Establishment of antigen-specific IgE transgenic mice to study pathological and immunobiological roles of IgE in vivo

α7 nicotinic acetylcholine receptor agonist attenuates allergen-induced immediate nasal response in murine model of allergic rhinitis

The expression of nicotinic acetylcholine receptor (nAChR) subunits on various immune cells suggests their involvement in allergic rhinitis. However, how exactly they contribute to this pathogenesis is not yet confirmed. Our present study examined the therapeutic potential of GTS-21, an α7 nAChR agonist, for treating allergic rhinitis by employing its mouse models. GTS-21 treatment reduced allergen-induced immediate nasal response in ovalbumin (OVA)-sensitized model. However, nasal hyperresponsiveness or eosinophil infiltration elicited in either the OVA-sensitized or T helper 2 cell-transplanted model was not affected by GTS-21. GTS-21 did not alter allergen-induced passive cutaneous anaphylaxis response in anti-dinitrophenyl IgE-sensitized mice. This evidence implies GTS-21's potential to alleviate allergic rhinitis without perturbing T cells or mast cells.

Basophils Orchestrating Eosinophils' Chemotaxis and Function in Allergic Inflammation

Eosinophils are well known to contribute significantly to Th2 immunity, such as allergic inflammations. Although basophils have often not been considered in the pathogenicity of allergic dermatitis and asthma, their role in Th2 immunity has become apparent in recent years. Eosinophils and basophils are present at sites of allergic inflammations. It is therefore reasonable to speculate that these two types of granulocytes interact in vivo. In various experimental allergy models, basophils and eosinophils appear to be closely linked by directly or indirectly influencing each other since they are responsive to similar cytokines and chemokines. Indeed, basophils are shown to be the gatekeepers that are capable of regulating eosinophil entry into inflammatory tissue sites through activation-induced interactions with endothelium. However, the direct evidence that eosinophils and basophils interact is still rarely described. Nevertheless, new findings on the regulation and function of eosinophils and basophils biology reported in the last 25 years have shed some light on their potential interaction. This review will focus on the current knowledge that basophils may regulate the biology of eosinophil in atopic dermatitis and allergic asthma.

Activation of the MEK-ERK Pathway Is Necessary but Not Sufficient for Breaking Central B Cell Tolerance

Newly generated bone marrow B cells are positively selected into the peripheral lymphoid tissue only when they express a B cell receptor (BCR) that is nonautoreactive or one that binds self-antigen with only minimal avidity. This positive selection process, moreover, is critically contingent on the ligand-independent tonic signals transduced by the BCR. We have previously shown that when autoreactive B cells express an active form of the rat sarcoma (RAS) oncogene, they upregulate the receptor for the B cell activating factor (BAFFR) and undergo differentiation in vitro and positive selection into the spleen in vivo, overcoming central tolerance. Based on the in vitro use of pharmacologic inhibitors, we further showed that this cell differentiation process is critically dependent on the activation of the mitogen-activated protein kinase kinase pathway MEK (MAPKK)-extracellular signal-regulated kinase (ERK), which is downstream of RAS. Here, we next investigated if activation of ERK is not only necessary but also sufficient to break central B cell tolerance and induce differentiation of autoreactive B cells in vitro and in vivo. Our results demonstrate that activation of ERK is critical for upregulating BAFFR and overcoming suboptimal levels of tonic BCR signals or low amounts of antigen-induced BCR signals during in vitro B cell differentiation. However, direct activation of ERK does not lead high avidity autoreactive B cells to increase BAFFR levels and undergo positive selection and differentiation in vivo. B cell-specific MEK-ERK activation in mice is also unable to lead to autoantibody secretion, and this in spite of a general increase of serum immunoglobulin levels. These findings indicate that additional pathways downstream of RAS are required for high avidity autoreactive B cells to break central and/or peripheral tolerance.

B Cell Intrinsic Mechanisms Constraining IgE Memory

Memory B cells and long-lived plasma cells are key elements of adaptive humoral immunity. Regardless of the immunoglobulin class produced, these cells can ensure long-lasting protection but also long-lasting immunopathology, thus requiring tight regulation of their generation and survival. Among all antibody classes, this is especially true for IgE, which stands as the most potent, and can trigger dramatic inflammatory reactions even when present in minute amounts. IgE responses and memory crucially protect against parasites and toxic components of venoms, conferring selective advantages and explaining their conservation in all mammalian species despite a parallel broad spectrum of IgE-mediated immunopathology. Long-term memory of sensitization and anaphylactic responses to allergens constitute the dark side of IgE responses, which can trigger multiple acute or chronic pathologic manifestations, some punctuated with life-threatening events. This Janus face of the IgE response and memory, both necessary and potentially dangerous, thus obviously deserves the most elaborated self-control schemes.

Polyclonal hyper-IgE mouse model reveals mechanistic insights into antibody class switch recombination

Preceding antibody constant regions are switch (S) regions varying in length and repeat density that are targets of activation-induced cytidine deaminase. We asked how participating S regions influence each other to orchestrate rearrangements at the IgH locus by engineering mice in which the weakest S region, Sε, is replaced with prominent recombination hotspot Sμ. These mice produce copious polyclonal IgE upon challenge, providing a platform to study IgE biology and therapeutic interventions. The insertion enhances ε germ-line transcript levels, shows a preference for direct vs. sequential switching, and reduces intraswitch recombination events at native Sμ. These results suggest that the sufficiency of Sμ to mediate IgH rearrangements may be influenced by context-dependent cues.

IgE knock-in mice suggest a role for high levels of IgE in basophil-mediated active systemic anaphylaxis

Immunoglobulin E (IgE) production is tightly regulated at the cellular and genetic levels and is believed to be central to allergy development. At least two cellular pathways exist that lead to systemic anaphylaxis reactions in vivo: IgE-sensitized mast cells and IgG1-sensitized basophils. Passive anaphylaxis, by application of allergen and allergen-specific antibodies in mice, indicates a differential contribution of immunoglobulin isotypes to anaphylaxis. However, analysis of a dynamic immunization-mediated antibody response in anaphylaxis is difficult. Here, we generated IgE knock-in mice (IgE(ki) ), which express the IgE heavy chain instead of IgG1, in order to analyze the contribution of IgG1 and IgE to active anaphylaxis in vivo. IgE(ki) mice display increased IgE production both in vitro and in vivo. The sensitization of IgE(ki) mice by immunization followed by antigen challenge leads to increased anaphylaxis. Homozygous IgE(ki) mice, which lack IgG1 due to the knock-in strategy, are most susceptible to active systemic anaphylaxis. The depletion of basophils demonstrates their importance in IgE-mediated anaphylaxis. Therefore, we propose that an enhanced, antigen-specific, polyclonal IgE response, as is the case in allergic patients, is probably the most efficient way to sensitize basophils to contribute to systemic anaphylaxis in vivo.

Monomeric IgE and mast cell development, survival and function

Mast cells play a major role in allergy and anaphylaxis, as well as a protective role in immunity against bacteria and venoms (innate immunity) and T-cell activation (acquired immunity).1,2 It was long thought that two steps are essential to mast cell activation. The first step (sensitization) occurs when antigen-specific IgE binds to its high-affinity IgE receptor (FcεRI) expressed on the surface of mast cells. The second step occurs when antigen (Ag) or anti-IgE binds antigen-specific IgE antibodies bound to FcεRI present on the mast cell surface (this mode of stimulation hereafter referred to as IgE+Ag or IgE+anti-IgE stimulation, respectively).Conventional wisdom has been that monomeric IgE plays only an initial, passive role in mast cell activation. However, recent findings have shown that IgE binding to its receptor FcεRI can mediate mast cell activation events even in the absence of antigen (this mode of stimulation hereafter referred to as IgE(-Ag) stimulation). Different subtypes of monomeric IgEs act via IgE(-Ag) stimulation to elicit varied effects on mast cells function, survival and differentiation. This chapter will describe the role of monomeric IgE molecules in allergic reaction, the various effects and mechanisms of action of IgE(-Ag) stimulation on mast cells and what possible developments may arise from this knowledge in the future. Since mast cells are involved in a variety of pathologic and protective responses, understanding the role that monomeric IgE plays in mast cell function, survival and differentiation will hopefully lead to better understanding and treatment of asthma and other allergic diseases, as well as improved understanding of host response to infections.

The role of IgE and repeated challenge in the induction of persistent increases in scratching behavior in a mouse model of allergic dermatitis

Previously, we indicated that athymic BALB/c-nu/nu (nude) mice that had been repeatedly treated with 2,4,6-trinitrochlorobenzene (TNCB) failed to exhibit chronic scratching behavior in spite of the accumulation of dermal mast cells in the lesion. The mice also failed to produce specific IgE or potent dermatitis. In the present study, therefore, we aimed to examine the role of IgE and repeated hapten treatment in the induction of scratching behavior and dermatitis using nude mice and trinitrophenol (TNP)-specific IgE-transgenic mice. The ears of nude mice were treated with TNCB 6 times at intervals of 48 h, and TNP-specific IgE was administered to the mice intravenously before the sixth TNCB treatment. The nude mice that had been supplemented with IgE exhibited a persistent increase in scratching behavior and continuous degranulation of mast cells. Furthermore, a potent immediate ear swelling was induced, although no biphasic dermatitis pattern was observed. On the other hand, the IgE-transgenic mice failed to exhibit persistent increases in scratching behavior after a single TNCB treatment, although biphasic ear swelling was observed. These results indicate that specific IgE plays an essential role in the induction of persistent increases in scratching behavior and continuous degranulation of mast cells. Furthermore, repeated challenge with the hapten also plays an important role in persistent increases in scratching behavior through accumulation and continuous activation of mast cells.

New insights into the roles for basophils in acute and chronic allergy

Basophils represent less than 1% of peripheral blood leukocytes. They are often recruited to the site of allergic inflammation, albeit in small numbers. However, it remained uncertain whether basophils play any significant role in allergic reactions or act as minor and redundant 'circulating mast cells'. We have recently demonstrated that basophils play critical roles in systemic anaphylaxis and chronic allergic inflammation, distinctively from mast cells. Basophils are one of the major players in the IgG- but not IgE-mediated systemic anaphylaxis, in contrast to mast cells. In response to the allergen-IgG immune complexes, basophils release the platelet-activating factor rather than histamine as the major chemical mediator to induce the systemic anaphylaxis. The depletion of basophils protects mice from death due to anaphylactic shock. Basophils also play a crucial role in the development of the IgE-mediated chronic allergic inflammation with massive eosinophil infiltration in the skin, independently of T cells and mast cells, even though basophils account for only approximately 2% of the infiltrates. The basophil depletion shows a therapeutic effect on on-going allergic inflammation. Accumulating evidence suggests that basophils function as initiators rather than effectors of the chronic allergic inflammation. Thus, basophils and their products seem to be promising therapeutic targets for allergic disorders.

Characterization of dog allergens Can f 1 and Can f 2. 1. Preparation of their recombinant proteins and antibodies

BACKGROUND

Recombinant dog allergens, rCan f 1 and rCan f 2, and their antibodies are good tools for the characterization of dog allergens in order to develop modern therapeutic and preventive methods for dog allergy.

METHODS

In this study, cDNA was synthesized from the mRNA of dog salivary glands and cloned into the pGEX4T vector. rCan f 1 and rCan f 2 containing glutathione S-transferase were prepared by an Escherichia coli expression system. The antibodies against the recombinant allergens were prepared in rabbit. The serum of patients with dog allergy was evaluated by ELISA and immunoblot, using the recombinant allergens, goat anti-human immunoglobulin (Ig) E (epsilon) labeled with biotin, and enzyme-labeled streptavidin. The binding of IgE in the serum of patients with dog allergy to dog saliva as a natural antigen was determined in the presence or absence of dog saliva, rCan f 1 and rCan f 2 as competitors. The anaphylactic potential of rCan f 1 and rCan f 2 was evaluated. The body temperature of the mice sensitized with rCan f 1 and rCan f 2 was monitored after intravenous injection of the allergens. The passive cutaneous anaphylaxis reaction was examined for rCan f 1 and rCan f 2. Dog salivary glands, dog saliva and dog hair/dander extracts were analyzed with antibodies by means of an immunoblot assay. The expression of the mRNA of Can f 1 and Can f 2 was verified in various dog tissues by reverse transcription polymerase chain reaction.

RESULTS

The E. coli expression system revealed the yield of rCan f 1 and rCan f 2 in 36 and 30 mg/l of culture. The molecular weights of rCan f 1 and rCan f 2 were 18 and 20 kDa in SDS-PAGE, respectively. rCan f 1 and rCan f 2 were found to bind to specific IgE in the serum of dog allergy patients. The binding of IgE in the patient serum for dog saliva was partially inhibited in the presence of rCan f 1 and rCan f 2. These recombinant allergens showed positive signals in passive cutaneous anaphylaxis reaction and induced anaphylactic shock in the mouse model, resulting in a decrease in body temperature. The polyclonal rabbit antibody for rCan f 1 bound to a protein of 20 kDa in the salivary gland, saliva and hair/dander extracts of dogs. The rabbit antibody for rCan f 2 bound to proteins in the saliva and the hair/dander extracts. The proteins possessed a molecular weight of 22/ 23 kDa. Reverse transcription polymerase chain reaction showed the presence of mRNA expression of Can f 1 and Can f 2 not only in the salivary gland but also in dog skin. A clear expression of Can f 2 mRNA was observed in dog skin.

CONCLUSIONS

The recombinant allergens and antibodies for Can f 1 and Can f 2 are available for immunological and biochemical characterization of dog allergens. The molecular weight of the natural Can f 1 and Can f 2 in dog saliva and hair/dander extracts showed a higher molecular weight than that of rCan f 1 and rCan f 2. The significance of dog skin as the tissue producing dog allergens, especially Can f 2, should be considered in further studies.

Mast cell survival and activation by IgE in the absence of antigen: a consideration of the biologic mechanisms and relevance

Mast cells are not only major effector cells in allergy and host defense against parasites and bacteria but also important cellular components in other immune responses. Recent studies on the effects of monomeric IgE on mast cell survival and activation have made an impact on our view of the IgE binding to its high-affinity receptors, Fc epsilonRI. Traditionally, IgE binding to Fc epsilonRI has been considered as a passive action of "sensitization" before receptor aggregation by Ag. However, recent studies indicate that at high concentrations some monoclonal IgEs have effects on mast cells similar to or identical to those induced by IgE+Ag stimulation. These effects may be due to induction of Fc epsilonRI aggregation by these IgEs in the absence of Ag. This review will synthesize recent findings of the heterogeneity of IgEs in their ability to induce survival and activation events, their mechanisms, the potential in vivo significance of IgE-Fc epsilonRI interactions, and the implications of the mouse studies to human diseases.

Basophils play a critical role in the development of IgE-mediated chronic allergic inflammation independently of T cells and mast cells

The recruitment of basophils into the sites of allergic inflammation is often observed. However, no definitive evidence has been provided that basophils are crucially involved in the pathogenesis of chronic allergic disorders. Here, we show that basophils are responsible for the development of IgE-mediated chronic allergic inflammation independently of T cells and mast cells. A single subcutaneous injection of multivalent antigens elicited not only immediate- and late-phase ear swelling but also delayed-onset ear swelling with massive eosinophil infiltration in mice sensitized with antigen-specific IgE. Mast cells were essential for the immediate- and late-phase ear swelling but dispensable for the delayed one. T cells were also dispensable for the latter. Transfer of FcRI-expressing basophils into FcRI-deficient mice restored the development of the delayed-onset allergic inflammation. These findings indicate a novel mechanism of development of chronic allergic inflammation that is induced by basophils through the interaction of antigen, IgE, and FcRI.

Ovalbumin-specific IgE modulates ovalbumin-specific T-cell response after repetitive oral antigen administration

BACKGROUND

Some patients outgrow their food allergies even though their serum antigen-specific IgE levels remain high.

OBJECTIVE

To elucidate the role of T cells in outgrowing food allergies in the presence of antigen-specific IgE, we tracked antigen-specific T-cell responses after oral antigen administration.

METHODS

Ovalbumin (OVA)-specific T-cell receptor (TCR) and OVA-specific IgE transgenic (Tg) mice (OVA-TCR/IgE-Tg) and OVA-specific TCR Tg (OVA-TCR-Tg) mice were fed with high doses of OVA or PBS every other day. After 7 administrations, OVA-specific proliferation and cytokine production of mononuclear cells of the spleen, mesenteric lymph nodes, and Peyer's patches and the number of splenic CD4 + CD25 + T cells were analyzed.

RESULTS

Without OVA administration, the splenocytes from OVA-TCR/IgE-Tg mice exhibited a higher proliferative response and produced more IL-4 and IL-10 and less IFN-gamma than those from OVA-TCR-Tg mice. The proliferative responses of the splenocytes from either OVA-TCR/IgE-Tg mice or OVA-TCR-Tg mice fed with OVA were significantly reduced compared with those from PBS-fed mice. The number of OVA-specific TCR + T cells decreased in the spleen from OVA-fed mice, whereas the number of CD4 + CD25 + T cells increased. The suppressed proliferation of splenocytes of OVA-fed mice was partially resumed by neutralization of TGF-beta1, but not of IL-10.

CONCLUSION

The presence of OVA-specific IgE modulated the OVA-specific responses of the splenocytes. Irrespective of the presence of OVA-specific IgE, repetitive oral administration of OVA induced tolerance, which seems to be composed of clonal deletion/anergy and TGF-beta1-mediated active suppression.

IgE-dependent enhancement of Th2 cell-mediated allergic inflammation in the airways

T helper 2 (Th2) cell-derived cytokines, including interleukin (IL)-4, IL-5 and IL-13, play important roles in causing allergic airway inflammation. In contrast to Th2 cells, however, the role of IgE and mast cells in inducing allergic airway inflammation is not understood fully. In the present study, we addressed this point using transgenic mice expressing trinitrophenyl (TNP)-specific IgE (TNP-IgE mice), which enable us to investigate the role of IgE without the influence of antigen-specific T cell activation and other immunoglobulins. When the corresponding antigen, TNP-BSA, was administered intranasally to TNP-IgE mice, a large number of CD4+ T cells were recruited into the airways. In contrast, TNP-BSA administration did not induce eosinophil recruitment into the airways or airway hyperreactivity. Furthermore, when ovalbumin (OVA)-specific Th2 cells were transferred to TNP-IgE mice and the mice were challenged with inhaled OVA, TNP-BSA administration increased OVA-specific T cell recruitment and then enhanced Th2 cell-mediated eosinophil recruitment into the airways. These results indicate that IgE-induced mast cell activation principally induces CD4+ T cell recruitment into the airways and thus plays an important role in enhancing Th2 cell-mediated eosinophilic airway inflammation by recruiting Th2 cells into the site of allergic inflammation.

Long term maintenance of IgE-mediated memory in mast cells in the absence of detectable serum IgE

Mast cells and basophils involved in allergic responses do not have clonotypic Ag receptors. However, they can acquire Ag specificity through binding of Ag-specific IgE to FcepsilonRI expressed on their surface. Previous studies demonstrated that IgE binding induced the stabilization and accumulation of FcepsilonRI on the cell surface and resulted in up-regulation of FcepsilonRI. In this study we have further analyzed the maintenance of IgE-mediated memory in mast cells and basophils in vivo by comparing kinetics of serum IgE levels, FcepsilonRI expression, and ability to induce systemic anaphylaxis. A single i.v. injection of trinitrophenyl-specific IgE induced 8-fold up-regulation of FcepsilonRI expression on peritoneal mast cells in B cell-deficient (micro m(-/-)) mice. Serum IgE levels became undetectable by day 6, but the treatment of mice with anti-IgE mAb induced a significant drop in body temperature on days 14, 28, and 42. The administration of trinitrophenyl -BSA, but not BSA, in place of anti-IgE mAb gave similar results, indicating the Ag specificity of the allergic response. This long term maintenance of Ag-specific reactivity in the allergic response was also observed in normal mice passively sensitized with IgE even though the duration was shorter than that in B cell-deficient mice. The appearance of IgE with a different specificity did not interfere with the maintenance of IgE-mediated memory of mast cells and basophils. These results suggest that IgE-mediated stabilization and up-regulation of FcepsilonRI enables mast cells and basophils not only to acquire Ag specificity, but also to maintain memory in vivo for lengthy periods of time.

Chronic inflammation of the skin can be induced in IgE transgenic mice by means of a single challenge of multivalent antigen

BACKGROUND

It is now widely accepted that IgE mediates immediate-type allergic response. However, the pathologic role of IgE is controversial in the chronic allergic inflammation observed in atopic diseases, such as asthma and atopic dermatitis.

OBJECTIVE

We investigated the role of IgE in cutaneous allergic reactions by using 2 newly developed lines of antigen-specific IgE transgenic mice.

METHODS

IgE transgenic mice were administered subcutaneously with corresponding antigens, and the subsequent ear swelling was measured.

RESULTS

A single subcutaneous administration of TNP-conjugated ovalbumin (OVA) into the ears of nonimmunized mice carrying the TNP-specific IgE transgene elicited immediate-phase and late-phase ear swelling as expected, which peaked at 20 minutes and 8 hours later, respectively. Interestingly, however, 2 to 3 days after the antigen challenge, more intense ear swelling appeared. Its magnitude and duration were dependent on the valency of TNP in OVA, as well as the dose of TNP-OVA, and it lasted over 1 month when 100 microg of OVA conjugated with 11 molecules of TNP was given. Interestingly, administration of OVA to OVA-specific IgE transgenic mice elicited immediate-phase and late-phase ear swelling but not third-phase ear swelling. Massive infiltration of inflammatory cells was observed in the third-phase ear swelling of TNP-specific IgE transgenic mice. Cyclosporine A almost completely inhibited the third-phase ear swelling and cellular infiltration, whereas an antihistamine, cyproheptadine, did not show any significant effect on the third-phase reaction.

CONCLUSION

These results indicate that IgE can trigger not only immediate-type hypersensitivity but also chronic allergic inflammation. Our findings highlight a novel immunopathologic role of IgE in chronic atopic disorders.

Regulation of mast-cell and basophil function and survival by IgE

Mast cells and basophils are important effector cells in T helper 2 (T(H)2)-cell-dependent, immunoglobulin-E-associated allergic disorders and immune responses to parasites. The crosslinking of IgE that is bound to the high-affinity receptor Fc epsilon RI with multivalent antigen results in the aggregation of Fc epsilon RI and the secretion of products that can have effector, immunoregulatory or autocrine effects. This response can be enhanced markedly in cells that have been exposed to high levels of IgE, which results in the increased surface expression of Fc epsilon RI. Moreover, recent work indicates that monomeric IgE (in the absence of crosslinking) can render mast cells resistant to apoptosis induced by growth-factor deprivation in vitro and, under certain circumstances, can induce the release of cytokines. So, the binding of IgE to Fc epsilon RI might influence mast-cell and basophil survival directly or indirectly, and can also regulate cellular function.

Lactobacillus casei strain Shirota suppresses serum immunoglobulin E and immunoglobulin G1 responses and systemic anaphylaxis in a food allergy model

BACKGROUND

Our previous study using allergen-sensitized murine splenocyte cultures has shown that Lactobacillus casei strain Shirota (LcS), a lactic acid bacterium widely used as a starter for fermented milk products, suppresses IgE production through promoting a dominant Th1-type response mediated by IL-12 induction.

OBJECTIVE

We tried to evaluate the ability of LcS to suppress both IgE response and allergic reactions in vivo using a food allergy model with ovalbumin-specific T cell receptor transgenic (OVA-TCR-Tg) mice.

METHODS

The ability of heat-killed LcS to induce IL-12 in serum was tested. OVA-TCR-Tg mice were fed a diet containing OVA for 4 weeks and injected with LcS intraperitoneally three times in the first week of this period. Cytokine and antibody secretion by splenocytes, and serum IgE and IgG1 responses were examined. The inhibitory effect of LcS on systemic anaphylaxis induced by intravenous challenge of OVA-fed OVA-TCR-Tg mice with OVA was also tested.

RESULTS

Intraperitoneal injection of LcS induced an IL-12 response in the serum of OVA-TCR-Tg mice. In the food allergy model, LcS administration skewed the pattern of cytokine production by splenocytes toward Th1 dominance, and suppressed IgE and IgG1 secretion by splenocytes. The ability of LcS to modulate cytokine production was blocked by anti-IL-12 antibody treatment. LcS also inhibited serum OVA-specific IgE and IgG1 responses and diminished systemic anaphylaxis.

CONCLUSION

LcS administration suppresses IgE and IgG1 responses and systemic allergic reactions in a food allergy model, suggesting a possible use of this lactic acid bacterium in preventing food allergy.

Drastic up-regulation of Fcepsilonri on mast cells is induced by IgE binding through stabilization and accumulation of Fcepsilonri on the cell surface

It has been shown that IgE binding to FcepsilonRI on mast cells results in increased FcepsilonRI expression, which in turn enhances IgE-dependent chemical mediator release from mast cells. Therefore, prevention of the IgE-mediated FcepsilonRI up-regulation would be a promising strategy for management of allergic disorders. However, the mechanism of IgE-mediated FcepsilonRI up-regulation has not been fully elucidated. In this study, we analyzed kinetics of FcepsilonRI on peritoneal mast cells and bone marrow-derived mast cells. In the presence of brefeldin A, which prevented transport of new FcepsilonRI molecules to the cell surface, levels of IgE-free FcepsilonRI on mast cells decreased drastically during culture, whereas those of IgE-bound FcepsilonRI were stable. In contrast, levels of FcgammaRIII on the same cells were stable even in the absence of its ligand, indicating that FcepsilonRI alpha-chain, but not beta- and gamma-chains, was responsible for the instability of IgE-free FcepsilonRI. As far as we analyzed, there was no evidence to support the idea that IgE binding to FcepsilonRI facilitated synthesis and/or transport of FcepsilonRI to the cell surface. Therefore, the stabilization and accumulation of FcepsilonRI on the cell surface through IgE binding appears to be the major mechanism of IgE-mediated FcepsilonRI up-regulation.