TNF-alpha and IL-1beta mediate inflammatory hypernociception in mice triggered by B1 but not B2 kinin receptor

Infection-associated vasculopathy in experimental chagas disease pathogenic roles of endothelin and kinin pathways

Acting at the interface between microcirculation and immunity, Trypanosoma cruzi induces modifications in peripheral tissues which translate into mutual benefits to host/parasite balance. In this chapter, we will review evidence linking infection-associated vasculopathy to the proinflammatory activity of a small subset of T. cruzi molecules, namely GPI-linked mucins, cysteine proteases (cruzipain), surface glycoproteins of the trans-sialidase family and/or parasite-derived eicosanoids (thromboxane A(2)). Initial insight into pathogenesis came from research in animal models showing that myocardial fibrosis is worsened as result of endothelin upregulation by infected cardiovascular cells. Paralleling these studies, the kinin system emerged as a proteolytic mechanism that links oedematogenic inflammation to immunity. Analyses of the dynamics of inflammation revealed that tissue culture trypomastigotes elicit interstitial oedema in peripheral sites of infection through synergistic activation of toll-like 2 receptors (TLR2) and G-protein-coupled bradykinin receptors, respectively, engaged by tGPI (TLR2 ligand) and kinin peptides (bradykinin B2 receptors (BK(2)R) ligands) proteolytically generated by cruzipain. Further downstream, kinins stimulate lymph node dendritic cells via G-protein-coupled BK(2)R, thus converting these specialized antigen-presenting cells into T(H)1 inducers. Tightly regulated by angiotensin-converting enzyme, the intact kinins (BK(2)R agonists) may be processed by carboxypeptidase M/N, generating [des-Arg]-kinins, which activates BK(1)R, a subtype of GPCR that is upregulated by cardiovascular cells during inflammation. Ongoing studies may clarify if discrepancies between proinflammatory phenotypes of T. cruzi strains may be ascribed, at least in part, to variable expression of TLR2 ligands and cruzipain isoforms.

Toll-like receptor 2/MyD88 signaling mediates zymosan-induced joint hypernociception in mice: participation of TNF-α, IL-1β and CXCL1/KC

Arthritic pain is a serious health problem that affects a large number of patients. Toll-like receptors (TLRs) activation within the joints has been implicated in pathophysiology of arthritis. However, their role in the genesis of arthritic pain needs to be demonstrated. In the present study, it was addressed the participation of TLR2 and TLR4 and their adaptor molecule MyD88 in the genesis of joint hypernociception (a decrease in the nociceptive threshold) during zymosan-induced arthritis. Zymosan injected in the tibio-tarsal joint induced mechanical hypernociception in C57BL/6 wild type mice that was reduced in TLR2 and MyD88 null mice. On the other hand, zymosan-induced hypernociception was similar in C3H/HePas and C3H/HeJ mice (TLR4 mutant mice). Zymosan-induced joint hypernociception was also reduced in TNFR1 null mice and in mice treated with IL-1 receptor antagonist or with an antagonist of CXCR1/2. Moreover, the joint production of TNF-α, IL-1β and CXCL1/KC by zymosan was dependent on TLR2/MyD88 signaling. Investigating the mechanisms by which TNF-α, IL-1β and CXCL1/KC mediate joint hypernociception, joint administration of these cytokines produced mechanical hypernociception, and they act in an interdependent manner. In last instance, their hypernociceptive effects were dependent on the production of hypernociceptive mediators, prostaglandins and sympathetic amines. These results indicate that in zymosan-induced experimental arthritis, TLR2/MyD88 is involved in the cascade of events of joint hypernociception through a mechanism dependent on cytokines and chemokines production. Thus, TLR2/MyD88 signaling might be a target for the development of novel drugs to control pain in arthritis.

Involvement of circulating platelets on the hyperalgesic response evoked by carrageenan and Bothrops jararaca snake venom

BACKGROUND

The role of platelets in hemostasis is well known, but few papers have reported their role in pain and edema induced by inflammatory agents.

OBJECTIVE

To evaluate the role of circulating platelets in the local injury induced by two diverse inflammatory agents, Bothrops jararaca venom (Bjv) and carrageenan.

METHODS

Rats were (i) rendered thrombocytopenic by administration of polyclonal anti-rat platelet IgG (ARPI) or busulfan, or (ii) treated with platelet inhibitors (aspirin or clopidogrel). Edema formation, local hemorrhage and the pain threshold were assessed after intraplantar injection of Bjv or carrageenan in rat hind paws. Additionally, whole platelets or platelet releasate were tested whether they directly induced hyperalgesia.

RESULTS

Platelet counts were markedly diminished in rats administered with either ARPI (± 88%) or busulfan (± 96%). Previous treatment with ARPI or busulfan slightly reduced edema induced by Bjv or carrageenan. Injection of Bjv, but not of carrageenan, induced a statistically significance increase in hemorrhage in the hind paws of thrombocytopenic rats. Remarkably, hyperalgesia evoked by Bjv or carrageenan was completely blocked in animals treated with ARPI or busulfan, or pre-treated with aspirin or clopidogrel. On the other hand, intraplantar administration of whole platelets or platelet releasate evoked hyperalgesia, which was inhibited by pre-incubation with alkaline phosphatase.

CONCLUSIONS

Thrombocytopenia or inhibition of platelet function drastically reduced hyperalgesia induced by injection of carrageenan or Bjv; moreover, platelets per se secrete phosphorylated compounds involved in pain mediation. Thus, blood platelets are crucial cells involved in the pain genesis, and their role therein has been underestimated.

Cytokines and pain

BACKGROUND AND OBJECTIVES

Cytokines are necessary for the inflammatory response, favoring proper wound healing. However, exaggerated proinflammatory cytokine production can manifest systemically as hemodynamic instability or metabolic derangements. The objective of this review was to describe the effects of cytokines in pain.

CONTENTS

This article reviews the effects of cytokines in pain. In diseases with acute or chronic inflammation, cytokines can be recognized by neurons and used to trigger several cell reactions that influence the activity, proliferation, and survival of immune cells, as well as the production and activity of other cytokines. Cytokines can be proinflammatory and anti-inflammatory. Proinflammatory cytokines are related with the pathophysiology of pain syndromes. Cells that secrete proinflammatory (IL-1, IL-2, IL-6, IL-7, and TNF) and anti-inflammatory (IL-4, IL-10, IL-13, and TGFβ) cytokines, the functions of each cytokine, and the action of those compounds on pain processing, have been described.

CONCLUSIONS

Cytokines have an important role in pain through different mechanisms in several sites of pain transmission pathways.

Ion channels in inflammation

Most physical illness in vertebrates involves inflammation. Inflammation causes disease by fluid shifts across cell membranes and cell layers, changes in muscle function and generation of pain. These disease processes can be explained by changes in numbers or function of ion channels. Changes in ion channels have been detected in diarrhoeal illnesses, pyelonephritis, allergy, acute lung injury and systemic inflammatory response syndromes involving septic shock. The key role played by changes in ion transport is directly evident in inflammation-induced pain. Expression or function of all major categories of ion channels like sodium, chloride, calcium, potassium, transient receptor potential, purinergic receptor and acid-sensing ion channels can be influenced by cyto- and chemokines, prostaglandins, leukotrienes, histamine, ATP, reactive oxygen species and protons released in inflammation. Key pathways in this interaction are cyclic nucleotide, phosphoinositide and mitogen-activated protein kinase-mediated signalling, direct modification by reactive oxygen species like nitric oxide, ATP or protons and disruption of the cytoskeleton. Therapeutic interventions to modulate the adverse and overlapping effects of the numerous different inflammatory mediators on each ion transport system need to target adversely affected ion transport systems directly and locally.

Enhancement of antinociception by coadministration of minocycline and a non-steroidal anti-inflammatory drug indomethacin in naïve mice and murine models of LPS-induced thermal hyperalgesia and monoarthritis

BACKGROUND

Minocycline and a non-steroidal anti-inflammatory drug (NSAID) indomethacin, have anti-inflammatory activities and are both used in the management of rheumatoid arthritis. However, there are no reports on whether coadministration of these drugs could potentiate each other's activities in alleviating pain and weight bearing deficits during arthritis.

METHODS

LPS was injected to BALB/c mice intraperitoneally (i.p.) to induce thermal hyperalgesia. The hot plate test was used to study thermal nociception in naïve BALB/c and C57BL/6 mice and BALB/c mice with LPS-induced thermal hyperalgesia and to evaluate antinociceptive effects of drugs administered i.p. Monoarthritis was induced by injection of LPS intra-articularly into the right hind (RH) limb ankle joint of C57BL/6 mice. Weight bearing changes and the effect of i.p. drug administration were analyzed in freely moving mice using the video-based CatWalk gait analysis system.

RESULTS

In naïve mice indomethacin (5 to 50 mg/kg) had no significant activity, minocycline (25 to 100 mg/kg) produced hyperalgesia to thermal nociception, however, coadministration of minocycline 50 mg/kg with indomethacin 5 or 10 mg/kg produced significant antinociceptive effects in the hot plate test. A selective inhibitor of COX-1, FR122047 (10 mg/kg) and a selective COX-2 inhibitor, CAY10404 (10 mg/kg) had no significant antinociceptive activities to thermal nociception in naïve mice, however, coadministration of minocycline, with CAY10404 but not FR122047 produced significant antinociceptive effects. In mice with LPS-induced hyperalgesia vehicle, indomethacin (10 mg/kg) or minocycline (50 mg/kg) did not produce significant changes, however, coadministration of minocycline plus indomethacin resulted in antinociceptive activity. LPS-induced RH limb monoarthritis resulted in weight bearing (RH/left hind (LH) limb paw pressure ratios) and RH/LH print area ratios deficits. Treatment with indomethacin (1 mg/kg) or minocycline (50 mg/kg) had no effects on the weight bearing and print area ratios deficits of monoarthritic mice. However, combination of minocycline plus indomethacin restored weight bearing and paw print area ratios of monoarthritic mice similar to that observed in non-arthritic control mice.

CONCLUSIONS

Coadministration of indomethacin or a selective COX-2 inhibitor, CAY10404 with minocycline potentiates their effects and results in antinociception against thermal nociception, reduction of thermal hyperalgesia and alleviation of weight bearing deficits in monoarthritic mice at doses where either drug alone has no significant activity. Thus, the coadministration of lower doses of a NSAID or a selective COX-2 inhibitor plus minocycline could be useful in the management of inflammatory pain and arthritis.

Caspase-1 is involved in the genesis of inflammatory hypernociception by contributing to peripheral IL-1β maturation

Background

Caspase-1 is a cysteine protease responsible for the processing and secretion of IL-1β and IL-18, which are closely related to the induction of inflammation. However, limited evidence addresses the participation of caspase-1 in inflammatory pain. Here, we investigated the role of caspase-1 in inflammatory hypernociception (a decrease in the nociceptive threshold) using caspase-1 deficient mice (casp1-/-).

Results

Mechanical inflammatory hypernociception was evaluated using an electronic version of the von Frey test. The production of cytokines, PGE₂ and neutrophil migration were evaluated by ELISA, radioimmunoassay and myeloperoxidase activity, respectively. The interleukin (IL)-1β and cyclooxygenase (COX)-2 protein expression were evaluated by western blotting. The mechanical hypernociception induced by intraplantar injection of carrageenin, tumour necrosis factor (TNF)α and CXCL1/KC was reduced in casp1-/- mice compared with WT mice. However, the hypernociception induced by IL-1β and PGE₂ did not differ in WT and casp1-/- mice. Carrageenin-induced TNF-α and CXCL1/KC production and neutrophil recruitment in the paws of WT mice were not different from casp1-/- mice, while the maturation of IL-1β was reduced in casp1-/- mice. Furthermore, carrageenin induced an increase in the expression of COX-2 and PGE₂ production in the paw of WT mice, but was reduced in casp1-/- mice.

Conclusion

These results suggest that caspase-1 plays a critical role in the cascade of events involved in the genesis of inflammatory hypernociception by promoting IL-1β maturation. Because caspase-1 is involved in the induction of COX-2 expression and PGE₂ production, our data support the assertion that caspase-1 is a key target to control inflammatory pain.

Treatment of murine osteoarthritis with TrkAd5 reveals a pivotal role for nerve growth factor in non-inflammatory joint pain

The origin of pain in osteoarthritis is poorly understood, but it is generally thought to arise from inflammation within the innervated structures of the joint, such as the synovium, capsule and bone. We investigated the role of nerve growth factor (NGF) in pain development in murine OA, and the analgesic efficacy of the soluble NGF receptor, TrkAD5. OA was induced in mice by destabilisation of the medial meniscus and pain was assessed by measuring hind-limb weight distribution. RNA was extracted from joints, and NGF and TNF expressions were quantified. The effect of tumour necrosis factor (TNF) and neutrophil blockade on NGF expression and pain were also assessed. NGF was induced in the joints during both post-operative (day 3) and OA (16weeks) pain, but not in the non-painful stage of disease (8weeks post-surgery). TrkAd5 was highly effective at suppressing pain in both phases. Induction of NGF in the post-operative phase of pain was TNF-dependent as anti-TNF reduced NGF expression in the joint and abrogated pain. However, TNF was not regulated in the late OA joints, and pain was not affected by anti-TNF therapy. Fucoidan, by suppressing cellular infiltration into the joint, was able to suppress post-operative, but not late OA pain. These results indicate that NGF is an important mediator of OA pain and that TrkAd5 represents a potent novel analgesic in this condition. They also suggest that, unlike post-operative pain, induction of pain in OA may not necessarily be driven by classical inflammatory processes.

Antinociceptive activities of the methanol extract of the bulbs of Dioscorea bulbifera L. var sativa in mice is dependent of NO-cGMP-ATP-sensitive-K(+) channel activation

ETHNOPHARMACOLOGICAL RELEVANCE

Dioscorea bulbifera var sativa is a medicinal plant commonly used in Cameroonian traditional medicine to treat pain and inflammation.

AIM

The present work evaluated the effects of the methanol extract of the bulbs of Dioscorea bulbifera in inflammatory and neuropathic models of pain and further investigated its possible mechanism of action.

MATERIALS AND METHODS

The effects of Dioscorea bulbifera administered orally at the doses of 250 and 500mg/kg were tested in mechanical hypernociception induced by intraplantar (i.pl.) injection of complete Freund's adjuvant (CFA), lipopolysaccharides (LPS) or prostaglandin-E(2) (PGE(2)), as well as in partial ligation sciatic nerve (PLSN), nociception induced by capsaicin and thermal hyperalgesia induced by i.pl. injection of CFA. The therapeutic effects of Dioscorea bulbifera on PGE(2)-induced hyperalgesia were evaluated in the absence and in the presence of l-NAME, an inhibitor of nitric oxide synthase (NOS) and glibenclamide, an inhibitor of ATP-sensitive potassium channels.

RESULTS

The extract showed significant antinociceptive effects in persistent pain induced by CFA and on neuropathic pain induced by PLSN. The effects of Dioscorea bulbifera persisted for 5 days after two administrations in CFA-induced hypernociception. Dioscorea bulbifera significantly inhibited acute LPS-induced pain but failed to reduce thermal hypernociception and capsaicin-induced spontaneous nociception. The antinociceptive effects of this plant extract in PGE(2) model was antagonized by either l-NAME or glibenclamide.

CONCLUSION

Present demonstrate the antinociceptive activities of Dioscorea bulbifera both in inflammatory and neuropathic models of pain and these effects may result, at least partially, from its ability to activate the NO-cGMP-ATP-sensitive potassium channels pathway.

Protein synthesis dependent effects of kinins on astrocyte prostaglandin synthesis

It has been shown that kinins and their receptors are over expressed in the brain under pathophysiological conditions such as inflammation. However, little is known about the possible role of kinins, and especially bradykinin in brain inflammation. Although kinins are thought to have immediate effects, peptides may also exert longer and protein synthesis dependent actions. To evaluate this possibility, we assessed the regulation of prostaglandin E(2) synthesis after 15h bradykinin or Lys-des-Arg(9)-bradykinin (B(1) receptor agonist) treatment in rat neonatal astrocytes. Bradykinin, dose dependently stimulated basal and lipopolysaccharide-induced prostaglandin E(2) production, whereas exposure of astrocytes to the B(1) receptor agonist decreased both basal and lipopolysaccharide-induced prostaglandin E(2) release in a dose-dependent manner. These kinin effects on PGE(2) synthesis were completely abrogated by actinomycin-D and cycloheximide, suggesting de novo synthesis of proteins. Bradykinin also increased cyclooxygenase-2 protein levels about 2-fold, while the B(1) receptor agonist decreased cyclooxygenase-2 protein expression. There was no change in cyclooxygenase-1 protein levels after treatment with either of the kinins. Our data suggest a delayed feedback regulatory mechanism of kinins on astrocyte inflammation, whereby astrocyte prostaglandin synthesis is initially enhanced by bradykinin (B(2)) and eventually blocked by kinin breakdown product, acting on B(1) receptors. At least part of this presumed feedback loop could be mediated by de novo protein synthesis of cyclooxygenase-2.

Mode of action of cytokines on nociceptive neurons

Cytokines are pluripotent soluble proteins secreted by immune and glial cells and are key elements in the induction and maintenance of pain. They are categorized as pro-inflammatory cytokines, which are mostly algesic, and anti-inflammatory cytokines, which have analgesic properties. Progress has been made in understanding the mechanisms underlying the action of cytokines in pain. To date, several direct and indirect pathways are known that link cytokines with nociception or hyperalgesia. Cytokines may act via specific cytokine receptors inducing downstream signal transduction cascades, which then modulate the function of other receptors like the ionotropic glutamate receptor, the transient vanilloid receptors, or sodium channels. This receptor activation, either through amplification of the inflammatory reaction, or through direct modulation of ion channel currents, then results in pain sensation. Following up on results from animal experiments, cytokine profiles have recently been investigated in human pain states. An imbalance of pro- and anti-inflammatory cytokine expression may be of importance for individual pain susceptibility. Individual cytokine profiles may be of diagnostic importance in chronic pain states, and, in the future, might guide the choice of treatment.

Cytokine and chemokine regulation of sensory neuron function

Pain normally subserves a vital role in the survival of the organism, prompting the avoidance of situations associated with tissue damage. However, the sensation of pain can become dissociated from its normal physiological role. In conditions of neuropathic pain, spontaneous or hypersensitive pain behavior occurs in the absence of the appropriate stimuli. Our incomplete understanding of the mechanisms underlying chronic pain hypersensitivity accounts for the general ineffectiveness of currently available options for the treatment of chronic pain syndromes. Despite its complex pathophysiological nature, it is clear that neuropathic pain is associated with short- and long-term changes in the excitability of sensory neurons in the dorsal root ganglia (DRG) as well as their central connections. Recent evidence suggests that the upregulated expression of inflammatory cytokines in association with tissue damage or infection triggers the observed hyperexcitability of pain sensory neurons. The actions of inflammatory cytokines synthesized by DRG neurons and associated glial cells, as well as by astrocytes and microglia in the spinal cord, can produce changes in the excitability of nociceptive sensory neurons. These changes include rapid alterations in the properties of ion channels expressed by these neurons, as well as longer-term changes resulting from new gene transcription. In this chapter we review the diverse changes produced by inflammatory cytokines in the behavior of sensory neurons in the context of chronic pain syndromes.

Angiotensin-converting enzyme limits inflammation elicited by Trypanosoma cruzi cysteine proteases: a peripheral mechanism regulating adaptive immunity via the innate kinin pathway

Tissue injury by pathogens induces a stereotyped inflammatory response that alerts the innate immune system of the potential threat to host integrity. Here, we review knowledge emerging from investigations of the role of the kinin system in the mechanisms that link innate to the adaptive phase of immunity. Progress in this field started with results demonstrating that bradykinin is an endogenous danger signal that induces dendritic cell (DC) maturation via G protein-coupled bradykinin B2 receptors (B2R). The immunostimulatory role of kinins was recently confirmed in two different mouse models of Trypanosoma cruzi infection, a parasitic protozoan equipped with kinin-releasing cysteine proteases (cruzipain). Infection by the intraperitoneal route showed that DCs from B2R-/- mice (susceptible phenotype) failed to sense kinin 'danger' signals proteolytically released by parasites, explaining why these mutant mice display lower frequencies of interferon-gamma-producing effector T-cells. Studies of the dynamics of inflammation in the subcutaneous model of infection revealed that the balance between cruzipain and angiotensin-converting enzyme, respectively acting as kinin-generating and degrading enzymes, governs extent of DC maturation and TH1 development via the B2R-dependent innate pathway. Studies of the kinin role in immunity may shed light on the relationship between proteolytic networks and the cytokine circuits that guide T-cell development.

Kinin B2 receptor regulates chemokines CCL2 and CCL5 expression and modulates leukocyte recruitment and pathology in experimental autoimmune encephalomyelitis (EAE) in mice

Background

Kinins are important mediators of inflammation and act through stimulation of two receptor subtypes, B₁ and B₂. Leukocyte infiltration contributes to the pathogenesis of autoimmune inflammation in the central nervous system (CNS), occurring not only in multiple sclerosis (MS) but also in experimental autoimmune encephalomyelitis (EAE). We have previously shown that the chemokines CCL2 and CCL5 play an important role in the adhesion of leukocytes to the brain microcirculation in EAE. The aim of the present study was to evaluate the relevance of B₂ receptors to leukocyte-endothelium interactions in the cerebral microcirculation, and its participation in CNS inflammation in the experimental model of myelin-oligodendrocyte-glycoprotein (MOG)_35–55-induced EAE in mice.

Methods

In order to evaluate the role of B2 receptor in the cerebral microvasculature we used wild-type (WT) and kinin B2 receptor knockout (B₂^-/-) mice subjected to MOG_35–55-induced EAE. Intravital microscopy was used to investigate leukocyte recruitment on pial matter vessels in B₂^-/- and WT EAE mice. Histological documentation of inflammatory infiltrates in brain and spinal cords was correlated with intravital findings. The expression of CCL5 and CCL2 in cerebral tissue was assessed by ELISA.

Results

Clinical parameters of disease were reduced in B₂^-/- mice in comparison to wild type EAE mice. At day 14 after EAE induction, there was a significant decrease in the number of adherent leukocytes, a reduction of cerebral CCL5 and CCL2 expressions, and smaller inflammatory and degenerative changes in B₂^-/- mice when compared to WT.

Conclusion

Our results suggest that B₂ receptors have two major effects in the control of EAE severity: (i) B₂ regulates the expression of chemokines, including CCL2 and CCL5, and (ii) B₂ modulates leukocyte recruitment and inflammatory lesions in the CNS.

Role of IL-18 in overt pain-like behaviour in mice

There are evidences that targeting IL-18 might be beneficial to inhibit inflammatory symptoms, including hypernociception (decrease in nociceptive threshold). The mechanism of IL-18 mechanical hypernociception depends on endothelin in rats and mice. However, the role of IL-18 in overt pain-like behaviour remains undetermined. Therefore, we addressed the role of IL-18 in writhing response induced by intraperitoneal (i.p.) injection of phenyl-p-benzoquinone (PBQ) and acetic acid in mice. Firstly, it was detected that PBQ and acetic acid i.p. injection induced a dose-dependent number of writhes in Balb/c mice. Subsequently, it was observed that the PBQ - but not the acetic acid-induced writhes were diminished in IL-18 deficient ((-/-)) mice. Therefore, considering that IFN-gamma, endothelin and prostanoids mediate IL-18-induced mechanical hypernociception, we also investigated the role of these mediators in the same model of writhing response in which IL-18 participates. It was noticed that PBQ-induced writhes were diminished in IFN-gamma(-/-) mice and by the treatment with bosentan (mixed endothelin ETA/ETB receptor antagonist), BQ 123 (cyclo[DTrp-DAsp-Pro-DVal-Leu], selective endothelin ETA receptor antagonist), BQ 788 (N-cys-2,6 dimethylpiperidinocarbonyl-l-methylleucyl-d-1-methoxycarboyl-d-norleucine, selective endothelin ETB receptor antagonist) or indomethacin (cycloxigenase inhibitor). Thus, IL-18, IFN-gamma, endothelin acting on endothelin ETA and ETB receptors, and prostanoids mediate PBQ-induced writhing response in mice. To conclude, these results further advance the understanding of the physiopathology of overt pain-like behaviour, and suggest for the first time a role for IL-18 in writhing response in mice.

IL-33 mediates antigen-induced cutaneous and articular hypernociception in mice

IL-33, a new member of the IL-1 family, signals through its receptor ST2 and induces T helper 2 (Th2) cytokine synthesis and mediates inflammatory response. We have investigated the role of IL-33 in antigen-induced hypernociception. Recombinant IL-33 induced cutaneous and articular mechanical hypernociception in a time- and dose-dependent manner. The hypernociception was inhibited by soluble (s) ST2 (a decoy receptor of IL-33), IL-1 receptor antagonist (IL-1ra), bosentan [a dual endothelin (ET)(A)/ET(B) receptor antagonist], clazosentan (an ET(A) receptor antagonist), or indomethacin (a cyclooxygenase inhibitor). IL-33 induced hypernociception in IL-18(-/-) mice but not in TNFR1(-/-) or IFNgamma(-/-) mice. The IL-33-induced hypernociception was not affected by blocking IL-15 or sympathetic amines (guanethidine). Furthermore, methylated BSA (mBSA)-induced cutaneous and articular mechanical hypernociception depended on TNFR1 and IFNgamma and was blocked by sST2, IL-1ra, bosentan, clazosentan, and indomethacin. mBSA also induced significant IL-33 and ST2 mRNA expression. Importantly, we showed that mBSA induced hypernociception via the IL-33 --> TNFalpha --> IL-1beta --> IFNgamma --> ET-1 --> PGE(2) signaling cascade. These results therefore demonstrate that IL-33 is a key mediator of immune inflammatory hypernociception normally associated with a Th1 type of response, revealing a hitherto unrecognized function of IL-33 in a key immune pharmacological pathway that may be amenable to therapeutic intervention.