The role of CD23 in allergic disease

Gene of the month: TFE 3

Transcription factor enhancer 3 (TFE3), on the short arm of chromosome Xp11.23 and its protein, belongs to the microphthalmia transcription family (MiTF) of transcription factors. It shares close homology with another member of the family, MiTF which is involved in melanocyte development. When a cell is stressed and/or starved, TFE3 protein translocates into the nucleus. TFE3 gene fusions with multiple different partner genes occur in several tumours with resultant nuclear expression of TFE3 protein. The main tumours associated with TFE3 gene fusions are: renal cell carcinoma, alveolar soft part sarcoma, a subset of epithelioid haemangioendotheliomas (EHE), some perivascular epithelioid cell tumours and rare examples of ossifying fibromyxoid tumour and malignant chondroid syringoma. TFE3 immunohistochemistry is of use in routine diagnostic practice with the aforementioned tumours harbouring TFE3 fusions leading to nuclear staining. In addition, there are tumours lacking TFE3 fusions but also display TFE3 nuclear immunolabeling, and these include: granular cell tumour, solid pseudopapillary neoplasm of the pancreas and ovarian sclerosing stromal tumour.

Platelets in Sepsis: An Update on Experimental Models and Clinical Data

Beyond their important role in hemostasis, platelets play a crucial role in inflammatory diseases. This becomes apparent during sepsis, where platelet count and activation correlate with disease outcome and survival. Sepsis is caused by a dysregulated host response to infection, leading to organ dysfunction, permanent disabilities, or death. During sepsis, tissue injury results from the concomitant uncontrolled activation of the complement, coagulation, and inflammatory systems as well as platelet dysfunction. The balance between the systemic inflammatory response syndrome (SIRS) and the compensatory anti-inflammatory response (CARS) regulates sepsis outcome. Persistent thrombocytopenia is considered as an independent risk factor of mortality in sepsis, although it is still unclear whether the drop in platelet count is the cause or the consequence of sepsis severity. The role of platelets in sepsis development and progression was addressed in different experimental in vivo models, particularly in mice, that represent various aspects of human sepsis. The immunomodulatory function of platelets depends on the experimental model, time, and type of infection. Understanding the molecular mechanism of platelet regulation in inflammation could bring us one step closer to understand this important aspect of primary hemostasis which drives thrombotic as well as bleeding complications in patients with sterile and infectious inflammation. In this review, we summarize the current understanding of the contribution of platelets to sepsis severity and outcome. We highlight the differences between platelet receptors in mice and humans and discuss the potential and limitations of animal models to study platelet-related functions in sepsis.

Emerging roles and regulation of MiT/TFE transcriptional factors

The MiT/TFE transcription factors play a pivotal role in the regulation of autophagy and lysosomal biogenesis. The subcellular localization and activity of MiT/TFE proteins are primarily regulated through phosphorylation. And the phosphorylated protein is retained in the cytoplasm and subsequently translocates to the nucleus upon dephosphorylation, where it stimulates the expression of hundreds of genes, leading to lysosomal biogenesis and autophagy induction. The transcription factor-mediated lysosome-to-nucleus signaling can be directly controlled by several signaling molecules involved in the mTORC1, PKC, and AKT pathways. MiT/TFE family members have attracted much attention owing to their intracellular clearance of pathogenic factors in numerous diseases. Recently, multiple studies have also revealed the MiT/TFE proteins as master regulators of cellular metabolic reprogramming, converging on autophagic and lysosomal function and playing a critical role in cancer, suggesting that novel therapeutic strategies could be based on the modulation of MiT/TFE family member activity. Here, we present an overview of the latest research on MiT/TFE transcriptional factors and their potential mechanisms in cancer.

Anti-IgE Treatment for Disorders Other Than Asthma

Immunoglobulin E (IgE) plays a key role in the pathogenesis of many allergic diseases. Thus, IgE-mediated immunologic pathways are an attractive target for intervention in allergic diseases. Omalizumab is a recombinant humanized monoclonal antibody that binds IgE and has been used treat allergic asthma for over a decade. Currently, omalizumab is approved for the treatment of both allergic asthma and chronic spontaneous urticaria. Since IgE plays a critical role in other allergic diseases, anti-IgE therapy has been evaluated in other allergic diseases in small clinical trials and case reports. Omalizumab has demonstrated efficacy in treating allergic rhinitis, atopic dermatitis, physical urticarias, mast cell disorders, food allergy, and other allergic diseases. In addition, the use of omalizumab with conventional allergen immunotherapy improves both safety and effectiveness.

Increased subsequent risk of myasthenia gravis in children with allergic diseases

Myasthenia gravis (MG) is an autoimmune disorder that affects the neuromuscular junction. The initiating factors of MG remain unclear. However, allergy has been regarded as a potential risk factor. We included 410 children with MG diagnosed between 2000 and 2008, as well as 1640 randomly selected controls. The odds ratios of MG were calculated to determine the association between MG and preexisting allergic diseases. The children with allergic diseases were at increased subsequent risk of MG, which was associated with the cumulative effect of the concurrent allergic diseases and the frequency of seeking medical care.

The nutrient-responsive transcription factor TFE3 promotes autophagy, lysosomal biogenesis, and clearance of cellular debris

The discovery of a gene network regulating lysosomal biogenesis and its transcriptional regulator transcription factor EB (TFEB) revealed that cells monitor lysosomal function and respond to degradation requirements and environmental cues. We report the identification of transcription factor E3 (TFE3) as another regulator of lysosomal homeostasis that induced expression of genes encoding proteins involved in autophagy and lysosomal biogenesis in ARPE-19 cells in response to starvation and lysosomal stress. We found that in nutrient-replete cells, TFE3 was recruited to lysosomes through interaction with active Rag guanosine triphosphatases (GTPases) and exhibited mammalian (or mechanistic) target of rapamycin complex 1 (mTORC1)-dependent phosphorylation. Phosphorylated TFE3 was retained in the cytosol through its interaction with the cytosolic chaperone 14-3-3. After starvation, TFE3 rapidly translocated to the nucleus and bound to the CLEAR elements present in the promoter region of many lysosomal genes, thereby inducing lysosomal biogenesis. Depletion of endogenous TFE3 entirely abolished the response of ARPE-19 cells to starvation, suggesting that TFE3 plays a critical role in nutrient sensing and regulation of energy metabolism. Furthermore, overexpression of TFE3 triggered lysosomal exocytosis and resulted in efficient cellular clearance in a cellular model of a lysosomal storage disorder, Pompe disease, thus identifying TFE3 as a potential therapeutic target for the treatment of lysosomal disorders.

Anti-immunoglobulin e therapy

The importance of immunoglobulin E (IgE) in atopic disorders such as asthma, allergic rhinitis, food allergies, and atopic dermatitis is well established. Elevation of total serum IgE is typically found in many atopic patients, and in predisposed individuals, allergen-specific IgE is produced. The availability of humanized monoclonal antibodies against IgE has provided a new therapeutic option and tool to explore the role IgE in allergic diseases and the effects of inhibiting IgE itself. Omalizumab is a humanized, monoclonal antibody that recognizes and binds to the Fc portion of the IgE molecule. Administration of omalizumab results in a rapid and substantial decrease in free IgE in serum. Consequently, the activity of cell populations involved in allergic inflammation, including mast cells, eosinophils, basophils, and antigen-presenting cells, is affected as well. Clinically, anti-IgE therapy has already been proven to be useful in the treatment of asthma and allergic rhinitis. The aim of this review is to provide an overview of the mechanisms of action of anti-IgE therapy as well as its efficacy in the treatment of allergic diseases, especially asthma. Considerations regarding dosing and safety of omalizumab will be addressed as well.

Transcription factor E3, a major regulator of mast cell-mediated allergic response

BACKGROUND

Microphthalmia transcription factor, an MiT transcription family member closely related to transcription factor E3 (TFE3), is essential for mast cell development and survival. TFE3 was previously reported to play a role in the functions of B and T cells; however, its role in mast cells has not yet been explored.

OBJECTIVE

We sought to explore the role played by TFE3 in mast cell function.

METHODS

Mast cell numbers were evaluated by using toluidine blue staining. FACS analysis was used to determine percentages of Kit and FcεRI double-positive cells in the peritoneum of wild-type (WT) and TFE3 knockout (TFE3(-/-)) mice. Cytokine and inflammatory mediator secretion were measured in immunologically activated cultured mast cells derived from either knockout or WT mice. In vivo plasma histamine levels were measured after immunologic triggering of these mice.

RESULTS

No significant differences in mast cell numbers between WT and TFE3(-/-) mice were observed in the peritoneum, lung, and skin. However, TFE3(-/-) mice showed a marked decrease in the number of Kit(+) and FcεRI(+) peritoneal and cultured mast cells. Surface expression levels of FcεRI in TFE3(-/-) peritoneal mast cells was significantly lower than in control cells. Cultured mast cells derived from TFE3(-/-) mice showed a marked decrease in degranulation and mediator secretion. In vivo experiments showed that the level of plasma histamine in TFE3(-/-) mice after an allergic trigger was substantially less than that seen in WT mice.

CONCLUSION

TFE3 is a novel regulator of mast cell functions and as such could emerge as a new target for the manipulation of allergic diseases.

Can anti-IgE therapy prevent airway remodeling in allergic asthma?

Airway remodeling is a central feature of asthma. It is exemplified by thickening of the lamina reticularis and structural changes to the epithelium, submucosa, smooth muscle, and vasculature of the airway wall. Airway remodeling may result from persistent airway inflammation. Immunoglobulin E (IgE) is an important mediator of allergic reactions and has a central role in airway inflammation and asthma-related symptoms. Anti-IgE therapies (such as omalizumab) have the potential to block an early step in the allergic cascade and therefore have the potential to reduce airway remodeling. The reduction in free IgE levels following anti-IgE therapy leads to reductions in high-affinity IgE receptor (FcεRI) expression on mast cells, basophils, and dendritic cells. This combined effect results in attenuation of several markers of inflammation, including peripheral and bronchial tissue eosinophilia and levels of granulocyte macrophage colony-stimulating factor, interleukin (IL)-2, IL-4, IL-5, and IL-13. Considering the previously demonstrated anti-inflammatory effects of anti-IgE therapy, along with results from a small study showing continued benefit after discontinuation of long-term treatment, a larger study to assess its effect on markers of airway remodeling is underway.

Isolation and phenotypic characterization of mucosal nasal lymphocytes by direct ex vivo analysis

Cellular inflammation of the nasal mucosa demonstrates a local immune response which plays an important role in allergic rhinitis. The aim of the present study was to characterize nasal mucosal lymphocytes regarding their activation and differentiation state by direct ex vivo flowcytometric analysis. Lymphocytes from the inferior turbinates were isolated by a mechanical method of preparation and, for comparison, from peripheral blood by Ficoll gradient centrifugation. Patients suffering from rhinitis or difficulty in nasal breathing were divided into an allergic (pollen-allergy, n = 13) and non-allergic group (n = 24). Expression of different T- and B-cell markers was determined by flowcytometric analysis. CD4+ T-cells from the nasal mucosa exhibited a memory phenotype (CD45RO+, 97%), were highly activated (CD69+, 43-73%), and showed low expression of the cutaneous lymphocyte antigen (CLA+, 5%). Nasal CD20+ B-lymphocytes expressed significantly higher levels of mIgE and lower levels of CD23 and CD80 than peripheral B-cells. Subsets of CD80+ (4%) and CD86+ (6%) CD20+ B-lymphocytes were identified in the nasal mucosa. No significant differences between allergic and non-allergic individuals were determined. As expected, the data show profound phenotypical differences between circulating peripheral blood and nasal mucosal lymphocytes. Activated memory lymphocytes are present in the nasal mucosa from allergic, but also non-allergic patients and may indicate to a significant role of a local inflammatory state without systemic criteria for allergy. In our study, we show that direct ex vivo isolation of lymphocytes is practicable method and offers a new technique to examine the local nasal allergic immune response using a multiparametric phenotypical analysis.

House dust and forage mite allergens and their role in human and canine atopic dermatitis

This article reviews the literature regarding the role of house dust and forage mite allergens in canine atopic dermatitis. The presence of immunoglobulin E (IgE) to these mites, especially to Dermatophagoides farinae, is common in both normal and atopic dogs. Exposure of dogs to the different mites is described both in the direct environment and in the coat of animals for house dust mites and in the food for forage mites. Allergens causing allergic disease in dogs seem to be different from those in humans. Dogs seem to react to high molecular weight allergens, compared to the low molecular weight group 1 and group 2 proteases that are commonly implicated in humans with atopic diseases. Despite numerous published studies dealing with this subject, a number of questions still need to be addressed to better understand the exact role of these mites in the pathogenesis of canine atopic dermatitis and to improve the quality of the allergens used in practice.

Changes of serum cytokines after the long term immunotherapy with Japanese hop pollen extracts

Japanese hop (Hop J) pollen has been considered as one of the major causative pollen allergens in the autumn season. We developed a new Hop J immunotherapy extract in collaboration with Allergopharma (Reinbeck, Germany) and investigated immunologic mechanisms during 3 yr immunotherapy. Twenty patients (13 asthma with rhinitis and 7 hay fever) were enrolled from Ajou University Hospital. Sera were collected before, 1 yr, and 3 yr after the immunotherapy. Changes of serum specific IgE, IgG1, and IgG4 levels to Hop J pollen extracts and serum IL-10, IL-12, TGF-beta1 and soluble CD23 levels were monitored by ELISA. Skin reactivity and airway hyper-responsiveness to methacholine were improved during the study period. Specific IgG1 increased at 1 yr then decreased again at 3 yr, and specific IgG4 levels increased progressively (p<0.05, respectively), whereas total and specific IgE levels showed variable responses with no statistical significance. IL-10, TGF-beta1 and soluble CD23 level began to decrease during first year and then further decreased during next two years with statistical significances. (p<0.05, respectively). In conclusion, these findings suggested the favorable effect of long term immunotherapy with Hop J pollen extracts can be explained by lowered IgE affinity and generation of specific IgG4, which may be mediated by IL-10 and TGF-beta1.

Omalizumab in asthma: approval and postapproval experience

Omalizumab is a humanized mouse monoclonal antibody that binds specifically to the constant region of the immunoglobulin (Ig)E heavy chain. Omalizumab exerts its effects by reducing free serum IgE levels and FcepsilonRI expression on several cell types. These effects have been shown to result in decreased airway inflammation and clinical improvement. In multiple studies, omalizumab has been shown to be efficacious in the treatment of moderate-to-severe persistent asthma and is currently approved by the US Food and Drug Administration for the treatment of moderate-to-severe allergic asthma in patients age 12 yr and older. Moreover, omalizumab has been demonstrated to be effective in the treatment of children and adults with seasonal and perennial allergic rhinitis. Postmarketing surveillance has shown omalizumab to be a relatively safe and well-tolerated medication.

Anti-CD23 monoclonal antibody, lumiliximab, inhibited allergen-induced responses in antigen-presenting cells and T cells from atopic subjects

BACKGROUND

CD23 plays a role in the regulation of IgE production and allergy-induced immune and inflammatory responses. A novel anti-CD23 monoclonal antibody, lumiliximab, is a potential therapeutic antibody recently demonstrated to be safe in human beings.

OBJECTIVE

This study investigated the effects of lumiliximab on allergen-induced immune responses from atopic subjects compared with blocking HLA-DR and costimulatory molecules, CD80 and CD86.

METHODS

Allergen-stimulated PBMCs from atopic subjects were pretreated with lumiliximab or antibodies to CD80, CD86, and HLA-DR. Cultures were analyzed for cell proliferation and IL-1beta, TNF-alpha, and IL-5 cytokine secretion. An allergen-specific T-cell line was developed and analyzed for lymphocyte proliferation in response to allergen with or without lumiliximab. Lumiliximab's effect on CD86 expression was evaluated by flow cytometry in the U937 monocytic cell line.

RESULTS

Lumiliximab reduced allergen-induced PBMC proliferation by 50% (n = 6; P = .006). In addition, cultures pretreated with lumiliximab had a reduction in the proinflammatory cytokines IL-1beta (P < .003) and TNF-alpha (P = .05) and the T(H)2 cytokine IL-5 (P = .002). Blocking CD86 resulted in greater reduction in proliferation than lumiliximab (P = .003) but similar effects in cytokine secretion. The anti-CD80 blocking antibody had no effect on cytokine production but did reduce proliferation. Furthermore, the addition of lumiliximab to cytokine stimulated U937 cells reduced surface expression of CD86 (P = .012).

CONCLUSION

These results indicate that the anti-CD23 mAb, lumiliximab, may be involved in modulating antigen presenting cells and reducing TH2-type immune responses. The use of this antibody may provide clinical benefit for treating allergic diseases.

Production of biologically active recombinant human soluble CD23 and its effect on PBMCs isolated from hyper-IgE blood

A recombinant form of human soluble CD23 (sCD23), the low affinity receptor for IgE (FcepsilonRII), was produced by PCR cloning the lectin-binding domain sequence into a bacterial expression vector. After renaturation and purification, the sCD23 bound IgE and divalent metal ions, indicating its activity. The recombinant human sCD23 exhibited similar proinflammatory properties as the native protein. Although interleukin-1beta, tumour necrosis factor-alpha, and nuclear factor-kappaB appeared not to be enhanced significantly in unstimulated RPMI 8866 B-lymphoblastoid and U937 promonocytic cell lines with 24 h incubation of recombinant sCD23, they were produced in both healthy and hyper-IgE-derived peripheral blood mononuclear cells, especially tumour necrosis factor-alpha. This study concludes that while recombinant and chimeric sCD23 may be useful in blocking IgE binding to immune cells and decreasing IgE synthesis by B-lymphocytes, the production of proinflammatory cytokines, particularly tumour necrosis factor-alpha will enhance immune responses in cases of asthma, allergy, and hyper-IgE syndrome.

The role of immunoglobulin E and immune inflammation: implications in allergic rhinitis

Immunoglobulin E (IgE) plays a critical role in the allergic inflammatory process in diseases such as allergic rhinitis. Cross-linking IgE bound to its receptor on cells by multivalent allergens initiates a chain of events resulting in allergic immune responses. Mast cells and basophils are involved in the early, immediate response, which is marked by cellular degranulation and the release of proinflammatory mediators, including histamine. Antigen-presenting cells are also activated by allergen-loaded IgE, resulting in immunomodulation of T-cell responses. The IgE molecule binds to two types of receptors, the high-affinity (Fc epsilonRI) and low-affinity (Fc epsilonRII or CD23) receptors, that have differing properties important in mediating allergen-induced responses. New therapies targeting the IgE molecule reduce allergen-stimulated immune responses and improve the clinical symptoms in subjects with allergic rhinitis. Understanding the role of the IgE molecule is necessary to appreciate the development and use of novel therapies targeting its actions.

Immunomodulation in asthma: a distant dream or a close reality?

The search for new treatments of asthma or any other disease for that matter is an infinite exercise. The scope for discovering new forms of treatment has increased now more than ever due to a better understanding of the molecular pathogenesis of the disease. Regulation of biomolecular or immunological events could occur at numerous points in the disease pathogenesis. This review describes the strategies to regulate the inappropriate immune responses that are elicited after exposure to an allergen. One such successful therapy is treatment with omalizumab, the anti-IgE antibody. Other therapies include cytokine antagonists, transcription factor antagonists, immunostimulatory DNA therapy, cytokine therapy and anti-T cell strategies. All these agents have been shown to be promising and could serve as an alternative approach to the treatment of asthma and maybe other allergic diseases.

Elevated expression of CD23 on peripheral blood B lymphocytes from patients with bullous pemphigoid: correlation with increased serum IgE

BACKGROUND

Increased serum IgE levels are occasionally found in patients with severe bullous pemphigoid (BP). CD23, a low affinity Fc receptor for IgE, is mainly expressed on mature B lymphocytes. Studies have suggested that serum levels of soluble CD23 (sCD23) correlate with serum IgE levels and disease severity in BP.

OBJECTIVE

The purpose of our study is to examine whether the expression of CD23 is elevated in BP and whether this expression correlates with serum IgE levels and disease severity.

METHODS

We measured CD23 expression on B cells from patients with active BP, pemphigus vulgaris, pemphigus foliaceus, and atopic dermatitis (AD), as well as healthy control subjects, using a flow cytometer. Serum levels of IgE and sCD23 were also measured.

RESULTS

The expression of CD23 was significantly higher in BP patients compared with healthy control subjects (P < 0.05), whereas the levels were normal in the other bullous diseases. CD23 expression tended to be higher in severe BP compared with moderate BP, and the levels in severe BP were comparable to the levels in AD. Furthermore, CD23 expression correlated positively with serum IgE levels (P < 0.002), and the IgE levels were significantly higher in severe BP than in moderate BP (P < 0.01 ). CD23 expression in BP did not correlate with sCD23 levels.

CONCLUSIONS

These results suggest that the up-regulated surface CD23 on B cells may be involved in IgE synthesis and inflammatory events in BP.

High frequency of allergic conjunctivitis in myasthenia gravis without thymoma

OBJECTIVES

To investigate the frequency of allergic disorders in myasthenia gravis (MG) patients and characterize the features of MG associated with allergic disorders.

METHODS

Frequencies of past and present common allergic disorders in 160 MG patients who visited the Department of Neurology, Kyushu University Hospital from April 2000 to July 2003 and in 81 neurological normal controls were studied.

RESULTS

Among various allergic disorders, the frequency of allergic conjunctivitis (AC) was significantly higher in MG patients (39/160, 24.4%, p(corr)=0.0112), especially with MG without thymoma (36/123, 29.3%, p(corr)=0.0016), in comparison to the controls (6/81, 7.4%). MG patients with AC showed a significantly higher rate of seronegative MG (43.6% vs. 17.4%, p=0.008) and a higher tendency of ocular MG (43.6% vs. 28.1%, p=0.071). Moreover, MG with AC had significantly lower anti-acetylcholine receptor antibody titers (median 6.8 nmol/l vs. median 23.6 nmol/l, p=0.0359) as well as a lower rate of coexisting thymoma (7.7% vs. 17.4%, p=0.016). The incidence of myasthenic crisis was also lower in MG with AC than without AC, yet the difference was not significant (7.7% vs. 15.7%).

CONCLUSION

There was a significant association of AC with MG especially for ocular or seronegative MG in cases without thymoma.

The Importance of Lys-352 of Human Immunoglobulin E in FcϵRII/CD23 Recognition

The interaction of immunoglobulin E (IgE) with its low affinity receptor (FcepsilonRII/CD23) plays a central role in the initiation and regulation of type I hypersensitivity responses. We have previously identified the importance of amino acid residues in the A-B loop of the Cepsilon3 domain of human IgE and implicated a region close to the glycosylation site at asparagine 371 as contributing to IgE-CD23 interaction. These residues were now targeted by site-directed mutagenesis. The IgE-CD23 interaction was assessed by semiquantitative flow cytometry. Replacement of the entire Cepsilon3 A-B loop (residues 341-356) with the homologous rat IgE sequence resulted in complete loss of human CD23 recognition, as did replacement of residues 346-353, indicating that class-specific effector residue(s) are contained within these eight amino acids. Lysine 352 within the A-B loop was identified as contributing directly to human CD23 interaction. Mutation to the rodent homologue glycine or glutamate resulted in a significant reduction in binding compared with native IgE, whereas conservative substitution with arginine effected a small, but statistically significant, enhancement of CD23 binding. Mutation of the Cepsilon3 glycosylation site at asparagine 371 to threonine or glutamine did not significantly affect CD23 recognition. Our results yield new insights into the structural basis of the hIgE-CD23 interaction and hold promise for the rational design of drugs that can manipulate IgE-mediated regulation of the allergic response.

Monoclonal anti-IgE antibody: a novel therapy for allergic airways disease

LEARNING OBJECTIVES

To familiarize the practitioner with a novel (monoclonal anti-immunoglobulin [Ig]E antibody) form of therapy for allergic airways disease. To understand the relevance of IgE as a therapeutic target. To appreciate the concepts behind the design of the molecule. To learn how anti-IgE was used in clinical trials. To anticipate the likely effects (efficacy and safety) in clinical use in patients with allergic asthma and with allergic rhinitis. To characterize the types of patients who might benefit from this therapy.

DATA SOURCES

Published data for preclinical and clinical studies.

RESULTS

Omalizumab is a nonimmunogenic, nonanaphylactogenic monoclonal anti-IgE antibody. In clinical use, omalizumab reduces levels of serum-free IgE. Given subcutaneously in patients with moderate-severe allergic asthma, omalizumab reduced exacerbations compared with placebo, and at the same time it allowed inhaled corticosteroids to be reduced or withdrawn. In patients with allergic rhinitis, omalizumab reduced the severity of symptoms and rescue antihistamine usage versus placebo. In both settings, quality of life was improved with active treatment relative to placebo. The drug seems safe and well tolerated.

CONCLUSION

As the first clinical anti-IgE agent, omalizumab is an interesting new addition to the currently available therapies for allergic airways disease. The benefits demonstrated underline the importance of IgE in these conditions. The use of anti-IgE in other IgE-mediated allergic diseases warrants further research.

Expression and purification of stable 33-kDa soluble human CD23 using the Drosophila S2 expression system

CD23, a 45-kDa type II membrane glycoprotein present on B cells, monocytes, and other human immune cells, is a low-affinity receptor for IgE. The extracellular region of the membrane-bound human CD23 is processed into at least four soluble (s) CD23 forms, with apparent molecular masses of 37, 33, 29, and 25 kDa. High levels of sCD23 are found in patients with allergy, certain autoimmune diseases, or chronic lymphocytic leukemia. Therefore, inhibition of the processing of membrane-bound CD23 to control the cytokine-like effects of sCD23 offers a novel therapeutic opportunity. While the 37-, 29-, and 25-kDa forms of sCD23 have been expressed previously as recombinant proteins, the 33-kDa form has not been purified and characterized. To further investigate the multiple roles of sCD23 fragments and to devise assays to identify potent small-molecule inhibitors of CD23 processing, we have produced the 33-kDa form of sCD23 using Chinese hamster ovary (CHO) and Drosophila S2 cells. The CHO-expressed 33-kDa protein was found to undergo proteolytic degradation during cell growth and during storage of purified protein, resulting in accumulation of a 25-kDa form. The Drosophila system expressed the 33-kDa sCD23 in a stable form that was purified and demonstrated to be more active than the CHO-derived 25-kDa form in a monocyte TNFalpha release assay.