Hyperactivity of Innate Immunity Triggers Pain via TLR2-IL-33-Mediated Neuroimmune Crosstalk

TLR2 Mediates Microglial Activation and Contributes to Central Sensitization in a Recurrent Nitroglycerin-induced Chronic Migraine Model

Central sensitization is an important pathophysiological mechanism underlying chronic migraine (CM). Previous studies have shown that microglial activation and subsequent inflammation in the trigeminal nucleus caudalis (TNC) contribute to central sensitization. Toll-like receptor 2 (TLR2) is a receptor expressed on the membrane of microglia and participates in central sensitization in inflammatory and chronic pain; however, its role in CM is unclear. Therefore, this study investigated TLR2 involvement in CM in detail. Mice treated with recurrent nitroglycerin (NTG) were used as a CM model. Hyperalgesia was assessed using a 50% paw mechanical threshold and a 50% periorbital threshold on a Von Frey filament pain meter. Western blotting and immunofluorescence analyses were used to detect the expression of TLR2, microglia, c-fos and CGRP in TNC. The expression of inflammatory factors (IL-6, IL-1β、 IL-10、TNF-α and IFN-β1) was detected using quantitative real-time polymerase chain reaction (qRT-PCR). A selective TLR2 antagonist (C29) was systematically administered to observe its effect on hyperalgesia, microglia activation and the expression of c-fos, CGRP and inflammatory factors. Recurrent administration of NTG resulted in acute and chronic hypersensitivity, accompanied by upregulation of TLR2 expression and microglial activation in TNC. C29 partially inhibited pain hypersensitivity. C29 suppressed microglial activation induced by NTG administration. Inhibition of TLR2 reduced the expression of c-fos and CGRP in TNC after NTG treatment. C29 inhibited the expression of inflammatory mediators in TNC. These data showed that microglial TLR2 plays a critical role in the pathogenesis of CM by regulating microglial activation in TNC.

Inflammation-induced mitochondrial and metabolic disturbances in sensory neurons control the switch from acute to chronic pain

Pain often persists in patients with an inflammatory disease, even when inflammation has subsided. The molecular mechanisms leading to this failure in pain resolution and the transition to chronic pain are poorly understood. Mitochondrial dysfunction in sensory neurons links to chronic pain, but its role in resolution of inflammatory pain is unclear. Transient inflammation causes neuronal plasticity, called hyperalgesic priming, which impairs resolution of pain induced by a subsequent inflammatory stimulus. We identify that hyperalgesic priming in mice increases the expression of a mitochondrial protein (ATPSc-KMT) and causes mitochondrial and metabolic disturbances in sensory neurons. Inhibition of mitochondrial respiration, knockdown of ATPSCKMT expression, or supplementation of the affected metabolite is sufficient to restore resolution of inflammatory pain and prevents chronic pain development. Thus, inflammation-induced mitochondrial-dependent disturbances in sensory neurons predispose to a failure in resolution of inflammatory pain and development of chronic pain.

IL-33/ST2 Signaling in the Pathogenesis of Chronic Pain and Itch

Interleukin-33 (IL-33) is an inflammatory factor with an extensive range of biological effects and pleiotropic roles in diseases. Evidence suggests that IL-33 and its receptor ST2 play a pivotal role in chronic pain and itch at the level of primary sensory neurons, the spinal cord, and the brain. In this review, we outline an evolving understanding of the roles and mechanisms of IL-33 in chronic pathological pain, including inflammatory, neuropathic, and cancer, and chronic pruritus, such as allergic contact dermatitis, atopic dermatitis, and dry skin. Understanding the key roles of IL-33/ST2 signaling may provide exciting insights into the mechanisms of chronic pain and itch and lead to new clues for therapeutic approaches to the resolution of chronic pain and itch.

IL-33/ST2 signaling in pain and itch: Cellular and molecular mechanisms and therapeutic potentials

Pain is a cardinal feature of many diseases. Chronic pain poses heavy burdens to the suffering patients, both physically and mentally. However, current mainstream medications for chronic pain, including opioids, antidepressants and non-steroid anti-inflammatory drugs are sometimes inefficient for chronic pain management and may cause side effects that limit long term usage. IL-33 belongs to IL-1 cytokine family and it exerts biological activities through binding to its specific receptor ST2. IL-33/ST2 signaling is very important in both innate and adaptive immunity. Emerging evidence indicates IL-33/ST2 signaling regulates pain in both immune and somatosensory systems through promoting neuro-immune or neuron-glia crosstalk, neuroinflammation and neuronal hyperexcitability. Some very latest studies indicate a vital part of IL-33/ST2 in mediating chronic itch. This work aims to overview the existing knowledge regarding the mechanisms of IL-33/ST2 involvement in pain and itch conditions, considering their potential similarities. We also summarized some key findings obtained from clinical studies. The targeting of IL-33/ST2 signaling holds promise for the development of novel therapeutic modalities in the management of pain and itch.

Type 2 neuroimmune circuits in the shaping of physiology

Type 2 immune responses drive a broad range of biological processes including defense from large parasites, immunity to allergens, and non-immunity-related functions, such as metabolism and tissue homeostasis. The symptoms provoked by type 2 immunity, such as vomiting, coughing or itching, encompass nervous system triggering. Here, we review recent findings that place type 2 neuroimmune circuits at the center stage of immunity at barrier surfaces. We emphasize the homeostatic functions of these circuitries and how deregulation may drive pathology and impact disease outcomes, including in the context of cancer. We discuss a paradigm wherein type 2 neuroimmune circuits are central regulators of organismal physiology.

Neuromedin U Induces Pulmonary ILC2 Activation via the NMUR1 Pathway during Acute Respiratory Syncytial Virus Infection

Activated group 2 innate lymphoid cells (ILC2s) play a crucial role in respiratory syncytial virus (RSV)-induced airway inflammation and allergy-like symptoms because of their ability to secrete large quantities of type 2 cytokines. Cytokines such as IL-33, IL-25, and thymic stromal lymphopoietin are activators of ILC2s. Besides, a regulatory effect of neurotransmitters on ILC2 activation has been reported recently. However, whether and how RSV infection induces neurotransmitter production in the lungs and regulates pulmonary ILC2 activation remains unclear. In this study, using a murine model established by intranasal infection with RSV, we found that acute RSV infection induced the production of a neurotransmitter, neuromedin U (NMU), in the lungs of RSV-infected mice and upregulated the expression of NMUR1 (neuromedin U receptor 1) on ILC2s. Moreover, in vivo administration of NMU exacerbated RSV-induced airway inflammation by promoting the proliferation and activation of pulmonary ILC2s via the NMUR1 pathway, which involved PI3K, mitogen-activated protein kinase kinase, and NFAT signaling proteins. Furthermore, pulmonary neurons responded to the stimulation of RSV infection and secreted NMU in a Toll-like receptor 4- and Toll-like receptor 7-dependent manner. Collectively, our data suggest that NMU is a powerful neuropeptide to activate ILC2s, highlighting the critical regulatory effects of neurotransmitters on antiviral, inflammatory, and tissue homeostasis at the mucosal barrier during a viral respiratory infection.

Soluble mediators in the function of the epidermal-immune-neuro unit in the skin

Skin is the largest, environmentally exposed (barrier) organ, capable of integrating various signals into effective defensive responses. The functional significance of interactions among the epidermis and the immune and nervous systems in regulating and maintaining skin barrier function is only now becoming recognized in relation to skin pathophysiology. This review focuses on newly described pathways that involve soluble mediator-mediated crosstalk between these compartments. Dysregulation of these connections can lead to chronic inflammatory diseases and/or pathologic conditions associated with chronic pain or itch.

Critical Players and Therapeutic Targets in Chronic Itch

Chronic itch is one of the most prominent clinical characteristics of diverse systematic diseases. It is a devastating sensation in pathological diseases. Despite its importance, there are no FDA-labelled drugs specifically geared toward chronic itch. The associated complex pathogenesis and diverse causes escalate chronic itch to being one of the top challenges in healthcare. Humanized antibodies against IL-13, IL-4, and IL-31 proved effective in treatment of itch-associated atopic dermatitis but remain to be validated in chronic itch. There are still no satisfactory anti-itch therapeutics available toward itch-related neuropeptides including GRP, BNP, SST, CGRP, and SP. The newly identified potential itch targets including OSM, NMB, glutamate, periostin, and Serpin E1 have opened new avenues for therapeutic development. Proof-of-principle studies have been successfully performed on antagonists against these proteins and their receptors in itch treatment in animal models. Their translational interventions in humans need to be evaluated. It is of great importance to summarize and compare the newly emerging knowledge on chronic itch and its pathways to promote the development of novel anti-itch therapeutics. The goal of this review is to analyze the different physiologies and pathophysiologies of itch mediators, whilst assessing their suitability as new targets and discussing future therapeutic development.

Huc-MSCs-derived exosomes attenuate inflammatory pain by regulating microglia pyroptosis and autophagy via the miR-146a-5p/TRAF6 axis

Background

Chronic inflammatory pain significantly reduces the quality of life and lacks effective interventions. In recent years, human umbilical cord mesenchymal stem cells (huc-MSCs)-derived exosomes have been used to relieve neuropathic pain and other inflammatory diseases as a promising cell-free therapeutic strategy. However, the therapeutic value of huc-MSCs-derived exosomes in complete Freund's adjuvant (CFA)-induced inflammatory pain remains to be confirmed. In this study, we investigated the therapeutic effect and related mechanisms of huc-MSCs-derived exosomes in a chronic inflammatory pain model.

Methods

C57BL/6J male mice were used to establish a CFA-induced inflammatory pain model, and huc-MSCs-derived exosomes were intrathecally injected for 4 consecutive days. BV2 microglia cells were stimulated with lipopolysaccharide (LPS) plus adenosine triphosphate (ATP) to investigate the effect of huc-MSCs-derived exosomes on pyroptosis and autophagy. Bioinformatic analysis and rescue experiments were used to demonstrate the role of miR-146a-5p/ TRAF6 in regulating pyroptosis and autophagy. Western blotting, RT-qPCR, small interfering RNA and Yo-Pro-1 dye staining were performed to investigate the related mechanisms.

Results

Huc-MSCs-derived exosomes alleviated mechanical allodynia and thermal hyperalgesia in CFA-induced inflammatory pain. Furthermore, huc-MSCs-derived exosomes attenuated neuroinflammation by increasing the expression of autophagy-related proteins (LC3-II and beclin1) and inhibiting the activation of NLRP3 inflammasomes in the spinal cord dorsal horn. In vitro, NLRP3 inflammasome components (NLRP3, caspase1-p20, ASC) and gasdermin D (GSDMD-F, GSDMD-N) were inhibited in BV2 cells pretreated with huc-MSCs-derived exosomes. Western blot and Yo-Pro-1 dye staining demonstrated that 3-MA, an autophagy inhibitor, weakened the protective effect of huc-MSCs-derived exosomes on BV2 cell pyroptosis. Importantly, huc-MSCs-derived exosomes transfected with miR-146a-5p mimic promoted autophagy and inhibited BV2 cell pyroptosis. TRAF6, as a target gene of miR-146a-5p, was knocked down via small-interfering RNA, which increased pyroptosis and inhibited autophagy.

Conclusion

Huc-MSCs-derived exosomes attenuated inflammatory pain via miR-146a-5p/TRAF6, which increased the level of autophagy and inhibited pyroptosis.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01522-6.

Electroacupuncture Ameliorates Mechanical Allodynia of a Rat Model of CRPS-I via Suppressing NLRP3 Inflammasome Activation in Spinal Cord Dorsal Horn Neurons

Complex regional pain syndrome type-I (CRPS-I) is a chronic neurological disorder that results in severe pain and affects patients' life quality. Conventional therapies usually lack effectiveness. Electroacupuncture (EA) is an effective physical therapy for relieving CRPS-I pain. However, the mechanism underlying EA-induced analgesia on CRPS-I still remain unknown. Spinal NLRP3 inflammasome was recently identified to contribute to pain and neuroinflammation in a rat model of CRPS-I by our group. Here, we aimed to study whether EA could inhibit spinal NLRP3 inflammasome activation, thus resulting in pain relief and attenuation of spinal neuroinflammation in the rat model of CRPS-I. We established the rat chronic post-ischemic pain (CPIP) model to mimic CRPS-I. CPIP rats developed remarkable mechanical allodynia that could be relieved by daily EA intervention. NLRP3 inflammasome was activated in spinal cord dorsal horn (SCDH) of CPIP rats, accompanied with over-production of pro-inflammatory cytokine IL-1β. Immunostaining revealed that the cellular distribution of NLRP3 was predominantly located in SCDH neurons. Pharmacological activation of NLRP3 inflammasome per se is sufficient to produce persistent mechanical allodynia in naïve animals, whereas blocking NLRP3 inflammasome attenuates mechanical allodynia of CPIP rats. EA exclusively reduced NLRP3 overexpression in SCDH neurons and attenuated spinal glial cell over-activation in CPIP rats. EA-induced anti-allodynia with attenuation of spinal glial cell over-activation were all mimicked by intrathecal blocking NLRP3 inflammasome and reversed by activating NLRP3 inflammasome, respectively, through pharmacological methods. Finally, spinal blocking IL-1β attenuated mechanical allodynia and spinal glial cell over-activation in CPIP rats, resembling the effects of EA. In all, these results demonstrate that spinal NLRP3 inflammasome activation contributes to mechanical allodynia of the rat model of CRPS-I and EA ameliorates mechanical allodynia through inhibiting NLRP3 inflammasome activation in SCDH neurons. Our study further supports EA can be used as an effective treatment for CRPS-I.

The PLAUR signaling promotes chronic pruritus

Chronic itch is a complex sensation of the skin frequently associated with skin diseases, such as atopic dermatitis (AD) and psoriasis. Although Serpin E1 is implicated in chronic itch, its receptor and signaling pathways involved in itch are not known. In this study, the clinical relevance of a putative Serpin E1 receptor PLAUR to chronic itch, and the neuro‐cutaneous Serpin E1‐PLAUR signaling are explored. We found that PLAUR is overexpressed in skin specimens of human lesional AD and lesional psoriasis, and sensory neurons innervating MC903‐induced AD‐like murine skin. Murine PLAUR⁺ sensory neurons responded to Serpin E1, resulting in enrichment of numerous itch‐ and inflammation‐related genes and their protein release. PLAUR resides in TLR2⁺ neurons and Serpin E1 stimulus led to transcriptional upregulation of TLR2 and its co‐signaling proteins. Agonists of TLR2 propagated itch‐related gene transcription including BNP, OSM, and PAR2. OSM induced acute itch in mice and promoted G‐CSF and IL‐8 release from human keratinocytes. Serpin E1 inhibitor reduced MC903‐induced itch, epidermal hyperplasia, immunocyte infiltration, and resulted in lower transcription/expression levels of Serpin E1 and OSM. Taken together, the PLAUR‐TLR2‐OSM signaling promotes skin‐nerve communication, cutaneous inflammation, and itch, all feeding into an aggravation of AD and exaggerated itch circuits.

Alarmin Cytokines as Central Regulators of Cutaneous Immunity

Skin acts as the primary interface between the body and the environment. The skin immune system is composed of a complex network of immune cells and factors that provide the first line of defense against microbial pathogens and environmental insults. Alarmin cytokines mediate an intricate intercellular communication between keratinocytes and immune cells to regulate cutaneous immune responses. Proper functions of the type 2 alarmin cytokines, thymic stromal lymphopoietin (TSLP), interleukin (IL)-25, and IL-33, are paramount to the maintenance of skin homeostasis, and their dysregulation is commonly associated with allergic inflammation. In this review, we discuss recent findings on the complex regulatory network of type 2 alarmin cytokines that control skin immunity and highlight the mechanisms by which these cytokines regulate skin immune responses in host defense, chronic inflammation, and cancer.

BRD4 Inhibition Attenuates Inflammatory Pain by Ameliorating NLRP3 Inflammasome-Induced Pyroptosis

Chronic pain, such as persistent inflammatory pain, remains a public health problem that has no effective treatment at present. Bromodomain-containing protein 4 (BRD4) inhibition, induced by JQ1 injection or BRD4 knockdown, has been used to attenuate inflammatory pain; However, it remains elusive whether BRD4 aggravates inflammatory pain by regulating inflammasome. Western blot and immunofluorescence staining showed that BRD4 expression increased after administration of complete Freund’s adjuvant (CFA) and reached its peak on day 3. Immunofluorescence staining showed that BRD4 was mainly colocalized with NeuN-positive neurons in the spinal cord, which was accompanied by upregulation of inflammasome component proteins, such as NLRP3, gasdermin D, and caspase-1. JQ1 was intrathecally injected into mice 1 h before CFA administration, and the mechanical and thermal hyperalgesia levels were measured on days 1, 3, and 7 after CFA administration. CFA-induced inflammatory pain, paw inflammation, and swelling were attenuated by pre-treatment with JQ1. To our knowledge, this study was the first to prove that NLRP3 inflammasome-induced neuronal pyroptosis participates in inflammatory pain. BRD4 inhibition decreased the expression of pyroptosis-related proteins by inhibiting the activation of NF-κB signaling pathway, both in vivo and in vitro. Taken together, BRD4 inhibition exerted analgesic and anti-inflammatory effects against inflammatory pain by inhibiting NF-κB and inflammasome activation, which protected neural cells from pyroptosis.

The IL-33-ILC2 pathway protects from amebic colitis

Entamoeba histolytica is a pathogenic protozoan parasite that causes intestinal colitis, diarrhea, and in some cases, liver abscess. Through transcriptomics analysis, we observed that E. histolytica infection was associated with increased expression of IL-33 mRNA in both the human and murine colon. IL-33, the IL-1 family cytokine, is released after cell injury to alert the immune system of tissue damage. Treatment with recombinant IL-33 protected mice from amebic infection and intestinal tissue damage; moreover, blocking IL-33 signaling made mice more susceptible to amebiasis. IL-33 limited the recruitment of inflammatory immune cells and decreased the pro-inflammatory cytokine IL-6 in the cecum. Type 2 immune responses were upregulated by IL-33 treatment during amebic infection. Interestingly, administration of IL-33 protected RAG2^-/- mice but not RAG2^-/-γc^-/- mice, demonstrating that IL-33-mediated protection required the presence of innate lymphoid cells (ILCs). IL-33 induced recruitment of ILC2 but not ILC1 and ILC3 in RAG2^-/- mice. At baseline and after amebic infection, there was a significantly higher IL13+ILC2s in C57BL/J mice, which are naturally resistant to amebiasis, than CBA/J mice. Adoptive transfer of ILC2s to RAG2^-/-γc^-/- mice restored IL-33-mediated protection. These data reveal that the IL-33-ILC2 pathway is an important host defense mechanism against amebic colitis.

Evidence That a TRPA1-Mediated Murine Model of Temporomandibular Joint Pain Involves NLRP3 Inflammasome Activation

This study investigates the role of transient receptor potential ankyrin 1 (TRPA1) in murine temporomandibular joint (TMJ) inflammatory hyperalgesia and the influence of the NLR family pyrin domain-containing 3 (NLRP3) inflammasome. Two distinct murine models of TMJ pain and inflammation (zymosan and CFA) were established. Spontaneous pain-like behaviours were observed as unilateral front paw cheek wipes. Ipsilateral cheek blood flow was used as a measure of ongoing inflammation, which, to our knowledge, is a novel approach to assessing real-time inflammation in the TMJ. Joint tissue and trigeminal ganglia were collected for ex vivo investigation. Both zymosan and CFA induced a time-dependent increase in hyperalgesia and inflammation biomarkers. Zymosan induced a significant effect after 4 h, correlating with a significantly increased IL-1β protein expression. CFA (50 µg) induced a more sustained response. The TRPA1 receptor antagonist A967079 significantly inhibited hyper-nociception. The NLRP3 inhibitor MCC950 similarly inhibited hyper-nociception, also attenuating inflammatory markers. In the trigeminal ganglia, CFA-induced CGRP expression showed trends of inhibition by A967079, whilst lba1 immunofluorescence was significantly inhibited by A967079 and MCC950, where the effect of TRPA1 inhibition lasted up to 14 days. Our results show that stimulation of TRPA1 is key to the TMJ pain. However, the inflammasome inhibitor exhibited similar properties in attenuating these pain-like behaviours, in addition to some inflammatory markers. This indicates that in addition to the therapeutic targeting of TRPA1, NLRP3 inhibition may provide a novel therapeutic strategy for TMJ inflammation and pain.

IL-33 signaling in sensory neurons promotes dry skin itch

BACKGROUND

Chronic pruritus, or itch, is common and debilitating, but the neuroimmune mechanisms that drive chronic itch are only starting to be elucidated. Recent studies demonstrate that the IL-33 receptor (IL-33R) is expressed by sensory neurons. However, whether sensory neuron-restricted activity of IL-33 is necessary for chronic itch remains poorly understood.

OBJECTIVES

We sought to determine if IL-33 signaling in sensory neurons is critical for the development of chronic itch in 2 divergent pruritic disease models.

METHODS

Plasma levels of IL-33 were assessed in patients with atopic dermatitis (AD) and chronic pruritus of unknown origin (CPUO). Mice were generated to conditionally delete IL-33R from sensory neurons. The contribution of neuronal IL-33R signaling to chronic itch development was tested in mouse models that recapitulate key pathologic features of AD and CPUO, respectively.

RESULTS

IL-33 was elevated in both AD and CPUO as well as their respective mouse models. While neuron-restricted IL-33R signaling was dispensable for itch in AD-like disease, it was required for the development of dry skin itch in a mouse model that mirrors key aspects of CPUO pathology.

CONCLUSIONS

These data highlight how IL-33 may be a predominant mediator of itch in certain contexts, depending on the tissue microenvironment. Further, this study provides insight into future therapeutic strategies targeting the IL-33 pathway for chronic itch.

Therapeutic Opportunities of Interleukin-33 in the Central Nervous System

Interleukin-33 (IL-33), a member of the IL-1 cytokine family, is involved in various diseases. IL-33 exerts its effects via its heterodimeric receptor complex, which comprises suppression of tumorigenicity 2 (ST2) and the IL-1 receptor accessory protein (IL-1RAP). Increasing evidence has demonstrated that IL-33/ST2 signaling plays diverse but crucial roles in the homeostasis of the central nervous system (CNS) and the pathogenesis of CNS diseases, including neurodegenerative diseases, cerebrovascular diseases, infection, trauma, and ischemic stroke. In the current review, we focus on the functional roles and cellular signaling mechanisms of IL-33 in the CNS and evaluate the potential for diagnostic and therapeutic applications.

A "Drug-Dependent" Immune System Can Compromise Protection against Infection: The Relationships between Psychostimulants and HIV

Psychostimulant use is a major comorbidity in people living with HIV, which was initially explained by them adopting risky behaviors that facilitate HIV transmission. However, the effects of drug use on the immune system might also influence this phenomenon. Psychostimulants act on peripheral immune cells even before they reach the central nervous system (CNS) and their effects on immunity are likely to influence HIV infection. Beyond their canonical activities, classic neurotransmitters and neuromodulators are expressed by peripheral immune cells (e.g., dopamine and enkephalins), which display immunomodulatory properties and could be influenced by psychostimulants. Immune receptors, like Toll-like receptors (TLRs) on microglia, are modulated by cocaine and amphetamine exposure. Since peripheral immunocytes also express TLRs, they may be similarly affected by psychostimulants. In this review, we will summarize how psychostimulants are currently thought to influence peripheral immunity, mainly focusing on catecholamines, enkephalins and TLR4, and shed light on how these drugs might affect HIV infection. We will try to shift from the classic CNS perspective and adopt a more holistic view, addressing the potential impact of psychostimulants on the peripheral immune system and how their systemic effects could influence HIV infection.

The NLRP3 inflammasome: an emerging therapeutic target for chronic pain

Chronic pain affects the life quality of the suffering patients and posts heavy problems to the health care system. Conventional medications are usually insufficient for chronic pain management and oftentimes results in many adverse effects. The NLRP3 inflammasome controls the processing of proinflammatory cytokine interleukin 1β (IL-1β) and is implicated in a variety of disease conditions. Recently, growing number of evidence suggests that NLRP3 inflammasome is dysregulated under chronic pain condition and contributes to pathogenesis of chronic pain. This review provides an up-to-date summary of the recent findings of the involvement of NLRP3 inflammasome in chronic pain and discussed the expression and regulation of NLRP3 inflammasome-related signaling components in chronic pain conditions. This review also summarized the successful therapeutic approaches that target against NLRP3 inflammasome for chronic pain treatment.

The IL33 receptor ST2 contributes to mechanical hypersensitivity in mice with neuropathic pain

Pathogen infection triggers pain via activation of the innate immune system. Toll-like receptors (TLRs) and Nod-like receptors (NLRs) are the main components of innate immunity and have been implicated in pain signaling. We previously revealed that the TLR2-NLRP3-IL33 pathway mediates inflammatory pain responses during hyperactivity of innate immunity. However, their roles in neuropathic pain had remained unclear. Here we report that although knockout of TLR2 or NLRP3 does not affect spared nerve injury (SNI)-induced neuropathic pain, intrathecal inhibition of IL33/ST2 signaling with ST2 neutralizing antibodies reverses mechanical thresholds in SNI mice compared to PBS vehicle treated animals. This effect indicates a universal role of IL33 in both inflammatory and neuropathic pain states, and that targeting the IL33/ST2 axis could be a potential therapeutic approach for pain treatment.