SHIP1 and its role for innate immune regulation-Novel targets for immunotherapy

Phosphoinositide-3-kinase/AKT (PI3K/AKT) signaling plays key roles in the regulation of cellular activity in both health and disease. In immune cells, this PI3K/AKT pathway is critically regulated by the phosphoinositide phosphatase SHIP1, which has been reported to modulate the function of most immune subsets. In this review, we summarize our current knowledge of SHIP1 with a focus on innate immune cells, where we reflect on the most pertinent aspects described in the current literature. We also present several small-molecule agonists and antagonists of SHIP1 developed over the last two decades, which have led to improved outcomes in several preclinical models of disease. We outline these promising findings and put them in relation to human diseases with unmet medical needs, where we discuss the most attractive targets for immune therapies based on SHIP1 modulation.

Macrophage immunotherapy: overcoming impediments to realize promise

As an essential component of immunity, macrophages have key roles in mammalian host defense, tissue homeostasis, and repair, as well as in disease pathogenesis and pathophysiology. A source of fascination and extensive research, in this Opinion we challenge the utility of the M1-M2 paradigm, and discuss the importance of accurate characterization of human macrophages. We comment on the application of single cell analytics to define macrophage subpopulations and how this could advance therapeutic options. We argue that human macrophage cell therapy can be used to alleviate many diseases, and offer a viewpoint on the knowledge gaps that must be filled to render such a therapeutic approach a reality and, ideally, a common future practice in precision medicine.

The role of phosphoinositide 3-kinases in immune-inflammatory responses: potential therapeutic targets for abdominal aortic aneurysm

The pathogenesis of abdominal aortic aneurysm (AAA) includes inflammatory responses, matrix metalloproteinases (MMPs) degradation, VSMC apoptosis, oxidative stress, and angiogenesis, among which the inflammatory response plays a key role. At present, surgery is the only curing treatment, and no effective drug can delay AAA progression in clinical practice. Therefore, searching for a signaling pathway related to the immune-inflammatory response is an essential direction for developing drugs targeting AAA. Recent studies have confirmed that the PI3K family plays an important role in many inflammatory diseases and is involved in regulating various cellular functions, especially in the immune-inflammatory response. This review focuses on the role of each isoform of PI3K in each stage of AAA immune-inflammatory response, making available explorations for a deeper understanding of the mechanism of inflammation and immune response during the formation and development of AAA.

Phosphatidylinositol 3-kinase p110δ drives intestinal fibrosis in SHIP deficiency

Crohn's disease is an immune-mediated disease characterized by inflammation along the gastrointestinal tract. Fibrosis requiring surgery occurs in one-third of people with Crohn's disease but there are no treatments for intestinal fibrosis. Mice deficient in the SH2 domain-containing inositolpolyphosphate 5'-phosphatase (SHIP), a negative regulator of phosphatidylinositol 3-kinase (PI3K) develop spontaneous Crohn's disease-like intestinal inflammation and arginase I (argI)-dependent fibrosis. ArgI is up-regulated in SHIP deficiency by PI3Kp110δ activity. Thus, we hypothesized that SHIP-deficient mice develop fibrosis due to increased PI3Kp110δ activity. In SHIP-deficient mice, genetic ablation or pharmacological inhibition of PI3Kp110δ activity reduced intestinal fibrosis, including muscle thickening, accumulation of vimentin⁺ mesenchymal cells, and collagen deposition. PI3Kp110δ deficiency or inhibition also reduced ileal inflammation in SHIP-deficient mice suggesting that PI3Kp110δ may contribute to inflammation. Targeting PI3Kp110δ activity may be an effective strategy to reduce intestinal fibrosis, and may be particularly effective in the subset of people with Crohn's disease, who have low SHIP activity.

SHIP negatively regulates type II immune responses in mast cells and macrophages

SHIP is a hematopoietic-specific lipid phosphatase that dephosphorylates PI3K-generated PI(3,4,5)-trisphosphate. SHIP removes this second messenger from the cell membrane blunting PI3K activity in immune cells. Thus, SHIP negatively regulates mast cell activation downstream of multiple receptors. SHIP has been referred to as the "gatekeeper" of mast cell degranulation as loss of SHIP dramatically increases degranulation or permits degranulation in response to normally inert stimuli. SHIP also negatively regulates Mϕ activation, including both pro-inflammatory cytokine production downstream of pattern recognition receptors, and alternative Mϕ activation by the type II cytokines, IL-4, and IL-13. In the SHIP-deficient (SHIP-/- ) mouse, increased mast cell and Mϕ activation leads to spontaneous inflammatory pathology at mucosal sites, which is characterized by high levels of type II inflammatory cytokines. SHIP-/- mast cells and Mϕs have both been implicated in driving inflammation in the SHIP-/- mouse lung. SHIP-/- Mϕs drive Crohn's disease-like intestinal inflammation and fibrosis, which is dependent on heightened responses to innate immune stimuli generating IL-1, and IL-4 inducing abundant arginase I. Both lung and gut pathology translate to human disease as low SHIP levels and activity have been associated with allergy and with Crohn's disease in people. In this review, we summarize seminal literature and recent advances that provide insight into SHIP's role in mast cells and Mϕs, the contribution of these cell types to pathology in the SHIP-/- mouse, and describe how these findings translate to human disease and potential therapies.

All Trans Retinoic Acid, Transforming Growth Factor β and Prostaglandin E2 in Mouse Plasma Synergize with Basophil-Secreted Interleukin-4 to M2 Polarize Murine Macrophages

In previous studies we found that macrophages (MФs) from SH2-containing inositol-5'-phosphatase (SHIP) deficient mice are M2 polarized while their wild type (WT) counterparts are M1 polarized and that this difference in MФ phenotype can be recapitulated during in vitro derivation from bone marrow if mouse plasma (MP), but not fetal calf serum, is added to standard M-CSF-containing cultures. In the current study we investigated the mechanism by which MP skews SHIP-/- but not +/+ MФs to an M2 phenotype. Our results suggest that SHIP-/- basophils constitutively secrete higher levels of IL-4 than SHIP+/+ basophils and this higher level of IL-4 is sufficient to skew both SHIP+/+ and SHIP-/- MФs to an M2 phenotype, but only when MP is present to increase the sensitivity of the MФs to this level of IL-4. MP increases the IL-4 sensitivity of both SHIP+/+ and -/- MФs not by increasing cell surface IL-4 or CD36 receptor levels, but by triggering the activation of Erk and Akt and the production of ROS, all of which play a critical role in sensitizing MФs to IL-4-induced M2 skewing. Studies to identify the factor(s) in MP responsible for promoting IL-4-induced M2 skewing suggests that all-trans retinoic acid (ATRA), TGFβ and prostaglandin E2 (PGE2) all play a role. Taken together, these results indicate that basophil-secreted IL-4 plays an essential role in M2 skewing and that ATRA, TGFβ and PGE2 within MP collaborate to dramatically promote M2 skewing by acting directly on MФs to increase their sensitivity to IL-4.

iNKT Cells Are Responsible for the Apoptotic Reduction of Basophils That Mediate Th2 Immune Responses Elicited by Papain in Mice Following γPGA Stimulation

Recent studies have demonstrated that Bacillus subtilis-derived poly-gamma glutamic acid (γPGA) treatment suppresses the development of allergic diseases such as atopic dermatitis (AD). Although basophils, an innate immune cell, are known to play critical roles in allergic immune responses and repeated long-term administration of γPGA results in decreased splenic basophils in an AD murine model, the underlying mechanisms by which γPGA regulates basophil frequency remain unclear. To investigate how γPGA modulates basophils, we employed basophil-mediated Th2 induction in vivo model elicited by the allergen papain protease. Repeated injection of γPGA reduced the abundance of basophils and their production of IL4 in mice, consistent with our previous study using NC/Nga AD model mice. The depletion of basophils by a single injection of γPGA was dependent on the TLR4/DC/IL12 axis. CD1d-dependent Vα14 TCR invariant natural killer T (iNKT) cells are known to regulate a variety of immune responses, such as allergy. Because iNKT cell activation is highly sensitive to IL12 produced by DCs, we evaluated whether the effect of γPGA on basophils is mediated by iNKT cell activation. We found that in vivo γPGA treatment did not induce the reduction of basophils in iNKT cell-deficient CD1d KO mice, suggesting the critical role of iNKT cells in γPGA-mediated basophil depletion at the early time points. Furthermore, increased apoptotic basophil reduction triggered by iNKT cells upon γPGA stimulation was mainly attributed to Th1 cytokines such as IFNγ and TNFα, consequently resulting in inhibition of papain-induced Th2 differentiation via diminishing basophil-derived IL4. Taken together, our results clearly demonstrate that γPGA-induced iNKT cell polarization toward the Th1 phenotype induces apoptotic basophil depletion, leading to the suppression of Th2 immune responses. Thus, elucidation of the crosstalk between innate immune cells will contribute to the design and development of new therapeutics for Th2-mediated immune diseases such as AD.

Role of anti-inflammatory cytokines IL-4 and IL-13 in systemic sclerosis

OBJECTIVE

The aim of this paper is to review the anti-inflammatory cytokines IL-4 and IL-13 and their receptor signals; we discuss new insight into their possible roles in systemic sclerosis (SSc) and their overlapping function in SSc.

INTRODUCTION

SSc is a connective tissue disease characterized by fibrosis. The exact etiology of SSc is unknown, and no therapy has been proved effective in modifying its course. Recently the roles of IL-4 and IL-13 in the development of SSc have been extensively considered. The possible roles of IL-4 and IL-13, especially their overlapping function, in SSc are not well documented.

METHODS

A literature survey was performed using a PubMed database search to gather complete information regarding IL-4 and IL-13 and their role in inflammation.

RESULTS AND CONCLUSIONS

The participation of complex pathways of IL-4 and IL-13 in the process of inflammation and fibrosis action in SSc is still not very clear, and some pathogenesis of regulation found in vitro needs to be further proved. There is still more work which could be done to achieve useful developments with therapeutic benefit in SSc.

SHIP1 intrinsically regulates NK cell signaling and education, resulting in tolerance of an MHC class I-mismatched bone marrow graft in mice

NK cells are an important component of host immune defense against malignancy and infection. NK cells are educated by MHC class I ligands to ensure self-tolerance while also promoting lytic competency against altered self and damaged self targets. However, the intracellular molecular events that culminate in tolerance and functional competency of educated NK cells remain undefined. Mice with germline deficiency in SHIP1 were shown to have a defective NK cell compartment. However, SHIP1 is expressed in all hematopoietic lineages, and consequently several hematolymphoid phenotypes have already been identified in certain cell types that are the result of SHIP1 deficiency in cells in separate and distinct lineages, that is, cell-extrinsic phenotypes. Thus, it was previously impossible to determine the NK cell-intrinsic role of SHIP1. In the present study, through the creation of an NK cell-specific deletion mouse model of SHIP1, we show that SHIP1 plays a profound NK lineage-intrinsic role in NK cell homeostasis, development, education, and cytokine production. Moreover, we show SHIP1 expression by NK cells is required for in vivo-mismatched bone marrow allograft rejection as well as for NK memory responses to hapten.

Signaling pathways activated by a protease allergen in basophils

Allergic diseases represent a significant burden in industrialized countries, but why and how the immune system responds to allergens remain largely unknown. Because many clinically significant allergens have proteolytic activity, and many helminths express proteases that are necessary for their life cycles, host mechanisms likely have evolved to detect the proteolytic activity of helminth proteases, which may be incidentally activated by protease allergens. A cysteine protease, papain, is a prototypic protease allergen that can directly activate basophils and mast cells, leading to the production of cytokines, including IL-4, characteristic of the type 2 immune response. The mechanism of papain's immunogenic activity remains unknown. Here we have characterized the cellular response activated by papain in basophils. We find that papain-induced IL-4 production requires calcium flux and activation of PI3K and nuclear factor of activated T cells. Interestingly, papain-induced IL-4 production was dependent on the immunoreceptor tyrosine-based activation motif (ITAM) adaptor protein Fc receptor γ-chain, even though the canonical ITAM signaling was not activated by papain. Collectively, these data characterize the downstream signaling pathway activated by a protease allergen in basophils.

Inositol polyphosphate phosphatases in human disease

Phosphoinositide signalling molecules interact with a plethora of effector proteins to regulate cell proliferation and survival, vesicular trafficking, metabolism, actin dynamics and many other cellular functions. The generation of specific phosphoinositide species is achieved by the activity of phosphoinositide kinases and phosphatases, which phosphorylate and dephosphorylate, respectively, the inositol headgroup of phosphoinositide molecules. The phosphoinositide phosphatases can be classified as 3-, 4- and 5-phosphatases based on their specificity for dephosphorylating phosphates from specific positions on the inositol head group. The SAC phosphatases show less specificity for the position of the phosphate on the inositol ring. The phosphoinositide phosphatases regulate PI3K/Akt signalling, insulin signalling, endocytosis, vesicle trafficking, cell migration, proliferation and apoptosis. Mouse knockout models of several of the phosphoinositide phosphatases have revealed significant physiological roles for these enzymes, including the regulation of embryonic development, fertility, neurological function, the immune system and insulin sensitivity. Importantly, several phosphoinositide phosphatases have been directly associated with a range of human diseases. Genetic mutations in the 5-phosphatase INPP5E are causative of the ciliopathy syndromes Joubert and MORM, and mutations in the 5-phosphatase OCRL result in Lowe's syndrome and Dent 2 disease. Additionally, polymorphisms in the 5-phosphatase SHIP2 confer diabetes susceptibility in specific populations, whereas reduced protein expression of SHIP1 is reported in several human leukaemias. The 4-phosphatase, INPP4B, has recently been identified as a tumour suppressor in human breast and prostate cancer. Mutations in one SAC phosphatase, SAC3/FIG4, results in the degenerative neuropathy, Charcot-Marie-Tooth disease. Indeed, an understanding of the precise functions of phosphoinositide phosphatases is not only important in the context of normal human physiology, but to reveal the mechanisms by which these enzyme families are implicated in an increasing repertoire of human diseases.

Inhibition of PI3K signaling spurs new therapeutic opportunities in inflammatory/autoimmune diseases and hematological malignancies

The phosphoinositide 3-kinase/mammalian target of rapamycin/protein kinase B (PI3K/mTOR/Akt) signaling pathway is central to a plethora of cellular mechanisms in a wide variety of cells including leukocytes. Perturbation of this signaling cascade is implicated in inflammatory and autoimmune disorders as well as hematological malignancies. Proteins within the PI3K/mTOR/Akt pathway therefore represent attractive targets for therapeutic intervention. There has been a remarkable evolution of PI3K inhibitors in the past 20 years from the early chemical tool compounds to drugs that are showing promise as anticancer agents in clinical trials. The use of animal models and pharmacological tools has expanded our knowledge about the contribution of individual class I PI3K isoforms to immune cell function. In addition, class II and III PI3K isoforms are emerging as nonredundant regulators of immune cell signaling revealing potentially novel targets for disease treatment. Further complexity is added to the PI3K/mTOR/Akt pathway by a number of novel signaling inputs and feedback mechanisms. These can present either caveats or opportunities for novel drug targets. Here, we consider recent advances in 1) our understanding of the contribution of individual PI3K isoforms to immune cell function and their relevance to inflammatory/autoimmune diseases as well as lymphoma and 2) development of small molecules with which to inhibit the PI3K pathway. We also consider whether manipulating other proximal elements of the PI3K signaling cascade (such as class II and III PI3Ks or lipid phosphatases) are likely to be successful in fighting off different immune diseases.

Modulation of macrophage activation and programming in immunity

Macrophages are central mediators of the immune, contributing both to the initiation and the resolution of inflammation. The concept of macrophage activation and program has stimulated interest in its definition, and functional significance in homeostasis and diseases. It has been known that macrophages could be differently activated and programmed into different functional subtypes in response to different types of antigen stumuli or different kinds of cytokines present in the microenvironment and could thus profoundly influence immune responses, but little is known about the state and exact regulatory mechanism of macrophage activation and program from cell or molecular signaling level in immunity. In this review, we summarize the recent finding regarding the regulatory mechanism of macrophage activation and program toward M1 and M2, especially on M2 macrophages.

Basophil modulation by cytokine instruction

Basophils have recently been recognized as critical effector cells in allergic reactions and protective immunity against helminths. Precise characterization of basophil biology could help to develop specific therapies that interfere with differentiation, tissue recruitment, or induction of effector functions and thereby ameliorate allergic disorders. The development, homeostasis, and effector functions of basophils are tightly regulated by extrinsic signals and in particular by cytokines. IL-3, GM-CSF, and thymic stromal lymphopoietin activate the STAT5 pathway that promotes proliferation, activation, and cytokine secretion but also induces a negative feedback loop via Pim-1 and SOCS proteins. Basophils further express receptors for IL-18 and IL-33, which are associated with the signaling adaptor MyD88 and activate the NF-κB and MAP kinase pathways. This review focuses on positive and negative regulation of basophils by these cytokines.

Interleukin-4- and interleukin-13-mediated alternatively activated macrophages: roles in homeostasis and disease

The macrophage, a versatile cell type prominently involved in host defense and immunity, assumes a distinct state of alternative activation in the context of polarized type 2 immune responses such as allergic inflammation and helminth infection. This alternatively activated phenotype is induced by the canonical type 2 cytokines interleukin (IL)-4 and IL-13, which mediate expression of several characteristic markers along with a dramatic shift in macrophage metabolic pathways that influence surrounding cells and tissues. We discuss recent advances in the understanding of IL-4- and IL-13-mediated alternatively activated macrophages and type 2 immune responses; such advances have led to an expanded appreciation for functions of these cells beyond immunity, including maintenance of physiologic homeostasis and tissue repair.

Myeloid cell-specific expression of Ship1 regulates IL-12 production and immunity to helminth infection

Helminth infection leads to the local proliferation and accumulation of macrophages in tissues. However, the function of macrophages during helminth infection remains unclear. SH2-containing inositol 5'-phosphatase 1 (Ship1, Inpp5d) is a lipid phosphatase that has been shown to play a critical role in macrophage function. Here, we identify a critical role for Ship1 in the negative regulation of interleukin (IL)-12/23p40 production by macrophages during infection with the intestinal helminth parasite Trichuris muris. Mice with myeloid cell-specific deletion of Ship1 (Ship1(ΔLysM) mice) develop a non-protective T-helper type 1 cell response and fail to expel parasites. Ship1-deficient macrophages produce heightened levels of IL-12/23p40 in vitro and in vivo and antibody blockade of IL-12/23p40 renders Ship1(ΔLysM) mice resistant to Trichuris infection. Our results identify a critical role for the negative regulation of IL-12/23p40 production by macrophages in the development of a protective T(H)2 cell response.

Pharmacological targeting of phosphoinositide lipid kinases and phosphatases in the immune system: success, disappointment, and new opportunities

The predominant expression of the γ and δ isoforms of PI3K in cells of hematopoietic lineage prompted speculation that inhibitors of these isoforms could offer opportunities for selective targeting of PI3K in the immune system in a range of immune-related pathologies. While there has been some success in developing PI3Kδ inhibitors, progress in developing selective inhibitors of PI3Kγ has been rather disappointing. This has prompted the search for alternative targets with which to modulate PI3K signaling specifically in the immune system. One such target is the SH2 domain-containing inositol-5-phosphatase-1 (SHIP-1) which de-phosphorylates PI(3,4,5)P₃ at the D5 position of the inositol ring to create PI(3,4)P₂. In this article, we first describe the current state of PI3K isoform-selective inhibitor development. We then focus on the structure of SHIP-1 and its function in the immune system. Finally, we consider the current state of development of small molecule compounds that potently and selectively modulate SHIP activity and which offer novel opportunities to manipulate PI3K mediated signaling in the immune system.

Targeting PI3K isoforms and SHIP in the immune system: new therapeutics for inflammation and leukemia

PI3K is critical for the normal function of the immune system, however dysregulated PI3K mediated signaling has been linked to the development of many immune mediated pathologies. This review describes current progress in the development of isoform-specific PI3K inhibitors that hold promise for the treatment of hematopoietic malignancies as well as for inflammatory and autoimmune diseases. A SH2-domain containing inositol-5-phosphatase (SHIP) is a regulator of PI3K signaling, and is also discussed as a potential drug target for immunomodulation and the treatment of leukemia. Recent progress has been made in the development of small molecule compounds that potently and selectively modulate SHIP activity and hence provide a novel mechanism to alter PI3K mediated signaling.

Understanding the roles of basophils: breaking dawn

Early studies that used parasite-infected interleukin-4 (IL-4) reporter animals led us to identify basophils as the primary source of IL-4 and hence propose the hypothesis that basophils trigger the development of antigen-specific T helper type 2 (Th2) immune responses in vivo. These findings appeared to resolve a long-standing puzzle underlying Th2 immunity, that is, 'what is the source of the initial IL-4 necessary for CD4 T-cell differentiation into Th2 effector cells?'. However, results from extensive investigations of the contribution of basophils to Th2 immunity unveiled some controversial data that cast doubt on the initial hypothesis. In this review, the consensus and the controversy regarding the roles of basophils in infection and immunity, as well as outstanding questions for the future, are discussed.

Phosphatidylinositol 3-kinase inhibitor suppresses inducible nitric oxide synthase expression in bronchiole epithelial cells in asthmatic rats

Inducible nitric oxide synthase (iNOS) is known to produce nitric oxide (NO), which is a main contributor to asthmatic airway inflammation. Recent studies have shown that phosphatidylinositol 3-kinase (PI3K) is ubiquitously expressed in airway epithelial cells and its inhibition could relieve airway inflammation and hyperresponsiveness. This study aimed to explore the interaction of PI3K and NO signaling in allergic asthma. We investigated the effects of PI3K inhibitor wortmannin on iNOS expression in bronchiole epithelial cells and NO, IL-4 and IFN-γ levels in lung tissues of asthmatic rat model, which was prepared by 10% OVA solution sensitization and 1% OVA aerosol challenge. Our results showed that the ratio of eosinophils to total cells in BALF, PI3K activity, NO and IL-4 levels in lung tissues was increased after OVA sensitization and challenge, but then was attenuated by the administration of wortmannin. In contrast, IFN-γ level in lung tissues was decreased after OVA sensitization and challenge and increased after the administration of wortmannin. The expression of iNOS protein in bronchiole epithelial cells, iNOS mRNA level and iNOS activity in lung tissues was markedly upregulated after OVA sensitization and challenge, but the upregulation was significantly antagonized by wortmannin. Taken together, these data provide evidence that PI3K functions upstream to modulate iNOS/NO signaling, which then promotes the development of airway inflammation in asthmatic animal model. PI3K inhibitor wortmannin could lead to reduced iNOS expression and NO production, therefore inhibiting airway inflammatory responses.

SHIP-deficient, alternatively activated macrophages protect mice during DSS-induced colitis

mϕ are heterogeneous in their functions, and although it is clear that inflammatory mϕ contribute to inflammation in IBDs, multiple lines of evidence suggest that M2a mϕ may offer protection during intestinal inflammation. In vivo SHIP-deficient mouse mϕ are M2a so SHIP-deficient mice provide a unique genetic model of M2a mϕ. Based on this, this study tested the hypothesis that SHIP-deficient, M2a mϕ protect mice from intestinal inflammation. The objectives were to compare the susceptibility of SHIP+/+ and SHIP-/- littermates with DSS-induced intestinal inflammation and to determine whether protection was mϕ-mediated and whether protection could be transferred to a susceptible host. We have found that SHIP-/- mice are protected during DSS-induced intestinal inflammation. SHIP-/- mice have delayed rectal bleeding and reduced weight loss, disruption of intestinal architecture, and immune cell infiltration during DSS-induced colitis relative to their WT littermates. Using liposome depletion of mϕ, we found that SHIP-/- mouse protection was indeed mϕ-mediated. Finally, we determined that SHIP-/- mϕ-mediated protection could be conferred to susceptible WT mice by adoptive transfer of M2a mϕ derived ex vivo. This study supports our hypothesis by demonstrating that SHIP-deficient, M2a mϕ are protective in this murine model of acute intestinal inflammation. Adoptive transfer of M2a mϕ to patients with IBDs offers a promising, new strategy for treatment that may be particularly useful in patients who are otherwise refractory to conventional therapies.

SHIP-deficient mice develop spontaneous intestinal inflammation and arginase-dependent fibrosis

Intestinal fibrosis is a serious complication of Crohn's disease (CD) that can lead to stricture formation, which requires surgery. Mechanisms underlying intestinal fibrosis remain elusive because of a lack of suitable mouse models. Herein, we describe a spontaneous mouse model of intestinal inflammation with fibrosis and the profibrotic role of arginase I. The Src homology 2 domain-containing inositol polyphosphate 5'-phosphatase-deficient (SHIP(-/-)) mice developed spontaneous discontinuous intestinal inflammation restricted to the distal ileum starting at the age of 4 weeks. Mice developed several key features resembling CD, including inflammation and fibrosis. Inflammation was characterized by abundant infiltrating Gr-1-positive immune cells, granuloma-like immune cell aggregates that contained multinucleated giant cells, and a mixed type 2 and type 17 helper T-cell cytokine profile. Fibrosis was characterized by a thickened ileal muscle layer, collagen deposition, and increased fibroblasts at the sites of collagen deposition. SHIP(-/-) ilea had increased arginase activity and arginase I expression that was inversely proportional to nitrotyrosine staining. SHIP(-/-) mice were treated with the arginase inhibitor S-(2-boronoethyl)-l-cysteine, and changes in the disease phenotype were measured. Arginase inhibition did not affect the number of immune cell infiltrates in the SHIP(-/-) mouse ilea; rather, it reduced collagen deposition and muscle hyperplasia. These findings suggest that arginase activity is a potential target to limit intestinal fibrosis in patients with CD.

CCAAT/enhancer-binding protein alpha (C/EBPalpha) is critical for interleukin-4 expression in response to FcepsilonRI receptor cross-linking

Basophils mediate many of their biological functions by producing IL-4. However, it is unknown how the Il4 gene is regulated in basophils. Here, we report that CCAAT/enhancer-binding protein α (C/EBPα), a major myeloid transcription factor, was highly expressed in basophils. We show that C/EBPα selectively activated Il4 promoter-luciferase reporter gene transcription in response to IgE cross-linking, but C/EBPα did not activate other known Th2 or mast cell enhancers. We found that the PI3K pathway and calcineurin were essential in C/EBPα-driven Il4 promoter-luciferase gene transcription. Our mutation analyses revealed that C/EBPα drove Il4 promoter-luciferase activity depending on its DNA binding domain. Mutation of the C/EBPα-binding site in the Il4 promoter region abolished C/EBPα-driven Il4 promoter-luciferase activity. Our results further showed that a mutation in nuclear factor of activated T cells (NFAT)-binding sites in the Il4 promoter also negated C/EBPα-driven Il4 promoter-luciferase activity. Our study demonstrates that C/EBPα, in cooperation with NFAT, directly regulates Il4 gene transcription.