Establishment of a sensitive radioimmunoassay for the detection of human IgE-binding factor (soluble CD23)

Atopy and the human IL-4 receptor alpha chain

BACKGROUND

Atopy is a common inherited disorder characterized by increased IgE responsiveness, but no functional analysis of the candidate genes related to atopy has been performed. IL-4 is important for B-cell production of IgE, and the human IL-4 receptor alpha chain (hIL-4Ralpha) is crucial for the binding and signal transduction of IL-4, so hIL-4Ralpha may be a candidate gene related to atopy.

OBJECTIVE

We examined the relationship between the variation at amino acid 50 of hIL-4Ralpha and atopic asthma.

METHODS

We performed a genetic study to investigate the relationship between the variation of amino acid 50 (isoleucine [Ile(50)] or valine [Val(50)]) and atopic asthma in a Japanese population and a functional study with the use of transfectants that expressed hIL4Ralpha bearing either Ile(50) or Val(50). Furthermore, we analyzed CD23 expression and IgE synthesis after IL-4 stimulation of peripheral blood mononuclear cells bearing either Ile(50) or Val(50).

RESULTS

The prevalence of Ile(50) was higher than that of Val(50) in individuals with atopic asthma, especially during childhood. In transfectants, germline epsilon transcription activity and Stat6 activity were upregulated by the Ile(50) variant, compared with Val(50), but receptor affinity for IL-4 was similar between the two. CD23 expression and IgE synthesis in response to IL-4 were augmented in Ile(50)-expressing peripheral mononuclear blood cells compared to cells expressing Val(50).

CONCLUSION

The Ile(50) variant of hIL-4Ralpha may be related to atopic asthma, particularly in children.

Cutting Edge: Dominant Effect of Ile50Val Variant of the Human IL-4 Receptor α-Chain in IgE Synthesis

Two variants of the IL-4R α-chain (IL-4Rα) gene have been recently identified in association with different atopic disorders. To clarify the etiological relationship between the two variants, we analyzed responsiveness to IL-4 of transfectants with four kinds of IL-4Rα carrying either Val or Ile at 50 and either Gln or Arg at 551. The substitution of Ile for Val augmented STAT6 activation, proliferation, and transcription activity of the Iε promoter by IL-4, whereas that of Arg for Gln did not change these IL-4 signals. Arg551 was not associated with atopic asthma in the Japanese population. CD23 expression and IgE synthesis by IL-4 were augmented in Ile50-bearing PBMC, compared with those bearing Val50. Taken together, substitution of Arg551 does not enhance the IL-4 signal for generation of germline ε transcript, whereas the substitution of Ile50 contributes to enhancement of IgE synthesis.

Decrease of serum levels of soluble CD23 during immunotherapy in patients with perennial allergic rhinitis

There is increasing in vitro evidence that soluble CD23 (sCD23) is capable of potentiating the synthesis of human IgE and is likely involved in the expression of allergic diseases. Our study has aimed at investigating whether serum sCD23 is elevated in patients with perennial allergic rhinitis as compared to nonatopic controls, whether sCD23 in perennial allergic rhinitis fluctuates during the natural course in untreated patients, and whether sCD23 is decreased by immunotherapy. This study included 139 patients with perennial allergic rhinitis due to Dermatophagoides farinae who gave informed consent to participation. They were divided into 2 groups--an untreated group and an immunotherapy group--according to their treatment background. Thirty-one nonallergic, healthy volunteers were included to serve as controls. Symptom scores and serum concentrations of IgE specific to D. farinae and sCD23 were examined twice in each patient: at enrollment (first evaluation) and on a variant time course after enrollment (second evaluation). Serum concentrations of sCD23 were measured by a sandwich enzyme-linked immunosorbent assay. The level of sCD23 in patients with perennial allergic rhinitis was significantly higher than that in nonatopic controls (p < .0001). The level of sCD23 in perennial allergic rhinitis was correlated with the level of specific IgE against D. farinae. The sCD23 level did not fluctuate during the natural course for a span of 2.8 +/- 2.7 years in untreated patients (p = .1337), but was significantly decreased in patients who received immunotherapy for 2.7 +/- 2.2 years (p < .0001). The rate of decrease in sCD23 was significantly correlated with the rate of decrease in specific IgE (rs = .523, p < .0001) and symptom scores (rs = .450, p < .0001). In conclusion, the reduction in sCD23 during immunotherapy is probably related to the decrease in specific IgE and also plays a role in mediating its clinical effect.

Immunotherapy decreases seasonal rise in serum-soluble CD23 in seasonal allergic rhinitis

There is increasing in vitro evidence that soluble CD23 (sCD23) is capable of potentiating IgE synthesis, but the in vivo physiologic significance remains to be established. This study investigated the seasonal changes in sCD23 in patients with seasonal allergic rhinitis. It included 112 adult patients with seasonal allergic rhinitis due to Japanese cedar pollens and 20 nonatopic healthy volunteers. The 64 patients of the pharmacotherapy group were treated with nonsedating antihistamine tablets alone throughout the pollen season and the remaining 48 patients of the immunotherapy group continued to be treated with immunotherapy. Serum concentrations of sCD23 were measured in each patient, before and during the pollen season of 1996, by a sandwich enzyme-linked immunosorbent assay. The serum levels of sCD23 in the pharmacotherapy group before the pollen season were significantly higher than those in the nonatopic group (P = .0130) and those in the immunotherapy group (P = .0316). Seasonal increase in sCD23 was significant in the pharmacotherapy group, irrespective of the clinical response (P < .0001). By contrast, sCD23 was not significantly increased in the good responders to immunotherapy (P = .1826), but was significantly increased in the poor responders to immunotherapy (P = .0052). A significant correlation between seasonal increase in rate in specific IgE and seasonal increase in rate in sCD23 was confirmed in both the pharmacotherapy group (rs = 0.321, P = .0107) and the immunotherapy group (rs = 0.474, P = .0012). In conclusion, seasonal rise in sCD23 is associated with and is probably involved in seasonal rise in specific IgE in patients with seasonal allergic rhinitis, and successful immunotherapy is capable of blunting seasonal increase in sCD23, thus resulting in attenuation of seasonal increase in specific IgE and clinical benefits during the pollen season.

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.

Inhibition of IL-4 receptor up-regulation on B cells by antisense oligodeoxynucleotide suppresses IL-4-induced human IgE production

IL-4 is shown to up-regulate its own receptor (IL-4R) on human lymphocytes, but the functional significance of up-regulated IL-4R is not clear regarding IgE production. This study investigated the possible role of IL-4-induced up-regulation of IL-4R on B cells in the induction of human IgE synthesis by means of antisense strategy. Among three antisense oligodeoxynucleotides designed against the downstream of translation initiation site of IL-4R cDNA, S-oligo 1, complementary to nucleotide 1-24, showed the strongest inhibition of the constitutive expression of IL-4R on Daudi cells. Addition of S-oligo 1 together with IL-4 also decreased the up-regulated but not constitutive levels of IL-4R on peripheral blood B cells without affecting the concomitant enhancement of CD23, CD40, HLA-DR and surface IgM expression, indicating that its effect is specific for IL-4R up-regulation. When S-oligo 1 was added to B cells costimulated with IL-4 and anti-CD40 MoAb, it induced a dose-dependent inhibition of IgE production. This inhibition was accompanied by a decrease in the expression of mature C epsilon transcripts, whereas the accumulation of germ-line C epsilon transcripts was not affected by S-oligo 1. These data suggest that the signal transduction mediated by the up-regulated IL-4R on B cells may be intimately associated with the induction of isotype switching to IgE that leads to mature C epsilon transcription and IgE production.

Recombinant soluble form of the human high-affinity immunoglobulin E (IgE) receptor inhibits IgE production through its specific binding to IgE-bearing B cells

A recombinant soluble form of the alpha subunit of the human high-affinity receptor for IgE (rsFc epsilon RI alpha), one of the potent IgE-binding molecules, was tested for its ability to regulate IL-4-induced IgE synthesis by human lymphocytes. Addition of rsFc epsilon RI alpha to cultures induced a dose-dependent inhibition of the T cell-dependent and independent synthesis of IgE. The suppression of IgE synthesis was observed at the protein and the mRNA levels, and it was IgE class specific. By flow cytometry, specific binding of rsFc epsilon RI alpha was detected on surface IgE-bearing B cells as well as on U266 cells, and it was completely blocked by preincubation with IgE. rsFc epsilon RI alpha bound to the cell surface IgE could be effectively dissociated not only by a large excess of IgE, but also by an anti-rsFc epsilon RI alpha mAb that competes with IgE for the binding to rsFc epsilon RI alpha. This mAb abolished the rsFc epsilon RI alpha-mediated suppression of IgE synthesis. These data suggest that rsFc epsilon RI alpha may have a function in selectively suppressing IgE synthesis through its interaction with the membrane-bound form of IgE.

Possible role of tyrosine kinase activity in interleukin 4-induced expression of germ-line C epsilon transcripts in a human Burkitt lymphoma B-cell line, DND39

Despite the recent advances in knowledge of the molecular mechanism by which interleukin-4 (IL-4) induces IgE production, little is known about the signal transduction pathway that leads to this event. This study investigated the signal transduction mechanism responsible for IL-4-induced expression of germ-line C epsilon transcripts with use of a human Burkitt lymphoma B-cell line, DND39, which is known to express germ-line C epsilon transcripts in response to IL-4. On stimulation with IL-4, the generation of inositol triphosphate was observed in the cells. In addition, this generation was associated with activation of phospholipase C-gamma 1 (PLC-gamma 1). Although herbimycin A, a potent inhibitor of tryosine kinase, inhibited IL-4-induced activation of PLC-gamma 1 and generation of inositol triphosphate, direct phosphorylation of PCL-gamma 1 was not determined. Nevertheless, IL-4 stimulation could induce activation of FYN but not LYN kinase, suggesting that additional molecule(s) might link FYN kinase to PLC-gamma 1. Interestingly, herbimycin A almost completely inhibited IL-4-induced expression of germ-line C epsilon transcripts when present during the entire culture period. These results indicate that the induction of germ-line C epsilon transcripts in IL-4-stimulated DND39 cells is essentially dependent on the activation of tyrosine kinase, possibly FYN kinase.

Serum levels of soluble IL-2R, IL-4, and soluble Fc epsilon RII in adult bronchial asthma

Examination was made of the serum levels of interleukin 4 (IL-4), soluble Fc epsilon RII (sFc epsilon RII), and soluble interleukin 2 receptor (sIL-2R) in 77 adult patients with bronchial asthma. All the patients had mild to moderate asthma and their symptoms were well controlled. The results were compared with values for 75 control subjects to clarify the involvement of these factors in the pathogenesis of bronchial asthma. Serum sIL-2R was elevated in asthmatics compared with control subjects (459.0 +/- 30.4 U/ml vs 251.5 +/- 10.0 U/ml; p < 0.001). The IL-4 and sFc epsilon RII levels were also elevated beyond those in the controls (IL-4: 1.89 +/- 0.13 pg/ml vs 1.08 +/- 0.15 pg/ml; p < 0.001) (sFc epsilon RII: 313.2 +/- 18.8 U/ml vs 228.8 +/- 6.7 U/ml, p < 0.001). A weak but significant correlation was observed between sIL-2R and sFc epsilon RII (r = 0.46, p < 0.001). Correlation among other parameters was not found. The patients were divided into atopic and nonatopic groups, based on the presence or absence of positive reaction to skin prick tests using extracts of common aeroallergens and positive specific IgE against house dust mite (Dermatophagoides pteronyssinus [Dp]). Mean IL-4 in the atopic group, with positive skin reaction and > 0.7 kU/L specific IgE against Dp was significantly elevated compared with the nonatopic group (2.35 +/- 0.26 pg/ml vs 1.56 +/- 0.12 pg/ml; p < 0.005). Such differences could not be detected in sIL-2R, sFc epsilon RII levels among the two groups. No significant correlation could be found among IL-4, sFc epsilon RII, and total IgE level. The activation of T cells and B cells would thus appear essential to the pathogenesis of bronchial asthma and the hypothesis that atopic status is associated with the preferential activation of TH2 cells which selectively produce IL-4 could be supported. The regulatory mechanism of IgE synthesis would not appear to be the only responsible factor.

Suppression of IgE production by IPD-1151T (suplatast tosilate), a new dimethylsulfonium agent: (2). Regulation of human IgE response

The ability of IPD-1151T to suppress the induction of human IgE synthesis was investigated with an in vitro model of IgE production mediated by an allergen-specific helper T cell line (SN-4) from a patient allergic to Japanese cedar pollen. IPD-1151T induced a concentration-dependent suppression of purified allergen (Cry j 1)-dependent IgE synthesis in autologous B cell cultures mediated by SN-4, without significantly affecting the IgG synthesis. In addition, the production of interleukin 4 (IL-4) by Cry j 1-activated SN-4 as well as that by phytohemagglutinin (PHA)-stimulated peripheral blood mononuclear cells (PBMC) of normal donors was inhibited in a concentration-dependent manner by the agent. Interestingly, IPD-1151T clearly depressed PHA-induced expression of IL-4 mRNA in normal PBMC, indicating that this agent inhibits IL-4 gene transcription. However, IPD-1151T had no antagonistic action on IL-4, since neither IL-4-induced expression of low-affinity IgE receptor (Fc epsilon RII/CD23) on normal B cells nor soluble Fc epsilon RII release from IL-4-stimulated B cells was affected by the agent. On the other hand, IPD-1151T had no effect on the production of interferon-gamma by both Cry j 1-stimulated SN-4 and anti-CD3 monoclonal antibody-activated T cells of normal donors. These results suggest that the selective suppression of IgE synthesis by IPD-1151T results from the inhibition of IL-4 production by T cells at the gene level.