Age-dependent increase of IgE-binding and FcepsilonRI expression on circulating basophils in children

Peripheral blood basophils are sparse in the circulation, but they express high-affinity receptors for IgE (FCepsilonRI) and bind IgE efficiently. The present study was performed to elucidate the role of IgE bound on the basophil surface in the development of allergic responses during infancy and early childhood. IgE-binding and FcepsilonRI expression on basophils were evaluated by two-color flow cytometry. Basophil-bound IgE increased rapidly and reached adult levels during infancy in atopic patients, while it gradually increased with advancing age in parallel with serum IgE in normal controls. IgE-binding and FcepsilonRI expression in atopic children were higher than in normal controls among various age groups. They correlated with serum IgE levels but reached a plateau when serum IgE exceeded 300 ng/mL. A low, but significant level of FcepsilonRI expression was observed on cord blood basophils, although IgE-binding was usually undetectable. Incubation of cord blood with IgE rapidly saturated the preexisting IgE receptors and basophil-bound IgE levels increased. When neonatal basophils were cultured for 48 h with IgE, FcepsilonRI expression was upregulated dose-dependently and IgE-binding increased further. The up-regulation of FcepsilonRI was completely inhibited by cycloheximide, indicating that it was dependent on de novo protein synthesis. These results suggest that IgE-binding on basophils serves as a sensitive indicator of allergic sensitization, and that IgE functions as a positive regulator of FcepsilonRI expression in vivo.

NC/Nga mice: a mouse model for atopic dermatitis

Atopic dermatitis (AD) is a common pruritic disease that occurs primarily in infancy and childhood. AD is characterized by itching and the patient having an individual or family history of atopic diseases. Although AD is also frequently associated with elevated serum IgE levels and with common environmental factors contributing to its pathogenesis, the etiology of AD is still unknown. We examined NC/Nga mice (NC mice) that showed AD-like skin lesions with aging as a possible mouse model for AD. NC mice were maintained under conventional (Conv) or specific pathogen-free (SPF) conditions. Clinical symptoms, serum IgE levels and histopathology of the skin were compared between these 2 groups, and we explored their application as a model of human AD. It was found that the skin lesions of inbred NC mice were clinically and histologically very similar to human AD when the mice were raised under Conv conditions, but not under SPF conditions, and we assumed that some kinds of environmental factors might trigger AD-like signs and symptoms in NC mice. To further investigate the pathophysiology and treatment of AD, a suitable animal model is absolutely required, and NC mice are very useful for this purpose.

Atopic asthma is dominant in elderly onset asthmatics: possibility for an alteration of mast cell function by aging through Fc receptor expression

The morbidity and mortality of elderly onset asthma have recently been on the increase. To evaluate the allergic status of the elderly onset asthmatics, we performed skin tests for allergens and estimated serum total IgE levels of the patients. The proportion of the skin-test-positive patients among the elderly onset asthmatics was significantly larger than that in the younger onset group, whereas no significant difference was observed in the frequency of patients with serum total IgE levels higher than the normal range (287.2 IU/ml). On the other hand, in the experiments with aged mice, isolated peritoneal mast cells (PMC) showed a considerable decrease in the FcgammaRIIB/III expression and higher degranulation triggered by 2.4G2, as compared to the PMC derived from young mice. Since FcgammaRIIB has been shown to act as a negative regulator, we speculate that in the aged mice Fc receptor-mediated mast cell function may be upregulated by a release from the negative regulation as a result of decreased FcgammaRIIB expression. Our results obtained from a mouse model system may help to understand pathophysiological mechanisms underlying elderly onset asthma.

Stimulatory function of paired immunoglobulin-like receptor-A in mast cell line by associating with subunits common to Fc receptors

Paired Ig-like receptors (PIR) are polymorphic type I transmembrane proteins belonging to an Ig superfamily encoded by multiple isotypic genes. They are expressed on immune cells such as mast cells, macrophages, and B lymphocytes. Two subtypes of PIR have been classified according to the difference in the primary structure of the PIR transmembrane and cytoplasmic regions. These subtypes are designated as PIR-A and PIR-B. In this study, the transmembrane and cytoplasmic regions of the PIR-A subtype were shown to mediate activation signal events such as cytoplasmic calcium mobilization, protein tyrosine phosphorylations, and degranulation in rat mast cell line RBL-2H3. The association of the Fc receptor gamma and beta subunits with PIR-A was shown to be responsible for PIR-A function but not required for membrane expression of PIR-A on COS-7 cells. We further revealed the role of two charged amino acid residues in the transmembrane region, namely arginine and glutamic acid, in PIR-A function and its association with the above subunits. In contrast to the inhibitory nature of the PIR-B subtype, present findings reveal that PIR-A potentially acts as a stimulatory receptor in mast cells, suggesting a mechanism for regulation of mast cell functions by the PIR family.

The transcription factors Elf-1 and GATA-1 bind to cell-specific enhancer elements of human high-affinity IgE receptor alpha-chain gene

Key regulatory regions necessary for the expression of the gene encoding FcepsilonRI alpha-chain, a component of the high-affinity IgE receptor primarily responsible for IgE-dependent allergic response, were investigated. Two regions, -74/-69 and -55/-47, which contained binding motifs for proteins belonging to the Ets family and the GATA family, respectively, were shown to be necessary for the activation of the alpha-chain promoter. Both the regulatory elements enhanced the promoter activity only in alpha-chain-producing cells PT18 and RBL-2H3 (mast cell lines), indicating that the elements required specific trans-acting proteins present in the alpha-chain-producing cells. EMSA using nuclear extracts and in vitro-translated proteins revealed that Elf-1 and GATA-1 bound to the enhancer elements. This is the first report describing the regulation in the expression of the FcepsilonRI alpha-chain.

Anti VLA-4 monoclonal antibody inhibits eosinophil infiltration in allergic conjunctivitis model of guinea pig

PURPOSE

To determine the contribution of very late activation antigen-4 (VLA-4) molecule to eosinophil infiltration into the conjunctiva in an actively sensitized allergic conjunctivitis model of guinea pig, effects of a monoclonal antibody against VLA-4 was examined in vivo.

METHODS

A rat anti-mouse VLA-4 mAb (PS 2. 3), which cross-reacts with guinea pig VLA-4, inhibited the adhesion and transmigration of guinea pig eosinophils to /through human umbilical vein endothelial cells (HUVEC) in vitro. Hartley guinea pigs were actively sensitized by intraperitoneal injection of ovalbumin with aluminum hydroxide. Two weeks later, 2.5% ovalbumin was dropped into the eye for the antigen challenge. In the treatment group, 4 mg/kg (body weight) of the anti VLA-4 mAb (PS2.3), and in the control group, the same amount of a control Ab was intraperitoneally injected respectively at 4 hours before the antigen challenge. From both groups, the eyelids and eyeballs were excised at 2, 4, 10, and 24 hours after the antigen challenge, fixed, stained with Hansel solution and the number of the infiltrating eosinophils in the conjunctiva was counted.

RESULTS

In the control group, infiltration of eosinophils to the conjunctiva increased with time, peaked at 12 hours, and then gradually decreased until 24 hours after the antigen challenge. In the anti VLA4-mAb treated group, eosinophil infiltration was almost completely inhibited at least until 24 hours after the antigen challenge.

CONCLUSION

VLA-4 molecule was elucidated to play a critical roll in the eosinophil infiltration in experimentally-induced allergic conjunctivitis model of guinea pig.

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

We have established transgenic mice that carry the genes coding for heavy and light chains of TNP-specific IgE. They produced high titers of TNP-specific IgE (20-40 microg/ml in serum) and their mast cells were heavily loaded with IgE. The level of FcepsilonRI expression on their mast cells was 6-8 times higher than that in non-transgenic littermates. The expression of low-affinity IgE receptor FcepsilonRII (CD23) on splenic B cells was also 6-8 times higher in the transgenic mice. Consistent with this, substantial amounts of IgE were detected on B cells in the transgenic mice. When challenged with i.v. administration of the corresponding antigen, the transgenic mice exhibited systemic anaphylactic symptoms such as a drastic drop of body temperature and extravasation of administered dye. Biphasic (immediate and delayed) ear swelling response was also elicited in a TNP-specific manner by epicutaneous antigen challenge without any prior sensitization. Thus, IgE produced in the transgenic mice was found to be biologically active to induce both local and systemic allergic reactions in vivo upon the challenge of the corresponding antigen. Taken together, the antigen-specific IgE transgenic mice established for the first time in this study appear to provide an attractive model system to study the pathological roles of IgE in acute and chronic phases of allergic inflammation as well as their immunobiological roles in vivo. They may also be useful to develop novel therapeutic strategies for atopic disorders.

IgE enhances Fc epsilon receptor I expression and IgE-dependent release of histamine and lipid mediators from human umbilical cord blood-derived mast cells: synergistic effect of IL-4 and IgE on human mast cell Fc epsilon receptor I expression and mediator release

We investigated the effects of IgE versus IL-4 on Fc epsilon RI surface expression in differentiated human mast cells derived in vitro from umbilical cord blood mononuclear cells. We found that IgE (at 5 micrograms/ml) much more strikingly enhanced surface expression of Fc epsilon RI than did IL-4 (at 0.1-100 ng/ml); similar results were also obtained with differentiated mouse mast cells. However, IL-4 acted synergistically with IgE to enhance Fc epsilon RI expression in these umbilical cord blood-derived human mast cells, as well as in mouse peritoneal mast cells derived from IL-4-/- or IL-4+/+ mice. We also found that: 1) IgE-dependent enhancement of Fc epsilon RI expression was associated with a significantly enhanced ability of these human mast cells to secrete histamine, PGD2, and leukotriene C4 upon subsequent passive sensitization with IgE and challenge with anti-IgE; 2) preincubation with IL-4 enhanced IgE-dependent mediator secretion in these cells even in the absence of significant effects on Fc epsilon RI surface expression; 3) when used together with IgE, IL-4 enhanced IgE-dependent mediator secretion in human mast cells to levels greater than those observed in cells that had been preincubated with IgE alone; and 4) batches of human mast cells generated in vitro from umbilical cord blood cells derived from different donors exhibited differences in the magnitude and pattern of histamine and lipid mediator release in response to anti-IgE challenge, both under baseline conditions and after preincubation with IgE and/or IL-4.

Expression and physical association of Fc alpha receptor and Fc receptor gamma chain in human mesangial cells

BACKGROUND

Most intensive investigations on the pathogenesis of IgA nephropathy have focused on the process before IgA deposition and the characteristics of IgA/IgA immune complex (IgA IC), but it still remains uncertain whether mesangial IgA ICs may cause glomerular injuries directly or are only secondary events of another pathological process. To assess the role of IgA ICs in IgA nephropathy, we investigated the characteristics of Fc alpha receptor (Fc alphaR) and FcR gamma chain which is a signalling subunit of FcR in human mesangial cells (MCs).

METHODS

Gene expression of Fc alphaR and FcR gamma chain of human cultured MCs was examined by RT-PCR and subsequent Southern blot analyses. Sequence analyses after subcloning were also performed for further confirmation. Expression of Fc alphaR and FcR gamma chain at the protein level and their physical association in MCs were determined by immunoprecipitation after stimulation of the cells with heat-aggregated IgA.

RESULTS

Two distinct cDNA products were amplified from each cultured MC line. The sequence of the major product of approximately 900 bp was completely identical to that of Fc alphaR previously described. The smaller product had a 288 bp deletion which corresponded to exon 2 encoding the extracellular domain 2 of Fc alphaR. Gene expression of FcR gamma chain was also confirmed. Furthermore, we proved the physical association of Fc alphaR with the FcR gamma chain by co-immunoprecipitation under stimulation with a high dose of the heat-aggregated IgA.

CONCLUSION

These findings suggested that polymeric IgA and/or IgA IC can directly activate MCs via Fc alphaR associated with the gamma chain. Our data also indicated that phenotypic variations of Fc alphaR occur on MC, such as splicing forms, the chain association and/or the alpha chain expression itself, which may contribute to the pathogenesis of IgA nephropathy.

Functional expression of the high affinity receptor for IgE (FcepsilonRI) in human platelets and its' intracellular expression in human megakaryocytes

The high affinity IgE receptor (FcepsilonRI) expressed on the cell surface of mast cells and basophils is the key molecule in triggering the IgE-mediated allergic reaction. Recently, it was elucidated that the FcepsilonRI is expressed on a variety of other cells like Langerhans cells, monocytes, and eosinophils, and the functional importance of the FcepsilonRI expression in Langerhans cells was also shown. Some studies suggest that human platelets may play important roles in allergic inflammation through the cell-surface expression of the FcepsilonRII and FcgammaRII. Here, we report that human platelets and megakaryocytes constitutively express the messenger RNA and protein for the FcepsilonRI. Although the FcepsilonRI is expressed on the cell surface of human platelets, it is only detected in the cytoplasm of human megakaryocytes. We also confirmed that human platelets express the genes for the alpha, beta, and gamma chains of the FcepsilonRI without any defined mutations. Furthermore, stimulation of human platelets via the FcepsilonRI induced the release of serotonin and RANTES (Regulated on Activation, Normal T Expressed, and presumably Secreted). Taken together, these results suggest a novel and important role for human platelets in perpetuating allergic inflammation through the expression of and activation via the FcepsilonRI.

Role of mast cells as a trigger of inflammation in Helicobacter pylori infection

Helicobacter pylori (H. pylori) induces severe inflammation and plays a key role in gastric mucosal diseases. In general, mast cells have been believed to play an important role in inflammation. Although mast cells were detected in the gastric mucosa, the role of mast cells in the gastric mucosal inflammation caused by H. pylori is still unclear. Therefore, we examined the effects of H. pylori water extract on the degranulation of mast cells to clarify the role of these cells in gastric mucosal inflammation induced by H. pylori. Mast cells prepared from rat abdominal cavity were incubated with H. pylori for 30 min. The protein concentrations of H. pylori water extract used in this study were 0.5-3 mg/ml. The degranulation of mast cells were monitored morphologically by phase contrast microscopy equipped with time-lapse video recording system and biochemically by measuring histamine and beta-hexosaminidase. H. pylori water extract induced the degranulation of mast cells dose-dependently. The identical experiment was performed without extracellular calcium, and no significant degranulation was found. The data indicates that the degranulation of mast cells by H. pylori water extract depend on extracellular calcium. The present results indicate that H. pylori might be involved in the gastric mucosal inflammation as a trigger of mast cell degranulation for releasing chemical mediators.

Induction of anaphylaxis in mouse intestine by orally administered antigen and its prevention with soluble high affinity receptor for IgE

Early symptoms of food allergy, including diarrhea, are caused by IgE-mediated anaphylactic reactions. To clarify the mechanisms of IgE-mediated anaphylactic reactions in the intestine induced by orally administered antigen, a mouse model was established by s.c. implantation of a murine hybridoma capable of producing monoclonal anti-trinitrophenyl IgE antibody. Morphologic and immunologic changes in the intestine, as well as the effect of the soluble high affinity IgE receptor alpha chain, were investigated after oral challenge with antigen in this mouse model. Diarrhea, a decrease in s.c. blood flow, an increase in vascular permeability, a substantial increase in serum histamine levels, and noticeable infiltration of mast cells and IgE-bearing cells into the lamina propria were observed around 30 min after antigen challenge. However, these changes were efficiently prevented by pretreatment of the mice with the soluble high affinity IgE receptor alpha chain. These findings suggested that oral administration of antigen actually induced anaphylactic shock in our mouse model. This reaction was most likely to be mediated by mast cell activation, in response to the IgE-antigen complex, and a soluble form of the high-affinity IgE receptor efficiently prevented this IgE-mediated anaphylactic reaction by trapping free IgE.

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.

IgE hyperproduction through enhanced tyrosine phosphorylation of Janus kinase 3 in NC/Nga mice, a model for human atopic dermatitis

IgE hyperproduction frequently observed in patients with atopic dermatitis (AD) may greatly contribute to the pathogenesis of AD, but its mechanisms are still unclear. NC/Nga mice raised in nonsterile circumstances spontaneously suffered from AD-like skin lesions with elevation of plasma IgE levels. We investigated mechanisms of the IgE hyperproduction in NC/Nga mice. Splenic T cells from SPF NC/Nga mice had a level of CD40 ligand (CD40L) expression comparable to that of BALB/c mice. Although there was no difference in the expression of CD40 on B cells between NC/Nga and BALB/c mice, B cells of NC/Nga mice produced much more IgE in the presence of soluble CD40L and IL-4. The stimulation with CD40L and/or IL-4 resulted in tyrosine phosphorylation of Janus kinase 3 (JAK3) in B cells, which was more strongly inducible in NC/Nga mice than in BALB/c mice. In B cells isolated from PBMC of AD patients with high serum IgE levels, JAK3 was constitutively phosphorylated at the tyrosine residue, and its phosphorylation was enhanced by the treatment with CD40L and/or IL-4 as was that in splenic B cells of NC/Nga mice with dermatitis and high IgE levels. Thus, it is suggested that constitutive and enhanced JAK3 phosphorylation in B cells highly sensitive to CD40L and IL-4 may be attributable to IgE hyperproduction in NC/Nga mice and patients with AD.

Chronic oral antigen exposure induces lymphocyte migration in anaphylactic mouse intestine

Persistent diarrhea, vomiting, and dehydration are symptoms often seen in patients suffering from food allergy after chronic antigen exposure; however, the precise mechanisms involved have not been well defined. In an effort to clarify the mechanisms of the chronic intestinal changes attributable to genuine IgE-mediated anaphylactic reactions induced by orally administered antigen, a mouse model was established by s.c. implantation of a murine hybridoma capable of producing monoclonal anti-trinitrophenyl IgE antibody, and the morphologic and immunologic changes occurring in the intestine upon chronic antigen exposure were investigated. In the early stage after ingestion of the antigen, diarrhea and noticeable infiltration of mast cells as well as eosinophils into the lamina propria were observed. A substantial increase in serum histamine levels as well as an increase in leukotriene C4 synthesis in the jejunal mucosa were observed 1 h after antigen challenge. Also, the synthesis of leukotriene B4 was significantly elevated for up to 9 h after antigen challenge. The expression of both intercellular adhesion molecule-1 (ICAM-1) on mucosal vascular endothelial cells and IAd on epithelial cells was markedly enhanced, and noticeable infiltration of eosinophils and lymphocytes was also confirmed in the mouse model after chronic antigen exposure. These findings suggest that oral antigen exposure induces anaphylactic reactions in the intestine mediated by mast cells and eosinophils in response to the IgE-antigen complex in the early phase, and also induces lymphocyte migration after chronic antigen exposure.

Production of IL-13 by human lung mast cells in response to Fcepsilon receptor cross-linkage

BACKGROUND

Cross-linkage of the high affinity Fcepsilon receptors (FcepsilonRI) on the surface of the mast cell by the allergen-IgE complex is a central event in the induction of allergic inflammatory reactions. However, the precise roles of human mast cells in the perpetuation of allergic inflammation is not well known. IL-13 plays an important role in the regulation of allergic inflammation, especially being involved in the induction of IgE synthesis.

OBJECTIVE

We investigated whether human lung mast cells have the capacity to produce IL-13 by cross-linking of the FcepsilonRI.

METHODS

Lung mast cells were purified by affinity magnetic selection with monoclonal antibody YB5.B8 against c-kit to achieve a final mast cell purity of more than 93%. Purified mast cells were precultured with human myeloma IgE (3 microg/mL) for 16 h before challenge with stem cell factor (SCF) (50 ng/mL) and anti-IgE (1 microg/mL). By RT-PCR, ELISA and immunocytochemistry, we evaluated the capacity of human lung mast cells to express and produce IL-13.

RESULTS

IgE-dependent activation of human lung mast cells caused an increase in IL-13 mRNA expression which persisted for up to 12 h. Immunoreactive IL-13 was detectable 24 h after activation of sensitized lung mast cells with SCF and anti-IgE in 6 of 13 non-asthmatic donors and a million of mast cells secreted 106.7 +/- 42.65 (mean +/- SE) pg of IL-13 into the culture supernatants. SCF alone induced 61.63 +/- 31.12 pg of IL-13 from 106 mast cells. This difference was statistically significant (P = 0.028, n = 13). Furthermore, we confirmed by immunocytochemistry that immunological activation induced an increase of intracellular IL-13.

CONCLUSION

These findings demonstrate the capacity of human lung mast cells to transcribe IL-13 after IgE-dependent activation and to synthesize and release IL-13.

Distinct contribution of Fc receptors and angiotensin II-dependent pathways in anti-GBM glomerulonephritis

BACKGROUND

The contribution of antibody and/or immune-complex to the pathogenesis of immunologically-mediated glomerulonephritis is not fully understood, although it has been recently clarified that Fc receptors (FcRs) play critical roles in the inflammatory cascade. We therefore re-evaluated the classical model of glomerulonephritis, anti-glomerular basement membrane antibody-induced glomerulonephritis (Anti-GBM GN), from the standpoint of FcRs and also investigated the residual FcR-independent mechanisms.

METHODS

We adopted an Anti-GBM GN mouse model that has two strains deficient in the FcR gamma chain [gamma(-/-)] or Fc gammaRIIB [RII(-/-)], and analyzed functional (urinary protein, serum creatinine, BUN) and pathological changes of the glomeruli. For the analyses of FcR-independent mechanisms, several doses of nephrotoxic serum were applied, and then mice were treated either with cobra venom factor or an angiotensin II type 1 receptor antagonist in gamma(-/-) mice.

RESULTS

In gamma(-/-) mice, renal injuries were dramatically attenuated with an absence of polymorphonuclear cell (PMN) influx, while RII(-/-) mice suffered accelerated glomerular injuries in spite of a normal PMN influx. In the absence of FcR-dependent effects in gamma(-/-) mice, the FcR-independent pathway lead to chronic renal damage characterized by mesangial proliferation and progressive expansion of mesangial area, with monocyte/macrophage accumulation and with the expression of alpha smooth muscle actin in the mesangial cells and interstitium. Those injuries in gamma(-/-) mice were not attenuated by the decomplementation, but completely abolished by using an angiotensin II type 1 receptor antagonist.

CONCLUSIONS

Our results clearly demonstrate that FcRs play a pivotal role in Anti-GBM GN, especially in its acute phase. We further clarified the existence of FcR and complement-independent but antibody-dependent pathway. Furthermore, we found that those pathological changes were strongly related to the renin-angiotensin system.

Resistance of Fc receptor- deficient mice to fatal glomerulonephritis

Immune complex-mediated inflammation is a common mechanism of various autoimmune diseases. Glomerulonephritis (GN) is one of these diseases, and the main mechanism of the induction of GN has been unclear. We examined the contribution of Fc receptors in the induction of nephrotoxic GN by establishing and analyzing mice deficient in the Fc receptor gamma chain (FcRgamma). Whereas all wild-type mice died from severe glomerulonephritis with hypernitremia by administration of anti-glomerular basement membrane (GBM) antibodies, all FcRgamma-deficient mice survived. Histologically, wild-type mice showed glomerular hypercellularity and thrombotic changes, whereas the renal tissue in FcRgamma-deficient mice was almost intact. Deposition of anti-GBM antibody as well as complement components in the GBM were equally observed in both wild-type and knockout mice. These results demonstrate that the triggering of this type of glomerulonephritis is completely dependent on FcR+ cells.

Human mast cells produce IL-13 by high-affinity IgE receptor cross-linking: enhanced IL-13 production by IL-4-primed human mast cells

BACKGROUND

Mast cells play a central role not only in the early phase of the allergic reaction, but also participate in the late phase of the allergic reaction through the allergen and IgE-dependent release of multifunctional cytokines.

OBJECTIVE

Using the recently established culture system for human mast cells, we examined the expression of a variety of cytokines in cord blood-derived human cultured mast cells (HCMCs) in response to different stimuli.

METHODS

HCMCs were grown from cord blood mononuclear cells in the presence of stem cell factor and IL-6 for 10 weeks. Cytokine mRNA expression in HCMCs by the different stimuli was examined by RT-PCR. Then taking 2 important cytokines, IL-13 and IL4, that share several functional properties and play important roles in allergic diseases, we examined protein as well as mRNA expression of both cytokines in HCMCs.

RESULTS

HCMCs did not express either IL-13 or IL-4 spontaneously. Stimulation with PMA + A23187 induced the expression of IL4 protein, as well as IL-13 protein, in their cytoplasm, although IL-4 secreted in the supernatant was below detectable levels in contrast to a significant amount of IL-13. Stimulation of HCMCs by cross-linking of the high-affinity IgE receptor (Fc(epsilon)RI) induced the expression of IL-13 mRNA and protein, but not IL4. Although we previously found that IL-4 upregulates Fc(epsilon)RI expression on HCMCs, when HCMCs were first cultured in the presence of IL4 and then activated through FC(epsilon)RI cross-linking, remarkable increase was found in IL-13 production. Furthermore, although IL-4 was still undetectable at protein level, IL-4 mRNA expression was induced in the IL-4-primed HCMCs stimulating Fc(epsilon)RI cross-linking. In addition, we examined the effects of these cytokines on the surface molecule expression in HCMCs. Although IL4 remarkably upregulated lymphocyte function-associated antigen-1, intercellular adhesion molecule-1, and Fc(epsilon)RI expression and downregulated c-kit expression in HCMCs, IL-13 did not.

CONCLUSIONS

Our observation that HCMCs produce IL-13 on cross-linking of Fc(epsilon)RI, which was enhanced by IL-4 priming, supports an important role of mast cells in amplification of allergic reaction and further suggests one of the mechanisms enhancing mast cell function in the microenvironment.

IgE-Fc epsilonRI-mast cell axis in the allergic cycle

The IgE and allergen dependent activation of mast cells via the high affinity IgE receptor (Fc epsilonRI) resulting in the release of inflammatory mediators is critical to the pathogenesis of atopic diseases like bronchial asthma and allergic rhinitis. However, mast cells are also involved in certain IgE-independent biological responses, and recent studies have highlighted the role of mast cells in host defense. In the light of this background, we have discussed our recent data on the immunophenotypic characteristics of nasal mast cells in patients with perennial allergic rhinitis (PAR) and chronic infective rhinitis (CIR) based on the expression of cytokines, the Fc epsilonRI, the cell-bound IgE, as well as the IgE-mediated mediator release (before and after saturation of the IgE receptors). Although nasal mast cells (NMC) from both groups of patients expressed a variety of cytokines, significant differences were observed in the proportion of cytokine expressing cells between PAR and CIR. NMC from PAR patients exhibited increased Fc epsilonRI expression, cell-bound IgE and IgE-mediated mediator release as compared with NMC from CIR patients, even after saturation of the IgE receptors. The density of IgE receptors and IgE molecules in NMC of PAR patients correlated well with the levels of serum IgE, and IL-4 upregulated the expression of the Fc epsilonRI in NMC. Moreover, NMC from PAR patients induced IgE synthesis in B cells. Taken together, these results and the recently demonstrated IgE-induced upregulation of the Fc epsilonRI expression in mast cells suggest critical roles for mast cells in promoting the allergic reaction through an IgE-Fc epsilonRI-mast cell axis.

The Fc receptor (FcR) gamma subunit is essential for IgE-binding activity of cell-surface expressed chimeric receptor molecules constructed from human high-affinity IgE receptor (Fc epsilon RI) alpha and FcR gamma subunits

The Fc receptor (FcR) gamma subunit was originally discovered as a homodimeric subunit of the high-affinity IgE receptor (FcepsilonRI). But it was recently found to be a common signal-generating subunit of Fc receptors including IgG Fc receptors (FcgammaRs) and IgA Fc receptor (FcalphaR), and furthermore to generate a signal also with stimuli through non-immune receptors. In addition, it plays an essential role in cell-surface expression of the FcepsilonRI and the FcgammaRIIIA isoform and also regulates cell-surface expression and ligand-binding affinity of the FcgammaRI. In this report, we addressed the possibility that the FcRgamma could affect the correct folding of the IgE-binding region of the FcepsilonRIalpha subunit by using the chimeric receptor molecules constructed from human FcepsilonRIalpha and FcRgamma. Furthermore, we demonstrated that the seven amino acid residues in the C-terminal region on the extracellular domain of the FcepsilonRlalpha were essential for maintaining the IgE-binding activity of the FcepsilonRIalpha exodomain on the cell membrane and/or may affect the correct folding of the alpha subunit itself within the cell.

Cultured basophils but not cultured mast cells induce human IgE synthesis in B cells after immunologic stimulation

By generating human mast cells and basophils from umbilical cord blood mononuclear cells cultured in the presence of appropriate cytokines, we investigated whether these two cultured cells could provide the cytokine and cell contact signals that are required to induce IgE synthesis in B cells. To activate cultured mast cells and basophils, cross-linking of cell surface high-affinity IgE receptor (Fc epsilonRI) was performed with specific antigen after sensitization with murine IgE. Upon Fc epsilonRI stimulation, basophils, but not mast cells, secreted significant amounts of immunoreactive IL-4 and IL-13 and expressed detectable CD40 ligand (CD40L) and a very low level of Fas ligand (FasL). These observations at the protein level were consistent with the data obtained at the gene transcriptional level, except for the faint expression of only IL-13 mRNA in mast cells. When added to normal human B cells, activated basophils induced IgE and IgG4 synthesis as well as soluble CD23 release. In contrast, neither IgE nor IgG4 synthesis could be induced by the interaction of B cells with activated mast cells, even in the presence of recombinant IL-4. The induction of IgE synthesis by activated basophils was completely abrogated by two neutralizing MoAbs against IL-4 and IL-13 and by a soluble form of CD40. This abrogation was accompanied by abolished mature C epsilon transcription in both cases. Addition of anti-FasL MoAb, however, did not significantly affect IgE induction mediated by activated basophils. These results demonstrate that unlike cultured mast cells, cultured basophils produce biologically active IL-4 and IL-13 and express functional CD40L after Fc epsilonRI stimulation, thereby contributing to IgE production by B cells, and suggest that relatively weak expression of FasL by cultured basophils is not involved in IgE regulation.