Mast Cell Cytokine Research Articles

FcεR1 and Toll-Like Receptors Mediate Synergistic Signals to Markedly Augment Production of Inflammatory Cytokines in Murine Mast Cells

RATIONALE: Mast cells mediate both IgE-dependent allergic reactions and protective responses against acute infections possibly through the activation of Toll-like receptors (TLRs). We investigated whether TLR ligands act in synergy with FcεRI receptor.

FcϵR1 and toll-like receptors mediate synergistic signals to markedly augment production of inflammatory cytokines in murine mast cells

AbstractMast cells mediate both IgE-dependent allergic reactions and protective responses against acute infections, possibly through the activation of Toll-like receptors (TLRs). We find that antigen interacts synergistically with TLR2 and TLR4 ligands to markedly enhance production of cytokines in murine mast cell lines. However, the TLR ligands neither stimulated degranulation and release of arachidonic acid nor influenced such responses to antigen, probably because these ligands failed to generate a necessary calcium signal. The enhanced cytokine production could be attributed to synergistic activation of mitogen-activated protein kinases in addition to the engagement of a more effective repertoire of transcription factors for cytokine gene transcription. The synergistic interactions of TLR ligands and antigen might have relevance to the exacerbation of IgE-mediated allergic diseases by infectious agents.

Novel collectin/C1q receptor mediates mast cell activation and innate immunity

Mast cells play a critical role in innate immunity, allergy, and autoimmune diseases. The receptor/ligand interactions that mediate mast cell activation are poorly defined. The alpha2beta1 integrin, a receptor for collagens, laminins, decorin, E-cadherin, matrix metalloproteinase-1 (MMP-1), endorepellin, and several viruses, has been implicated in normal developmental, inflammatory, and oncogenic processes. We recently reported that alpha2 integrin subunit-deficient mice exhibited markedly diminished neutrophil and IL-6 responses during Listeria monocytogenes- and zymosan-induced peritonitis. Peritoneal mast cells require alpha2beta1 integrin expression for activation in response to pathogens, yet the ligand and molecular mechanisms by which the alpha2beta1 integrin induces activation and cytokine secretion remain unknown. We now report that the alpha2beta1 integrin is a novel receptor for multiple collectins and the C1q complement protein. We demonstrate that the alpha2beta1 integrin provides a costimulatory function required for mast cell activation and cytokine secretion. This finding suggests that the alpha2beta1 integrin is not only important for innate immunity but may serve as a critical target for the regulation of autoimmune/allergic disorders.

Increased Expression of Genes Linked to FcεRI Signaling and to Cytokine and Chemokine Production in Lyn-Deficient Mast Cells

Cross-linking the high-affinity IgE receptor, FcepsilonRI, on mast cells activates signaling pathways leading to the release of preformed inflammatory mediators and the production of cytokines and chemokines associated with allergic disorders. Bone marrow-derived mast cells (BMMCs) from Lyn-deficient (Lyn-/-) mice are hyperresponsive to FcepsilonRI cross-linking with multivalent Ag. Previous studies linked the hyperresponsive phenotype in part to increased Fyn kinase activity and reduced SHIP phosphatase activity in the Lyn-/- BMMCs in comparison with wild-type (WT) cells. In this study, we compared gene expression profiles between resting and Ag-activated WT and Lyn-/- BMMCs to identify other factors that may contribute to the hyperresponsiveness of the Lyn-/- cells. Among genes implicated in the positive regulation of FcepsilonRI signaling, mRNA for the tyrosine kinase, Fyn, and for several proteins contributing to calcium regulation are more up-regulated following Ag stimulation in Lyn-/- BMMCs than in WT BMMCs. Conversely, mRNA for the low-affinity IgG receptor (FcgammaRIIB), implicated in negative regulation of FcepsilonRI-mediated signaling, is more down-regulated in Ag-stimulated Lyn-/- BMMCs than in WT BMMCs. Genes coding for proinflammatory cytokines and chemokines (IL-4, IL-6, IL-13, CSF, CCL1, CCL3, CCL5, CCL7, CCL9, and MIP1beta) are all more highly expressed in Ag-stimulated Lyn-/- mast cells than in WT cells. These microarray data identify Lyn as a negative regulator in Ag-stimulated BMMCs of the expression of genes linked to FcepsilonRI signaling and also to the response pathways that lead to allergy and asthma.

Protein kinase C α, βI, and βII isozymes regulate cytokine production in mast cells through MEKK2/ERK5-dependent and -independent pathways

Regulation of MAPK pathways by PKC isoforms was examined in murine bone marrow-derived mast cells (BMMCs). The PKCα, βI, and βII isoforms showed the most robust activation after FcεR1-mediated stimulation by anti-ovalbumin specific IgE and ovalbumin (IgE-ova). PKCα, βI, and βII were all involved in activation of JNK, MEKK2, and ERK5, with differential relative contributions of each isoform to specific MAPK pathway components. BMMCs from mice lacking MEKK2 showed reduced production (50–60%) of IL-6, IL-13, and TNF-α after stimulation, demonstrating MEKK2-dependent and -independent pathways for cytokine production. Cytokine production was stimulated by over-expression of PKC in cells from MEKK2-deficient and wild-type mice. Activation of ERK5 did not occur in BMMCs lacking MEKK2, indicating that MEKK2-independent cytokine production was also ERK5-independent. Since MAPK modules differentially regulate mast cell functions, including degranulation and cytokine production, it is suggested that specific functions could be targeted by inhibiting specific PKC isoforms.

A role for the Mycoplasma pneumoniae adhesin P1 in interleukin (IL)-4 synthesis and release from rodent mast cells

Mycoplasma pneumoniae is a respiratory tract pathogen associated with exacerbations in patients with chronic asthma, yet relatively little is known about the potential role of this organism in asthma pathogenesis. Our previous studies demonstrated that RBL-2H3 mast cells co-cultured with M. pneumoniae released preformed inflammatory mediators, synthesized multiple cytokine mRNA species, and released IL-4 protein. In this study, we sought to determine the mechanism by which M. pneumoniae activates mast cell cytokine production. Cytokine mRNA upregulation and IL-4 protein production in RBL cells were induced almost exclusively by plastic-adherent M. pneumoniae cultures (MpA). Organisms grown under non-adherent conditions (MpN) were unable to induce cytokine responses efficiently. Western blots demonstrated that MpA was enriched for P1, the major M. pneumoniae adhesin, compared to MpN. M. pneumoniae-induced IL-4 release from RBL cells was inhibited >85% by anti-P1 monoclonal antibodies. Additionally, a P1-deficient strain of the bacteria was unable to efficiently induce IL-4 release. Desialation of RBL cell surface glycoproteins by neuraminidase treatment eliminated IL-4 release. We conclude that P1 plays an important role in M. pneumoniae-induced cytokine responses in RBL mast cells and that direct contact between the organism and sialated residues on the RBL surface mediates this activation.

IL-4-Induced Priming of Human Intestinal Mast Cells for Enhanced Survival and Th2 Cytokine Generation Is Reversible and Associated with Increased Activity of ERK1/2 and c-Fos

In synergy with stem cell factor (SCF), IL-4 strongly enhances mast cell proliferation and shifts IgE-dependent cytokine production in mature human mast cells toward an increased release of Th2 cytokines such as IL-3, IL-5, and IL-13 and a decreased IL-6 expression. In this study we analyzed the kinetics and the mechanisms of these IL-4 effects on mast cells purified from intestinal tissue. If the cells were first cultured with IL-4 for 14 days and then without IL-4 for another 14 days, mast cells lost the capacity of producing higher amounts of Th2 cytokines and regained the capacity of producing IL-6. The IL-4-induced up-regulation of mast cell proliferation and FcepsilonRI expression was also reversible if IL-4 was withdrawn for 14 days. Interestingly, in contrast to IL-4, proliferation and phenotype of human intestinal mast cells were not affected by IL-13 although both cytokines were capable of inducing STAT6 activation. Instead, IL-4 treatment (but not IL-13 treatment) was associated with an increased activity of ERK1/2 and c-Fos, the downstream target of ERK1/2 and component of the transcription factor AP-1. Consistently, mast cell proliferation and cytokine expression in response to IL-4 was blocked by the MEK inhibitor PD98059. In summary, our data show that the IL-4 effects on human intestinal mast cell functions are reversible and accompanied by an increased activity of ERK1/2 and c-Fos.

Mast cell accumulation and cytokine expression in the tight skin mouse model of scleroderma

The tight skin (Tsk) mouse develops many pathological changes seen in human scleroderma, such as increased collagen content and mast cell density. Although associations between mast cell expansion and skin fibrosis have been reported, the mechanisms underlying mast cell accumulation remain unclear. In this study, we have measured the density of skin mast cells in Tsk mice and their normal littermates (pa/pa) of 4-36 weeks of age, and in the skin heterografted between Tsk and pa/pa mice. Cytokines related to mast cell differentiation, proliferation and migration were examined by using RNase protection assays. Skin mast cell density in Tsk mice was significantly increased from 12 weeks of age, compared to that in pa/pa mice. The expression of transforming growth factor-beta1 (TGF-beta1), and to a lesser extent, stem cell factor (SCF) and interleukin-15 (IL-15) mRNA was higher in Tsk mice, compared to that in control mice. Mast cell density was unchanged in Tsk skin grafted onto pa/pa hosts, but dramatically increased in pa/pa skin grafted onto Tsk hosts. This latter mast cell hyperplasia was associated with the increases in mRNA levels of TGF-beta1, SCF and IL-15, whereas little change in cytokine levels was seen in heterografted Tsk skin. These results suggest that locally produced cytokines in Tsk skin influence mast cell accumulation in this animal model of human scleroderma.

A role for the Mycoplasma pneumoniae adhesin P1 in Interleukin (IL)-4 Synthesis and release from mast cells

RATIONALE:Mycoplasma pneumoniae is a respiratory tract pathogen that has been associated with exacerbations in patients with asthma, yet relatively little is known about its potential role in asthma pathogenesis. Our previous studies demonstrated that M. pneumoniae activates RBL-2H3 mast cells to release preformed inflammatory mediators, synthesize multiple cytokine mRNA species, and release IL-4 protein. In this study, we examined the mechanism by which M. pneumoniae activates mast cell cytokine production.

The CD200 Receptor Is a Novel and Potent Regulator of Murine and Human Mast Cell Function

CD200R is a member of the Ig supergene family that is primarily expressed on myeloid cells. Recent in vivo studies have suggested that CD200R is an inhibitory receptor capable of regulating the activation threshold of inflammatory immune responses. Here we provide definitive evidence that CD200R is expressed on mouse and human mast cells and that engagement of CD200R by agonist Abs or ligand results in a potent inhibition of mast cell degranulation and cytokine secretion responses. CD200R-mediated inhibition of FcepsilonRI activation was observed both in vitro and in vivo and did not require the coligation of CD200R to FcepsilonRI. Unlike the majority of myeloid inhibitory receptors, CD200R does not contain a phosphatase recruiting inhibitory motif (ITIM); therefore, we conclude that CD200R represents a novel and potent inhibitory receptor that can be targeted in vivo to regulate mast cell-dependent pathologies.

Molecular Mechanisms of CD200 Inhibition of Mast Cell Activation

CD200 and its receptor CD200R are both type I membrane glycoproteins that contain two Ig-like domains. Engagement of CD200R by CD200 inhibits activation of myeloid cells. Unlike the majority of immune inhibitory receptors, CD200R lacks an ITIM in the cytoplasmic domain. The molecular mechanism of CD200R inhibition of myeloid cell activation is unknown. In this study, we examined the CD200R signaling pathways that control degranulation of mouse bone marrow-derived mast cells. We found that upon ligand binding, CD200R is phosphorylated on tyrosine and subsequently binds to adapter proteins Dok1 and Dok2. Upon phosphorylation, Dok1 binds to SHIP and both Dok1 and Dok2 recruit RasGAP, which mediates the inhibition of the Ras/MAPK pathways. Activation of ERK, JNK, and p38 MAPK are all inhibited by CD200R engagement. The reduced activation of these MAPKs is responsible for the observed inhibition of mast cell degranulation and cytokine production. Similar signaling events were also observed upon CD200R engagement in mouse peritoneal cells. These data define a novel inhibitory pathway used by CD200R in modulating mast cell function and help to explain how engagement of this receptor in vivo regulates myeloid cell function.

Nitric Oxide Inhibits IgE-Dependent Cytokine Production and Fos and Jun Activation in Mast Cells

NO is a cell-derived radical reported to inhibit mast cell degranulation and subsequent allergic inflammation, although whether its action is nonspecific or occurs via specific molecular mechanisms remains unknown. To examine this question, we set out to determine whether NO inhibits mast cell cytokine production, and, if so, whether it also alters FcepsilonRI-dependent signal transduction. As hypothesized, the radical inhibited IgE/Ag-induced IL-4, IL-6, and TNF production. Although NO did not influence phosphorylated JNK, p38 MAPK, or p44/42 MAPK, it did inhibit phosphorylation of phospholipase Cgamma1 and the AP-1 transcription factor protein c-Jun, but not NF-kappaB or CREB. NO further completely abrogated IgE/Ag-induced DNA-binding activity of the nuclear AP-1 proteins Fos and Jun. These results show that NO is capable of inhibiting FcepsilonRI-dependent mast cell cytokine production at the level of gene regulation, and suggest too that NO may contribute to resolution of allergic inflammation.

P-21 Activated Kinase 1 (Pak1) Is Critical for Normal Mast Cell Degranulation and Cytokine Production in Response to Antigen Stimulation of the High Affinity IgE Receptor.

Mast cells participate in normal and pathogenic inflammatory processes, including innate host defense, allergy, and asthma. Stimulation of the mast cell high-affinity IgE receptor (FcεR) by receptor cross-linking activates multiple downstream signaling pathways resulting in degranulation and de novo synthesis of multiple cytokines. However, the molecular mechanisms underlying these processes are incompletely defined. It is known that Rac2 deficient murine bone marrow derived mast cells (BMMCs) have impaired degranulation, but the downstream effectors that modulate this function are unknown. We hypothesized that p-21 activated kinase 1 (Pak1), a downstream effector of Rac proteins, is important in degranulation and de novo cytokine synthesis. Mature BMMCs from wild-type (WT) and Pak1 KO mice were sensitized with anti-DNP IgE then stimulated with DNP-HSA to stimulate FcεR. Interestingly, Pak1 KO BMMCs showed significant impairment in degranulation, as demonstrated by a 3-fold reduction in the percent of B-hexosaminidase released upon IgE stimulation. IgE stimulation of mast cell results not only in degranulation, but also in the production of TNFα, which is critical in the early recruitment of neutrophils to sites of acute inflammation. TNFαsynthesis is influenced by a number of transcription factors, many which are regulated by Erk. Since Pak1 has been shown, in overexpression systems, to phosphorylate Raf and Mek to activate Erk, we examined Erk activation in WT and Pak1 KO BMMCs in response to IgE stimulation. Pak1 KO BMMCs have a 50% reduction in phospho-Erk as compared to controls. We then tested another MAPK member important in mast cell cytokine synthesis, p38, and found phospho-p38 to be decreased in Pak1 KO BMMCs as well. Further, IgE-stimulated Pak1 KO BMMCs produce only 20–30% as much TNFαas controls. To define the role of Pak1 in cytokine production as specific for TNFαversus a more global defect, we also studied IL-6 synthesis and are able to report a 50% reduction in IL-6 production by Pak1 KO BMMCs. Our results indicate that Pak1 is important in BMMC degranulation, cytokine production, and MAPK activation in response to FcεR stimulation. These studies identify Pak1 as a potential therapeutic target in pathologic inflammation. Mechanisms by which Pak1 may be influencing mast cell degranulation as well as further study of transcription factors important in mast cell cytokine production are under current investigation.

Preferential Uptake of Gamma Tocopherol by Mast Cells. Does This Uptake Affect Mast Cell Cytokine Production?.

Vitamin E, the main lipid soluble antioxidant, exists in eight different forms, of which α-tocopherol and γ-tocopherol are the two major forms. Previous experiments showed vitamin E uptake by macrophages that contribute to inflammation and immunity. On the other hand, vitamin E has structural similarity to the thiazolidinedione, troglitazone, a peroxisome proliferator-activated receptor (PPAR) agonist. In previous experiments we found that troglitazone (TGZ), a PPAR gamma agonist, had a negative effect on mast cell cytokine production. We therefore wondered whether vitamin E enters human mast cells, and if so, does this modulate mast cell cytokine production? We choose (interleukin) IL-6 for its pro-inflammatory properties and because it's known to be produced by mast cells in response to stimulants used in the experiment. In this study we try to answer these two questions. Cultured human mast cell line (HMC-1) was first incubated for 24 hrs with pharmacological concentrations of both alpha and gamma forms of vitamin E (10 μM). The mast cells were then activated with phorbol-12-myristate-13-acetate [PMA (50ng/ml)] and ionomycin (5μm) for 24 hours and cell-free supernatants collected. In additional experiments, IL-1ß (10ng/mL) was added to activate mast cells. IL-6 levels in the supernatants were determined in each well utilizing ELISA. Mast cell concentrations of alpha or gamma tocopherol were measured by high pressure liquid chromatography [HPLC] and electrochemical analysis. Mast cells pre-incubated in alpha and gamma forms of vitamin E at 10 μM did not affect mast cell IL-6 production. Mast cells, however, showed uptake of both forms of tocopherols but more pronounced uptake of the gamma form (13181.05 pmole/well of gamma compared to 8742.99 pmole/well of alpha tocopherol). We conclude that mast cells appear to store both alpha and gamma tocopherols but preferentially more gamma tocopherol. Though Vitamin E and PPAR agonists have similar structures, they did not show similar effect on mast cell cytokine production, suggesting they might have different mechanisms of action.

Inhibitory activity of Chrysanthemi sibirici herba extract on RBL-2H3 mast cells and compound 48/80-induced anaphylaxis

The effects of extracts from various oriental medicinal herbs on mast cell-mediated allergic reaction were investigated. Among them, Chrysanthemi sibirici herba ethanol extract exerted the potent inhibitory activity on antigen-induced degranulation in RBL-2H3 mast cells. Chrysanthemi sibirici herba dose-dependently inhibited DNP–BSA or compound 48/80-induced degranulation in RBL-2H3 mast cells, with IC 50 values of approximately 49 μg/ml and 76 μg/ml, respectively. This extract strongly suppressed compound 48/80-induced systemic anaphylaxis by 48.7% at a dose of 300 mg/kg in mice. Chrysanthemi sibirici herba also inhibited the expression of TNF-α and the activation of the MAP kinase, ERK1/2, which is critical for the production of inflammatory cytokines in mast cells, as indicated by the suppression of activating phosphorylation of ERK1/2. These results lead us to conclude that Chrysanthemi sibirici herba may be used clinically to treat various allergic diseases.

A molecular understanding of mast cell activation and the promise of anti-allergic therapeutics.

Mast cells are central to allergic disease. Their immediate (exocytosis of granule-stored allergic-mediators) and delayed (de novo synthesis of inflammatory mediators) response to an allergen underlies the symptoms seen in acute; and chronic allergic disease. Thus, intervention in the allergen-mediated activation of mast cells is a long sought after goal in the treatment and management of allergic disease. The recent gain in deciphering the molecular mechanisms underlying immunoglobulin E (IgE)-mediated mast cell activation has provided optimism for the development of new therapeutic strategies. Among the most promising is the use of humanized anti-IgE antibodies that inhibit binding of IgE to its high affinity receptor (FcepsilonRI) on the mast cell. Other strategies target molecules proximal to FcepsilonRI, whose activities are central in mast cell activation. One such molecule, Syk kinase, has been targeted by various approaches including a small molecule inhibitor that specifically abrogates mast cell degranulation. More recently, various molecules that function to promote protein-protein interactions (adapters) were demonstrated as essential to mast cell degranulation and cytokine production. It remains to be seen if these molecules hold therapeutic promise for disease intervention. Additional studies identifying molecules required for mast cell granule fusion and content exocytosis also bodes well for discovery of new therapeutic targets. While our understanding of IgE-mediated mast cell activation is still at its inception, the modest success in identifying molecules essential to this process affords some confidence for better treatment of allergic disease.

Adenosine-activated mast cells induce IgE synthesis by B lymphocytes: an A2B-mediated process involving Th2 cytokines IL-4 and IL-13 with implications for asthma.

Adenosine provokes bronchoconstriction in asthmatics through acute activation of mast cells, but its potential role in chronic inflammation has not been adequately characterized. We hypothesized that adenosine up-regulates Th2 cytokines in mast cells, thus promoting IgE synthesis by B lymphocytes. We tested this hypothesis in human mast cells (HMC-1) expressing A(2A), A(2B), and A(3) adenosine receptors. The adenosine analog 5'-N-ethylcarboxamidoadenosine (NECA) (10 microM) increased mRNA expression of IL-1beta, IL-3, IL-4, IL-8, and IL-13, but not IL-2 and IFN-gamma. Up-regulation of IL-4 and IL-13 was verified using RT-PCR and ELISA; 10 microM NECA increased IL-13 concentrations in HMC-1 conditioned medium 28-fold, from 7.6 +/- 0.3 to 215 +/- 4 pg/ml, and increased IL-4 concentrations 6-fold, from 19.2 +/- 0.1 to 117 +/- 2 pg/ml. This effect was mediated by A(2B) receptors because neither the selective A(2A) agonist 2-p-(2-carboxyethyl)phenethylamino-NECA nor the selective A(3) agonist N(6)-(3-iodobenzyl)-N-methyl-5'-carbamoyladenosine reproduced it, and the selective A(2B) antagonist 3-isobutyl-8-pyrrolidinoxanthine prevented it. Constitutive expression of CD40 ligand on HMC-1 surface was not altered by NECA. Human B lymphocytes cocultured for 12 days with NECA-stimulated HMC-1 produced 870 +/- 33 pg IgE per 10(6) B cells, whereas lymphocytes cocultured with nonstimulated HMC-1, or cultured alone in the absence or in the presence of NECA, produced no IgE. Thus, we demonstrated induction of IgE synthesis by the interaction between adenosine-stimulated mast cells and B lymphocytes, and suggest that this mechanism is involved in the amplification of the allergic inflammatory responses associated with asthma.

Differential regulation of mast cell cytokines by both dexamethasone and the p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580.

Activated mast cells generate multiple cytokines but it is not known if these can be differentially regulated by pharmacological agents. We report here that the glucocorticoid dexamethasone (DEX) preferentially inhibited Ag-induced expression of IL-4 and IL-6 mRNA relative to TNF-alpha mRNA in RBL-2H3 cells. Likewise, the drug more readily inhibited release of IL-4 than TNF-alpha protein. SB203580, an inhibitor of p38 mitogen-activated protein kinase (MAPK), enhanced Ag-induced TNF-alpha mRNA expression without affecting IL-4 or IL-6 mRNA. At the protein level, SB203580 exerted little effect on TNF-alpha release but inhibited IL-4 release; notably, the ratio of TNF-alpha : IL-4 increased markedly with the concentration of SB203580, confirming the differential regulation of these cytokines. PD98059, an inhibitor of MAPK kinase (MEK), a component of the p44/42 MAPK pathway, partially inhibited Ag-induced expression of mRNA for all three cytokines while cyclosporin A inhibited Ag-induced IL-4 and IL-6 mRNA more readily than TNF-alpha mRNA. Ag activation of the cells led to phosphorylation of p38 and p44/42 MAPK but this was not influenced by DEX. In conclusion, mast cell cytokines can be differentially regulated pre- and post-translationally by DEX and SB203580 but there does not appear to be a direct mechanistic link between the actions of these two drugs.

Lymphotoxin-beta receptor activation by activated T cells induces cytokine release from mouse bone marrow-derived mast cells.

Lymphotoxin-beta receptor (LTbetaR) signaling is known to play a key role in embryonic lymphoid organ formation as well as maintenance of lymphoid architecture. Activation of the LTbetaR is induced by either the heterotrimeric lymphotoxin-alpha(1)beta(2) (LTalpha(1)beta(2)) or the homotrimeric LIGHT (homologous to lymphotoxins, exhibits inducible expression, and competes with HSV gpD for herpes virus entry mediator, a receptor expressed by T lymphocyte). Both ligands are expressed on activated lymphocytes. As mast cells reside in close proximity to activated T cells in some inflammatory tissues, we examined the expression of LTbetaR on bone marrow-derived mast cells and asked whether the LTbetaR-ligand interaction would allow communication between mast cells and activated T cells. We found that mast cells express LTbetaR at the mRNA as well as at the protein level. To investigate LTbetaR-specific mast cell activation, the LTbetaR on BMMC from either wild-type or LTbetaR-deficient mice was stimulated with recombinant mouse LIGHT or agonistic mAbs in the presence of ionomycin. LTbetaR-specific release of the cytokines IL-4, IL-6, TNF, and the chemokines macrophage inflammatory protein 2 and RANTES was detected. Moreover, coculture of mast cells with T cells expressing the LTbetaR ligands also entailed the release of these cytokines. Interference with a specific LTbetaR inhibitor resulted in significant suppression of mast cell cytokine release. These data clearly show that LTbetaR expressed on mast cells can transduce a costimulatory signal in T cell-dependent mast cell activation.

Mast cell–mediated inflammatory responses require the α2β1 integrin

AbstractAlthough the α2β1 integrin is widely expressed and has been extensively studied, it has not been previously implicated in mast cell biology. We observed that α2 integrin subunit-deficient mice exhibited markedly diminished neutrophil and interleukin-6 responses during Listeria monocytogenes– and zymosan-induced peritonitis. Since exudative neutrophils of wild-type mice expressed little α2β1 integrin, it seemed unlikely that this integrin mediated neutrophil migration directly. Here, we demonstrate constitutive α2β1 integrin expression on peritoneal mast cells. Although α2-null mice contain normal numbers of peritoneal mast cells, these α2-null cells do not support in vivo mast cell–dependent inflammatory responses. We conclude that α2β1 integrin provides a costimulatory function required for mast cell activation and cytokine production in response to infection.