In contrast to resident constitutive mast cells (CMCs), mucosal MCs (MMCs) appear in the lung and trachea of sensitized mice only following inhalation challenge. We monitored the influx and maturation of MCs by their expression of Kit, FcɛRI, β7-integrin and side scatter (SSC) by flow cytometry. Influx of MC progenitors (MCps) (FcɛRIlo, Kitint, β7hi, and SSClo) peaks 1 day after challenges and subsides to baseline by day 7 after challenge. The mature MMCs appear as a distinct population on day 7 and peak at day 14 with higher SSC and FcɛRI expression, but lower β7 and Kit expression. A distinct transitional population is present between 1 and 7 days after challenge. Maturation occurs more rapidly in the trachea. The resident tracheal CMCs had higher SSC, FcɛRI, and Kit and lower β7-integrin expression than the MMCs. By histology, the MMCs follow similar kinetics to the flow cytometry-identified mature MMCs and are notably persistent for >42 days. Steroid treatment reduced inflammation and MCp influx but had no effect on established MMCs. Thus, changes in SSC, FcɛRI, and Kit together with the expression of αE/α4:β7-integrins characterizes the development of induced MMCs from MCps and distinguishes them from resident CMCs in the trachea and large airways.

Interleukin (IL)-4 has critical roles in allergic disorders, including food hypersensitivity. The direct effects of the cytokine on the survival and function of mast cells, the key effectors of food anaphylaxis, have not been established. In this study, we demonstrate that IL-4 induces a marked intestinal mastocytosis in mice. This phenotype is reproduced in animals expressing Il4rαF709 , an activating variant of the IL-4 receptor α-chain (IL-4Rα). Il4rαF709 mice exhibit enhanced anaphylactic reactions but unaltered physiological responses to vasoactive mediators. IL-4 induces Bcl-2 and Bcl-X L and enhances survival and stimulates proliferation in cultured bone marrow–derived mast cells (BMMC). These effects are STAT6 (signal transducer and activator of transcription factor 6)-dependent and are amplified in Il4rαF709 BMMC. In competitive bone marrow chimeras, Il4rαF709 mast cells display a substantial competitive advantage over wild-type mast cells, which, in turn, prevail over IL-4Rα −/− mast cells in populating the intestine, establishing a cell-intrinsic effect of IL-4 in intestinal mast cell homeostasis. Our results demonstrate that IL-4-signaling is a key determinant of mast cell expansion in food allergy.

Background: In atopic subjects food ingestion drives the production of IgE antibodies that can trigger hypersensitivity reactions. The IL-4 pathway plays a critical role in this response, and genetic polymorphisms in its components have been linked to allergy.Objective: We sought to test whether an activating mutation in the IL-4 receptor (IL-4R) alpha chain enhances allergic responses to a food antigen.Methods: F709 mice, in which the IL-4R alpha immunoreceptor tyrosine-based inhibitory motif is inactivated, were gavage fed with ovalbumin (OVA). Reactions to OVA challenge and immune responses, including antibody production and T(H)2 responses, were assessed.Results: F709 mice, but not wild-type control animals, sensitized by means of gavage with OVA and either cholera toxin or staphylococcal enterotoxin B, displayed mast cell activation and systemic anaphylaxis on enteral challenge. Anaphylaxis was elicited even in F709 mice enterally sensitized with OVA alone. Bone marrow chimera experiments established that the increased sensitivity conferred by the F709 genotype was mediated mostly by hematopoietic cells but that nonhematopoietic cells also contributed. F709 mice exhibited increased intestinal permeability to macromolecules. The F709 genotype conferred increased OVA-specific IgE but not IgG1 responses, local and systemic TH2 responses, and intestinal mast cell hyperplasia compared with wild-type mice. Anaphylaxis was abrogated in F709 mice lacking IgE or the high-affinity receptor for IgE (FceRI).Conclusion: Augmented IL-4Ra signaling confers increased intestinal permeability and dramatically enhanced sensitivity to food allergens. Unlike anaphylaxis to injected antigens, which in rodents can be mediated by either IgE or IgG antibodies, the food-induced response in F709 mice is solely IgE dependent. (J Allergy Clin Immunol 2011;127:795-805.)

RATIONALE: Basophils have been shown to present antigen and may drive Th2 lymphocyte development upon exposure to certain allergens and helminths yet the location of activation, trigger for maturation, and survival kinetics are not well characterized. METHODS: Papain, a papaya-derived cysteine protease that can cause human hypersensitivity manifested by asthma and anaphylaxis, was injected into footpads of BALB/c and IL-4/eGFP reporter mice. At various times post injection, we isolated the popliteal draining lymph node (DLN) and used flow cytometry to enumerate and characterize the basophils that had moved into the nodes. These cells were identified as the FcεRIα+, CD49b+, B220-, CD4-, and c-kit- population. We assessed this population for expression of IL-4, MHC Class II, and CD200R1, and Annexin V staining. RESULTS: We verified previous findings that basophils peak 2.5-3 days after footpad injection, then rapidly decline. 29.4% of basophils expressed IL-4 one day after injection, rising to 82.6% at day 2 and 88% at day 3. MHC class II and CD200R1 (proposed as a marker of activation) were expressed and remained constant from the earliest time point at which this population could be identified. In addition, most basophils were positive for Annexin V at day 2. CONCLUSIONS: Expression of MHC Class II, CD200R1, and IL-4 by basophils identified in the DLN 2 days after papain injection suggests basophils arrive in the DLN in an activated state, or are activated very rapidly after recruitment. Their disappearance within several days of arrival occurs at least in part via cell death, possibly apoptosis.

Employing mast cell (MC) neutralizing antibodies and stabilizing agents, we have previously demonstrated a critical role for MCs in the regulation of intestinal epithelial permeability in mice. We hypothesize that a MC-derived serine protease, chymase, is an important mediator of intestinal epithelial permeability. Jejunal levels of mouse mast cell protease-4 (mMCP-4), the murine functional homologue to human chymase, were analyzed by quantitative real-time PCR and immunohistochemistry in wild-type BALB/c (WT) mice and in a murine model of intestinal mastocytosis using intestinal IL-9 Tg (iIL-9 Tg) mice. To examine the effect of chymase on intestinal epithelial permeability, confluent colonic adenocarcinoma Caco2-bbe cells were exposed to 0, 2.5 or 5U of human skin-derived chymase basolaterally for 24 hours and intestinal epithelial permeability measured in Ussing Chambers by monitoring the mucosal to serosal flux of FITC-dextran and the inversely correlating transepithelial resistance (TER). Intestinal mastocytosis was associated with a significant increase in jejunal mMCP-4 mRNA levels (10.1 ± 1.0 fold; p < 0.0001) in iIL-9 Tg mice compared to WT. Furthermore, jejunum from iIL-9 Tg mice displayed strong and diffuse mMCP-4 positive immunohistochemical staining in comparison to very low levels of punctate staining in jejunum from WT mice. Exposure of Caco2-bbe monolayers to chymase induced a significant decrease in the TER (2.5U: 125.9 ± 47.6, p < 0.05; 5U: 192.4 ± 19.9, p < 0.005; vs control: 297.5 ± 15.9 Ω/cm2) and increase in FITC-dextran permeability (2.5U: 12926 ± 2277, p < 0.05; 5U: 11752 ± 2063, p < 0.01; vs control: 3474 ± 457 ng/ml) compared to controls. Collectively, these data suggest that MC-derived chymase may play an important role in MC-mediated intestinal epithelial permeability.

In light of recent observations that IgE can support the expansion and survival of cultured mast cells, we examined the role of IgE in the homeostasis of airway mast cells in a mouse model of allergic asthma. Mice were subjected to repeated inhalations of an aqueous extract of Aspergillus fumigatus (Af) and the number, function and phenotype of mast cells was studied by histological and flow cytometric techniques. Repeated inhalation of Af induces a significant expansion of mast cells in the airways of wild-type mice. Mast cell expansion is accompanied by increased expression of FcepsilonRI and elevated levels of mouse mast cell protease-1 (mMCP-1) and IL-5. In contrast, both mast cell expansion and the levels of FcepsilonRI, mMCP-1 and IL-5 were significantly reduced in IgE-/- mice. IgE is not required for the recruitment of mast cell progenitors to the airways, but enhances the survival of differentiated mast cells in vivo. Mast cell-driven migration of allergen-specific T cells is also reduced in the absence of IgE. Decreased mast cell expansion in IL-3-/- mice suggests that IgE-induced mast cell expansion may occur via an IL-3-dependent mechanism. Our data identify a critical role for IgE in mast cell homeostasis during allergic inflammation in vivo and suggest novel mechanisms whereby therapeutic blockade of IgE may provide clinical benefit for patients with asthma.

Mast cells (MCs) are found principally in peripheral tissues yet are of bone marrow origin. Recent studies in mice trace the MC lineage from the common myeloid progenitor through the granulocyte-macrophage progenitor in the bone marrow to a committed MC progenitor (MCP). Additionally, at least in the mouse, a bipotent basophil-MC progenitor has been identified in the spleen, suggesting a physiologic role for this organ in MC development. MCPs are especially abundant in the mouse intestine, likely ensuring the capacity for a rapid expansion of MCs in the intestinal epithelium during the effector response to helminth infection and perhaps providing a pool of committed cells capable of redistribution to other tissues. Migration of MCPs to the intestine is constitutive and controlled by alpha chemokine receptor 2 and alpha4beta7 integrins expressed on the MCPs, with the latter integrin interacting with endothelial vascular cell adhesion molecule 1 and mucosal addressin cell adhesion molecule 1. In contrast, normal mouse lung tissue contains few MCPs and MCs, and these cellular reservoirs are not affected by the lack of alpha chemokine receptor 2 or alpha4beta7 integrin. Nonetheless, robust recruitment of MCPs to the lung occurs during experimentally induced allergic pulmonary inflammation and requires alpha4beta7 and alpha4beta1 integrins interacting with vascular cell adhesion molecule 1 but not with mucosal addressin cell adhesion molecule 1. Thus although MCs are present in all organs, the pathways responsible for the trafficking of MCPs from the circulation are organ specific and include both constitutive and inducible systems, ensuring both resident MCs and the potential for incremental recruitment in accord with the requirements of the immune response. These findings in mice await confirmation in human subjects.

Basophils and mast cells are multifunctional hematopoietic effectors that co-operate to mount a variety of allergic and innate immune responses. Their origin and developmental relationships, however, have not yet been resolved, and remain as one of the major issues in the biology of hematopoiesis. Here we report that progenitors bipotent for basophils and mast cells(basophil/mast cell progenitors: BMCPs) are prospectively isolatable within murine spleen. We have shown that the β7-integrin(β7) is an essential molecule for tissue-specific homing of putative precursors for intestinal mast cells (J Exp Med 194:1243, 2001). To identify a candidate population that seeds intestinal progenitors for mast cells, we searched for β7+ cells in the bone marrow and the spleen. Lin−c-Kit+ spleen cells contained a fraction of cells expressing β7 at high levels. They also expressed FcγRII/III, but the majority of these cells did not express FcεRIα. These Lin−c-Kit+FcγRII/III+β7hiFcεRIα−/locells exclusively differentiated into mature mast cells and basophils. Strikingly, single Lin−c-Kit+FcγRII/III+β7hiFcεRIα−/locells formed colonies containing both basophils and mast cells as well as pure mast cell or basophil colonies. We thus named these cells as BMCPs. In 2-day cultures, purified BMCPs upregulated FcεRIα, giving rise to Lin−CD34+FcεRIαhic-Kit+ and Li− CD34+FcεRIαhic-Kit− blastic cell populations, and they differentiated exclusively into mast cells and basophils, respectively. Based on this phenotype, we searched for precursors committed to either lineage in vivo. The Lin−CD34+ bone marrow cells contained FcεRIαhic-Kit−cells, which differentiated exclusively into basophils. We named this population as basophil progenitors (BaPs). Since mast cell progenitors(MCPs) were not isolatable as a distinct population in the bone marrow or the spleen, we searched for MCPs in the intestine. We newly identified CD45+Li− CD34+β7hiFcεRIαlocells in the intestine, and these cells exclusively formed pure mast cell colonies, which were named as intestinal MCPs. Since the expression of C/EBPα was dramatically increased in BaPs but was downregulated in MCPs, we hypothesized that it plays a key role in the basophil versus the mast cell lineage commitment. To test this hypothesis, we disrupted or overexpressed C/EBPα at the BMCP stage. BMCPs disrupted with C/EBPα gave rise exclusively to mast cells, while, BMCPs overexpressing C/EBPα differentiated mainly into basophils, suggesting that C/EBPα plays a primary role in deciding the basophil vs. mast cell fate at the BMCP stage. Thus, differentiation of the BMCPs into committed progeny may lead to selective migration, BaPs to the bone marrow or MCPs to peripheral tissues, and this fate decision is controlled principally by C/EBPα. These newly identified progenitors should be useful to analyze the mechanism of commitment into each of these lineages, and could also be therapeutic targets for a variety of allergic and autoimmune disorders.

Homing of mast cell progenitors (MCps) to the mouse small intestine involves the interaction of alpha4beta7 integrin with mucosal addressin cellular adhesion molecule-1 (MAdCAM-1). We now demonstrate the dependence of this process on CXC chemokine receptor 2 (CXCR2) and vascular cell adhesion molecule-1 (VCAM-1) using null strains and mice sublethally irradiated and bone marrow (BM) reconstituted (SIBR) with wild-type or null BM or with wild-type BM followed by administration of blocking antibody. The intestinal MCp concentration in CXCR2(-/-) mice was reduced by 67%, but was unaltered in CC chemokine receptor 2(-/-) (CCR2(-/-)), CCR3(-/-), or CCR5(-/-) mice. SIBR mice given CXCR2(-/-) BM had an intestinal MCp concentration that was 76% less than that in BALB/c BM reconstituted mice. Antibody blockade of VCAM-1 or of CXCR2 in SIBR mice reduced intestinal MCp reconstitution, and mice lacking endothelial VCAM-1 also had a marked reduction relative to wild-type mice. Finally, the half-life of intestinal MCps in wild-type mice was less than one week on the basis of a more than 50% reduction by administration of anti-alpha4beta7 integrin or anti-CXCR2. Thus, the establishment and maintenance of MCps in the small intestine is a dynamic process that requires expression of the alpha4beta7 integrin and the alpha-chemokine receptor CXCR2.

Ischemia with subsequent reperfusion (IR) injury is a significant clinical problem that occurs after physical and surgical trauma, myocardial infarction, and organ transplantation. IR injury of mouse skeletal muscle depends on the presence of both natural IgM and an intact C pathway. Disruption of the skeletal muscle architecture and permeability also requires mast cell (MC) participation, as revealed by the fact that IR injury is markedly reduced in c-kit defective, MC-deficient mouse strains. In this study, we sought to identify the pathobiologic MC products expressed in IR injury using transgenic mouse strains with normal MC development, except for the lack of a particular MC-derived mediator. Histologic analysis of skeletal muscle from BALB/c and C57BL/6 mice revealed a strong positive correlation (R(2) = 0.85) between the extent of IR injury and the level of MC degranulation. Linkage between C activation and MC degranulation was demonstrated in mice lacking C4, in which only limited MC degranulation and muscle injury were apparent. No reduction in injury was observed in transgenic mice lacking leukotriene C(4) synthase, hemopoietic PGD(2) synthase, N-deacetylase/N-sulfotransferase-2 (enzyme involved in heparin biosynthesis), or mouse MC protease (mMCP) 1. In contrast, muscle injury was significantly attenuated in mMCP-5-null mice. The MCs that reside in skeletal muscle contain abundant amounts of mMCP-5 which is the serine protease that is most similar in sequence to human MC chymase. We now report a cytotoxic activity associated with a MC-specific protease and demonstrate that mMCP-5 is critical for irreversible IR injury of skeletal muscle.

Basophils and mast cells, which are selectively endowed with the high-affinity IgE receptor and mediate a range of adaptive and innate immune responses, have an unknown developmental relationship. Here, by evaluating the expression of the beta7 integrin, a molecule that is required for selective homing of mast cell progenitors (MCPs) to the periphery, we identified bipotent progenitors that are capable of differentiating into either cell type in the mouse spleen. These basophil/mast cell progenitors (BMCPs) gave rise to basophils and mast cells at the single-cell level and reconstituted both mucosal and connective tissue mast cells. We also identified the basophil progenitor (BaP) and the MCP in the bone marrow and the gastrointestinal mucosa, respectively. We further show that the granulocyte-related transcription factor CCAAT/enhancer-binding protein alpha (C/EBPalpha) plays a primary role in the fate decision of BMCPs, being expressed in BaPs but not in MCPs. Thus, circulating basophils and tissue mast cells share a common developmental stage at which their fate decision might be controlled principally by C/EBPalpha.

RATIONALE: Phenotypically heterogeneous populations of mast cells (MCs) originate from a single bone marrow derived precursor (MCp) that lacks distinctive granules.Although allergic or helminth induced mucosal inflammation involves reactive MC hyperplasia, the responsible mechanisms are incompletely studied.METHODS: Using a limiting dilution and MC colony formation assay, we evaluated changes in MCp number in the lung due to T-helper Class 2 polarized immune responses.As mature MC are increased during inflammation, we wished to test the hypothesis that this increase was due to an influx of MCp.We induced pulmonary inflammation by ip sensitization of mice with ovalbumin in alum, followed by aerosolized ovalbumin challenge.RESULTS: A ~5 fold increase in MCp concentration was detectable in the lung after 3 days of challenge in sensitized BALB/c or C57BL/6 mice.Continued challenge enhanced the MCp yield and resulted in the appearance of mature MC in the lung.Although β7-integrin deficient mice had normal numbers of baseline MCp in their lung, these mice exhibited a 65% reduction in ovalbumin induced pulmonary MCp recruitment which was not apparent in either their +/+ controls or α ε -deficient mice.CONCLUSIONS: Taken together, these findings demonstrate distinct integrin requirements for basal and inflammation induced MCp recruitment to the lung, and specifically implicate the α4β7 integrin heterodimer as a requirement for the inflammatory recruitment of MCp to the lung.

Trichinella spiralis infection elicits a vigorous IgE response and pronounced intestinal and splenic mastocytosis in mice. Since IgE both activates mast cells (MC) and promotes their survival in culture, we examined its role in MC responses and parasite elimination in T. spiralis-infected mice. During primary infection, wild-type but not IgE-deficient (IgE(-/-)) BALB/c mice mounted a strong IgE response peaking 14 days into infection. The splenic mastocytosis observed in BALB/c mice following infection with T. spiralis was significantly diminished in IgE(-/-) mice while eosinophil responses were not diminished in either the blood or jejunum. Similar levels of peripheral blood eosinophilia and jejunal mastocytosis occurred in wild-type and IgE-deficient animals. Despite the normal MC response in the small intestine, serum levels of mouse MC protease-1 also were lower in parasite-infected IgE(-/-) animals and these animals were slower to eliminate the adult worms from the small intestine. The number of T. spiralis larvae present in the skeletal muscle of IgE(-/-) mice 28 days after primary infection was about twice that in BALB/c controls, and the fraction of larvae that was necrotic was reduced in the IgE-deficient animals. An intense deposition of IgE in and around the muscle larvae was observed in wild-type but not in IgE null mice. We conclude that IgE promotes parasite expulsion from the gut following T. spiralis infection and participates in the response to larval stages of the parasite. Furthermore, our observations support a role for IgE in the regulation of MC homeostasis in vivo.

PU.1 and GATA transcription factors appear to antagonize each other's function in the development of distinct lineages of the hematopoietic system. In contrast, we demonstrate that PU.1, like GATA-2, is essential for the generation of mast cells. PU.1-/- hematopoietic progenitors can be propagated in IL-3 and differentiate into mast cells or macrophages upon restoration of PU.1 activity. Using these progenitors and a conditionally activatable PU.1 protein, we show that PU.1 can negatively regulate expression of the GATA-2 gene. In the absence of GATA-2, PU.1 promotes macrophage but not mast cell differentiation. Reexpression of GATA-2 in such progenitors enables the generation of mast cells. We propose a developmental model in which cooperative function or antagonistic crossregulation by PU.1 of GATA-2 promotes distinct myeloid cell fates.

Previous studies have revealed that autoantibodies, complement components, and Fc receptors each participate in the pathogenesis of erosive arthritis in K/BxN mice. However, it is not known which cellular populations are responsive to these inflammatory signals. We find that two strains of mice deficient in mast cells, W/W-v and Sl/Sl(d) were resistant to development of joint inflammation and that susceptibility was restored in the W/W-v strain by mast cell engraftment. Thus, mast cells may function as a cellular link between autoantibodies, soluble mediators, and other effector populations in inflammatory arthritis.

The CCR3 binds at least seven different CC chemokines and is expressed on eosinophils, mast cells (MC), and a subset of Th cells (Th2) that generate cytokines implicated in mucosal immune responses. Using mice with a targeted disruption of CCR3 (CCR3(-/-)) and their +/+ littermates, we investigated the role of CCR3 in the amplification of tissue eosinophilia and MC hyperplasia in the mouse after infection with Trichinella spiralis. In CCR3(-/-) mice, eosinophils are not recruited to the jejunal mucosa after infection and are not present in the skeletal muscle adjacent to encysting larvae. In addition, the number of cysts in the skeletal muscle is increased and the frequency of encysted larvae exhibiting necrosis is reduced. The CCR3(-/-) mice exhibit the expected MC hyperplasia in the jejunum and caecum and reject the adult worms from the small intestine at a normal rate. This study is consistent with distinct functions for MC (adult worm expulsion) and eosinophils (toxicity to larvae) in immunity to a helminth, T. spiralis, and defines the essential requirement for CCR3 in eosinophil, but not MC recruitment to tissues.

We have observed extensive mast cell degranulation in the reperfused hindlimb muscle of the mouse, accompanied by pathological changes within the muscle. As quantitated by the tissue:blood (125)I permeability ratio, both the hindlimbs and lungs exhibited a significant increment in permeability during hindlimb reperfusion. In lungs of the same mice, mast cell-derived chymase mMCP-1 coats alveolar macrophages, an event noted by us in acid-induced direct lung injury. Mast cells in the lung contain mMCP-1, whereas those in the muscle do not. Neither extensive muscle injury nor an increased pulmonary permeability index occurs in the mast cell-deficient W/W(v) mice. We conclude that the mast cell is a key mediator in both local ischemia-reperfusion injury (I-R) of muscle and consequent remote lung injury.

Genomic blot analysis raised the possibility that uncharacterized tryptase genes reside on chromosome 17 at the complex containing the three genes that encode mouse mast cell protease (mMCP) 6, mMCP-7, and transmembrane tryptase (mTMT). Probing of GenBank's expressed sequence tag data base with these three tryptase cDNAs resulted in the identification of an expressed sequence tag that encodes a portion of a novel mouse serine protease (now designated mouse tryptase 4 (mT4) because it is the fourth member of this family). 5′- and 3′-rapid amplification of cDNA ends approaches were carried out to deduce the nucleotide sequence of the full-length mT4 transcript. This information was then used to clone its ∼5.0-kilobase pair gene. Chromosome mapping analysis of its gene, sequence analysis of its transcript, and comparative protein structure modeling of its translated product revealed that mT4 is a new member of the chromosome 17 family of mouse tryptases. mT4 is 40–44% identical to mMCP-6, mMCP-7, and mTMT, and this new serine protease has all of the structural features of a functional tryptase. Moreover, mT4 is enzymatically active when expressed in insect cells. Due to its 17-mer hydrophobic domain at its C terminus, mT4 is a membrane-anchored tryptase more analogous to mTMT than the other members of its family. As assessed by RNA blot, reverse transcriptase-polymerase chain reaction, and/or in situ hybridization analysis, mT4 is expressed in interleukin-5-dependent mouse eosinophils, as well as in ovaries and testes. The observation that recombinant mT4 is preferentially retained in the endoplasmic reticulum of transiently transfected COS-7 cells suggests a convertase-like role for this integral membrane serine protease.