Nlrp3-dependent IL-1β inhibits CD103+ dendritic cell differentiation in the gut

Regulation and therapeutic potential of NLRP3 inflammasome in intestinal diseases

The NOD-like receptor family, particularly the protein 3 that contains the pyrin domain (NLRP3), is an intracellular sensing protein complex responsible for detecting patterns associated with pathogens and injuries. NLRP3 plays a crucial role in the innate immune response. Currently, a wide range of research has indicated the crucial importance of NLRP3 in various inflammatory conditions. Similarly, the NLRP3 inflammasome plays a significant role in preserving intestinal balance and impacting the advancement of diseases. In addition, several randomized trials have demonstrated the safety and efficacy of targeting NLRP3 in the treatment of colitis, colorectal cancer, and related diseases. This review explores the mechanisms of NLRP3 assembly and activation in the gut. We describe its pathological significance in intestinal diseases. Finally, we summarize current and future therapeutic approaches targeting NLRP3 for intestinal diseases.

Swaying the advantage: multifaceted functions of inflammasomes in adaptive immunity

Eukaryotic cells are equipped with cytoplasmic sensors that recognize diverse pathogen- or danger-associated molecular patterns. In cells of the myeloid lineage, activation of these sensors leads to the assembly of a multimeric protein complex, called the inflammasome, that culminates in the production of inflammatory cytokines and pyroptosis. Recently, investigation of the inflammasomes in lymphocytes led to the discovery of functional pathways that were initially believed to be confined to the innate arm of the immune system. Thus, the adapter protein apoptosis-associated speck-like protein containing a CARD (ASC) was documented to play a critical role in antigen uptake by dendritic cells, and regulation of T- and B-cell motility at several stages, and absent in melanoma 2 (AIM2) was found to act as a modulator of regulatory T-cell differentiation. Remarkably, NLRP3 was demonstrated to act as a transcription factor that controls Th2 cell polarization, and as a negative regulator of regulatory T-cell differentiation by limiting Foxp3 expression. In B lymphocytes, NLRP3 plays a role in the transcriptional network that regulates B-cell development and homing, and its activation is essential for germinal center formation and maturation of high-affinity antibody responses. Such recently discovered inflammasome-mediated functions in T and B lymphocytes offer multiple cross-talk opportunities for the innate and adaptive arms of the immune system. A better understanding of the dialog between inflammasomes and intracellular components could be beneficial for therapeutic purposes in restoring immune homeostasis and mitigating inflammation in a wide range of disorders.

Metagenomic Sequencing Combined with Metabolomics to Explore Gut Microbiota and Metabolic Changes in Mice with Acute Myocardial Infarction and the Potential Mechanism of Allicin

Background

Acute myocardial infarction (AMI) is a significant contributor to global morbidity and mortality. Allicin exhibits promising therapeutic potential in AMI as a primary bioactive component derived from garlic; however, its underlying mechanisms remain incompletely elucidated.

Methods

Our study induced AMI in mice by ligating the left coronary artery, and administered allicin orally for 28 days. The cardioprotective effects of allicin treatment were comprehensively assessed using echocardiography, histopathological examinations, intestinal barrier function, and serum inflammatory factors. The potential mechanisms of allicin were elucidated through analysis of metagenomics and serum metabolomics. Network pharmacology (NP) was used to further investigate and validate the possible molecular mechanisms of allicin.

Results

Our findings revealed allicin's capacity to ameliorate cardiac impairments, improve intestinal barrier integrity, and reduce serum IL-18 and IL-1β levels after AMI. Further analysis demonstrated that the administration of allicin has the potential to ameliorate intestinal flora disorder following AMI by modulating the abundance of beneficial bacteria, such as g_Lactobacillus, g_Prevotella, g_Alistipes, and g_Limosilactobacillus, while reducing the abundance of harmful bacteria g_Parasutterella. Additionally, it exhibits the ability to enhance myocardial energy metabolism flexibility through modulating metabolites and key enzymes associated with the fatty acid metabolic pathway. Mechanistically, NP and in vivo experiments indicated that allicin might suppress pyroptosis and reduce inflammatory response via blocked activation of the NF-κB-mediated NLRP3/Caspase-1/GSDMD pathway. Moreover, Spearman correlation analysis suggested a significant association between the allicin-induced alterations in microbiota and metabolites with cardiac function and inflammatory cytokines.

Conclusion

Our study demonstrated that allicin alleviated myocardial injury and reduced inflammatory response by inhibiting the NF-κB-mediated NLRP3/Caspase-1/GSDMD pathway while remodeling microbiota disturbance, improving serum metabolic disorder, and enhancing the intestinal barrier. These research findings offer a novel perspective on the potential therapeutic value of allicin as an adjunctive dietary supplement to conventional treatments for AMI.

Optimized Spheroid Model of Pancreatic Cancer Demonstrates Influence of Macrophage-T Cell Interaction for Intratumoral T Cell Motility

BACKGROUND

Most spheroid models use size measurements as a primary readout parameter; some models extend analysis to T cell infiltration or perform caspase activation assays. However, to our knowledge, T cell motility analysis is not regularly included as an endpoint in imaging studies on cancer spheroids.

METHODS

Here, we intend to demonstrate that motility analysis of macrophages and T cells is a valuable functional endpoint for studies on molecular interventions in the tumor microenvironment. In particular, T cell migration analysis represents the final step of effector function, as T cells engage with targets cells upon cytotoxic interaction, which is represented by an arrest within the spheroid volume. Therefore, T cell arrest is a novel readout parameter of T cell effector function in spheroids.

RESULTS

Here, we demonstrate that incubation of macrophages with nigericin for NLRP3 activation increases T cell velocity, but results in decreased T cellular arrest. This is paralleled by reduced rejection kinetics of pancreatic cancer spheroids in the presence of antigen-dependent T cells and nigericin-treated macrophages. Our model demonstrates consistent changes in T cell motility upon coculturing of T cells and tumors cells with macrophages, including influences of molecular interventions such as NLRP3 activation.

CONCLUSIONS

Motility analysis using a spheroid model of pancreatic cancer is a more sophisticated alternative to in vitro cytotoxicity assays measuring spheroid size. Ultimately, an optimized spheroid model might replace at least some aspects of animal experiments investigating T cell effector function.

Terpinen-4-ol Improves the Intestinal Barrier Function of the Colon in Immune-Stressed Weaning Piglets

The aim of this study was to investigate the effects of terpinen-4-ol (TER) supplementation on the intestinal barrier function of pigs. Five groups of fifty 28-day-old piglets with comparable body weights were randomly assigned to the following groups: the control group (CON), the lipopolysaccharide group (LPS), the low TER group (PLT), the middle TER group (PMT), and the high TER group (PHT). The basal diet was given to the CON and LPS groups, and 30, 60, or 90 mg/kg TER was added to the basal diet for the TER groups. After the 21-day trial period, piglets in the LPS and TER groups received an intraperitoneal injection of 100 μg/kg body weight of LPS, whereas the piglets in the CON group received an injection of 0.9% normal saline solution. The results showed that LPS stimulation resulted in a decrease (p < 0.05) in the depth of colonic crypts in piglets, which was greater (p < 0.05) in the TER group. Compared with those in the CON group, the number of goblet cells and MUC2 expression were decreased in the colon of piglets in the LPS group, while these parameters were increased in the PMT group (p < 0.05). The malondialdehyde (MDA) content was greater in the colon of the LPS group than in that of the CON group, while the activities of glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), and catalase (CAT) were lower in the colon of the LPS group; conversely, the MDA content was lower in the colons of the PLT and PMT groups than in those of the LPS group (p < 0.05). TER also reduced (p < 0.05) LPS-induced upregulation of IL-1β and TNF-α expression, along with the relative gene expression of NLRP3, ASC, and caspase-1 in the colon of piglets (p < 0.05). Compared with those in the CON group, the abundances of Firmicutes and UCG-005 in the LPS group were lower (p < 0.05), and those in the TER group were significantly greater than those in the LPS group. Compared with those in the CON group, the abundance of Proteobacteria in the LPS group increased (p < 0.05), while the abundance of Actinobacteria and Phascolarctobacterium increased (p < 0.05) in the colon of the PHT group compared with that in the LPS group. In conclusion, TER effectively improved the intestinal barrier function of the colon in weaning piglets. Based on the results of this study, the appropriate dose of TER in the diets of weaning piglets was 60 mg/kg.

Administration of ROS-Scavenging Cerium Oxide Nanoparticles Simply Mixed with Autoantigenic Peptides Induce Antigen-Specific Immune Tolerance against Autoimmune Encephalomyelitis

The scavenging ability of cerium oxide nanoparticles (CeNPs) for reactive oxygen species has been intensively studied in the field of catalysis. However, the immunological impact of these particles has not yet been thoroughly investigated, despite intensive research indicating that modulation of the reactive oxygen species could potentially regulate cell fate and adaptive immune responses. In this study, we examined the intrinsic capability of CeNPs to induce tolerogenic dendritic cells via their reactive oxygen species-scavenging effect when the autoantigenic peptides were simply mixed with CeNPs. CeNPs effectively reduced the intracellular reactive oxygen species levels in dendritic cells in vitro, leading to the suppression of costimulatory molecules as well as NLRP3 inflammasome activation, even in the presence of pro-inflammatory stimuli. Subcutaneously administrated PEGylated CeNPs were predominantly taken up by antigen-presenting cells in lymph nodes and to suppress cell maturation in vivo. The administration of a mixture of PEGylated CeNPs and myelin oligodendrocyte glycoprotein peptides, a well-identified autoantigen associated with antimyelin autoimmunity, resulted in the generation of antigen-specific Foxp3+ regulatory T cells in mouse spleens. The induced peripheral regulatory T cells actively inhibited the infiltration of autoreactive T cells and antigen-presenting cells into the central nervous system, ultimately protecting animals from experimental autoimmune encephalomyelitis when tested using a mouse model mimicking human multiple sclerosis. Overall, our findings reveal the potential of CeNPs for generating antigen-specific immune tolerance to prevent multiple sclerosis, opening an avenue to restore immune tolerance against specific antigens by simply mixing the well-identified autoantigens with the immunosuppressive CeNPs.

Macrophage polarization in inflammatory bowel disease

The growing prevalence of inflammatory bowel disease (IBD) has encouraged research efforts, which have contributed to gradual improvements in our understanding of IBD diagnosis and therapeutic approaches. The pathogenesis of IBD has not been fully elucidated; however, the combined actions of environmental, genetic, immune factors, and microbial organisms are believed to cause IBD. In the innate immune system, macrophages play important roles in maintaining intestinal health and in the development of IBD. Macrophages can be polarized from M0 into several phenotypes, among which M1 and M2 play critical roles in IBD development and the repair of intestinal homeostasis and damage. Certain macrophage-related IBD studies already exist; however, the functions of each phenotype have not been fully elucidated. As technology develops, understanding the link between macrophages and IBD has increased, including the growing knowledge of the developmental origins of intestinal macrophages and their performance of comprehensive functions. This review describes macrophage polarization in IBD from the perspectives of macrophage development and polarization, macrophage changes in homeostasis and IBD, metabolic changes, and the mechanisms of macrophage polarization in IBD. The discussion of these topics provides new insights into immunotherapy strategies for IBD. Video Abstract.

A Narrative Review of Cytokine Networks: Pathophysiological and Therapeutic Implications for Inflammatory Bowel Disease Pathogenesis

Inflammatory bowel disease (IBD) is a lifelong inflammatory immune mediated disorder, encompassing Crohn's disease (CD) and ulcerative colitis (UC); however, the cause and specific pathogenesis of IBD is yet incompletely understood. Multiple cytokines produced by different immune cell types results in complex functional networks that constitute a highly regulated messaging network of signaling pathways. Applying biological mechanisms underlying IBD at the single omic level, technologies and genetic engineering enable the quantification of the pattern of released cytokines and new insights into the cytokine landscape of IBD. We focus on the existing literature dealing with the biology of pro- or anti-inflammatory cytokines and interactions that facilitate cell-based modulation of the immune system for IBD inflammation. We summarize the main roles of substantial cytokines in IBD related to homeostatic tissue functions and the remodeling of cytokine networks in IBD, which may be specifically valuable for successful cytokine-targeted therapies via marketed products. Cytokines and their receptors are validated targets for multiple therapeutic areas, we review the current strategies for therapeutic intervention and developing cytokine-targeted therapies. New biologics have shown efficacy in the last few decades for the management of IBD; unfortunately, many patients are nonresponsive or develop therapy resistance over time, creating a need for novel therapeutics. Thus, the treatment options for IBD beyond the immune-modifying anti-TNF agents or combination therapies are expanding rapidly. Further studies are needed to fully understand the immune response, networks of cytokines, and the direct pathogenetic relevance regarding individually tailored, safe and efficient targeted-biotherapeutics.

Cell type-specific roles of NLRP3, inflammasome-dependent and -independent, in host defense, sterile necroinflammation, tissue repair, and fibrosis

The NLRP3 inflammasome transforms a wide variety of infectious and non-infectious danger signals that activate pro-inflammatory caspases, which promote the secretion of IL-1β and IL-18, and pyroptosis, a pro-inflammatory form of cell necrosis. Most published evidence documents the presence and importance of the NLRP3 inflammasome in monocytes, macrophages, and neutrophils during host defense and sterile forms of inflammation. In contrast, in numerous unbiased data sets, NLRP3 inflammasome-related transcripts are absent in non-immune cells. However, an increasing number of studies report the presence and functionality of the NLRP3 inflammasome in almost every cell type. Here, we take a closer look at the reported cell type-specific expression of the NLRP3 inflammasome components, review the reported inflammasome-dependent and -independent functions, and discuss possible explanations for this discrepancy.

NLRP3 inflammasome in digestive diseases: From mechanism to therapy

Digestive system diseases remain a formidable challenge to human health. NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome is the most characteristic multimeric protein complex and is involved in a wide range of digestive diseases as intracellular innate immune sensors. It has emerged as a research hotspot in recent years. In this context, we provide a comprehensive review of NLRP3 inflammasome priming and activation in the pathogenesis of digestive diseases, including clinical and preclinical studies. Moreover, the scientific evidence of small-molecule chemical drugs, biologics, and phytochemicals, which acts on different steps of the NLRP3 inflammasome, is reviewed. Above all, deep interrogation of the NLRP3 inflammasome is a better insight of the pathomechanism of digestive diseases. We believe that the NLRP3 inflammasome will hold promise as a novel valuable target and research direction for treating digestive disorders.

How Gut Microbiota Are Shaped by Pattern Recognition Receptors in Colitis and Colorectal Cancer

Simple Summary

The pathogenesis of intestinal inflammatory disorders such as colitis and colorectal cancer is complicated and dysregulation of gut microbiota is considered an important contributing factor. Inflammation is often initiated by the activation of pattern recognition receptors. However, the relationship between these innate immune receptors and gut microbiota is not fully understood. Here, we show that pattern recognition receptors not only recognize pathogens and initiate inflammatory signal transduction to induce immune responses, but also influence the composition of intestinal microorganisms, thus affecting the development of intestinal inflammation and cancer through various mechanisms. This suggests that the modification of innate immune receptors and relevant molecules could be therapeutic targets for the treatment of colitis and colorectal cancer by regulating gut microbiota.

Abstract

Disorders of gut microbiota have been closely linked to the occurrence of various intestinal diseases including colitis and colorectal cancer (CRC). Specifically, the production of beneficial bacteria and intestinal metabolites may slow the development of some intestinal diseases. Recently, it has been proposed that pattern recognition receptors (PRRs) not only recognize pathogens and initiate inflammatory signal transduction to induce immune responses but also influence the composition of intestinal microorganisms. However, the mechanisms through which PRRs regulate gut microbiota in the setting of colitis and CRC have rarely been systematically reviewed. Therefore, in this paper, we summarize recent advances in our understanding of how PRRs shape gut microbiota and how this influences the development of colitis and CRC.

Genotype-phenotype associations of polymorphisms within the gene locus of NOD-like receptor pyrin domain containing 3 in Swiss inflammatory bowel disease patients

Background

Genetic variations within the regulatory region of the gene encoding NOD-like receptor pyrin domain containing 3 (NLRP3) have been associated with Crohn’s Disease (CD). NLRP3 is part of the NLRP3-inflammasome that mediates the maturation of IL-1β and IL-18. Carrying the major allele of the single nucleotide polymorphisms (SNPs) rs10733113, rs4353135 and rs55646866 is associated with an increased risk for CD. We here studied the impact of these polymorphisms on clinical characteristics in patients of the Swiss IBD Cohort Study (SIBDCS).

Methods

We included 981 Crohn’s disease (CD) patients and 690 ulcerative colitis (UC) patients of the SIBDCS. We analyzed whether three CD-associated NLRP3 polymorphisms have an impact on the clinical disease course in these patients.

Results

In CD patients presence of the major allele (G) of rs10733113 was associated with less surgeries and lower maximal CDAI and a similar trend was observed for rs55646866 and rs4353135. Presence of the major allele of all three SNPs was negatively correlated to maximal CDAI. In UC patients homozygous genotype for the major allele (CC) for rs55646866 was associated with a higher age at diagnosis and a higher MTWAI index. Homozygous genotype for the major allele of all three polymorphisms was associated with a higher number of ambulatory visits and longer hospital stays.

Conclusions

In CD patients presence of the major allele of all three polymorphisms was associated with markers of a less severe disease course, while in UC the homozygous genotype for all major alleles suggested a more severe disease activity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12876-021-01880-9.

C646 Protects Against DSS-Induced Colitis Model by Targeting NLRP3 Inflammasome

Numerous pieces of evidence have identified that the NLRP3 inflammasome plays a pivotal role in the development and pathogenesis of colitis. Targeting the NLRP3 inflammasome represents a potential therapeutic treatment. Our previous studies have suggested that acetylation of NLRP3 is indispensable to NLRP3 inflammasome activation, and some acetyltransferase inhibitors could suppress the NLRP3 inflammasome activation. Here, we identified that C646, an inhibitor of histone acetyltransferase p300, exerts anti-inflammatory effects in DSS-induced colitis mice by targeting the NLRP3 inflammasome. Mechanistically, C646 not only inhibits NF-κB activation, leading to the decreased expression of pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α) and NLRP3, but also suppresses the NLRP3 inflammasome assembly by disrupting the interaction between NLRP3 and ASC. In addition, C646 attenuated the LPS-induced acute systemic inflammation model. Thus, our results demonstrate the ability of C646 to suppress the NLRP3 inflammasome activity and its potential application in the treatment of inflammatory bowel disease.

Inflammasomes in dendritic cells: Friend or foe?

Inflammasomes are cytosolic multiprotein complexes that crucially contribute to host defense against pathogens but are also involved in the pathogenesis of autoinflammatory diseases. Inflammasome formation leads to activation of effector caspases (caspase-1, 4, 5, or 11), the proteolytic maturation of IL-1β and IL-18 as well as cleavage of the pore-forming protein Gasdermin D. Dendritic cells are major regulators of immune responses as they bridge innate and adaptive immunity. We here summarize the current knowledge on inflammasome expression and formation in murine bone marrow-, human monocyte-derived as well as murine and human primary dendritic cells. Further, we discuss both, the beneficial and detrimental, involvement of inflammasome activation in dendritic cells in cancer, infections, and autoimmune diseases. As inflammasome activation is typically accompanied by Gasdermin d-mediated pyroptosis, which is an inflammatory form of programmed cell death, inflammasome formation in dendritic cells seems ill-advised. Therefore, we propose that hyperactivation, which is inflammasome activation without the induction of pyroptosis, may be a general model of inflammasome activation in dendritic cells to enhance Th1, Th17 as well as cytotoxic T cell responses.

Inflammasomes and adaptive immune responses

A fundamental concept in immunology is that the innate immune system initiates or instructs downstream adaptive immune responses. Inflammasomes are central players in innate immunity to pathogens, but how inflammasomes shape adaptive immunity is complex and relatively poorly understood. Here we highlight recent work on the interplay between inflammasomes and adaptive immunity. We address how inflammasome-dependent release of cytokines and antigen activates, shapes or even inhibits adaptive immune responses. We consider how distinct tissue or cellular contexts may alter the effects of inflammasome activation on adaptive immunity and how this contributes to beneficial or detrimental outcomes in infectious diseases, cancer and autoimmunity. We aspire to provide a framework for thinking about inflammasomes and their connection to the adaptive immune response.

Gut microbiota, NLR proteins, and intestinal homeostasis

The gastrointestinal tract harbors a highly complex microbial community, which is referred to as gut microbiota. With increasing evidence suggesting that the imbalance of gut microbiota plays a significant role in the pathogenesis of multiple diseases, interactions between the host immune system and the gut microbiota are now attracting emerging interest. Nucleotide-binding and leucine-rich repeat–containing receptors (NLRs) encompass a large number of innate immune sensors and receptors, which mediate the activation of Caspase-1 and the subsequent release of mature interleukin-1β and interleukin-18. Several family members have been found to restrain rather than activate inflammatory cytokines and immune signaling. NLR family members are central regulators of pathogen recognition, host immunity, and inflammation with utmost importance in human diseases. In this review, we focus on the potential roles played by NLRs in controlling and shaping the microbiota community and discuss how the functional axes interconnecting gut microbiota with NLRs impact the modulation of colitis, inflammatory bowel diseases, and colorectal cancer.

Targeting the NLRP3 inflammasome as new therapeutic avenue for inflammatory bowel disease

The incidence and prevalence of inflammatory bowel disease (IBD) are increasing worldwide. Current approved medication for IBD treatment in the clinic mainly includes corticosteroids and neutralization antibodies to pro-inflammatory cytokines. However, drug resistance and severe side effect hinder long-term efficacy of these agents. The NOD-like receptor family pyrin domain containing protein 3 (NLRP3) is exclusively expressed in several inflammatory and autoimmune diseases. Excessive expression, aberrant activation, polymorphism, and gain-of-function mutation of the NLRP3 inflammasome contribute to IBD pathogenesis. In this article, we summarize the regulatory factors to NLRP3, and review recently developed NLRP3 inhibitors and their preclinical and clinical applications in treating inflammatory and autoimmune diseases. We present our views on the therapeutic potential of NLRP3 inhibitors as emerging therapeutic avenue for IBD.

Dietary Indole-3-Carbinol Activates AhR in the Gut, Alters Th17-Microbe Interactions, and Exacerbates Insulitis in NOD Mice

The diet represents one environmental risk factor controlling the progression of type 1 diabetes (T1D) in genetically susceptible individuals. Consequently, understanding which specific nutritional components promote or prevent the development of disease could be used to make dietary recommendations in prediabetic individuals. In the current study, we hypothesized that the immunoregulatory phytochemcial, indole-3-carbinol (I3C) which is found in cruciferous vegetables, will regulate the progression of T1D in nonobese diabetic (NOD) mice. During digestion, I3C is metabolized into ligands for the aryl hydrocarbon receptor (AhR), a transcription factor that when systemically activated prevents T1D. In NOD mice, an I3C-supplemented diet led to strong AhR activation in the small intestine but minimal systemic AhR activity. In the absence of this systemic response, the dietary intervention led to exacerbated insulitis. Consistent with the compartmentalization of AhR activation, dietary I3C did not alter T helper cell differentiation in the spleen or pancreatic draining lymph nodes. Instead, dietary I3C increased the percentage of CD4+RORγt+Foxp3- (Th17 cells) in the lamina propria, intraepithelial layer, and Peyer's patches of the small intestine. The immune modulation in the gut was accompanied by alterations to the intestinal microbiome, with changes in bacterial communities observed within one week of I3C supplementation. A transkingdom network was generated to predict host-microbe interactions that were influenced by dietary I3C. Within the phylum Firmicutes, several genera (Intestinimonas, Ruminiclostridium 9, and unclassified Lachnospiraceae) were negatively regulated by I3C. Using AhR knockout mice, we validated that Intestinimonas is negatively regulated by AhR. I3C-mediated microbial dysbiosis was linked to increases in CD25high Th17 cells. Collectively, these data demonstrate that site of AhR activation and subsequent interactions with the host microbiome are important considerations in developing AhR-targeted interventions for T1D.

Microbiota metabolites modulate the T helper 17 to regulatory T cell (Th17/Treg) imbalance promoting resilience to stress-induced anxiety- and depressive-like behaviors

Chronic stress disrupts immune homeostasis while gut microbiota-derived metabolites attenuate inflammation, thus promoting resilience to stress-induced immune and behavioral abnormalities. There are both peripheral and brain region-specific maladaptations of the immune response to chronic stress that produce interrelated mechanistic considerations required for the design of novel therapeutic strategies for prevention of stress-induced psychological impairment. This study shows that a combination of probiotics and polyphenol-rich prebiotics, a synbiotic, attenuates the chronic-stress induced inflammatory responses in the ileum and the prefrontal cortex promoting resilience to the consequent depressive- and anxiety-like behaviors in male mice. Pharmacokinetic studies revealed that this effect may be attributed to specific synbiotic-produced metabolites including 4-hydroxyphenylpropionic, 4-hydroxyphenylacetic acid and caffeic acid. Using a model of chronic unpredictable stress, behavioral abnormalities were associated to strong immune cell activation and recruitment in the ileum while inflammasome pathways were implicated in the prefrontal cortex and hippocampus. Chronic stress also upregulated the ratio of activated proinflammatory T helper 17 (Th17) to regulatory T cells (Treg) in the liver and ileum and it was predicted with ingenuity pathway analysis that the aryl hydrocarbon receptor (AHR) could be driving the synbiotic's effect on the ileum's inflammatory response to stress. Synbiotic treatment indiscriminately attenuated the stress-induced immune and behavioral aberrations in both the ileum and the brain while in a gut-immune co-culture model, the synbiotic-specific metabolites promoted anti-inflammatory activity through the AHR. Overall, this study characterizes a novel synbiotic treatment for chronic-stress induced behavioral impairments while defining a putative mechanism of gut-microbiota host interaction for modulating the peripheral and brain immune systems.

Wheat-derived arabinoxylans reduced M2-macrophage functional activity, but enhanced monocyte-recruitment capacity

The immunomodulatory properties of non-digestible polysaccharides (NDPs) have been recognized in in vitro and in vivo studies. The latter mostly demonstrated altered frequencies and inflammatory status of immune cells as clinical parameters. Most of the NDP activity will be exerted in the intestine where they can directly interact with macrophages. The predominant macrophage phenotype in the intestine is M2-like, with M1-like macrophages arising during inflammation. Here, we investigated transcriptional and functional impact on these macrophage phenotypes by NDP-treatment (i.e. yeast-derived soluble β-glucan (yeast-βG), apple-derived RG-I (apple-RGI), shiitake-derived β-glucan (shiitake-βG) or wheat-derived arabinoxylan (wheat-AX)). Wheat-AX, and to a lesser extent shiitake-βG and apple-RGI but not yeast-βG, reduced endocytosis and antigen processing capacity of M1- and M2-like macrophages. Moreover, the NDPs, and most notably wheat-AX, strongly induced transcription and secretion of a unique set of cytokines and chemokines. Conditioned medium from wheat-AX-treated M2-like macrophages subsequently demonstrated strongly increased monocyte recruitment capacity. These findings are in line with clinically observed immunomodulatory aspects of NDPs making it tempting to speculate that clinical activity of some NDPs is mediated through enhanced chemoattraction and modifying activity of intestinal immune cells.

Smad7 Controls Immunoregulatory PDL2/1-PD1 Signaling in Intestinal Inflammation and Autoimmunity

Smad7, a negative regulator of TGF-β signaling, has been implicated in the pathogenesis and treatment of inflammatory bowel diseases (IBDs), including Crohn's disease (CD) and ulcerative colitis (UC). Here, we found that Smad7 mediates intestinal inflammation by limiting the PDL2/1-PD1 axis in dendritic cells (DCs) and CD4+T cells. Smad7 deficiency in DCs promotes TGF-β responsiveness and the co-inhibitory molecules PDL2/1 on DCs, and it further imprints T cell-PD1 signaling to promote Treg differentiation. DC-specific Smad7 deletion mitigates DSS-induced colitis by inducing CD103+PDL2/1+DCs and Tregs. In addition, Smad7 deficiency in CD4+T cells promotes PD1 and PD1-induced Tregs in vitro. The transfer of Smad7-deficient CD4+T cells enhances Tregs in vivo and protects against T cell-mediated colitis. Furthermore, Smad7 antisense ameliorates DSS-induced UC, increasing TGF-β and PDL2/1-PD1 signaling. Enhancing PD1 signaling directly via Fc-fused PDL2/1 is also beneficial. Our results identify how Smad7 mediates intestinal inflammation and leverages these pathways therapeutically, providing additional strategies for IBD intervention.

Role of NLRP3 inflammasome in inflammatory bowel diseases

Inflammasomes are multiprotein intracellular complexes which are responsible for the activation of inflammatory responses. Among various subtypes of inflammasomes, NLRP3 has been a subject of intensive investigation. NLRP3 is considered to be a sensor of microbial and other danger signals and plays a crucial role in mucosal immune responses, promoting the maturation of proinflammatory cytokines interleukin 1β (IL-1β) and IL-18. NLRP3 inflammasome has been associated with a variety of inflammatory and autoimmune conditions, including inflammatory bowel diseases (IBD). The role of NLRP3 in IBD is not yet fully elucidated as it seems to demonstrate both pathogenic and protective effects. Studies have shown a relationship between genetic variants and mutations in NLRP3 gene with IBD pathogenesis. A complex interaction between the NLRP3 inflammasome and the mucosal immune response has been reported. Activation of the inflammasome is a key function mediated by the innate immune response and in parallel the signaling through IL-1β and IL-18 is implicated in adaptive immunity. Further research is needed to delineate the precise mechanisms of NLRP3 function in regulating immune responses. Targeting NLRP3 inflammasome and its downstream signaling will provide new insights into the development of future therapeutic strategies.

Dual immune functions of IL-33 in inflammatory bowel disease

Interleukin-33 (IL-33) has emerged as a critical regulator in a variety of diseases, including inflammatory bowel disease (IBD). IL-33 can be produced by various tissues and cells, and typically induces Th2-type immune responses via binding to the receptor ST2. In addition, accumulated data have shown that IL-33 also plays a modulatory role in the function of regulatory T cells (Tregs), B cells, and innate immune cells such as macrophages and innate lymphoid cells (ILCs). IBD, including Crohn's disease and ulcerative colitis, are characterized by aberrant immunological responses leading to intestinal tissue injury and destruction. Although IL-33 expression is increased in IBD patients and correlates with the patients' disease activity index, mechanistic studies to date have demonstrated both pathogenic and protective roles in animal models of experimental colitis. In this review, we will summarize the roles and mechanisms of IL-33 in IBD, which is essential to understand the pathogenesis of IBD and determine potential therapies.

Impact of NLRP3 inflammasome on immune modulation mechanism in inflammatory bowel disease

The pathogenesis of inflammatory bowel disease (IBD) is closely related to the internal immune environment. NLRP3 inflammasome participates in the innate immune response and T cell immune response. During chronic inflammation, typical NLRP3 inflammasomes are activated, thus increasing the secretion of IL-1β and IL-18 from lamina propria macrophages and dendritic cells. The release of IL-1β and IL-18 induces T cells to differentiate into pathogenic Th1 and Th17 phenotypes, maintaining the inflammatory response. In the acute inflammation stage, IL-1β mainly promotes the healing and repair of intestinal epithelial cells. Therefore, NLRP3 inflammasome has a protective effect on intestinal epithelial cells. Besides, the expression of IL-1β leads to Th17/Treg imbalance, which is also closely related to the pathogenesis of IBD. Thus, NLRP3 acts as a molecular switch of intestinal homeostasis by shifting local immune cells toward an inflammatory phenotype via IL-1β.

Effects of dietary supplementation with Lactobacillus acidophilus on the performance, intestinal physical barrier function, and the expression of NOD-like receptors in weaned piglets

Lactobacillus supplementation is beneficial to the barrier function of the intestinal physical barrier in piglets. However, the mechanisms underlying this beneficial function remain largely unknown. Here, we investigated the effects of dietary supplementation with Lactobacillus acidophilus on the performance, intestinal physical barrier functioning, and NOD-like receptors (NLRs) expression in weaned piglets. Sixteen weaned piglets were randomly allocated to two groups. The control group received a corn-soybean basal diet, while the treatment group received the same diet adding 0.1% L. acidophilus, for 14 days. As a result, dietary L. acidophilus supplementation was found to increase the average daily gain (ADG) (P < 0.05), reduced serum diamine oxidase (DAO) activity (P < 0.05), increased the mRNA expression and protein abundance of occludin in the jejunum and ileum (P < 0.01), reduced the mRNA levels of NOD1 (P < 0.01), receptor interacting serine/threonine kinase 2 (RIPK2) (P < 0.05), nuclear factor κB (NF-κB) (P < 0.01), NLR family pyrin domain containing 3 (NLRP3) (P < 0.01), caspase-1 (P < 0.01), interleukin 1β (IL-1β) (P < 0.05) and IL-18 (P < 0.01) in the jejunum tissues of the weaned pigs. The expression of NLRP3 (P < 0.05), caspase-1 (P < 0.01), IL-1β (P < 0.05) and IL-18 (P < 0.05) was also reduced in the ileum tissues of the weaned pigs. These results showed that L. acidophilus supplementation improves the growth performance, enhances the intestinal physical barrier function, and inhibits the expression of NOD1 and NLRP3 signaling-pathway-related genes in jejunum and ileum tissues. They also suggest that L. acidophilus enhances the intestinal physical barrier functioning by inhibiting IL-1β and IL-18 pro-inflammatory cytokines via the NOD1/NLRP3 signaling pathway in weaned piglets.

Helicobacter pylori evasion strategies of the host innate and adaptive immune responses to survive and develop gastrointestinal diseases

Helicobacter pylori (H. pylori) is a bacterial pathogen that resides in more than half of the human population and has co-evolved with humans for more than 58,000 years. This bacterium is orally transmitted during childhood and is a key cause of chronic gastritis, peptic ulcers and two malignant cancers including MALT (mucosa-associated lymphoid tissue) lymphoma and adenocarcinoma. Despite the strong innate and adaptive immune responses, H. pylori has a long-term survival in the gastric mucosa. In addition to the virulence factors, survival of H. pylori is strongly influenced by the ability of bacteria to escape, disrupt and manipulate the host immune system. This bacterium can escape from recognition by innate immune receptors via altering its surface molecules. Moreover, H. pylori subverts adaptive immune response by modulation of effector T cell. In this review, we discuss the immune-pathogenicity of H. pylori by focusing on its ability to manipulate the innate and acquired immune responses to increase its survival in the gastric mucosa, leading up to gastrointestinal disorders. We also highlight the mechanisms that resulted to the persistence of H. pylori in gastric mucosa.