressed from the wild potato relative Solanum commersonii. Resistance to R. solanacearum was evaluated by damaged root inoculation under controlled conditions. Both INIA Iporá and 09509.6 potato lines expressing AtEFR showed greater resistance to R. solanacearum, with no detectable bacteria in tubers evaluated by multiplex-PCR and plate counting. Notably, AtEFR expression and the introgression of quantitative resistance from S. commersonii had a significant additive effect in 09509.6-AtEFR lines. These results show that the combination of heterologous expression of AtEFR with quantitative resistance introgressed from wild relatives is a promising strategy to develop BW resistance in potato.

Sensing of Bacterial Cyclic Dinucleotides by the Oxidoreductase RECON Promotes NF-κB Activation and Shapes a Proinflammatory Antibacterial State

Bacterial and host cyclic dinucleotides (cdNs) mediate cytosolic immune responses through the STING signaling pathway, although evidence suggests that alternative pathways exist. We used cdN-conjugated beads to biochemically isolate host receptors for bacterial cdNs, and we identified the oxidoreductase RECON. High-affinity cdN binding inhibited RECON enzyme activity by simultaneously blocking the substrate and cosubstrate sites, as revealed by structural analyses. During bacterial infection of macrophages, RECON antagonized STING activation by acting as a molecular sink for cdNs. Bacterial infection of hepatocytes, which do not express STING, revealed that RECON negatively regulates NF-κB activation. Loss of RECON activity, via genetic ablation or inhibition by cdNs, increased NF-κB activation and reduced bacterial survival, suggesting that cdN inhibition of RECON promotes a proinflammatory, antibacterial state that is distinct from the antiviral state associated with STING activation. Thus, RECON functions as a cytosolic sensor for bacterial cdNs, shaping inflammatory gene activation via its effects on STING and NF-κB.

Chitin receptor-mediated activation of MAP kinases and ROS production in rice and Arabidopsis

Rapid induction of plant immune responses is essential to inhibit colonization and invasion by pathogens. Plants can recognize pathogen-associated molecular patterns (PAMPs) including fungal chitin and bacterial flagellin using pattern-recognition receptors (PRRs), which trigger the intracellular activation of mitogen-activated protein kinase (MAPK) cascades and the production of reactive oxygen species (ROS). MAPK activation and ROS production play pivotal roles in the induction of robust immune responses. Recent investigation of chitin- and flagellin-induced immune signaling revealed that receptor-like cytoplasmic kinases (RLCKs) connect PRR-mediated pathogen recognition to MAPK activation and ROS production. In addition, although the MAPK cascade is mediated by 3 sequentially activated protein kinases, MAPK kinase kinase (MAPKKK), MAPK kinase (MAPKK), and MAPK, how MAPKKKs are activated downstream of PRRs in plants has not been identified until recently. In this review, we summarize recent findings of RLCK-mediated MAPK activation and ROS production in rice and Arabidopsis.

TLR2 activation induces antioxidant defence in human monocyte-macrophage cell line models

When monocytes are recruited to inflammation/infection sites, extravasate and differentiate into macrophages, they encounter increasing levels of oxidative stress, both from exogenous and endogenous sources. In this study, we aimed to determine whether there are specific biochemical mechanisms responsible for an increase in oxidative stress resistance in differentiating macrophages. We performed experiments on in vitro cell line models of the monocyte-macrophage differentiation axis (less differentiated THP-1 cells and more differentiated Mono Mac 6 cells). At the same time, we verified the hypothesis that activating monocyte/macrophage innate immune response by pathogens (exemplified by stimulating the TLR2 pattern recognition receptor) would further strengthen cellular antioxidant defences. We found that resistance to exogenous oxidative stress increased substantially both during differentiation and upon activation of TLR2. This increase in antioxidant resistance was accompanied by decrease in free radical damage to cellular proteins. On the molecular level, this resistance was mediated especially by increased levels and activity of glutathione, glutathione-related antioxidant enzymes and Mn superoxide dismutase, as shown by gene expression assays, Western blotting and enzyme activity assays. Moreover, upon TLR2 activation additional molecular mechanisms came into play, conferring additional resistance levels even upon differentiated macrophage-like cells, mainly related to thioredoxin-linked antioxidant enzymes.

Differential Induction of Immunogenic Cell Death and Interferon Expression in Cancer Cells by Structured ssRNAs

Activation of the RNA-sensing pattern recognition receptor (PRR) in cancer cells leads to cell death and cytokine expression. This cancer cell death releases tumor antigens and damage-associated molecular patterns (DAMPs) that induce anti-tumor immunity. However, these cytokines and DAMPs also cause adverse inflammatory and thrombotic complications that can limit the overall therapeutic benefits of PRR-targeting anti-cancer therapies. To overcome this problem, we generated and evaluated two novel and distinct ssRNA molecules (immunogenic cell-killing RNA [ICR]2 and ICR4). ICR2 and ICR4 differentially stimulated cell death and PRR signaling pathways and induced different patterns of cytokine expression in cancer and innate immune cells. Interestingly, DAMPs released from ICR2- and ICR4-treated cancer cells had distinct patterns of stimulation of innate immune receptors and coagulation. Finally, ICR2 and ICR4 inhibited in vivo tumor growth as effectively as poly(I:C). ICR2 and ICR4 are potential therapeutic agents that differentially induce cell death, immune stimulation, and coagulation when introduced into tumors.

Highly Expression of CD11b and CD32 on Peripheral Blood Mononuclear Cells from Patients with Adult-Onset Still's Disease

BACKGROUND

We investigated the potential role of several pattern-recognition receptors (PRRs; CD11b, CD11c, CD32, CD206, CD209, and dectin-1) in adult-onset Still's disease (AOSD).

METHODS

The study included 13 untreated AOSD patients, 19 rheumatoid arthritis (RA) patients (as a disease control), and 19 healthy controls (HCs). The PRRs were quantified in peripheral blood using flow cytometry. The serum levels of interleukin-17 (IL-17), IL-18, and IL-23 were measured by enzyme-linked immunosorbent assay.

RESULTS

Significantly higher mean frequencies of cells presenting CD11b and CD32 from whole blood were observed in patients with AOSD than in patients with RA or HC. The levels of IL-17, IL-18, and IL-23 were elevated in AOSD patients compared to HCs. CD11b frequencies from whole cells correlated with systemic scores, lactate dehydrogenase (LDH) levels, aspartate transaminase levels, interleukin-23 (IL-23) levels, and IL-18. Frequencies of CD209 from granulocytes were significantly correlated with systemic scores, and the erythrocyte sedimentation rate and levels of C-reactive protein, ferritin, LDH, IL-23, and interleukin-18 (IL-18).

CONCLUSIONS

Elevated frequencies of circulating CD11b-positive cells and positive correlations with disease activity markers suggest that circulating CD11b-positive cells contribute to the pathogenesis of AOSD.

Localization of Toll-like Receptor (TLR) 2 and TLR4 mRNA in the Colorectal Mucosa of Miniature Dachshunds with Inflammatory Colorectal Polyps

Inflammatory colorectal polyps (ICRPs) are characterized by the formation of multiple or solitary polyps with marked neutrophil infiltration in the colorectal area, and are speculated to be a novel form of breed-specific canine idiopathic inflammatory bowel disease (IBD). In human IBD, toll-like receptor (TLR) 2 and TLR4 have been reported to be involved in the pathogenesis of the disease. The aim of this study was to evaluate the expression of TLR2 and TLR4 mRNA in the colorectal mucosa of dogs with ICRPs by in-situ hybridization using an RNAscope assay. Samples of inflamed colorectal mucosa (n = 5) and non-inflamed mucosa (n = 5) from miniature dachshunds (MDs) with ICRPs and colonic mucosa from healthy beagles (n = 5) were examined. TLR2 and TLR4 hybridization signals were localized to the colorectal epithelium, inflammatory cells and fibroblasts in the inflamed colorectal mucosa of affected dogs. The signals were significantly greater in inflamed colorectal epithelium compared with non-inflamed epithelium of MDs with ICRPs and healthy beagles (P <0.05). These results suggest that increased expression of TLR2 and TLR4 mRNA in the inflamed colorectal mucosa results from not only inflammatory cell infiltration, but also the upregulation of TLR2 and TLR4 mRNA in the colonic epithelium.

Parasitic Cuscuta factor(s) and the detection by tomato initiates plant defense

Dodders (Cuscuta spp.) are holoparasitic plants that enwind stems of host plants and penetrate those by haustoria to connect to the vascular bundles. Having a broad host plant spectrum, Cuscuta spp infect nearly all dicot plants - only cultivated tomato as one exception is mounting an active defense specifically against C. reflexa. In a recent work we identified a pattern recognition receptor of tomato, "Cuscuta Receptor 1" (CuRe1), which is critical to detect a "Cuscuta factor" (CuF) and initiate defense responses such as the production of ethylene or the generation of reactive oxygen species. CuRe1 also contributes to the tomato resistance against C. reflexa. Here we point to the fact that CuRe1 is not the only relevant component for full tomato resistance but it requires additional defense mechanisms, or receptors, respectively, to totally fend off the parasite.

Formyl peptide receptor modulators: a patent review and potential applications for inflammatory diseases (2012-2015)

INTRODUCTION

The activation of leukocytes and the subsequent immune cascade play an essential role in sterile and infectious inflammation. Dysregulation of these immune responses or excess leukocyte activation can induce tissue damage, organ dysfunction and mortality. Formyl peptide receptors (FPRs) are functionally diverse pattern recognition receptors responsible for recognizing different endogenous damage-associated molecular patterns or exogenous pathogen-associated molecular patterns. FPRs mediate leukocyte activation during inflammation. FPR1 antagonists and FPR2 agonists have demonstrated significant anti-inflammatory effects based on in vitro and in vivo studies. An increasing number of synthesized compounds targeting FPRs, especially potential FPR1 antagonists and FPR2 agonists, have been disclosed in patents. Areas covered: This article summarizes the current pharmacology patents related to FPR family modulators and their therapeutic indications based on a review of patent applications disclosed between 2012 and 2015. Expert opinion: In this review, FPR1 modulators comprise β-1,3-glucan synthase inhibitors containing an FPR ligand moiety, template-fixed peptidomimetics, cyclosporin H, and dipeptide derivatives. FPR2 modulators include phenylurea, bridged spiro[2.4]heptane ester, naphthalene, aminotriazole, polycyclic pyrrolidine-2,5-dione, imidazolidine-2,4-dione, (2-ureidoacetamido)alkyl, amide, oxazolyl-methylether, oxazole, thiazole, and crystalline potassium salt derivatives. These compounds have potential applications for human conditions such as inflammatory lung diseases, ischemia-reperfusion injury, sepsis, inflammatory bowel disease, and wound healing. FPRs are emerging as important targets for treating leukocyte-dominant inflammation.

Endosomal recognition of Lactococcus lactis G121 and its RNA by dendritic cells is key to its allergy-protective effects

BACKGROUND

Bacterial cowshed isolates are allergy protective in mice; however, the underlying mechanisms are largely unknown. We examined the ability of Lactococcus lactis G121 to prevent allergic inflammatory reactions.

OBJECTIVE

We sought to identify the ligands and pattern recognition receptors through which L lactis G121 confers allergy protection.

METHODS

L lactis G121-induced cytokine release and surface expression of costimulatory molecules by untreated or inhibitor-treated (bafilomycin and cytochalasin D) human monocyte-derived dendritic cells (moDCs), bone marrow-derived mouse dendritic cells (BMDCs), and moDC/naive CD4⁺ T-cell cocultures were analyzed by using ELISA and flow cytometry. The pathology of ovalbumin-induced acute allergic airway inflammation after adoptive transfer of BMDCs was examined by means of microscopy.

RESULTS

L lactis G121-treated murine BMDCs and human moDCs released T_H1-polarizing cytokines and induced T_H1 T cells. Inhibiting phagocytosis and endosomal acidification in BMDCs or moDCs impaired the release of T_H1-polarizing cytokines, costimulatory molecule expression, and T-cell activation on L lactis G121 challenge. In vivo allergy protection mediated by L lactis G121 was dependent on endosomal acidification in dendritic cells (DCs). Toll-like receptor (Tlr) 13^-/- BMDCs showed a weak response to L lactis G121 and were unresponsive to its RNA. The T_H1-polarizing activity of L lactis G121-treated human DCs was blocked by TLR8-specific inhibitors, mediated by L lactis G121 RNA, and synergistically enhanced by activation of nucleotide-binding oligomerization domain-containing protein (NOD) 2.

CONCLUSION

Bacterial RNA is the main driver of L lactis G121-mediated protection against experimentally induced allergy and requires both bacterial uptake by DCs and endosomal acidification. In mice L lactis G121 RNA signals through TLR13; however, the most likely intracellular receptor in human subjects is TLR8.

Negative prognostic impact of regulatory T cell infiltration in surgically resected esophageal cancer post-radiochemotherapy

Ever accumulating evidence indicates that the long-term effects of radiotherapy and chemotherapy largely depend on the induction (or restoration) of an anticancer immune response. Here, we investigated this paradigm in the context of esophageal carcinomas treated by neo-adjuvant radiochemotherapy, in a cohort encompassing 196 patients. We found that the density of the FOXP3⁺ regulatory T cell (Treg) infiltrate present in the residual tumor (or its scar) correlated with the pathological response (the less Tregs the more pronounced was the histological response) and predicted cancer-specific survival. In contrast, there was no significant clinical impact of the frequency of CD8⁺ cytotoxic T cells. At difference with breast or colorectal cancer, a loss-of-function allele of toll like receptor 4 (TLR4) improved cancer-specific survival of patients with esophageal cancer. While a loss-of-function allele of purinergic receptor P2X, ligand-gated ion channel, 7 (P2RX7) failed to affect cancer-specific survival, its presence did correlate with an increase in Treg infiltration. Altogether, these results corroborate the notion that the immunosurveillance seals the fate of patients with esophageal carcinomas treated with conventional radiochemotherapy.

Four receptor-like cytoplasmic kinases regulate development and immunity in rice

Receptor-like cytoplasmic kinases (RLCKs) represent a large family of proteins in plants. However, few RLCKs have been well characterized. Here, we report the functional characterization of four rice RLCKs - OsRLCK57, OsRLCK107, OsRLCK118 and OsRLCK176 from subfamily VII. These OsRLCKs interact with the rice brassinosteroid receptor, OsBRI1 in yeast cell, but not the XA21 immune receptor. Transgenic lines silenced for each of these genes have enlarged leaf angles and are hypersensitive to brassinolide treatment compared to wild type rice. Transgenic plants silenced for OsRLCK57 had significantly fewer tillers and reduced panicle secondary branching, and lines silenced for OsRLCK107 and OsRLCK118 produce fewer seeds. Silencing of these genes decreased Xa21 gene expression and compromised XA21-mediated immunity to Xanthomonas oryzae pv. oryzae. Our study demonstrates that these OsRLCKs negatively regulate BR signalling, while positively regulating immune responses by contributing to the expression of the immune receptor XA21.

TRIF-dependent TLR signaling, its functions in host defense and inflammation, and its potential as a therapeutic target

Toll/IL-1R domain-containing adaptor-inducing IFN-β (TRIF)-dependent signaling is required for TLR-mediated production of type-I IFN and several other proinflammatory mediators. Various pathogens target the signaling molecules and transcriptional regulators acting in the TRIF pathway, thus demonstrating the importance of this pathway in host defense. Indeed, the TRIF pathway contributes to control of both viral and bacterial pathogens through promotion of inflammatory mediators and activation of antimicrobial responses. TRIF signaling also has both protective and pathologic roles in several chronic inflammatory disease conditions, as well as an essential function in wound-repair processes. Here, we review our current understanding of the regulatory mechanisms that control TRIF-dependent TLR signaling, the role of the TRIF pathway in different infectious and noninfectious pathologic states, and the potential for manipulating TRIF-dependent TLR signaling for therapeutic benefit.

Alarmins and Antitumor Immunity

PURPOSE

Alarmins are constitutively present endogenous molecules that essentially act as early warning signals for the immune system. We provide a brief overview of major alarmins and highlight their roles in tumor immunity.

METHODS

We searched PubMed up to January 10, 2016, using alarmins and/or damage-associated molecular patterns (DAMPs), as key words. We selected and reviewed articles that focused on the discovery and functions of alarmin and their roles in tumor immunity.

FINDINGS

Alarmins are essentially endogenous immunostimulatory DAMP molecules that are exposed in response to danger (eg, infection or tissue injury) as a result of degranulation, cell death, or induction. They are sensed by chemotactic receptors and pattern recognition receptors to induce immune responses by promoting the recruitment and activation of leukocytes, particularly antigen-presenting cells.

IMPLICATIONS

Accumulating data suggest that certain alarmins, High-mobility group nucleosome-binding protein 1 (HMGN1) in particular, contribute to the generation of antitumor immunity. Some alarmins can also be used as cancer biomarkers. Therefore, alarmins can potentially be applied for our fight against cancers.

Vimentin in Bacterial Infections

Despite well-studied bacterial strategies to target actin to subvert the host cell cytoskeleton, thus promoting bacterial survival, replication, and dissemination, relatively little is known about the bacterial interaction with other components of the host cell cytoskeleton, including intermediate filaments (IFs). IFs have not only roles in maintaining the structural integrity of the cell, but they are also involved in many cellular processes including cell adhesion, immune signaling, and autophagy, processes that are important in the context of bacterial infections. Here, we summarize the knowledge about the role of IFs in bacterial infections, focusing on the type III IF protein vimentin. Recent studies have revealed the involvement of vimentin in host cell defenses, acting as ligand for several pattern recognition receptors of the innate immune system. Two main aspects of bacteria-vimentin interactions are presented in this review: the role of vimentin in pathogen-binding on the cell surface and subsequent bacterial invasion and the interaction of cytosolic vimentin and intracellular pathogens with regards to innate immune signaling. Mechanistic insight is presented involving distinct bacterial virulence factors that target vimentin to subvert its function in order to change the host cell fate in the course of a bacterial infection.

Pentraxin 3: an immune modulator of infection and useful marker for disease severity assessment in sepsis

The acute phase protein pentraxin 3 (PTX3) is a pattern recognition receptor involved in regulation of the host immune response. This relatively newly discovered member of the pentraxin superfamily elicits both immunostimulatory and immunoregulatory functions preventing autoimmune pathology and orchestrated clearance of pathogens through opsonization of damage- and pathogen-associated molecular patterns (DAMP/PAMP). Thus, PTX3 has been described as a possible evolutionary precursor to immunoglobulins. While shown to provide protection against specific bacterial and fungal pathogens, persistent elevation of PTX3 levels following initial onset of infection appear to predict poor patient outcome and may contribute to disease sequelae such as tissue damage and coagulopathy. Measurement of PTX3 following onset of sepsis may improve patient risk assessment and thus be useful in guiding subsequent therapeutic interventions including steroidal anti-inflammatory and altered antibiotic therapies. In this review, we summarize the role of PTX3 in inflammatory syndromes and its utility as a marker of sepsis disease severity.

Effect of yeast-derived products and distillers dried grains with solubles (DDGS) on growth performance, gut morphology, and gene expression of pattern recognition receptors and cytokines in broiler chickens

An experiment was carried out to investigate the effect of yeast-derived products and distillers' dried grains with solubles (DDGS) on growth performance, small intestinal morphology, and innate immune response in broiler chickens from 1 to 21 d of age. Nine replicates of 5 birds each were assigned to dietary treatments consisting of a control diet without antibiotic (C), and diets containing 11 mg/kg of virginiamycin, 0.25% of yeast cell wall (YCW), 0.2% of a commercial product Maxi-Gen Plus, 0.025% of nucleotides, 0.05% of nucleotides, or a diet containing 10% of DDGS. On d 21, 5 birds per treatment were euthanized and approximately 5-cm long duodenum, jejunum, and ileum segments were collected for intestinal morphology measurements. Cecal tonsils and spleen were collected to measure the gene expression of toll-like receptors TLR2b, TLR4, and TLR21, macrophage mannose receptor (MMR), and cytokines IFN-γ, IL-12, IL-10, and IL-4. No significant difference was observed for growth performance parameters. However, diets containing 0.05% of nucleotides and YCW significantly increased (P < 0.05) villus height in the jejunum. Furthermore, the number of the goblet cells per unit area in the ileum was increased (P < 0.05) in diets supplemented with yeast-derived products. The expression of TLR2b in the spleen was down-regulated for diets supplemented with nucleotides and antibiotic. In addition, lower expression of TLR21 and MMR was observed in the spleen of birds receiving yeast-derived products and antibiotic. However, expression of TLR4 in the spleen was up-regulated in diets supplemented with YCW and nucleotides. The expression of IFN-γ and IL-12 was down-regulated in the spleen of birds fed diets supplemented with yeast-derived products. In addition, inclusion of YCW, Maxi-Gen Plus, or 0.05% of nucleotides down-regulated the expression of IL-10 and IL-4 in the cecal tonsils. In conclusion, down-regulation of receptors and cytokines in spleen and cecal tonsils of birds fed diets supplemented with yeast-derived products may suggest that yeast products do not exert immune stimulating effect under normal health conditions.

Initiating protease with modular domains interacts with β-glucan recognition protein to trigger innate immune response in insects

The autoactivation of an initiating serine protease upon binding of pattern recognition proteins to pathogen surfaces is a crucial step in eliciting insect immune responses such as the activation of Toll and prophenoloxidase pathways. However, the molecular mechanisms responsible for autoactivation of the initiating protease remains poorly understood. Here, we investigated the molecular basis for the autoactivation of hemolymph protease 14 (HP14), an initiating protease in hemolymph of Manduca sexta, upon the binding of β-1,3-glucan by its recognition protein, βGRP2. Biochemical analysis using HP14 zymogen (proHP14), βGRP2, and the recombinant proteins as truncated forms showed that the amino-terminal modular low-density lipoprotein receptor class A (LA) domains within HP14 are required for proHP14 autoactivation that is stimulated by its interaction with βGRP2. Consistent with this result, recombinant LA domains inhibit the activation of proHP14 and prophenoloxidase, likely by competing with the interaction between βGRP2 and LA domains within proHP14. Using surface plasmon resonance, we demonstrated that immobilized LA domains directly interact with βGRP2 in a calcium-dependent manner and that high-affinity interaction requires the C-terminal glucanase-like domain of βGRP2. Importantly, the affinity of LA domains for βGRP2 increases nearly 100-fold in the presence of β-1,3-glucan. Taken together, these results present the first experimental evidence to our knowledge that LA domains of an insect modular protease and glucanase-like domains of a βGRP mediate their interaction, and that this binding is essential for the protease autoactivation. Thus, our study provides important insight into the molecular basis underlying the initiation of protease cascade in insect immune responses.

Macrophages polarization is mediated by the combination of PRR ligands and distinct inflammatory cytokines

Macrophages recognize microbes through Pattern Recognition Receptors (PRRs), and then release pro-inflammatory and anti-inflammatory cytokines. Recent studies have highlighted that collaboration between different PRRs. However, these studies have neglected the crosstalk between various PRRs on macrophages. In the present study, we investigated the interplay of nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) (NOD1, NOD2) and TLRs (TLR1, 2, 3, 4, 5, 6, 7, 8) in terms of macrophage activation, the expression and production of cytokines. The macrophages were stimulated with a single PRR ligand or a combination of TLR and NOD ligands. After 8 h of incubation, the mRNA expression of interleukin-1β (IL-1β), IL-4, IL-6, IL-10, IL-12p35, IL-12p40, IL-13, and interferon-γ (IFN-γ) was evaluated. The production of these cytokines was also measured. NOD2 synergized with TLR3 agonists on enhancement of IL-10 release. However, the combination of NOD1 with TLR3 ligands showed little effect on IL-10 production. Moreover, NOD2 inhibited the percentages of CD11b + F4/80 + cells activated by TLR3 agonist.

The maize disease resistance gene Htn1 against northern corn leaf blight encodes a wall-associated receptor-like kinase

Northern corn leaf blight (NCLB) caused by the hemibiotrophic fungus Exserohilum turcicum is an important foliar disease of maize that is mainly controlled by growing resistant maize cultivars. The Htn1 locus confers quantitative and partial NCLB resistance by delaying the onset of lesion formation. Htn1 represents an important source of genetic resistance that was originally introduced from a Mexican landrace into modern maize breeding lines in the 1970s. Using a high-resolution map-based cloning approach, we delimited Htn1 to a 131.7-kb physical interval on chromosome 8 that contained three candidate genes encoding two wall-associated receptor-like kinases (ZmWAK-RLK1 and ZmWAK-RLK2) and one wall-associated receptor-like protein (ZmWAK-RLP1). TILLING (targeting induced local lesions in genomes) mutants in ZmWAK-RLK1 were more susceptible to NCLB than wild-type plants, both in greenhouse experiments and in the field. ZmWAK-RLK1 contains a nonarginine-aspartate (non-RD) kinase domain, typically found in plant innate immune receptors. Sequence comparison showed that the extracellular domain of ZmWAK-RLK1 is highly diverse between different maize genotypes. Furthermore, an alternative splice variant resulting in a truncated protein was present at higher frequency in the susceptible parents of the mapping populations compared with in the resistant parents. Hence, the quantitative Htn1 disease resistance in maize is encoded by an unusual innate immune receptor with an extracellular wall-associated kinase domain. These results further highlight the importance of this protein family in resistance to adapted pathogens.

Immunosurveillance in esophageal carcinoma: The decisive impact of regulatory T cells

Neoadjuvant radiochemotherapy of esophageal carcinomas causes a variable degree of depletion of tumor-infiltrating FOXP3⁺ regulatory T cells (Tregs). The frequency of local Tregs in the operative specimens negatively correlates with the pathological response and overall patient survival. These results underscore the importance of immunosurveillance in determining the fate of patients with esophageal cancers treated with radiochemotherapy.

Enhancement of innate immune system in monocot rice by transferring the dicotyledonous elongation factor Tu receptor EFR

The elongation factor Tu (EF-Tu) receptor (EFR) in cruciferous plants specifically recognizes the N-terminal acetylated elf18 region of bacterial EF-Tu and thereby activates plant immunity. It has been demonstrated that Arabidopsis EFR confers broad-spectrum bacterial resistance in the EFR transgenic solanaceous plants. Here, the transgenic rice plants (Oryza sativa L. ssp. japonica cv. Zhonghua 17) and cell cultures with constitutive expression of AtEFR were developed to investigate whether AtEFR senses EF-Tu and thus enhances bacterial resistance in the monocot plants. We demonstrated that the Xanthomonas oryzae-derived elf18 peptide induced oxidative burst and mitogen-activated protein kinase activation in the AtEFR transgenic rice cells and plants, respectively. Pathogenesis-related genes, such as OsPBZ1, were upregulated dramatically in transgenic rice plant and cell lines in response to elf18 stimulation. Importantly, pretreatment with elf18 triggered strong resistance to X. oryzae pv. oryzae in the transgenic plants, which was largely dependent on the AtEFR expression level. These plants also exhibited enhanced resistance to rice bacterial brown stripe, but not to rice fungal blast. Collectively, the results indicate that the rice plants with heterologous expression of AtEFR recognize bacterial EF-Tu and exhibit enhanced broad-spectrum bacterial disease resistance and that pattern recognition receptor-mediated immunity may be manipulated across the two plant classes, dicots and monocots.

Safety, tolerability and pharmacodynamics of a novel immunomodulator, MIS416, in patients with chronic progressive multiple sclerosis

Background

Preclinical studies have demonstrated that MIS416, a bacterially derived immune modulator, targets myeloid cells following systemic delivery. MIS416 stimulated myeloid cells have the capacity to regulate innate inflammation, a potential therapeutic target for progressive multiple sclerosis.

Objectives

To determine the safety, tolerability, pharmacodynamics and maximum tolerated dose and/or recommended Phase 2 dose of MIS416.

Methods

An open-label, non-randomized, phase II, dose-escalation study, in patients with progressive multiple sclerosis: dose-escalation phase, with MIS416 administered once weekly for four weeks to determine maximum tolerated dose; and dose-confirmation phase, administered once weekly for up to 12 weeks.

Results

The safety profile indicates the majority of adverse events were mild or moderate, tolerable, self-limiting and consistent with the known bioactivity of MIS416 (acute flu-like symptoms). Maximum tolerated dose was not reached. A dose of 500 µg/week was recommended for the Phase 2 dose.

Conclusion

MIS416 is well tolerated at a dose of 500 µg/week. The adverse event profile is consistent with the mechanism of action of MIS416, indicating bioactivity within the signal transduction pathways and supported by induction of a known MIS416 pharmacodynamic marker. It is recommended that safety and efficacy of MIS416 is investigated further in a larger randomized controlled trial.

http://clinicaltrials.gov reference NCT01191996

Expression patterns of flagellin sensing 2 map to bacterial entry sites in plant shoots and roots

Pathogens can colonize all plant organs and tissues. To prevent this, each cell must be capable of autonomously triggering defence. Therefore, it is generally assumed that primary sensors of the immune system are constitutively present. One major primary sensor against bacterial infection is the flagellin sensing 2 (FLS2) pattern recognition receptor (PRR). To gain insights into its expression pattern, the FLS2 promoter activity in β-glucuronidase (GUS) reporter lines was monitored. The data show that pFLS2::GUS activity is highest in cells and tissues vulnerable to bacterial entry and colonization, such as stomata, hydathodes, and lateral roots. GUS activity is also high in the vasculature and, by monitoring Ca(2+) responses in the vasculature, it was found that this tissue contributes to flg22-induced Ca(2+) burst. The FLS2 promoter is also regulated in a tissue- and cell type-specific manner and is responsive to hormones, damage, and biotic stresses. This results in stimulus-dependent expansion of the FLS2 expression domain. In summary, a tissue- and cell type-specific map of FLS2 expression has been created correlating with prominent entry sites and target tissues of plant bacterial pathogens.

Cytosolic RNA:DNA hybrids activate the cGAS-STING axis

Intracellular recognition of non-self and also self-nucleic acids can result in the initiation of potent pro-inflammatory and antiviral cytokine responses. Most recently, cGAS was shown to be critical for the recognition of cytoplasmic dsDNA. Binding of dsDNA to cGAS results in the synthesis of cGAMP(2'-5'), which then binds to the endoplasmic reticulum resident protein STING. This initiates a signaling cascade that triggers the induction of an antiviral immune response. While most studies on intracellular nucleic acids have focused on dsRNA or dsDNA, it has remained unexplored whether cytosolic RNA:DNA hybrids are also sensed by the innate immune system. Studying synthetic RNA:DNA hybrids, we indeed observed a strong type I interferon response upon cytosolic delivery of this class of molecule. Studies in THP-1 knockout cells revealed that the recognition of RNA:DNA hybrids is completely attributable to the cGAS-STING pathway. Moreover, in vitro studies showed that recombinant cGAS produced cGAMP upon RNA:DNA hybrid recognition. Altogether, our results introduce RNA:DNA hybrids as a novel class of intracellular PAMP molecules and describe an alternative cGAS ligand next to dsDNA.

Ontogeny of intestinal epithelial innate immune responses

Emerging evidence indicates that processes during postnatal development might significantly influence the establishment of mucosal host-microbial homeostasis. Developmental and adaptive immunological processes but also environmental and microbial exposure early after birth might thus affect disease susceptibility and health during adult life. The present review aims at summarizing the current understanding of the intestinal epithelial innate immune system and its developmental and adaptive changes after birth.

Two apextrin-like proteins mediate extracellular and intracellular bacterial recognition in amphioxus

Animals exploit different germ-line-encoded proteins with various domain structures to detect the signature molecules of pathogenic microbes. These molecules are known as pathogen-associated molecular patterns (PAMPs), and the host proteins that react with PAMPs are called pattern recognition proteins (PRPs). Here, we present a novel type of protein domain structure capable of binding to bacterial peptidoglycan (PGN) and the minimal PGN motif muramyl dipeptide (MDP). This domain is designated as apextrin C-terminal domain (ApeC), and its presence was confirmed in several invertebrate phyla and subphyla. Two apextrin-like proteins (ALP1 and ALP2) were identified in a basal chordate, the Japanese amphioxus Branchiostoma japonicum (bj). bjALP1 is a mucosal effector secreted into the gut lumen to agglutinate the Gram-positive bacterium Staphylococcus aureus via PGN binding. Neutralization of secreted bjALP1 by anti-bjALP1 monoclonal antibodies caused serious damage to the gut epithelium and rapid death of the animals after bacterial infection. bjALP2 is an intracellular PGN sensor that binds to TNF receptor-associated factor 6 (TRAF6) and prevents TRAF6 from self-ubiquitination and hence from NF-κB activation. MDP was found to compete with TRAF6 for bjALP2, which released TRAF6 to activate the NF-κB pathway. BjALP1 and bjALP2 therefore play distinct and complementary functions in amphioxus gut mucosal immunity. In conclusion, discovery of the ApeC domain and the functional analyses of amphioxus ALP1 and ALP2 allowed us to define a previously undocumented type of PRP that is represented across different animal phyla.

PtLGBP, a pattern recognition receptor in Portunus trituberculatus involved in the immune response against different challenges

Lipopolysaccharide and b-1,3-glucan binding protein (LGBP) is a pattern recognition receptor that can recognize and bind LPS and b-1,3-glucan. LGBP has crucial roles in innate immune defense against Gram-negative bacteria and fungi. In this study, LGBP functions in Portunus trituberculatus innate immunity were analyzed. First, the mRNA expression of PtLGBP in hemocytes, hepatopancreas, and muscle toward three typical pathogen-associated molecular patterns (PAMPs) stimulations were examined using real-time PCR. Results show that the overall trend of relative expressions of the LGBP gene in three tissues is consistent, showing up-down trend. In each group, the highest expression of the LGBP gene was at 3 and 12 h post-injection. The LGBP gene is also expressed significantly higher in the hemocytes and hepatopancreas than in the muscle. The highest level of LGBP was in the lipopolysaccharides (LPS) and glucan-injected group, whereas the lowest level was in the PGN-injected group. Furthermore, bacterial agglutination assay with polyclonal antibody specifically for PtLGBP proved that the recombinant PtLGBP (designated as rPtLGBP) could exhibit obvious agglutination activity toward Gram-negative bacteria Escherichia coli, Vibrio parahaemolyticus, and V. alginolyticus; Gram-positive bacteria Bacillus subtilis; and fungi Saccharomyces cerevisiae. LGBP in Portunus trituberculatus possibly served as a multi-functional PRR. In addition, LGBP is not only involved in the immune response against Gram-negative and fungi, as manifested in other invertebrates, but also has a significant role in anti-Gram-positive bacteria infection.

Priming and activation of NADPH oxidases in plants and animals

In mammals, engagement of Toll-like receptors by microbe-associated molecular patterns enhances the responsiveness of NADPH oxidases. Two recent papers report a similar 'priming' mechanism for the plant oxidase RbohD. Despite lacking structural homology, the functional parallels between plants and animals reveal that a common regulatory logic arose by convergent evolution.

The immunological, environmental, and phylogenetic perpetrators of metastatic leishmaniasis

Cutaneous leishmaniases have persisted for centuries as chronically disfiguring parasitic infections affecting millions of people across the subtropics. Symptoms range from the more prevalent single, self-healing cutaneous lesion to a persistent, metastatic disease, where ulcerations and granulomatous nodules can affect multiple secondary sites of the skin and delicate facial mucosa, even sometimes diffusing throughout the cutaneous system as a papular rash. The basis for such diverse pathologies is multifactorial, ranging from parasite phylogeny to host immunocompetence and various environmental factors. Although complex, these pathologies often prey on weaknesses in the innate immune system and its pattern recognition receptors. This review explores the observed and potential associations among the multifactorial perpetrators of infectious metastasis and components of the innate immune system.

Differential responses to rhinovirus- and influenza-associated pulmonary exacerbations in patients with cystic fibrosis

RATIONALE

The mechanism by which viruses cause exacerbations of chronic airway disease and the capacity of patients with cystic fibrosis (CF) to respond to viral infection are not precisely known.

OBJECTIVES

To determine the antiviral response to infection in patients with CF.

METHODS

Sputum was collected from patients with CF with respiratory exacerbation. Viruses were detected in multiplex polymerase chain reaction (PCR)-based assays. Gene expression of 84 antiviral response genes was measured, using a focused quantitative PCR gene array.

MEASUREMENTS AND MAIN RESULTS

We examined 36 samples from 23 patients with respiratory exacerbation. Fourteen samples tested virus-positive and 22 virus-negative. When we compared exacerbations associated with rhinovirus (RV, n = 9) and influenza (n = 5) with virus-negative specimens, we found distinct patterns of antiviral gene expression. RV was associated with greater than twofold induction of five genes, including those encoding the monocyte-attracting chemokines CXCL10, CXCL11, and CXCL9. Influenza was associated with overexpression of 20 genes, including those encoding the cytokines tumor necrosis factor and IL-12; the kinases MEK, TBK-1, and STAT-1; the apoptosis proteins caspase-8 and caspase-10; the influenza double-stranded RNA receptor RIG-I and its downstream effector MAVS; and pyrin, an IFN-stimulated protein involved in influenza resistance.

CONCLUSIONS

We conclude that virus-induced exacerbations of CF are associated with immune responses tailored to specific infections. Influenza induced a more potent response consisting of inflammation, whereas RV infection had a pronounced effect on chemokine expression. As far as we are aware, this study is the first to compare specific responses to different viruses in live patients with chronic airway disease.

Activation of an innate immune response in the schistosome-transmitting snail Biomphalaria glabrata by specific bacterial PAMPs

Injection of crude lipopolysaccharide (LPS) from Escherichia coli into the hemocoel of Biomphalaria glabrata stimulates cell proliferation in the amebocyte-producing organ (APO). However, it is not known if mitogenic activity resides in the lipid A or O-polysaccharide component of LPS. Moreover, the possible role of substances that commonly contaminate crude LPS and that are known to stimulate innate immune responses in mammals, e.g., peptidoglycan (PGN), protein, or bacterial DNA, is unclear. Therefore, we tested the effects of the following injected substances on the snail APO: crude LPS, ultrapurified LPS (lacking lipoprotein contamination), two forms of lipid A, (diphosphoryl lipid A and Kdo2-lipid A), O-polysaccharide, Gram negative PGN, both crude and ultrapurified (with and without endotoxin activity, respectively), Gram positive PGN, PGN components Tri-DAP and muramyl dipeptide, and bacterial DNA. Whereas crude LPS, ultrapurified LPS, and crude PGN were mitogenic, ultrapurified PGN was not. Moreover, LPS components, PGN components, and bacterial DNA were inactive. These results suggest that it is the intact LPS molecule which stimulates cell division in the APO.

Fusobacterium nucleatum activates the immune response through retinoic acid-inducible gene I

Retinoic acid-inducible gene I (RIG-I) is a cytosolic pattern recognition receptor involved in the sensing of RNA viruses and the initiation of antiviral responses. Fusobacterium nucleatum, a Gram-negative anaerobic bacterium associated with periodontal disease, is capable of invading cells. We hypothesized that F. nucleatum's ability to invade cells allows the microorganism to activate the immune response through RIG-I. Bacterial invasion was found to be necessary for F. nucleatum-induced nuclear factor kappa B (NF-κB) activation. Following invasion of the human periodontal ligament fibroblast (PDLF), F. nucleatum was located in the cytosol. F. nucleatum infection led to an 80-fold increase in RIG-I expression. Silencing RIG-I in PDLF by siRNA led to a significant decrease of NF-κB activation and expression of proinflammatory genes. Additionally, F. nucleatum was able to secrete nucleic acids, and introduction of F. nucleatum RNA into PDLF led to a RIG-I-dependent activation of NF-κB. Our findings showed RIG-I to be involved in the recognition of F. nucleatum. The function of RIG-I is likely to be broad and not limited to sensing of viruses only. Hence, this receptor may play an important role in detecting invasive forms of oral pathogens and contribute to inflammation in periodontal tissues.

Polyinosinic-polycytidylic acid initiates ovarian innate antiviral response and inhibits steroidogenesis in female mice

Viral infection may perturb ovarian functions. However, innate antiviral response in the ovary has not been intensively investigated. In this study, we examined the innate antiviral system in the mouse ovary and the impacts of antiviral response on steroidogenesis. Major virus sensors, including Toll-like receptor 3 (TLR3), retinoic acid-inducible gene I, and melanoma differentiation-associated gene 5, are predominantly expressed in ovarian stromal and granulosa cells. Polyinosinic-polycytidylic acid (poly [I:C]) is a common agonist of TLR3, retinoic acid-inducible gene I, and melanoma differentiation-associated gene 5. Intraperitoneal injection of poly (I:C) activated nuclear factor kappa B and interferon (IFN) regulatory factor 3 in the ovarian cells and induced the expression of proinflammatory cytokines, including tumor necrosis factor alpha, interleukin 6, and type 1 IFNs (IFNA/B). Moreover, poly (I:C) upregulated the expression of several antiviral proteins, including 2'-5'-oligoadenylate synthetase, IFN-stimulated gene 15, and Mx GTPase 1. The innate antiviral response in the ovary was significantly reduced in Tlr3-deficient mice. Notably, we demonstrated that poly (I:C) injection inhibits steroidogenesis enzyme expression and decreases plasma estradiol and testosterone levels. The results show that the mouse ovary is equipped with innate antiviral state, and the antiviral response perturbs ovarian endocrine function.

An Update on PYRIN Domain-Containing Pattern Recognition Receptors: From Immunity to Pathology

Cytosolic pattern recognition receptors (PRRs) sense a wide range of endogenous danger-associated molecular patterns as well as exogenous pathogen-associated molecular patterns. In particular, Nod-like receptors containing a pyrin domain (PYD), called NLRPs, and AIM2-like receptors (ALRs) have been shown to play a critical role in host defense by facilitating clearance of pathogens and maintaining a healthy gut microflora. NLRPs and ALRs both encode a PYD, which is crucial for relaying signals that result in an efficient innate immune response through activation of several key innate immune signaling pathways. However, mutations in these PRRs have been linked to the development of auto-inflammatory and autoimmune diseases. In addition, they have been implicated in metabolic diseases. In this review, we summarize the function of PYD-containing NLRPs and ALRs and address their contribution to innate immunity, host defense, and immune-linked diseases.

Molecular cloning and expression of TLR in the Eisenia andrei earthworm

Toll-like receptors (TLRs) play an important role in defense responses to pathogens in invertebrates. Here we characterize the first TLR isolated from an oligochaete annelid, namely, Eisenia andrei (EaTLR) and show its expression pattern. The full-length EaTLR cDNA consists of 2615 bp encoding a putative protein of 675 amino acids. The predicted amino acid sequence comprises of an extracellular domain containing 31 amino acid signal peptide and seven leucine-rich repeats (LRR), capped with cysteine-rich N- and C-terminal LRRs followed by a transmembrane domain and cytoplasmic Toll/IL-1R domain (TIR). TIR domains of twenty individual earthworms were sequenced and the variability suggesting the presence of a high number of TLR genes in the genome of E. andrei was observed. Phylogenetic analysis revealed the highest similarity of EaTLR with polychaete annelid, Capitella teleta and TLRs of mollusks and echinoderms. Finally, the highest constitutive expression of EaTLR was observed in the digestive tract. Gene expression was significantly increased in coelomocytes of E. andrei after the challenge with Gram-positive bacteria.

Toll-like receptor 9 and 21 have different ligand recognition profiles and cooperatively mediate activity of CpG-oligodeoxynucleotides in zebrafish

CpG-oligodeoxynucleotides (CpG-ODNs) are potent immune stimuli currently under investigation as antimicrobial agents for different species. Toll-like receptor (TLR) 9 and TLR21 are the cellular receptors of CpG-ODN in mammals and chickens, respectively. The avian genomes lack TLR9, whereas mammalian genomes lack TLR21. Although fish contain both of these genes, the biological functions of fish TLR9 and TLR21 have not been investigated previously. In this study, we comparatively investigated zebrafish TLR9 (zebTLR9) and TLR21 (zebTLR21). The two TLRs have similar expression profiles in zebrafish. They are expressed during early development stages and are preferentially expressed in innate immune function-related organs in adult fish. Results from cell-based activation assays indicate that these two zebrafish TLRs are functional, responding to CpG-ODN but not to other TLR ligands. zebTLR9 broadly recognized CpG-ODN with different CpG motifs, but CpG-ODN with GACGTT or AACGTT had better activity to this TLR. In contrast, zebTLR21 responded preferentially to CpG-ODN with GTCGTT motifs. The distinctive ligand recognition profiles of these two TLRs were determined by their ectodomains. Activation of these two TLRs by CpG-ODN occurred inside the cells and was modulated by UNC93B1. The biological functions of these two TLRs were further investigated. The CpG-ODNs that activate both zebTLR9 and zebTLR21 were more potent than others that activate only zebTLR9 in the activation of cytokine productions and were more bactericidal in zebrafish. These results suggest that zebTLR9 and zebTLR21 cooperatively mediate the antimicrobial activities of CpG-ODN. Overall, this study provides a molecular basis for the activities of CpG-ODN in fish.

An updated view of the intracellular mechanisms regulating cross-presentation

Cross-presentation involves the presentation of peptides derived from internalized cargo on major histocompatibility complex class I molecules by dendritic cells, a process critical for tolerance and immunity. Detailed studies of the pathways mediating cross-presentation have revealed that this process takes place in a specialized subcellular compartment with a unique set of proteins. In this review, we focus on the recently appreciated role for intracellular vesicular traffic, which serves to equip compartments such as endosomes and phagosomes with the necessary apparatus for conducting the various steps of cross-presentation. We also consider how these pathways may integrate with inflammatory signals particularly from pattern recognition receptors that detect the presence of microbial components during infection. We discuss the consequences of such signals on initiating cross-presentation to stimulate adaptive CD8 T cell responses.