Prostaglandin E₂ constrains systemic inflammation through an innate lymphoid cell-IL-22 axis

Facilitation of IL-22 production from innate lymphoid cells by prostaglandin E2 prevents experimental lung neutrophilic inflammation

Acute lung injury is a neutrophil-dominant, life-threatening disease without effective therapies and better understanding of the pathophysiological mechanisms involved is an urgent need. Here we show that interleukin (IL)-22 is produced from innate lymphoid cells (ILC) and is responsible for suppression of experimental lung neutrophilic inflammation. Blocking prostaglandin E2 (PGE2) synthesis reduces lung ILCs and IL-22 production, resulting in exacerbation of lung neutrophilic inflammation. In contrast, activation of the PGE2 receptor EP4 prevents acute lung inflammation. We thus demonstrate a mechanism for production of innate IL-22 in the lung during acute injury, highlighting potential therapeutic strategies for control of lung neutrophilic inflammation by targeting the PGE2/ILC/IL-22 axis.

Purine metabolism controls innate lymphoid cell function and protects against intestinal injury

Inflammatory bowel disease (IBD) is a condition of chronic inflammatory intestinal disorder with increasing prevalence but limited effective therapies. The purine metabolic pathway is involved in various inflammatory processes including IBD. However, the mechanisms through which purine metabolism modulates IBD remain to be established. Here, we found that mucosal expression of genes involved in the purine metabolic pathway is altered in patients with active ulcerative colitis (UC), which is associated with elevated gene expression signatures of the group 3 innate lymphoid cell (ILC3)-interleukin (IL)-22 pathway. In mice, blockade of ectonucleotidases (NTPDases), critical enzymes for purine metabolism by hydrolysis of extracellular adenosine 5'-triphosphate (eATP) into adenosine, exacerbates dextran-sulfate sodium-induced intestinal injury. This exacerbation of colitis is associated with reduction of colonic IL-22-producing ILC3s, which afford essential protection against intestinal inflammation, and is rescued by exogenous IL-22. Mechanistically, activation of ILC3s for IL-22 production is reciprocally mediated by eATP and adenosine. These findings reveal that the NTPDase-mediated balance between eATP and adenosine regulates ILC3 cell function to provide protection against intestinal injury and suggest potential therapeutic strategies for treating IBD by targeting the purine-ILC3 axis.

Prostaglandin E2 hydrogel improves cutaneous wound healing via M2 macrophages polarization

Wound healing is regulated by a complex series of events and overlapping phases. A delicate balance of cytokines and mediators in tissue repair is required for optimal therapy in clinical applications. Molecular imaging technologies, with their versatility in monitoring cellular and molecular events in living organisms, offer tangible options to better guide tissue repair by regulating the balance of cytokines and mediators at injured sites.

Methods: A murine cutaneous wound healing model was developed to investigate if incorporation of prostaglandin E₂ (PGE₂) into chitosan (CS) hydrogel (CS+PGE₂ hydrogel) could enhance its therapeutic effects. Bioluminescence imaging (BLI) was used to noninvasively monitor the inflammation and angiogenesis processes at injured sites during wound healing. We also investigated the M1 and M2 paradigm of macrophage activation during wound healing.

Results: CS hydrogel could prolong the release of PGE₂, thereby improving its tissue repair and regeneration capabilities. Molecular imaging results showed that the prolonged release of PGE₂ could ameliorate inflammation by promoting the M2 phenotypic transformation of macrophages. Also, CS+PGE₂ hydrogel could augment angiogenesis at the injured sites during the early phase of tissue repair, as revealed by BLI. Furthermore, our results demonstrated that CS+PGE₂ hydrogel could regulate the balance among the three overlapping phases—inflammation, regeneration (angiogenesis), and remodeling (fibrosis)—during cutaneous wound healing.

Conclusion: Our findings highlight the potential of the CS+PGE₂ hydrogel as a novel therapeutic strategy for promoting tissue regeneration via M2 macrophage polarization. Moreover, molecular imaging provides a platform for monitoring cellular and molecular events in real-time during tissue repair and facilitates the discovery of optimal therapeutics for injury repair by regulating the balance of cytokines and mediators at injured sites.

Interplay of innate lymphoid cells and the microbiota

Innate lymphoid cells (ILC) are a recently identified group of innate lymphocytes that are preferentially located at barrier surfaces. Barrier surfaces are in direct contact with complex microbial ecosystems, collectively referred to as the microbiota. It is now believed that the interplay of the microbiota with host components (i.e. epithelial cells and immune cells) promotes host fitness by regulating organ homeostasis, metabolism, and host defense against pathogens. In this review, we will give an overview of this multifaceted interplay between ILC and components of the microbiota.

Mesenchymal Stromal Cells Stimulate the Proliferation and IL-22 Production of Group 3 Innate Lymphoid Cells

Infusion of mesenchymal stromal cells (MSCs) is a promising and increasingly applied therapy for patients who suffer from a variety of inflammatory diseases, including graft-versus-host disease (GvHD), a common and life-threatening complication after allogeneic hematopoietic stem cell transplantation. The therapeutic effect of MSCs is mainly ascribed to their ability to suppress T cells and to support tissue repair. However, clinical response rates in patients with GvHD are limited to 50%, and the determinants for MSC responsiveness are unknown. We recently reported that high frequencies of activated group 3 innate lymphoid cells (ILC3s) before and after allogeneic hematopoietic stem cell transplantation were associated with a lower risk of GvHD. This may be related to IL-22 production by ILC3s, a cytokine important for intestinal epithelial cell homeostasis. In this study, we investigated whether ILC3s may contribute to the therapeutic effect of MSCs by studying the interaction between MSCs and ILC3s in vitro. ILC3s isolated from human tonsils were cocultured with human bone marrow-derived MSCs for 5 d in the presence of IL-2. Coculture with MSCs enhanced the proliferation and IL-22 production of ILC3s. Reciprocally, ILC3s promoted ICAM-1 and VCAM-1 expression on MSCs. For both directions, the activation was mainly mediated by cell-cell contact and by MSC-derived IL-7 and likely by aryl hydrocarbon receptor ligands. Thus, in addition to inhibiting the proliferation of alloreactive T cells, MSCs also promote the expansion and IL-22 production of ILC3s, which may contribute to healthy homeostasis and wound repair in the treatment of various inflammatory conditions in the intestine, including GvHD.

The Tumor Necrosis Factor Superfamily Member RANKL Suppresses Effector Cytokine Production in Group 3 Innate Lymphoid Cells

While signals that activate group 3 innate lymphoid cells (ILC3s) have been described, the factors that negatively regulate these cells are less well understood. Here we found that the tumor necrosis factor (TNF) superfamily member receptor activator of nuclear factor κB ligand (RANKL) suppressed ILC3 activity in the intestine. Deletion of RANKL in ILC3s and T cells increased C-C motif chemokine receptor 6 (CCR6)⁺ ILC3 abundance and enhanced production of interleukin-17A (IL-17A) and IL-22 in response to IL-23 and during infection with the enteric murine pathogen Citrobacter rodentium. Additionally, CCR6⁺ ILC3s produced higher amounts of the master transcriptional regulator RORγt at steady state in the absence of RANKL. RANKL-mediated suppression was independent of T cells, and instead occurred via interactions between CCR6⁺ ILC3s that expressed both RANKL and its receptor, RANK. Thus, RANK-RANKL interactions between ILC3s regulate ILC3 abundance and activation, suggesting that cell clustering may control ILC3 activity.

Arachidonic acid in health and disease with focus on hypertension and diabetes mellitus: A review

Arachidonic acid (AA 20:4n-6) is an essential component of cell membranes and modulates cell membrane fluidity. AA is metabolized by cyclo-oxygenase (COX), lipoxygenase (LOX) and cytochrome P450 enzymes to form several metabolites that have important biological actions. Of all the actions, role of AA in the regulation of blood pressure and its ability to prevent both type 1 and type 2 diabetes mellitus seems to be interesting. Studies showed that AA and its metabolites especially, lipoxin A4 (LXA4) and epoxyeicosatrienoic acids (EETs), potent anti-inflammatory metabolites, have a crucial role in the pathobiology of hypertension and diabetes mellitus. AA, LXA4 and EETs regulate smooth muscle function and proliferation, voltage gated ion channels, cell membrane fluidity, membrane receptors, G-coupled receptors, PPARs, free radical generation, nitric oxide formation, inflammation, and immune responses that, in turn, participate in the regulation blood pressure and pathogenesis of diabetes mellitus. In this review, role of AA and its metabolites LXA4 and EETs in the pathobiology of hypertension, pre-eclampsia and diabetes mellitus are discussed. Based on several lines of evidences, it is proposed that a combination of aspirin and AA could be of benefit in the prevention and management of hypertension, pre-eclampsia and diabetes mellitus.

The oxidized linoleic acid metabolite 12,13-DiHOME mediates thermal hyperalgesia during inflammatory pain

Eicosanoids play a crucial role in inflammatory pain. However, there is very little knowledge about the contribution of oxidized linoleic acid metabolites in inflammatory pain and peripheral sensitization. Here, we identify 12,13-dihydroxy-9Z-octadecenoic acid (12,13-DiHOME), a cytochrome P450-derived linoleic acid metabolite, as crucial mediator of thermal hyperalgesia during inflammatory pain. We found 12,13-DiHOME in increased concentrations in peripheral nervous tissue during acute zymosan- and complete Freund's Adjuvant-induced inflammatory pain. 12,13-DiHOME causes calcium transients in sensory neurons and sensitizes the transient receptor potential vanilloid 1 (TRPV1)-mediated intracellular calcium increases via protein kinase C, subsequently leading to enhanced TRPV1-dependent CGRP-release from sensory neurons. Peripheral injection of 12,13-DiHOME in vivo causes TRPV1-dependent thermal pain hypersensitivity. Finally, application of the soluble epoxide hydrolase (sEH)-inhibitor TPPU reduces 12,13-DiHOME concentrations in nervous tissue and reduces zymosan- and CFA-induced thermal hyperalgesia in vivo. In conclusion, we identify a novel role for the lipid mediator 12,13-DiHOME in mediating thermal hyperalgesia during inflammatory pain and propose a novel mechanism that may explain the antihyperalgesic effects of sEH inhibitors in vivo.

Prostaglandin E2 Inhibits Group 2 Innate Lymphoid Cell Activation and Allergic Airway Inflammation Through E-Prostanoid 4-Cyclic Adenosine Monophosphate Signaling

Evidence is accumulating that group 2 innate lymphoid cells (ILC2) play an important role in allergic airway inflammation by producing a large amount of type 2 cytokines. But it remains poorly understood how its activities are properly controlled in vivo. Here, we demonstrated that prostaglandin E₂ (PGE₂) had a profound inhibitory effect on IL-33-induced ILC2 expansion and IL-5 and IL-13 production in vitro. This effect was mimicked by PGE₁-alcohol but attenuated by ONO-AE3-208, indicating a selective action through the E-prostanoid 4 (EP4) receptor. In the IL-33-induced asthma model, coadministration of PGE₂ or PGE₁-alcohol resulted in diminished IL-5 and IL-13 production, reduced eosinophilia and alleviated lung pathology. In contrast, EP4-deficient mice displayed an exacerbated inflammatory response in another ILC2-mediated asthma model induced by Alternaria extract. Mechanistic studies demonstrated that the PGE₂-mediated inhibition of ILC2 was dependent on cyclic adenosine monophosphate (cAMP) production. Further downstream, PGE₂-EP4-cAMP signaling led to suppression of GATA3 and ST2 expression, which is known to be critical for ILC2 activation. These findings reveal a novel function of PGE₂ as a negative regulator of ILC2 activation and highlight an endogenous counter-regulatory mechanism for the control of innate allergic inflammatory responses.

Role of lipid mediators and control of lymphocyte responses in type 2 immunopathology

Type 2 immunopathology is a cardinal feature of allergic diseases and involves cooperation between adaptive immunity and innate effector responses. Virtually all cell types relevant to this pathology generate leukotriene and/or prostaglandin mediators that derive from arachidonic acid, express receptors for such mediators, or both. Recent studies highlight prominent functions for these mediators in communication between the innate and adaptive immune systems, as well as amplification or suppression of type 2 effector responses. This review focuses on recent advances and insights, and highlights existing and potential therapeutic applications of drugs that target these mediators or their receptors, with a special emphasis on their regulation of the innate and adaptive lymphocytes relevant to type 2 immunopathology.

Interleukin 22 prevents lipopolysaccharide- induced preterm labor in mice

Preterm birth is widespread and causes 35% of all neonatal deaths. Infants who survive face potential long-term complications. A major contributing factor of preterm birth is infection. We investigated the role of interleukin 22 (IL22) as a potential clinically relevant cytokine during gestational infection. IL22 is an effector molecule secreted by immune cells. While the expression of IL22 was reported in normal nonpregnant endometrium and early pregnancy decidua, little is known about uterine IL22 expression during mid or late gestational stages of pregnancy. Since IL22 has been shown to be an essential mediator in epithelial regeneration and wound repair, we investigated the potential role of IL22 during defense against an inflammatory response at the maternal-fetal interface. We used a well-established model to study infection and infection-associated inflammation during preterm birth in the mouse. We have shown that IL22 is upregulated to respond to an intrauterine lipopolysaccharide administration and plays an important role in controlling the risk of inflammation-induced preterm birth. This paper proposes IL22 as a treatment method to combat infection and prevent preterm birth in susceptible patients.

Prostaglandin E2 stimulates adaptive IL-22 production and promotes allergic contact dermatitis

BACKGROUND

Atopic dermatitis (AD) and allergic contact dermatitis (ACD) are both forms of eczema and are common inflammatory skin diseases with a central role of T cell-derived IL-22 in their pathogenesis. Although prostaglandin (PG) E2 is known to promote inflammation, little is known about its role in processes related to AD and ACD development, including IL-22 upregulation.

OBJECTIVES

We sought to investigate whether PGE2 has a role in IL-22 induction and development of ACD, which has increased prevalence in patients with AD.

METHODS

T-cell cultures and in vivo sensitization of mice with haptens were used to assess the role of PGE2 in IL-22 production. The involvement of PGE2 receptors and their downstream signals was also examined. The effects of PGE2 were evaluated by using the oxazolone-induced ACD mouse model. The relationship of PGE2 and IL-22 signaling pathways in skin inflammation were also investigated by using genomic profiling in human lesional AD skin.

RESULTS

PGE2 induces IL-22 from T cells through its receptors, E prostanoid receptor (EP) 2 and EP4, and involves cyclic AMP signaling. Selective deletion of EP4 in T cells prevents hapten-induced IL-22 production in vivo, and limits atopic-like skin inflammation in the oxazolone-induced ACD model. Moreover, both PGE2 and IL-22 pathway genes were coordinately upregulated in human AD lesional skin but were at less than significant detection levels after corticosteroid or UVB treatments.

CONCLUSIONS

Our results define a crucial role for PGE2 in promoting ACD by facilitating IL-22 production from T cells.

mPGES1-Dependent Prostaglandin E2 (PGE2) Controls Antigen-Specific Th17 and Th1 Responses by Regulating T Autocrine and Paracrine PGE2 Production

The integration of inflammatory signals is paramount in controlling the intensity and duration of immune responses. Eicosanoids, particularly PGE₂, are critical molecules in the initiation and resolution of inflammation and in the transition from innate to acquired immune responses. Microsomal PGE synthase 1 (mPGES1) is an integral membrane enzyme whose regulated expression controls PGE₂ levels and is highly expressed at sites of inflammation. PGE₂ is also associated with modulation of autoimmunity through altering the IL-23/IL-17 axis and regulatory T cell (Treg) development. During a type II collagen-CFA immunization response, lack of mPGES1 impaired the numbers of CD4⁺ regulatory (Treg) and Th17 cells in the draining lymph nodes. Ag-experienced mPGES1^-/- CD4⁺ cells showed impaired IL-17A, IFN-γ, and IL-6 production when rechallenged ex vivo with their cognate Ag compared with their wild-type counterparts. Additionally, production of PGE₂ by cocultured APCs synergized with that of Ag-experienced CD4⁺ T cells, with mPGES1 competence in the APC compartment enhancing CD4⁺ IL-17A and IFN-γ responses. However, in contrast with CD4⁺ cells that were Ag primed in vivo, exogenous PGE₂ inhibited proliferation and skewed IL-17A to IFN-γ production under Th17 polarization of naive T cells in vitro. We conclude that mPGES1 is necessary in vivo to mount optimal Treg and Th17 responses during an Ag-driven primary immune response. Furthermore, we uncover a coordination of autocrine and paracrine mPGES1-driven PGE₂ production that impacts effector T cell IL-17A and IFN-γ responses.

Metabolic Regulation of Innate Lymphoid Cell-Mediated Tissue Protection-Linking the Nutritional State to Barrier Immunity

Innate lymphoid cells (ILC) are a recently described group of tissue-resident immune cells that play essential roles in maintaining and protecting the tissue barrier against invading pathogens. Extensive research has revealed that ILC-mediated immune responses are controlled by dietary components and metabolites. An additional role of ILC as important direct regulators of host metabolism and glucose tolerance is emerging. This suggests that ILC may act as key dietary sensors integrating nutritional and metabolic stress to facilitate both maintenance of barrier sites and a coordinated immune response protecting these tissues. In this respect, investigations have begun to determine how different ILC responses are metabolically fueled and the impact of nutrient availability on the regulation of ILC function. Here, we discuss the current literature concerning dietary and metabolic control of ILC. In particular, we address whether the dietary and metabolic control of ILC and their simultaneous influence on host metabolism may function as a coordinated program of barrier defense.

Group 3 Innate Lymphoid Cells: Communications Hubs of the Intestinal Immune System

The maintenance of mammalian health requires the generation of appropriate immune responses against a broad range of environmental and microbial challenges, which are continually encountered at barrier tissue sites including the skin, lung, and gastrointestinal tract. Dysregulated barrier immune responses result in inflammation, both locally and systemically in peripheral organs. Group 3 innate lymphoid cells (ILC3) are constitutively present at barrier sites and appear to be highly specialized in their ability to sense a range of environmental and host-derived signals. Under homeostatic conditions, ILC3 respond to local cues to maintain tissue homeostasis and restrict inflammatory responses. In contrast, perturbations in the tissue microenvironment resulting from disease, infection, or tissue damage can drive dysregulated pro-inflammatory ILC3 responses and contribute to immunopathology. The tone of the ILC3 response is dictated by a balance of “exogenous” signals, such as dietary metabolites and commensal microbes, and “endogenous” host-derived signals from stromal cells, immune cells, and the nervous system. ILC3 must therefore have the capacity to simultaneously integrate a wide array of complex and dynamic inputs in order to regulate barrier function and tissue health. In this review, we discuss the concept of ILC3 as a “communications hub” in the intestinal tract and associated lymphoid tissues and address the variety of signals, derived from multiple biological systems, which are interpreted by ILC3 to modulate the release of downstream effector molecules and regulate cell–cell crosstalk. Successful integration of environmental cues by ILC3 and downstream propagation to the broader immune system is required to maintain a tolerogenic and anti-inflammatory tone and reinforce barrier function, whereas dysregulation of ILC3 responses can contribute to the onset or progression of clinically relevant chronic inflammatory diseases.

Group III phospholipase A2 promotes colitis and colorectal cancer

Lipid mediators play pivotal roles in colorectal cancer and colitis, but only a limited member of the phospholipase A₂ (PLA₂) subtypes, which lie upstream of various lipid mediators, have been implicated in the positive or negative regulation of these diseases. Clinical and biochemical evidence suggests that secreted PLA₂ group III (sPLA₂-III) is associated with colorectal cancer, although its precise role remains obscure. Here we have found that sPLA₂-III-null (Pla2g3 ^-/-) mice are highly resistant to colon carcinogenesis. Furthermore, Pla2g3 ^-/- mice are less susceptible to dextran sulfate-induced colitis, implying that the amelioration of colonic inflammation by sPLA₂-III ablation may underlie the protective effect against colon cancer. Lipidomics analysis of the colon revealed significant reduction of pro-inflammatory/pro-tumorigenic lysophosholipids as well as unusual steady-state elevation of colon-protective fatty acids and their oxygenated metabolites in Pla2g3 ^-/- mice. Overall, our results establish a role of sPLA₂-III in the promotion of colorectal inflammation and cancer, expand our understanding of the divergent roles of multiple PLA₂ enzymes in the gastrointestinal tract, and point to sPLA₂-III as a novel druggable target for colorectal diseases.

Tumour-derived PGD2 and NKp30-B7H6 engagement drives an immunosuppressive ILC2-MDSC axis

Group 2 innate lymphoid cells (ILC2s) are involved in human diseases, such as allergy, atopic dermatitis and nasal polyposis, but their function in human cancer remains unclear. Here we show that, in acute promyelocytic leukaemia (APL), ILC2s are increased and hyper-activated through the interaction of CRTH2 and NKp30 with elevated tumour-derived PGD2 and B7H6, respectively. ILC2s, in turn, activate monocytic myeloid-derived suppressor cells (M-MDSCs) via IL-13 secretion. Upon treating APL with all-trans retinoic acid and achieving complete remission, the levels of PGD2, NKp30, ILC2s, IL-13 and M-MDSCs are restored. Similarly, disruption of this tumour immunosuppressive axis by specifically blocking PGD2, IL-13 and NKp30 partially restores ILC2 and M-MDSC levels and results in increased survival. Thus, using APL as a model, we uncover a tolerogenic pathway that may represent a relevant immunosuppressive, therapeutic targetable, mechanism operating in various human tumour types, as supported by our observations in prostate cancer.Group 2 innate lymphoid cells (ILC2s) modulate inflammatory and allergic responses, but their function in cancer immunity is still unclear. Here the authors show that, in acute promyelocytic leukaemia, tumour-activated ILC2s secrete IL-13 to induce myeloid-derived suppressor cells and support tumour growth.

IL-33 Signaling Regulates Innate IL-17A and IL-22 Production via Suppression of Prostaglandin E2 during Lung Fungal Infection

Members of the IL-1 family play protective and regulatory roles in immune defense against the opportunistic mold Aspergillus fumigatus In this study, we investigated the IL-1 family member IL-33 in lung defense against A. fumigatus IL-33 was detected in the naive lung, which further increased after exposure to A. fumigatus in a dectin-1-independent manner. Mice deficient in the receptor for IL-33 (Il1rl1-/-) unexpectedly demonstrated enhanced lung clearance of A. fumigatus IL-33 functioned as a negative regulator of multiple inflammatory cytokines, as IL-1α, IL-1β, IL-6, IL-17A, and IL-22 were significantly elevated in fungal-exposed Il1rl1-/- mice. Subsequently, IL-33 administration to normal mice attenuated fungal-induced IL-17A and IL-22, but not IL-1α, IL-1β, or IL-6, production. IL-33-mediated regulation of IL-17A and IL-22 did not involve the modulation of IL-23 but rather PGE2; PGE2 was significantly increased in fungal-exposed Il1rl1-/- mice, and normal mice produced less PGE2 after fungal exposure when administered IL-33, suggesting that IL-33-mediated regulation of IL-17A and IL-22 occurred at the level of PGE2 This was confirmed by in vivo cyclooxygenase 2 inhibition, which attenuated fungal-induced IL-17A and IL-22, as well as IL-1α, IL-1β, and IL-6, production in Il1rl1-/- mice, resulting in impaired fungal clearance. We also show that a PGE2 receptor agonist increased, whereas a PGE2 synthase inhibitor decreased, the levels of IL-17A and IL-22 but not IL-1α, IL-1β, or IL-6. This study establishes novel mechanisms of innate IL-17A/IL-22 production via PGE2 and regulation of the PGE2/IL-17A/IL-22 axis via IL-33 signaling during lung fungal exposure.

The intricate connection between diet, microbiota, and cancer: A jigsaw puzzle

The microbial community has a decisive role in determining our health and disease susceptibility. Presumably, this is closely associated with the complex community network of bacteria, fungi, archaea and viruses that reside our guts. This dynamic ecosystem exists in a symbiotic relationship with its host and plays a fundamental role in the hosts' physiological functions. The microbial community is highly personalized and therefore exhibits a high degree of inter-individual variability, which is dependent on host specifics such as genetic background, physiology and lifestyle. Although the gut microbiota is shaped early on during birth, there are several factors that affect the composition of microbiota during childhood and adulthood. Among them diet appears to be a consistent and prominent one. The metabolic activity of bacteria affects food digestion, absorption, energy production, and immunity. Thus, definition of the microbiota composition and functional profiles in response to a particular diet may lead to critical information on the direct and indirect role/use of the bacterial community during health and disease. In this review, I discuss gut microbiota and its potential link to cancer with specific emphasis on metabolism and diet.

PGE2 pulsing of murine bone marrow cells reduces migration of daughter monocytes/macrophages in vitro and in vivo

Monocytes/macrophages differentiating from bone marrow (BM) cells pulsed for 2 hours at 37°C with a stabilized derivative of prostaglandin E₂, 16,16-dimethyl PGE₂ (dmPGE₂), migrated less efficiently toward a chemoattractant than monocytes/macrophages differentiated from BM cells pulsed with vehicle. To confirm that the effect on BM cells was long lasting and to replicate human BM transplantation, chimeric mice were established with donor BM cells pulsed for 2 hours with dmPGE₂ before injection into marrow-ablated congenic recipient mice. After 12 weeks, when high levels (90%) of engraftment were obtained, regenerated BM-derived monocytes/macrophages differentiating in vitro or in vivo migrated inefficiently toward the chemokines colony-stimulating factor-1 (CSF-1) and chemokine (C-C motif) ligand 2 (CCL2) or thioglycollate, respectively. Our results reveal long-lasting changes to progenitor cells of monocytes/macrophages by a 2-hour dmPGE₂ pulse that, in turn, limits the migration of their daughter cells to chemoattractants and inflammatory mediators.

Innate lymphoid cells: major players in inflammatory diseases

Recent years have seen a marked increase in our understanding of innate lymphoid cells (ILCs). ILCs can be classified into different groups based on their similarity to T cell subsets in terms of their expression of key transcription factors and cytokine production. Various immunological functions of ILCs have been described, and increasing numbers of studies have implicated these cells in inflammatory disorders. Here, we detail the roles of ILCs in inflammatory diseases; we cover type 2 inflammatory diseases (such as asthma, chronic rhinosinusitis and atopic dermatitis), as well as inflammatory bowel diseases, psoriasis and other systemic or organ-specific inflammatory and autoimmune diseases. Future directions in the field are discussed, together with potential avenues of treatment.

Noninvasive vaccination as a casus belli to redeem vaccine value in the face of anti-vaccine movements

Formidable anti-vaccine movements have been growing as a menace to disrupt beneficial vaccine programs. Although the vaccination-associated adverse effects commonly perceived by vaccine resisters usually represent over-reactions to rare manifestations, converging evidence shows that vaccination-associated health threats could be pervasive when systemic inflammation is considered as a side effect that oozes over time. An anti-vaccine movement thus may not be so unfounded even though the myriad cascades triggered by systemic inflammation have not been brought to a clear focus during any anti-vaccine campaign. Since both pro- and anti-vaccine groups are acting on the same primal impulse - "keep people healthy," reconciliation between the two warring factions should be achievable on a palatable trend that fosters the development of noninvasive vaccines which tend to induce local and transient inflammation along the interface with diminished potential to percolate through internal organs.

A tightly regulated IL-22 response maintains immune functions and homeostasis in systemic viral infection

Interleukin-22 (IL-22) plays an important role in host immunity and tissue homeostasis in infectious and inflammatory diseases. However, the function and regulation of IL-22 in viral infection remain largely unknown. Here, we report that viral infection triggered early IL-22 production from the liver and lymphoid organs. γδ T cells are the main immune cells to produce IL-22 in the liver, a process mediated by the IL-23/phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin complex 1 (mTORC1) signaling pathway. In the presence of IL-23, IL-22 production is independent of aryl hydrocarbon receptor (AhR) signaling. In acute and persistent viral infections, IL-22 deficiency resulted in thymic and splenic hypertrophy, while excessive IL-22 induced atrophy in these lymphoid organs. Moreover, IL-22 deficiency enhanced T cell responses to promote viral clearance, but increased IL-22 in vivo decreased T cell numbers and functions in the liver and lymphoid tissues. Together, our findings reveal a significant effect of the IL-23/PI3K/mTORC1 axis on regulating IL-22 production and also identify a novel role of IL-22 in controlling antiviral T cell responses in the non-lymphoid and lymphoid organs during acute and persistent viral infections.

Can Parasitic Worms Cure the Modern World's Ills?

There has been increasing recognition that the alarming surge in allergy and autoimmunity in the industrialised and developing worlds shadows the rapid eradication of pathogens, such as parasitic helminths. Appreciation of this has fuelled an explosion in research investigating the therapeutic potential of these worms. This review considers the current state-of-play with a particular focus on exciting recent advances in the identification of potential novel targets for immunomodulation that can be exploited therapeutically. Furthermore, we contemplate the prospects for designing worm-derived immunotherapies for an ever-widening range of inflammatory diseases, including, for example, obesity, cardiovascular disease, and ageing as well as neurodevelopmental disorders like autism.

Helminths in the gastrointestinal tract as modulators of immunity and pathology

Helminth parasites are highly prevalent in many low- and middle-income countries, in which inflammatory bowel disease and other immunopathologies are less frequent than in the developed world. Many of the most common helminths establish themselves in the gastrointestinal tract and can exert counter-inflammatory influences on the host immune system. For these reasons, interest has arisen as to how parasites may ameliorate intestinal inflammation and whether these organisms, or products they release, could offer future therapies for immune disorders. In this review, we discuss interactions between helminth parasites and the mucosal immune system, as well as the progress being made toward identifying mechanisms and molecular mediators through which it may be possible to attenuate pathology in the intestinal tract.

Innate lymphoid cells as regulators of immunity, inflammation and tissue homeostasis

Research over the last 7 years has led to the formal identification of innate lymphoid cells (ILCs), increased the understanding of their tissue distribution and has established essential functions of ILCs in diverse physiological processes. These include resistance to pathogens, the regulation of autoimmune inflammation, tissue remodeling, cancer and metabolic homeostasis. Notably, many ILC functions appear to be regulated by mechanisms distinct from those of other innate and adaptive immune cells. In this Review, we focus on how group 2 ILC (ILC2) and group 3 ILC (ILC3) responses are regulated and how these cells interact with other immune and non-immune cells to mediate their functions. We highlight experimental evidence from mouse models and patient-based studies that have elucidated the effects of ILCs on the maintenance of tissue homeostasis and the consequences for health and disease.

Antigen-Presenting Human γδ T Cells Promote Intestinal CD4+ T Cell Expression of IL-22 and Mucosal Release of Calprotectin

The cytokine IL-22 plays a critical role in mucosal barrier defense, but the mechanisms that promote IL-22 expression in the human intestine remain poorly understood. As human microbe-responsive Vγ9/Vδ2 T cells are abundant in the gut and recognize microbiota-associated metabolites, we assessed their potential to induce IL-22 expression by intestinal CD4+ T cells. Vγ9/Vδ2 T cells with characteristics of APCs were generated from human blood and intestinal organ cultures, then cocultured with naive and memory CD4+ T cells obtained from human blood or the colon. The potency of blood and intestinal γδ T-APCs was compared with that of monocytes and dendritic cells, by assessing CD4+ T cell phenotypes and proliferation as well as cytokine and transcription factor profiles. Vγ9/Vδ2 T cells in human blood, colon, and terminal ileum acquired APC functions upon microbial activation in the presence of microenvironmental signals including IL-15, and were capable of polarizing both blood and colonic CD4+ T cells toward distinct effector fates. Unlike monocytes or dendritic cells, gut-homing γδ T-APCs employed an IL-6 independent mechanism to stimulate CD4+ T cell expression of IL-22 without upregulating IL-17. In human intestinal organ cultures, microbial activation of Vγ9/Vδ2 T cells promoted mucosal secretion of IL-22 and ICOSL/TNF-α-dependent release of the IL-22 inducible antimicrobial protein calprotectin without modulating IL-17 expression. In conclusion, human γδ T-APCs stimulate CD4+ T cell responses distinct from those induced by myeloid APCs to promote local barrier defense via mucosal release of IL-22 and calprotectin. Targeting of γδ T-APC functions may lead to the development of novel gut-directed immunotherapies and vaccines.

Adipose-derived mesenchymal stem cells modulate CD14++CD16+ expression on monocytes from sepsis patients in vitro via prostaglandin E2

BACKGROUND

Mesenchymal stem cells (MSCs) have been shown to reduce sepsis-induced inflammation and improve survival in mouse models of sepsis. CD16⁺ monocytes are proinflammatory and abundant in inflammatory conditions such as sepsis. The primary objective in this exploratory study was to determine the effects of adipose-derived MSCs (ASCs) on three subsets of monocytes from sepsis patients in vitro and to delineate the underlying mechanism.

METHODS

This is a prospective cohort study of patients admitted to the medical intensive care unit (ICU) at an academic medical center. The levels of CD14⁺⁺CD16⁺, CD14⁺CD16⁺⁺, and CD14⁺⁺CD16^- monocytes from 23 patients in the early phase of severe sepsis or septic shock as well as 25 healthy volunteers were determined via flow cytometry after coculture with or without ASCs. To determine the molecular mechanisms, the effects of exogenous prostaglandin E2 (PGE2) and the cyclooxygenase-2 (COX-2) inhibitor NS-398 on monocyte phenotypes and cytokine expression were also examined.

RESULTS

Basal levels of CD14⁺⁺CD16⁺ but not CD14⁺CD16⁺⁺ monocytes were significantly elevated in severe sepsis and septic shock. A positive linear relationship existed between the levels of CD14⁺⁺CD16⁺ monocytes and the Acute Physiology and Chronic Health Evaluation (APACHE) II score as well as Sequential Organ Failure Assessment (SOFA) score. Coculture of ASCs with monocytes from sepsis patients for 24 h significantly reduced CD14⁺⁺CD16⁺ expression while increasing the CD14⁺⁺CD16^- phenotype. The coculture also significantly elevated PGE2, COX-2, and prostaglandin E2 receptor (EP)4 levels generated from monocytes. Functionally, ASCs reduced the tumor necrosis factor (TNF)-α and increased the interleukin (IL)-10 secretion in monocytes of septic patients. Furthermore, the effects of ASCs on the CD14⁺⁺CD16⁺ phenotype and cytokine expression were mimicked by exogenous PGE2 and abolished by the COX-2 inhibitor NS-398. Additionally, ASCs also modified levels of monocyte phenotypes in a mouse model of sepsis.

CONCLUSIONS

Levels of CD14⁺⁺CD16⁺ monocytes positively correlate with disease severity scores in the early phase of severe sepsis and septic shock. ASCs switch monocytes of sepsis patients from CD14⁺⁺CD16⁺ to CD14⁺⁺CD16^- in vitro and modulate the production of inflammatory cytokines. The immunomodulatory effect of ASCs on monocytes is PGE2-dependent. ASCs may exert their therapeutic effect on sepsis via altering monocyte phenotypes and functions.

Ligand activation of the Ah receptor contributes to gastrointestinal homeostasis

The Ah receptor (AHR) is capable of binding a structurally diverse group of compounds that can be found in the diet, produced by bacteria in the gut and through endogenous metabolism. The gastrointestinal tract is a rich source of AHR ligands, which have been shown to protect the gut upon challenge with either pathogenic bacteria or toxic chemicals. The human AHR can be activated by a broader range of ligands compared to the mouse AHR, suggesting that studies in mice may underestimate the impact of AHR ligands in the human gut. The protective effect of AHR activation appears to be due to modulating the immune system within the gut. While several mechanisms have been established, due to the increasingly pleotropic nature of the AHR, other mechanisms of action likely exist that remain to be identified. The major contributors to AHR function in the gut and the most appropriate level of receptor activation that maintains intestinal homeostasis warrants further investigation.

Obesity-associated cancer risk: the role of intestinal microbiota in the etiology of the host proinflammatory state

Obesity increases the risks of many cancers. One important mechanism behind this association is the obesity-associated proinflammatory state. Although the composition of the intestinal microbiome undoubtedly can contribute to the proinflammatory state, perhaps the most important aspect of host-microbiome interactions is host exposure to components of intestinal bacteria that stimulate inflammatory reactions. Systemic exposures to intestinal bacteria can be modulated by dietary factors through altering both the composition of the intestinal microbiota and the absorption of bacterial products from the intestinal lumen. In particular, high-fat and high-energy diets have been shown to facilitate absorption of bacterial lipopolysaccharide (LPS) from intestinal bacteria. Biomarkers of bacterial exposures that have been measured in blood include LPS-binding protein, sCD14, fatty acids characteristic of intestinal bacteria, and immunoglobulins specific for bacterial LPS and flagellin. The optimal strategies to reduce these proinflammatory exposures, whether by altering diet composition, avoiding a positive energy balance, or reducing adipose stores, likely differ in each individual. Biomarkers that assess systemic bacterial exposures therefore should be useful to (1) optimize and personalize preventive approaches for individuals and groups with specific characteristics and to (2) gain insight into the possible mechanisms involved with different preventive approaches.

Eicosanoid receptors: Targets for the treatment of disrupted intestinal epithelial homeostasis

The importance of cyclooxygenase and lipoxygenase pathways and the consequent eicosanoid synthesis in the physiology and pathophysiology of the intestinal epithelium is currently being established. Each eicosanoid (prostanoid, leukotriene, hydroxyeicosatetraenoic acid) preferentially recognizes one or more receptors coupled to one or more signal-transduction processes. This overview focuses on the role of eicosanoid receptors in the maintenance of intestinal epithelium physiology through the control of proliferation/differentiation/apoptosis processes. Furthermore, it is reported that the role of these receptors on the regulation of the barrier function of the intestinal epithelium have arisen through the regulation of absorption/secretion processes, tight-junction state and the control of the intestinal immune response. Also, this review considers the implication of AA cascade in the disruption of epithelial homeostasis during inflammatory bowel diseases and colorectal cancer as well as the therapeutic values and potential of the eicosanoid receptors as novel targets for the treatments of the pathologies above mentioned.

The whipworm (Trichuris suis) secretes prostaglandin E2 to suppress proinflammatory properties in human dendritic cells

Clinical trials have shown that administration of the nematode Trichuris suis can be beneficial in treating various immune disorders. To provide insight into the mechanisms by which this worm suppresses inflammatory responses, an active component was purified from T. suis soluble products (TsSPs) that suppress---- TNF and IL-12 secretion from LPS-activated human dendritic cells (DCs). Analysis by liquid chromatography tandem mass spectrometry identified this compound as prostaglandin (PG)E2. The purified compound showed similar properties compared with TsSPs and commercial PGE2 in modulating LPS-induced expression of many cytokines and chemokines and in modulating Rab7B and P2RX7 expression in human DCs. Furthermore, the TsSP-induced reduction of TNF secretion from DCs is reversed by receptor antagonists for EP2 and EP4, indicating PGE2 action. T. suis secretes extremely high amounts of PGE2 (45-90 ng/mg protein) within their excretory/secretory products but few related lipid mediators as established by metabololipidomic analysis. Culture of T. suis with several cyclooxygenase (COX) inhibitors that inhibit mammalian prostaglandin synthesis affected the worm's motility but did not inhibit PGE2 secretion, suggesting that the worms can synthesize PGE2 via a COX-independent pathway. We conclude that T. suis secretes PGE2 to suppress proinflammatory responses in human DCs, thereby modulating the host's immune response.-Laan, L. C., Williams, A. R., Stavenhagen, K., Giera, M., Kooij, G., Vlasakov, I., Kalay, H., Kringel, H., Nejsum, P., Thamsborg, S. M., Wuhrer, M., Dijkstra, C. D., Cummings, R. D., van Die, I. The whipworm (Trichuris suis) secretes prostaglandin E2 to suppress proinflammatory properties in human dendritic cells.

Protective Effect of Galectin-1 during Histoplasma capsulatum Infection Is Associated with Prostaglandin E2 and Nitric Oxide Modulation

Histoplasma capsulatum is a dimorphic fungus that develops a yeast-like morphology in host's tissue, responsible for the pulmonary disease histoplasmosis. The recent increase in the incidence of histoplasmosis in immunocompromised patients highlights the need of understanding immunological controls of fungal infections. Here, we describe our discovery of the role of endogenous galectin-1 (Gal-1) in the immune pathophysiology of experimental histoplasmosis. All infected wild-type (WT) mice survived while only 1/3 of Lgals1^−/− mice genetically deficient in Gal-1 survived 30 days after infection. Although infected Lgals1^−/− mice had increased proinflammatory cytokines, nitric oxide (NO), and elevations in neutrophil pulmonary infiltration, they presented higher fungal load in lungs and spleen. Infected lung and infected macrophages from Lgals1^−/− mice exhibited elevated levels of prostaglandin E₂ (PGE₂, a prostanoid regulator of macrophage activation) and prostaglandin E synthase 2 (Ptgs2) mRNA. Gal-1 did not bind to cell surface of yeast phase of H. capsulatum, in vitro, suggesting that Gal-1 contributed to phagocytes response to infection rather than directly killing the yeast. The data provides the first demonstration of endogenous Gal-1 in the protective immune response against H. capsulatum associated with NO and PGE₂ as an important lipid mediator in the pathogenesis of histoplasmosis.

Zonulin Regulates Intestinal Permeability and Facilitates Enteric Bacteria Permeation in Coronary Artery Disease

Several studies have reported an association between enteric bacteria and atherosclerosis. Bacterial 16S ribosomal RNA (rRNA) gene belong to Enterobacteriaceae have been detected in atherosclerotic plaques. How intestinal bacteria go into blood is not known. Zonulin reversibly modulate intestinal permeability (IP), the circulating zonulin levels were increased in diabetes, obesity, all of which are risk factors for atherosclerosis. It is unclear whether the circulating zonulin levels were changed in coronary artery disease (CAD) patients and modulate IP. The 16S rRNA gene of bacteria in blood sample was checked by 454 pyrosequencing. The zonulin levels were determined by enzyme-linked immunosorbent assay (ELISA) methods. The distribution of zonulin was detected by confocal immunofluorescence microscopy. Bacteria and Caco-2 cell surface micro-structure were checked by transmission electron microscopy. A high diversity of bacterial 16S rRNA gene can be detected in samples from CAD patients, most of them (99.4%) belong to Enterobacteriaceaes, eg. Rahnella. The plasma zonulin levels were significantly higher in CAD patients. Pseudomonas fluorescens exposure significantly increased zonulin expression and decreased IP in a time dependent manner. The elevated zonulin increase IP and may facilitate enteric translocation by disassembling the tight junctions, which might explain the observed high diversity of bacterial 16S rRNA genes in blood samples.