Allergen-induced CD23 on CD4+ T lymphocytes and CD21 on B lymphocytes in patients with allergic asthma: evidence and regulation

Variability of total and free IgE levels and IgE receptor expression in allergic subjects in and out of pollen season

The inter- and intra-individual variability and seasonal variation of IgE, and high (FcεRI)- and low-affinity (CD23) IgE receptor expression in blood of seasonal allergic rhinitis (SAR) subjects, is not well studied. Thirty-two otherwise healthy subjects with a history of SAR to birch pollen and a positive skin prick test to birch pollen were sampled three times out of the pollen season and three times during the pollen season. FcεRI and CD23 expressions were analysed using flow cytometry. Total IgE was analysed using ImmunoCAP(®) and free IgE was analysed with a novel customised research assay using an IgG-FcεRI-chimera protein coupled to ImmunoCAP as capture reagent, ImmunoCAP-specific IgE conjugate and ImmunoCAP IgE calibrators. The performance of the free IgE assay was compared well with the reference ImmunoCAP total IgE assay. The working range of the assay was 0.35-200 kU/l IgE. FcεRI expression on basophils and CD23 expression on B cells showed low intrasubject variability both in and out of the pollen season (<10% CV). There was a small seasonal difference with lower total IgE levels (120 versus 128 kU/l; P = 0.004) and FcεRI expression (283 versus 325 mean fluorescence intensity (MFI); P < 0.001) during the pollen season. IgE, FcεRI expression and CD23 expression fulfilled biomarker and assay requirements of variability, and allergen exposure affected the biomarkers only to a minor degree. The free IgE assay may be used for measurement of free IgE levels in patients after anti-IgE antibody treatment.

TLR4-mediated signaling induces MMP9-dependent cleavage of B cell surface CD23

IgE production is inversely regulated by circulating and B cell surface levels of the low affinity IgE receptor, CD23. To begin to understand physiologic determinants of CD23 expression, we analyzed effects of BCR and TLR stimulation on CD23 levels. BCR and TLR 2, 3, 4, 6, and 9 agonists induced CD23 down-modulation from the cell surface. However, among the ligands only TLR4 agonists induced transcriptional activation of CD23 and generation of significant soluble CD23. These responses were induced by LPS both in vitro and in vivo, and were seen in both murine and human B cells. LPS also induced expression of matrix metalloprotease 9 (MMP9) and failed to induce CD23 cleaving activity in MMP9(-/-) cells, thus implicating MMP9 in the LPS-induced release of CD23 from the cell surface. Finally, type 1 transitional B cells uniquely produce MMP9 in response to LPS, suggesting a mechanism wherein endotoxin induces T1 cell expression of MMP9, which mediates cleavage of CD23 on distinct, mature B cells.

IL-4 induced CD23 (FcepsilonRII) up-regulation in equine peripheral blood mononuclear cells and pulmonary alveolar macrophages

The objectives of this study were to quantify the induction of equine CD23 transcripts in equine peripheral blood mononuclear cells (PBMCs) and pulmonary alveolar macrophages cultured with recombinant equine IL-4 (rEq IL-4). PBMCs were isolated from blood drawn from four healthy horses. Bronchoalveolar lavage (BAL) fluid was collected from three healthy horses and alveolar macrophages were purified using adherence to plastic for 120 min. PBMCs and alveolar macrophages were cultured using four different conditions: rEq IL-4 and LPS, LPS alone, rEq IL-4 alone and a media control. Total RNA was isolated from cells cultured for 24 or 48 h. Reverse transcribed mRNA was amplified and quantified in real-time polymerase chain reaction (RT PCR) using a fluorescein labeled internal TaqMan probe for CD23 expression. Without exception, the relative value for CD23 mRNA transcripts from equine PBMCs and pulmonary alveolar macrophages cultured with rEq IL-4 for 24 and 48 h were higher than those cultured with LPS alone or the untreated control. Furthermore, morphologic changes were noted in alveolar macrophages cultured with rEq IL-4 prompting an investigation of cytokine expression levels. Alveolar macrophages cultured with LPS exhibited increased IL-8 and IL-12 p40 expression when compared to rEq IL-4, rEq IL-4 + LPS or the untreated control. These findings support two conclusions, (1) equine CD23 has a role in IL-4 mediated immune responses in the horse and (2) rEq IL-4 can modulate LPS-induced, pro-inflammatory cytokine production by equine pulmonary alveolar macrophages.

Effect of cysteinyl leukotriene receptor antagonist on CD11b and CD23 expression in asthmatic children

BACKGROUND

Cysteinyl leukotrienes are potent pro-inflammatory mediators that contribute to the pathophysiologic features observed in allergic asthma. Inhibitors of leukotriene receptors represent novel therapy in asthma treatment. In addition to the protection from early asthmatic responses, these drugs have recently been shown to protect from late airway responses too.

METHODS

We studied the effect of treatment with an oral antagonist of cysteinyl leukotriene receptors on the increased expression of the low-affinity IgE receptor, CD23, on B cells, and of its ligands, CD11b and CD11c, on CD4(+) T cells and monocytes in peripheral blood of patients with allergic asthma. In this uncontrolled open-label study, 14 children with allergic asthma received montelukast, a cysteinyl leukotrine receptor antagonist, for a period of 6 weeks after demonstrating forced expiratory volume in 1 s (FEV(1)) of less than 80% of the predicted value. Samples of peripheral heparinized blood and sera were obtained before and after therapy completion. Three-colour immunofluorescence analysis was performed, and expression of CD11b and CD11c on CD4(+) T lymphocytes and monocytes as well as the expression of CD21 and CD23 on B cells were determined (n=12). Peripheral blood eosinophil count, changes in FEV(1) and peak expiratory flow rate (PEFR), asthma exacerbations, and as-needed use of beta-agonist were also monitored.

RESULTS

Montelukast improved FEV(1) and PEFR, and decreased peripheral eosinophil counts in all study patients. There was no significant change in the expression of CD21 and CD23 on B cells. The expression of CD11c on CD4(+) T cells and of both CD11b and CD11c on monocytes remained similar to the pretreatment expression. However, the percentage of CD11b(+)CD4(+) T lymphocytes significantly decreased after treatment with montelukast. This was accompanied by a significant decrease in the levels of total IgE.

CONCLUSION

The capacity of 6-week montelukast therapy to reduce the percentage of CD11b CD4(+) T cells might be a mechanism leading to the immune response modulation on this T cell subset interaction with CD23-expressing B cells and subsequent down-regulation of IgE synthesis.

The biology of IGE and the basis of allergic disease

Allergic individuals exposed to minute quantities of allergen experience an immediate response. Immediate hypersensitivity reflects the permanent sensitization of mucosal mast cells by allergen-specific IgE antibodies bound to their high-affinity receptors (FcepsilonRI). A combination of factors contributes to such long-lasting sensitization of the mast cells. They include the homing of mast cells to mucosal tissues, the local synthesis of IgE, the induction of FcepsilonRI expression on mast cells by IgE, the consequent downregulation of FcgammaR (through an insufficiency of the common gamma-chains), and the exceptionally slow dissociation of IgE from FcepsilonRI. To understand the mechanism of the immediate hypersensitivity phenomenon, we need explanations of why IgE antibodies are synthesized in preference to IgG in mucosal tissues and why the IgE is so tenaciously retained on mast cell-surface receptors. There is now compelling evidence that the microenvironment of mucosal tissues of allergic disease favors class switching to IgE; and the exceptionally high affinity of IgE for FcepsilonRI can now be interpreted in terms of the recently determined crystal structures of IgE-FcepsilonRI and IgG-FcgammaR complexes. The rate of local IgE synthesis can easily compensate for the rate of the antibody dissociation from its receptors on mucosal mast cells. Effective mechanisms ensure that allergic reactions are confined to mucosal tissues, thereby minimizing the risk of systemic anaphylaxis.

CD5-positive and CD5-negative human B cells converge to an indistinguishable population on signalling through B-cell receptors and CD40

Whether CD5 on B cells marks a subset functionally distinct from the conventional CD5 negative (CD5neg) adult population or is more an indicator of activation, remains contentious. Here we have investigated whether CD5 positive (CD5pos) and CD5neg B cells can be distinguished in terms of their response to surrogate signals aimed to model, in vitro, T-cell dependent (TD) and T-independent (TI) encounters with antigen in vivo: the predominantly CD5pos B-cell population found in cord blood, CD5 B cells positively selected from tonsils and their CD5neg counterparts, were compared. Neonatal B cells displayed a near-identical phenotype to that of adult CD5pos B cells, being characterized by uniform immunoglobulin M (IgM), immunoglobulin D (IgD), CD23 and CD44 coexpression. When cultured with anti-IgM maintained at high density on CD32-tranfected mouse L cells to model TI responses or on CD40 ligand (CD40L)-bearing L cells (with or without captured anti-IgM) to model TD encounters, DNA synthesis was stimulated to a similar extent in all three populations. Focusing on CD5 and CD23, we found that - although the signals delivered promoted distinct profiles of expression - under each condition of activation, the phenotypes that emerged for adult CD5pos and CD5neg B cells were remarkably similar. Neonatal B cells displayed a greater diminution in CD5 expression than adult CD5pos B cells following CD40 signals but otherwise the two populations again behaved similarly. The inclusion of interleukin-4 (IL-4) to cultures where cells were costimulated via surface (s)IgM and CD40 resulted in a complete loss of CD5 expression and a corresponding hyperexpression of CD23, irrespective of the population studied. The near-identical response of CD5pos and CD5neg B cells to surrogate TD or TI signals in vitro and their convergence to indistinguishable phenotypes is wholly supportive of CD5 being a fluctuating marker of activation rather than it delineating functionally distinct subsets.

The interplay between T helper subset cytokines and IL-12 in directing human B lymphocyte differentiation

This study asks how T helper (TH) subset cytokines impact upon IL-12-directed change in B cells engaged in signaling via the B cell receptor and CD40, essential components in the initiation of T-dependent B cell responses. For B cells stimulated in this way, IL-12 promoted a distinct phenotype highlighted by the hyper-expression of CD38: the Th1 cytokine IFN-gamma reproduced the IL-12 effects while neutralizing antibody to IFN-gamma reversed IL-12-dependent change. The divergent pathway of differentiation promoted by the Th2 cytokine IL-4 (characterized by hyper-induction of CD23) was left unchecked by IL-12. IL-10 was found to dampen IL-12 actions by suppressing IL-12-dependent IFN-gamma production but failed to perturb the effects of exogenous IFN-gamma. Thus, IL-12--by invoking autocrine IFN-gamma production--promotes phenotypic deviation in B cells engaging T-dependent signals. The reversal of such Th1 driving of B cells by IL-10 only when the source of IFN-gamma is endogenous and the inability of IL-12 to impact upon IL-4-directed differentiation suggest a progressive and hierarchical commitment of B cells to polarization during a developing T-dependent response dominated at the level of the Th cell rather than that of the dendritic cell.

CD23 and allergic pulmonary inflammation: potential role as an inhibitor

CD23, a receptor for immunoglobulin E, is expressed at increased levels in asthmatic and atopic individuals and has been associated with disorders characterized by chronic inflammation. Using an established murine model, we employed several complementary strategies to investigate the role of CD23 in allergic pulmonary inflammation and airway hyperresponsiveness (AHR). Specifically, these approaches included the modulation of CD23 function in vivo by administration of anti-CD23 monoclonal antibody (mAb) or Fab fragments to wild-type mice and the analysis of CD23-deficient mice. Administration of anti-CD23 mAb, but not anti-CD23 Fab fragments, produced attenuation of pulmonary inflammation, AHR, and CD8(+) T-cell activation. On the basis of a model that the anti-CD23 mAb transduces, whereas the Fab fragment inhibits, CD23 signaling, these results suggest that CD23 negatively regulates pulmonary inflammation and AHR. This hypothesis is supported by our observation that CD23-deficient mice developed increased inflammation and AHR after sensitization and challenge with allergen. Together, these results indicate that CD23 negatively regulates pulmonary inflammation and airway hyperreactivity.

Structure and functions of CD23

This review summarizes recent data on CD23, a low affinity receptor for IgE (Fc epsilon RII). CD23 is the only FcR which does not belong to the immunoglobulin gene superfamily. The CD23 molecule was discovered independently as an IgE receptor on human lymphoblastoid B cells [1], as a cell surface marker expressed on Epstein-Barr-Virus-transformed B cells (EBVCS) [2] and as a B-cell activation antigen (Blast 2) [3]. CD23 was shown to be a low affinity receptor for IgE [4,5]. Similar to most FcR, soluble forms of CD23 (sCD23) are released into extracellular fluids. The soluble fragments formed by proteolytic cleavage of surface CD23 are not only capable of binding IgE (IgE binding factors) but also exhibit multiple functions that are not IgE related. These observations together with the finding that CD23 displays significant homology with Ca(2+)-dependent (C-type) animal lectins, suggested the existence of natural ligands other than IgE. The recent finding that CD23 interacts with CD21, CD11b and CD11c indicates that CD23 should be viewed not only as a low affinity IgE receptor but also as an adhesion molecule involved in cell-cell interaction. After a brief overview of the molecular structure, there follows a discussion of the biological activities ascribed to human CD23.

Distinct modulation by interferon-gamma (IFN-gamma) of CD23 expression on B and T lymphocytes of atopic subjects

The low-affinity IgE receptor (FcepsilonRII/CD23) plays a role in IgE production. Cytokines participating in IgE synthesis also modulate CD23 expression on lymphocytes, but whether this modulation is different in atopic subjects remains unclear. We studied CD23 expression on B and T lymphocytes in 10 asthmatic patients with Dermatophagoides pteronyssinus hypersensitivity and 10 healthy non-atopic subjects. Studies were performed by flow cytometry, in phytohaemagglutinin (PHA) or IL-4-stimulated mononuclear cell cultures, alone or in the presence of IFN-gamma. Soluble CD23 (sCD23) released in the culture supernatants was measured by enzyme-linked immunoassay. Both PHA and IL-4 induced the expression of CD23 on lymphocytes of atopic and non-atopic subjects. Whereas PHA increased both the percentage and mean fluorescence intensity of CD23+ B and T cells, IL-4 alone did not increase the percentage of CD23+ T cells. The effects of IFN-gamma were different in both groups, since it was able to reduce the percentage of PHA-stimulated CD23+ T cells only in non-atopic individuals. In non-atopic subjects more than atopic, levels of sCD23 were increased in the supernatants of PHA and IL-4 cultures. These results show that the modulation of CD23 expression is different on B and T cells, and that IFN-gamma acts differently in atopic and non-atopic individuals.

Dendritic cells generated from human blood in granulocyte macrophage-colony stimulating factor and interleukin-7

Dendritic cells (DC), with potentially important clinical applications, have been generated from human peripheral blood monocytes in the presence of GM-CSF and IL-4 (G4 DC). In the present report we show that DC with a novel phenotype can be generated from blood adherent mononuclear cells in the presence of GM-CSF and IL-7 (G7 DC). Adherent cells from PBMC, cultured in GM-CSF (600 U/ml) and IL-7 (6 U/ml), were transformed over 7 days into cells with DC morphology, at a yield of 1.2-1.6 x 10(6) per 10(7) PBMC. G7 DC not only expressed class I and class II MHC, CD1a, CD11c, CD23, CD40, CD54, CD58, CD80, CD86 and CD95, like G4 DC, but also CD21, which is the complement receptor type 2, a ligand for CD23 and a receptor for EBV and IFN-alpha. G7 DC were at least one log more effective in the autologous MLR and at least two logs more effective in the allogeneic MLR, than PBMC. They elicited proliferative responses of CD4 T cells to tetanus toxoid and CD8 T cells to an EBV peptide, and stronger T-cell cytotoxicity to EBV peptide than G4 DC. Expression of CD21 by G7 DC suggests that IL-7 delivers a distinct signal to DC precursors and that G7 DC may be functionally distinct.

B cell hybridoma presents both B-cell and T-cell epitopes for stimulating antibody production via CD23 pathway

CD23+ B cell hybridoma 17A11, pulsed with IgE:TNP-KLH triggered IgA, IgG, and IgE antibody production via CD23-mediated presentation. Prior anti-CD23 treatment abrogated 95% of the humoral antibody responses. Both B and T cell epitopes were presented by 17A11 B cell epitopes as recognized by IgG but not T cell epitopes were sensitive to treatment with 0.2 M acetic acid. Efficacy of antigen presentation via CD23 on 17A11 was comparable to that mediated via surface immunoglobulins (sIg) on a CD23 negative 4.5 parental fusion partner B cell line. This is the first demonstration that IgE:TNP-KLH pulsed B cell hybridomas present both B- and T-cell epitopes in stimulating IgA, IgG, and IgE antibody production, and raise a pertinent issue whether IgE antibodies produced under pathophysiological conditions may serve as positive feedback signal for sustaining production of different classes of antibodies.

Role and modulation of T-cell cytokines in allergy

Allergic sensitization and the development of effector functions are controlled by IL-4-secreting and IL-5-secreting type 2 T cells. Recent studies have provided new insights into the events triggering the development of type 1 and type 2 T cells, the discrimination of type 1 and type 2 effector T cells from various T-cell subsets, and the improvement of established and new therapeutic strategies, which are aimed at modulating such T-cell functions in the allergic patient.

Effect of an asthmatic attack on CD23 and CD21 expression on lymphocytes from allergic children during the allergen season

BACKGROUND

The overproduction of IgE antibodies by atopic individuals in response to inhaled aeroallergen, forms the basis of an allergic disease. Furthermore, the exposure to allergen might trigger the symptom exacerbation.

OBJECTIVE

In children with bronchial asthma, the possible effects of seasonal, natural exposure to allergen on the expression of CD21 and CD23 antigens on B lymphocytes, and on the expression of HLA-DR, CD45RA and CD45RO on CD4+ T cells investigated.

METHODS

Heparinized blood samples were obtained from 15 children with bronchial asthma allergic to Dermatophagoides pteronyssinus (Der p) at the time of an acute asthmatic attack and 2-4 weeks after the attack when the peak expiratory flow (PEF) was stabilized. The samples were analysed on a flow cytometer after the three-colour immunofluorescence staining had been performed.

RESULTS

The increased proportion of B cells expressing CD23 antigen was found at the time of attack rather than after stabilization. Serum levels of total and Der p-specific IgE increased 2-4 weeks after the asthmatic attack. This increase was accompanied by a further increase in the expression of CD23 antigen on CD21- B lymphocytes. In 10 out of 15 tested children, we found CD23 expressed on CD4+HLA-DR+ T cells during the asthmatic attack. No significant difference was found in the expression of CD45RA and CD45RO.

CONCLUSION

Since we have previously demonstrated the increased percentage of CD23 on CD21- B cells in allergic children as compared with controls, we speculate that natural exposure to the allergen which caused the increase in total and specific IgE levels might be related to the increased expression of CD23 on CD21- B cells.

Functional significance of CD23- on CD23-transfected Th2 clone

CD23, a low-affinity IgE Fc receptor, is not displayed on most resting T cells but its expression has been shown to be transiently induced in vivo and in vitro on some CD4+ T cells [1-4] and in vivo on CD8+ T cells by IgE-secreting hybridoma tumors [5]. To investigate the functional role of CD23 on T cells, we inserted a CD23 construct into an expression vector driven by a CD2 promoter and transfected it into a murine Th2 clone D10.G4.1 (D10). We stimulated the transfected D10 cells (D10.3M.24) with anti-TCR antibody in the presence or absence of IgE, and measured IL-4, IL-5 and IL-6 production in the culture supernatants. Activation of D10.3M.24 cells by anti-TCR antibody induced greater levels of IL-4, IL-5 and IL-6 production, when the TCR and CD23 were co-crosslinked by TNP anti-TCR and IgE anti-TNP antibodies. IgG anti-TNP antibody did not enhance lymphokine production by D10.3M.24 cells. The enhanced lymphokine production by IgE was blocked by monoclonal anti-CD23 antibody. IgE anti-TNP antibody did not enhance lymphokine production by the wild-type D10 cells induced by TNP anti-TCR antibody. These studies show that when co-crosslinked with the TCR, CD23 can modulate the lymphokine production in activated Th2 cells. Since CD23 binds to IgE and also binds to CD21 [6], a complement receptor commonly expressed on B cells, T-cell CD23 could play an immunoregulatory role during cognate T-B cell interaction and during IgE antibody responses.

CD23/CD21 interaction is required for presentation of soluble protein antigen by lymphoblastoid B cell lines to specific CD4+ T cell clones

Previous studies have documented a role for membrane-bound CD23 (the low affinity Fc epsilon RII) in presentation of alloantigens by B cells. The aim of the present study was to examine the involvement of cell surface CD23 in presentation of more conventional soluble protein antigens to T cells. We show that antibodies to CD23 and to its lymphocyte-associated second ligand, CD21, inhibit presentation of the cow's milk allergen casein, by autologous CD23+CD21+ B-EBV cell lines to casein-specific HLA-DP-restricted CD4+ T cell clones obtained from patients with either reaginic or enterophatic forms of cow's milk protein intolerance. Maximal inhibition was achieved when the antibodies were added at the initiation of the culture. The absence of specific inhibition by an anti-DR alpha monoclonal antibody (mAb) argues against a steric hindrance phenomenon impeding access of the T cell receptor to major histocompatibility complex class II molecules. Rather, anti-CD23 and anti-CD21 mAb-induced inhibition of antigen presentation seems to affect at least partly, heterotypic conjugate formation through CD23/CD21 interaction. Double immunofluorescence labeling of the T cell clones and antibody inhibition of T/B conjugate formation shows that functional CD23 and CD21 molecules are induced on T cells following contact with B-EBV cell lines. Taken together, these data indicate that CD23/CD21 interactions between T and B cells are required for presentation of soluble protein antigens by B-EBV cell lines to specific CD4+ T cells. The potential implications of these findings for allergen-specific T cell activation are discussed.