IgE class-specific regulatory factor(s) and Fc epsilon receptors on lymphocytes

Expression of a constitutively active Stat6 in vivo alters lymphocyte homeostasis with distinct effects in T and B cells

IL-4 is a critical cytokine in the regulation of immune responses and genesis of atopy. Engagement of the IL-4R activates multiple signaling pathways, including the transcription factor Stat6. Stat6-deficient mice demonstrate the importance of this factor in lymphocyte proliferation, gene expression, and Th cell differentiation. Recently, a mutant Stat6 (Stat6VT) was generated that is transcriptionally active independent of IL-4 stimulation. To determine the ability of a constitutively active Stat6 to mimic IL-4-stimulated responses, we have generated transgenic mice expressing Stat6VT under control of the CD2 locus control region, restricting expression to lymphoid populations. The phenotype of Stat6VT transgenic mice is similar, but not identical, to IL-4 transgenic mice, suggesting a critical role for Stat6-independent signaling pathways in the generation of some IL-4 responses in vivo. The expression of a constitutively active Stat6 in vivo increases surface expression of IL-4-induced genes and increases serum levels of IgG1 and IgE, compared with nontransgenic mice. Stat6VT expression increases Th2 differentiation in vivo and in vitro. Stat6VT expression also dramatically alters homeostasis of peripheral lymphocyte populations resulting in decreased CD3(+) cells and increased B220(+) cells, compared with nontransgenic littermates. Altered T and B cell populations correlate with an activated phenotype and increased cell death in transgenic T cell, but not B cell, populations. Together these results suggest that expression of a constitutively active Stat6 has distinct effects on B and T lymphocytes.

Wheat gliadin promotes the interleukin-4-induced IgE production by normal human peripheral mononuclear cells through a redox-dependent mechanism

Increased levels of serum IgE have been described in gliadin-intolerant patients; however, biological mechanisms implicated in this immunoglobulin production remained unknown. In this study, we demonstrated that in vitro crude gliadins and gliadin lysates (Glilys) promoted the IL-4-induced IgE production by human peripheral blood mononuclear cells (PBMC), indicating that the biological process related to gliadin intolerance and/or allergy may lead to IgE production in vivo. It was found that crude gliadin and Glilys potentiated, after 13 days of culture in a dose-dependent manner, IL-4-induced IgE production and, to a lesser extent, the IgG production, while they did not affect IgA or IgM productions. This promoting effect of gliadin and Glilys on the IL-4-induced activation of normal human PBMC was also observed on the early release (2 days) of the soluble fraction of CD23, suggesting its possible involvement in IgE potentiation. The promoting effect of crude gliadin and Glilys appeared to be indirect because they did not modify purified B-lymphocytes IgE production after IL-4 and anti-CD40 monoclonal antibody stimulation. In addition, as revealed by luminol-dependent chemiluminescence, we demonstrated that crude gliadin and Glilys promoted a substantial production of free radicals by normal human PBMC, treated or not with IL-4. This redox imbalance associated with an increased IgE production led us to evaluate the effect of pharmacological antioxidants (N-acetyl-cysteine (NAC) and Cu/Zn-superoxide dismutase (SOD1)) on IgE production by human PBMC. The NAC and the intracellularly delivered SOD1 were found to suppress the IL-4+/-crude gliadin or Glilys-induced IgE production by normal human PBMC. Taken together, these data indicated that gliadin specifically enhanced IL-4-induced IgE production by normal human PBMC, probably by the regulation of redox pathways, and that this 'pro-allergenic' effect could be counteracted by natural antioxidants: thiols and/or vectorized SOD1.

Role of nitric oxide in the promoting effect of HIV type 1 infection and of gp120 envelope glycoprotein on interleukin 4-induced IgE production by normal human mononuclear cells

Increased levels of serum IgE have been described in HIV-1 infection; however, mechanisms implicated in this immunoglobulin production remain unknown. In this study, we demonstrate that in vitro infection of human peripheral blood mononuclear cells (PBMCs) by HIV-1 monocytotropic (Ba-L) or lymphocytotropic (LAI) strains promotes IL-4-induced IgE production, indicating that the HIV-1 infectious process may participate in the IgE production observed in vivo. The effect of membrane glycoproteins (gp160, gp120, and gp41) was also evaluated. It was found that gp120 specifically potentiates in a dose-dependent manner IL-4-induced IgE production and does not affect IL-4-induced IgG, IgA, or IgM production. In these experiments, gp160 was also found to upregulate IL-4-induced IgE production, whereas gp41 was ineffective. This effect of gp120, gp160, and HIV-1 infection on IgE synthesis was not observed in the absence of IL-4. In the presence of IL-4, the inducing effect of gp120 appeared to be indirect because gp120 did not modify purified B lymphocyte IgE production after IL-4 and anti-CD40 monoclonal antibody stimulation. As HIV-1 infection is associated with alterations of PBMC redox metabolism, the role of nitric oxide (NO) in this IgE production by human PBMCs was evaluated. In the presence of a specific inhibitor of NO synthase pathways (L-NAME), IgE production induced by IL-4 and gp120 was abolished. Taken together, these data indicate that HIV-1 envelope glycoprotein gp120 (and gp160) specifically enhances IL-4-induced IgE production by normal human PBMCs, probably through the regulation of the nitric oxide pathway.

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.

Serum levels of IgE-binding factor (soluble CD23) in diseases associated with elevated IgE

Several in-vitro experiments suggest that the low affinity receptor for IgE (Fc epsilon RII) and its soluble fragment (IgE-binding factor, IgE-BF) are multi-functional molecules and more particularly that they are capable of regulating the synthesis of human IgE. In an attempt to examine the in-vivo significance of these in-vitro observations, the serum level of IgE-BF was measured in individuals with allergic or parasitic diseases, both associated with an increased production of IgE. IgE-BF was measured by a radioimmunoassay employing two mAbs against Fc epsilon RII (mAbER). We first compared 257 allergic subjects to 172 non-allergic controls matched for age and sex. Statistical analysis of the data, after logarithmic transformation of IgE-BF and IgE values, revealed that despite a great overlap, the allergic subjects had significantly higher levels of IgE-BF. The correlation between IgE and IgE-BF was very weak but significant. Allergic or non-allergic children had significantly higher IgE-BF levels than the corresponding groups of adults; moreover, the inverse correlation between age and IgE-BF levels was significant only in the children and not in the adults. The IgE-BF levels were not influenced by gender, by hyposensitization therapy or by treatment with local steroids. Subjects receiving systemic steroids had lower IgE-BF levels than untreated subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Human IgE-binding factors

The production of IgE antibodies is known to be regulated by isotype-specific mechanisms that are not antigen specific. During the last decade several studies have indicated that soluble factors with affinity for IgE (IgE-binding factors, IgE-BFs) may exert such a role by interacting with IgE-bearing B lymphocytes. In the human, some of these IgE-BFs appear to be identical to soluble CD23, a B-cell surface marker thought to be involved in the control of B-cell proliferation or differentiation. In this article, Guy Delespesse and colleagues summarize several new findings regarding the cellular origin, structure and function of IgE-BFs/sCD23.

Release of IgD-binding factor by T cells under the influence of interleukin 2, interleukin 4, or cross-linked IgD

Helper T cells with receptors specific for IgD have immunoaugmenting properties. We have now detected soluble IgD-binding factor in cell supernatants immobilized on nitrocellulose paper by their ability to bind 125I-labeled IgD. IgD-binding factor is released by normal splenic T cells stimulated with recombinant interleukin 2, recombinant interleukin 4, or crosslinked IgD in amounts paralleling the induction of IgD receptors on the cells. IgD receptors are constitutively produced by antigen-specific helper T-cell hybridomas 2H10 and A3.4C6. Incubation of these hybridoma cells with recombinant interleukin 2 increases release of IgD-binding factor while reducing expression of IgD receptors. Specificity of the binding factor for IgD is established by (i) competitive inhibition; (ii) the ability of the binding factor to bind radiolabeled IgD and not monoclonal IgE, IgG2a, or polyclonal IgG; and (iii) the removal of the binding factor on passage through an IgD-Sepharose column and recovery in a subsequent acid eluate.

Up-regulation of receptors for IgA on activated human B lymphocytes

Expression of receptors for the Fc part of IgA (Fc alpha R) by T lymphocytes was recently shown to be up-regulated after activation by T cell mitogens in the absence of IgA. We describe a similar increase on activated human B lymphocytes. Fc alpha R were determined by labelling with human secretory IgA (0.5 mg/ml) and flow cytometry analysis after staining with fluoresceinated goat anti-IgA or goat anti-secretory component F(ab')2 fragments. B-enriched cell suspensions were prepared from peripheral blood or tonsils and activated by Staphylococcus aureus Cowan I, anti-IgM antibodies or E. coli lipopolysaccharide. All three activators increased the percentage of Fc alpha R positive cells although only the former induced significant DNA synthesis. Finally recombinant interleukin 1 (10 nM) and interleukin 2 (10 IU/ml) but not interleukin 4 (300 units/ml) nor low-molecular-weight B cell growth factor induced an increase of Fc alpha R expression. The data show that Fc alpha R can be up-regulated on human B cells in the absence of exposure to IgA.

IgE-binding factors: their possible role in the regulation of IgE synthesis

B cell-derived IgE-BFs (sCD23) are cleavage fragments of surface Fc epsilon R II. Their production is increased by IL4 and suppressed by IFN-gamma and IFN-alpha. IgE-BFs are likely to play a role in the regulation of human IgE synthesis as shown by the following two observations: i. MabER specifically blocks both the spontaneous IgE by synthesis by atopic B cells and the IL4-induced IgE synthesis by normal lymphocytes, ii. purified IgE-BFs enhance the IL4-induced and the spontaneous IgE synthesis. Soluble fragments of Fc epsilon R II also display BCGF-like activity although the exact structure of these fragments is not yet identified. The cDNA coding for Fc epsilon R II has been cloned and functionally expressed. The predicted amino acid sequence reveals no homology between human and rodent IgE-BFs indicating that they are unrelated molecules.