Mincle as a potential intervention target for the prevention of inflammation and fibrosis (Review)

Macrophage‑inducible C‑type lectin receptor (Mincle) is predominantly found on antigen‑presenting cells. It can recognize specific ligands when stimulated by certain pathogens such as fungi and Mycobacterium tuberculosis. This recognition triggers the activation of the nuclear factor‑κB pathway, leading to the production of inflammatory factors and contributing to the innate immune response of the host. Moreover, Mincle identifies lipid damage‑related molecules discharged by injured cells, such as Sin3‑associated protein 130, which triggers aseptic inflammation and ultimately hastens the advancement of renal damage, autoimmune disorders and malignancies by fostering tissue inflammation. Presently, research on the functioning of the Mincle receptor in different inflammatory and fibrosis‑associated conditions has emerged as a popular topic. Nevertheless, there remains a lack of research on the impact of Mincle in promoting long‑lasting inflammatory reactions and fibrosis. Additional investigation is required into the function of Mincle receptors in chronological inflammatory reactions and fibrosis of organ systems, including the progression from inflammation to fibrosis. Hence, the present study showed an overview of the primary roles and potential mechanism of Mincle in inflammation, fibrosis, as well as the progression of inflammation to fibrosis. The aim of the present study was to clarify the potential mechanism of Mincle in inflammation and fibrosis and to offer perspectives for the development of drugs that target Mincle.

Decoding Toll-like receptors: Recent insights and perspectives in innate immunity

Toll-like receptors (TLRs) are an evolutionarily conserved family in the innate immune system and are the first line of host defense against microbial pathogens by recognizing pathogen-associated molecular patterns (PAMPs). TLRs, categorized into cell surface and endosomal subfamilies, recognize diverse PAMPs, and structural elucidation of TLRs and PAMP complexes has revealed their intricate mechanisms. TLRs activate common and specific signaling pathways to shape immune responses. Recent studies have shown the importance of post-transcriptional regulation in TLR-mediated inflammatory responses. Despite their protective functions, aberrant responses of TLRs contribute to inflammatory and autoimmune disorders. Understanding the delicate balance between TLR activation and regulatory mechanisms is crucial for deciphering their dual role in immune defense and disease pathogenesis. This review provides an overview of recent insights into the history of TLR discovery, elucidation of TLR ligands and signaling pathways, and their relevance to various diseases.

Identification and functional analysis of Toll-like receptor 2 from razor clam Sinonovacula constricta

Toll-like receptor 2 (TLR2) is a member of TLR family that plays important roles in the innate immune system, such as pathogen recognition and inflammation regulation. In this study, the TLR2 homologue was cloned from razor clam Sinonovacula constricta (denoted as ScTLR2) and its immune function was explored. The full-length cDNA of ScTLR2 comprised 2890 nucleotides with a 5'-UTR of 218 bp, an open reading frame of 2169 bp encoding 722 amino acids and a 3'-UTR of 503 bp. The deduced amino acid of ScTLR2 showed similar structure to TLR2 homologue with a conserved signal peptide, four LRR domains, one LRR-TYP domain, one LRR-CT domain, one transmembrane domain and a conserved TIR domain. ScTLR2 mRNA was detected in all examined tissues with the highest expression in the gill. After Vibrio parahaemolyticus challenge, the mRNA expression of ScTLR2 was significantly induced both in gill and haemocytes. The recombinant ScTLR2-LRR protein could bind all tested PAMPs including LPS, PGN and MAN. Bacterial agglutination assay showed that rScTLR2 could agglutinate the six tested bacteria with a calcium dependent manner. More importantly, ScTLR2 silencing by siRNA transfection could significantly depress the mRNA expression of Myd88, NF-κB, Tollip, IRF1, and IRF8. The survival rate of S. constricta was markedly decreased after V. parahaemolyticus challenge under this condition. Our current study demonstrated that ScTLR2 served as a pattern recognition receptor to induce immune response against invasive pathogen.

Fungal Cell Wall-Associated Effectors: Sensing, Integration, Suppression, and Protection

The cell wall (CW) of plant-interacting fungi, as the direct interface with host plants, plays a crucial role in fungal development. A number of secreted proteins are directly associated with the fungal CW, either through covalent or non-covalent interactions, and serve a range of important functions. In the context of plant-fungal interactions many are important for fungal development in the host environment and may therefore be considered fungal CW-associated effectors (CWAEs). Key CWAE functions include integrating chemical/physical signals to direct hyphal growth, interfering with plant immunity, and providing protection against plant defenses. In recent years, a diverse range of mechanisms have been reported that underpin their roles, with some CWAEs harboring conserved motifs or functional domains, while others are reported to have novel features. As such, the current understanding regarding fungal CWAEs is systematically presented here from the perspective of their biological functions in plant-fungal interactions. An overview of the fungal CW architecture and the mechanisms by which proteins are secreted, modified, and incorporated into the CW is first presented to provide context for their biological roles. Some CWAE functions are reported across a broad range of pathosystems or symbiotic/mutualistic associations. Prominent are the chitin interacting-effectors that facilitate fungal CW modification, protection, or suppression of host immune responses. However, several alternative functions are now reported and are presented and discussed. CWAEs can play diverse roles, some possibly unique to fungal lineages and others conserved across a broad range of plant-interacting fungi. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Different roles of Ca2+ and chitohexose in peanut (Arachis Hypogaea) photosynthetic responses to PAMP-immunity

Background

During active infections, plants prevent further spread of pathogenic microorganisms by inducing the rapid programmed death of cells around the infection point. This phenomenon is called the hypersensitive response and is a common feature of plant immune responses. Plants recognize conserved structures of pathogenic microorganisms, called pathogen-associated molecular patterns (PAMPs), e.g., flagellin 22 (flg22) and chitohexose, which bind to receptors on plant cells to induce various immune-response pathways. Although abiotic stresses are known to alter photosynthesis, the different effects of flg22 and chitohexose, which are involved into PAMP-induced signaling, on photosynthesis needs further study.

Methods

In the present study, we assessed the role of PAMPs in peanut (Arachis hypogaea) photosynthesis, particularly, the interaction between PAMPs and Ca2+ signal transduction pathway.

Results

Both flg22 and chitohexose significantly promoted the expression of the pathogenesis-related genes PR-4 and PR-10, as did Ca2+. We found that Ca2+ is involved in downregulating the photosystem II (PSII) reaction center activity induced by the flg22 immune response, but the role of chitohexose is not obvious. Additionally, Ca2+ significantly reduced the non-photochemical energy dissipation in the flg22- and chitohexose-induced immune response.

Conclusion

These results indicated that flg22 and chitohexose can trigger peanut immune pathways through the Ca2+ signaling pathway, but they differ in their regulation of the activity of the PSII reaction center.

DNA at the center of mammalian innate immune recognition of bacterial biofilms

Historically, the study of innate immune detection of bacterial infections has focused on the recognition of pathogen-associated molecular patterns (PAMPs) from bacteria growing as single cells in planktonic phase. However, over the past two decades, studies have highlighted an adaptive advantage of bacteria: the formation of biofilms. These structures are complex fortresses that stand against a hostile environment, including antibiotics and immune responses. Extracellular DNA (eDNA) is a crucial component of the matrix of most known biofilms. In this opinion article, I propose that eDNA is a universal PAMP that the immune system uses to recognize biofilms. Outstanding questions concern the discrimination between biofilm-associated eDNA and DNA from planktonic bacteria, the innate receptors involved, and the immune response to biofilms.

PAMPs and DAMPs in Sepsis: A Review of Their Molecular Features and Potential Clinical Implications

Sepsis is a serious organ dysfunction caused by a dysregulated immune host reaction to a pathogen. The innate immunity is programmed to react immediately to conserved molecules, released by the pathogens (PAMPs), and the host (DAMPs). We aimed to review the molecular mechanisms of the early phases of sepsis, focusing on PAMPs, DAMPs, and their related pathways, to identify potential biomarkers. We included studies published in English and searched on PubMed® and Cochrane®. After a detailed discussion on the actual knowledge of PAMPs/DAMPs, we analyzed their role in the different organs affected by sepsis, trying to elucidate the molecular basis of some of the most-used prognostic scores for sepsis. Furthermore, we described a chronological trend for the release of PAMPs/DAMPs that may be useful to identify different subsets of septic patients, who may benefit from targeted therapies. These findings are preliminary since these pathways seem to be strongly influenced by the peculiar characteristics of different pathogens and host features. Due to these reasons, while initial findings are promising, additional studies are necessary to clarify the potential involvement of these molecular patterns in the natural evolution of sepsis and to facilitate their transition into the clinical setting.

Accelerating the understanding of Aspergillus terreus: Epidemiology, physiology, immunology and advances

Aspergillus species encompass a variety of infections, ranging from invasive aspergillosis to allergic conditions, contingent upon the immune status of the host. In this spectrum, Aspergillus terreus stands out due to its emergence as a notable pathogen and its intrinsic resistance to amphotericin-B. The significance of Aspergillus-associated infections has witnessed a marked increase in the past few decades, particularly with the increasing number of immunocompromised individuals. The exploration of epidemiology, morphological transitions, immunopathology, and novel treatment approaches such as new antifungal drugs (PC945, olorofim) and combinational therapy using antifungal drugs and phytochemicals (Phytochemicals: quercetin, shikonin, artemisinin), also using immunotherapies to modulate immune response has resulted in better outcomes. Furthermore, in the context COVID-19 era and its aftermath, fungal infections have emerged as a substantial challenge for both immunocompromised and immunocompetent individuals. This is attributed to the use of immune-suppressing therapies during COVID-19 infections and the increase in transplant cases. Consequently, this review aims to provide an updated overview encompassing the epidemiology, germination events, immunopathology, and novel drug treatment strategies against Aspergillus terreus-associated infections.

Expression of RNautophagy/DNautophagy-related genes is regulated under control of an innate immune receptor

Double-stranded RNA (dsRNA) is a molecular pattern uniquely produced in cells infected with various viruses as a product or byproduct of replication. Cells detect such molecules, which indicate non-self invasion, and induce diverse immune responses to eliminate them. The degradation of virus-derived molecules can also play a role in the removal of pathogens and suppression of their replication. RNautophagy and DNautophagy are cellular degradative pathways in which RNA and DNA are directly imported into a hydrolytic organelle, the lysosome. Two lysosomal membrane proteins, SIDT2 and LAMP2C, mediate nucleic acid uptake via this pathway. Here, we showed that the expression of both SIDT2 and LAMP2C is selectively upregulated during the intracellular detection of poly(I:C), a synthetic analog of dsRNA that mimics viral infection. The upregulation of these two gene products upon poly(I:C) introduction was transient and synchronized. We also observed that the induction of SIDT2 and LAMP2C expression by poly(I:C) was dependent on MDA5, a cytoplasmic innate immune receptor that directly recognizes poly(I:C) and induces various antiviral responses. Finally, we showed that lysosomes can target viral RNA for degradation via RNautophagy and may suppress viral replication. Our results revealed a novel degradative pathway in cells as a downstream component of the innate immune response and provided evidence suggesting that the degradation of viral nucleic acids via RNautophagy/DNautophagy contributes to the suppression of viral replication.

A comprehensive review on the dynamic role of toll-like receptors (TLRs) in frontier aquaculture research and as a promising avenue for fish disease management

Toll-like receptors (TLRs) represent a conserved group of germline-encoded pattern recognition receptors (PRRs) that recognize pathogen-associated molecular patterns (PAMPs) and play a crucial role in inducing the broadly acting innate immune response against pathogens. In recent years, the detection of 21 different TLR types in various fish species has sparked interest in exploring the potential of TLRs as targets for boosting immunity and disease resistance in fish. This comprehensive review offers the latest insights into the diverse facets of fish TLRs, highlighting their history, classification, architectural insights through 3D modelling, ligands recognition, signalling pathways, crosstalk, and expression patterns at various developmental stages. It provides an exhaustive account of the distinct TLRs induced during the invasion of specific pathogens in various fish species and delves into the disparities between fish TLRs and their mammalian counterparts, highlighting the specific contribution of TLRs to the immune response in fish. Although various facets of TLRs in some fish, shellfish, and molluscs have been described, the role of TLRs in several other aquatic organisms still remained as potential gaps. Overall, this article outlines frontier aquaculture research in advancing the knowledge of fish immune systems for the proper management of piscine maladies.

Non-Canonical Inflammasome Pathway: The Role of Cell Death and Inflammation in Ehrlichiosis

Activating inflammatory caspases and releasing pro-inflammatory mediators are two essential functions of inflammasomes which are triggered in response to pathogen-associated molecular patterns (PAMPs) or danger-associated molecular patterns (DAMPs). The canonical inflammasome pathway involves the activation of inflammasome and its downstream pathway via the adaptor ASC protein, which causes caspase 1 activation and, eventually, the cleavage of pro-IL-1b and pro-IL-18. The non-canonical inflammasome pathway is induced upon detecting cytosolic lipopolysaccharide (LPS) by NLRP3 inflammasome in Gram-negative bacteria. The activation of NLRP3 triggers the cleavage of murine caspase 11 (human caspase 4 or caspase 5), which results in the formation of pores (via gasdermin) to cause pyroptosis. Ehrlichia is an obligately intracellular bacterium which is responsible for causing human monocytic ehrlichiosis (HME), a potentially lethal disease similar to toxic shock syndrome and septic shock syndrome. Several studies have indicated that canonical and non-canonical inflammasome activation is a crucial pathogenic mechanism that induces dysregulated inflammation and host cellular death in the pathophysiology of HME. Mechanistically, the activation of canonical and non-canonical inflammasome pathways affected by virulent Ehrlichia infection is due to a block in autophagy. This review aims to explore the significance of non-canonical inflammasomes in ehrlichiosis, and how the pathways involving caspases (with the exception of caspase 1) contribute to the pathophysiology of severe and fatal ehrlichiosis. Improving our understanding of the non-canonical inflammatory pathway that cause cell death and inflammation in ehrlichiosis will help the advancement of innovative therapeutic, preventative, and diagnostic approaches to the treatment of ehrlichiosis.

Interplay of Extracellular Vesicles and TLR4 Signaling in Hepatocellular Carcinoma Pathophysiology and Therapeutics

Hepatocellular carcinoma (HCC) stands as a significant contributor to global cancer-related mortality. Chronic inflammation, often arising from diverse sources such as viral hepatitis, alcohol misuse, nonalcoholic fatty liver disease (NAFLD), and nonalcoholic steatohepatitis (NASH), profoundly influences HCC development. Within this context, the interplay of extracellular vesicles (EVs) gains prominence. EVs, encompassing exosomes and microvesicles, mediate cell-to-cell communication and cargo transfer, impacting various biological processes, including inflammation and cancer progression. Toll-like receptor 4 (TLR4), a key sentinel of the innate immune system, recognizes both pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs), thereby triggering diverse signaling cascades and pro-inflammatory cytokine release. The intricate involvement of the TLR4 signaling pathway in chronic liver disease and HCC pathogenesis is discussed in this study. Moreover, we delve into the therapeutic potential of modulating the TLR4 pathway using EVs as novel therapeutic agents for HCC. This review underscores the multifaceted role of EVs in the context of HCC and proposes innovative avenues for targeted interventions against this formidable disease.

Toll-like receptor may be involved in acquired immune response in pearl oyster Pinctada fucata

The increasing experimental evidence suggests that there are some forms of specific acquired immunity in invertebrates, in which Toll-like receptors (TLRs) play vital roles in activating innate and adaptive immunity and have been comprehensively investigated in mammalian species. Yet, the immune mechanisms underlying TLR mediation in mollusks remain obscure. In this study, we identified a TLR13 gene in the pearl oyster Pinctada fucata for the first time and named it PfTLR13 which consists of a 5'-untranslated terminal region (5'-UTR) of 543 bp, an open reading frame (ORF) of 2667 bp, and a 3'-UTR of 729 bp. We found that PfTLR13 mRNA was expressed in all tissues examined, with the highest level in the gills. The expression of PfTLR13 in the gills of oysters exposed to Vibrio alginolyticus or pathogen-associated molecular patterns (PAMPs) (including LPS, PGN, and poly(I:C)) was significantly higher than in the control group. Interestingly, the immune response to the first stimulation was weaker than the response to the second stimulation, suggesting that the primary stimulation may lead to immune priming of TLR in pearl oysters, similar to acquired immunity in vertebrates. Furthermore, we found that PfTLR13 expression was differentially associated with allograft and xenograft in the pearl oyster P. fucata, with the highest expression levels observed at 12 h post-allograft and 24 h post-xenograft. Overall, our findings provide new insights into the immune mechanisms underlying TLR mediation in mollusks and suggest that PfTLR13 may play a crucial role in the specific acquired immunity of pearl oysters.

Antibiotics in Chronic Liver Disease and Their Effects on Gut Microbiota

Impairments in liver function lead to different complications. As chronic liver disease progresses (CLD), hypoalbuminemia and alterations in bile acid compositions lead to changes in gut microbiota and, therefore, in the host-microbiome interaction, leading to a proinflammatory state. Alterations in gut microbiota composition and permeability, known as gut dysbiosis, have important implications in CLD; alterations in the gut-liver axis are a consequence of liver disease, but also a cause of CLD. Furthermore, gut dysbiosis plays an important role in the progression of liver cirrhosis and decompensation, particularly with complications such as hepatic encephalopathy and spontaneous bacterial peritonitis. In relation to this, antibiotics play an important role in treating CLD. While certain antibiotics have specific indications, others have been subjected to continued study to determine whether or not they have a modulatory effect on gut microbiota. In contrast, the rational use of antibiotics is important, not only because of their disrupting effects on gut microbiota, but also in the context of multidrug-resistant organisms. The aim of this review is to illustrate the role of gut microbiota alterations in CLD, the use and impact of antibiotics in liver cirrhosis, and their harmful and beneficial effects.

New promising routes in peptic ulcers: Toll-like receptors and semaphorins

Peptic ulcers (PU) are one of the commonest yet problematic diseases found to be existing in the majority of the population. Today, drugs from a wide range of therapeutic classes are available for the management of the disease. Still, the complications of the condition are difficult to tackle and the side effect profile is quite a concern. The literature indicates that Toll-like receptors (TLRs) and Semaphorins (SEMAs) have been under study for their various pharmacological actions over the past few decades. Both these signalling pathways are found to regulate immunological and inflammatory responses. Moreover, receptors and signalling molecules from the family of TLRs and SEMAs are found to have bacterial recognition and antibacterial properties which are essential in eradicating Helicobacter pylori (H. pylori), one of the major causative agents of PU. Our understanding of SEMAs, a class of proteins involved in cell signalling, is relatively less developed compared to TLRs, another class of proteins involved in the immune response. SEMAs and TLRs play different roles in biological processes, with SEMAs primarily involved in guiding cell migration and axon guidance during development, while TLRs are responsible for recognizing pathogens and initiating an immune response. Here, in this review, we will discuss in detail the signalling cascade of TLRs and SEMAs and thereby understand its association with PU for future therapeutic targeting. The review also aims at providing an overview of the study that has been into exploring the role of these signalling pathways in the management of PU.

Functional Characterization of Verticillium dahliae Race 3-Specific Gene VdR3e in Virulence and Elicitation of Plant Immune Responses

Verticillium dahliae is a soilborne fungal pathogen that causes disease on many economically important crops. Based on the resistance or susceptibility of differential cultivars in tomato, isolates of V. dahliae are divided into three races. Avirulence (avr) genes within the genomes of the three races have also been identified. However, the functional role of the avr gene in race 3 isolates of V. dahliae has not been characterized. In this study, bioinformatics analysis showed that VdR3e, a cysteine-rich secreted protein encoded by the gene characterizing race 3 in V. dahliae, was likely obtained by horizontal gene transfer from the fungal genus Bipolaris. We demonstrate that VdR3e causes cell death by triggering multiple defense responses. In addition, VdR3e localized at the periphery of the plant cell and triggered immunity depending on its subcellular localization and the cell membrane receptor BAK1. Furthermore, VdR3e is a virulence factor and shows differential pathogenicity in race 3-resistant and -susceptible hosts. These results suggest that VdR3e is a virulence factor that can also interact with BAK1 as a pathogen-associated molecular pattern (PAMP) to trigger immune responses. IMPORTANCE Based on the gene-for-gene model, research on the function of avirulence genes and resistance genes has had an unparalleled impact on breeding for resistance in most crops against individual pathogens. The soilborne fungal pathogen, Verticillium dahliae, is a major pathogen on many economically important crops. Currently, avr genes of the three races in V. dahliae have been identified, but the function of avr gene representing race 3 has not been described. We investigated the characteristics of VdR3e-mediated immunity and demonstrated that VdR3e acts as a PAMP to activate a variety of plant defense responses and induce plant cell death. We also demonstrated that the role of VdR3e in pathogenicity was host dependent. This is the first study to describe the immune and virulence functions of the avr gene from race 3 in V. dahliae, and we provide support for the identification of genes mediating resistance against race 3.

Chemiluminescence-Based Assay to Monitor Early Oxidative Bursts in Soybean (Glycine max) Lateral Roots

The reactive oxygen species (ROS) burst assay is a valuable tool for studying pattern-triggered immunity (PTI) in plants. During PTI, the interaction between pathogen recognition receptors (PRRs) and pathogen-associated molecular patterns (PAMPs) leads to the rapid production of ROS in the apoplastic space. The resultant ROS can be measured using a chemiluminescent approach that involves the usage of horseradish peroxidase and luminol. Although several methods and protocols are available to detect early ROS bursts in leaf tissues, no dedicated method is available for root tissues. Here, we have established a reliable method to measure the PAMP-triggered ROS burst response in soybean lateral roots. In plants, lateral roots are the potential entry and colonization sites for pathogens in the rhizosphere. We have used important PAMPs such as chitohexaose, flagellin 22 peptide fragment, and laminarin to validate our method. In addition, we provide a detailed methodology for the isolation and application of fungal cell wall components to monitor the oxidative burst in soybean lateral roots. Furthermore, we provide methodology for performing ROS burst assays in soybean leaf discs with laminarin and fungal cell walls. This approach could also be applied to leaf and root tissues of other plant species to study the PTI response upon elicitor treatment. © 2023 Wiley Periodicals LLC. Basic Protocol: Reactive oxygen species (ROS) burst assay in soybean lateral root tissues Alternate Protocol: ROS burst assay in soybean leaf discs Support Protocol: Isolating fungal cell wall fractions.

Bacterial translocation occurs early in cirrhosis and triggers a selective inflammatory response

BACKGROUND

Experimental data suggest that bacterial translocation (BT) promotes systemic inflammation, portal hypertension, and circulatory dysfunction in advanced chronic liver disease (ACLD).

METHODS

Patients with ACLD undergoing hepatic venous pressure gradient (HVPG) measurement and absence of acute decompensation or infections were included (n = 249). Serum biomarkers of BT (lipopolysaccharide [LPS], lipoteichoic acid [LTA], bacterial DNA [bactDNA]), systemic inflammation and markers of circulatory dysfunction were assessed. T-cell subsets in intestinal biopsies (n = 7 ACLD, n = 4 controls) were analyzed by flow cytometry.

RESULTS

Patients had a median HVPG of 18 (12-21) mmHg and 56% had decompensated ACLD. LPS (0.04 [0.02-0.06] vs. 0.64 [0.30-1.06] EU/mL), LTA (4.53 [3.58-5.97] vs. 43.2 [23.2-109] pg/mL), and detection of bactDNA (≥ 5 pg/mL; 5% vs. 41%) were markedly higher in patients with ACLD than healthy controls (n = 40; p < 0.001) but were similar between different clinical stages of compensated and decompensated ACLD and displayed no meaningful correlation with HVPG and systemic hemodynamics. TNF-α and IL-10 correlated with LPS (Spearman's rs = 0.523, p < 0.001/rs = 0.143, p = 0.024) but not with LTA. Presence of bactDNA was associated with higher LPS (0.54 [0.28-0.95] vs. 0.88 [0.32-1.31] EU/mL, p = 0.001) and TNF-α (15.3 [6.31-28.1] vs. 20.9 [13.8-32.9] pg/mL). Patients with ACLD exhibited a decreased CD4:CD8-ratio and increased TH1-cells in the intestinal mucosa as compared to controls. During a median FU of 14.7 (8.20-26.5) months, bacterial antigens did not predict decompensation or liver-related death (in contrast to HVPG, IL-6, and MAP) as well as infections at 24 months.

CONCLUSION

BT occurs already in early ACLD stages and triggers a systemic inflammatory response via TNF-α and IL-10. Interestingly, BT markers showed no clear correlation with portal hypertension and circulatory dysfunction in patients with stable ACLD.

CLINICAL TRIAL NUMBER

NCT03267615.

Various Energetic Metabolism of Microglia in Response to Different Stimulations

The activation of the microglia plays an important role in the neuroinflammation induced by different stimulations associated with Alzheimer's disease (AD). Different stimulations, such as pathogen-associated molecular patterns (PAMPs), damage-associated molecular patterns (DAMPs) and cytokines, trigger a consequence of activation in the microglia with diverse changes of the microglial cell type response in AD. The activation of the microglia is often accompanied by metabolic changes in response to PAMPs, DAMPs and cytokines in AD. Actually, we do not know the distinct differences on the energetic metabolism of microglia when subject to these stimuli. This research assessed the changes of the cell type response and energetic metabolism in mouse-derived immortalized cells (BV-2 cells) induced by a PAMP (LPS), DAMPs (Aβ and ATP) and a cytokine (IL-4) in mouse-derived immortalized cells (BV-2 cells) and whether the microglial cell type response was improved by targeting the metabolism. We uncovered that LPS, a proinflammatory stimulation of PAMPs, modified the morphology from irregular to fusiform, with stronger cell viability, fusion rates and phagocytosis in the microglia accompanied by a metabolic shift to the promotion of glycolysis and the inhibition of oxidative phosphorylation (OXPHOS). Aβ and ATP, which are two known kinds of DAMPs that trigger microglial sterile activation, induced the morphology from irregular to amoebic, and significantly decreased others in the microglia, accompanied by boosting or reducing both glycolysis and OXPHOS. Monotonous pathological changes and energetic metabolism of microglia were observed under IL-4 exposure. Further, the inhibition of glycolysis transformed the LPS-induced proinflammatory morphology and decreased the enhancement of LPS-induced cell viability, the fusion rate and phagocytosis. However, the promotion of glycolysis exerted a minimal effect on the changes of morphology, the fusion rate, cell viability and phagocytosis induced by ATP. Our study reveals that microglia induced diverse pathological changes accompanied by various changes in the energetic metabolism in response to PAMPs, DAMPs and cytokines, and it may be a potential application of targeting the cellular metabolism to interfere with the microglia-mediated pathological changes in AD.

Recombinant Domain of Flagellin Promotes In Vitro a Chemotactic Inflammatory Profile in Human Immune Cells Independently of a Dendritic Cell Phenotype

Flagellin is the major component of the flagellum in gram-positive and -negative bacteria and is also the ligand for the Toll-like receptor 5 (TLR5). The activation of TLR5 promotes the expression of proinflammatory cytokines and chemokines and the subsequent activation of T cells. This study evaluated a recombinant domain from the amino-terminus D1 domain (rND1) of flagellin from Vibrio anguillarum, a fish pathogen, as an immunomodulator in human peripheral blood mononuclear cells (PBMCs) and monocyte-derived dendritic cells (MoDCs). We demonstrated that rND1 induced an upregulation of proinflammatory cytokines in PBMCs, characterized at the transcriptional level by an expression peak of 220-fold for IL-1β, 20-fold for IL-8, and 65-fold for TNF-α. In addition, at the protein level, 29 cytokines and chemokines were evaluated in the supernatant and were correlated with a chemotactic signature. MoDCs treated with rND1 showed low levels of co-stimulatory and HLA-DR molecules and kept an immature phenotype with a decreased phagocytosis of dextran. We probed that rND1 from a non-human pathogen promotes modulation in human cells, and it may be considered for further studies in adjuvant therapies based on pathogen-associated patterns (PAMPs).

Eructophagy: macrophages use autophagic machinery to burp out parts of their meal

The phagolysosome is an antimicrobial and degradative organelle that plays key roles in macrophage-mediated inflammatory and homeostatic functions. Whereas mature phagolysosomes are known to sequester and degrade their contents into basic nutrients, they were not previously assigned an active role in amplifying inflammation. We have described a novel macrophage process in which partially digested immunostimulatory PAMPs are released extracellularly from the mature phagolysosome via discrete events we term eructophagy. Eructophagy is induced by proinflammatory stimuli, negatively regulated by IL4 and MTOR, and is dependent on key autophagy proteins, including fusion machinery of degradative and secretory autophagy. We propose that macrophages use eructophagy to release processed PAMPs/DAMPs to amplify local inflammation.

The progress to establish optimal animal models for the study of acute-on-chronic liver failure

Acute-on-chronic liver failure (ACLF) defines a complicated and multifaceted syndrome characterized by acute liver dysfunction following an acute insult on the basis of chronic liver diseases. It is usually concurrent with bacterial infection and multi-organ failure resulting in high short-term mortality. Based on the cohort studies in ACLF worldwide, the clinical course of ACLF was demonstrated to comprise three major stages including chronic liver injury, acute hepatic/extrahepatic insult, and systemic inflammatory response caused by over-reactive immune system especially bacterial infection. However, due to the lack of optimal experimental animal models for ACLF, the progress of basic study on ACLF is limping. Though several experimental ACLF models were established, none of them can recapitulate and simulate the whole pathological process of ACLF patients. Recently, we have developed a novel mouse model for ACLF combining chronic liver injury [injection of carbon tetrachloride (CCl₄) for 8 weeks], acute hepatic insult (injection of a double dose CCl₄), and bacterial infection (intraperitoneal injection of Klebsiella pneumoniae), which could recapitulate the major clinical features of patients with ACLF worsened by bacterial infection.

What Exactly Is Inflammation (and What Is It Not?)

In medicine, inflammation is a fuzzy, overused word first coined by the Romans, the intended meaning and precise definition of which varies according to the person and the clinical context. It tends to carry a negative connotation as a response gone awry, like a raging, out-of-control wildfire that requires immediate control and containment lest it destroy all in its path; however, frequently overlooked or lost in the shuffle is the primordial importance of inflammation to health and survival. The precise definition of inflammation matters for several reasons, not least because of the over-liberal use of anti-inflammatory drugs to inhibit inflammation, which may, contrary to prevailing dogma that all inflammation is harmful, act counterproductively to prevent restitutio ad integrum. Using fire as a central analogy, this overview attempts to define inflammation, the better to determine how to manage it, i.e., whether to fan its flames, let it burn out, or suppress it entirely.

Self-referential immune recognition through C-type lectin receptors

The term "lectin" is derived from the Latin word lego- (aggregate) (Boyd & Shapleigh, 1954). Indeed, lectins' folds can flexibly alter their pocket structures just like Lego blocks, which enables them to grab a wide-variety of substances. Thus, this useful fold is well-conserved among various organisms. Through evolution, prototypic soluble lectins acquired transmembrane regions and signaling motifs to become C-type lectin receptors (CLRs). While CLRs seem to possess certain intrinsic affinity to self, some CLRs adapted to efficiently recognize glycoconjugates present in pathogens as pathogen-associated molecular patterns (PAMPs) and altered self. CLRs further extended their diversity to recognize non-glycosylated targets including pathogens and self-derived molecules. Thus, CLRs seem to have developed to monitor the internal/external stresses to maintain homeostasis by sensing various "unfamiliar" targets. In this review, we will summarize recent advances in our understanding of CLRs, their ligands and functions and discuss future perspectives.

Recent advances in the activation and regulation of the cGAS-STING pathway

The cGAS-STING pathway is responsible for cytoplasmic double-stranded DNA (dsDNA) -triggered innate immunity and involved in the pathology of various diseases including infection, autoimmune diseases, neurodegeneration and cancer. Understanding the activation and regulatory mechanisms of this pathway is critical to develop therapeutic strategies toward these diseases. Here, we review the signal transduction, cellular functions and regulations of cGAS and STING, particularly highlighting the latest understandings on the activation of cGAS by dsDNA and/or Manganese (Mn²⁺), STING trafficking, sulfated glycosaminoglycans (sGAGs)-induced STING polymerization and activation, and also regulation of the cGAS-STING pathway by different biocondensates formed via phase separation of proteins from host cells and viruses.

Rooting Out the Mechanisms of Root-Knot Nematode-Plant Interactions

Root-knot nematodes (RKNs; Meloidogyne spp.) engage in complex parasitic interactions with many different host plants around the world, initiating elaborate feeding sites and disrupting host root architecture. Although RKNs have been the focus of research for many decades, new molecular tools have provided useful insights into the biological mechanisms these pests use to infect and manipulate their hosts. From identifying host defense mechanisms underlying resistance to RKNs to characterizing nematode effectors that alter host cellular functions, the past decade of research has significantly expanded our understanding of RKN-plant interactions, and the increasing number of quality parasite and host genomes promises to enhance future research efforts into RKNs. In this review, we have highlighted recent discoveries, summarized the current understanding within the field, and provided links to new and useful resources for researchers. Our goal is to offer insights and tools to support the study of molecular RKN-plant interactions.

Ablation of Siglec-E augments brain inflammation and ischemic injury

Sialic acid immunoglobulin-like lectin E (Siglec-E) is a subtype of pattern recognition receptors found on the surface of myeloid cells and functions as a key immunosuppressive checkpoint molecule. The engagement between Siglec-E and the ligand α_2,8-linked disialyl glycans activates the immunoreceptor tyrosine-based inhibitory motif (ITIM) in its intracellular domain, mitigating the potential risk of autoimmunity amid innate immune attacks on parasites, bacteria, and carcinoma. Recent studies suggest that Siglec-E is also expressed in the CNS, particularly microglia, the brain-resident immune cells. However, the functions of Siglec-E in brain inflammation and injuries under many neurological conditions largely remain elusive. In this study, we first revealed an anti-inflammatory role for Siglec-E in lipopolysaccharide (LPS)-triggered microglial activation. We then found that Siglec-E was induced within the brain by systemic treatment with LPS in mice in a dose-dependent manner, while its ablation exacerbated hippocampal reactive microgliosis in LPS-treated animals. The genetic deficiency of Siglec-E also aggravated oxygen-glucose deprivation (OGD)-induced neuronal death in mouse primary cortical cultures containing both neurons and glial cells. Moreover, Siglec-E expression in ipsilateral brain tissues was substantially induced following middle cerebral artery occlusion (MCAO). Lastly, the neurological deficits and brain infarcts were augmented in Siglec-E knockout mice after moderate MCAO when compared to wild-type animals. Collectively, our findings suggest that the endogenous inducible Siglec-E plays crucial anti-inflammatory and neuroprotective roles following ischemic stroke, and thus might underlie an intrinsic mechanism of resolution of inflammation and self-repair in the brain.

Recognition of Microbe- and Damage-Associated Molecular Patterns by Leucine-Rich Repeat Pattern Recognition Receptor Kinases Confers Salt Tolerance in Plants

In plants, a first layer of inducible immunity is conferred by pattern recognition receptors (PRRs) that bind microbe- and damage-associated molecular patterns to activate pattern-triggered immunity (PTI). PTI is strengthened or followed by another potent form of immunity when intracellular receptors recognize pathogen effectors, termed effector-triggered immunity. Immunity signaling regulators have been reported to influence abiotic stress responses as well, yet the governing principles and mechanisms remain ambiguous. Here, we report that PRRs of a leucine-rich repeat ectodomain also confer salt tolerance in Arabidopsis thaliana, following recognition of cognate ligands such as bacterial flagellin (flg22 epitope) and elongation factor Tu (elf18 epitope), and the endogenous Pep peptides. Pattern-triggered salt tolerance (PTST) requires authentic PTI signaling components; namely, the PRR-associated kinases BAK1 and BIK1 and the NADPH oxidase RBOHD. Exposure to salt stress induces the release of Pep precursors, pointing to the involvement of the endogenous immunogenic peptides in developing plant tolerance to high salinity. Transcriptome profiling reveals an inventory of PTST target genes, which increase or acquire salt responsiveness following a preexposure to immunogenic patterns. In good accordance, plants challenged with nonpathogenic bacteria also acquired salt tolerance in a manner dependent on PRRs. Our findings provide insight into signaling plasticity underlying biotic or abiotic stress cross-tolerance in plants conferred by PRRs.[Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Resolving adjuvant mode of action to enhance vaccine efficacy

Adjuvants are a miscellaneous range of molecules and materials that can enhance the magnitude, functionality, breadth and durability of immune responses. Despite the multiplicity of compounds with adjuvant properties, less than a dozen are in clinical use in vaccines against infectious diseases. While many factors have contributed to their slow development, among the major challenges are the high safety and efficacy standards set by current adjuvants in human vaccines and our limited understanding of how adjuvants mediate their effects. This review outlines why it is so difficult to elucidate their mechanism of action, highlights areas that require in-depth research and discusses recent advancements that are revitalising adjuvant development. It is hoped that a fuller understanding of adjuvant sensing, signalling and function will facilitate the design of vaccines that promote sustained protective immunity against challenging bacterial and viral pathogens.

The simultaneous perception of self- and non-self-danger signals potentiates plant innate immunity responses

The simultaneous perception of endogenous and exogenous danger signals potentiates PAMP-triggered immunity in tomato and other downstream defence responses depending on the origin of the signal. Abstract Plant cells perceive a pathogen invasion by recognising endogenous or exogenous extracellular signals such as Damage-Associated Molecular Patterns (DAMPs) or Pathogen-Associated Molecular Patterns (PAMPs). In particular, DAMPs are intracellular molecules or cell wall fragments passive or actively released to the apoplast, whose extracellular recognition by intact cells triggers specific immune signalling, the so-called DAMP-triggered immunity. The extracellular recognition of DAMPs and PAMPs leads to a very similar intracellular signalling, and this similarity has generated a biological need to know why plants perceive molecules with such different origins and with overlapped innate immunity responses. Here, we report that the simultaneous perception of DAMPs and a PAMP strengthens early and late plant defence responses. To this aim, we studied classical PTI responses such as the generation of ROS and MAPK phosphorylation, but we also monitored the biosynthesis of phytocytokines and performed a non-targeted metabolomic analysis. We demonstrate that co-application of the bacterial peptide flagellin with the DAMPs cyclic AMP or cellobiose amplifies PAMP-triggered immunity responses. Both co-applications enhanced the synthesis of phytocytokines, but only simultaneous treatments with cAMP strengthened the flagellin-dependent metabolomic responses. In addition, cAMP and cellobiose treatments induced resistance against the hemibiotrophic bacteria Pseudomonas syringae pv. tomato DC3000. Overall, these results indicate that the complex mixture of DAMPs and PAMPs carries specific information that potentiates plant defence responses. However, downstream responses seem more specific depending on the composition of the mixture.

Plant Antimicrobial Peptides (PAMPs): Features, Applications, Production, Expression, and Challenges

The quest for an extraordinary array of defense strategies is imperative to reduce the challenges of microbial attacks on plants and animals. Plant antimicrobial peptides (PAMPs) are a subset of antimicrobial peptides (AMPs). PAMPs elicit defense against microbial attacks and prevent drug resistance of pathogens given their wide spectrum activity, excellent structural stability, and diverse mechanism of action. This review aimed to identify the applications, features, production, expression, and challenges of PAMPs using its structure–activity relationship. The discovery techniques used to identify these peptides were also explored to provide insight into their significance in genomics, transcriptomics, proteomics, and their expression against disease-causing pathogens. This review creates awareness for PAMPs as potential therapeutic agents in the medical and pharmaceutical fields, such as the sensitive treatment of bacterial and fungal diseases and others and their utilization in preserving crops using available transgenic methods in the agronomical field. PAMPs are also safe to handle and are easy to recycle with the use of proteases to convert them into more potent antimicrobial agents for sustainable development.

'Candidatus Liberibacter asiaticus'-Encoded BCP Peroxiredoxin Suppresses Lipopolysaccharide-Mediated Defense Signaling and Nitrosative Stress In Planta

The lipopolysaccharides (LPS) of gram-negative bacteria trigger a nitrosative and oxidative burst in both animals and plants during pathogen invasion. Liberibacter crescens strain BT-1 is a surrogate for functional genomic studies of the uncultured pathogenic 'Candidatus Liberibacter' spp. that are associated with severe diseases such as citrus greening and potato zebra chip. Structural determination of L. crescens LPS revealed the presence of a very long chain fatty acid modification. L. crescens LPS pretreatment suppressed growth of Xanthomonas perforans on nonhost tobacco (Nicotiana benthamiana) and X. citri subsp. citri on host orange (Citrus sinensis), confirming bioactivity of L. crescens LPS in activation of systemic acquired resistance (SAR). L. crescens LPS elicited a rapid burst of nitric oxide (NO) in suspension cultured tobacco cells. Pharmacological inhibitor assays confirmed that arginine-utilizing NO synthase (NOS) activity was the primary source of NO generation elicited by L. crescens LPS. LPS treatment also resulted in biological markers of NO-mediated SAR activation, including an increase in the glutathione pool, callose deposition, and activation of the salicylic acid and azelaic acid (AzA) signaling networks. Transient expression of 'Ca. L. asiaticus' bacterioferritin comigratory protein (BCP) peroxiredoxin in tobacco compromised AzA signaling, a prerequisite for LPS-triggered SAR. Western blot analyses revealed that 'Ca. L. asiaticus' BCP peroxiredoxin prevented peroxynitrite-mediated tyrosine nitration in tobacco. 'Ca. L. asiaticus' BCP peroxiredoxin (i) attenuates NO-mediated SAR signaling and (ii) scavenges peroxynitrite radicals, which would facilitate repetitive cycles of 'Ca. L. asiaticus' acquisition and transmission by fecund psyllids throughout the limited flush period in citrus.[Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Genomic and transcriptomic identification of the cathepsin superfamily in the Mediterranean mussel Mytilus galloprovincialis

Cathepsins are lysosomal enzymes that participate in important physiological processes, such as development, tissue remodelling, senescence and innate and adaptive immunity. The description of these proteins in molluscs is fragmented and incomplete. In the present work, we identified most of the cathepsin family members in the bivalve Mytilus galloprovincialis by screening published genomic and transcriptomic information. In this specie, the cathepsin family is composed of 41 proteins showing a high diversification of cathepsins D, L and F, not previously observed in other taxonomic groups. Specific set of cathepsins are constitutively expressed in the different mussel tissues. Transcriptomic analyses suggested coordinated activity of the different cathepsins and their sequential activation during larval development. Cathepsins also play an important role in the immune response of bivalves, and different immune pathways seem to be activated in response to Vibrio splendidus infection.

A novel ML protein functions as a pattern recognition protein in antibacterial responses in Eriocheir sinensis

The myeloid differentiation factor 2 (MD-2)-related lipid recognition (ML) domain is present in MD-2, MD-1, GM2-activator protein (GM2A) and Niemann-Pick disease type C2 (NPC2). ML proteins function in antibacterial signal transduction and lipid metabolism in vertebrates, but the mechanism in invertebrates is unknown. In this study, we found that ML proteins were involved in bacterial resistance in Chinese mitten crab (Eriocheir sinensis). One member, EsML3, a soluble, bacterial-induced pattern recognition protein was upregulated in hemocytes following bacterial challenge. Recombinant EsML3 bound to Gram-negative bacteria (Vibrio parahaemolyticus) and Gram-positive bacteria (Staphylococcus aureus) by interaction with peptidoglycan, lipopolysaccharide. EsML3 showed no direct bacteriostatic or bacteriocidal activity. Pre-incubating bacteria with rEsML3 significantly promoted in vivo bacterial clearance. EsML3 also promoted phagocytic activity and plays a role against bacterial infection. In summary, EsML3 mediates cellular immune responses by recognising invasive microorganisms, promoting bacterial clearance and phagocytosis against bacterial infection in crab.

Interferon gamma, lipopolysaccharide, and modified-live viral vaccines stimulation alter the mRNA expression of tumor necrosis factor α, inducible nitric oxide synthase, and interferon β in bovine alveolar macrophages

To understand the pathogenesis of bovine respiratory disease (BRD), it is necessary to elucidate the mechanisms of alveolar macrophage regulation by cytokines and pathogen-associated molecular patterns (PAMPs). Moreover, "non-specific effects (NSEs)" an innate immune regulatory mechanism in response to vaccines containing PAMPs, has recently attracted attention. It may be applied to BRD control, but there is limited knowledge in bovine. To investigate this, we stimulated alveolar macrophages in vitro with lipopolysaccharide (LPS), polyinosinic-polycytidylic acid sodium salt (Poly I:C), interferon gamma (IFN-γ), and modified-live viral (MLV) vaccines, respectively, and analyzed changes in tumor necrosis factor alpha (TNF-α), inducible nitric oxide synthase (iNOS), and interferon beta (IFN-β) mRNA expression levels. mRNA expression levels of TNF-α, iNOS, and IFN-β were significantly increased in bovine alveolar macrophages stimulated by IFN-γ and MLV vaccine; LPS, IFN-γ, and MLV vaccine; and MLV vaccine only, respectively. Additionally, all MLV vaccine-stimulated mRNA expression increases were observed in a concentration-dependent manner. These results revealed in part, the mechanism of bovine alveolar macrophage regulation by cytokines and PAMPs. Understanding the regulatory mechanisms of alveolar macrophages will contribute to understanding the pathogenesis of BRD and preventive and therapeutic BRD management based on NSEs.

Scavenger receptors in host defense: from functional aspects to mode of action

Scavenger receptors belong to a superfamily of proteins that are structurally heterogeneous and encompass the miscellaneous group of transmembrane proteins and soluble secretory extracellular domain. They are functionally diverse as they are involved in various disorders and biological pathways and their major function in innate immunity and homeostasis. Numerous scavenger receptors have been discovered so far and are apportioned in various classes (A-L). Scavenger receptors are documented as pattern recognition receptors and known to act in coordination with other co-receptors such as Toll-like receptors in generating the immune responses against a repertoire of ligands such as microbial pathogens, non-self, intracellular and modified self-molecules through various diverse mechanisms like adhesion, endocytosis and phagocytosis etc. Unlike, most of the scavenger receptors discussed below have both membrane and soluble forms that participate in scavenging; the role of a potential scavenging receptor Angiotensin-Converting Enzyme-2 has also been discussed whereby only its soluble form might participate in preventing the pathogen entry and replication, unlike its membrane-bound form. This review majorly gives an insight on the functional aspect of scavenger receptors in host defence and describes their mode of action extensively in various immune pathways involved with each receptor type. Video abstract.

Molecular and Microscopic Methods of Quantifying Candida albicans Cell Wall PAMP Exposure

The cell wall of Candida albicans is a multilayered structure consisting of polysaccharides and proteins. The inner cell wall layer is comprised of chitin and β1-3 and β1-6-glucan which contribute to the overall shape and structure of the cell, while the outer layer of highly glycosylated mannoproteins provides key functional traits such as cell adhesion required for virulence. However, the cell wall is not a static structure but is constantly being remodeled in response to the external environment. Given that all of the cell wall components act as pathogen-associated molecular patterns (PAMPs) that are recognized by a variety of receptors on the surface of innate immune cells, remodeling of the cell wall can have a dramatic impact on the host-pathogen interaction. For example, during growth in standard media, C. albicans shields its major cell wall PAMPs from the innate immune system, but during growth in acidic environments as encountered during colonization of the female reproductive tract, key PAMPs become exposed on the fungal cell surface initiating a strong pro-inflammatory innate immune response. The impact of environmental adaptation on fungal cell wall remodeling, and the subsequent impact this has on the host-pathogen interaction, has been the subject of much research. In this chapter, we outline techniques to assess cell wall components in both resting and environmentally adapted C. albicans cells.

Labelling of Candida auris Cell Walls to Examine Levels of PAMP Exposure by Flow Cytometry and Fluorescence Microscopy

Pathogen-associated molecular patterns (PAMPs) of the fungal cell wall are primary targets for the innate immune system of animals. Therefore, characterizing PAMP exposure of fungal pathogens helps to elucidate how they interact with their hosts at a molecular level. Fluorescent labelling can be used to monitor exposure of multiple fungal cell wall PAMPs in a single experiment. Here, we describe a protocol to simultaneously label chitin, mannan, and β-1,3-glucan in Candida auris to study these PAMPs by fluorescence microscopy and allow high-throughput examination of their exposure by flow cytometry.

Toll-Like Receptors (TLRs) in Health and Disease: An Overview

Toll-like receptors were discovered as proteins playing a crucial role in the dorsoventral patterning during embryonic development in the Drosophila melanogaster (D. melanogaster) almost 40 years ago. Subsequently, further research also showed a role of the Toll protein or Toll receptor in the recognition of Gram-positive bacterial and fungal pathogens infecting D. melanogaster. In 1997, the human homolog was reported and the receptor was named the Toll-like receptor 4 (TLR4) that recognizes lipopolysaccharide (LPS) of the Gram-negative bacteria as a pathogen-associated molecular pattern (PAMP). Identification of TLR4 in humans filled the long existing gap in the field of infection and immunity, addressing the mystery surrounding the recognition of foreign pathogens/microbes by the immune system. It is now known that mammals (mice and humans) express 13 different TLRs that are expressed on the outer cell membrane or intracellularly, and which recognize different PAMPs or microbe-associated molecular patterns (MAMPs) and death/damage-associated molecular patterns (DAMPs) to initiate the protective immune response. However, their dysregulation generates profound and prolonged pro-inflammatory immune responses responsible for different inflammatory and immune-mediated diseases. This chapter provides an overview of TLRs in the control of the immune response, their association with different diseases, including TLR single nucleotide polymorphisms (SNPs), interactions with microRNAs (miRs), use in drug development and vaccine design, and expansion in neurosciences to include pain, addiction, metabolism, reproduction, and wound healing.

The Effects of Pathogen-Associated Molecular Patterns on Peripheral Blood Monocytes in Patients with Non-alcoholic Fatty Liver Disease

BACKGROUND

Innate immune responses to gut-derived pathogen-associated molecular patterns (PAMPs) have been implicated in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). Whether NAFLD patients have increased sensitivity to PAMP exposure has yet to be reported.

METHODS

Peripheral blood mononuclear cell (PBMC)/monocytes were exposed to lipopolysaccharide (LPS), Pam3CSK4, or BSA conjugated palmitate in vitro. Changes in toll-like receptors (TLR), cytokines, and chemokine receptors (CR) expressions were documented by flow cytometry and/or enzyme-linked immunoabsorbent assays (ELISAs).

RESULTS

TLR2 and TLR4 expression were similar at baseline and increased to a similar extent (TLR2) or remained unchanged (TLR4) following PAMP exposure in NAFLD and healthy control (HC) monocytes. Proinflammatory IL-1β and IL-6 levels were similar at baseline but increased in a concentration-dependent manner to a greater extent in NAFLD PBMCs. CCR1 and CCR2 expressions at baseline were similar and decreased to a similar extent in NAFLD and HC monocytes. The extent of PAMP-induced proinflammatory cytokine release correlated with evidence of hepatocyte injury (CK18M30 levels).

DISCUSSION

NAFLD patients have increased proinflammatory cytokine responses following exposure to PAMPs relative to HC subjects. This response is concentration-dependent and correlates with the extent of hepatic injury.

Multilayer regulatory landscape during pattern-triggered immunity in rice

Upon fungal and bacterial pathogen attack, plants launch pattern-triggered immunity (PTI) by recognizing pathogen-associated molecular patterns (PAMPs) to defend against pathogens. Although PTI-mediated response has been widely studied, a systematic understanding of the reprogrammed cellular processes during PTI by multi-omics analysis is lacking. In this study, we generated metabolome, transcriptome, proteome, ubiquitome and acetylome data to investigate rice (Oryza sativa) PTI responses to two PAMPs, the fungi-derived chitin and the bacteria-derived flg22. Integrative multi-omics analysis uncovered convergence and divergence of rice responses to these PAMPs at multiple regulatory layers. Rice responded to chitin and flg22 in a similar manner at the transcriptome and proteome levels, but distinct at the metabolome level. We found that this was probably due to post-translational regulation including ubiquitination and acetylation, which reshaped gene expression by modulating enzymatic activities, and possibly led to distinct metabolite profiles. We constructed regulatory atlas of metabolic pathways, including the defence-related phenylpropanoid and flavonoid biosynthesis and linoleic acid derivative metabolism. The multi-level regulatory network generated in this study sets the foundation for in-depth mechanistic dissection of PTI in rice and potentially in other related poaceous crop species.

ACLY Nuclear Translocation in Human Macrophages Drives Proinflammatory Gene Expression by NF-κB Acetylation

Macrophage stimulation by pathogen-associated molecular patterns (PAMPs) like lipopolysaccharide (LPS) or lipoteichoic acid (LTA) drives a proinflammatory phenotype and induces a metabolic reprogramming to sustain the cell’s function. Nevertheless, the relationship between metabolic shifts and gene expression remains poorly explored. In this context, the metabolic enzyme ATP citrate lyase (ACLY), the producer of citrate-derived acetyl-coenzyme A (CoA), plays a critical role in supporting a proinflammatory response. Through immunocytochemistry and cytosol–nucleus fractionation, we found a short-term ACLY nuclear translocation. Protein immunoprecipitation unveiled the role of nuclear ACLY in NF-κB acetylation and in turn its full activation in human PBMC-derived macrophages. Notably, sepsis in the early hyperinflammatory phase triggers ACLY-mediated NF-κB acetylation. The ACLY/NF-κB axis increases the expression levels of proinflammatory genes, including SLC25A1—which encodes the mitochondrial citrate carrier—and ACLY, thus promoting the existence of a proinflammatory loop involving SLC25A1 and ACLY genes.

A STING inhibitor suppresses EBV-induced B cell transformation and lymphomagenesis

Epstein‐Barr virus‐associated lymphoproliferative disease (EBV‐LPD) is frequently fatal. Innate immunity plays a key role in protecting against pathogens and cancers. The stimulator of interferon genes (STING) is regarded as a key adaptor protein allowing DNA sensors recognizing exogenous cytosolic DNA to activate the type I interferon signaling cascade. In terms of EBV tumorigenicity, the role of STING remains elusive. Here we showed that treatment with the STING inhibitor, C‐176, suppressed EBV‐induced transformation in peripheral blood mononuclear cells. In an EBV‐LPD mouse model, C‐176 treatment also inhibited tumor formation and prolonged survival. Treatment with B cells alone did not affect EBV transformation, but suppression of EBV‐induced transformation was observed in the presence of T cells. Even without direct B cell‐T cell contact in a transwell system, the inhibitor reduced the transformation activity, indicating that intercellular communication by humoral factors was critical to prevent EBV‐induced transformation. These findings suggest that inhibition of STING signaling pathway with C‐176 could be a new therapeutic target of EBV‐LPD.

Immune discrimination of environmental spectrum through C-type lectin receptors

Our bodies are continuously assaulted by infection and tissue damage; most of these injurious insults are primarily sensed by immune receptors to maintain tissue homeostasis. Although immune recognition of proteins or nucleic acids has been well characterized, the molecular mechanisms by which immune receptors discriminate lipids to elicit suitable immune responses remain elusive. Recent studies have demonstrated that the C-type lectin receptor (CLR) family functions as immune sensors for adjuvant lipids derived from pathogens and damaged-tissues, thereby promoting innate/acquired immunity. In this review, we will discuss how these receptors recognize lipid components to initiate appropriate, but sometimes deleterious, immune responses against environmental stimuli. We will also discuss an aspect of inhibitory CLRs; their ligands might reflect normal self which silences the immune response regarded as "silence"-associated molecular patterns or may be associated with escape strategies of pathogens as "evasion"-associated molecular patterns.

Phytophthora infection signals-induced translocation of NAC089 is required for endoplasmic reticulum stress response-mediated plant immunity

Plants deploy various immune receptors to recognize pathogen-derived extracellular signals and subsequently activate the downstream defense response. Recently, increasing evidence indicates that the endoplasmic reticulum (ER) plays a part in the plant defense response, known as ER stress-mediated immunity (ERSI), that halts pathogen infection. However, the mechanism for the ER stress response to signals of pathogen infection remains unclear. Here, we characterized the ER stress response regulator NAC089, which was previously reported to positively regulate programed cell death (PCD), functioning as an ERSI regulator. NAC089 translocated from the ER to the nucleus via the Golgi in response to Phytophthora capsici culture filtrate (CF), which is a mixture of pathogen-associated molecular patterns (PAMPs). Plasma membrane localized co-receptor BRASSINOSTEROID INSENSITIVE 1-associated receptor kinase 1 (BAK1) was required for the CF-mediated translocation of NAC089. The nuclear localization of NAC089, determined by the NAC domain, was essential for immune activation and PCD. Furthermore, NAC089 positively contributed to host resistance against the oomycete pathogen P. capsici and the bacteria pathogen Pseudomonas syringae pv. tomato (Pst) DC3000. We also proved that NAC089-mediated immunity is conserved in Nicotiana benthamiana. Together, we found that PAMP signaling induces the activation of ER stress in plants, and that NAC089 is required for ERSI and plant resistance against pathogens.

Using PAMPs and DAMPs as adjuvants in cancer vaccines

Immunotherapy for cancer has attracted considerable attention. As one of the immunotherapeutics, tumor vaccines exert great potential for cancer immunotherapy. The most important components in tumor vaccines are antigens and adjuvants, which determine the therapeutic safety and efficacy, respectively. After decades of research, many types of adjuvants have been developed. Although these adjuvants can induce strong and long-lasting immune responses in tumor immunity, they also cause more severe toxic side effects and are therefore not suitable for use in humans. With the development of innate immunity research, pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) are receiving more attention in vaccine design. However, whether they have the potential to become new adjuvants remains to be elucidated. The purpose of this review is to provide newideas for the research and development of new adjuvants by discussing the mechanisms and related functions of PAMPs and DAMPs.

Differential Expression of Long Non-Coding RNA (lncRNA) in Mediterranean Mussel (Mytilus galloprovincialis) Hemocytes under Immune Stimuli

The Mediterranean mussel is one of the most economically relevant bivalve mollusk species in Europe and China. The absence of massive mortalities and their resistance to pathogens affecting other cultured bivalves has been under study in recent years. The transcriptome response of this species to different immune stimuli has been extensively studied, and even the complexity of its genome, which has recently been sequenced, has been suggested as one of the factors contributing to this resistance. However, studies concerning the non-coding RNA profiles remain practically unexplored-especially those corresponding to the lncRNAs. To the best of our knowledge, this is the second characterization and study of lncRNAs in this bivalve species. In this work, we identified the potential repertoire of lncRNAs expressed in mussel hemocytes, and using RNA-Seq we analyzed the lncRNA profile of mussel hemocytes stimulated in vitro with three different immune stimuli: LPS, poly I:C, and β-glucans. Compared to unstimulated hemocytes, LPS induced the highest modulation of lncRNAs, whereas poly I:C and β-glucans induced a similar discrete response. Based on the potential cis-regulatory activity of the lncRNAs, we identified the neighboring protein-coding genes of the regulated lncRNAs to estimate-at least partially-the processes in which they are implicated. After applying correlation analyses, it seems that-especially for LPS-the lncRNAs could participate in the regulation of gene expression, and substantially contribute to the immune response.

Hot water extract of Pleurotus pulmonarius stalk waste enhances innate immune response and immune-related gene expression in red hybrid tilapia Oreochromis sp. following challenge with pathogen-associated molecular patterns

In aquaculture, commercial fish such as red hybrid tilapia are usually raised at high density to boost the production within a short period of time. This overcrowded environment, however, may cause stress to the cultured fish and increase susceptibility to infectious diseases. Antibiotics and chemotherapeutics are used by fish farmers to overcome these challenges, but this may increase the production cost. Studies have reported on the potential of mushroom polysaccharides that can act as immunostimulants to enhance the immune response and disease resistance in fish. In the current study, hot water extract (HWE) from mushroom stalk waste (MSW) was used to formulate fish feed and hence administered to red hybrid tilapia to observe the activation of immune system. Upon 30 days of feeding, the fish were challenged with pathogen-associated molecular patterns (PAMPs) such as lipopolysaccharides (LPS) and polyinosinic:polycytidylic acid (poly (I:C)) to mimic bacterial and viral infection, respectively. HWE supplementation promoted better feed utilisation in red hybrid tilapia although it did not increase the body weight gain and specific growth rate compared to the control diet. The innate immunological parameters such as phagocytic activity and respiratory burst activity were significantly higher in HWE-supplemented group than that of the control group following PAMPs challenges. HWE-supplemented diet also resulted in higher mRNA transcription of il1b and tnfa in midgut, spleen and head kidney at 1-day post PAMPs injection. Tlr3 exhibited the highest upregulation in the HWE fed fish injected with poly (I:C). At 3-days post PAMPs injection, both ighm and tcrb expression were upregulated significantly in the spleen and head kidney. Results showed that HWE supplementation enhances the immune responses of red hybrid tilapia and induced a higher serum bactericidal activity against S. agalactiae.

Thrombosis in COVID-19 infection: Role of platelet activation-mediated immunity

Background

Thrombosis plays an important role in the Coronavrus Disease 2019 (COVID-19) infection-related complications such as acute respiratory distress syndrome and myocardial infarction. Multiple factors such as oxygen demand injuries, endothelial cells injury related to infection, and plaque formation.

Main body

Platelets obtained from the patients may have severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA, showing that the increased activation potential recommends platelet can be hyper-activated in severely ill SARS-CoV-2 cases. Platelets contain multiple receptors that interact with specific ligands. Pathogen’s receptors such as Toll-like receptors (TLRs), NOD-like receptor, C-type lectin receptor family, glycoprotein (GP) such as GPαIIbβ3 and GPIbα which allow pathogens to interact with platelets. Platelet TLRs and NOD2 are involved in platelet activation and thrombosis. Accordingly, TLRs are critical receptors that could recognize various endogenous damage-associated molecular patterns and exogenous pathogen-associated molecular patterns (PAMPs). TLRs are considered as important components in the activation of innate immunity response against pathogenic and non-pathogenic components like damaged tissues. TLRs-1,-2,-4,-6,-7 expression on or within platelets has been reported previously. Various PAMPs were indicated to be capable of binding to platelet-TLRs and inducing both the activation and promotion of downstream proinflammatory signaling cascade.

Conclusion

It is possible that the increased TLRs expression and TLR-mediated platelets activation during COVID-19 may enhance vascular and coronary thrombosis. It may be hypothesized using TLRs antagonist and monoclonal antibody against P-selectin, as the marker of leukocyte recruitment and platelet activation, besides viral therapy provide therapeutic advances in fighting against the thrombosis related complications in COVID-19.

Viral proteins recognized by different TLRs

Virus invasion activates the host's innate immune response, inducing the production of numerous cytokines and interferons to eliminate pathogens. Except for viral DNA/RNA, viral proteins are also targets of pattern recognition receptors. Membrane-bound receptors such as Toll-like receptor (TLR)1, TLR2, TLR4, TLR6, and TLR10 relate to the recognition of viral proteins. Distinct TLRs perform both protective and detrimental roles for a specific virus. Here, we review viral proteins serving as pathogen-associated molecular patterns and their corresponding TLRs. These viruses are all enveloped, including respiratory syncytial virus, hepatitis C virus, measles virus, herpesvirus human immunodeficiency virus, and coronavirus, and can encode proteins to activate innate immunity in a TLR-dependent way. The TLR-viral protein relationship plays an important role in innate immunity activation. A detailed understanding of their pathways contributes to a novel direction for vaccine development.