Interleukin-13 Receptor α1-Dependent Responses in the Intestine Are Critical to Parasite Clearance

Intestinal Permeability in Disorders of Gut-Brain Interaction: From Bench to Bedside

Intestinal barrier function lies at a critical interface of a range of peripheral and central processes that influence disorders of gut-brain interactions (DGBI). Although rigorously tested, the role of barrier dysfunction in driving clinical phenotype of DGBI remains to be fully elucidated. In vitro, in vivo, and ex vivo strategies can test various aspects of the broader permeability and barrier mechanisms in the gut. Luminal mediators of host, bacterial, and dietary origin can influence the barrier function and a disrupted barrier can also influence the luminal milieu. Critical to our understanding is how barrier dysfunction is influenced by stress and other comorbidities that associate with DGBI and the crosstalk between barrier and neural, hormonal, and immune responses. Additionally, the microbiome's significant role in the communication between the brain and gut has led to the integrative model of a microbiome gut-brain axis with reciprocal interactions between brain networks and networks composed of multiple cells in the gut, including immune cells, enterochromaffin cells, gut microbiota and the derived luminal mediators. This review highlights the techniques for assessment of barrier function, appraises evidence for barrier dysfunction in DGBI including mechanistic studies in humans, as well as provides an overview of therapeutic strategies that can be used to directly or indirectly restore barrier function in DGBI patients.

Differential resistance to nematode infection is associated with the genotype- and age-dependent pace of intestinal T cell homing

The resistance of inbred mice to nematode infections varies depending on the extent of protective Th2 responses. Here, we compared two mouse lines differing in resistance to infection with the enteric nematode Heligmosomoides polygyrus bakeri despite the similar instruction of GATA-3+ T effector cells. Resistant BALB/c mice rapidly recruited high numbers of Th2 cells to the gut within the 1-week time frame required for larval development in the intestinal submucosa. C57BL/6 mice failed in the optimal control of early nematode fitness, with mucosal Th2 response peaking after 2 weeks when the larvae had left the tissue and relocated to the gut lumen as adult worms. The faster homing of Th2 cells to the gut of BALB/c mice is related to the extensive expression of the chemokine receptor CCR9 in GATA-3+ cells and higher frequencies of aldehyde dehydrogenase expressing dendritic cells present in mesenteric lymph nodes. Furthermore, nematode-infected older BALB/c mice displayed impaired resistance due to delayed mucosal homing of effector cells, which synergized with more numerous Th2/1 hybrid cells acting as IFN-γ-dependent confounders of type 2 responses. Hence, the distinct kinetics of effector cell recruitment to the infected gut and the quality of GATA-3+ T cell responses contribute to the genotype- and age-dependent resistance to intestinal nematode infections.

Modulation of intestinal epithelial permeability by chronic small intestinal helminth infections

Increased permeability of the intestinal epithelial layer is linked to the pathogenesis and perpetuation of a wide range of intestinal and extra-intestinal diseases. Infecting humans with controlled doses of helminths, such as human hookworm (termed hookworm therapy), is proposed as a treatment for many of the same diseases. Helminths induce immunoregulatory changes in their host which could decrease epithelial permeability, which is highlighted as a potential mechanism through which helminths treat disease. Despite this, the influence of a chronic helminth infection on epithelial permeability remains unclear. This study uses the chronically infecting intestinal helminth Heligmosomoides polygyrus to reveal alterations in the expression of intestinal tight junction proteins and epithelial permeability during the infection course. In the acute infection phase (1 week postinfection), an increase in intestinal epithelial permeability is observed. Consistent with this finding, jejunal claudin-2 is upregulated and tricellulin is downregulated. By contrast, in the chronic infection phase (6 weeks postinfection), colonic claudin-1 is upregulated and epithelial permeability decreases. Importantly, this study also investigates changes in epithelial permeability in a small human cohort experimentally challenged with the human hookworm, Necator americanus. It demonstrates a trend toward small intestinal permeability increasing in the acute infection phase (8 weeks postinfection), and colonic and whole gut permeability decreasing in the chronic infection phase (24 weeks postinfection), suggesting a conserved epithelial response between humans and mice. In summary, our findings demonstrate dynamic changes in epithelial permeability during a chronic helminth infection and provide another plausible mechanism by which chronic helminth infections could be utilized to treat disease.

Helminths' therapeutic potential to treat intestinal barrier dysfunction

The intestinal barrier is a dynamic multi-layered structure which can adapt to environmental changes within the intestinal lumen. It has the complex task of allowing nutrient absorption while limiting entry of harmful microbes and microbial antigens present in the intestinal lumen. Excessive entry of microbial antigens via microbial translocation due to 'intestinal barrier dysfunction' is hypothesised to contribute to the increasing incidence of allergic, autoimmune and metabolic diseases, a concept referred to as the 'epithelial barrier theory'. Helminths reside in the intestinal tract are in intimate contact with the mucosal surfaces and induce a range of local immunological changes which affect the layers of the intestinal barrier. Helminths are proposed to prevent, or even treat, many of the diseases implicated in the epithelial barrier theory. This review will focus on the effect of helminths on intestinal barrier function and explore whether this could explain the proposed health benefits delivered by helminths.

Tralokinumab therapy for moderate-to-severe atopic dermatitis: Clinical outcomes with targeted IL-13 inhibition

Atopic dermatitis (AD) is a chronic, inflammatory, intensely pruritic skin disorder associated with significant patient burden. Interleukin (IL)-13 is a cytokine that acts as a driver of immune dysregulation, skin-barrier dysfunction, and microbiome dysbiosis that characterizes AD, and is consistently overexpressed in AD skin. Tralokinumab is a fully human immunoglobulin (Ig) G4 monoclonal antibody that binds specifically to IL-13 with high affinity, thereby inhibiting subsequent downstream IL-13 signaling. Three pivotal phase 3 clinical trials demonstrated that tralokinumab 300 mg every other week, as monotherapy or in combination with topical corticosteroids as needed, provides significant improvements in signs and symptoms of moderate-to-severe AD, as measured by Investigator's Global Assessment 0/1 (clear/almost clear) and Eczema Area and Severity Index-75 at Week 16. Improvements were observed soon after tralokinumab initiation and were maintained over 52 weeks of therapy. Tralokinumab significantly improved patient-reported outcomes such as itch and sleep, and demonstrated a safety profile comparable with placebo; conjunctivitis during tralokinumab therapy was generally mild. Similar results were observed in a phase 3 adolescent trial. The role of IL-13 in the pathophysiology of AD justifies a targeted approach and a wealth of clinical data supports tralokinumab as a new therapeutic option for people with moderate-to-severe AD.

Resistin-like molecules: a marker, mediator and therapeutic target for multiple diseases

Resistin-like molecules (RELMs) are highly cysteine-rich proteins, including RELMα, RELMβ, Resistin, and RELMγ. However, RELMs exhibit significant differences in structure, distribution, and function. The expression of RELMs is regulated by various signaling molecules, such as IL-4, IL-13, and their receptors. In addition, RELMs can mediate numerous signaling pathways, including HMGB1/RAGE, IL-4/IL-4Rα, PI3K/Akt/mTOR signaling pathways, and so on. RELMs proteins are involved in wide range of physiological and pathological processes, including inflammatory response, cell proliferation, glucose metabolism, barrier defense, etc., and participate in the progression of numerous diseases such as lung diseases, intestinal diseases, cardiovascular diseases, and cancers. Meanwhile, RELMs can serve as biomarkers, risk predictors, and therapeutic targets for these diseases. An in-depth understanding of the role of RELMs may provide novel targets or strategies for the treatment and prevention of related diseases. Video abstract.

Purinergic P2X7 Receptor Mediates the Elimination of Trichinella spiralis by Activating NF-κB/NLRP3/IL-1β Pathway in Macrophages

Trichinellosis is one of most neglected foodborne zoonoses worldwide. During Trichinella spiralis infection, the intestinal immune response is the first line of defense and plays a vital role in the host's resistance. Previous studies indicate that purinergic P2X7 receptor (P2X7R) and pyrin domain-containing protein 3 (NLRP3) inflammasome are involved in the intestinal immune response in T. spiralis infection. However, the precise role of P2X7R and its effect on NLRP3 remains largely underdetermined. In this study, we aimed to investigate the role of P2X7R in the activation of NLRP3 in macrophages during the intestinal immune response against T. spiralis We found that T. spiralis infection upregulated expression of P2X7R and activation of NLRP3 in macrophages in mice. In vivo, P2X7R deficiency resulted in increased intestinal adult and muscle larval burdens, along with decreased expression of NLRP3/interleukin-1β (IL-1β) in macrophages from the infected mice with T. spiralis In In vitro experiments, P2X7R blockade inhibited activation of NLRP3/IL-1β via NF-κB and thus reduced the capacity of macrophages to kill newborn larvae of T. spiralis These results indicate that P2X7R mediates the elimination of T. spiralis by activating the NF-κB/NLRP3/IL-1β pathway in macrophages. Our findings contribute to the understanding of the intestinal immune mechanism of T. spiralis infection.

The Intestinal Epithelium at the Forefront of Host-Helminth Interactions

Gastrointestinal helminth infection still constitutes a major public health issue, particularly in the developing world. As these parasites can undergo a large part of their lifecycle within the intestinal tract the host has developed various structural and cellular specializations at the epithelial barrier to contend with infection. Detailed characterization of these cells will provide important insights about their contributions to the protective responses mediated against helminths. Here, we discuss how key components of the intestinal epithelium may function to limit the initial establishment of helminths, and how these cells are altered during an active response to infection.

Co-expulsion of Ascaridia galli and Heterakis gallinarum by chickens

Worm expulsion is known to occur in mammalian hosts exposed to mono-species helminth infections, whilst this phenomenon is poorly described in avian hosts. Mono-species infections, however, are rather rare under natural circumstances. Therefore, we quantified the extent and duration of worm expulsion by chickens experimentally infected with both Ascaridia galli and Heterakis gallinarum, and investigated the accompanying humoral and cell-mediated host immune responses in association with population dynamics of the worms. Results demonstrated the strong co-expulsion of the two ascarid species in three phases. The expulsion patterns were characterized by non-linear alterations separated by species-specific time thresholds. Ascaridia galli burden decreased at a daily expulsion rate (e) of 4.3 worms up to a threshold of 30.5 days p.i., followed by a much lower second expulsion rate (e = 0.46), which resulted in almost, but not entirely, complete expulsion. Heterakis gallinarum was able to induce reinfection within the experimental period (9 weeks). First generation H. gallinarum worms were expelled at a daily rate of e = 0.8 worms until 36.4 days p.i., and thereafter almost no expulsion occurred. Data on both humoral and tissue-specific cellular immune responses collectively indicated that antibody production in chickens with multispecies ascarid infections is triggered by Th2 polarisation. Local Th2 immune responses and mucin-regulating genes are associated with the regulation of worm expulsion. In conclusion, the chicken host is able to eliminate the vast majority of both A. galli and H. gallinarum in three distinct phases. Worm expulsion was strongly associated with the developmental stages of the worms, where the elimination of juvenile stages was specifically targeted. A very small percentage of worms was nevertheless able to survive, reach maturity and induce reinfection if given sufficient time to complete their life cycle. Both humoral and local immune responses were associated with worm expulsion.

Helminths and intestinal barrier function

Approximately one-sixth of the worlds' population is infected with helminths and this class of parasite takes a major toll on domestic livestock. The majority of species of parasitic helminth that infect mammals live in the gut (the only niche for tapeworms) where they contact the hosts' epithelial cells. Here, the helminth-intestinal epithelial interface is reviewed in terms of the impact on, and regulation of epithelial barrier function, both intrinsic (epithelial permeability) and extrinsic (mucin, bacterial peptides, commensal bacteria) elements of the barrier. The data available on direct effects of helminths on epithelial permeability are scant, fragmentary and pales in comparison with knowledge of mobilization of immune reactions and effector cells in response to helminth parasites and how these impact intestinal barrier function. The interaction of helminth-host and helminth-host-bacteria is an important determinant of gut form and function and precisely defining these interactions will radically alter our understanding of normal gut physiology and pathophysiological reactions, revealing new approaches to infection with parasitic helminths, bacterial pathogens and idiopathic auto-inflammatory disease.

Intraperitoneal administration of the anti-IL-23 antibody prevents the establishment of intestinal nematodes in mice

Previous studies have established that an increased Th-9 response creates a hostile environment for nematode parasites. Given that IL-23, a cytokine required for maintenance of the IL-17-secreting phenotype, has inhibitory effects on IL-9 production, we hypothesized that reducing circulating IL-23 by treatment with anti-IL-23 antibodies would reduce the establishment and development of parasitic intestinal nematodes. In this study, we show that animals treated with anti-IL-23 monoclonal antibodies showed a drastic reduction in the number of mouse pinworms (Aspiculuris tetraptera) recovered from the intestine (p < 0.001) at 23 days post-infection compared to the untreated animals. The cytokine levels in Peyer's patches (PP) in treated and infected animals increase the expression of interleukins such as IL-25, IL-21, and IL-9, augmenting mucus production in the crypts, and boosting chemokines, such as OX40 and CCL20 in the mucosa. Our results suggest that the Th17/Th2 regulatory mechanism provoked by the administration of the anti-IL-23 antibody prevents the implantation of the intestinal nematode in mice. The diminished inflammatory IL-17 levels alter the Th9 environment perhaps as a consequence of IL-17 inhibiting IL-9 expression. These Th9 conditions may explain the successful treatment against Inflammatory Bowel Disease (IBD) both with antibodies against IL-23 or through parasitization with nematodes.

Chronic features of allergic asthma are enhanced in the absence of resistin-like molecule-beta

Asthma is characterized by inflammation and architectural changes in the lungs. A number of immune cells and mediators are recognized as initiators of asthma, although therapeutics based on these are not always effective. The multifaceted nature of this syndrome necessitate continued exploration of immunomodulators that may play a role in pathogenesis. We investigated the role of resistin-like molecule-beta (RELM-β), a gut antibacterial, in the development and pathogenesis of Aspergillus-induced allergic airways disease. Age and gender matched C57BL/6J and Retnlb^−/− mice rendered allergic to Aspergillus fumigatus were used to measure canonical markers of allergic asthma at early and late time points. Inflammatory cells in airways were similar, although Retnlb^−/− mice had reduced tissue inflammation. The absence of RELM-β elevated serum IgA and pro-inflammatory cytokines in the lungs at homeostasis. Markers of chronic disease including goblet cell numbers, Muc genes, airway wall remodelling, and hyperresponsiveness were greater in the absence RELM-β. Specific inflammatory mediators important in antimicrobial defence in allergic asthma were also increased in the absence of RELM-β. These data suggest that while characteristics of allergic asthma develop in the absence of RELM-β, that RELM-β may reduce the development of chronic markers of allergic airways disease.

Pathological and therapeutic roles of innate lymphoid cells in diverse diseases

Innate lymphoid cells (ILCs) are a recently defined type of innate-immunity cells that belong to the lymphoid lineage and have lymphoid morphology but do not express an antigen-specific B cell or T-cell receptor. ILCs regulate immune functions prior to the formation of adaptive immunity and exert effector functions through a cytokine release. ILCs have been classified into three groups according to the transcription factors that regulate their development and function and the effector cytokines they produce. Of note, ILCs resemble T helper (Th) cells, such as Th1, Th2, and Th17 cells, and show a similar dependence on transcription factors and distinct cytokine production. Despite their short history in immunology, ILCs have received much attention, and numerous studies have revealed biological functions of ILCs including host defense against pathogens, inflammation, tissue repair, and metabolic homeostasis. Here, we describe recent findings about the roles of ILCs in the pathogenesis of various diseases and potential therapeutic targets.

Interleukin-13/interleukin-4 receptor pathway is crucial for production of Sda-sialomucin in mouse small intestinal mucosa by Nippostrongylus brasiliensis infection

Mucin is a major component of mucus in gastrointestinal mucosa. Increase of specific sialomucins having Sd^a blood group antigen, NeuAcα2-3(GalNAcβ1-4)Galβ1-4GlcNAcβ-, is considered to be associated with expulsion of the parasitic intestinal nematode Nippostrongylus brasiliensis. In this study, we examined the relationship between interleukin (IL)-13 pathway and expression of Sd^a-sialomucins in small intestinal mucosa with N. brasiliensis infection. Nematode infection induced marked increases in small intestinal mucins that reacted with anti-Sd^a antibody in wild type (wt) mice. However, this increase due to infection was supressed in IL-4 receptor α deficient (IL-4Rα^-/-) mice, which lack both IL-4 and IL-13 signaling via IL-4R, and severe combined immunodeficient (SCID) mice, which have defects in B- and T-lymphocytes. Analysis using tandem mass spectroscopy showed that Sd^a-glycans were not expressed in small intestinal mucins in IL-4Rα^-/- and SCID mice after infection despite the appearance of Sd^a-glycans in the infected wt mice. Inoculation of recombinant IL-13 into the infected SCID mice restored expression of Sd^a-glycan. Our results suggest that the IL-13/IL-4R axis is important for the production of Sd^a-sialomucins in the host intestinal mucosa with parasitic nematode infection.

IL-22 Upregulates Epithelial Claudin-2 to Drive Diarrhea and Enteric Pathogen Clearance

Diarrhea is a host response to enteric pathogens, but its impact on pathogenesis remains poorly defined. By infecting mice with the attaching and effacing bacteria Citrobacter rodentium, we defined the mechanisms and contributions of diarrhea and intestinal barrier loss to host defense. Increased permeability occurred within 2 days of infection and coincided with IL-22-dependent upregulation of the epithelial tight junction protein claudin-2. Permeability increases were limited to small molecules, as expected for the paracellular water and Na+ channel formed by claudin-2. Relative to wild-type, claudin-2-deficient mice experienced severe disease, including increased mucosal colonization by C. rodentium, prolonged pathogen shedding, exaggerated cytokine responses, and greater tissue injury. Conversely, transgenic claudin-2 overexpression reduced disease severity. Chemically induced osmotic diarrhea reduced colitis severity and C. rodentium burden in claudin-2-deficient, but not transgenic, mice, demonstrating that claudin-2-mediated protection is the result of enhanced water efflux. Thus, IL-22-induced claudin-2 upregulation drives diarrhea and pathogen clearance.

Parasites, nutrition, immune responses and biology of metabolic tissues

Nutritional immunology, immunometabolism and identification of novel immunotherapeutic targets are areas of active investigation in parasitology. There is a well-documented crosstalk among immune cells and cells in metabolically active tissues that is important for homeostasis. The numbers and function of these cells are altered by obesity leading to inflammation. A variety of helminths spend some part of their life cycle in the gastrointestinal tract and even entirely enteral nematode infections exert beneficial effects on glucose and lipid metabolism. The foundation of this review is the ability of enteric nematode infections to improve obesity-induced type 2 diabetes and the metabolic syndrome, which are significant health issues in developed areas. It considers the impact of nutrition and specific nutritional deficiencies, which are occur in both undeveloped and developed areas, on the host's ability mount a protective immune response against parasitic nematodes. There are a number of proposed mechanisms by which parasitic nematodes can impact metabolism including effects gastrointestinal hormones, altering epithelial function and changing the number and/or phenotype of immune cells in metabolic tissues. Nematodes can also exert their beneficial effects through Th2 cytokines that activate the transcription factor STAT6, which upregulates genes that regulate glucose and lipid metabolism.

Effect of predatory bacteria on the gut bacterial microbiota in rats

Bdellovibrio bacteriovorus and Micavibrio aeruginosavorus are Gram-negative proteobacteria that are obligate predators of other Gram-negative bacteria and are considered potential alternatives to antibiotics. Most studies focusing on predatory bacteria have been performed in vitro, thus the effect of predatory bacteria on a live host, including the impact on the ecology of the native microbiota, has yet to be fully examined. In this study, intrarectal inoculations of Sprague-Dawley rats with predatory bacteria were performed. Additionally, feces were collected for seven days post-inoculation to determine the effect on gut bacterial diversity. Rat colonic tissue exhibited no abnormal histopathological effects due to predatory bacteria. A modest increase in pro-inflammatory cytokines was measured in the colons of rats inoculated with predatory bacteria by 24 and 48 hours, with all but IL-13 returning to baseline by seven days. V4 16S rRNA gene sequencing of fecal DNA demonstrated minimal shifts in taxonomic representation over the week due to predatory bacteria. Changes in bacterial populations due to exposure to B. bacteriovorus are predicted to contribute to health, however, an overgrowth of Prevotella was observed due to exposure to M. aeruginosavorus. This study further addresses safety concerns associated with the potential use of predatory bacteria to treat infections.

Neuroimmune Modulation of Gut Function

Neuroimmune communications are facilitated by the production of neurotransmitters by immune cells and the generation of immune mediators by immune cells, which form a functional entity called the "neuroimmune synapse." There are several mechanisms that further facilitate neuroimmune interactions including the anatomic proximity between immune cells and nerves, the expression of receptors for neurotransmitters on immune cells and for immune mediators on nerves, and the receptor-mediated activation of intracellular signaling pathways that modulate nerve and immune phenotype and function. The bidirectional communication between nerves and immune cells is implicated in allostasis, a process that describes the continuous adaptation to an ever-changing environment. Neuroimmune interactions are amplified during inflammation by the influx of activated immune cells that significantly alter the microenvironment. In this context, the types of neurotransmitters released by activated neurons or immune cells can exert pro- or anti-inflammatory effects. Dysregulation of the enteric nervous system control of gastrointestinal functions, such as epithelial permeability and secretion as well as smooth muscle contractility, also contribute to the chronicity of inflammation. Persistent active inflammation in the gut leads to neuroimmune plasticity, which is a structural and functional remodeling in both the neural and immune systems. The importance of neuroimmune interactions has made them an emerging target in the development of novel therapies for GI pathologies.