Regulation of intestinal homeostasis by innate immune cells

From bench to bedside: exploring curcumin-driven signaling pathways in immune cells for cancer management

The use of natural compounds as effective therapeutic agents is an expanding area of health and disease research. Curcumin, a bioactive component derived from the rhizome of the turmeric plant (Curcuma longa L.), has been primarily used in culinary applications for several centuries, but now its potential health benefits are the focus of growing scientific research. Interestingly, some studies have found that curcumin has antitumorigenic effects due to its ability to influence the tumor microenvironment and possibly promote immune system response by modulating specific signaling pathways in immune cells. The interaction of curcumin with immune cells in the field of cancer chemoprevention is a complex area of research. It has been suggested that curcumin might promote T cell recruitment, reduce neutrophil and macrophage accumulation in the tumor microenvironment, and prevent the conversion of infiltrating lymphocytes into immunosuppressive subpopulations. Thus, its possible mechanisms of action also include a shift of the immune balance toward activation by reversing the prevalence of immunosuppressive cells. With innovations and improvements in our understanding of the potential benefits of curcumin on immune cells in cancer prevention and treatment, it is important to have an overview of current findings. Therefore, in this study, we aim to provide a review of the latest discoveries regarding curcumin in the field of cancer and immune cell research.

The interaction between intestinal microenvironment and stroke

BACKGROUND

Stroke is not only a major cause of disability but also the third leading cause of death, following heart disease and cancer. It has been established that stroke causes permanent disability in 80% of survivors. However, current treatment options for this patient population are limited. Inflammation and immune response are major features that are well-recognized to occur after a stroke. The gastrointestinal tract hosts complex microbial communities, the largest pool of immune cells, and forms a bidirectional regulation brain-gut axis with the brain. Recent experimental and clinical studies have highlighted the importance of the relationship between the intestinal microenvironment and stroke. Over the years, the influence of the intestine on stroke has emerged as an important and dynamic research direction in biology and medicine.

AIMS

In this review, we describe the structure and function of the intestinal microenvironment and highlight its cross-talk relationship with stroke. In addition, we discuss potential strategies aiming to target the intestinal microenvironment during stroke treatment.

CONCLUSION

The structure and function of the intestinal environment can influence neurological function and cerebral ischemic outcome. Improving the intestinal microenvironment by targeting the gut microbiota may be a new direction in treating stroke.

Effects of dietary lycopene supplementation on intestinal morphology, antioxidant capability and inflammatory response in finishing pigs

In this study, eighteen healthy Duroc × Landrace × Yorkshire barrows with initial body weight of 63.89 ± 1.15 kg were randomly allotted to three treatments and fed a basal diet or a basal diet supplemented with 100 mg/kg and 200 mg/kg lycopene, respectively. Data showed that villus height to crypt depth ratio increased with 200 mg/kg lycopene (p < 0.05) in the jejunum. In duodenum, the malondialdehyde content was decreased (p < 0.05) in 100 and 200 mg/kg lycopene groups. Furthermore, in the jejunum, dietary 100 and 200 mg/kg lycopene supplementation increased (p < 0.05) catalase activity. In the duodenum, interleukin-1β (IL-1β), nuclear factor-κB and tumor necrosis factor-α contents were decreased (p < 0.05) in 200 mg/kg lycopene group. In the jejunum, IL-1β content was reduced (p < 0.05) and IL-1β mRNA expression was down-regulated (p = 0.046) in 200 mg/kg lycopene group. Additionally, claudin-1 mRNA and protein levels in 200 mg/kg group were also increased (p < 0.05). These results indicated that dietary lycopene supplementation could maintain intestinal health, which was associated with improving intestinal morphology, enhancing tight junction function, inhibiting inflammatory response, and elevating antioxidant capacity in finishing pigs.

Manipulating resident microbiota to enhance regulatory immune function to treat inflammatory bowel diseases

Altered intestinal microbial composition (dysbiosis) and metabolic products activate aggressive mucosal immune responses that mediate inflammatory bowel diseases (IBD). This dysbiosis impairs the function of regulatory immune cells, which normally promote mucosal homeostasis. Normalizing and maintaining regulatory immune cell function by correcting dysbiosis provides a promising approach to treat IBD patients. However, existing microbe-targeted therapies, including antibiotics, prebiotics, probiotics, and fecal microbial transplantation, provide variable outcomes that are not optimal for current clinical application. This review discusses recent progress in understanding the dysbiosis of IBD and the basis for therapeutic restoration of homeostatic immune function by manipulating an individual patient's microbiota composition and function. We believe that identifying more precise therapeutic targets and developing appropriate rapid diagnostic tools will guide more effective and safer microbe-based induction and maintenance treatments for IBD patients that can be applied in a personalized manner.

Bacillus coagulans GBI-30, 6068 decreases upper respiratory and gastrointestinal tract symptoms in healthy Mexican scholar-aged children by modulating immune-related proteins

This randomized, double-blind, parallel and placebo-controlled study aimed to evaluate the effect of Bacillus coagulans GBI-30, 6086® probiotic (GanedenBC³⁰®) against upper respiratory tract infections (URTI) and gastrointestinal tract infections (GITI) in eighty healthy school-aged children (6-8 years old). The participants received daily a sachet containing either GanedenBC³⁰ (1 × 10⁹ colony-forming units) or placebo (maltodextrin) for three months. GanedenBC³⁰ significantly decreased the incidence of URTI symptoms including nasal congestion, bloody nasal mucus, itchy nose, and hoarseness. The duration of the URTI-associated symptoms of hoarseness, headache, red eyes, and fatigue was also decreased. GanedenBC³⁰ supplementation also significantly reduced the incidence rate of flatulence. These beneficial effects were associated with the modulation of serum TNFα, CD163, G-CSF, ICAM-1, IL-6, IL-8, MCP-2, RAGE, uPAR, and PF4. Therefore, probiotic B. coagulans GBI-30, 6086 modulated immune-related proteins in healthy children, decreasing several URTI and GITI symptoms, thus, this functional ingredient may contribute to a healthier lifestyle.

Microbiome modulates intestinal homeostasis against inflammatory diseases

Eliminating prophylactic antibiotics in food animal production has exerted pressure on discovering antimicrobial alternatives (e.g. microbiome) to reduce elevated intestinal diseases. Intestinal tract is a complex ecosystem coupling host cells with microbiota. The microbiota and its metabolic activities and products are collectively called microbiome. Intestinal homeostasis is reached through dynamic and delicate crosstalk between host immunity and microbiome. However, this balance can be occasionally broken, which results in intestinal inflammatory diseases such as human Inflammatory Bowel Diseases, chicken necrotic enteritis, and swine postweaning diarrhea. In this review, we introduce the intestinal immune system, intestinal microbiome, and microbiome modulation of inflammation against intestinal diseases. The purpose of this review is to provide updated knowledge on host-microbe interaction and to promote using microbiome as new antimicrobial strategies to reduce intestinal diseases.

Interactions between bile salts, gut microbiota, and hepatic innate immunity

Bile salts are the water-soluble end products of hepatic cholesterol catabolism that are released into the duodenum and solubilize lipids due to their amphipathic structure. Bile salts also act as endogenous ligands for dedicated nuclear receptors that exert a plethora of biological processes, mostly related to metabolism. Bile salts are actively reclaimed in the distal part of the small intestine, released into the portal system, and subsequently extracted by the liver. This enterohepatic cycle is critically dependent on dedicated bile salt transporters. In the intestinal lumen, bile salts exert direct antimicrobial activity based on their detergent property and shape the gut microbiota. Bile salt metabolism by gut microbiota serves as a mechanism to counteract this toxicity and generates bile salt species that are distinct from those of the host. Innate immune cells of the liver play an important role in the early recognition and effector response to invading microbes. Bile salts signal primarily via the membrane receptor TGR5 and the intracellular farnesoid-x receptor, both present in innate immune cells. In this review, the interactions between bile salts, gut microbiota, and hepatic innate immunity are discussed.

Regulatory Roles of Flavonoids on Inflammasome Activation during Inflammatory Responses

Inflammation is an innate immune response to noxious stimuli to protect the body from pathogens. Inflammatory responses consist of two main steps: priming and triggering. In priming, inflammatory cells increase expressions of inflammatory molecules, while in triggering, inflammasomes are activated, resulting in cell death and pro-inflammatory cytokine secretion. Inflammasomes are protein complexes comprising intracellular pattern recognition receptors (PRRs) (e.g., nucleotide-binding oligomerization domain-like receptors (NLRs), absent in melanoma 2 (AIM2), and caspases-4/5/11) and pro-caspase-1 with or without a bipartite adaptor molecule ASC. Inflammasome activation induces pyroptosis, inflammatory cell death, and stimulates caspase-1-mediated secretion of interleukin (IL)-1b and IL-18. Flavonoids are secondary metabolites found in various plants and are considered as critical ingredients promoting health and ameliorating various disease symptoms. Anti-inflammatory activity of flavonoids and underlying mechanisms have been widely studied. This review introduces current knowledge on different types of inflammasomes and their activation during inflammatory responses and discusses recent studies regarding anti-inflammatory roles of flavonoids as suppressors of inflammasomes in inflammatory conditions. Understanding the regulatory effects of flavonoids on inflammasome activation will increase our knowledge of flavonoid-mediated anti-inflammatory activity and provide new insights into the development of flavonoid preparations to prevent and treat human inflammatory diseases.

Role of inflammasomes in inflammatory autoimmune rheumatic diseases

Inflammasomes are intracellular multiprotein complexes that coordinate anti-pathogenic host defense during inflammatory responses in myeloid cells, especially macrophages. Inflammasome activation leads to activation of caspase-1, resulting in the induction of pyroptosis and the secretion of pro-inflammatory cytokines including interleukin (IL)-1β and IL-18. Although the inflammatory response is an innate host defense mechanism, chronic inflammation is the main cause of rheumatic diseases, such as rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), ankylosing spondylitis (AS), and Sjögren's syndrome (SS). Since rheumatic diseases are inflammatory/autoimmune disorders, it is reasonable to hypothesize that inflammasomes activated during the inflammatory response play a pivotal role in development and progression of these diseases. Indeed, previous studies have provided important observations that inflammasomes are actively involved in the pathogenesis of inflammatory/autoimmune rheumatic diseases. In this review, we summarize the current knowledge on several types of inflammasomes during macrophage-mediated inflammatory responses and discuss recent research regarding the role of inflammasomes in the pathogenesis of inflammatory/autoimmune rheumatic diseases. This avenue of research could provide new insights for the development of promising therapeutics to treat inflammatory/autoimmune rheumatic diseases.

Roles of ginsenosides in inflammasome activation

Inflammation is an innate immune response that protects the body from pathogens, toxins, and other dangers and is initiated by recognizing pathogen-associated molecular patterns or danger-associated molecular patterns by pattern-recognition receptors expressing on or in immune cells. Intracellular pattern-recognition receptors, including nucleotide-binding oligomerization domain-like receptors (NLRs), absent in melanoma 2, and cysteine aspartate–specific protease (caspase)-4/5/11 recognize various pathogen-associated molecular patterns and danger-associated molecular patterns and assemble protein complexes called “inflammasomes.” These complexes induce inflammatory responses by activating a downstream effector, caspase-1, leading to gasdermin D –mediated pyroptosis and the secretion of proinflammatory cytokines, such as interleukin (IL)-1β and IL-18. Ginsenosides are natural steroid glycosides and triterpene saponins found exclusively in the plant genus Panax. Various ginsenosides have been identified, and their abilities to regulate inflammatory responses have been evaluated. These studies have suggested a link between ginsenosides and inflammasome activation in inflammatory responses. Some types of ginsenosides, including Rh1, Rg3, Rb1, compound K, chikusetsu saponin IVa, Rg5, and Rg1, have been clearly demonstrated to inhibit inflammatory responses by suppressing the activation of various inflammasomes, including the NLRP3, NLRP1, and absent in melanoma 2 inflammasomes. Ginsenosides have also been shown to inhibit caspase-1 and to decrease the expression of IL-1β and IL-18. Given this body of evidence, the functional relationship between ginsenosides and inflammasome activation provides new insight into the understanding of the molecular mechanisms of ginsenoside-mediated antiinflammatory actions. This relationship also has applications regarding the development of antiinflammatory remedies by ginsenoside-mediated targeting of inflammasomes, which could be used to prevent and treat inflammatory diseases.

Tabetri™ (Tabebuia avellanedae Ethanol Extract) Ameliorates Osteoarthritis Symptoms Induced by Monoiodoacetate through Its Anti-Inflammatory and Chondroprotective Activities

Although osteoarthritis (OA), a degenerative joint disease characterized by the degradation of joint articular cartilage and subchondral bones, is generally regarded as a degenerative rather than inflammatory disease, recent studies have indicated the involvement of inflammation in OA pathogenesis. Tabebuia avellanedae has long been used to treat various diseases; however, its role in inflammatory response and the underlying molecular mechanisms remain poorly understood. In this study, the pharmacological effects of Tabetri (Tabebuia avellanedae ethanol extract (Ta-EE)) on OA pathogenesis induced by monoiodoacetate (MIA) and the underlying mechanisms were investigated using experiments with a rat model and in vitro cellular models. In the animal model, Ta-EE significantly ameliorated OA symptoms and reduced the serum levels of inflammatory mediators and proinflammatory cytokines without any toxicity. The anti-inflammatory activity of Ta-EE was further confirmed in a macrophage-like cell line (RAW264.7). Ta-EE dramatically suppressed the production and mRNA expressions of inflammatory mediators and proinflammatory cytokines in lipopolysaccharide-stimulated RAW264.7 cells without any cytotoxicity. Finally, the chondroprotective effect of Ta-EE was examined in a chondrosarcoma cell line (SW1353). Ta-EE markedly suppressed the mRNA expression of matrix metalloproteinase genes. The anti-inflammatory and chondroprotective activities of Ta-EE were attributed to the targeting of the nuclear factor-kappa B (NF-κB) and activator protein-1 (AP-1) signaling pathways in macrophages and chondrocytes.

H. pylori attenuates TNBS-induced colitis via increasing mucosal Th2 cells in mice

There is an epidemiological inverse relationship between Helicobacter pylori (H. pylori) infection and Crohn's disease (CD). However, whether H. pylori plays a protective role against CD remains unclear. Since 2, 4, 6-trinitrobenzene sulfonic acid (TNBS)-induced colitis is thought to resemble CD, we investigated whether H. pylori can attenuate TNBS-induced colitis in mice. Here we show that H. pylori can attenuate the severity of TNBS-induced colitis. In addition, H. pylori not only down-regulates Th17 and Th1 cytokine expression, but can up-regulate Th2 cytokine expression and increase the Th2:Th17 ratio of CD4+ T in the colonic mucosa of TNBS-induced colitis. Our results indicate that H. pylori attenuates TNBS-induced colitis mainly through increasing Th2 cells in murine colonic mucosa. Our finding offers a novel view on the role of H. pylori in regulating gastrointestinal immunity, and may open a new avenue for development of therapeutic strategies in CD by making use of asymptomatic H. pylori colonization.

Caspase-11 non-canonical inflammasome: a critical sensor of intracellular lipopolysaccharide in macrophage-mediated inflammatory responses

Inflammatory responses mediated by macrophages are part of the innate immune system, whose role is to protect against invading pathogens. Lipopolysaccharide (LPS) found in the outer membrane of Gram-negative bacteria stimulates an inflammatory response by macrophages. During the inflammatory response, extracellular LPS is recognized by Toll-like receptor 4, one of the pattern recognition receptors that activates inflammatory signalling pathways and leads to the production of inflammatory mediators. The innate immune response is also triggered by intracellular inflammasomes, and inflammasome activation induces pyroptosis and the secretion of pro-inflammatory cytokines such as interleukin-1β (IL-1β) and IL-18 by macrophages. Cysteine-aspartic protease (caspase)-11 and the human orthologues caspase-4/caspase-5 were recently identified as components of the 'non-canonical inflammasome' that senses intracellular LPS derived from Gram-negative bacteria during macrophage-mediated inflammatory responses. Direct recognition of intracellular LPS facilitates the rapid oligomerization of caspase-11/4/5, which results in pyroptosis and the secretion of IL-1β and IL-18. LPS is released into the cytoplasm from Gram-negative bacterium-containing vacuoles by small interferon-inducible guanylate-binding proteins encoded on chromosome 3 (GBP^chr3 )-mediated lysis of the vacuoles. In vivo studies have clearly shown that caspase-11^-/- mice are more resistant to endotoxic septic shock by excessive LPS challenge. Given the evidence, activation of caspase-11 non-canonical inflammasomes by intracellular LPS is distinct from canonical inflammasome activation and provides a new paradigm in macrophage-mediated inflammatory responses.

NOD2 up-regulates TLR2-mediated IL-23p19 expression via NF-κB subunit c-Rel in Paneth cell-like cells

IL-23p19 plays important roles in intestinal antimicrobial immunity, while its over-expression can lead to intestinal inflammation. However, the bacterial compounds and the type of pattern recognition receptor involved in the inducible expression of IL-23p19 in Paneth cells remain unclear. Here we show that the mRNA expression of IL-23p19 was increased in Paneth cell (PC)-like cells stimulated by Toll-like receptor 2 (TLR2) ligands, peptidoglycan (PGN) and Pam3CSK4, and was further increased in the presence of nucleotide-binding oligomerization domain 2 (NOD2)-ligand muramyl dipeptide (MDP). However, its mRNA expression was decreased in NOD2-knockdown PC-like cells. Additionally, the c-Rel activation was increased in Pam3CSK4- or PGN-stimulated PC-like cells, but the PGN-induced c-Rel activation was decreased in NOD2-knockdown PC-like cells and had no significant difference compared with Pam3CSK4-induced c-Rel activation. Our results suggest that NOD2 up-regulates TLR2-mediated IL-23p19 expression via increasing c-Rel activation in PC-like cells. This finding might provide us with a novel therapeutic target for inflammatory bowel disease to inhibit IL-23p19 over-expression via the NOD2-c-Rel pathway.

Inter-individual variability and genetic influences on cytokine responses to bacteria and fungi

Little is known about the inter-individual variation of cytokine responses to different pathogens in healthy individuals. To systematically describe cytokine responses elicited by distinct pathogens and to determine the effect of genetic variation on cytokine production, we profiled cytokines produced by peripheral blood mononuclear cells from 197 individuals of European origin from the 200 Functional Genomics (200FG) cohort in the Human Functional Genomics Project (http://www.humanfunctionalgenomics.org), obtained over three different years. We compared bacteria- and fungi-induced cytokine profiles and found that most cytokine responses were organized around a physiological response to specific pathogens, rather than around a particular immune pathway or cytokine. We then correlated genome-wide single-nucleotide polymorphism (SNP) genotypes with cytokine abundance and identified six cytokine quantitative trait loci (QTLs). Among them, a cytokine QTL at the NAA35-GOLM1 locus markedly modulated interleukin (IL)-6 production in response to multiple pathogens and was associated with susceptibility to candidemia. Furthermore, the cytokine QTLs that we identified were enriched among SNPs previously associated with infectious diseases and heart diseases. These data reveal and begin to explain the variability in cytokine production by human immune cells in response to pathogens.

Functional Role of Milk Fat Globule-Epidermal Growth Factor VIII in Macrophage-Mediated Inflammatory Responses and Inflammatory/Autoimmune Diseases

Inflammation involves a series of complex biological processes mediated by innate immunity for host defense against pathogen infection. Chronic inflammation is considered to be one of the major causes of serious diseases, including a number of autoimmune/inflammatory diseases, cancers, cardiovascular diseases, and neurological diseases. Milk fat globule-epidermal growth factor 8 (MFG-E8) is a secreted protein found in vertebrates and was initially discovered as a critical component of the milk fat globule. Previously, a number of studies have reported that MFG-E8 contributes to various biological functions including the phagocytic removal of damaged and apoptotic cells from tissues, the induction of VEGF-mediated neovascularization, the maintenance of intestinal epithelial homeostasis, and the promotion of mucosal healing. Recently, emerging studies have reported that MFG-E8 plays a role in inflammatory responses and inflammatory/autoimmune diseases. This review describes the characteristics of MFG-E8-mediated signaling pathways, summarizes recent findings supporting the roles of MFG-E8 in inflammatory responses and inflammatory/autoimmune diseases, and discusses MFG-E8 targeting as a potential therapeutic strategy for the development of anti-inflammatory/autoimmune disease drugs.

The joint power of sex and stress to modulate brain-gut-microbiota axis and intestinal barrier homeostasis: implications for irritable bowel syndrome

BACKGROUND

Intestinal homeostasis is a dynamic process that takes place at the interface between the lumen and the mucosa of the gastrointestinal tract, where a constant scrutiny for antigens and toxins derived from food and microorganisms is carried out by the vast gut-associated immune system. Intestinal homeostasis is preserved by the ability of the mucus layer and the mucosal barrier to keep the passage of small-sized and antigenic molecules across the epithelium highly selective. When combined and preserved, immune surveillance and barrier's selective permeability, the host capacity of preventing the development of intestinal inflammation is optimized, and viceversa. In addition, the brain-gut-microbiome axis, a multidirectional communication system that integrates distant and local regulatory networks through neural, immunological, metabolic, and hormonal signaling pathways, also regulates intestinal function. Dysfunction of the brain-gut-microbiome axis may induce the loss of gut mucosal homeostasis, leading to uncontrolled permeation of toxins and immunogenic particles, increasing the risk of appearance of intestinal inflammation, mucosal damage, and gut disorders. Irritable bowel syndrome is prevalent stress-sensitive gastrointestinal disorder that shows a female predominance. Interestingly, the role of stress, sex and gonadal hormones in the regulation of intestinal mucosal and the brain-gut-microbiome axis functioning is being increasingly recognized.

PURPOSE

We aim to critically review the evidence linking sex, and stress to intestinal barrier and brain-gut-microbiome axis dysfunction and the implications for irritable bowel syndrome.

How evolution tells us to induce allotolerance

Modern immunology, in many ways, is based on 3 major paradigms: the clonal selection theory (Medawar, Burnet; 1953/1959), the pattern recognition theory (Janeway; 1989), and the danger/injury theory (Matzinger, Land; 1994). The last theory holds that any cell stress and tissue injury including allograft injury, via induction of damage-associated molecular patterns, induces immunity including alloimmunity leading to allograft rejection. On the other hand, the concept precludes that "non-self " per se induces immunity as proposed by the two former theories. Today, the danger/injury model has been largely accepted by immunologists, as documented by a steadily increasing number of publications. In particular, overwhelming evidence in support of the correctness of the model has come from recent studies on the gut microbiota representing a huge assemblage of "non-self. " Here, harmless noninjurious commensal microbes are protected by innate immunity-based immune tolerance whereas intestinal injury-causing pathogenic microbes are immunology attacked. The ability of the immune system to discriminate between harmless beneficial "non-self " to induce tolerance and harmful life-threatening "non-self " to induce immunity has apparently emerged during evolution: Protection of innate immunity-controlled beneficial "non-self " (eg, as reflected by microbiotas but also by the fetus of placental mammals) as well as immune defense responses to injuring/injured "non-self " (eg, as reflected by plant resistance to biotic and abiotic stress and allograft rejection in mammals) evolved under pressure across the tree of life, that is, in plants, lower and higher invertebrates as well as lower and higher vertebrates. And evolution tells us why the overall existence of protected microbiotas really makes sense: It is the formation of the "holobiont, " - a metaorganism - that is, the host plus all of its associated microorganisms that - in terms of a strong unit of selection in evolution - provides that kind of fitness to all species on earth to successfully live, survive and reproduce. In other words: "We all evolve, develop, grow, and reproduce as multigenomic ecosystems! Regarding reproduction, another impressive example of active immunologic protection of "nonself " refers to pregnancy in placental mammals that emerged about 400 millions of years ago. Similar to "non-self " microbiotas, pregnancy in placental mammals reflects an evolution-driven phenomenon on the basis of innate immunity-controlled tolerance induction to semiallogeneic non-injuring/non-injured "non-self " aiming to ensure reproduction! Altogether, the lesson learned from evolution of how to avoid allograft rejection is clear: prevent allograft injury to induce allotolerance, in other words: create a "transplant holobiont. ".

Intestinal barrier function and the brain-gut axis

The luminal-mucosal interface of the intestinal tract is the first relevant location where microorganism-derived antigens and all other potentially immunogenic particles face the scrutiny of the powerful mammalian immune system. Upon regular functioning conditions, the intestinal barrier is able to effectively prevent most environmental and external antigens to interact openly with the numerous and versatile elements that compose the mucosal-associated immune system. This evolutionary super system is capable of processing an astonishing amount of antigens and non-immunogenic particles, approximately 100 tons in one individual lifetime, only considering food-derived components. Most important, to develop oral tolerance and proper active immune responses needed to prevent disease and inflammation, this giant immunogenic load has to be managed in a way that physiological inflammatory balance is constantly preserved. Adequate functioning of the intestinal barrier involves local and distant regulatory networks integrating the so-called brain-gut axis. Along this complex axis both brain and gut structures participate in the processing and execution of response signals to external and internal changes coming from the digestive tract, using multidirectional pathways to communicate. Dysfunction of brain-gut axis facilitates malfunctioning of the intestinal barrier, and vice versa, increasing the risk of uncontrolled immunological reactions that may trigger mucosal and brain low-grade inflammation, a putative first step to the initiation of more permanent gut disorders. In this chapter, we describe the structure, function and interactions of intestinal barrier, microbiota and brain-gut axis in both healthy and pathological conditions.

Pathogenesis of necrotizing enterocolitis: modeling the innate immune response

Necrotizing enterocolitis (NEC) is a major cause of morbidity and mortality in premature infants. The pathophysiology is likely secondary to innate immune responses to intestinal microbiota by the premature infant's intestinal tract, leading to inflammation and injury. This review provides an updated summary of the components of the innate immune system involved in NEC pathogenesis. In addition, we evaluate the animal models that have been used to study NEC with regard to the involvement of innate immune factors and histopathological changes as compared to those seen in infants with NEC. Finally, we discuss new approaches to studying NEC, including mathematical models of intestinal injury and the use of humanized mice.

Functional roles of Syk in macrophage-mediated inflammatory responses

Inflammation is a series of complex biological responses to protect the host from pathogen invasion. Chronic inflammation is considered a major cause of diseases, such as various types of inflammatory/autoimmune diseases and cancers. Spleen tyrosine kinase (Syk) was initially found to be highly expressed in hematopoietic cells and has been known to play crucial roles in adaptive immune responses. However, recent studies have reported that Syk is also involved in other biological functions, especially in innate immune responses. Although Syk has been extensively studied in adaptive immune responses, numerous studies have recently presented evidence that Syk has critical functions in macrophage-mediated inflammatory responses and is closely related to innate immune response. This review describes the characteristics of Syk-mediated signaling pathways, summarizes the recent findings supporting the crucial roles of Syk in macrophage-mediated inflammatory responses and diseases, and discusses Syk-targeted drug development for the therapy of inflammatory diseases.