Mast Cell-deficient Mice Research Articles

IL‐33 induces skin inflammation with mast cell and neutrophil activation

Psoriasis is a common chronic autoimmune condition of the skin characterized by hyperplasia of epidermal keratinocytes associated with pro-inflammatory cytokines. IL-33 is a new member of the IL-1 superfamily that signals through the ST2 receptor and was originally defined as an inducer of T helper 2 (Th2) cytokines. Recently, broader immune activatory potential has been defined for IL-33 particularly via mast cell activation and neutrophil migration. Here, we show that ST2(-/-) mice exhibit reduced cutaneous inflammatory responses compared with WT mice in a phorbol ester-induced model of skin inflammation. Furthermore, injections of IL-33 into the ears of mice induce an inflammatory skin lesion. This inflammatory response was partially dependent on mast cells as mast cell-deficient mice (Kit(W-sh/W-sh) ) showed delayed responses to IL-33. IL-33 also recruited neutrophils to the ear, an effect mediated in part by increased production of the chemokine KC (CXCL1). Finally, we show that IL-33 expression is up-regulated in the epidermis of clinical psoriatic lesions, compared with healthy skin. These results therefore demonstrate that IL-33 may play a role in psoriasis-like plaque inflammation. IL-33 targeting may provide a new treatment strategy for psoriasis.

Genetic Variation Determines Mast Cell Functions in Experimental Asthma

Mast cell-deficient mice are a key for investigating the function of mast cells in health and disease. Allergic airway disease induced as a Th2-type immune response in mice is employed as a model to unravel the mechanisms underlying inception and progression of human allergic asthma. Previous work done in mast cell-deficient mouse strains that otherwise typically mount Th1-dominated immune responses revealed contradictory results as to whether mast cells contribute to the development of airway hyperresponsiveness and airway inflammation. However, a major contribution of mast cells was shown using adjuvant-free protocols to achieve sensitization. The identification of a traceable genetic polymorphism closely linked to the Kit(W-sh) allele allowed us to generate congenic mast cell-deficient mice on a Th2-prone BALB/c background, termed C.B6-Kit(W-sh). In accordance with the expectations, C.B6-Kit(W-sh) mice do not develop IgE- and mast cell-dependent passive cutaneous anaphylaxis. Yet, unexpectedly, C.B6-Kit(W-sh) mice develop full-blown airway inflammation, airway hyperresponsiveness, and mucus production despite the absence of mast cells. Thus, our findings demonstrate a major influence of genetic background on the contribution of mast cells in an important disease model and introduce a novel strain of mast cell-deficient mice.

Interdicting protease-activated receptor-2-driven inflammation with cell-penetrating pepducins

Protease-activated receptor-2 (PAR2), a cell surface receptor for trypsin-like proteases, plays a key role in a number of acute and chronic inflammatory diseases of the joints, lungs, brain, gastrointestinal tract, and vascular systems. Despite considerable effort by the pharmaceutical industry, PAR2 has proven recalcitrant to targeting by small molecule inhibitors, which have been unable to effectively prevent the interaction of the protease-generated tethered ligand with the body of the receptor. Here, we report the development of first-in-class cell-penetrating lipopeptide "pepducin" antagonists of PAR2. The design of the third intracellular (i3) loop pepducins were based on a structural model of a PAR2 dimer and by mutating key pharmacophores in the receptor intracellular loops and analogous pepducins. Individual pharmacophores were identified, which controlled constitutive, agonist, and antagonist activities. This approach culminated in the identification of the P2pal-18S pepducin which completely suppressed trypsin and mast cell tryptase signaling through PAR2 in neutrophils and colon cancer cells. The PAR2 pepducin was highly efficacious in blocking PAR2-dependent inflammatory responses in mouse models. These effects were lost in PAR2-deficient and mast-cell-deficient mice, thereby validating the specificity of the pepducin in vivo. These data provide proof of concept that PAR2 pepducin antagonists may afford effective treatments of potentially debilitating inflammatory diseases and serve as a blueprint for developing highly potent and specific i3-loop-based pepducins for other G protein-coupled receptors (GPCRs).

Abstract 469: Mast cell inhibition by the BTK inhibitor PCI-32765 as a potential therapy in pancreatic cancer

Abstract A strong association between inflammation and cancer has long been recognized but the cause and effect relationship linking the two remains unclear. We previously showed that Myc, a pleiotropic transcription factor that is over-expressed in many human cancers, when expressed in a β cell tumor model, triggers rapid recruitment of mast cells to the tumor site, a recruitment that is absolutely required for macroscopic tumor expansion. Indeed, such tumors did not grow in mast cell deficient mice. Furthermore, treatment of established β cell tumors with cromolyn, a stabilizer that prevents mast cell degranulation, rapidly triggered hypoxia and cell death of tumor and endothelial cells. Our results suggested that inhibitors of mast cell function may prove therapeutically useful in restraining expansion and promoting regression of insulinomas and possibly other pancreatic cancers. However, such compounds have not yet been developed for systemic administration and applications in cancer therapy. In fact, there are no clinically effective systemic mast-cell blockers. Therefore, we tested PCI-32765 (Pharmacyclics, Inc.), a Bruton tyrosine kinase (BTK) inhibitor in clinical trials for treatment of B cell non-Hodgkin lymphoma, for its ability to inhibit mast cell function and tumorigenesis in our mouse model of β cell neoplasia and in a well characterized LSLKRasG12D model of pancreatic adenocarcinoma (PDAC). Here we compare and contrast the effects of long term treatment with PCI-32765 on mast cell degranulation, tumor growth and vasculature in both mouse models, establishing for the first time the therapeutic potential of mast cell inhibition by PCI-32765 in the treatment of insulinomas and other pancreatic cancers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 469. doi:10.1158/1538-7445.AM2011-469

Mast cell-deficient mice show attenuated thermal pain responses (163.18)

Abstract Pain is a cardinal component of inflammation and a significant public health issue. Inflammatory cytokines such as TNF-alpha, IL-1beta, CXCL1/IL-8, as well as neutrophil influx have been implicated in the potentiation of peripheral inflammatory pain in models of thermal and mechanical hindpaw hypernociception in rodents.. Degranulation of mast cells has been shown to be important for phosphorylation of Erk in nociceptive neurons in a rat model of migraine-like stimulation. Mechanical bladder pain in a model of interstitial cystitis was abrogated in mast cell deficient mice. We show that degranulation of plantar mast cells caused by direct secretagogue treatment or passive antibody sensitization and challenge, causes reduction in paw withdrawal latencies as well as significant edema, neutrophil influx, and upregulation of local TNF-alpha and IL-1beta levels, as well as histamine release in the hindpaws of mice in a model of thermal pain. Mast cell-deficient C57BL/6 Wsh/Wsh mice show no edema, histamine release or pain response indicated by reduction in paw withdrawal latencies. This suggests that while pain is a complex and multifactorial physiology, tissue sentinel mast cells may be a critical initiator of inflammatory pain in both protective and allergic/pathological contexts.

Regulatory T cells enhance mast cell production of IL6 via a TGFβ dependent innate mechanism (168.20)

Abstract Recently, Tregs have been proposed to limit mast cell degranulation upon antigen stimulation. However, mast cells also produce many cytokines that regulate both innate and adaptive immunity. Here we show that Tregs inhibit mast cell (BMMC) degranulation but, surprisingly, promotes IL6 in response to innate (LPS or PGN) and adaptive (IgE) activation. This required cell-cell contact and did not require activation via the TCR. Blockade of OX40/OX40L pathway inhibited the Treg effects on BMMC degranulation but had no effect on IL6 production. Conversely, blockade of surface bound-TGFβ ablated IL6 production, suggesting that Tregs influence mast cell responses via distinct mechanisms. Furthermore, TGFβ was sufficient to promote enhanced IL6 but had no effect on degranulation. In innate immunity, IL6 and Tregs have been suggested to influence neutrophil clearance and resolution of inflammation. In an LPS-driven model of lung injury, Treg depletion elevated lung neutrophilia in response to LPS. Similarly, mast cell deficient mice displayed significantly elevated neutrophilia in the lung that was fully corrected upon reconstitution with wildtype mast cells but not by IL6 deficient mast cells, suggesting a critical role for mast cell derived IL-6 in neutrophil clearance during innate inflammation. Our data suggests that Tregs are important in limiting the severity of the inflammatory response during innate activation and that they may do so by promoting mast cell production of IL-6.

Mast cells induce a novel pro-inflammatory function of myeloid-derived suppressor cells (151.2)

Abstract Mast cells and myeloid-derived suppressor cells (MDSC) are both increased at sites of growing tumors. Like mast cells, MDSC have recently been suggested to function in parasitic or bacterial infection. We have tested the effects of mast cell-MDSC interactions in vitro and in a mouse model of parasitic infection. Surprisingly, co-culture of these cells resulted in a drastic increase in pro-inflammatory mediator release, which was attributed entirely to MDSC. MDSC depletion from mice infected with Nippostrongylus brasiliensis resulted in delayed worm expulsion and a drastically increased intestinal worm burden reminiscent of mast cell-deficient mice. Mast cells can therefore reprogram MDSC to a pro-inflammatory phenotype, suggesting that the evolutionary purpose of these suppressive cells may be to potentiate inflammatory Th2 responses necessary for parasite expulsion.

CB1 receptors mediate rimonabant-induced pruritic responses in mice: investigation of locus of action

Cannabinoids have recently been identified as potential neuronal modulators of pruritic response, representing a potential target in the treatment of itch associated with a variety of pathophysiologic conditions. While the selective CB(1) receptor antagonist rimonabant is an established pruritic agent in both animal and clinical testing, its receptor mechanism of action and anatomical loci remain unclear. The purpose of this study was to determine whether CB(1) receptor blockade is critical to rimonabant-induced scratching and to identify differences in scratching response based on different routes of administration. Furthermore, experiments were designed to elucidate any evidence as to whether rimonabant elicits scratching behavior through common immunologic hypersensitivity mechanisms. Rimonabant was equally effective at producing scratching via intraperitoneal and local subcutaneous injection. This compound also produced an intense scratching response when administered intrathecally, but had no effects after intracerebroventricular administration. Repeated administration of rimonabant led to a decreased magnitude of scratching. While rimonabant-induced scratching was not attenuated either by pretreatment with the H(1) receptor antagonist loratadine or in mast cell-deficient mice, it lacked efficacy in CB(1) (-/-) mice. Rimonabant is a potent and fully effective pruritogen when administered spinally or systemically and requires CB(1) receptors to induce scratching, suggesting an important spinal CB(1) receptor component of action. The lack of responsiveness to H(1) antagonism or mast cell deficiency supports previous findings that cannabinoids modulate itch through neuronal mechanisms, and not by traditional hypersensitivity activation.

Cutting Edge: The Murine High-Affinity IgG Receptor FcγRIV Is Sufficient for Autoantibody-Induced Arthritis

K/BxN serum-induced passive arthritis was reported to depend on the activation of mast cells, triggered by the activating IgG receptor FcγRIIIA, when engaged by IgG1 autoantibodies present in K/BxN serum. This view is challenged by the fact that FcγRIIIA-deficient mice still develop K/BxN arthritis and because FcγRIIIA is the only activating IgG receptor expressed by mast cells. We investigated the contribution of IgG receptors, IgG subclasses, and cells in K/BxN arthritis. We found that the activating IgG2 receptor FcγRIV, expressed only by monocytes/macrophages and neutrophils, was sufficient to induce disease. K/BxN arthritis occurred not only in mast cell-deficient W(sh) mice, but also in mice whose mast cells express no activating IgG receptors. We propose that at least two autoantibody isotypes, IgG1 and IgG2, and two activating IgG receptors, FcγRIIIA and FcγRIV, contribute to K/BxN arthritis, which requires at least two cell types other than mast cells, monocytes/macrophages, and neutrophils.

Mast Cells Increase Vascular Permeability by Heparin-Initiated Bradykinin Formation In Vivo

Activated mast cells trigger edema in allergic and inflammatory disease. We report a paracrine mechanism by which mast cell-released heparin increases vascular permeability invivo. Heparin activated the protease factor XII, which initiates bradykinin formation in plasma. Targeting factor XII or kinin B2 receptors abolished heparin-triggered leukocyte-endothelium adhesion and interfered with a mast cell-driven drop in blood pressure in rodents. Intravital laser scanning microscopy and tracer measurements showed heparin-driven fluid extravasation in mouse skin microvessels. Ablation of factor XII or kinin B2 receptors abolished heparin-induced skin edema and protected mice from allergen-activated mast cell-driven leakage. In contrast, heparin and activated mast cells induced excessive edema in mice deficient in the major inhibitor of factor XII, C1 esterase inhibitor. Allergen exposure triggered edema attacks in hereditary angioedema patients, lacking C1 esterase inhibitor. The data indicate that heparin-initiated bradykinin formation plays a fundamental role in mast cell-mediated diseases.

Mast Cells Are an Essential Component of Human Radiation Proctitis and Contribute to Experimental Colorectal Damage in Mice

Radiation proctitis is characterized by mucosal inflammation followed by adverse chronic tissue remodeling and is associated with substantial morbidity and mortality. Mast cell hyperplasia has been associated with diseases characterized by pathological tissue remodeling and fibrosis. Rectal tissue from patients treated with radiotherapy shows mast cell hyperplasia and activation, suggesting that these cells play a role in the development of radiation-induced sequelae. To investigate the role of mast cells in radiation damage, experimental radiation proctitis was induced in a mast cell-deficient (W(sh)/W(sh)) mouse model. The colon and rectum of W(sh)/W(sh) and wild-type mice were exposed to 27-Gy single-dose irradiation and studied after 2 and 14 weeks. Irradiated rodent rectum showed mast cell hyperplasia. W(sh)/W(sh) mice developed less acute and chronic rectal radiation damage than their control littermates. Tissue protection was associated with increased tissue neutrophil influx and expression of several inflammatory mediators immediately after radiation exposure. It was further demonstrated that mast cell chymase, tryptase, and histamine could change human muscularis propria smooth muscle cells into a migrating/proliferating and proinflammatory phenotype. These data show that mast cells have deleterious effects on both acute and chronic radiation proctitis, possibly by limiting acute tissue neutrophil influx and by favoring phenotypic orientation of smooth muscle cells, thus making them active participants in the radiation-induced inflammatory process and dystrophy of the rectal wall.

Mast Cell-Derived IL-10 Suppresses Germinal Center Formation by Affecting T Follicular Helper Cell Function

The most prevalent cancer diagnosed in the world is sunlight-induced skin cancer. In addition to being a complete carcinogen, UV radiation, the causative agent of skin cancer, induces immune suppression. Because UV-induced immune suppression is a well-recognized risk factor for skin cancer induction, it is crucial to understand the mechanisms underlying UV-induced immune suppression. Mast cells, which have recently emerged as immune regulatory cells, are particularly important in UV-induced immune suppression. UV exposure does not induce immune suppression in mast cell-deficient mice. We report that UV irradiation blocks germinal center (GC) formation, Ab secretion, and T follicular helper (Tfh) cell function, in part by altering the expression of transcription factors BCL-6 and BLIMP-1. No suppression of GC formation, Tfh cell IL-21 expression, or Ab secretion was observed in UV-irradiated mast cell-deficient (Kit(W-sh/W-sh)) mice. When mast cell-deficient mice were reconstituted with wild type mast cells, immune suppression was restored. Reconstituting the mast cell-deficient mice with bone marrow-derived mast cells from IL-10-deficient mice failed to restore the ability of UV radiation to suppress GC formation. Our findings demonstrate a function for mast cells, suppression of Tfh cell production, GC formation, and Ab production in vivo.

Tissue Eosinophilia in a Mouse Model of Colitis Is Highly Dependent on TLR2 and Independent of Mast Cells

The mechanisms initiating eosinophil influx into sites of inflammation have been well studied in allergic disease but are poorly understood in other settings. This study examined the roles of TLR2 and mast cells in eosinophil accumulation during a nonallergic model of eosinophilia-associated colitis. TLR2-deficient mice (TLR2(-/-)) developed a more severe colitis than wild-type mice in the dextran sodium sulfate (DSS) model. However, they had significantly fewer eosinophils in the submucosa of the cecum (P < 0.01) and mid-colon (P < 0.01) than did wild-type mice after DSS treatment. Decreased eosinophilia in TLR2(-/-) mice was associated with lower levels of cecal CCL11 (P < 0.01). Peritoneal eosinophils did not express TLR2 protein, but TLR2 ligand injection into the peritoneal cavity induced local eosinophil recruitment, indicating that TLR2 activation of other cell types can mediate eosinophil recruitment. After DSS treatment, mast cell-deficient (Kit(W-sh/W-sh)) mice had similar levels of intestinal tissue eosinophilia were observed as those in wild-type mice. However, mast cell-deficient mice were partially protected from DSS-induced weight loss, an effect that was reversed by mast cell reconstitution. Overall, this study indicates a critical role for indirect TLR2-dependent pathways, but not mast cells, in the generation of eosinophilia in the large intestine during experimental colitis and has important implications for the regulation of eosinophils at mucosal inflammatory sites.

Morphine decreases early peritoneal innate immunity responses in Swiss–Webster and C57BL6/J mice through the inhibition of mast cell TNF-α release

ObjectiveTo characterize immunosuppressive effects of morphine on the early innate immunity response of cytokine production in peritoneal cavity after LPS challenge. MethodsThe effects of a single i.p. administration of morphine (3.1 or 31mg/kg) on LPS-induced tumor necrosis factor α (TNF-α) and monocyte chemoattractant protein-1 (CCL2) intraperitoneal release was tested in Swiss–Webster, C57BL/6J, mast cell deficient KitWsh/Wsh (W-sh) and mast cell reconstituted (W-sh-rec) mice. ResultsMorphine was found to inhibit LPS-induced TNF-α but not CCL2 release in the peritoneal cavity. Studies on mast cell deficient and reconstituted mice indicate that resident mast cells mediate selective morphine immunosuppression in the peritoneal cavity.

Mast cells contribute to altered vascular reactivity and ischemia-reperfusion injury following cerium oxide nanoparticle instillation

Cerium oxide (CeO2) represents an important nanomaterial with wide ranging applications. However, little is known regarding how CeO2 exposure may influence pulmonary or systemic inflammation. Furthermore, how mast cells would influence inflammatory responses to a nanoparticle exposure is unknown. We thus compared pulmonary and cardiovascular responses between C57BL/6 and B6.Cg-KitW-sh mast cell deficient mice following CeO2 nanoparticle instillation. C57BL/6 mice instilled with CeO2 exhibited mild pulmonary inflammation. However, B6.Cg-KitW-sh mice did not display a similar degree of inflammation following CeO2 instillation. Moreover, C57BL/6 mice instilled with CeO2 exhibited altered aortic vascular responses to adenosine and an increase in myocardial ischemia/reperfusion injury which was absent in B6.Cg-KitW-sh mice. In vitro CeO2 exposure resulted in increased production of PGD2, TNF-α, IL-6 and osteopontin by cultured mast cells. These findings demonstrate that CeO2 nanoparticles activate mast cells contributing to pulmonary inflammation, impairment of vascular relaxation and exacerbation of myocardial ischemia/reperfusion injury.

Mast cells protect against airway Mycoplasma pneumoniae under allergic conditions

Infection with Mycoplasma pneumoniae (Mp) in asthma can occur both acutely and chronically with an associated Th2 inflammatory response and/or increased numbers of bronchial mast cells. Mast cells have previously been shown to promote mycoplasma clearance in mice; however, it is unknown whether mast cells would aid Mp clearance under allergic conditions. Our aim was to determine the impact of allergic inflammation on mast cell-mediated lung Mp clearance. Furthermore, as we have previously demonstrated an essential role for IL-6 in lung Mp clearance we also investigated the role of mast cell-derived IL-6. Mast cell-deficient (WBB6F1/J-Kit(W)/Kit(W-v)) mice were challenged with ovalbumin to induce airway inflammation before Mp infection. The role of mast cell-derived IL-6 in bacterial clearance was further investigated by reconstitution of mast cell-deficient mice with IL-6(-/-) mast cells. Allergic mast cell-deficient mice exhibited increased lung Mp burden compared with control littermates. Intravenous adoptive transfer of wild-type and IL-6(-/-) mast cells significantly improved Mp clearance in mast cell-deficient mice. Acutely after Mp infection, allergen-challenged mast cell-deficient mice had increased levels of the pro-inflammatory cytokines IL-6 and TNF-alpha in the bronchoalveolar lavage (BAL) fluid. The total number of neutrophils was also increased in mast cell-deficient mice. Our results establish that mast cells aid host defense against Mp in an allergic setting and that while IL-6 is necessary for lung Mp clearance, mast cell-derived IL-6 is not required.

IL-33 Is Produced by Mast Cells and Regulates IgE-Dependent Inflammation

BackgroundIL-33 is a recently characterized IL-1 family cytokine and found to be expressed in inflammatory diseases, including severe asthma and inflammatory bowl disease. Recombinant IL-33 has been shown to enhance Th2-associated immune responses and potently increase mast cell proliferation and cytokine production. While IL-33 is constitutively expressed in endothelial and epithelial cells, where it may function as a transcriptional regulator, cellular sources of IL-33 and its role in inflammation remain unclear.Methodology/Principal FindingsHere, we identify mast cells as IL-33 producing cells. IgE/antigen activation of bone marrow-derived mast cells or a murine mast cell line (MC/9) significantly enhanced IL-33. Conversely, recombinant IL-33 directly activated mast cells to produce several cytokines including IL-4, IL-5 and IL-6 but not IL-33. We show that expression of IL-33 in response to IgE-activation required calcium and that ionomycin was sufficient to induce IL-33. In vivo, peritoneal mast cells expressed IL-33 and IL-33 levels were significantly lower within the skin of mast cell deficient mice, compared to littermate controls. Local activation of mast cells promotes edema, followed by the recruitment of inflammatory cells. We demonstrate using passive cutaneous anaphylaxis, a mast cell-dependent model, that deficiency in ST2 or antibody blockage of ST2 or IL-33 ablated the late phase inflammatory response but that the immediate phase response was unaffected. IL-33 levels in the skin were significantly elevated only during the late phase.Conclusions/SignificanceOur findings demonstrate that mast cells produce IL-33 after IgE-mediated activation and that the IL-33/ST2 pathway is critical for the progression of IgE-dependent inflammation.

Lipopolysaccharide-Mediated Mast Cell Activation Induces IFN-γ Secretion by NK Cells

Mast cells (MCs) that are well known for their important effector function in IgE-associated immune responses play a key role in innate immune defenses. In this study, we investigate the interaction between MCs and NK cells in vitro and in vivo. We show that mouse bone marrow-derived cultured MCs activated with LPS, polyinosinic-polycytidylic acid, or CpG can stimulate NK cells to secrete increasing concentrations of IFN-gamma. MCs induce a 20-fold increase in IFN-gamma release from NK cells after LPS stimulation. This enhancement of IFN-gamma secretion is cell contact dependent and TNF-alpha independent. Furthermore, we show that this interaction is in part mediated by OX40 ligand on MCs. NK cell-mediated cytotoxicity was not affected by the presence of MCs. Intracellular IFN-gamma levels in splenic NK cells are significantly decreased after i.p. injection of LPS in mast cell-deficient (C57BL/6 Kit(wsh/wsh)) mice in comparison with wild-type mice. In conclusion, our data show for the first time a direct mast cell-dependent NK cell activation. This interaction might play an important role in innate immune defense, as it is dependent on the presence of stimulators relevant in innate immune responses.

Does IgE-mediated mast cell activation reduce oral tolerance to food antigens?

Mast cell activation in response to food allergens can result in symptoms such as anaphylaxis. It is unclear how this activation impacts on the immune response to other foods that are present. The objective of this study was to investigate the role of immunoglobulin E (IgE)-mediated mast cell activation in the regulation of oral tolerance to a food antigen using a mouse model. Oral tolerance to common food allergens – egg protein (OVA) or peanut - was established in C57Bl/6 mice. Mice were then immunized and challenged with the relevant food antigen. One group had mast cells activated via IgE/antigen at the site of immunization to food antigen. Antibody responses to food antigen were compared between groups. This was repeated with OVA in mast cell-deficient (kitw-sh/w-sh) mice. Oral tolerance was successfully induced by OVA-feeding as assessed by specific IgE, IgA, IgG1, and IgG2a antibody responses. Tolerance was not maintained in the IgG1 and IgG2a subclasses when mast cells were activated at the site of immunization in OVA-fed animals. OVA-feeding also induced tolerance in mast cell-deficient animals, but IgE/antigen treatment did not modulate OVA-specific antibody production. Feeding peanut butter reduced the anti-peanut IgE response to peanut immunization, but this tolerance was not maintained if mast cells were activated at the site of immunization in peanut-fed animals. These findings suggest that mast cell activation may reduce the effective tolerance to food antigens. This research highlights a possible role for mast cell activation in the development of multiple food allergies that could aid in the design of novel preventative strategies. This work was supported by AllerGen NCE Inc. and by the Natural Sciences and Engineering Research Council.

Abstract 3849: Mast cell inhibition by Btk inhibitor PCI-32765 as a potential cancer therapy

Abstract An association between inflammation and cancer has long been recognized but the cause and effect relationship linking the two remains unclear. Myc is a pleiotropic transcription factor that is over-expressed in many human cancers and instructs multiple extracellular aspects of the tumor tissue phenotype, including remodeling of tumor stroma and angiogenesis. We have shown in a β cell tumor model that Myc activation in vivo triggers rapid recruitment of mast cells to the tumor site, a recruitment that is absolutely required for macroscopic tumor expansion. Indeed, such tumors did not grow in mast cell deficient mice. Furthermore, treatment of established β cell tumors with cromolyn, a stabilizer that prevents mast cell degranulation, rapidly triggered hypoxia and cell death of tumor and endothelial cells. Inhibitors of mast cell function may therefore prove therapeutically useful in restraining expansion and survival of pancreatic cancer. However, such compounds have not yet been developed for systemic administration and applications in cancer therapy. In fact, there are no clinically effective mast-cell blockers. Therefore, we tested PCI-32765 (Pharmacyclics, Inc.), a Bruton's tyrosine kinase (BTK) inhibitor in clinical trials for B cell non-Hodgkin's lymphoma, for its ability to inhibit mast cell function and tumorigenesis in our mouse model of β cell neoplasia. Here we show that long term treatment with PCI-32765 prevents mast cell degranulation and causes tumor regression and vasculature collapse. Surprisingly, the compound also displays an unexpected anti-proliferative effect on tumor cells - but not surrounding normal tissue - which is still under investigation. Our results once more support the idea that mast cell inhibition could be beneficial in the treatment of insulinomas and possibly other pancreatic cancers and suggests that PCI-32765 could open the way to clinical studies assessing this potential. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3849.