Paeoniflorin inhibits IgE-mediated allergic reactions by suppressing the degranulation of mast cells though binding with FcϵRI alpha subunits.

Paeoniflorin (PF), a monoterpene glycoside isolated from the aqueous extract of the Chinese herb Radix Paeoniae Alba, has been used for treating various inflammatory diseases. In this study, we aimed to investigate the anti-allergic activities of PF. The anti-anaphylactic activity of PF was investigated using mast cell (MC) degranulation assay as well as Ca2+ influx in vitro and skin swelling and extravasation assays in vivo. The results showed that PF inhibited MC degranulation (histamine release from 74.5 ± 4.95 ng/ml to 58.7 ± 6.06 ng/ml) and Ca2+ influx challenged by DNP-BSA in vitro. In addition, PF reduced the degree of swelling and Evans blue exudation in mice paws. Furthermore, PF dose-dependently reduced serum inflammatory mediator release in mice sensitized with ovalbumin for 48 h by inhibiting MC degranulation. Molecular docking study revealed that PF bound better with the α subunit of FcϵRI than with the ß subunit. SPR revealed that PF had a strong affinity interaction with FcϵRI α subunit and the KD value was (7.08 ± 0.97) e-6 M. Our findings revealed that PF inhibited anaphylactic responses in vivo and in vitro, and it can be considered a novel FcϵRI inhibitor for preventing MC-related allergic diseases.

The histone deacetylase inhibitor valproic acid attenuates phospholipase Cγ2 and IgE-mediated mast cell activation.

Mast cell activation through the high-affinity IgE receptor (FcεRI) plays a central role in allergic reactions. FcεRI-mediated activation triggers multiple signaling pathways leading to degranulation and synthesis of different inflammatory mediators. IgE-mediated mast cell activation can be modulated by different molecules, including several drugs. Herein, we investigated the immunomodulatory activity of the histone deacetylase inhibitor valproic acid (VPA) on IgE-mediated mast cell activation. To this end, bone marrow-derived mast cells (BMMC) were sensitized with IgE and treated with VPA followed by FcεRI cross-linking. The results indicated that VPA reduced mast cell IgE-dependent degranulation and cytokine release. VPA also induced a significant reduction in the cell surface expression of FcεRI and CD117, but not other mast cell surface molecules. Interestingly, VPA treatment inhibited the phosphorylation of PLCγ2, a key signaling molecule involved in IgE-mediated degranulation and cytokine secretion. However, VPA did not affect the phosphorylation of other key components of the FcεRI signaling pathway, such as Syk, Akt, ERK1/2, or p38. Altogether, our data demonstrate that VPA affects PLCγ2 phosphorylation, which in turn decreases IgE-mediated mast cell activation. These results suggest that VPA might be a key modulator of allergic reactions and might be a promising therapeutic candidate.

Activation of Human Peripheral Basophils in Response to High IgE Antibody Concentrations without Antigens.

Basophils and mast cells have high affinity IgE receptors (FcεRI) on their plasma membrane and play important roles in FcεRI-associated allergic diseases, such as pollen allergy, food allergy, chronic spontaneous urticarial (CSU), and atopic dermatitis (AD). To date, several reports have revealed that high IgE antibody concentrations activate mast cells-which reside in tissue-in the absence of any antigens (allergens). However, IgE antibody-induced activation of basophils-which circulate in blood-has not been reported. Here, we investigated whether IgE antibodies may regulate functions of human peripheral basophils without antigens in vitro. We successfully removed IgE antibodies bound to FcεRI on the surface of human peripheral basophils by treating with 0.1% lactic acid. We also demonstrated that high IgE antibody concentrations (>1 µM) induced histamine release, polarization, and CD203c upregulation of IgE antibody-stripped basophils. Thus, high IgE antibody concentrations directly activate basophils, which express IgE-free FcεRI on the cell surface. This mechanism may contribute to the pathogenesis of patients with AD and CSU who have higher serum IgE concentrations compared to healthy donors.

Ergosterol and its derivatives from Grifola frondosa inhibit antigen-induced degranulation of RBL-2H3 cells by suppressing the aggregation of high affinity IgE receptors.

Grifola frondosa is an edible mushroom consumed as a health food and/or traditional medicine in Asia. However, the anti-allergic effects of G. frondosa are not yet understood. In this study, we demonstrated the effects of G. frondosa extract (GFE) on IgE-mediated allergic responses, using antigen-stimulated RBL-2H3 cells. Three active compounds: ergosterol, 6ß-methoxyergosta-7,22-dien-3ß,5α-diol (MEDD), and 6-oxoergosta-7,22-dien-3ß-ol (6-OXO) were isolated from GFE and shown to inhibit the antigen-induced release of ß-hexosaminidase and histamine. Among the three active components, we focused on ergosterol because of its high content in GFE. Ergosterol inhibited the aggregation of high-affinity IgE receptor (FcεRI), which is the first step in the activation of mast cells and antigen-induced tyrosine phosphorylation. Furthermore, ergosterol suppressed antigen-increased IL-4 and TNF-α mRNA. Taken together, our findings suggest that G. frondosa, including ergosterol and its derivatives as active components, has the potential to be a novel functional food that prevents type I allergies.

The effect of omalizumab treatment on the low affinity immunoglobulin E receptor (CD23/fc epsilon RII) in patients with severe allergic asthma.

BACKGROUND: Omalizumab is an anti-immunoglobulin E (IgE) monoclonal antibody used in the treatment of severe asthma. Its therapeutic efficacy is primarily attributed to reduction of serum-free IgE and in the expression of high-affinity IgE receptor, fc epsilon RI. However, its effect on the low-affinity IgE receptor fc epsilon RII/CD23 in vivo has not been evaluated. AIM: To determine whether CD23 plays a role in the inflammatory process in severe uncontrolled asthma and whether anti-IgE therapy modulates fc epsilon RII/CD23 expression in these patients. METHODS: We evaluated the expression of IgE receptors fc epsilon RI, fc epsilon RII/CD23, and soluble CD23 (sCD23), and the activation state of peripheral blood monocytes (tumor necrosis factor alpha, interleukin (IL) 1-beta, transforming growth factor (TGF) beta expression) in the patients with severe asthma before and after 24 weeks of omalizumab treatment and in the healthy controls. Cytokine expression of monocytes in response to different stimulation (IL-4, IL-4 plus IgE, IL-4 plus IgE plus anti-IgE, and IL-4 plus IgE plus anti-IgE plus anti-CD23 for 72 hours) was determined by enzyme-linked immunosorbent assay. RESULTS: Treatment with omalizumab (for 24 weeks) improved disease control and pulmonary function (forced expiratory volume in the first second of expiration, 64.5 versus 74%; p = 0.021). Mean ± SE expression of fc epsilon RI on monocytes was higher in the patients with asthma versus the controls (45.7 ± 12.2% versus 18.6 ± 5.8%; p = 0.04) and was reduced after omalizumab treatment (45.7 ± 12.2% versus 15.6 ± 4.4%; p = 0.027). Mean ± SE TGF-beta levels in supernatants from monocytes were reduced in the patients treated with omalizumab (211 ± 6 pg/mL versus 184 ± 9 pg/mL; p = 0.036). CONCLUSION: Modulation of the low affinity IgE receptor CD23 in severe asthma is complex, and sCD23 may inversely reflect disease activity. Treatment with omalizumab was associated with reduced monocyte activation.

Longitudinal study of the expression of FcεRI and IgE on basophils and dendritic cells in association with basophil function in two patients with severe allergic asthma treated with Omalizumab.

Severe asthma is a challenging disease, and omalizumab has been an important tool to help clinicians address more efficiently this problem. Besides reduction of free and total serum IgE levels, there are a number of other immunologic effects of omalizumab that may be of relevance in its therapeutic action. We report two mite-allergic severe asthmatic patients successfully treated with omalizumab for one year. Clinically, patients improved gradually, with no further need for systemic steroids or emergency department visits during that treatment period, and with Asthma Control Test (ACT) scores showing controlled disease, although pulmonary function didn't show any significant improvement. Immunologically, we observed marked down-regulation of surface IgE and FcεRI on basophils, plasmacytoid and myeloid dendritic cells, as well as a reduction of basophil activation after specific allergen stimulation. These effects were clearly evident immediately after one month but were enhanced at 3, 6 and 12 months of omalizumab treatment, suggesting an advantage to continuing this therapy, and raising the hypothesis of some markers being useful to assess immunological responses to omalizumab, which could assist in the clinician's decision to stop or to restart this treatment.

Single-walled carbon nanotube exposure induces membrane rearrangement and suppression of receptor-mediated signalling pathways in model mast cells.

Carbon nanotubes (CNT) are environmental challenges to the respiratory and gastrointestinal mucosa, and to the dermal immune system. Mast cells (MC) are pro-inflammatory immunocytes that reside at these interfaces with the environment. Mast cells are sources of pro-inflammatory mediators (histamine, serotonin, matrix-active proteases, eicosanoids, prostanoids, cytokines and chemokines), which are released in a calcium-dependent manner following immunological challenge or physico-chemical stimulation. Since C-60 fullerenes, which share geometry with CNT, are suppressive of mast cell-driven inflammatory responses, we explored the effects of unmodified SWCNT aggregates on mast cell signaling pathways, phenotype and pro-inflammatory function. We noted SWCNT suppression of antigen-induced signalling pathways and pro-inflammatory degranulation responses. Mast cells recognize unmodified SWCNT by remodeling the plasma membrane, disaggregating the cortical actin cytoskeleton and relocalizing clathrin. Clathrin was also identified as a component of an affinity-purified 'interactome' isolated from MC using an SWCNT affinity matrix for mast cell lysates. Together, these data are consistent with the ability of SWCNT to suppress mast cell pro-inflammatory function via a novel recognition mechanism.

The significance of chloride in the inhibitory action of disodium cromoglycate on immunologically-stimulated rat peritoneal mast cells.

BACKGROUND: The microelectrode array (MEA) was used to investigate the pharmacological relevance of chloride (Cl-) ions in antigen-dependent mast cell activation and the inhibitory effect of disodium cromoglycate (DSCG) on mast cell activation. METHODS: The movements of ions across the cellular membrane and the potential relationship between Cl- channels and DSCG during immunological activation were investigated using the MEA. The results were then subsequently compared with the amount of histamine released from anti-IgE activated peritoneal mast cells. RESULTS: The inclusion of charybdotoxin (ChTX) in Cl--free buffer showed that the measured field potentials during antigen-stimulated peritoneal mast cell were a combination of Cl- influx and K+ efflux. The delayed onset time of Cl- influx indicated the presence of a delayed outwardly-rectifying Cl- current in the antigen-stimulated peritoneal mast cells. The use of 5-nitro-2-(3-phenylpropylamino) benzoic acid demonstrated that the activated mast cell membrane potential can be stabilised, thereby reducing the amount of histamine released from the anti-IgE activated mast cells. The correlation between the results of the histamine release assay and the electrophysiological measurements demonstrated the importance of Cl- to anti-IgE dependent mast cell activation. The inhibitory effect of DSCG on anti-IgE activated cells, however, did not correlate with the presumed influx of Cl-. CONCLUSIONS: The MEA data suggest that Cl- influx is crucial to IgE-dependent mast cell degranulation. GENERAL SIGNIFICANCE: While the MEA cannot yield information about single channel properties, it is convenient to use and can provide information on the global changes in electrophysiological responses of non-excitable cells.

Inorganic arsenite inhibits IgE receptor-mediated degranulation of mast cells.

Millions of people worldwide are exposed to arsenic (As), a toxicant which increases the risk of various cancers, cardiovascular disease and several other health problems. Arsenic is a potent endocrine disruptor, including of the estrogen receptor. It was recently shown that environmental estrogen-receptor disruptors can affect the signaling of mast cells, which are important players in parasite defense, asthma and allergy. Antigen (Ag) or allergen crosslinking of IgE-bound receptors on mast cells leads to signaling, culminating in degranulation, the release of histamine and other mediators. Because As is an endocrine disruptor and because endocrine disruptors have been found to affect degranulation, here we have tested whether sodium arsenite affects degranulation. Using the rat basophilic leukemia (RBL) mast cell model, we have measured degranulation in a fluorescence assay. Arsenic alone had no effect on basal levels of degranulation. However, As strongly inhibited Ag-stimulated degranulation at environmentally relevant concentrations, in a manner that is very dependent on concentrations of both As and Ag. The concentrations of As effective at inhibiting degranulation were not cytotoxic. This inhibition may be a mechanism underlying the traditional Chinese medicinal use of As to treat asthma. These data indicate that As may inhibit the ability of humans to fight off parasitic disease.

Development of a two-part strategy to identify a therapeutic human bispecific antibody that inhibits IgE receptor signaling.

The development of bispecific antibodies as therapeutic agents for human diseases has great clinical potential, but broad application has been hindered by the difficulty of identifying bispecific antibody formats that exhibit favorable pharmacokinetic properties and ease of large-scale manufacturing. Previously, the development of an antibody technology utilizing heavy chain knobs-into-holes mutations and a single common light chain enabled the small-scale generation of human full-length bispecific antibodies. Here we have extended the technology by developing a two-part bispecific antibody discovery strategy that facilitates proof-of-concept studies and clinical candidate antibody generation. Our scheme consists of the efficient small-scale generation of bispecific antibodies lacking a common light chain and the hinge disulfides for proof-of-concept studies coupled with the identification of a common light chain bispecific antibody for large-scale production with high purity and yield. We have applied this technology to generate a bispecific antibody suitable for development as a human therapeutic. This antibody directly inhibits the activation of the high affinity IgE receptor FcepsilonRI on mast cells and basophils by cross-linking FcepsilonRI with the inhibitory receptor FcgammaRIIb, an approach that has strong therapeutic potential for asthma and other allergic diseases. Our approach for producing human bispecific full-length antibodies enables the clinical application of bispecific antibodies to a validated therapeutic pathway in asthma.

Substance P downregulates expression of the high affinity IgE receptor (FcepsilonRI) by human mast cells.

The effect of the neuropeptide substance P (SP) on human mast cell (MC) phenotype is poorly understood. In this study, SP effects on human MC expression of the high affinity IgE receptor (FcepsilonRI) were characterized. SP downregulated expression of FcepsilonRI mRNA and protein by approximately 50% and in a concentration dependent manner, the effect was partially mediated by engagement of the neurokinin-1 receptor (NK1R) and resulted in reduced mast cell activation. Sensitization of MC with IgE prior to SP exposure protected MC from SP-mediated FcepsilonRI downregulation. SP release may inhibit MC responses to allergens and these results may have implications in neuroinflammatiion and stress.

Use of lipid rafting for the analysis of human basophil activation by flow cytometry.

BACKGROUND: Human leukocyte activation induced by specific and non-specific stimuli is characterized by the formation of lipid rafts defined as lipid-ordered domains that are more tightly packed than the surrounding non-raft phase of the bilayer. These lipid rafts are formed in parallel with profound membrane reorganization. OBJECTIVES: Analyse the rafting and non-rafting proteins present on the activated and resting basophil membrane and study their interest for the flow cytometric analysis of basophil activation. METHODS: Human basophils obtained from samples used for diagnostic cellular tests such as basophil or lymphocyte activation tests were stimulated either by the formyl-methionyl-leucyl-phenylalanine peptide (fMLP), by an anti-IgE or by an allergen. After 40 min at 37 degrees C, they were labelled by different antibodies conjugated to fluorescent dyes as an anti-IgE FITC, an anti-CCR3 PE, an anti-CD63, an anti-CD203c PE, an anti-11b, annexin V FITC or by cholera toxin FITC. Moreover, several experiments were analysed using an Amnis cytometer, allowing one to obtain the picture of the analysed cells. RESULTS: Anti-IgE or specific allergen elicits a membrane neo expression of CD63 at a high density and is poorly represented on resting basophil membrane. Upon an IgE-dependant activation some of the markers already present on resting basophil membrane, as CD203c, are up regulated and others, such as the IgE/IgE FcepsilonRI receptor and CCR3 are down regulated and submitted to the formation of clusters demonstrated by the pictures taken with the Amnis cytometer. For non-IgE dependant activators, such as fMLP, the picture was different since IgE was not down regulated, whereas CCR3 was down regulated. As demonstrated using annexin V or the cholera toxin used for analysing apoptosis, these phenomenon were paralleled by the formation of lipid rafts, gangliosides domains, such as GM1, which is accessible from the extra cellular medium. CONCLUSIONS: Basophil activation leads to membrane events close to the apoptosis phenomenon. The flow cytometric analysis of these membrane events may lead to protocols for allergen-induced activation and, may significantly increase cellular test sensitivity, particularly for drugs allergy diagnosis for which the usual protocols, such as those using CD63 alone, are insufficiently sensitive.

Phospholipase d promotes lipid microdomain-associated signaling events in mast cells.

Initial IgE-dependent signaling events are associated with detergent-resistant membrane microdomains. Following Ag stimulation, the IgE-receptor (Fc(epsilon)RI ) accumulates within these domains. This facilitates the phosphorylation of Fc(epsilon)RI subunits by the Src kinase, Lyn, and the interaction with adaptor proteins, such as the linker for activation of T cells. Among the phospholipases (PL) subsequently activated, PLD is of interest because of its presence in lipid microdomains and the possibility that its product, phosphatidic acid, may regulate signal transduction and membrane trafficking. We find that in Ag-stimulated RBL-2H3 mast cells, the association of Fc(epsilon)RI with detergent-resistant membrane fractions is inhibited by 1-butanol, which subverts production of phosphatidic acid to the biologically inert phosphatidylbutanol. Furthermore, the knockdown of PLD2, and to a lesser extent PLD1 with small inhibitory RNAs, also suppressed the accumulation of Fc(epsilon)RI and Lyn in these fractions as well as the phosphorylation of Src kinases, Fc(epsilon)RI , linker for activation of T cells, and degranulation. These effects were accompanied by changes in distribution of the lipid microdomain component, ganglioside 1, in the plasma membrane as determined by binding of fluorescent-tagged cholera toxin B subunit and confocal microscopy in live cells. Collectively, these findings suggest that PLD activity plays an important role in promoting IgE-dependent signaling events within lipid microdomains in mast cells.

IgE-mediated allergen gene vaccine platform targeting human antigen-presenting cells through the high-affinity IgE receptor.

BACKGROUND: Treatment of IgE-mediated food allergy with standard protein-based allergen immunotherapy has proved both unsuccessful and hazardous. Allergen gene vaccination represents a promising alternative, but difficulties in gene targeting and expression in antigen-presenting cells represent a major limitation for efficient gene vaccination. OBJECTIVE: We sought to construct a genetically engineered human epsilon-polylysine (EPL) fusion protein that binds allergen gene expression systems and targets the gene vaccine complex to antigen-presenting cells through the interaction of EPL and the high-affinity receptor for IgE for efficient allergen gene vaccination. METHODS: Genetic engineering was used to design and produce the EPL fusion gene, consisting of the human CHepsilon2-4 linked to 55 lysine residues, and the conventional approaches were used to characterize the biologic features of EPL. RESULTS: EPL was assembled as functional dimers and capable of binding DNA plasmids in both an EPL protein and plasmid DNA concentration-dependent manner. EPL targeted plasmid DNA to the high-affinity receptor for IgE on cell surfaces and increased the model gene uptake/expression. The EPL-DNA complexes were shown not to trigger mast cell degranulation. CONCLUSION: EPL is able to function as a gene carrier system to target allergen gene to the high-affinity receptor for IgE-expressing cells through ligand receptor-mediated interactions.

Counter regulation of the high affinity IgE receptor, FcepsilonRI, on human airway dendritic cells by IL-4 and IL-10.

BACKGROUND: Immunoglobulin E is a signalling molecule within the environment of the respiratory tract, the high affinity receptor for which, FcepsilonRI, is expressed by dendritic cells (DC). Little is known, however, of the expression and function of FcepsilonRI on DC in the human respiratory tract. METHODS: CD1c(+) DC were purified from surgically resected nasal turbinates of 11 atopic and 12 nonatopic patients with chronic rhinosinusitis. Expression of FcepsilonRI was determined by flow cytometry. Cytokine production by DC was determined by cytometric bead array. RESULTS: Expression of FcepsilonRI was significantly elevated on respiratory tract dendritic cells (RTDC) from atopic as compared to nonatopic patients. Activation of RTDC through FcepsilonRI induced production of the pro-inflammatory cytokines IL-6 and TNF-alpha, and the anti-inflammatory cytokine IL-10. The production of IL-6 and TNF-alpha was elevated in atopic compared to nonatopic patients studied. Conversely IL-10 production was elevated in nonatopic patients. Concomitant activation of FcepsilonRI and stimulation of RTDC with IL-4 inhibited production of IL-10 by RTDC. Neutralization experiments with anti-IL-10 Ab enhanced whereas addition of exogenous IL-10 to RTDC inhibited FcepsilonRI-mediated inflammatory cytokine production. CONCLUSION: The function of FcepsilonRI on RTDC from patients with rhinosinusitis is susceptible to counter regulation by IL-4 and IL-10.

Houttuynia cordata water extract suppresses anaphylactic reaction and IgE-mediated allergic response by inhibiting multiple steps of FcepsilonRI signaling in mast cells.

Houttuynia cordata has been used as a traditional medicine in Korea and is known to have antioxidant, anti-cancer and anti-allergic activities. The precise effect of H. cordata, however, remains unknown. In this study, we investigated the effects of H. cordata water extract (HCWE) on passive cutaneous anaphylaxis (PCA) in mice and on IgE-mediated allergic response in rat mast RBL-2H3 cells. Oral administration of HCWE inhibited IgE-mediated systemic PCA in mice. HCWE also reduced antigen (DNP-BSA)-induced release of beta-hexosaminidase, histamine, and reactive oxygen species in IgE-sensitized RBL-2H3 cells. In addition, HCWE inhibited antigen-induced IL-4 and TNF-alpha production and expression in IgE-sensitized RBL-2H3 cells. HCWE inhibited antigen-induced activation of NF-kappaB and degradation of IkappaB-alpha. To investigate the inhibitory mechanism of HCWE on degranulation and cytokine production, we examined the activation of intracellular FcepsilonRI signaling molecules. HCWE suppressed antigen-induced phosphorylation of Syk, Lyn, LAT, Gab2, and PLC gamma2. Further downstream, antigen-induced phosphorylation of Akt and MAP kinases (ERK1/2 and JNK1/2 but not p38 MAP kinase) were inhibited by HCWE. Taken together, the in vivo/in vitro anti-allergic effect of HCWE suggests possible therapeutic applications of this agent in inflammatory allergic diseases through inhibition of cytokines and multiple events of FcepsilonRI-dependent signaling cascades in mast cells.

Eosinophils in bronchial mucosa of asthmatics after allergen challenge: effect of anti-IgE treatment.

BACKGROUND: Anti-IgE, omalizumab, inhibits the allergen response in patients with asthma. This has not been directly related to changes in inflammatory conditions. We hypothesized that anti-IgE exerts its effects by reducing airway inflammation. To that end, the effect of anti-IgE on allergen-induced inflammation in bronchial biopsies in 25 patients with asthma was investigated in a randomized, double-blind, placebo-controlled study. METHODS: Allergen challenge followed by a bronchoscopy at 24 h was performed at baseline and after 12 weeks of treatment with anti-IgE or placebo. Provocative concentration that causes a 20% fall in forced expiratory volume in 1 s (PC(20)) methacholine and induced sputum was performed at baseline, 8 and 12 weeks of treatment. Changes in the early and late responses to allergen, PC(20), inflammatory cells in biopsies and sputum were assessed. RESULTS: Both the early and late asthmatic responses were suppressed to 15.3% and 4.7% following anti-IgE treatment as compared with placebo (P < 0.002). This was paralleled by a decrease in eosinophil counts in sputum (4-0.5%) and postallergen biopsies (15-2 cells/0.1 mm(2)) (P < 0.03). Furthermore, biopsy IgE+ cells were significantly reduced between both the groups, whereas high-affinity IgE receptor and CD4+ cells were decreased within the anti-IgE group. There were no significant differences for PC(20) methacholine. CONCLUSION: The response to inhaled allergen in asthma is diminished by anti-IgE, which in bronchial mucosa is paralleled by a reduction in eosinophils and a decline in IgE-bearing cells postallergen without changing PC(20) methacholine. This suggests that the benefits of anti-IgE in asthma may be explained by a decrease in eosinophilic inflammation and IgE-bearing cells.

An immunoglobulin E-reactive chimeric human immunoglobulin G1 anti-idiotype inhibits basophil degranulation through cross-linking of FcepsilonRI with FcgammaRIIb.

BACKGROUND: IgE binds to mast cells and basophils via its high-affinity receptor, FcepsilonRI, and cross-linking of FcepsilonRI-bound IgE molecules by allergen leads to the release of allergic mediators characteristic of type I hypersensitivity reactions. Previous work has shown that cross-linking of FcepsilonRI with FcgammaRIIb, an ITIM-containing IgG receptor, leads to inhibition of basophil triggering. 2G10, a chimeric human IgG1 anti-idiotype, has broad reactivity with human IgE and as such has the potential to bind simultaneously to FcepsilonRI-bound IgE, via its Fab regions, and the negative regulatory receptor, FcgammaRIIb, via its Fc region. OBJECTIVE: To assess the ability of human 2G10 to inhibit anti-IgE and allergen-driven basophil degranulation through cross-linking of FcepsilonRI-bound IgE with FcgammaRIIb. METHODS: 2G10 was assessed for its ability to bind to FcgammaRIIb on transfected cells and on purified basophils. In the basophil degranulation assay, basophils were purified from peripheral blood of atopic individuals and activated with either anti-IgE or the house dust mite allergen Der p 1, in the presence or absence of human 2G10. Basophil activation was quantified by analysis of CD63 and CD203c expression on the cell surface, and IL-4 expression intracellularly, using flow cytometery. RESULTS: Human 2G10 was able to bind to FcgammaRIIb on transfected cells and on purified basophils, and induce a dose-dependent inhibition of both anti-IgE and Der p 1-driven degranulation of basophils. CONCLUSION: The inhibition of basophil degranulation by the human IgG1 anti-idiotype 2G10 highlights the therapeutic potential of IgE-reactive IgG antibodies in restoring basophil integrity through recruitment of the inhibitory receptor FcgammaRIIb.