Induction of Interleukin-9-Producing Mucosal Mast Cells Promotes Susceptibility to IgE-Mediated Experimental Food Allergy.

Experimental IgE-mediated food allergy depends on intestinal anaphylaxis driven by interleukin-9 (IL-9). However, the primary cellular source of IL-9 and the mechanisms underlying the susceptibility to food-induced intestinal anaphylaxis remain unclear. Herein, we have reported the identification of multifunctional IL-9-producing mucosal mast cells (MMC9s) that can secrete prodigious amounts of IL-9 and IL-13 in response to IL-33, and mast cell protease-1 (MCPt-1) in response to antigen and IgE complex crosslinking, respectively. Repeated intragastric antigen challenge induced MMC9 development that required T cells, IL-4, and STAT6 transcription factor, but not IL-9 signals. Mice ablated of MMC9 induction failed to develop intestinal mastocytosis, which resulted in decreased food allergy symptoms that could be restored by adoptively transferred MMC9s. Finally, atopic patients that developed food allergy displayed increased intestinal expression of Il9- and MC-specific transcripts. Thus, the induction of MMC9s is a pivotal step to acquire the susceptibility to IgE-mediated food allergy.

A novel mast cell-dependent allergic peritonitis model.

Typical murine models of allergic inflammation are induced by the combination of ovalbumin and aluminum hydroxide. However, accumulating evidence indicates that, in models of asthma and atopic dermatitis, allergic inflammation can be generated in the absence of aluminum hydroxide. Moreover, co-administration of Staphylococcus aureus enterotoxin B with ovalbumin can enhance inflammation. The objective of this study was to establish a rapid and mast cell-dependent murine model of allergic inflammation by inducing allergic peritonitis using ovalbumin and S. aureus enterotoxin B. Allergic peritonitis was induced in C57BL/6 mice by subcutaneous sensitization and intraperitoneal challenge with ovalbumin and S. aureus enterotoxin B. Disease characteristics were assessed by flow cytometry, enzyme-linked immunosorbent assay (ELISA), trypan blue exclusion and colorimetric assays. The time-course of the allergic peritonitis revealed a peak of peritoneal inflammation 48 h after challenge, as assessed by total cells and eosinophil counts. The decrease of cell numbers started 96 h post-challenge, with complete clearance within 168 h. Moreover, significantly higher levels of tryptase and increased vascular permeability were found 30 min following challenge. Allergic inflammation induction by ovalbumin and S. aureus enterotoxin B was impaired in mast cell-deficient mice and partially restored by mice reconstitution with bone marrow-derived mast cells, indicating the mast cell role in this model. We present a novel model of allergic peritonitis that is mast cell-dependent, simple and robust. Moreover, the use of S. aureus enterotoxin B better resembles human allergic inflammation, which is known to be characterized by the colonization of S. aureus.

Mast Cells Granular Contents Are Crucial for Deep Vein Thrombosis in Mice.

RATIONALE: Deep vein thrombosis (DVT) and its complication pulmonary embolism have high morbidity reducing quality of life and leading to death. Cellular mechanisms of DVT initiation remain poorly understood. OBJECTIVE: We sought to determine the role of mast cells (MCs) in DVT initiation and validate MCs as a potential target for DVT prevention. METHODS AND RESULTS: In a mouse model, DVT was induced by partial ligation (stenosis) of the inferior vena cava. We demonstrated that 2 strains of mice deficient for MCs were completely protected from DVT. Adoptive transfer of in vitro differentiated MCs restored thrombosis. MCs were present in the venous wall, and the number of granule-containing MCs decreased with thrombosis. Pharmacological depletion of MCs granules or prevention of MC degranulation also reduced DVT. Basal plasma levels of von Willebrand factor and recruitment of platelets to the inferior vena cava wall after DVT induction were reduced in MC-deficient mice. Stenosis application increased plasma levels of soluble P-selectin in wild-type but not in MC-deficient mice. MC releasate elevated ICAM-1 (intercellular adhesion molecule-1) expression on HUVEC (human umbilical vein endothelial cells) in vitro. Topical application of compound 48/80, an MC secretagogue, or histamine, a Weibel-Palade body secretagogue from MCs, potentiated DVT in wild-type mice, and histamine restored thrombosis in MC-deficient animals. CONCLUSIONS: MCs exacerbate DVT likely through endothelial activation and Weibel-Palade body release, which is, at least in part, mediated by histamine. Because MCs do not directly contribute to normal hemostasis, they can be considered potential targets for prevention of DVT in humans.

Bile duct ligation-induced biliary hyperplasia, hepatic injury, and fibrosis are reduced in mast cell-deficient KitW-sh mice.

Activated mast cells (MCs) release histamine (HA) and MCs infiltrate the liver following bile duct ligation (BDL), increasing intrahepatic bile duct mass (IBDM) and fibrosis. We evaluated the effects of BDL in MC-deficient (KitW-sh ) mice. Wild-type (WT) and KitW-sh mice were subjected to sham or BDL for up to 7 days and KitW-sh mice were injected with cultured mast cells or 1× phosphate-buffered saline (PBS) before collecting serum, liver, and cholangiocytes. Liver damage was assessed by hematoxylin and eosin and alanine aminotransferase levels. IBDM was detected by cytokeratin-19 expression and proliferation by Ki-67 immunohistochemistry (IHC). Fibrosis was detected by IHC, hydroxyproline content, and by qPCR for fibrotic markers. Hepatic stellate cell (HSC) activation and transforming growth factor-beta 1 (TGF-ß1) expression/secretion were evaluated. Histidine decarboxylase (HDC) and histamine receptor (HR) expression were detected by qPCR and HA secretion by enzymatic immunoassay. To evaluate vascular cells, von Willebrand factor (vWF) and vascular endothelial growth factor (VEGF)-C expression were measured. In vitro, cultured HSCs were stimulated with cholangiocyte supernatants and alpha-smooth muscle actin levels were measured. BDL-induced liver damage was reduced in BDL KitW-sh mice, whereas injection of MCs did not mimic BDL-induced damage. In BDL KitW-sh mice, IBDM, proliferation, HSC activation/fibrosis, and TGF-ß1 expression/secretion were decreased. The HDC/HA/HR axis was ablated in sham and BDL KitW-sh mice. vWF and VEGF-C expression decreased in BDL KitW-sh mice. In KitW-sh mice injected with MCs, IBDM, proliferation, fibrosis, and vascular cell activation increased. Stimulation with cholangiocyte supernatants from BDL WT or KitW-sh mice injected with MCs increased HSC activation, which decreased with supernatants from BDL KitW-sh mice. CONCLUSION: MCs promote hyperplasia, fibrosis, and vascular cell activation. Knockout of MCs decreases BDL-induced damage. Modulation of MCs may be important in developing therapeutics for cholangiopathies. (Hepatology 2017;65:1991-2004).

Long-term survival of the mouse ES cell-derived mast cell, MEDMC-BRC6, in mast cell-deficient KitW-sh/W-sh mice.

Mast cells (MCs) play pivotal roles in allergic reactions and the host defense against microbial infection through the IgE-dependent and IgE-independent signaling pathways. MC lines that can be analyzed both in vitro and in vivo would be useful for the study of MC-dependent immune responses. Here, we investigated the functional characteristics of a mouse embryonic stem cell-derived MC-like cell line, MEDMC-BRC6. The cell line expressed FcεRI and c-Kit and showed degranulation and production of inflammatory cytokines and chemokines, including TNF-α, IL-6 and MCP-1, upon cross-linking FcεRI with IgE. These cytokines and chemokines were also produced by the cell line by stimulation of TLR2 and TLR4. MEDMC-BRC6 survived in the peritoneal cavity and the ear skin for at least 6 months after the transfer into genetically compatible MC-deficient KitW-sh/W-sh mice, in which systemic anaphylaxis was successfully induced. Thus, MEDMC-BRC6 cells represent a potent tool for investigating the functions of MCs in vitro and in vivo.

Pathways of immediate hypothermia and leukocyte infiltration in an adjuvant-free mouse model of anaphylaxis.

BACKGROUND: Conflicting results have been obtained regarding the roles of Fc receptors and effector cells in models of active systemic anaphylaxis (ASA). In part, this might reflect the choice of adjuvant used during sensitization because various adjuvants might differentially influence the production of particular antibody isotypes. OBJECTIVE: We developed an "adjuvant-free" mouse model of ASA and assessed the contributions of components of the "classical" and "alternative" pathways in this model. METHODS: Mice were sensitized intraperitoneally with ovalbumin at weekly intervals for 6 weeks and challenged intraperitoneally with ovalbumin 2 weeks later. RESULTS: Wild-type animals had immediate hypothermia and late-phase intraperitoneal inflammation in this model. These features were reduced in mice lacking the IgE receptor FcεRI, the IgG receptor FcγRIII or the common γ-chain FcRγ. FcγRIV blockade resulted in a partial reduction of inflammation without any effect on hypothermia. Depletion of monocytes/macrophages with clodronate liposomes significantly reduced the hypothermia response. By contrast, depletion of neutrophils or basophils had no significant effects in this ASA model. Both the hypothermia and inflammation were dependent on platelet-activating factor and histamine and were reduced in 2 types of mast cell (MC)-deficient mice. Finally, engraftment of MC-deficient mice with bone marrow-derived cultured MCs significantly exacerbated the hypothermia response and restored inflammation to levels similar to those observed in wild-type mice. CONCLUSION: Components of the classical and alternative pathways contribute to anaphylaxis in this adjuvant-free model, with key roles for MCs and monocytes/macrophages.

Mast cells contribute to bleomycin-induced lung inflammation and injury in mice through a chymase/mast cell protease 4-dependent mechanism.

Mast cells (MCs) are found in large numbers in lungs of patients with pulmonary fibrosis. However, the functions of MCs in lung fibrosis remain largely unknown. We assessed the role of MCs and MC protease 4 (MCPT4), the mouse counterpart of human MC chymase, in a mouse model of bleomycin (BLM)-induced lung injury. We found that levels of inflammation in the bronchoalveolar lavage and the lung, as well as levels of lung fibrosis, were reduced 7 d after intranasal delivery of BLM MC-deficient Kit(W-sh/W-sh) mice compared with wild-type (WT) mice. Confirming the implication of MCs in these processes, we report that the levels of inflammation and fibrosis observed in Kit(W-sh/W-sh) mice can be restored to those observed in WT mice after the adoptive transfer of bone marrow-derived cultured MCs into Kit(W-sh/W-sh) mice. Additionally, we show that levels of inflammation and fibrosis are also reduced in MC chymase MCPT4-deficient mice as compared with WT mice at day 7, suggesting a role for MC-derived MCPT4 in these processes. Our results support the conclusion that MCs can contribute to the initial lung injury induced by BLM through release of the MCPT4 chymase.

Does ß-hexosaminidase function only as a degranulation indicator in mast cells? The primary role of ß-hexosaminidase in mast cell granules.

ß-Hexosaminidase, which is generally present in the lysosome, is essential for glycoprotein metabolism in the maintenance of cell homeostasis. In mast cells (MCs), large amounts of ß-hexosaminidase are present in the granules as opposed to the lysosome, and the biological role of MC ß-hexosaminidase has yet to be fully elucidated. Therefore, we investigated the biological role of ß-hexosaminidase in MC granules. Bone marrow-derived MCs from C57BL/6 (BL/6-BMMC) or ß-hexosaminidase gene-deficient (hexb(-/-)-BMMC) mice were transplanted into MC-deficient (WBB6F1/J-Kit(W)/Kit(W-v) [W/W(v)]) mice to generate MC-reconstituted models. In asthma model experiments, no differences were observed in the symptoms of BL/6, W/W(v), BL/6-BMMC-reconstituted W/W(v), or hexb(-/-)-BMMC-reconstituted W/W(v) mice. In Staphylococcus epidermidis experimental infection model experiments, the severity of symptoms and frequency of death were markedly higher in W/W(v) and hexb(-/-)-BMMC-reconstituted W/W(v) mice than in BL/6 and BL/6-BMMC-reconstituted W/W(v) mice. The growth of S. epidermidis in an in vitro study was clearly inhibited by addition of BL/6-BMMC lysate, but not by addition of hexb(-/-)-BMMC lysate. Moreover, suppression of bacterial proliferation was completely recovered when bacteria were incubated with hexb(-/-)-BMMC lysate plus ß-hexosaminidase. Transmission electron microscopy indicated that the cell wall of S. epidermidis was heavily degraded following coincubation of bacteria with BL/6-BMMC lysate, but not following coincubation with hexb(-/-)-BMMC lysate. These findings strongly suggest that MC granule ß-hexosaminidase is crucial for defense against bacterial invasion, but is not involved in the allergic response. Our results also suggest that the bactericidal mechanism of ß-hexosaminidase involves degradation of bacterial cell wall peptidoglycan.

The cardiac repair benefits of inflammation do not persist: evidence from mast cell implantation.

Multiple mechanisms contribute to progressive cardiac dysfunction after myocardial infarction (MI) and inflammation is an important mediator. Mast cells (MCs) trigger inflammation after MI by releasing bio-active factors that contribute to healing. c-Kit-deficient (Kit(W/W-v) ) mice have dysfunctional MCs and develop severe ventricular dilatation post-MI. We explored the role of MCs in post-MI repair. Mouse wild-type (WT) and Kit(W/W-v) MCs were obtained from bone marrow (BM). MC effects on fibroblasts were examined in vitro by proliferation and gel contraction assays. MCs were implanted into infarcted mouse hearts and their effects were evaluated using molecular, cellular and cardiac functional analyses. In contrast to WT, Kit(W/W-v) MC transplantation into Kit(W/W-v) mice did not improve cardiac function or scar size post-MI. Kit(W/W-v) MCs induced significantly reduced fibroblast proliferation and contraction compared to WT MCs. MC influence on fibroblast proliferation was Basic fibroblast growth factor (bFGF)-dependent and MC-induced fibroblast contractility functioned through transforming growth factor (TGF)-ß. WT MCs transiently rescue cardiac function early post-MI, but the benefits of BM cell implantation lasted longer. MCs induced increased inflammation compared to the BM-injected mice, with increased neutrophil infiltration and infarct tumour necrosis factor-α (TNF-α) concentration. This augmented inflammation was followed by increased angiogenesis and myofibroblast formation and reduced scar size at early time-points. Similar to the functional data, these beneficial effects were transient, largely vanishing by day 28. Dysfunctional Kit(W/W-v) MCs were unable to rescue cardiac function post-MI. WT MC implantation transiently enhanced angiogenesis and cardiac function. These data suggest that increased inflammation is beneficial to cardiac repair, but these effects are not persistent.

Mast cells protect from skin tumor development and limit tumor growth during cutaneous de novo carcinogenesis in a Kit-dependent mouse model.

Epidermal tumors belong to the most frequent type of neoplasms, and tumor-associated accumulation of mast cells (MCs) has first been observed more than a century ago. Therefore, MCs have been implicated in tumor development and growth; however, the results regarding the role of MC in cutaneous de novo carcinogenesis are still controversially discussed. Here, we subjected MC-deficient Kit(W) /Kit(W-v) mice to chemical skin carcinogenesis. Tumors were induced using the carcinogen 7,12-dimethylbenz[a]-anthracene and subsequent treatment with the tumor promoter 12-tetradecanoyl-phorbol-13-acetat. The treatment resulted in pronounced inflammatory cell infiltrates that were diminished in MC-deficient animals. Unexpectedly, tumor development and growth was significantly increased in MC-deficient Kit(W) /Kit(W-v) mice. The repair of their MC deficiency by local adoptive transfer of MCs normalized tumor incidence and growth. The recruitment of skin-infiltrating immune cells, particularly of F4/80+ monocytes, Gr-1+ granulocytes, B220+ B cells and CD8+ T lymphocytes, to sites of tumor development was, in part, also controlled by MCs. Recent evidence indicated the importance of local antitumor tissue immunity which prevents tumor development. These findings suggest a critical role for MCs in mediating these host antitumor immune responses in the skin.

Mast cell chymase protects against renal fibrosis in murine unilateral ureteral obstruction.

Mast cell release of chymase is important in tissue remodeling and may participate in inflammation leading to fibrosis and organ failure. Here we analyzed the function of chymase in unilateral ureteral obstruction, an established accelerated model of renal tubulointerstitial fibrosis. Mice deficient in mouse mast cell protease 4 (mMCP4), the functional counterpart of human chymase, had increased obstruction-induced fibrosis when compared to wild-type mice indicating a protective effect of mMCP4. Engraftment of mast cell-deficient Kit(Wsh/Wsh) mice with wild type, but not mMCP4-deficient mast cells, restored protection confirming the role of mMCP4. Kidneys of mMCP4-deficient mice had higher levels of renal tubular damage, interstitial fibrosis, collagen deposition, increased α-smooth muscle actin, and decreased E-cadherin expression compared to the kidneys of wild-type mice. Further analysis showed an elevated inflammatory response in mMCP4-deficient mice with increased levels of kidney-infiltrating macrophages and T cells and local profibrotic TGF-ß1 and CCL2. Granulated and degranulated mast cells and mMCP4 were mainly found in the kidney capsule, respectively, before and after ureteral obstruction. Analysis of mMCP4 substrates showed that it mediates its anti-fibrotic actions by degrading interstitial deposits of fibronectin, a known promoter of inflammatory cell infiltration and adhesion. Thus, mast cell released mMCP4 has anti-fibrotic potential in acutely induced obstructive nephropathy.

Double expression of CD34 and CD117 on bone marrow progenitors is a hallmark of the development of functional mast cell of Callithrix jacchus (common marmoset).

Mast cells (MCs) are developed from hematopoietic progenitor cells and play an important role in inflammation. Study of the kinetics of development and accumulation of primate MC in vivo is crucial for the control of human inflammatory diseases, as evolution of the immune system is quite rapid and inflammation including MC response is considered to be different between mouse and human. In the present study, we examined the development of MC from hematopoietic progenitors of Callithrix jacchus (common marmoset), an experimental animal of nonhuman primates. Bone marrow cells were fractionated for the expression of CD34 and CD117 by cell sorting. MCs were developed in vitro or by transplanting the cells to NOD/SCID/IL-2γc knockout (NOG) mice. In vitro culture of CD34(+)CD117(+) (double positive, DP) cells with stem cell factor could generate high-affinity Fc epsilon receptor (FcεR)-expressing CD117(+) cells with typical granules. The developed MC released ß-hexosaminidase and produced leukotriene C(4) after the stimulation of FcεRI. Transplantation of DP cells gave rise to a marked expansion of CD34(-)CD45(+)CD117(+)FcεR(+) cells in NOG mice. They expressed transcripts encoding chymase 1 and tryptase ß. Differentiation of CD34(-)CD117(+) cells to MCs was relatively limited compared with the DP cells, similarly to human MCs. These results suggest that this marmoset system provides a good model for human MC development.

Cutting edge: mast cells regulate disease severity in a relapsing-remitting model of multiple sclerosis.

Mast cells (MCs) exert a significant pathologic influence on disease severity in C57BL/6 (B6) strain-dependent experimental allergic encephalomyelitis (EAE), a model of primary progressive multiple sclerosis (MS). However, relapsing-remitting MS, which is modeled in SJL mice, is the more prevalent form. Given genetically determined heterogeneity in numbers and responsiveness of MCs from various strains of mice, we asked whether these cells also influence this more clinically relevant MS model using SJL-Kit(W/W-v) mice. Similar to the commercially available WBB6F(1)-Kit(W/W-v) mice, SJL-Kit(W/W-v) mice are MC-deficient, anemic, and neutropenic and have normal T cell compartments. They exhibit significantly reduced disease severity, but retain the relapsing-remitting course, a phenotype reversed by selective MC reconstitution. These data confirm that MC influence is not confined to an isolated model of EAE and reveal a new system to study the effects of MC heterogeneity on relapsing-remitting EAE and other SJL strain-specific diseases.

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.

Mast cell activation and degranulation promotes renal fibrosis in experimental unilateral ureteric obstruction.

Progressive renal fibrosis is the final common pathway leading to renal failure irrespective of the initiating cause. Clinical studies of renal fibrosis found that prominent mast cell accumulation correlated with worse outcomes. Mast cells are pluripotent innate immune cells that synthesize and secrete profibrotic mediators. Here we use mast cell-deficient (Kit(W-sh/W-sh)) mice to define a functional pathogenic role for these cells in the development of renal fibrosis. Intrarenal collagen deposition was significantly decreased in mast cell-deficient compared to wild-type mice 7 and 14 days after unilateral ureteric obstruction. The intrarenal expression of mRNAs for transforming growth factor-ß, α-smooth muscle actin, chemokines, and renal macrophages and CD4(+) T cells were also decreased in mast cell-deficient mice. Reconstitution of the mast cell population in mast cell-deficient mice with wild-type bone marrow-derived mast cells restored the pattern and intensity of renal fibrosis to levels seen in wild-type mice following ureteric ligation. Interestingly, the mast cells were recruited, activated, and degranulated within 6 h of ureteric ligation. A mast cell stabilizer that impairs degranulation, disodium chromoglycate, significantly attenuated renal fibrosis following ureteric ligation in wild-type mice. Thus, mast cells promote renal fibrosis and their targeting may offer therapeutic potential in the treatment of renal fibrosis.

Mast cells contribute to the mucosal adjuvant effect of CTA1-DD after IgG-complex formation.

Mast cell activation is one of the most dramatic immune-mediated responses the body can encounter. In the worst scenario (i.e., anaphylaxis), this response is fatal. However, the importance of mast cells as initiators and effectors of both innate and adaptive immunity in healthy individuals has recently been appreciated. It was reported that mast cell activation can be used as an adjuvant to promote Ag-specific humoral immune responses upon vaccination. In this study, we have used a clinically relevant mucosal adjuvant, cholera toxin A1 subunit (CTA1)-DD, which is a fusion protein composed of CTA1, the ADP-ribosylating part of cholera toxin, and DD, two Ig-binding domains derived from Staphylococcus aureus protein A. CTA1-DD in combination with polyclonal IgG induced degranulation and production of TNF-alpha from mouse mast cells. Furthermore, CTA1-DD and polyclonal IgG complex induced mast cell degranulation in mouse skin tissue and nasal mucosa. We also found that intranasal immunization with hapten (4-hydroxy-3-nitrophenyl) acetyl (NP) coupled to chicken gammaglobulin admixed with CTA1-DD complexed with polyclonal IgG greatly enhanced serum IgG anti-NP Ab responses and stimulated higher numbers of NP-specific plasma cells in the bone marrow as compared with that observed in mice immunized with NP-chicken gammaglobulin with CTA1-DD alone. This CTA1-DD/IgG complex-mediated enhancement was mast cell dependent because it was absent in mast cell-deficient Kit(W-sh/W-sh) mice. In conclusion, our data suggest that a clinically relevant adjuvant, CTA1-DD, exerts additional augmenting effects through activation of mucosal mast cells, clearly demonstrating that mast cells could be further exploited for improving the efficacy of mucosal vaccines.

Mast cells regulate homeostatic intestinal epithelial migration and barrier function by a chymase/Mcpt4-dependent mechanism.

Altered intestinal barrier function is postulated to be a central predisposing factor to intestinal diseases, including inflammatory bowel diseases and food allergies. However, the mechanisms involved in maintaining homeostatic intestinal barrier integrity remain undefined. In this study, we demonstrate that mice deficient in mast cells (Kit(W-sh/W-sh) [Wsh]) or mast cell chymase (Mcpt4(-/-)) have significantly decreased basal small intestinal permeability compared with wild-type (WT) mice. Altered intestinal barrier function was linked to decreased intestinal epithelial cell migration along the villus/crypt axis, altered intestinal morphology, and dysregulated claudin-3 crypt expression. Remarkably, engraftment of Wsh mice with WT but not Mcpt4(-/-) mast cells restored intestinal epithelial cell migration, morphology, and intestinal epithelial barrier function. Collectively, these findings identify a mechanism by which mast cells regulate homeostatic intestinal epithelial migration and barrier function.

Mast cell-derived TNF can exacerbate mortality during severe bacterial infections in C57BL/6-KitW-sh/W-sh mice.

We used mast cell-engrafted genetically mast cell-deficient C57BL/6-Kit(W-sh/W-sh) mice to investigate the roles of mast cells and mast cell-derived tumor necrosis factor in two models of severe bacterial infection. In these mice, we confirmed findings derived from studies of mast cell-deficient WBB6F(1)-Kit(W/W-v) mice indicating that mast cells can promote survival in cecal ligation and puncture (CLP) of moderate severity. However, we found that the beneficial role of mast cells in this setting can occur independently of mast cell-derived tumor necrosis factor. By contrast, using mast cell-engrafted C57BL/6-Kit(W-sh/W-sh) mice, we found that mast cell-derived tumor necrosis factor can increase mortality during severe CLP and can also enhance bacterial growth and hasten death after intraperitoneal inoculation of Salmonella typhimurium. In WBB6F(1)-Kit(W-sh/W-sh) mice, mast cells enhanced survival during moderately severe CLP but did not significantly change the survival observed in severe CLP. Our findings in three types of genetically mast cell-deficient mice thus support the hypothesis that, depending on the circumstances (including mouse strain background, the nature of the mutation resulting in a mast cell deficiency, and type and severity of infection), mast cells can have either no detectable effect or opposite effects on survival during bacterial infections, eg, promoting survival during moderately severe CLP associated with low mortality but, in C57BL/6-Kit(W-sh/W-sh) mice, increasing mortality during severe CLP or infection with S. typhimurium.

Bone marrow-derived mast cells accumulate in the central nervous system during inflammation but are dispensable for experimental autoimmune encephalomyelitis pathogenesis.

Reports showing that W/W(v) mice are protected from experimental autoimmune encephalomyelitis (EAE, a murine model of multiple sclerosis), have implicated mast cells as an essential component in disease susceptibility, but the role of mast cell trafficking has not been addressed. In this study, we have used both mast cell transplantation and genetic mutations (Cd34(-/-), W/W(v), W(sh)/W(sh)) to investigate the role of mast cell trafficking in EAE in detail. We show, for the first time, that bone marrow-derived mast cells are actively recruited to the CNS during EAE. Unexpectedly, however, we found that EAE develops unabated in two independent genetic backgrounds in the complete absence of mast cells or bone marrow-derived mast cell reconstitution. We conclude that although mast cells do accumulate in the brain and CNS during demyelinating disease via peripheral mast cell trafficking, they are completely dispensable for development of disease.

Angiogenic effects of cell therapy within a biomaterial scaffold in a rat hind limb ischemia model.

Critical limb ischemia (CLI) is a life- and limb-threatening condition affecting 1-10% of humans worldwide with peripheral arterial disease. Cellular therapies, such as bone marrow-derived mesenchymal stem cells (MSCs) have been used for the treatment of CLI. However, little information is available regarding the angiogenic potency of MSCs and mast cells (MC) in angiogenesis. The aim of this study was to evaluate the ability of MCs and MSCs to induce angiogenesis in a rat model of ischemic hind limb injury on a background of a tissue engineered hydrogel scaffold. Thirty rats were randomly divided into six control and experimental groups as follows: (a) Control healthy (b) Ischemic positive control with right femoral artery transection, (c) ischemia with hydrogel scaffold, (d) ischemia with hydrogel plus MSC, (e) ischemia with hydrogel plus MC and (f) ischemia with hydrogel plus MSC and MCs. 106 of each cell type, isolated from bone marrow stroma, was injected into the transected artery used to induce hind limb ischemia. The other hind limb served as a non-ischemic control. After 14 days, capillary density, vascular diameter, histomorphometry and immunohistochemistry at the transected location and in gastrocnemius muscles were evaluated. Capillary density and number of blood vessels in the region of the femoral artery transection in animals receiving MSCs and MCs was increased compared to control groups (P < 0.05). Generally the effect of MCs and MSCs was similar although the combined MC/MSC therapy resulted in a reduced, rather than enhanced, effect. In the gastrocnemius muscle, immunohistochemical and histomorphometric observation showed a great ratio of capillaries to muscle fibers in all the cell-receiving groups (P < 0.05). The data indicates that the combination of hydrogel and cell therapy generates a greater angiogenic potential at the ischemic site than cell therapy or hydrogels alone.