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Routine clinical assays, such as conventional immunohistochemistry, often fail to resolve the regional heterogeneity of complex inflammatory skin conditions. Here we introduce MANTIS (Multiplexed Annotated Tissue Imaging System), a flexible analytic pipeline compatible with routine practice, specifically-designed for spatially-resolved immune phenotyping of the skin in experimental or clinical samples. Based on phenotype attribution matrices coupled to α-shape algorithms, MANTIS projects a representative digital immune landscape, while enabling automated detection of major inflammatory clusters and concomitant single-cell data quantification of biomarkers. We observed that severe pathological lesions from systemic lupus erythematosus, Kawasaki syndrome or COVID-19-associated skin manifestations share common quantitative immune features, while displaying a non-random distribution of cells with the formation of disease-specific dermal immune structures. Given its accuracy and flexibility, MANTIS is designed to solve the spatial organization of complex immune environments to better apprehend the pathophysiology of skin manifestations.

Mast cells (MCs) are heterogenous tissue-resident immune cells associated with blood vessels and neurons. However, the extent to which specialized MCs can exhibit micro-environment-specific functions is unclear. Using single cell RNA sequencing, we characterize connective tissue-type and mucosal MCs across organs and found that they can be discriminated based on MrgprB2 expression. While MrgprB2+ connective MCs are enriched in neuroreceptors, develop during the embryogenesis and renew independently of the bone marrow (BM); MrgprB2neg mucosal MCs arise postnatally, are sensitive to signals from the microbiome and renewed by BM progenitors. Importantly, MrgprB2+, but not MrgprB2neg MCs are required for food-induced anaphylactic shock. In the gut, MrgprB2+ MCs occur in contact with substance P-secreting enteric neurons and the specific depletion of either MrgprB2+ MCs or substance P results in dysregulation of gut contractions. Thus, we demonstrate that two independent MC populations exist in multiple organs, with different developmental dynamics and biological programming.

Postoperative shivering and cold hypersensitivity are major side effects of acute and chronic opioid treatments respectively. TRPM8 is a cold and menthol-sensitive channel found in a subset of dorsal root ganglion (DRG) nociceptors. Deletion or inhibition of the TRPM8 channel was found to prevent the cold hyperalgesia induced by chronic administration of morphine. Here, we examined the mechanisms by which morphine was able to promote cold hypersensitivity in DRG neurons and transfected HEK cells. Mice daily injected with morphine for 5 days developed cold hyperalgesia. Treatment with morphine did not alter the expressions of cold sensitive TREK-1, TRAAK and TRPM8 in DRGs. However, TRPM8-expressing DRG neurons isolated from morphine-treated mice exhibited hyperexcitability. Sustained morphine treatment in vitro sensitized TRPM8 responsiveness to cold or menthol and reduced activation-evoked desensitization of the channel. Blocking phospholipase C (PLC) as well as protein kinase C beta (PKCβ), but not protein kinase A (PKA) or Rho-associated protein kinase (ROCK), restored channel desensitization. Identification of two PKC phosphorylation consensus sites, S1040 and S1041, in the TRPM8 and their site-directed mutation were able to prevent the MOR-induced reduction in TRPM8 desensitization. Our results show that activation of MOR by morphine 1) promotes hyperexcitability of TRPM8-expressing neurons and 2) induces a PKCβ-mediated reduction of TRPM8 desensitization. This MOR-PKCβ dependent modulation of TRPM8 may underlie the onset of cold hyperalgesia caused by repeated administration of morphine. Our findings point to TRPM8 channel and PKCβ as important targets for opioid-induced cold hypersensitivity.

The peripheral nervous system and the immune system are virtually distributed in all organs in mouse and human. They act in concert to constitute an exceptional sensory system capable of sensing threatening stimuli, including allergens, and triggering appropriate biological responses. Recent advances in the field have revealed that tissue-resident mast cells and nearby sensory neurons could form functional neuroimmune clusters driven by bidirectional interactions and predisposed to significantly influence major allergic conditions. In this review, we highlight recent discoveries that paved the way toward a better understanding of how mast cells and sensory neurons can communicate to regulate basic features of allergic disorders in different organs.

International audience; Allergic skin diseases, such as atopic dermatitis, are clinically characterized by severe itching and type 2 immunity-associated hypersensitivity to widely distributed allergens, including those derived from house dust mites (HDMs). Here we found that HDMs with cysteine protease activity directly activated peptidergic nociceptors, which are neuropeptide-producing nociceptive sensory neurons that express the ion channel TRPV1 and Tac1, the gene encoding the precursor for the neuropeptide substance P. Intravital imaging and genetic approaches indicated that HDM-activated nociceptors drive the development of allergic skin inflammation by inducing the degranulation of mast cells contiguous to such nociceptors, through the release of substance P and the activation of the cationic molecule receptor MRGPRB2 on mast cells. These data indicate that, after exposure to HDM allergens, activation of TRPV1+Tac1+ nociceptor–MRGPRB2+ mast cell sensory clusters represents a key early event in the development of allergic skin reactions.

Summary Many patients with visceral inflammation develop pain and psychiatric comorbidities such as major depressive disorder, worsening the quality of life and increasing the risk of suicide. Here we show that neuroimmune activation in mice with dextran sodium sulfate-induced colitis is accompanied by the development of pain and depressive behaviors. Importantly, treatment with the flavonoid luteolin prevented both neuroimmune responses and behavioral abnormalities, suggesting a new potential therapeutic approach for patients with inflammatory bowel diseases., Graphical Abstract, Highlights • Acute colitis triggers long-term events related to depression • Leukocytes infiltrate into brain vasculature • Luteolin abolishes leukocyte infiltration and visceral hypersensitivity • Luteolin abolishes depression-related behaviors, Pathophysiology; Behavioral Neuroscience; Cellular Neuroscience; Immunity

Current analgesic treatments for Interstitial Cystitis/Bladder Pain Syndrome (IC/BPS) are limited. Here, we propose a novel antinociceptive strategy exploiting the opioid-mediated analgesic properties of T lymphocytes to relieve from bladder pain. In a chronic model of IC/BPS in rats, we show that a secondary T cell response against intravesically administered ovalbumin prevents from visceral pain in OVA-primed animals. The analgesic effect is associated with the recruitment of T lymphocytes within the inflamed mucosa and is reversed by naloxone-methiodide, a peripheral opioid receptor antagonist. Similarly, intravesical instillation of BCG or tetanus toxoid antigens in vaccinated rats protects from pain in the same model. We show opioid-dependent analgesic properties of local vaccine antigen recall in a preclinical rat model of chronic cystitis. Since BCG bladder instillation is regularly used in humans (as anticancer therapy), our results open it as a new therapeutic positioning for a pain management indication for IC/BPS patients.

Background: Peritoneal carcinomatosis often results in alterations in intestinal peristalsis and recurrent abdominal pain. Pain management in these patients is often unsatisfactory. This study aimed to investigate whether endothelin-1 (EDN1) was involved in pain mediation in peritoneal carcinomatosis, and thus whether the EDN1 pathway could be a new therapeutic target for peritoneal carcinomatosis-associated pain.Methods: EDN1 plasma levels and abdominal pain severity were assessed in patients with abdominal tumors, with or without peritoneal carcinomatosis, and in healthy donors. The effects of EDN1 on the visceromotor response to colorectal distension, and on colonic contractions were then examined in mice, and the mechanism of action of EDN1 was then investigated by measuring the impact of EDN1 exposure on calcium mobilization in cultured neurons. Inhibition studies were also performed to determine if the effects of EDN1 exposure could be reversed by EDN1-specific receptor antagonists.Results: A positive correlation between EDN1 plasma levels and abdominal pain was identified in patients with peritoneal carcinomatosis. EDN1 exposure increased visceral sensitivity and the amplitude of colonic contractions in mice and induced calcium mobilization by direct binding to its receptors on sensory neurons. The effects of EDN1 were inhibited by antagonists of the EDN1 receptors.Conclusions: This preliminary study, using data from patients with peritoneal carcinomatosis combined with data from experiments performed in mice, suggests that EDN1 may play a key role mediating pain in peritoneal carcinomatosis. Our findings suggest that antagonists of the EDN1 receptors might be beneficial in the management of pain in patients with peritoneal carcinomatosis.

Postoperative shivering and cold hypersensitivity are major side effects of acute and chronic opioid treatments respectively. TRPM8 is a cold and menthol-sensitive channel found in a subset of dorsal root ganglion (DRG) nociceptors. Deletion or inhibition of the TRPM8 channel was found to prevent the cold hyperalgesia induced by chronic administration of morphine. Here, we examined the mechanisms by which morphine was able to promote cold hypersensitivity in DRG neurons and transfected HEK cells. Mice daily injected with morphine for five days developed cold hyperalgesia. Treatment with morphine did not alter the expressions of cold sensitive TREK-1, TRAAK and TRPM8 in DRGs. However, TRPM8-expressing DRG neurons isolated from morphine-treated mice exhibited hyperexcitability. Sustained morphine treatment in vitro sensitized TRPM8 responsiveness to cold or menthol and reduced activation-evoked desensitization of the channel. Blocking the phospholipase C (PLC) as well as protein kinase C beta (PKCβ), but not protein kinase A (PKA) or Rho-associated protein kinase (ROCK), restored channel desensitization. Identification of two PKC phosphorylation consensus sites, S1040 and S1041, in the TRPM8 and their site-directed mutation were able to prevent the MOR-induced reduction in TRPM8 desensitization. Our results show that activation of MOR by morphine 1) promotes hyperexcitability of TRPM8-expressing neurons and 2) induces a PKCβ-mediated reduction of TRPM8 desensitization. This MOR-PKCβ dependent modulation of TRPM8 may underlie the onset of cold hyperalgesia caused by repeated administration of morphine. Our findings point to TRPM8 channel and PKCβ as important targets for opioid-induced cold hypersensitivity.

International audience; Recent studies revealed the existence of unique functional links between mast cells and nociceptors in the skin. Here, we propose that mast cells and nociceptors form a single regulatory unit in both physiology and disease. In this model, MrgprB2/X2 signaling is a primary mechanism by which mast cells functionally interact with nociceptors to form specialized neuroimmune clusters that regulate pain, inflammation, and itch.

T lymphocytes play a pivotal role in endogenous regulation of inflammatory visceral pain. The analgesic activity of T lymphocytes is dependent on their production of opioids, a property acquired on antigen activation. Accordingly, we investigated whether an active recruitment of T lymphocytes within inflamed colon mucosa via a local vaccinal strategy may counteract inflammation-induced visceral pain in mice. Mice were immunized against ovalbumin (OVA). One month after immunization, colitis was induced by adding 3% (wt/vol) dextran sulfate sodium into drinking water containing either cognate antigen OVA or control antigen bovine serum albumin for 5 days. Noncolitis OVA-primed mice were used as controls. Visceral sensitivity was then determined by colorectal distension. Oral administration of OVA but not bovine serum albumin significantly reduced dextran sulfate sodium-induced abdominal pain without increasing colitis severity in OVA-primed mice. Analgesia was dependent on local release of enkephalins by effector anti-OVA T lymphocytes infiltrating the inflamed mucosa. The experiments were reproduced with the bacillus Calmette-Guerin vaccine as antigen. Similarly, inflammatory visceral pain was dramatically alleviated in mice vaccinated against bacillus Calmette-Guerin and then locally administered with live Mycobacterium bovis. Together, these results show that the induction of a secondary adaptive immune response against vaccine antigens in inflamed mucosa may constitute a safe noninvasive strategy to relieve from visceral inflammatory pain.

BACKGROUND:Endogenous opioids, including enkephalins, are fundamental regulators of pain. In inflammatory conditions, the local release of opioids by leukocytes at the inflammatory site inhibits nociceptor firing, thereby inducing analgesia. Accordingly, in chronic intestinal Th1/Th17-associated inflammation, enkephalins released by colitogenic CD4+ T lymphocytes relieve inflammation-induced visceral pain. The present study aims to investigate whether mucosal T-cell-derived enkephalins also exhibit a potent anti-inflammatory activity as described for exogenous opioid drugs in Th1/Th17-associated colitis.METHODS:The anti-inflammatory effects of endogenous opioids were investigated in both Th1/Th17-associated (transfer of CD4+CD45RBhigh T lymphocytes) and Th2-associated (oxazolone) colitis models in mice. Inflammation-induced colonic damage and CD4+ T cell subsets were compared in mice treated or not treated with naloxone methiodide, a peripheral antagonist of opioid receptors. The anti-inflammatory activity of T-cell-derived enkephalins was further estimated by comparison of colitis severity in immunodeficient mice into which naïve CD4+CD45RBhigh T lymphocytes originating from wild-type or enkephalin-knockout mice had been transferred.RESULTS:Peripheral opioid receptor blockade increases the severity of Th1/Th17-induced colitis and attenuates Th2 oxazolone colitis. The opposite effects of naloxone methiodide treatment in these two models of intestinal inflammation are dependent on the potency of endogenous opioids to promote a Th2-type immune response. Accordingly, the transfer of enkephalin-deficient CD4+CD45RBhigh T lymphocytes into immunodeficient mice exacerbates inflammation-induced colonic injury.CONCLUSIONS:Endogenous opioids, including T-cell-derived enkephalins, promote a Th2-type immune response, which, depending on the context, may either attenuate (Th1/Th17-associated) or aggravate (Th2-associated) intestinal inflammation.

Neuropathic pain caused by disease or dysfunction of the nervous system is one of the most difficult pain conditions to treat. Symptoms include a hypersensitivity to mechanical and thermal stimuli, processed by specialized nociceptors that constitute the first line of defence of the somatosensory system. The detection of these stimuli depends on the TRP ion channel family, which activates upon damaging pressure, extreme temperature, or toxic endogenous and exogenous chemicals. This review will summarize the current knowledge of the contribution of TRP channels, particularly the thermosensitive TRP, including TRPV1, TRPA1 and TRPM8 channels that play a central role in the sensitization of nociceptive transduction. We will discuss the pharmacology of these receptors and their relative success in preclinical and clinical studies.

Immune activation may underlie the pathogenesis of irritable bowel syndrome (IBS), but the evidence is conflicting. We examined whether peripheral CD4+ T-cells from IBS patients demonstrated immune activation and changes in cytokine production. To gain mechanistic insight, we examined whether immune activation correlated with psychological stress and changing symptoms over time. IBS patients (n = 29) and healthy volunteers (HV; n = 29) completed symptom and psychological questionnaires. IBS patients had a significant increase in CD4+ T-cells expressing the gut homing marker integrin β7 (p = 0.023) and lymphoid marker CD62L (p = 0.026) compared to HV. Furthermore, phytohaemagglutinin stimulated CD4+ T-cells from IBS-D patients demonstrated increased TNFα secretion when compared to HV (p = 0.044). Increased psychological scores in IBS did not correlate with TNFα production, while stress hormones inhibited cytokine secretion from CD4+ T-cells of HV in vitro. IBS symptoms, but not markers of immune activation, decreased over time. CD4+ T-cells from IBS-D patients exhibit immune activation, but this did not appear to correlate with psychological stress measurements or changing symptoms over time. This could suggest that immune activation is a surrogate of an initial trigger and/or ongoing parallel peripheral mechanisms.

Pain and inflammation are inherently linked responses to injury, infection, or chronic diseases. Given that acute inflammation in humans or mice enhances the analgesic properties of opioids, there is much interest in determining the inflammatory transducers that prime opioid receptor signaling in primary afferent nociceptors. Here, we found that activation of the transient receptor potential vanilloid type 1 (TRPV1) channel stimulated a mitogen-activated protein kinase (MAPK) signaling pathway that was accompanied by the shuttling of the scaffold protein β-arrestin2 to the nucleus. The nuclear translocation of β-arrestin2 in turn prevented its recruitment to the μ-opioid receptor (MOR), the subsequent internalization of agonist-bound MOR, and the suppression of MOR activity that occurs upon receptor desensitization. Using the complete Freund's adjuvant (CFA) inflammatory pain model to examine the role of TRPV1 in regulating endogenous opioid analgesia in mice, we found that naloxone methiodide (Nal-M), a peripherally restricted, nonselective, and competitive opioid receptor antagonist, slowed the recovery from CFA-induced hypersensitivity in wild-type, but not TRPV1-deficient, mice. Furthermore, we showed that inflammation prolonged morphine-induced antinociception in a mouse model of opioid receptor desensitization, a process that depended on TRPV1. Together, our data reveal a TRPV1-mediated signaling pathway that serves as an endogenous pain-resolution mechanism by promoting the nuclear translocation of β-arrestin2 to minimize MOR desensitization. This previously uncharacterized mechanism may underlie the peripheral opioid control of inflammatory pain. Dysregulation of the TRPV1-β-arrestin2 axis may thus contribute to the transition from acute to chronic pain.

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder that is characterized by chronic abdominal pain concurrent with altered bowel habit. Polyunsaturated fatty acid (PUFA) metabolites are increased in abundance in IBS and are implicated in the alteration of sensation to mechanical stimuli, which is defined as visceral hypersensitivity. We sought to quantify PUFA metabolites in patients with IBS and evaluate their role in pain. Quantification of PUFA metabolites by mass spectrometry in colonic biopsies showed an increased abundance of 5-oxoeicosatetraenoic acid (5-oxoETE) only in biopsies taken from patients with IBS with predominant constipation (IBS-C). Local administration of 5-oxoETE to mice induced somatic and visceral hypersensitivity to mechanical stimuli without causing tissue inflammation. We found that 5-oxoETE directly acted on both human and mouse sensory neurons as shown by lumbar splanchnic nerve recordings and Ca2+ imaging of dorsal root ganglion (DRG) neurons. We showed that 5-oxoETE selectively stimulated nonpeptidergic, isolectin B4 (IB4)-positive DRG neurons through a phospholipase C (PLC)- and pertussis toxin-dependent mechanism, suggesting that the effect was mediated by a G protein-coupled receptor (GPCR). The MAS-related GPCR D (Mrgprd) was found in mouse colonic DRG afferents and was identified as being implicated in the noxious effects of 5-oxoETE. Together, these data suggest that 5-oxoETE, a potential biomarker of IBS-C, induces somatic and visceral hyperalgesia without inflammation in an Mrgprd-dependent manner. Thus, 5-oxoETE may play a pivotal role in the abdominal pain associated with IBS-C. ispartof: SCIENCE SIGNALING vol:11 issue:561 ispartof: location:United States status: published

International audience; Interplay between physiological systems in the body plays a prominent role in health and disease. At the cellular level, such interplay is orchestrated through the binding of specific ligands to their receptors expressed on cell surface. G protein-coupled receptors (GPCR) are seven-transmembrane domain receptors that initiate various cellular responses and regulate homeostasis. In this review, we focus on particular GPCRs named Mas-related G protein-coupled receptors (Mrgprs) mainly expressed by sensory neurons and specialized immune cells. We describe the different subfamilies of Mrgprs and their specific ligands, as well as recent advances in the field that illustrate the role played by these receptors in neuro-immune biological processes, including itch, pain and inflammation in diverse organs.

Intestinal inflammation results in the production of inflammatory pain-inducing mediators that may directly activate colon sensory neurons. Endogenous opioids produced by mucosal effector CD4(+) T lymphocytes identified as colitogenic may paradoxically counterbalance the local pro-algesic effect of inflammatory mediators by acting on opioid receptors expressed on sensory nerve endings. The review will focus on the endogenous immune-mediated regulation of visceral inflammatory pain, current pain treatments in inflammatory bowel diseases and prospectives on new opioid therapeutic opportunities to alleviate pain but avoiding common centrally-mediated side effects.

Opioids remain the gold standard for the treatment of moderate to severe pain. However, their analgesic properties come with important side effects, including pruritus, which occurs frequently after systemic or neuraxial administration. Although part of the opioid-induced itch is mediated centrally, recent evidence shows that the opioid receptor system in the skin also modulates itch. The goal of our study was to identify the peripherally located transducer mechanisms involved in opioid-induced pruritus. Scratching behaviors in response to an intradermal injection of the mu-opioid receptor (MOR) agonist [D-Ala2, N-MePhe4, Gly-ol]-enkephalin (DAMGO) was quantified in mast cell-, PAR2- and TRPV1-deficient mice or following ablation of TRPV1+ sensory neurons. We found that mast cells−/−, PAR-2−/−, or TRPV1−/− mice still exhibit DAMGO-induced itch responses. However, we show that ablation of TRPV1+ neurons or acute TRPV1 activation by capsaicin abolishes DAMGO-induced itch. Overall, our work shows that peripheral DAMGO-induced itch is dependent on the presence of TRPV1-expressing pruriceptors, but not the TRPV1 channel itself. Activation of these fibers by capsaicin prevents the opioid-induced itch.

International audience; The accumulation of adverse events in utero and during childhood differentially increases the vulnerability to psychiatric diseases in men and women. Gut microbiota is highly sensitive to the early environment and has been recently hypothesized to affect brain development. However, the impact of early-life adversity on gut microbiota, notably with regards to sex differences, remains to be explored. We examined the effects of multifactorial early-life adversity on behavior and microbiota composition in C3H/HeN mice of both sexes exposed to a combination of maternal immune activation (lipopolysaccharide injection on embryonic day 17, 120 μg/kg, i.p.), maternal separation (3hr per day from postnatal day (PND)2 to PND14) and maternal unpredictable chronic mild stress. At adulthood, offspring exposed to multi-hit early adversity showed sex-specific behavioral phenotypes with males exhibiting deficits in social behavior and females showing increased anxiety in the elevated plus maze and increased compulsive behavior in the marble burying test. Early adversity also differentially regulated gene expression in the medial prefrontal cortex (mPFC) according to sex. Interestingly, several genes such as Arc, Btg2, Fosb, Egr4 or Klf2 were oppositely regulated by early adversity in males versus females. Finally, 16S-based microbiota profiling revealed sex-dependent gut dysbiosis. In males, abundance of taxa belonging to Lachnospiraceae and Porphyromonadaceae families or other unclassified Firmicutes, but also Bacteroides, Lactobacillus and Alloprevotella genera was regulated by early adversity. In females, the effects of early adversity were limited and mainly restricted to Lactobacillus and Mucispirillum genera. Our work reveals marked sex differences in a multifactorial model of early-life adversity, both on emotional behaviors and gut microbiota, suggesting that sex should systematically be considered in preclinical studies both in neurogastroenterology and psychiatric research.

Acute inflammation in humans or mice enhances the analgesic properties of opioids. However, the inflammatory transducers that prime opioid receptor signaling in nociceptors are unknown. We found that TRPV1−/− mice are insensitive to peripheral opioid analgesia in an inflammatory pain model. We report that TRPV1 channel activation drives a MAPK signaling pathway accompanied by the shuttling of β-arrestin2 to the nucleus. This shuttling in turn prevents: β-arrestin2-receptor recruitment, subsequent internalization of agonist-bound mu opioid receptor (MOR), and suppression of DAMGO-induced inhibition of N-type calcium current observed upon desensitization. Consequently, inflammation-induced activation of TRPV1 preserves opioid analgesic potency in a mouse model of opioid receptor desensitization. Overall, our work reveals a TRPV1-mediated signaling mechanism, involving β-arrestin2 nuclear translocation, that underlies the peripheral opioid control of inflammatory pain. Our data single out TRPV1 channels as modulators of opioid analgesia.

Pain is a main symptom of inflammatory diseases and often persists beyond clinical remission. Although we have a good understanding of the mechanisms of sensitization at the periphery during inflammation, little is known about the mediators that drive central sensitization. Recent reports have identified hematopoietic colony-stimulating factors as important regulators of tumor- and nerve injury-associated pain. Using a mouse model of colitis, we identify the proinflammatory cytokine granulocyte-colony–stimulating factor (G-CSF or Csf-3) as a key mediator of visceral sensitization. We report that G-CSF is specifically up-regulated in the thoracolumbar spinal cord of colitis-affected mice. Our results show that resident spinal microglia express the G-CSF receptor and that G-CSF signaling mediates microglial activation following colitis. Furthermore, healthy mice subjected to intrathecal injection of G-CSF exhibit pronounced visceral hypersensitivity, an effect that is abolished by microglial depletion. Mechanistically, we demonstrate that G-CSF injection increases Cathepsin S activity in spinal cord tissues. When cocultured with microglia BV-2 cells exposed to G-CSF, dorsal root ganglion (DRG) nociceptors become hyperexcitable. Blocking CX3CR1 or nitric oxide production during G-CSF treatment reduces excitability and G-CSF–induced visceral pain in vivo. Finally, administration of G-CSF–neutralizing antibody can prevent the establishment of persistent visceral pain postcolitis. Overall, our work uncovers a DRG neuron–microglia interaction that responds to G-CSF by engaging Cathepsin S-CX3CR1-inducible NOS signaling. This interaction represents a central step in visceral sensitization following colonic inflammation, thereby identifying spinal G-CSF as a target for treating chronic abdominal pain.

Background & Aims A dysregulated response of CD4 + T cells against the microbiota contributes to the development of inflammatory bowel disease. Effector CD4 + T cells, generated in response to microbe-derived antigens, can reduce somatic inflammatory pain through the local release of opioids. We investigated whether colitogenic CD4 + T cells that accumulate in the inflamed colon also produce opioids and are able to counteract inflammation-induced visceral pain in mice. Methods Colitis was induced via transfer of naive CD4 + CD45RB high T cells to immune-deficient mice or by administration of dextran sulfate sodium. Mice without colitis were used as controls. Samples of colon tissue were collected, and production of opioids by immune cells from inflamed intestine was assessed by quantitative polymerase chain reaction and cytofluorometry analyses. The role of intestinal opioid tone in inflammation-induced visceral hypersensitivity was assessed by colorectal distention. Results In mice with T cell– or dextran sulfate sodium–induced colitis, colitogenic CD4 + T cells (T-helper 1 and Th17 cells) accumulated in the inflamed intestine and expressed a high level of endogenous opioids. In contrast, macrophages and epithelial cells did not express opioids; opioid synthesis in the myenteric plexus was not altered on induction of inflammation. In mice with colitis, the local release of opioids by colitogenic CD4 + T cells led to significant reduction of inflammation-associated visceral hypersensitivity. Conclusions In mice, colitogenic Th1 and Th17 cells promote intestinal inflammation and colonic tissue damage but have simultaneous opioid-mediated analgesic activity, thereby reducing abdominal pain.

Endogenous opioids, including enkephalins, are fundamental regulators of pain. In inflammatory conditions, the local release of opioids by leukocytes at the inflammatory site inhibits nociceptor firing, thereby inducing analgesia. Accordingly, in chronic intestinal TThe anti-inflammatory effects of endogenous opioids were investigated in both TPeripheral opioid receptor blockade increases the severity of TEndogenous opioids, including T-cell-derived enkephalins, promote a T

International audience

Quiescent phases of inflammatory bowel disease (IBD) are often accompanied by chronic abdominal pain. Although the transient receptor potential vanilloid 1 (TRPV1) ion channel has been postulated as an important mediator of visceral hypersensitivity, its functional role in postinflammatory pain remains elusive. This study aimed at establishing the role of TRPV1 in the peripheral sensitization underlying chronic visceral pain in the context of colitis. Wild-type and TRPV1-deficient mice were separated into three groups (control, acute colitis, and recovery), and experimental colitis was induced by oral administration of dextran sulfate sodium (DSS). Recovery mice showed increased chemically and mechanically evoked visceral hypersensitivity 5 wk post-DSS discontinuation, at which point inflammation had completely resolved. Significant changes in nonevoked pain-related behaviors could also be observed in these animals, indicative of persistent discomfort. These behavioral changes correlated with elevated colonic levels of substance P (SP) and TRPV1 in recovery mice, thus leading to the hypothesis that SP could sensitize TRPV1 function. In vitro experiments revealed that prolonged exposure to SP could indeed sensitize capsaicin-evoked currents in both cultured neurons and TRPV1-transfected human embryonic kidney (HEK) cells, a mechanism that involved TRPV1 ubiquitination and subsequent accumulation at the plasma membrane. Importantly, although TRPV1-deficient animals experienced similar disease severity and pain as wild-type mice in the acute phase of colitis, TRPV1 deletion prevented the development of postinflammatory visceral hypersensitivity and pain-associated behaviors. Collectively, our results suggest that chronic exposure of colon-innervating primary afferents to SP could sensitize TRPV1 and thus participate in the establishment of persistent abdominal pain following acute inflammation.

Painful sensation is a hallmark of microbe-induced inflammation. This inflammatory pain is downregulated a few days after infection by opioids locally released by effector T lymphocytes generated in response to microbe-derived antigens. This review focuses on the endogenous regulation of inflammatory pain associated with adaptive T-cell response and puts in perspective the clinical consequences of the opioid-mediated analgesic activity of colitogenic T lymphocytes in inflammatory bowel disease.

Inflammatory bowel diseases (IBD) are characterized by an uncontrolled inflammatory response to colonic luminal content involving both innate and adaptive immunity. Indeed, aberrant responses of CD4+ Th1 and Th17 lymphocytes against microbiota highly contribute to the development of IBD. We have previously shown that effector CD4+ T lymphocytes generated in response to microbes are responsible for inflammatory pain relief that occurs spontaneously within the few days following the initiation of the immune response. The endogenous T cell-dependent regulation of inflammatory pain is mediated by the local release of opioids that have been synthesized upon the activation of CD4+ T lymphocytes within draining lymph nodes (Boue J, et al. J. Immunol., 2011, 186:5078-5084). Given that the production of opioids is not restricted to a particular phenotype of effector CD4+ T lymphocytes (Boue J, et al. Pain, 2012, 153, 485-493), we wondered whether colitogenic CD4+ Th17 and Th1 lymphocytes that accumulate within inflamed colon also produce opioids and contribute to reduce inflammation-induced visceral pain. For this purpose, we used the colitis model induced by the transfer of Naive CD4+CD45RBhigh T lymphocytes into immune-deficient SCID mice. In this model, in which the absence of efficient regulation of the T cell response against microbiota leads to chronic inflammation of the gut, we showed that Th1 and Th17 lymphocytes isolated from inflamed colon 6 weeks after T cell transfer, expressed high level of endogenous opioids. The production of opioids by colitogenic CD4+ T lymphocytes was responsible for a significant reduction of inflammation-associated abdominal pain as assessed by colorectal distension. Indeed, visceral sensitivity was increased in mice locally treated with an opioid receptor antagonist, unable to cross the blood-brain barrier. Taken together, our results indicate that colitogenic mucosal CD4+ T lymphocytes that play a pivotal role in colitis pathogenesis reduce pain associated with inflammationinduced tissue injury.

Inflammatory bowel diseases (IBD) are characterized by an uncontrolled inflammatory response to colonic luminal content involving both innate and adaptive immunity. Indeed, aberrant responses of CD4+ Th1 and Th17 lymphocytes against microbiota highly contribute to the development of IBD. We have previously shown that effector CD4+ T lymphocytes generated in response to microbes are responsible for inflammatory pain relief that occurs spontaneously within the few days following the initiation of the immune response. The endogenous T cell-dependent regulation of inflammatory pain is mediated by the local release of opioids that have been synthesized upon the activation of CD4+ T lymphocytes within draining lymph nodes (Boue J, et al. J. Immunol., 2011, 186:5078-5084). Given that the production of opioids is not restricted to a particular phenotype of effector CD4+ T lymphocytes (Boue J, et al. Pain, 2012, 153, 485-493), we wondered whether colitogenic CD4+ Th17 and Th1 lymphocytes that accumulate within inflamed colon also produce opioids and contribute to reduce inflammation-induced visceral pain. For this purpose, we used the colitis model induced by the transfer of Naive CD4+CD45RBhigh T lymphocytes into immune-deficient SCID mice. In this model, in which the absence of efficient regulation of the T cell response against microbiota leads to chronic inflammation of the gut, we showed that Th1 and Th17 lymphocytes isolated from inflamed colon 6 weeks after T cell transfer, expressed high level of endogenous opioids. The production of opioids by colitogenic CD4+ T lymphocytes was responsible for a significant reduction of inflammation-associated abdominal pain as assessed by colorectal distension. Indeed, visceral sensitivity was increased in mice locally treated with an opioid receptor antagonist, unable to cross the blood-brain barrier. Taken together, our results indicate that colitogenic mucosal CD4+ T lymphocytes that play a pivotal role in colitis pathogenesis reduce pain associated with inflammationinduced tissue injury.

The body is innervated by a meshwork of heterogeneous peripheral neurons (including sensory neurons) which project virtually to all the organs. Peripheral neurons have been studied extensively in the context of their primary function of initiation of voluntary and involuntary movement, transmission of sensations and induction of appropriate behavioral response such as withdrawal to avoid tissue injury or scratching to remove irritating molecules. More recently, breakthrough articles have shown that, on top of their primary function of signal transmission to the spinal cord and brain, peripheral neurons (including afferent neurons) could directly sense environmental alarms and consequently regulate the development of various type of immune responses through the release of neuropeptides or growth factors. In this review, we discuss recent advances in the neural regulation of the immune response, both in physiological and pathological contexts by taking into account the type of organs (lungs, skin and gut), subtypes of peripheral neurons (sympathetic, nociceptive and intrinsic gut neurons) or immune cells and strains of pathogens studied. We also highlight future challenges in the field and potential therapeutic innovations targeting neuro-immune interactions.