IL-33 potentiates histaminergic itch

BACKGROUND

Itch is a common symptom that can greatly diminish quality of life. Histamine is a potent endogenous pruritogen, and while antihistamines are often the first-line treatment for itch, in conditions like chronic spontaneous urticaria (CSU), many patients remain symptomatic while receiving maximal doses. Mechanisms that drive resistance to antihistamines are poorly defined.

OBJECTIVES

Signaling of the alarmin cytokine IL-33 in sensory neurons is postulated to drive chronic itch by inducing neuronal sensitization to pruritogens. Thus, we sought to determine if IL-33 can augment histamine-induced (histaminergic) itch.

METHODS

Itch behavior was assessed in response to histamine after IL-33 or saline administration. Various stimuli and conditional and global knockout mice were utilized to dissect cellular mechanisms. Multiple existing transcriptomic data sets were evaluated, including single-cell RNA sequencing of human and mouse skin, microarrays of isolated mouse mast cells at steady state and after stimulation with IL-33, and microarrays of skin biopsy samples from subjects with CSU and healthy controls.

RESULTS

IL-33 amplifies histaminergic itch independent of IL-33 signaling in sensory neurons. Mast cells are the top expressors of the IL-33 receptor in both human and mouse skin. When stimulated by IL-33, mouse mast cells significantly increase IL-13 levels. Enhancement of histaminergic itch by IL-33 relies on a mast cell- and IL-13-dependent mechanism. IL-33 receptor expression is increased in lesional skin of subjects with CSU compared to healthy controls.

CONCLUSIONS

Our findings suggest that IL-33 signaling may be a key driver of histaminergic itch in mast cell-associated pruritic conditions such as CSU.

Interleukin-13 inhibition by tralokinumab reduces inducible T-cell costimulator-positive innate lymphoid cells in skin lesions of atopic dermatitis

Despite the low frequency of skin ILCs and the limited number of samples analyzed in this study, our data indicate that ICOS+ ILCs express IL-13Rα1 and that the density of ICOS+ ILCs decreased four weeks after initiation of treatment with tralokinumab.

Signalling of multiple interleukin (IL)-17 family cytokines via IL-17 receptor A drives psoriasis-related inflammatory pathways

Background

The interleukin (IL)‐23/IL‐17 immune axis is of central importance in psoriasis. However, the impact of IL‐17 family cytokines other than IL‐17A in psoriasis has not been fully established.

Objectives

To elucidate the contribution of IL‐17 family cytokines in psoriasis.

Methods

To address the expression and localization of IL‐17 family cytokines, lesional and nonlesional skin samples from patients with psoriasis were analysed by several complementary methods, including quantitative polymerase chain reaction, immunoassays, in situ hybridization and immunohistochemistry. Mechanistic studies assessing the functional activity of IL‐17 family cytokines were performed using ex vivo cultured human skin biopsies and primary human keratinocytes.

Results

We demonstrated that IL‐17A, IL‐17F, IL‐17A/F and IL‐17C are expressed at increased levels in psoriasis lesional skin and induce overlapping gene expression responses in ex vivo cultured human skin that correlate with the transcriptomic signature of psoriasis skin. Furthermore, we showed that brodalumab, in contrast to ixekizumab, normalizes gene expression responses induced by the combination of IL‐17A, IL‐17F, IL‐17A/F and IL‐17C in human keratinocytes.

Conclusions

Several IL‐17 ligands signalling through IL‐17RA are overexpressed in psoriasis skin and induce similar psoriasis‐related inflammatory pathways demonstrating their relevance in relation to therapeutic intervention in psoriasis.

What is already known about this topic?

The key role of interleukin (IL)‐17A in psoriasis is well established.

Previous studies have shown that IL‐17A, IL‐17F and IL‐17C are overexpressed in psoriasis skin, whereas contradictory results have been published for IL‐17E.

IL‐17 family cytokines induce secretion of inflammatory mediators such as antimicrobial peptides, chemokines and cytokines involved in the pathophysiology of psoriasis.

What does this study add?

Levels of IL‐17A/F are increased in lesional psoriasis skin but markedly lower than IL‐17A and IL‐17F.

In ex vivo cultured human skin, a physiologically relevant model, IL‐17A, IL‐17F, IL‐17A/F and IL‐17C show functional redundancy in shaping the psoriasis transcriptome.

IL‐17RA antagonism normalizes expression of psoriasis‐related genes in keratinocytes induced by the combination of IL‐17 family cytokines.

What is the translational message?

Overexpression and functional redundancy of IL‐17 family cytokines in psoriasis may explain why some patients with psoriasis with primary or secondary failure of response to secukinumab or ixekizumab achieve a clinical response after switching to brodalumab.

Linked Comment: M. Sugaya. Br J Dermatol 2021; 185:483.

Development and characterization of a human Th17-driven ex vivo skin inflammation model

Skin models mimicking features of psoriasis-related inflammation are needed to support the development of new drugs in dermatology. Reconstructed skin models lack tissue complexity, including a fully competent skin barrier, and presence and/or diversity of immune cells. Here, we describe InflammaSkin®, a novel human Th17-driven ex vivo skin inflammation model. In this model, skin-resident T cells are in situ activated by intradermal injection of anti-CD3 and anti-CD28 antibodies and Th17 cell polarization is sustained by culture in a chemically defined medium supplemented with IL-1β, IL-23 and TGF-β for seven days. The acquired Th17 signature is demonstrated by the sustained secretion of IL-17A, IL-17AF, IL-17F, IL-22, IFN-γ, and to some degree IL-15 and TNF-α observed in the activated ex vivo skin inflammation model compared with the non-activated skin model control. Furthermore, expression of S100A7 and Keratin-16 by keratinocytes and loss of epidermal structure integrity occur subsequently to in situ Th17cell activation, demonstrating cellular crosstalk between Th17 cells and keratinocytes. Finally, we demonstrate the use of this model to investigate the modulation of the IL-23/IL-17 immune axis by topically applied anti-inflammatory compounds. Taken together, we show that by in situ activation of skin-resident Th17 cells, the InflammaSkin® model reproduces aspects of inflammatory responses observed in psoriatic lesions and could be used as a translational tool to assess efficacy of test compounds.

Blood natural killer cell deficiency reveals an immunotherapy strategy for atopic dermatitis

Atopic dermatitis (AD) is a widespread, chronic skin disease associated with aberrant allergic inflammation. Current treatments involve either broad or targeted immunosuppression strategies. However, enhancing the immune system to control disease remains untested. We demonstrate that patients with AD harbor a blood natural killer (NK) cell deficiency that both has diagnostic value and improves with therapy. Multidimensional protein and RNA profiling revealed subset-level changes associated with enhanced NK cell death. Murine NK cell deficiency was associated with enhanced type 2 inflammation in the skin, suggesting that NK cells play a critical immunoregulatory role in this context. On the basis of these findings, we used an NK cell-boosting interleukin-15 (IL-15) superagonist and observed marked improvement in AD-like disease in mice. These findings reveal a previously unrecognized application of IL-15 superagonism, currently in development for cancer immunotherapy, as an immunotherapeutic strategy for AD.

Assessing Specialized Metabolite Diversity in the Cosmopolitan Plant Genus Euphorbia L

Coevolutionary theory suggests that an arms race between plants and herbivores yields increased plant specialized metabolite diversity and the geographic mosaic theory of coevolution predicts that coevolutionary interactions vary across geographic scales. Consequently, plant specialized metabolite diversity is expected to be highest in coevolutionary hotspots, geographic regions, which exhibit strong reciprocal selection on the interacting species. Despite being well-established theoretical frameworks, technical limitations have precluded rigorous hypothesis testing. Here we aim at understanding how geographic separation over evolutionary time may have impacted chemical differentiation in the cosmopolitan plant genus Euphorbia. We use a combination of state-of-the-art computational mass spectral metabolomics tools together with cell-based high-throughput immunomodulatory testing. Our results show significant differences in specialized metabolite diversity across geographically separated phylogenetic clades. Chemical structural diversity of the highly toxic Euphorbia diterpenoids is significantly reduced in species native to the Americas, compared to Afro-Eurasia. The localization of these compounds to young stems and roots suggest a possible ecological relevance in herbivory defense. This is further supported by reduced immunomodulatory activity in the American subclade as well as herbivore distribution patterns. We conclude that computational mass spectrometric metabolomics coupled with relevant ecological data provide a strong tool for exploring plant specialized metabolite diversity in a chemo-evolutionary framework.

Epigenetic control of IL-23 expression in keratinocytes is important for chronic skin inflammation

The chronic skin inflammation psoriasis is crucially dependent on the IL-23/IL-17 cytokine axis. Although IL-23 is expressed by psoriatic keratinocytes and immune cells, only the immune cell-derived IL-23 is believed to be disease relevant. Here we use a genetic mouse model to show that keratinocyte-produced IL-23 is sufficient to cause a chronic skin inflammation with an IL-17 profile. Furthermore, we reveal a cell-autonomous nuclear function for the actin polymerizing molecule N-WASP, which controls IL-23 expression in keratinocytes by regulating the degradation of the histone methyltransferases G9a and GLP, and H3K9 dimethylation of the IL-23 promoter. This mechanism mediates the induction of IL-23 by TNF, a known inducer of IL-23 in psoriasis. Finally, in keratinocytes of psoriatic lesions a decrease in H3K9 dimethylation correlates with increased IL-23 expression, suggesting relevance for disease. Taken together, our data describe a molecular pathway where epigenetic regulation of keratinocytes can contribute to chronic skin inflammation.

Although IL-23 is expressed by psoriatic keratinocytes as well as immune cells, only the immune cell derived IL-23 is thought to be important for the development of psoriasis. Here the authors provide evidence that keratinocyte-produced IL-23 is sufficient to cause a chronic skin inflammation.

Translational Animal Models of Atopic Dermatitis for Preclinical Studies

There is a medical need to develop new treatments for patients suffering from atopic dermatitis (AD). To improve the discovery and testing of novel treatments, relevant animal models for AD are needed. Generally, these animal models mimic different aspects of the pathophysiology of human AD, such as skin barrier defects and Th2 immune bias with additional Th1 and Th22, and in some populations Th17, activation. However, the pathomechanistic characterization and pharmacological validation of these animal models are generally incomplete. In this paper, we review animal models of AD in the context of preclinical use and their possible translation to the human disease. Most of these models use mice, but we will also critically evaluate dog models of AD, as increasing information on disease mechanism show their likely relevance for the human disease.

Distinct molecular signatures of mild extrinsic and intrinsic atopic dermatitis

Atopic dermatitis (AD) is a common inflammatory skin disease with underlying defects in epidermal function and immune responses. In this study, we used microarray analysis to investigate differences in gene expression in lesional skin from patients with mild extrinsic or intrinsic AD compared to skin from healthy controls and from lesional psoriasis skin. The primary aim was to identify differentially expressed genes involved in skin barrier formation and inflammation, and to compare our results with those reported for patients with moderate and severe AD. In contrast to severe AD, expression of the majority of genes associated with skin barrier formation was unchanged or upregulated in patients with mild AD compared to normal healthy skin. Among these, no significant differences in the expression of filaggrin (FLG) and loricrin at both mRNA and protein level were found in lesional skin from patients with mild AD, despite the presence of heterozygous FLG mutations in the majority of patients with mild extrinsic AD. Several inflammation-associated genes such as S100A9, MMP12, CXCL10 and CCL18 were highly expressed in lesional skin from patients with mild psoriasis and were also increased in patients with mild extrinsic and intrinsic AD similar to previous reports for severe AD. Interestingly, expression of genes involved in inflammatory responses in intrinsic AD resembled that of psoriasis more than that of extrinsic AD. Overall, differences in expression of inflammation-associated genes found among patients with mild intrinsic and extrinsic AD correlated with previous findings for patients with severe intrinsic and extrinsic AD.

IL-1β-dependent activation of dendritic epidermal T cells in contact hypersensitivity

Substances that penetrate the skin surface can act as allergens and induce a T cell-mediated inflammatory skin disease called contact hypersensitivity (CHS). IL-17 is a key cytokine in CHS and was originally thought to be produced solely by CD4(+) T cells. However, it is now known that several cell types, including γδ T cells, can produce IL-17. In this study, we determine the role of γδ T cells, especially dendritic epidermal T cells (DETCs), in CHS. Using a well-established model for CHS in which 2,4-dinitrofluorobenzene (DNFB) is used as allergen, we found that γδ T cells are important players in CHS. Thus, more IL-17-producing DETCs appear in the skin following exposure to DNFB in wild-type mice, and DNFB-induced ear swelling is reduced by ∼50% in TCRδ(-/-) mice compared with wild-type mice. In accordance, DNFB-induced ear swelling was reduced by ∼50% in IL-17(-/-) mice. We show that DNFB triggers DETC activation and IL-1β production in the skin and that keratinocytes produce IL-1β when stimulated with DNFB. We find that DETCs activated in vitro by incubation with anti-CD3 and IL-1β produce IL-17. Importantly, we demonstrate that the IL-1R antagonist anakinra significantly reduces CHS responses, as measured by decreased ear swelling, inhibition of local DETC activation, and a reduction in the number of IL-17(+) γδ T cells and DETCs in the draining lymph nodes. Taken together, we show that DETCs become activated and produce IL-17 in an IL-1β-dependent manner during CHS, suggesting a key role for DETCs in CHS.

IL-23-mediated epidermal hyperplasia is dependent on IL-6

Psoriasis is a chronic inflammatory skin disease primarily driven by Th17 cells. IL-23 facilitates the differentiation and induces complete maturation of Th17 cells. Lesional psoriatic skin has increased levels of IL-23 and recent studies show that intradermal injections of IL-23 induce a psoriasis-like skin phenotype in mice. We have now characterized the IL-23-induced skin inflammation in mice at the molecular level and found a significant correlation with the gene expression profile from lesional psoriatic skin. As observed in psoriasis, the pathogenesis of the IL-23-induced skin inflammation in mice is driven by Th17 cells. We demonstrate a dramatic upregulation of IL-6 mRNA and protein after intradermal injections of IL-23 in mice. Using IL-6(-/-) mice we show that IL-6 is essential for development of the IL-23-elicited responses. Despite producing high levels of IL-22, IL-6(-/-) mice were unable to express the high-affinity IL-22 receptor chain and produced minimal IL-17A in response to intradermal injections of IL-23. In conclusion, we provide evidence for the critical role played by IL-6 in IL-23-induced skin inflammation and show that IL-6 is required for expression of IL-22R1A.

The Immune Privilege of the Eye: Human Retinal Pigment Epithelial Cells Selectively Modulate T-Cell ActivationIn Vitro

PURPOSE

To examine the effect of human retinal pigment epithelial (RPE) cells on phytohemagglutinin (PHA) activation of T cells.

METHODS

Resting peripheral blood lymphocytes (PBLs) were stimulated with PHA with or without the presence of gamma-irradiated RPE cells. Proliferation and the cell cycle profile were thereafter investigated by 3H-thymidine incorporation and flow cytometric analysis. In addition, the PBLs expression of CD69, major histocompatibility complex (MHC) class I and II, CD3, as well as the IL-2 receptor chains were evaluated by flow cytometry, and the content of IL-2 in cell culture supernatant was measured by ELISA.

RESULTS

Human RPE cells were found to suppress PHA-induced proliferation, cyclin A, IL-2R-alpha and -gamma, and CD71 expression and decrease the production of IL-2; but RPE cells do not inhibit the PHA-induced expression of early activation markers CD69, MHC class I and II, and of cyclin D of the PBLs.

CONCLUSIONS

These results are the first to indicate that RPE cells impede generation of activated T cells by interfering with the induction of high-affinity IL-2R-alphabetagamma, IL-2 production, and the expression of CD71 and cyclin A.

Nonmalignant T cells stimulate growth of T-cell lymphoma cells in the presence of bacterial toxins

Bacterial toxins including staphylococcal enterotoxins (SEs) have been implicated in the pathogenesis of cutaneous T-cell lymphomas (CTCLs). Here, we investigate SE-mediated interactions between nonmalignant T cells and malignant T-cell lines established from skin and blood of CTCL patients. The malignant CTCL cells express MHC class II molecules that are high-affinity receptors for SE. Although treatment with SE has no direct effect on the growth of the malignant CTCL cells, the SE-treated CTCL cells induce vigorous proliferation of the SE-responsive nonmalignant T cells. In turn, the nonmalignant T cells enhance proliferation of the malignant cells in an SE- and MHC class II-dependent manner. Furthermore, SE and, in addition, alloantigen presentation by malignant CTCL cells to irradiated nonmalignant CD4(+) T-cell lines also enhance proliferation of the malignant cells. The growth-promoting effect depends on direct cell-cell contact and soluble factors such as interleukin-2. In conclusion, we demonstrate that SE triggers a bidirectional cross talk between nonmalignant T cells and malignant CTCL cells that promotes growth of the malignant cells. This represents a novel mechanism by which infections with SE-producing bacteria may contribute to pathogenesis of CTCL.

Jak3- and JNK-dependent vascular endothelial growth factor expression in cutaneous T-cell lymphoma

Biopsies from patients with cutaneous T-cell lymphoma (CTCL) exhibit stage-dependent increase in angiogenesis. However, the molecular mechanisms responsible for the increased angiogenesis are unknown. Here we show that malignant CTCL T cells spontaneously produce the potent angiogenic protein, vascular endothelial growth factor (VEGF). Dermal infiltrates of CTCL lesions show frequent and intense staining with anti-VEGF antibody, indicating a steady, high production of VEGF in vivo. Moreover, the VEGF production is associated with constitutive activity of Janus kinase 3 (Jak3) and the c-Jun N-terminal kinases (JNKs). Sp600125, an inhibitor of JNK activity and activator protein-1 (AP-1) binding to the VEGF promoter, downregulates the VEGF production without affecting Jak3 activity. Similarly, inhibitors of Jak3 inhibit the VEGF production without affecting JNK activity. Downregulation of Stat3 with small interfering RNA has no effect, whereas curcumin, an inhibitor of both Jak3 and the JNKs, almost completely blocks the VEGF production. In conclusion, we provide evidence of VEGF production in CTCL, which is promoted by aberrant activation of Jak3 and the JNKs. Inhibition of VEGF-inducing pathways or neutralization of VEGF itself could represent novel therapeutic modalities in CTCL.

Increased Sensitivity to Interferon-α in Psoriatic T Cells

Psoriasis is a chronic inflammatory skin disease characterized by abnormal epidermal proliferation. Several studies have shown that skin-infiltrating activated T cells and cytokines play a pivotal role during the initiation and maintenance of the disease. Interferon (IFN)-alpha plays an important role in host defense against infections, but recent data have also implicated IFN-alpha in psoriasis. Thus, IFN-alpha induces or aggravates psoriasis in some patients, and mice lacking a transcriptional attenuator of IFN-alpha/beta signaling spontaneously develop a psoriasis-like inflammatory skin disease characterized by CD8(+)-infiltrating T cells. In this study, we therefore investigate IFN-alpha signaling in T cells isolated from involved skin of psoriatic patients. We show that psoriatic T cells have increased and prolonged responses to IFN-alpha, on the level of signal transducers and activators of transcription (STAT) activation, compared with infiltrating T cells from skin of non-psoriatic donors. Functionally, the increased IFN-alpha signaling leads to an increased binding of STAT4 to the IFN-gamma promotor, IFN-gamma production, and inhibition of T cell growth. In contrast, to STAT responses to other cytokines were not changed in psoriasis. In conclusion, we provide evidence that psoriatic T cells have an increased sensitivity to IFN-alpha. Thus, our data suggest that increased IFN-alpha signaling is involved in the pathogenesis of psoriasis.

Interleukin-4- and -13-induced hypercontractility of human intestinal muscle cells-implication for motility changes in Crohn's disease

Crohn's disease is an idiopathic inflammatory condition. However, little is known about the changes that occur in the muscularis externa, despite the fact that this tissue contributes to motility changes and stricture formation. We characterized immune activity in the muscularis externa from intestinal segments of Crohn's disease patients and evaluated the role of IL-4 and -13 as well as signal transducer and activator of transcription (STAT)6 in the contractility of the cultured human intestinal smooth muscle cells. CD3+ve cells (P < 0.01) and IL-4 protein (P < 0.01) were significantly increased in the muscularis externa of Crohn's disease patients compared with noninflamed controls. Preincubation of human cultured smooth muscle cells with IL-4 (P < 0.001) or IL-13 (P < 0.05) significantly enhanced carbachol-induced contraction, and this was significantly inhibited by the STAT6 inhibitor leflunomide (P < 0.0001). A similar profile was observed in muscle cells isolated from Crohn's disease patients. Both IL-4 and IL-13 increased specific STAT6-DNA binding in control cells, and this was inhibited by anti-STAT6 Ab (P < 0.05) or leflunomide (P < 0.05). IL-4 and IL-13 mediate the hypercontractility of intestinal muscle via a STAT6 pathway at the level of the smooth muscle cell. The STAT6 pathway may contribute to the hypercontractility of intestinal muscle in Crohn's disease.

Constitutive SOCS-3 expression protects T-cell lymphoma against growth inhibition by IFNα

Signal transducer and activator of transcription (Stat)3 is constitutively activated in cutaneous T-cell lymphoma (CTCL), where it protects tumour cells against apoptosis. The constitutive activation of Stat3 leads to a constitutive expression of suppressor of cytokine signalling (SOCS)-3. In healthy cells, SOCS-3 is transiently expressed following cytokine stimulation and functions as a negative feedback inhibitor of the Stat3-activating kinases. Here, we attempt to resolve the apparent paradox of a simultaneous SOCS-3 expression and Stat3 activation in the same cells. We show that (i) SOCS-3 expression in tumour cells is equal to or higher than in cytokine-stimulated nonmalignant T cells, (ii) SOCS-3 is not mutated in CTCL, (iii) overexpression of SOCS-3 blocks IFNalpha-mediated growth inhibition without affecting Stat3 activation, growth, and apoptosis, and (iv) inhibition of SOCS-3 by a dominant negative Stat3 (Stat3D) increases the IFNalpha-mediated growth inhibition. Taken together, these data show that SOCS-3 does not inhibit Stat3 activation, growth, and survival in CTCL. In contrast, SOCS3 protects tumour cells against growth inhibition by IFNalpha. Unlike SOCS-1, SOCS-3 is therefore not a tumour suppressor but rather a protector of tumour cells.

In vivo activation of STAT3 in cutaneous T-cell lymphoma. Evidence for an antiapoptotic function of STAT3

A characteristic feature of neoplastic transformation is a perpetual activation of oncogenic proteins. Here, we studied signal transducers and activators of transcription (STAT) in patients with mycosis fungoides (MF)/cutaneous T-cell lymphoma (CTCL). Malignant lymphocytes in dermal infiltrates of CTCL tumors showed frequent and intense nuclear staining with anti-PY-STAT3 antibody, indicating a constitutive activation of STAT3 in vivo in tumor stages. In contrast, only sporadic and faint staining was observed in indolent lesions of patch and plaque stages of MF. Moreover, neoplastic lymphocytes in the epidermal Pautrier abscesses associated with early stages of MF did not express activated STAT3. To address the role of STAT3 in survival/apoptosis, CTCL tumor cells from an advanced skin tumor were transfected with either wild-type STAT3 (STAT3wt) or dominant-negative STAT3 (STAT3D). Forced inducible expression of STAT3D triggered a significant increase in tumor cells undergoing apoptosis, whereas forced expression of STAT3wt or empty vector had no effect. In conclusion, a profound in vivo activation of STAT3 is observed in MF tumors but not in the early stages of MF. Moreover, STAT3 protects tumor cells from apoptosis in vitro. Taken together, these findings suggest that STAT3 is a malignancy factor in CTCL.

Constitutive STAT3 activation in intestinal T cells from patients with Crohn's disease

Via cytoplasmic signal transduction pathways, cytokines induce a variety of biological responses and modulate the outcome of inflammatory diseases and malignancies. Crohn's disease is a chronic inflammatory bowel disease of unknown etiology. Perturbation of the intestinal cytokine homeostasis is believed to play a pivotal role, but the pathogenesis of Crohn's disease is not fully understood. Here, we study intestinal T cells from Crohn's disease and healthy volunteers. We show that STAT3 and STAT4 are constitutively activated in Crohn's patients but not in healthy volunteers. The activation is specific, because other STAT proteins are not constitutively activated. Furthermore, the STAT3 regulated protein, SOCS3, is also constitutively expressed in Crohn's patients but not in healthy volunteers. Taken together, these data provide evidence of abnormal STAT/SOCS signaling in Crohn's disease. This aberrant activation, so far noted only in malignant cells, establish a new critical approach for better understanding the immunopathogenesis of Crohn's disease.

Protein phosphatase 2A (PP2A) regulates interleukin-4-mediated STAT6 signaling

Interleukin-4 (IL-4) plays a pivotal role in the induction and maintenance of allergy by promoting Th2 differentiation and B cell isotype switching to IgE. Studies on STAT6-deficient mice have demonstrated the essential role of STAT6 in mediating the biological functions of IL-4. IL-4 induces tyrosine phosphorylation of STAT6, which in turn leads to transcription of IL-4-specific genes. In addition, serine phosphorylation of STAT6 has recently been reported. Here we study the functional role of STAT6 serine phosphorylation and the kinases and phosphatases involved. We show that inhibition of protein phosphatase 2A (PP2A) induces serine phosphorylation of STAT6 and severely inhibits DNA binding of STAT6. In contrast, IL-4-induced tyrosine phosphorylation of Janus kinase-1 and STAT6 is not affected, suggesting that PP2A acts downstream of Janus kinases in IL-4 signaling. In conclusion, we provide the first evidence that PP2A plays a crucial role in the regulation of STAT6 function.

Neural change in Trichinella-infected mice is MHC II independent and involves M-CSF-derived macrophages

Intestinal inflammation due to nematode infection impairs enteric cholinergic nerve function and induces hypercontractility of intestinal muscle. Macrophages have been implicated in the neural changes, but the subpopulation and mechanism involved are unknown. We examined whether macrophages alter nerves by virtue of their ability to activate lymphocytes via major histocompatibility complex (MHC) II-restricted antigen presentation. We also attempted to evaluate the role of macrophage subsets using op/op mice deficient in macrophage colony-stimulating factor (M-CSF). ACh release from the myenteric plexus was measured in MHC II- and M-CSF-deficient (op/op) mice infected with Trichinella spiralis. F4/80-positive macrophages and interleukin-1 beta were constitutively present in op/op and op/? mice but increased only in op/? mice postinfection. After infection, a marked suppression of ACh release occurred only in infected MHC II-deficient and op/? mice. Muscle hypercontractility remained evident in infected op/? mice. Treatment with M-CSF restored macrophage number, and this was accompanied by suppression of cholinergic nerve function during infection. Thus M-CSF plays a critical role in this model by recruiting a subset of macrophages that selectively suppresses enteric neural function.

Neurotransmitters modulate cytokine-stimulated interleukin 6 secretion in rat intestinal smooth muscle cells

BACKGROUND & AIMS

Cytokine production by resident cells of the richly innervated muscularis externa may contribute to neuromuscular changes observed during intestinal inflammation. This study investigated neurotransmitter modulation of cytokine production by intestinal smooth muscle.

METHODS

We measured interleukin (IL)-6 messenger RNA expression by reverse-transcription polymerase chain reaction, IL-6 by bioassay, and cyclic adenosine monophosphate by enzyme immunoassay in rat cultured intestinal smooth muscle cells exposed to IL-1beta, in the presence or absence of neurotransmitters.

RESULTS

IL-1beta significantly increased IL-6 messenger RNA and protein. This was dose-dependently enhanced by vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP), and norepinephrine and inhibited by [LYS1,PRO2,5,ARG3,4,TYR6]VIP and propranolol, respectively. Forskolin mimicked the stimulatory effects of these neurotransmitters on IL-6 secretion, and the protein kinase inhibitor6-22 amide abolished the actions of VIP, CGRP, and norepinephrine, but not that of human recombinant IL-1beta, on IL-6 secretion. These agents each increased cyclic adenosine monophosphate activity in muscle substance P, and the neurokinin 1 agonist Ac-[Arg6,Sar9,Met(O2)11] substance P(6-11) inhibited the IL-1beta-induced IL-6 release.

CONCLUSIONS

This study shows neuropeptide and sympathetic modulation of IL-1beta-induced IL-6 production by intestinal smooth muscle. These interactions may contribute to altered muscle function during intestinal inflammation.