In vitro IgE inhibition in B cells by anti-CD23 monoclonal antibodies is functionally dependent on the immunoglobulin Fc domain (original) (raw)
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The expression of murine B cell CD23, in vivo, is regulated by its ligand, IgE
International Immunology, 1998
up-regulation of CD23 could be elicited in vivo as well. In IgE -/mice, i.v. infusion of IgE corrected CD23 expression to wild-type levels. Our results demonstrate that IgE directly participates in CD23 regulation in vivo. This positive feedback loop may constitute a mechanism for the amplification of ongoing allergic responses.
Journal of immunology (Baltimore, Md. : 1950), 1988
We have produced three different mAb specific for human IgE-Fc. Their binding pattern to either heat-denatured IgE or a family of overlapping IgE-derived recombinant peptides and their ability to affect interaction of IgE with its low affinity receptor Fc epsilon R2/CD23 demonstrate that they recognize distinct epitopes on the IgE molecule. All three mAb were able to induce basophil degranulation as measured by the induction of histamine release. mAb 173 recognizes a thermolabile epitope in the CH4 domain. It does not affect the binding of IgE to Fc epsilon R2/CD23. mAb 272 recognizes a thermostable epitope that maps to a sequence of 36 amino acids (AA) spanning part of the CH2 and CH3 domain and it does not affect the binding of IgE to Fc epsilon R2/CD23. mAb 27 recognizes a thermolabile epitope located on a 10 AA stretch (AA 367-376) in the CH3 domain. This area contains one N-linked oligosaccharide (Asn-371), but the antibody is not directed against carbohydrate because it binds ...
Cellular Immunology, 1997
change little with B cell activation. Coactivation strongly inhibited e-germline transcript levels but the The capacity of CD23 to regulate IgE production was presence of CD23-expressing cells did not. Thus, coacevaluated in both an in vitro and an in vivo system. tivation potentially operates prior to isotype switch-The decreased IgE response seen in CD23 transgenic ing, while high CD23 coculture blocks either recombimice was confirmed and observed to occur at all antination or more likely B cell differentiation to high Ig gen doses used. In addition, purified B cells from the producers stage. Our data support the hypothesis that Tg animals in general exhibited lower IgE production
Uncoupling of Natural IgE Production and CD23 Surface Expression Levels
PLoS ONE, 2013
CD23, the low affinity receptor for immunoglobulin E (IgE), has been proposed to play a critical role in the regulation of IgE production, based on altered IgE levels in CD23-deficient mice and transgenic mouse models, as well as in mouse strains with mutations in the CD23 gene, e.g. 129 substrains. Here, we have investigated a mouse line termed LxT1 that expresses reduced CD23 surface levels on B cells, and its influence on natural IgE production. Extensive phenotypic analysis showed that CD23 surface expression was reduced in LxT1 compared to the control, without affecting B cell development in general. This CD23 low surface level in LxT1 mice is not as a result of reduced CD23 mRNA expression levels or intracellular accumulation, but linked to a recessive locus, a 129-derived region spanning 28 Mb on chromosome 8, which includes the CD23 gene. Sequence analysis confirmed five mutations within the CD23 coding region in LxT1 mice, the same as those present in New Zealand Black (NZB) and 129 mice. However, this CD23 low phenotype was not observed in all 129 substrains despite carrying these same CD23 mutations in the coding region. Moreover, serum IgE levels in LxT1 mice are as low as those in the C57BL/6 (B6) strain, and much lower than those in 129 substrains. These data indicate that the CD23 surface level and serum IgE level are uncoupled and that neither is directly regulated by the mutations within the CD23 coding region. This study suggests that caution should be taken when interpreting the immunological data derived from mice with different genetic background, especially if the gene of interest is thought to influence CD23 surface expression or serum IgE level.
Allergology International, 2002
Background: Both a recombinant soluble form of the high-affinity IgE receptor α subunit (rsFc ε RI α ) and anti-IgE antibody have been shown to be involved in the regulation of IgE synthesis. However, the mechanisms of IgE regulation by two such IgE-binding agents remain unclear. In the present study, we investigated whether rsFc ε RI α and anti-IgE antibody modulated IgE synthesis in an identical or different manner. Methods: Normal human B cells stimulated with interleukin (IL)-4 plus anti-CD40 antibody were analyzed for the regulatory effects of rsFc ε RI α and anti-IgE antibody on the expression of C ε transcipts, the autocrine production of IL-6 and the induction of apoptosis. Results: Both rsFc ε RI α and anti-IgE antibody inhibited mature C ε transcription, without affecting germline C ε transcription. In addition, rsFc ε RI α was effective in decreasing IL-6 production at a later stage when IgEexpressing B cells were generated, whereas F(ab ′ ) 2 , but not the Fab fragment, of anti-IgE antibody induced apoptosis in the cells. Although these three agents almost equally recognized IgE expressed on B cells, rsFc ε RI α was unable to induce apoptotic cell death and the Fab fragment was similarly ineffective in the regulation of IL-6 production. The addition of IL-6 to cultures containing rsFc ε RI α significantly restored its suppressive effect on IgE synthesis. Conclusions: These results indicate that regulation of IgE synthesis by rsFc ε RI α differs from that by anti-IgE antibody.
Molecular and cellular targets of anti-IgE antibodies
Allergy, 2005
In 1966 Ishizaka et al. (1) opened a new era in the pathophysiology of immunological disorders when they identified and purified IgE from the serum of allergic patients. Like other immunoglobulins, IgE consists of two light chains and two e-heavy chains and can be detected in two forms, a secreted and a membrane-bound form ). mIgE is a transmembrane protein which behaves like a classical antigen receptor on B lymphocytes (2). Previous experiments in our and other laboratories showed that the expression of functional mIgE is essential for generating a humoral IgE and IgG1 response in mice (3, 4). The transmembrane domain and the cytoplasmic tail are encoded by two exons M1 (transmembrane domain) and M2 (cytoplasmic tail). The cytoplasmic domains of mIgs are different in size and range from only three amino acid residues in the case of mIgM and mIgD to 28 residues for the mIg subclasses. The mIg transmembrane segments are about 25 amino acids long, are highly homologous between all Ig-subclasses and have the potential for interaction with other polypeptides (5). Beside these 25 membrane-spanning amino acids, M1 additionally encodes isotype specific extracellular spacer segments. The spacers differ in lengths (13-21 amino acids) and show high variability between the different Ig isotypes. In the early nineties it became evident that human IgE molecules, unlike other immunoglobulin classes, bind specifically and with a very high affinity (Ka ¼ 10 9 M) to receptors (FceRI) on the surface of human basophils and mast cells (6). IgE cross-linking of FceRI + cells by specific antigens results in the release of a variety of preformed (e.g. histamine) and de novo synthesized chemical mediators (e.g. prostaglandins) and cytokines that exert their effects by interacting with specific receptors on target organs. Despite the fact that IgE is known for more than 30 years, we must admit that, so far, we failed to define significant biological functions for the IgE molecule. Because IgE titres are elevated in individuals suffering from helminthic infestations, IgE was thought to play a role in the defence against worms (7, 8). It was surprising to realize that treatment with anti-IgE antibodies of mice infected with Schistosoma mansoni or Nippostrongylus brasiliensis resulted in accelerated elimination of parasites and in a decreased worm burden and reduction in the number of eggs, which Immunoglobulin E (IgE) was the last of the immunoglobulins discovered. It is present in very low amounts (nano-to micro-gram per ml range) in the serum of normal healthy individuals and normal laboratory mouse strains and has a very short half-life. This contrasts with the other immunoglobulin classes, which are present in much higher concentrations (micro-to milligram per ml range) and form a substantial component of serum proteins. Immunoglobulins play a role in homeostatic mechanisms and they represent the humoral arm of defence against pathogenic organisms. Since IgE antibodies play a key role in allergic disorders, a number of approaches to inhibit IgE antibody production are currently being explored. In the recent past the use of nonanaphylactic, humanized anti-IgE antibodies became a new therapeutic strategy for allergic diseases. The therapeutic rational beyond the idea derives from the ability of the anti-IgE antibodies to bind to the same domains on the IgE molecule that interact with the highaffinity IgE receptor, thereby interfering with the binding of IgE to this receptor without cross-linking the IgE on the receptor (nonanaphylactic anti-IgE antibodies). Treatment with anti-IgE antibodies leads primarily to a decrease in serum IgE levels. As a consequence thereof, the number of high-affinity IgE receptors on mast cells and basophils decreases, leading to a lower excitability of the effector cells reducing the release of inflammatory mediator such as histamine, prostaglandins and leukotrienes. Experimental studies in mice indicate that injection of some monoclonal anti-IgE antibodies also inhibited IgE production in vivo. The biological mechanism behind this reduction remains speculative. A possible explanation may be that these antibodies can also interact with membrane bound IgE on B cells, which could interfere the IgE production.
International Immunopharmacology, 2009
Monocytes and macrophages of individuals with allergic diseases express increased levels of the low-affinity IgE receptors (FcεRII or CD23) on their surfaces. The cross-linking of CD23-bound IgE antibody by allergen activates the cells to release inflammatory mediators. In mast cells, the binding of IgE to the high-affinity IgE receptors (FcεRI) has recently been shown to activate these cells independent of allergen. It has not been determined if such is true of the binding of IgE to the low-affinity receptors. The purpose of this study was, therefore, to determine whether monomeric IgE alone can activate CD23-bearing human monocytes and how this may relate to the activation by IgE/anti-IgE immune complex. Purified monocytes, cultured for 48 h with IL-4 to up-regulate CD23 were sensitized with human myeloma IgE and further cultured for 24 h with or without anti-human IgE antibody. The release of cytokines TNF-α and MIP-1α (as an index of activation) was determined by enzyme immunoassay. Results showed that in IL-4-treated/CD23-bearing monocytes, sensitization with IgE alone caused a release of TNF-α and MIP-1α. The addition of anti-IgE antibody to cross-link the bound IgE resulted in the enhancement of the response. Such activation by monomeric IgE and IgE/anti-IgE immune complex was blocked with an anti-CD23 antibody, confirming the specific involvement of CD23 molecules. Neither of the activation modalities elevated intracellular cAMP, contrary to previous report. These results show for the first time, that in CD23-bearing monocytes, IgE sensitization alone can activate monocytes, and that ligation of such IgE by anti-IgE antibody only enhances the response. These observations have implications for the understanding of the pathophysiology of IgE-dependent inflammation accompanying many allergic diseases.
Soluble CD23 Controls IgE Synthesis and Homeostasis in Human B Cells
Journal of immunology (Baltimore, Md. : 1950), 2012
CD23, the low-affinity receptor for IgE, exists in membrane and soluble forms. Soluble CD23 (sCD23) fragments are released from membrane (m)CD23 by the endogenous metalloprotease a disintegrin and metalloprotease 10. When purified tonsil B cells are incubated with IL-4 and anti-CD40 to induce class switching to IgE in vitro, mCD23 is upregulated, and sCD23 accumulates in the medium prior to IgE synthesis. We have uncoupled the effects of mCD23 cleavage and accumulation of sCD23 on IgE synthesis in this system. We show that small interfering RNA inhibition of CD23 synthesis or inhibition of mCD23 cleavage by an a disintegrin and metalloprotease 10 inhibitor, GI254023X, suppresses IL-4 and anti-CD40–stimulated IgE synthesis. Addition of a recombinant trimeric sCD23 enhances IgE synthesis in this system. This occurs even when endogenous mCD23 is protected from cleavage by GI254023X, indicating that IgE synthesis is positively controlled by sCD23. We show that recombinant trimeric sCD23 binds to cells coexpressing mIgE and mCD21 and caps these proteins on the B cell membrane. Upregulation of IgE by sCD23 occurs after class-switch recombination, and its effects are isotype-specific. These results suggest that mIgE and mCD21cooperate in the sCD23-mediated positive regulation of IgE synthesis on cells committed to IgE synthesis. Feedback regulation may occur when the concentration of secreted IgE becomes great enough to allow binding to mCD23, thus preventing further release of sCD23. We interpret these results with the aid of a model for the upregulation of IgE by sCD23.