Involvement of Fc{varepsilon}:RII/CD23 and L-argininedependent pathway in IgE-mediated stimulation of human monocyte functions

Elevated IgE levels are commonly observed during the Inflammatoryresponses In allergy and a variety of Infections. This Ig activatesthe release of multiple mediators from monocytes/ macrophages.In the present work, we attempted to clarify the IgE-dependentevents Involved In the activation of monocyte functions. IgE–antI–IgEImmune complexes induce the production of tumor necrosis factor-oxygen radicals, IL-6 and thromboxane B₂ from normal human purifiedmonocytes. Expression and cross-linkage of FcRII/CD23 were essentialfor these IgE-medlated effects. Cytoldne production followingCD23 llgation depended on nitric oxide transduction pathway,as It was Inhibited by N^Q-monomethyt-L-arginine, a competitiveInhibitor of the conversion of L-arginine to L-citroline bynitric oxide synthase. Furthermore, addition of the nitric oxidechemical donator, Sin-1, enhanced IgE-lnduced monoMne release.CD23-ligatlon also Induced the production of nitrites by thesecells. This work linked CD23 to the L-arginine-dependent transductionpathway and shows their involvement In IgE-medlated stimulationof human monocytes.     

Granulocyte macrophage colony stimulating factor induces Fc{varepsilon}RII/CD23 expression on normal human polymorphonuclear neutrophils

Three major molecules have been recognized as IgE-binding structureson hematopoletic cells: the heterotrimeric high-affinity receptorfor IgE (FcRI), the low-affinity receptor for IgE (FcRII/CD23)and the Mac-2/IgE-bindlng protein (BP). The latter has beenshown to be expressed on polymorphonuclear neutrophils (PMN),where it regulates IgE-dependent activation. Experiments wereundertaken to determine whether the IgE-binding capacity ofPMN is mediated exclusively by this molecule. No detectablebinding of human myeloma IgE to unstimulated PMN from normalvolunteers could be evidenced. In contrast, PMN stimulated withgranulocyte macrophage colony stimulating factor (GM-CSF) (500U/ml) for 24 h displayed positive IgE binding. This bindingwas significantly inhibited in the presence of mAb directedagainst Mac-2/BP and also in the presence of anti-CD23 mAb,but not of anti-FcRI mAb or isotype-matched controls. By flowcytometry, CD23 expression was detected on GM-CSF-primed PMNby several anti-CD23 mAb, including EBVCS-5, BB10 or Mab135,which recognize different epitopes. CD23 was also evidencedby immuno cytochemistry in GM-CSF-primed PMN. By in situ hybridization,GM-CSF-treated PMN exhibited a hybridization signal for CD23mRNA and the presence of the CD23b isoform-specific mRNA wasdetected by RT-PCR. These findings Indicate that PMN can synthesizeCD23 molecules under GM-CSF induction. This strong CD23 expressionmight be of physiopathological relevance in IgE-dependent activationduring allergic processes.     

Stimulation of prostaglandin (PG) F2{alpha} and PGE2 release by tumour necrosis factor-{alpha} and interleukin-1{alpha} in cultured human luteal phase endometrial cells

Tumour necrosis factor- (TNF-) and interleukin-1 (IL-1) areimportant mediators of cell signalling in the uterus. Prostaglandins(PG) have been implicated in the increase of endometrial vascularpermeability which occurs during the implantation process. Thisstudy evaluates the effect of these two pleiotropic cytokineson PGF₂ and PGE₂ release from human luteal phase endometrialglandular epithelial cells (GEC) and stromal cells (STC) inculture. Basal PGF and PGE release did not differ significantlyfrom each other or among cell types, and declined significantlywith increasing number of days in culture. On day 3, basal PGrelease had decreased to half of that on day 1 of culture. However,both cell types were still able to respond to the addition ofexogenous arachidonic acid (5 µM) on day 3 of culture,with PG release by GEC being elevated 7- to 10-fold and by STCmoderately, but still significantly, on day 4. The permissiveeffect of arachidonic acid on the stimulation of PG releasemay indicate the down-regulation of phospholipase A₂ with continuedtime in culture. However, the addition of arachidonic acid (5µM) on day 0 of culture, while able to cause significantlyincreased PG release from GEC, had no effect on STC. In contrast,the addition of a combination of arachidonic acid (5 µM),and either recombinant human TNF- (10 µg rhTNF-/I) or10 µg rhlL-1/I, had a synergistic action and caused thesignificantly increased release of PGF and PGE from both celltypes, compared with that achieved with either arachidonic acidor the cytokine alone (although GEC responded more than STC).During the first 24 h after the addition of rhTNF- or rhlL-1,both cytokines stimulated PG release from both cell types ina dose- and time-dependent fashion. Neither cycloheximide (10µM) nor actinomycin D (10 µM) affected basal PGrelease, but both blocked cytokine-induced PG release from bothcell types. These results suggest that there is a differentialcontrol of human endometrial cell PG biosynthesis, and thatPG release may be regulated through gene activation.     

Over-expression of CD3{varepsilon} transgenes blocks T lymphocyte development

We have reported previously that mice carrying >30 copiesof the human CD3 transgene completely lose their T lymphocytesand NK cells (36). Here we demonstrate by immunohistology thatin the most severely immunodeficient mouse, tg26, the thymusis very small, has sizeable vacuoles and does not contain recognizableT lymphocytes except for a small percentage of Thy- 1⁺ cellsand B cells. Cell surface phenotyping and TCR and -ßrearrangement studies confirm that the arrest in T lymphocytedevelopment precedes the arrest in rag-1^null, rag-2^null andTCRß^null mice. Since the T cell progenitors in whichthe arrest occurred were absent in the transgenic mice, indirectapproaches were taken to examine the causes of the block inT cell development. Analyses of 12 independently establishedmutant mouse lines, generated with five different transgenicconstructs, revealed that the severity of the abrogation inT cell development was dependent on the number of copies oftransgenes. Since the number of transgene copies generally correlatedwith the levels of expression of the transgenic CD3 proteins,we concluded that over-expression of the CD3 protein was thelikely cause of the block in T lymphocyte development. The Tcell immunodeficiency was caused by either the human or themurine CD3 protein. Since transgene coded mRNAs were found insignificantly higher quantities than endogenous CD3 mRNAs infetal thymi on days 13 and 14 of gestation, over-expressiontook place very early in development, probably prematurely.Over-expression of the CD3 transgene in thymocyte precursorsmay therefore affect T lymphocyte development in the absenceof TCR and possibly in the absence of the other CD3 proteins.More importantly, over-expression of the CD3 protein in thymocytesof mice with a low copy number of transgenes had a significanteffect on late thymic development Over-expression of the CD3protein in immature thymocytes mimicked the effects caused byexposure of CD4^–; CD8^– thymocytes to anti-CD3 treatment:apoptosis and lack of TCRß expression. We thereforespeculate that in the homozygous tg26 animals the arrest inT cell development was caused by excessive signal transductionevents rather than by a toxic effect of the transgenic protein.     

In vivo administration of TNF-{alpha} prevents EMC-M virus induced viral encephalitis

EMC-M virus causes a monophasic paralytic syndrome characterizedby encephalltic lesions in the brain and patchy demyellnatinglesions in the spinal cord and nerve roots of BALB/c mice. Sincethe replication of EMC virus in vitro is inhibited by tumornecrosis factor (TNF)- we have studied the effect of in vivoadministration of this cytokine on the acute disease. Our studiesshow that periodic administration of TNF- to animals infectedwith EMC-M reduces viral titers in the brain, and decreasesthe degree of clinical paralysis and the severityof the inflammatorylesions in the brain.     

Involvement of {alpha}1 and {alpha}4 integrins in gut mucosal injury of graft-versus-host disease

We have investigated the involvement of adhesion molecules inthe lymphocyte infiltration associated with acute intestinalgraft-versus-host disease (GVHD) induced by injection of C3Hlymph node cells into irradiated (C3H x DBA/2)F₁ mice. Firstwe analyzed the expression profile of adhesion molecules including1, 2, 4, 5, 6, L and ß7 integrins, CD44 and L-selectinof lymphocytes from lymph nodes and gut mucosa in normal mice.In normal mice, intraepithelial lymphocytes (IEL) and laminapropria lymphocytes (LPL) uniquely showed increased expressionof 1, 2 and ß7 integrins, and decreased expressionof L-selectin compared with that of lymphocytes of the lymphnodes and Peyer's patches. In mice with GVHD, IEL and LPL ofdonor lymph node cells origin underwent phenotyplc changes characterizedby the increased expression of 1, L and ß7 integrins,and the loss of L-selectin. The expression profile of adhesionmolecules on IEL and LPL of GVHD mice resembled that of normalmice except for the lack of 2 integrin. Treatment of GVHD micewith anti-1,-4 or-ß7 integrin antibody alone partiallyprevented the mucosal pathology of intestinal GVHD, whereasonly mice treated with anti-1 showed reduced donor lymphocyticinfiltration into the intestinal mucosa. In contrast, treatmentwith anti-L or anti-CD44 antibody did not affect the intestinalGVHD. Furthermore, dual blockade of both 1 and 4 integrins completelyinhibited the mucosal pathology and donor lymphocyte infiltrationof intestinal GVHD. These results indicate that 1 and 4 integrinsplay an important role in the pathology of intestinal GVHD.     

Identification, in mouse macrophages and in serum, of a soluble receptor for the Fc portion of IgG (Fc{gamma}R) encoded by an alternatively spliced transcript of the Fc{gamma}RII gene

Low affinity FcR are a heterogeneous group of glycoproteinswhich exist in transmembrane (TM) as well as in soluble forms.Two membrane isoforms of the murine type II FcR, FcRilb1 andFc;Rilb2, have been described. They result from the translationof alternatively spliced premRNA, FcRilb2 lacking sequencesof the first intracytoplasmic domain (IC1). Soluble forms ofFcR (sFcR) have previously been shown to result from proteolysisof membrane receptors. We report here the identification, inmacrophages, of a mRNA derived from the FCRll gene by splicingexons encoding the TM and IC1 domains, i.e. corresponding toa TM-deleted FcRllb2 mRNA. A soluble protein possibly encodedby this mRNA was identified in macrophage supernatants. In accordancewith FcR nomenclature, we propose to name this new FcRll IsoformFcRllb3. It is the most abundant 8FcR present in serum, as comparedwith 8FcR resulting from cleavage of membrane FcR.     

Involvement of protein kinase C-{varepsilon} in glucocorticoid-induced apoptosis in thymocytes

Apoptosis is induced in immature thymocytes by physiologicalpeak levels of glucocortlcold hormones, especially in murineand rat cells. Endogenous glucocortlcolds may have some rolein thymic selection. Glucocorticold-lnduced thymocyte apoptosisappears to be dependent on protein kinase C (PKC), since itis inhibited by PKC inhibitors. PKC Is a family of closely relatedenzymes, consisting of Ca²⁺-dependent (PKC-, -ßI,-ßII, and ) and Ca²⁺-Independent (PKC-, -ß,(L), -, -, and -) isozymes. In the present study, we analyzedthe role of PKC in glucocorticold-lnduced apoptosis in murinethymocytes and found that glucocorticold selectively inducesan increase in Ca²⁺ -Independent PKC activity in the paniculatefraction of Immature thymocytes but not in that of mature Tcells. The increase as well as the apoptosis was inhibited byactlnomycln D, cyclohexlmkte, or the glucocortteoid receptorantagonist, RU 38486. Immunoblottlng studies revealed the selectivetranslocatlon of PKC-from the cytosollc fraction to the paniculatefraction upon glucocortlcold treatment. These results suggestthat glucocorticold-lnduced apoptosis in immature thymocytesinvolves glucocorticold receptor-mediated and selective activationof PKC-through de novo synthesis of macromolecules.     

Pregnancy: Cervical ripening with the cytokines interleukin 8, interleukin 1{beta} and tumour necrosis factor {alpha} in guinea-pigs

It has been suggested that the collagenolytic enzymes releasedfrom white blood cells which infiltrate the pregnant human uterinecervix at term are responsible for connective tissue changeswhich take place during the ripening process. Similarly, aninfiltration of inflammatory cells occurs in pregnant guinea-pigseither spontaneously at term or at preterm after treatment withthe antiprogestin onapristone. The objective of this study wasto evaluate the effects of the inflammatory cytokines interleukin8 (IL-8), interleukin 1 (IL-1), tumour necrosis factor (TNF-)and a combination of IL-1 and TNF- on cervical ripening in guinea-pigsduring advanced pregnancy. The cytokines were applied locally(intracervically) in a gel for 2 days and the effects were assessedon the third day by both extensibility measurements and morphologicalevaluation. IL-8 treatment on days 42 and 43 post coitum (p.c)and on days 48 and 49 p.c. (term: day 67± 3 p.c.) significantly(P < 0.05) increased cervical extensibility at both stagesof pregnancy. Although IL-1 treatment (days 42 and 43 p.c.)led to a slight increase in cervical extensibility, this effectwas not statistically significant. An electron microscope studyperformed on days 48 and 49 p.c. revealed a pronounced cervicalripening accompanied by the dissolution of collagen fibres,stromal oedema and the infiltration of polymorphonuclear leukocytesin all cytokine-treated groups. The morphological effects ofIL-8 and IL-1 were indistinguishable from those observed duringnormal cervical ripening at term. In contrast, TNF-, both aloneand in combination with IL-1, brought about a severe inflammatoryreaction with a massive infiltration of lymphocytes, marcophagesand polymorphonuclear leukocytes at the investigated dose. Weconclude that the local application of the inflammatory cytokinesIL-8, IL-1 and TNF- produces cervical ripening without inducinglabour in pregnant guinea-pigs; the morphological effects ofIL-8 and IL-1 being similar to the physiological cervical ripening.Our data support the view that cytokines, particularly IL-8,may play an important role during physiological, pathologicaland induced cervical ripening and could be clinically usefulas an adjunct to labour and delivery.     

Maternal serum levels of interferon-gamma and interleukin-2 soluble receptor-alpha predict the outcome of early IVF pregnancies

BACKGROUND: Elevated maternal serum levels of interleukin-2 soluble receptor-alpha (IL-2 sRalpha), tumour necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) have been associated with pregnancy loss. The aim of our study was to evaluate the predictive value of these cytokines in the outcome of early IVF pregnancies. METHODS: One hundred and fifty-nine consecutive IVF patients who were subsequently diagnosed to have a biochemical pregnancy (n = 23), a first-trimester miscarriage (n = 19) or a normal term delivery (n = 117) were included in this study. Serum was collected from the initial pregnancy test, 11 days after a day 3 embryo transfer, and all samples were analysed for IL-2 sRalpha, TNF-alpha and IFN-gamma by commercially available enzyme-linked immunosorbent assay (ELISA) kits. RESULTS: IL-2 sRalpha levels were significantly higher in patients with an early pregnancy loss compared with patients with a normal term delivery (849.5 +/- 69.6 versus 693.5 +/- 31.2 pg/ml, P = 0.02), and a cut-off point of IL-2 sRalpha >1000 pg/ml predicted a poor pregnancy outcome (44.4 versus 22.7% pregnancy loss, IL-2 sRalpha >or=1000 versus IL-2 sRalpha <1000 pg/ml; P = 0.02). IFN-gamma-positive patients had twice the risk for poor IVF pregnancy outcome compared with IFN-gamma-negative subjects (40.8 versus 20.0%, respectively; P < 0.02), including a significantly lower implantation rate (37.6 +/- 0.05 versus 50.0 +/- 0.03%, respectively; P = 0.02). There was no difference in pregnancy outcome based upon serum levels, or the ability to detect the presence of TNF-alpha. No differences in levels of these cytokines were found based on the aetiology of the patients' infertility. CONCLUSIONS: Elevated maternal serum levels of IL-2 sRalpha and IFN-gamma as early as 11 days after embryo transfer are associated with poor IVF pregnancy outcome.     

Ligand-induced autoregulation of IL-2 receptor {alpha} chain expression in murine T cell lines

The IL-2 receptor (IL-2R) is composed of three chains a, ßand . In mice, contrary to the human system, we have previouslydemonstrated that the IL-2Rß complex does not bindIL-2. Therefore, mouse IL-2 response is completely dependenton the expression of the IL-2R gene product. T cell clones expressingmouse IL-2Rß and the human IL-2R transgene have beenstudied. When cells are grown in IL-4, mouse IL-2R is not expressed.However, exposure to IL-2 leads to the expression of the endogenousmurine IL-2R subunit. The T cell line expressing mouse IL-2Rand human IL-2Rß can grow in IL-2 but does not expressendogenous murine IL-2 R. Transfection of these cells with thehuman IL-2R gene restores the capacity to induce murine IL-2R.This result demonstrates that IL-2-IL-2R interactions are requiredfor induction of IL-2R. The kinetics of induction and deinductionof murine IL-2R have been studied using clone 18.III. From negativecells, expression of murine IL-2R is a very slow phenomenon.From cells fully expressing IL-2R, deinduction is a two-stepprocess: after a rapid decrease of IL-2R the cells continueto express, for a long period of time, basal levels of murineIL-2R. When cells expressing basal levels of IL-2R are exposedto IL-2, induction of IL-2R is a very rapid phenomenon. Theautoregulatory loop formed by IL-2-IL-2R therefore displaysdifferent levels of functioning.     

Soluble human high-affinity receptor for IgE abrogates the IgE-mediated allergic reaction

The high-affinity receptor for IgE (FcRI) has a tetrameric structurecomposed of one, one ß, and two disulfide-linked subunits, of which the subunit binds IgE with high affinity.A recombinant soluble form of the ectodomain of the human FcRIsubunit (rsFcRI) was recently generated by gene engineeringand was verified to bind IgE with an affinity as high as thatof native FcRI on the cell surface. rsFcRI was prepared on alarge scale in order to analyze its biological function. rsFcRIcompletely inhibited IgE binding to the cell surface, resultingin abrogation of the chemical mediator release from RBL-2H3cells. Furthermore it completely abolished the passive cutaneousanaphylaxis (PCA) response by trapping IgE specifically whenitwas administered into rats prior to IgE sensltizatlon. Evenafter IgE sensitizatlon, treatment of rsFcRI substantially reducedthe PCA response. It was finally shown that rsFcRI inhibitedIgE binding to human peripheral blood basophils and the histaminerelease from them. In this paper we address the ability of rsFcRIto specifically prevent the IgE-mediated allergic reaction.     

Molecular cloning and characterization of guinea pig Fc{gamma}RIII: expression but not function is independent of the {gamma} chain of Fc{gamma}FceRI

We have isolated two cDNA clones encoding the guinea pig receptorfor the Fc portion of lgG2 (Fc2R) from a guinea pig peritonealmacrophage cDNA library. Analysis of the predicted amino acidsequence of the one cDNA clone indicated that the guinea pigFc2R Is a type I transmembrane protein and has 72% DNA sequencehomology and 57% protein sequence homology with the human FcRIII.Therefore, we propose that the guinea pig Fc2R Is referred toas guinea pig FcRIII. The most important finding In this reportis that the obtained cDNA directed the cell surface expressionof the Fc2R on COS-7 cells without association with the chainof the high-affinity IgE receptor (FcRly) which is requiredfor human and mouse FcRIII to be expressed on the cell surface.Furthermore, we demonstrated that the endocytosis activity ofFcRIII is dependent upon the association with FcRl, suggestingthat FcRl is Involved in the functions of guinea pig FcRIII.The other clone was found to lack the sequence encoding transmembraneand cytoplasmic domains, suggesting the presence of a solubleform of guinea pig FcRIII. Northern blot analysis and RT-PCRshowed that a transmembrane form of guinea pig FcRIII was expressedin peritoneal macrophages, but not in neutrophils In spite ofthe fact that they express Fc2R, indicating that the Fc2R onneutrophils is a product of a distinct gene.     

Rapid acceleration of neutrophil apoptosis by tumor necrosis factor-{alpha}

We demonstrate here that human necrosis factor-, a potent neutrophilactivator, induces rapid (within 3 h) apoptosis of these cells,i.e. neutrophils treated with this cytokine exhibit (I) lightand electron microscopic changes characteristic to apoptoticcells, (II) reduced propidium iodide binding to DNA, and (III)the ladder form of DNA, as shown by agarose gel electrophoresis.These results suggest that apoptosis acceleration may be involvedin processes by which neutrophils are prevented from damagingtissues.     

Integrins and adhesion molecules: Tumour necrosis factor-{alpha}-mediated dyscohesion of epithelial cells is associated with disordered expression of cadherin/{beta}-catenin and disassembly of actin filaments

Tumour necrosis factor (TNF)- induced, in a time- and dose-dependentfashion, dyscohesion (cell-cell dissociation) of the endometrialepithelial cells. TNF- impaired the ability of cells to aggregateand to attain compaction. The cell-cell adherent junction isa specialized region of the plasma membrane where cadherin moleculesact as adhesion molecules and actin filaments are densely associatedwith the plasma membrane through a well-developed plasmalemmalundercoat. Dyscohesion induced by TNF- was associated with thedisordered expression of cadherin\-catenin at the sites of cell-cellcontact. In addition, within the time-frame that dyscohesionwas induced, TNF- down-regulated the expression of actin mRNAonly at 100 ng/ml without modulating the overall amount of actinprotein, its -isoform or the amount of ribosylated actin. However,TNF--mediated dyscohesion of epithelial cells was associatedwith loss of plasmalemmal undercoat as well as intracytoplasmicaggregates of F-actin and a simultaneous increase in G-actin.The effect of cytochalasin-B, which disrupts actin filamentson cell-cell binding, was less pronounced than the effect ofTNF-, suggesting that the effect of this cytokine on dyscohesionis not solely dependent on the disassembly of actin filaments.These findings show that the induction of disordered expressionof adhesion molecules, as well as disassembly of actin filaments,are implicated in the dyscohesion induced by TNF-.     

Time-dependent effects of transforming growth factor {alpha} on aromatase activity in human granulosa cells

Transforming growth factor a (TGF) is implicated as a paracrinegrowth factor in the regulation of human granulosa cell function.To investigate this further, we have examined the actions ofTGF on the basal and folliclestimulating hormone (FSH)-stimulatedaromatase activity of human granulosa cells to determine howthis growth factor influences oestrogen biosynthesis in thefollicle. Granulosa cells from women having in-vitro fertilizationduring untreated or gonadotrophin-stimulated cycles were culturedfor 1–6 days in the presence or absence of FSH or TGFat a range of doses. Aromatase activity, expressed as oestradiolproduction, was determined after culture during a 3 h test period.After 2 days, TGF (1–300 ng/ml) decreased basal and FSH-stimulatedaromatase activity in a dose-dependent manner (ED50 = 3 ng/ml).In contrast, after 4 days, TGF enhanced both basal and FSH-stimulatedaromatase activity. Repeated experiments revealed a consistentpattern of inhibition on day 2, which was more marked in thepresence of FSH (reduction by 30.6 ± 9.1%, mean ±SEM; n = 14; P < 0.01), and stimulation on day 4 in boththe absence (increased by 61.4 ± 20.6%, mean ±SEM; n = 6; P < 0.05) and presence of FSH (increased by 36.0± 15.2%, mean ± SEM; n = 8; P < 0.05). Theresults provide further evidence that TGF is a paracrine factorin the control of oestrogen biosynthesis, but the actions canbe either inhibitory or stimulatory depending on the durationof exposure.     

Implantation: Tumour necrosis factor {alpha} inhibits in-vitro decidualization of human endometrial stromal cells

Interleukin-1 (IL-1) has been reported previously to inhibitthe in-vitro decidualization of human endometrial stromal cellsas assessed by progesterone-induced prolactin production andmorphological transformation. In this study we examined whetherother cytokines, such as tumour necrosis factor-(TNF), interferon-(IFN), IFN or granulocyte-macrophage colony-stimulating factor(GM-CSF), could affect the decidualization of human endometrialstromal cells in vitro. Of these cytokines, TNF significantlysuppressed prolactin production in a dose-dependent manner,with no apparent effect on cell number. The morphological transformationof endometrial stromal cells was also inhibited by TNF. TNFand IL-1 significantly suppressed cAMP-stimulated prolactinproduction by endometrial stromal cells. Neither the progesteroneconcentration in the supernatant of the endometrial stromalcell culture system nor intracellular calcium concentrationof the endometrial stromal cells were affected by the additionof TNF or IL-1. These results indicated that TNF and IL-1 suppressboth progesterone-induced and cAMP-mediated prolactin productionin endometrial stromal cells, and that this inhibition was notattributable to direct effects on progesterone metabolism orrelated to Ca2+-mediated signal transduction. These experimentssuggested that a local increase of TNF and IL-1 under certainpathological conditions in vivo may disturb blastocyst implantationand/or the maintenance of pregnancy by inhibiting the decidualizationof endometrial stromal cells.     

Fc receptor beta subunit is required for full activation of mast cells through Fc receptor engagement

The high-affinity IgE receptor (Fc epsilonRI) and the low-affinity IgG receptor (Fc gammaRIII) on mast cells are the key molecules involved in triggering the allergic reaction. These receptors share the common beta subunit (FcRbeta) which contains an immunoreceptor tyrosine-based activation motif and transduces the signals of these receptors' aggregation. In rodents, FcRbeta is essential for the cell surface expression of the Fc epsilonRI. In humans, the FcRbeta gene was reported to be one of the candidate genes causing atopic diseases. However, the role of FcRbeta in vivo still remains ambiguous. To elucidate the functions of FcRbeta, we developed the mice lacking FcRbeta [FcRbeta(-/-)]. The FcRbeta(-/-) mice lacked the expression of the Fc epsilonRI on mast cells and IgE-mediated passive cutaneous anaphylaxis (PCA) was not induced in FcRbeta(-/-) mice as was expected. In these mice, the expression of IgG receptors on mast cells was augmented but the IgG-mediated PCA reaction was attenuated. Although with bone marrow-derived cultured mast cells from FcRbeta(-/-), adhesion to fibronectin and Ca2+ flux upon aggregation of IgG receptors were enhanced, mast cells co-cultured with 3T3 fibroblasts exhibited impaired degranulation on receptor aggregation. These observations indicate that FcRbeta accelerates the degranulation of mature mast cells via the IgG receptor in connective tissues.