Senescent jejunal mast cells and eosinophils in the mouse preferentially translocate to the spleen and draining lymph node, respectively, during the recovery phase of helminth infection

Mast Cell Activation Syndrome Update-A Dermatological Perspective

Mast cells (MCs) are infamous for their role in potentially fatal anaphylaxis reactions. In the last two decades, a more complex picture has emerged, as it has become obvious that MCs are much more than just IgE effectors of anaphylaxis. MCs are defenders against a host of infectious and toxic aggressions (their interactions with other components of the immune system are not yet fully understood) and after the insult has ended, MCs continue to play a role in inflammation regulation and tissue repair. Unfortunately, MC involvement in pathology is also significant. Apart from their role in allergies, MCs can proliferate clonally to produce systemic mastocytosis. They have also been implicated in excessive fibrosis, keloid scaring, graft rejection and chronic inflammation, especially at the level of the skin and gut. In recent years, the term MC activation syndrome (MCAS) was proposed to account for symptoms caused by MC activation, and clear diagnostic criteria have been defined. However, not all authors agree with these criteria, as some find them too restrictive, potentially leaving much of the MC-related pathology unaccounted for. Here, we review the current knowledge on the physiological and pathological roles of MCs, with a dermatological emphasis, and discuss the MCAS classification.

Age related changes in the dermal mast cells and the associated changes in the dermal collagen and cells: A histological and electron microscopy study

Mast cells are widely distributed bone marrow cells. They have a crucial role in the dermal aging process. The aim of the present study was to describe the biochemical and the histological changes that occur in the aged dermal mast cells and to demonstrate the associated changes in the dermal cells and fibers as well. Sixteen male albino rats were used and divided into two groups; the control group (8-10 weeks) and the aged group (20-22 weeks). The rats were decapitated then processed for further biochemical and histological studies. The mean area fraction for collagen fibers was measured. In the aged group, there was a significant increase in the skin histamine and heparin levels if compared with the control one. Furthermore, there was an apparent increase in intact and degranulated dermal mast cells if compared with the control one. The dermal collagen bundles were apparently decreased and appeared distorted with wide spacing. Additionally, there were apparently large sized eosinophils with more cytoplasmic granules. Direct contact between mast, fibroblast, and macrophage cells was noticed. The average area fraction of collagen fibers was significantly increased in the aged group if compared with the control one. It could be concluded that the secretory activity of dermal mast cells was significantly increased in the aged skin group. Also, this study demonstrated the implicated role of mast cell in aged skin changes. Further long-term studies are needed to validate the prophylactic or therapeutic potential by intentional hindering of mast cell degranulation in aged skin.

Recognition Sites for Microbes and Components of the Immune System on Human Mast Cells: Relationship to CD Antigens and Implications for Host Defense

Traditionally, mast cells (MCs) have been considered to play an important role in allergic disorders and helminth infections. More recently, MCs have been implicated in a variety of different infectious diseases including life-threatening disorders caused by viruses and bacteria. Apart from recognition through specific IgE, MCs are considered to recognize such bacteria and viruses via specific cell surface binding sites. In addition, MCs interact with diverse components and cells of the immune system and thereby may facilitate the targeting and the elimination of invading microbes in the tissues. The current article provides an overview on MC antigens contributing to microbe recognition and targeting as an important element of natural host-defense.

IgE and mast cells in host defense against parasites and venoms

IgE-dependent mast cell activation is a major effector mechanism underlying the pathology associated with allergic disorders. The most dramatic of these IgE-associated disorders is the fatal anaphylaxis which can occur in some people who have developed IgE antibodies to otherwise innocuous antigens, such as those contained in certain foods and medicines. Why would such a highly "maladaptive" immune response develop in evolution and be retained to the present day? Host defense against parasites has long been considered the only beneficial function that might be conferred by IgE and mast cells. However, recent studies have provided evidence that, in addition to participating in host resistance to certain parasites, mast cells and IgE are critical components of innate (mast cells) and adaptive (mast cells and IgE) immune responses that can enhance host defense against the toxicity of certain arthropod and animal venoms, including enhancing the survival of mice injected with such venoms. Yet, in some people, developing IgE antibodies to insect or snake venoms puts them at risk for having a potentially fatal anaphylactic reaction upon subsequent exposure to such venoms. Delineating the mechanisms underlying beneficial versus detrimental innate and adaptive immune responses associated with mast cell activation and IgE is likely to enhance our ability to identify potential therapeutic targets in such settings, not only for reducing the pathology associated with allergic disorders but perhaps also for enhancing immune protection against pathogens and animal venoms.

The multifaceted mast cell in inflammatory bowel disease

Mast cells (MCs) are tissue-resident immune cells that carry out protective roles against pathogens. In disease states, such as inflammatory bowel disease, these granulocytes release a diverse array of mediators that contribute to inflammatory processes. They also participate in wound repair and tissue remodeling. In this review, the composition of MCs and how their phenotypes can be altered during inflammation of the gastrointestinal tract is detailed. Animal and human clinical studies that have implicated the participation of MCs in inflammatory bowel disease are reviewed, including the contribution of the cell's mediators to clinical symptoms, stress-triggered inflammation, and fistula and strictures. Studies that have focused on negating the proinflammatory roles of MCs and their mediators in animal models suggest new targets for therapies for patients with inflammatory bowel disease.

Qualitative and quantitative studies of eosinophils in parasitic infections

Th2 responses such as peripheral and tissue eosinophilia are characteristic features in the host animals infected with Strongyloides venezuelensis and Trichinella spiralis. Th2 responses are characterized by a specific profile of cytokines and chemokines induced during the course of infection. In this chapter, we describe the methodology that is utilized in our laboratories to study the production of cytokine, chemokine, and antibodies related to the eosinophilia seen in mice infected with the parasites. Furthermore, protocols are described for the different methods used to study eosinophil functions in the blood and tissues of these experimental models of parasitic infections.

Development of mast cells and importance of their tryptase and chymase serine proteases in inflammation and wound healing

Mast cells (MCs) are active participants in blood coagulation and innate and acquired immunity. This review focuses on the development of mouse and human MCs, as well as the involvement of their granule serine proteases in inflammation and the connective tissue remodeling that occurs during the different phases of the healing process of wounded skin and other organs. The accumulated data suggest that MCs, their tryptases, and their chymases play important roles in tissue repair. While MCs initially promote healing, they can be detrimental if they are chronically stimulated or if too many MCs become activated at the same time. The possibility that MCs and their granule serine proteases contribute to the formation of keloid and hypertrophic scars makes them potential targets for therapeutic intervention in the repair of damaged skin.

Extracellular forms of Mycobacterium bovis BCG in the mucosal lymphatic tissues following oral vaccination

Oral vaccination with BCG provides protective systemic immunity against pathogenic mycobacterial challenge. In this study, the anatomical distribution of Mycobacterium bovis BCG following oral vaccination was investigated. Replicating bacteria in the Peyer's patches and mesenteric lymph nodes were present as solitary rods or clusters of two to three bacteria, the majority of which were isolated ex vivo as extracellular forms. Only a minority were shown to be associated with typical antigen-presenting cells. Acid-fast staining of mast cell granules in lymphoid tissues revealed a potential pitfall for these analyses and may explain previous reports of acid-fast 'coccoid' forms of mycobacteria in tissues.

The translational repressor T-cell intracellular antigen-1 (TIA-1) is a key modulator of Th2 and Th17 responses driving pulmonary inflammation induced by exposure to house dust mite

T-cell intracellular antigen-1 (TIA-1) is a translational repressor that dampens the production of proinflammatory cytokines and enzymes. In this study we investigated the role of TIA-1 in a mouse model of pulmonary inflammation induced by exposure to the allergenic extract (Df) of the house dust mite Dermatophagoides farinae. When intranasally challenged with a low dose of Df, mice lacking TIA-1 protein (Tia-1(-/-)) showed more severe airway and tissue eosinophilia, infiltration of lung bronchovascular bundles, and goblet cell metaplasia than wild-type littermates. Tia-1(-/-) mice also had higher levels of Df-specific IgE and IgG(1) in serum and ex vivo restimulated Tia-1(-/-) lymph node cells and splenocytes transcribed and released more Th2/Th17 cytokines. To evaluate the site of action of TIA-1, we studied the response to Df in bone marrow chimeras. These experiments revealed that TIA-1 acts on both hematopoietic and non-hematopoietic cells to dampen pulmonary inflammation. Our results identify TIA-1 as a negative regulator of allergen-mediated pulmonary inflammation in vivo. Thus, TIA-1 might be an important player in the pathogenesis of bronchial asthma.

Mast cell interleukin-2 production contributes to suppression of chronic allergic dermatitis

The incidence of chronic allergic dermatitis is rapidly increasing. Regulatory control of this disease has not been adequately explored. Here we report that mast cell-derived interleukin-2 (IL-2) contributes to the suppression of chronic allergic dermatitis. Mice deficient in IL-2 production, or deficient in mast cells (Kit(W-sh/W-sh)), showed exacerbated dermatitis upon repeated oxazolone challenge when compared to their wild-type counterparts. Adoptive transfer of wild-type, but not Il2(-/-), mast cells into Kit(W-sh/W-sh) mice dampened the inflammatory response. During the course of disease, mast cell expansion occurred at the site of inflammation and also in the spleen, where production of IL-2 by mast cells was markedly enhanced. In the absence of mast cell IL-2 production, the ratio of activated to regulatory T cells at the site of inflammation was increased. Thus, MC-derived IL-2 contributes to the maintenance of suppression in chronic allergic skin inflammation.

Immunobiology of intestinal eosinophils - a dogma in the changing?

Infiltration of eosinophils into the intestinal mucosa is a typical hallmark of antiparasite immune responses and inflammatory disorders of the intestinal tract, and eosinophils are thought to contribute to these processes by release of their cytotoxic granule content. However, utilizing novel tools to study eosinophils, it has been recognized that eosinophils are constitutively present in the gastrointestinal tract. In addition, as the dogmatic antiparasite function of eosinophils has proven difficult to document experimentally, it has become increasingly clear that eosinophils are likely to have a more complex role than previously appreciated. Thus, the prevailing dogma of eosinophils merely as antiparasitic effector cells is changing. Instead, it has been suggested that eosinophils can contribute also to several other processes in the intestinal mucosa, e.g. local tissue homeostasis and adaptive immune responses. This review describes the current knowledge regarding the characteristics and functions of intestinal eosinophils, and the regulation of eosinophil trafficking to the intestinal mucosa during the steady state and inflammation. Finally, potential additional and new roles of intestinal eosinophils in the intestinal mucosal immune system are discussed.

The purinergic G protein-coupled receptor 6 inhibits effector T cell activation in allergic pulmonary inflammation

We show that the P2Y(6) receptor, a purinergic G protein-coupled receptor with a high affinity for the nucleotide uridine diphosphate, is an important endogenous inhibitor of T cell function in allergic pulmonary inflammation. Mice conditionally deficient in P2Y(6) receptors [p2ry6 (flox/flox);cre/+ mice] exhibited severe airway and tissue pathology relative to P2Y(6)-sufficient [p2ry6 (flox/flox)] littermates (+/+ mice) when treated intranasally with an extract of the dust mite Dermatophagoides farinae (Df). P2Y(6) receptors were inducibly expressed by lung, lymph node, and splenic CD4(+) and CD8(+) T cells of Df-treated +/+ mice. Df-restimulated P2Y(6)-deficient lymph node cells produced higher levels of Th1 and Th2 cytokines, and polyclonally stimulated P2Y(6)-deficient CD4(+) T cells proliferated faster than comparably stimulated P2Y(6)-sufficient cells. The absence of P2Y(6) receptors on CD4(+) cells, but not APCs, was sufficient to amplify cytokine generation. Thus, P2Y(6) receptors protect the lung against exuberant allergen-induced pulmonary inflammation by inhibiting the activation of effector T cells.

Eosinophils in the zebrafish: prospective isolation, characterization, and eosinophilia induction by helminth determinants

Eosinophils are granulocytic leukocytes implicated in numerous aspects of immunity and disease. The precise functions of eosinophils, however, remain enigmatic. Alternative models to study eosinophil biology may thus yield novel insights into their function. Eosinophilic cells have been observed in zebrafish but have not been thoroughly characterized. We used a gata2:eGFP transgenic animal to enable prospective isolation and characterization of zebrafish eosinophils, and demonstrate that all gata2(hi) cells in adult hematopoietic tissues are eosinophils. Although eosinophils are rare in most organs, they are readily isolated from whole kidney marrow and abundant within the peritoneal cavity. Molecular analyses demonstrate that zebrafish eosinophils express genes important for the activities of mammalian eosinophils. In addition, gata2(hi) cells degranulate in response to helminth extract. Chronic exposure to helminth- related allergens resulted in profound eosinophilia, demonstrating that eosinophil responses to allergens have been conserved over evolution. Importantly, infection of adult zebrafish with Pseudocapillaria tomentosa, a natural nematode pathogen of teleosts, caused marked increases in eosinophil number within the intestine. Together, these observations support a conserved role for eosinophils in the response to helminth antigens or infection and provide a new model to better understand how parasitic worms activate, co-opt, or evade the vertebrate immune response.

Involvement of mast cells in eosinophilic esophagitis

BACKGROUND

Eosinophilic esophagitis (EE) is an emerging disorder with poorly understood pathogenesis.

OBJECTIVE

Whereas prior studies have primarily focused on the role of eosinophils in disease diagnosis and pathogenesis, this study investigates the involvement of mast cells.

METHODS

Total and degranulated mast cell counts were correlated to microarray and RT-PCR data to generate transcriptome expression profiles related to mast cell number and degranulation in patients with EE and healthy control subjects.

RESULTS

Esophageal mastocytosis and mast cell degranulation were readily apparent in patients with EE compared with control subjects (P < .01), as assessed by staining for total mast cells and the presence of extracellular mast cell tryptase (P < .01). Microarray analysis revealed that mast cell levels correlated with the dysregulation of 0.8% (301 genes) of the genome, which was partially distinct from the genes that correlated with tissue eosinophilia. The expression of transcripts for the mast cell proteases carboxypeptidase A3 and tryptase, but not chymase, correlated with mast cell levels and distinguished patients with EE from control subjects. Suprabasilar mast cell counts (P < .01) and degranulation (P < .01) were proportional with KIT ligand mRNA expression. Treatment of patients with EE with swallowed fluticasone propionate normalized levels of mast cells and the mast cell-related transcriptome in responder patients.

CONCLUSION

Herein we have identified local mastocytosis and mast cell degranulation in the esophagi of patients with EE; identified an esophageal mast cell-associated transcriptome that is significantly divergent from the eosinophil-associated transcriptome, with carboxypeptidase A3 mRNA levels serving as the best mast cell surrogate marker; and provided evidence for the involvement of KIT ligand in the pathogenesis of EE.

Inhibition of Th2 adaptive immune responses and pulmonary inflammation by leukocyte Ig-like receptor B4 on dendritic cells

We previously established that the inhibitory receptor LILRB4 mitigates LPS-induced, neutrophil-dependent pathologic effector mechanisms in inflammation. We now report that LILRB4 on dendritic cells (DCs) counterregulates development of an adaptive Th2 immune response and ensuing inflammation in a model of allergic pulmonary inflammation, initiated by inhalation sensitization with OVA and LPS followed by airway challenge with OVA. We found that Lilrb4(-/-) mice had significantly exacerbated eosinophilic pulmonary inflammation, as assessed in bronchoalveolar lavage and lung tissue, as well as elevated levels of OVA-specific IgE and Th2 cytokines produced by OVA-restimulated lymph node cells. LILRB4 was preferentially expressed on MHC class II(high)CD86(high) OVA-bearing DCs in lung-draining lymph nodes after sensitization or challenge. Moreover, the lymph nodes of Lilrb4(-/-) mice had significantly more of these mature DCs after challenge with OVA, which was accompanied by significantly more IL-4-producing lymphocytes, compared with Lilrb4(+/+) mice. Sensitization of naive Lilrb4(+/+) mice by transfer of OVA-LPS-pulsed Lilrb4(-/-) bone marrow-derived DCs was sufficient to confer exacerbated allergic lung pathology upon challenge with OVA, compared with mice that received Lilrb4(+/+) bone marrow-derived DCs. Our findings establish that maturation and migration of pulmonary DCs to lymph nodes in response to Ag and an innate immune stimulus is associated with upregulated expression of LILRB4. In addition, this receptor attenuates the number of these mature DCs and attendant IL-4-producing lymphocytes in the lymph nodes, and accordingly, the ability of DCs to elicit pathologic Th2 pulmonary inflammation.

Characterization of cis-regulatory elements conferring mercury-induced interleukin-4 gene expression in rat mast cells: a role for signal transducer and activator of transcription 6 and TATA box binding sites

We have previously shown that oxidative stress is involved in the pathogenesis of a mercuric chloride (HgCl(2))-induced, T helper type 2 (Th2)-driven autoimmune syndrome in Brown Norway (BN) rats. In the context of the syndrome, the oxidative stress-induced mast cell response seems to determine the development of the early phase of vasculitis, while oxidative stress-mediated interleukin (IL)-4 production may contribute to the subsequent Th2-driven autoimmune response. However, the molecular basis of IL-4 gene transcription induced by HgCl(2) in mast cells remains unknown. In the present study, we dissect the critical regulatory mechanisms in the IL-4 gene promoter in the rat mast cell line RBL-2H3. Immunoprecipitation provided evidence that treatment with HgCl(2) increased phosphorylation of signal transducer and activator of transcription 6 (STAT6). Transient transfection reporter analyses with a series of 5' end deletions of the IL-4 promoter produced evidence that STAT6 and TATA box binding sites are important in HgCl(2)-induced IL-4 gene expression. Subsequent elimination of one or both sites by site-directed mutagenesis significantly inhibited IL-4 promoter activity. Our results provide evidence that STAT6 and TATA box regulatory elements play an important role in HgCl(2)-induced IL-4 transcription in rat mast cells.

Relationship between mast cells and the colitis with relapse induced by trinitrobenzesulphonic acid in Wistar rats

The present study aimed to clarify the role of mast cells in colitis with relapse induced in Wistar rats by trinitrobenzenosulphonic acid. Colitis induction increased the histamine concentration in the colon, which peaked on day 26. The number of mast cells, probably immature, was ten times higher on day 8. Different from animals infected with intestinal parasites, after colitis remission, mast cells do not migrate to the spleen, showing that mast cell proliferation presents different characteristics depending on the inflammation stimuli. Treatment with sulfasalazine, doxantrazole, quercetin, or nedocromil did not increase the histamine concentration or the mast cell number in the colon on day 26, thereby showing absence of degranulation of these cells. In conclusion, although mast cell proliferation is associated with colitis, these cells and their mediators appear to play no clear role in the colitis with relapses.

Comparison of histochemical methods for murine eosinophil detection in an RSV vaccine-enhanced inflammation model

A comparative study of histochemical detection of eosinophils in fixed murine tissue is lacking. Five histochemical methods previously reported for eosinophil detection were quantitatively and qualitatively compared in an established murine RSV vaccine-enhanced inflammation model. Nonspecific neutrophil staining was evaluated in tissue sections of neutrophilic soft tissue lesions and bone marrow from respective animals. Eosinophils had granular red to orange-red cytoplasmic staining, depending on the method, whereas neutrophils had, when stained, a more homogenous cytoplasmic pattern. Nonspecific background staining of similar coloration was variably seen in vascular walls and erythrocytes. Astra Blue/Vital New Red, Congo Red, Luna, Modified Hematoxylin and Eosin, and Sirius Red techniques were all effective in detecting increased eosinophil recruitment compared to controls; however, differences in eosinophil quantification varied significantly between techniques. Astra Blue/Vital New Red had the best specificity for differentiating eosinophils and neutrophils but had a reduced ability to enumerate eosinophils and was the most time intensive. The Luna stain had excessive nonspecific staining of tissues and a reduced enumeration of infiltrating eosinophils, which made it suboptimal. For multiple parameters such as eosinophil detection, specificity, and contrast with background tissues, the Sirius Red followed by Congo Red and Modified Hematoxylin and Eosin methods were useful, each with their own staining qualities.

Eosinophils and Trichinella infection: toxic for the parasite and the host?

Peripheral blood and tissue eosinophilia characterize trichinellosis in humans, and present in addition to the increased total IgE levels that occur in many helminth infections. Both processes are the consequence of T-helper 2 activation. Blood and tissue eosinophilia begins with eosinophilopoiesis in the bone marrow, which is followed by the migration of eosinophils through the circulatory system, the eosinophil infiltration of tissues at the inflammatory foci and, finally, degranulation and cell death. Recently, some aspects of eosinophilia caused by Trichinella spiralis infection have been elucidated; however, the protective role of this population of cells against Trichinella parasites remains controversial. Furthermore, when eosinophils are numerous, they can be toxic for host tissues. This review discusses these issues in both human and rodent infection models.

Mouse mast cell tryptase mMCP-6 is a critical link between adaptive and innate immunity in the chronic phase of Trichinella spiralis infection

Although the innate immune function of mast cells in the acute phase of parasitic and bacterial infections is well established, their participation in chronic immune responses to indolent infection remains incompletely understood. In parasitic infection with Trichinella spiralis, the immune response incorporates both lymphocyte and mast cell-dependent effector functions for pathogen eradication. Among the mechanistic insights still unresolved in the reaction to T. spiralis are the means by which mast cells respond to parasites and the mast cell effector functions that contribute to the immunologic response to this pathogen. We hypothesized that mast cell elaboration of tryptase may comprise an important effector component in this response. Indeed, we find that mice deficient in the tryptase mouse mast cell protease-6 (mMCP-6) display a significant difference in their response to T. spiralis larvae in chronically infected skeletal muscle tissue. Mechanistically, this is associated with a profound inability to recruit eosinophils to larvae in mMCP-6-deficient mice. Analysis of IgE-deficient mice demonstrates an identical defect in eosinophil recruitment. These findings establish that mast cell secretion of the tryptase mMCP-6, a function directed by the activity of the adaptive immune system, contributes to eosinophil recruitment to the site of larval infection, thereby comprising an integral link in the chronic immune response to parasitic infection.

CD4 T cells activated in the mesenteric lymph node mediate gastrointestinal food allergy in mice

A localized Th2 milieu has been observed in the intestine of subjects with food allergic disorders; however, the role of T cells in the pathophysiology of these disorders remains poorly understood. Our aim was to examine sites of T cell activation in response to food challenge, identify potential factors responsible for T cell recruitment to the gut, and determine the role of T cells in disease. BALB/c mice were systemically sensitized to ovalbumin (OVA) and repeatedly fed with OVA to induce allergic diarrhea. Local cytokine and chemokine expressions were assessed by quantitative PCR, and cytokine secretion levels in the mesenteric lymph node (MLN) were determined by ELISA. Homing molecule expression was determined by flow cytometry, and the role of CD4(+) T cells in promoting disease was tested by adoptive transfer. Mice developed diarrhea associated with changes in epithelial ion transport, mast cell infiltration, intestinal IgE secretion, and local upregulation of Th2 cytokines and the Th2 chemokines CCL1, CCL17, and CCL22 in the small intestine. T cell activation occurred in the MLN before symptom onset, and a single feed of OVA induced T cell proliferation, alpha(4)beta(7) upregulation, and CD62L downregulation. Cells from the MLN, including purified CD4(+) T cells, were able to transfer allergic diarrhea to naive mice. A gut-homing phenotype induced in the MLN and selective upregulation of Th2 chemoattractants are likely important factors in the gastrointestinal recruitment of pathological Th2-skewed CD4(+) T cells in food allergy.

The BH3-only protein Puma plays an essential role in cytokine deprivation induced apoptosis of mast cells

Mast cells play critical roles in the regulation of inflammation. One characteristic feature of mast cells is their relatively long lifespan in vivo. Members of the Bcl-2 protein family are regulators of cell survival and apoptosis, where the BH3-only proteins are critical proapoptotic proteins. In this study we investigated the role of the BH3-only proteins Noxa, Bad, Bim, Bmf, Bid, and Puma in apoptosis of mucosal-like mast cells (MLMCs) and connective tissue-like mast cells (CTLMCs). We demonstrate that Puma is critical for the induction of mast-cell death following cytokine deprivation and treatment with the DNA-damaging agent etoposide in MLMCs and CTLMCs. Using p53-/- mast cells, we found that cytokine deprivation-induced apoptosis, in contrast to that elicited by etoposide, is p53-independent. Interestingly, mast cells deficient in FOXO3a, previously proposed as a transcription factor for Puma induction in response to growth factor deprivation, were markedly resistant to cytokine withdrawal compared with wild-type cells. Moreover, overexpression of phosphorylation-deficient, constitutively active FOXO3a caused an up-regulation of Puma. In conclusion, our data demonstrate a pivotal role for Puma in the regulation of cytokine deprivation-induced mast-cell apoptosis and suggest a plausible role for Puma in the regulation of mast cell numbers in vivo.

Pathways of murine mast cell development and trafficking: tracking the roots and routes of the mast cell

The appreciation of the role of the mast cell (MC) in inflammatory processes has expanded dramatically during the last decade. Many of these processes, especially more prolonged responses, are accompanied by an increase in the number of MCs, and much of this increase is likely because of recruitment of immature progenitors with subsequent maturation under the control of the tissue microenvironment. We have begun to identify many of the cell-surface molecules that control this influx and have traced the development of these cells back to their hematopoietic roots. This development proceeds along the myelomonocytic pathway with distinct intermediates having been identified in both bone marrow and spleen. The expression of alpha4beta7 integrins has played a prominent role in this process, as it helped identify a bipotent basophil MC precursor in the spleens of C57BL/6 mice. This integrin also controls basal influx into the intestine and, along with alpha4beta1 integrins, plays a critical role in recruitment to inflamed lungs. Investigation of chemokines and chemokine receptors in these processes led to the identification of a dual role for the murine interleukin-8 receptor CXCR2. This alpha-chemokine receptor affects MC progenitor trafficking by its expression by MC progenitors and by its expression on stromal cells, likely endothelium, affecting trafficking to both intestine under basal conditions and lung during inflammatory recruitment.

Dendritic cell expression of the transcription factor T-bet regulates mast cell progenitor homing to mucosal tissue

The transcription factor T-bet was identified in CD4⁺ T cells, and it controls interferon γ production and T helper type 1 cell differentiation. T-bet is expressed in certain other leukocytes, and we recently showed (Lord, G.M., R.M. Rao, H. Choe, B.M. Sullivan, A.H. Lichtman, F.W. Luscinskas, and L.H. Glimcher. 2005. Blood. 106:3432–3439) that it regulates T cell trafficking. We examined whether T-bet influences homing of mast cell progenitors (MCp) to peripheral tissues. Surprisingly, we found that MCp homing to the lung or small intestine in T-bet^−/− mice is reduced. This is reproduced in adhesion studies using bone marrow–derived MCs (BMMCs) from T-bet^−/− mice, which showed diminished adhesion to mucosal addresin cellular adhesion molecule–1 (MAdCAM-1) and vascular cell adhesion molecule–1 (VCAM-1), endothelial ligands required for MCp intestinal homing. MCp, their precursors, and BMMCs do not express T-bet, suggesting that T-bet plays an indirect role in homing. However, adoptive transfer experiments revealed that T-bet expression by BM cells is required for MCp homing to the intestine. Furthermore, transfer of WT BM-derived dendritic cells (DCs) to T-bet^−/− mice restores normal MCp intestinal homing in vivo and MCp adhesion to MAdCAM-1 and VCAM-1 in vitro. Nonetheless, T-bet^−/− mice respond vigorously to intestinal infection with Trichinella spiralis, eliminating a role for T-bet in MC recruitment to sites of infection and their activation and function. Therefore, remarkably, T-bet expression by DCs indirectly controls MCp homing to mucosal tissues.

Acute trichinellosis increases susceptibility to Giardia lamblia infection in the mouse model

The intestinal protozoan parasite Giardia lamblia causes diarrhoea in humans and animals. In the present study, we used the C57BL/6 inbred mouse model to assess the impact of a nematode (Trichinella spiralis) infection on the course of a G. lamblia (clone GS/M-83-H7) infection. Acute trichinellosis coincided with transient intestinal inflammation and generated an intestinal environment that strongly promoted growth of G. lamblia trophozoites although the local anti-Giardia immunoglobulin (Ig) A production was not affected. This increased G. lamblia infection intensity correlated with intestinal mast cell infiltration, mast cell degranulation, and total IgE production. Furthermore, a G. lamblia single-infection investigated in parallel also resulted in intestinal mast cell accumulation but severe infiltration was triggered in the absence of IgE. Recently, intestinal mast cells emerging during a G. lamblia infection were reported to be involved in those immunological mechanisms that control intestinal proliferation of the parasite in mice. This anti-giardial activity was assumed to be related to the capacity of mast cells to produce IL-6. However, this previous assumption was questioned by our present immunohistological findings indicating that murine intestinal mast cells, activated during a G. lamblia infection were IL-6-negative. In the present co-infection experiments, mast cells induced during acute trichinellosis were not able to control a concurrent G. lamblia infection. This observation makes it feasible that the T. spiralis infection created an immunological and physiological environment that superimposed the anti-giardial effect of mast cells and thus favoured intestinal growth of G. lamblia trophozoites in double-infected mice. Furthermore, our findings raise the possibility that intestinal inflammation e.g. as a consequence of a 'pre-existing' nematode infection is a factor which contributes to increased susceptibility of a host to a G. lamblia infection. The phenomenon of a 'pre-existing' nematode infection prior to a G. lamblia infection is a frequent constellation in endemic areas of giardiasis and may therefore have a direct impact on the epidemiological situation of the disease.

Cysteinyl leukotrienes regulate Th2 cell-dependent pulmonary inflammation

The Th2 cell-dependent inflammatory response is a central component of asthma, and the ways in which it is regulated is a critical question. The cysteinyl leukotrienes (cys-LTs) are 5-lipoxygenase pathway products implicated in asthma, in particular, by their function as smooth muscle constrictors of airways and microvasculature. To elucidate additional roles for cys-LTs in the pathobiology of pulmonary inflammation, we used an OVA sensitization and challenge protocol with mice lacking leukotriene C(4) synthase (LTC(4)S), the terminal enzyme for cys-LT generation. Ag-induced pulmonary inflammation, characterized by eosinophil infiltration, goblet cell hyperplasia with mucus hypersecretion, and accumulation and activation of intraepithelial mast cells was markedly reduced in LTC(4)S(null) mice. Furthermore, Ag-specific IgE and IgG1 in serum, Th2 cell cytokine mRNA expression in the lung, and airway hyperresponsiveness to methacholine were significantly reduced in LTC(4)S(null) mice compared with wild-type controls. Finally, the number of parabronchial lymph node cells from sensitized LTC(4)S(null) mice and their capacity to generate Th2 cell cytokines ex vivo after restimulation with Ag were also significantly reduced. In contrast, delayed-type cutaneous hypersensitivity, a prototypic Th1 cell-dependent response, was intact in LTC(4)S(null) mice. These findings provide direct evidence of a role for cys-LTs in regulating the initiation and/or amplification of Th2 cell-dependent pulmonary inflammation.

T cell proliferation by direct cross-talk between OX40 ligand on human mast cells and OX40 on human T cells: comparison of gene expression profiles between human tonsillar and lung-cultured mast cells

Mast cells (MCs) are the primary effector cells in allergic reactions and have also been found to activate T cells and to reside in close physical proximity to T cells. However, the molecular mechanisms involved in the MC-T cell interaction remain unclear. We hypothesized that human tonsillar MCs, which locate in the interfollicular areas, might interact with T cells. Thus, we first established a culture system of human tonsillar MCs and then compared gene expression profiles of tonsillar MCs with that of lung MCs before and after aggregation of FcepsilonRI by using high-density oligonucleotide probe arrays. Here we show that resting tonsillar MCs, when compared with lung MCs, revealed significantly higher expression levels for CC chemokines (CCL3 and 4), which recruit T cells, and for TNFR superfamilies (OX40 ligand and 4-1BB ligand), which induce proliferation of T cells. After aggregation of FcepsilonRI, not only tonsillar MCs but also lung MCs up-regulated the expression of these molecules. We confirmed that T cell proliferation is induced in direct cross-talk by the MC surface molecule OX40 ligand. These results suggest that human MCs may play important roles in adaptive immunity through the T cell responses.

Mast cells in inflammatory arthritis

Mast cells are present in limited numbers in normal human synovium, but in rheumatoid arthritis and other inflammatory joint diseases this population can expand to constitute 5% or more of all synovial cells. Recent investigations in a murine model have demonstrated that mast cells can have a critical role in the generation of inflammation within the joint. This finding highlights the results of more than 20 years of research indicating that mast cells are frequent participants in non-allergic immune responses as well as in allergy. Equipped with a diversity of surface receptors and effector capabilities, mast cells are sentinels of the immune system, detecting and delivering a first response to invading bacteria and other insults. Accumulating within inflamed tissues, mast cells produce cytokines and other mediators that may contribute vitally to ongoing inflammation. Here we review some of the non-allergic functions of mast cells and focus on the potential role of these cells in murine and human inflammatory arthritis.

Expression profiling reveals novel innate and inflammatory responses in the jejunal epithelial compartment during infection with Trichinella spiralis

Infection with intestinal nematodes induces profound pathological changes to the gut that are associated with eventual parasite expulsion. We have applied expression profiling as an initial screening process with oligonucleotide microarrays (Affymetrix MG-U74AV2 gene chips) and time course kinetics to investigate gene transcription triggered by the intraepithelial nematode Trichinella spiralis in jejunal epithelium from BALB/c mice. Of the 4,114 genes detected, 2,617 were present in all uninfected and T. spiralis-infected replicates, 8% of which were notably upregulated, whereas 12% were downregulated at the time of worm expulsion (day 14 postinfection). Upregulation of goblet cell mucin gene transcripts intestinal mucin gene 3 (MUC3), calcium chloride channel 5 (CLCA5), and goblet cell gene 4 (GOB4) is consistent with enhanced production and alteration of mucus, whereas a 60- to 70-fold upregulation of transcripts for mast cell proteases 1 and 2 (MCPT-1 and -2) is consistent with intraepithelial mucosal mast cell recruitment. Importantly, there was novel expression of sialyltransferase 4C (SIAT4C), small proline-rich protein 2A (SPRR2A), and resistin-like molecule beta (RELMbeta) on day 14 postinfection. In contrast, DNase I and regenerating protein 3 (REG3) transcripts were substantially downregulated. Time course analyses revealed early (within 48 h of infection) induction of Siat4c, Sprr2A, and Relmbeta and later (within 120 h) induction of Mcpt-1 and -2. The findings demonstrate early innate responses and later inflammatory changes within the epithelium. The early epithelial responses may be associated both with repair (Sprr2A) and with the development of innate immunity (Siat4c and Relmbeta).

Attenuation of Th1 effector cell responses and susceptibility to experimental allergic encephalomyelitis in histamine H2 receptor knockout mice is due to dysregulation of cytokine production by antigen-presenting cells

Histamine, a biogenic amine with both neurotransmitter and vasoactive properties, is well recognized as an immunomodulatory agent in allergic and inflammatory reactions. It also plays a regulatory role in the development of antigen-specific immune responses. CD4+ T-cells from histamine H1 receptor (H1R)-deficient (H1RKO) mice produce significantly less interferon-gamma and more interleukin (IL)-4 in in vitro recall assays compared to wild-type controls. H1RKO mice are also less susceptible to acute early-phase experimental allergic encephalomyelitis indicating that H1R signaling in CD4+ T cells plays a central role in regulating pathogenic T-cell responses. In this study, we show that mice lacking histamine H2 receptor (H2RKO) are similar to H1RKO mice in that they develop encephalitogen-specific T-cell responses as assessed by proliferation and IL-2 production and present with less severe acute early-phase experimental allergic encephalomyelitis. However, unlike T cells from H1RKO mice, which exhibit a strong Th2 bias, T cells from H2RKO mice do not. Rather, they are uniquely characterized by a significant inhibition of Th1 effector cell responses. Given that both histamine and adjuvants such as pertussis toxin modulate antigen-presenting cell (APC) maturation and function, including T-cell-polarizing activity, we analyzed the cytokines/chemokines secreted by APCs from wild-type, H1RKO, and H2RKO mice. Significant differences in cytokine/chemokine production by APCs from unimmunized and immunized mice were delineated. APCs from H2RKO mice produce significantly less IL-12 and IL-6 and markedly greater amounts of MCP-1 compared to wild-type and H1RKO mice. Because MCP-1 is known to inhibit IL-12 production, the failure of H2RKO mice to generate encephalitogenic Th1 effector cell responses is consistent with inhibition of negative regulation of MCP-1 secretion by H2R signaling in APCs.

Cysteinyl leukotriene 1 receptor controls the severity of chronic pulmonary inflammation and fibrosis

The cysteinyl leukotrienes (cys-LTs), leukotriene (LT) C(4), LTD(4), and LTE(4), are smooth muscle constrictors that signal via the CysLT(1) receptor. Here we report that the cys-LTs play an important role in chronic pulmonary inflammation with fibrosis induced by bleomycin in mice. Targeted disruption of LTC(4) synthase, the pivotal enzyme for cys-LT biosynthesis, protected significantly against alveolar septal thickening by macrophages and fibroblasts and collagen deposition. In contrast, targeted disruption of the CysLT(1) receptor significantly increased both the concentration of cys-LTs in the bronchoalveolar lavage fluid and the magnitude of septal thickening as defined by morphology, digital image analysis, and deposition of reticular fibers. These findings change our understanding of the pathobiology mediated by the cys-LTs by revealing their role in chronic inflammation with fibrosis, likely via the CysLT(2) receptor, and by uncovering a dual role for the CysLT(1) receptor, namely proinflammatory acute constriction of smooth muscle and antiinflammatory counteraction of chronic injury.

IL-10 Inhibits FcεRI Expression in Mouse Mast Cells

FcepsilonRI expression and function is a central aspect of allergic disease. Using bone marrow-derived mouse mast cell populations, we have previously shown that the Th2 cytokine IL-4 inhibits FcepsilonRI expression and function. In the current study we show that the Th2 cytokine IL-10 has similar regulatory properties, and that it augments the inhibitory effects of IL-4. FcepsilonRI down-regulation was functionally significant, as it diminished inflammatory cytokine production and IgE-mediated FcepsilonRI up-regulation. IL-10 and IL-4 reduced FcepsilonRI beta protein expression without altering the alpha or gamma subunits. The ability of IL-4 and IL-10 to alter FcepsilonRI expression by targeting the beta-chain, a critical receptor subunit known to modulate receptor expression and signaling, suggests the presence of a Th2 cytokine-mediated homeostatic network that could serve to both initiate and limit mast cell effector function.

IgE Enhances Parasite Clearance and Regulates Mast Cell Responses in Mice Infected withTrichinella spiralis

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.

Mast Cells Exert Effects Outside the Central Nervous System to Influence Experimental Allergic Encephalomyelitis Disease Course

Previous studies using mast cell-deficient mice (W/W(v)) revealed that mast cells influence disease onset and severity of experimental allergic/autoimmune encephalomyelitis (EAE), the murine model for multiple sclerosis. The mast cell populations of these mice can be restored by transferring bone marrow-derived mast cells (BMMCs). Studies using the W/W(v) reconstitution model have lead to major advances in our understanding of mast cell roles in vivo. However, despite its common use, details regarding the sites and kinetics of mast cell repopulation have remained largely uncharacterized. In this study, we examined the kinetics and tissue distribution of green fluorescent protein(+) BMMCs in reconstituted W/W(v) mice to identify sites of mast cell influence in EAE. Reconstitution of naive animals with BMMCs does not restore mast cell populations to all organs, notably the brain, spinal cord, lymph nodes, and heart. Despite the absence of mast cells in the CNS, reconstituted mice exhibit an EAE disease course equivalent to that induced in wild-type mice. Mast cells are found adjacent to T cell-rich areas of the spleen and can migrate to the draining lymph node after disease induction. These data reveal that mast cells can act outside the CNS to influence EAE, perhaps by affecting the function of autoreactive lymphocytes.

The role of mast cells in allergy and autoimmunity

Two potential outcomes of dysregulated immunity are allergy and autoimmunity. Both are characterized by localized inflammation that leads to the injury and/or destruction of target tissues. Until recently, it was generally accepted that the mechanisms that govern these disease processes are quite disparate; however, new discoveries suggest that the mast cell may underlie much of the pathology in both these disease syndromes. Amongst these discoveries is the observation that mast cell-deficient mice exhibit significantly reduced disease severity compared to wild-type littermates in a murine model of multiple sclerosis (MS) and drugs that block mast cell function can improve clinical symptoms in this model. In addition, gene microarray analysis has revealed that the expression of several mast cell-specific genes is increased in the central nervous system plaques of MS patients. Although well established as effector cells in allergic inflammation, the location of mast cells and the wealth of inflammatory mediators they express make it likely that they have profound effects on many other autoimmune processes.

Mechanisms underlying mast cell influence on EAE disease course

It is well established that CD4(+) T cells are of central importance in mediating the autoimmune destruction associated with the neurological demyelinating disease Multiple sclerosis (MS) and the rodent model of MS, EAE (experimental allergic encephalomyelitis). However, other cells also play a critical role in the inflammatory events that lead to the varying degrees of myelin and axonal damage observed in this disease syndrome. In this review, we present evidence that mast cells, best studied in the context of allergic disease, contribute to EAE disease pathology. Using mast cell-deficient mice, we demonstrate that mast cells are necessary for the full manifestation of MOG-induced EAE disease and show that cross-linking of Fc receptors is one mechanism of mast cell activation in disease. In addition, we provide evidence that mast cells exert influences outside the CNS, perhaps through the effects on the generation of the anti-MOG T cell response.

CCR3 is required for tissue eosinophilia and larval cytotoxicity after infection with Trichinella spiralis

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.

Mast cell growth, differentiation, and death

Mast cells (MC) begin development in the bone marrow. Following initial lineage commitment, the cells move into the vasculature as a committed progenitor (MCp) that is poorly phenotypically defined, but appears to be an agranular cell lacking the high-affinity IgE receptor characteristic of the mature tissue-localized MC. Full maturation occurs after the cells move into the various tissues. In the mouse, MCp localizing in the connective tissues appear to differentiate into mature MC, whereas those localizing in the lung and mucosal compartment of the small intestine remain largely as committed MCp. Movement of the MCp into the small intestine is controlled by the alpha 4 beta 7 integrin, whereas the factors controlling movement into other tissues remain to be defined. Following an inflammatory stimulus, Th2-derived cytokines drive the maturation process of these MCps, leading to the mature mucosal MC hyperplasia associated with events such as an intestinal helminth infection and possibly human allergy such as asthma and rhinitis. The expanded MC number disappears as the stimulus resolves. Various routes are used in the resolution of the MC hyperplasia including apoptosis, shedding along with the villous epithelium, and recirculation back to the spleen for elimination. Unlike the reactive MC that appears in association with inflammation, the connective tissue-localized MC is a long-lived radiation-resistant cell, which appears to depend principally on the presence of stem cell factor (SCF) for its persistence.

CCR3 is essential for skin eosinophilia and airway hyperresponsiveness in a murine model of allergic skin inflammation

The CC chemokine receptor 3 (CCR3) is expressed by eosinophils, mast cells, and Th2 cells. We used CCR3(-/-) mice to assess the role of CCR3 in a murine model of allergic skin inflammation induced by repeated epicutaneous sensitization with ovalbumin (OVA), and characterized by eosinophil skin infiltration, local expression of Th2 cytokines, and airway hyperresponsiveness (AHR) to inhaled antigen. Eosinophils and the eosinophil product major basic protein were absent from the skin of sham and OVA-sensitized CCR3(-/-) mice. Mast cell numbers and expression of IL-4 mRNA were normal in skin of CCR3(-/-) mice, suggesting that CCR3 is not important for infiltration of the skin by mast cells and Th2 cells. CCR3(-/-) mice produced normal levels of OVA-specific IgE, and their splenocytes secreted normal amounts of IL-4 and IL-5 following in vitro stimulation with OVA, indicating effective generation of systemic Th2 helper responses. Recruitment of eosinophils to lung parenchyma and bronchoalveolar lavage (BAL) fluid was severely impaired in CCR3(-/-) mice, which failed to develop AHR to methacholine following antigen inhalation. These results suggest that CCR3 plays an essential role in eosinophil recruitment to the skin and the lung and in the development of AHR.

Eosinophils promote allergic disease of the lung by regulating CD4(+) Th2 lymphocyte function

Eosinophils are primarily thought of as terminal effectors of allergic responses and of parasite elimination. However, limited studies suggest a more discrete immunomodulatory role for this leukocyte during these inflammatory responses. In this investigation, we highlight the potential of eosinophils to act as APCs and thus modulators of allergic responses by influencing Th2 cell function. In response to Ag provocation of the allergic lung, eosinophils rapidly trafficked to sites of Ag deposition (airways lumen) and presentation (lung-associated lymph nodes and T cell-rich paracortical zones). Eosinophils from the allergic lung expressed class II MHC peptides, T cell costimulatory molecules (CD80 and CD86), and rapidly internalized and processed Ag that was sampled from within the airway lumen. Ag-loaded eosinophils promoted the production of IL-4, IL-5, and IL-13 in cocultures with in vitro-polarized Th2 cells and induced IL-5 production in a dose-dependent manner from Ag-specific CD4(+) T cells isolated from allergic mice. In addition, Ag-loaded eosinophils primed for Th2 cell-driven allergic disease of the lung when transferred to naive mice. Thus, eosinophils have the potential to not only activate Th2 cells to release disease-modulating cytokines but also to assist in priming the immune system for allergic responses. This investigation highlights the potential of eosinophils to not only act as terminal effector cells but also to actively modulate allergic inflammation by amplifying Th2 cell responses.

Mast cell lineage development and phenotypic regulation

Three cornerstones of mast cell development are an absolute dependence on the presence of stem cell factor, T-cell-independent and T-cell-dependent tissue mast cell populations derived from a single lineage, and a diversity of phenotypes for mature tissue mast cells as defined by immunohistochemical and biochemical properties. The in vivo biology of the mast cell in the mouse has been deduced through the availability of mice with genetic and induced gene disruptions, whereas limited but compatible findings for the human have been acquired through the study of patients with systemic mastocytosis and T-cell deficiency. The characteristics of mast cells recognized from these in situ circumstances can be used to establish culture systems for obtaining mouse and human mast cells from progenitor cell sources. These cells allow studies of receptor-mediated gene regulation by cytokines derived from both stromal cells and T cells.

Mast cells/basophils in the peripheral blood of allergic individuals who are HIV-1 susceptible due to their surface expression of CD4 and the chemokine receptors CCR3, CCR5, and CXCR4

A population of metachromatic cells with mast cell (MC) and basophil features was identified recently in the peripheral blood of patients with several allergic disorders. This study now shows that these metachromatic cells express on their surface the high-affinity IgE receptor (FcepsilonRI), CD4, and the chemokine receptors CCR3, CCR5, and CXCR4, but not the T-cell surface protein CD3 and the monocyte/macrophage surface protein CD68. This population of MCs/basophils can be maintained ex vivo for at least 2 weeks, and a comparable population of cells can be generated in vitro from nongranulated hematopoietic CD3(-)/CD4(+)/CD117(-) progenitors. Both populations of MCs/basophils are susceptible to an M-tropic strain of human immunodeficiency virus 1 (HIV-1). Finally, many patients with acquired immunodeficiency syndrome have HIV-1-infected MCs/basophils in their peripheral blood. Although it is well known that HIV-1 can infect CD4(+) T cells and monocytes, this finding is the first example of a human MC or basophil shown to be susceptible to the retrovirus. (Blood. 2001;97:3484-3490)

Tryptase 4, a new member of the chromosome 17 family of mouse serine proteases

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 approximately 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.

Delayed expulsion of the nematode Trichinella spiralis in mice lacking the mucosal mast cell-specific granule chymase, mouse mast cell protease-1

Expulsion of gastrointestinal nematodes is associated with pronounced mucosal mast cell (MMC) hyperplasia, differentiation, and activation, accompanied by the systemic release of MMC granule chymases (chymotrypsin-like serine proteases). The beta-chymase mouse mast cell protease-1 (mMCP-1) is expressed predominantly by intraepithelial MMCs, and levels in the bloodstream and intestinal lumen are maximal at the time of worm expulsion in parasitized mice. To address the in vivo functions of MMC-specific beta-chymases, we have generated transgenic mice that lack the mMCP-1 gene. They were backcrossed onto a congenic BALB/c background to investigate the response to nematode infection. The deletion of the mMCP-1 gene is associated with significantly delayed expulsion of Trichinella spiralis and increased deposition of muscle larvae in BALB/c mice despite the presence of normal and sometimes increased numbers of MMCs. Neither worm fecundity nor worm burdens were altered in Nippostrongylus-infected mMCP-1(-/)- BALB/c mice. These data demonstrate, for the first time, that the ablation of an MMC-derived effector molecule compromises the expulsion process.