Differentiation between control subjects and patients with chronic spontaneous urticaria based on the ability of anti-IgE autoantibodies (AAbs) to induce FcεRI crosslinking, as compared to anti-FcεRIα AAbs

A Comparison of Natural and Therapeutic Anti-IgE Antibodies

Immunoglobulin E (IgE) plays a critical role for the immune system, fighting against parasites, toxins, and cancer. However, when it reacts to allergens without proper regulation, it can cause allergic reactions, including anaphylaxis, through a process initiated by effector cells such as basophils and mast cells. These cells display IgE on their surface, bound to the high-affinity IgE receptor FcεRI. A cross-linking antigen then triggers degranulation and the release of inflammatory mediators from the cells. Therapeutic monoclonal anti-IgE antibodies such as omalizumab, disrupt this process and are used to manage IgE-related conditions such as severe allergic asthma and chronic spontaneous urticaria. Interestingly, naturally occurring anti-IgE autoantibodies circulate at surprisingly high levels in healthy humans and mice and may thus be instrumental in regulating IgE activity. Although many open questions remain, recent studies have shed new light on their role as IgE regulators and their mechanism of action. Here, we summarize the latest insights on natural anti-IgE autoantibodies, and we compare their functional features to therapeutic monoclonal anti-IgE autoantibodies.

Novel IgE crosslinking-induced luciferase expression method using human-rat chimeric IgE receptor-carrying mast cells

BACKGROUND

The measurement of antigen-specific serum IgE is common in clinical assessments of type I allergies. However, the interaction between antigens and IgE won't invariably trigger mast cell activation. We previously developed the IgE crosslinking-induced luciferase expression (EXiLE) method using the RS-ATL8 mast cell line; however, the method may not be sensitive enough in some cases.

METHODS

In this study, we introduced an NF-AT-regulated luciferase reporter gene into the RBL-2H3 rat mast cell line and expressed a chimeric high-affinity IgE receptor (FcεRI) α chain gene, comprising an extracellular domain from humans and transmembrane/intracellular domains from rats.

RESULTS

We generated multiple clones expressing the chimeric receptor. Based on their responsiveness and proliferation, we selected the HuRa-40 clone. This cell line exhibited significantly elevated human α chain expression compared to RS-ATL8 cells, demonstrating a 10-fold enhancement of antigen-specific reactivity. Reproducibility across different batches and operators was excellent. Moreover, we observed a detectable response inhibition by an anti-allergy drugs (omalizumab and cyclosporin A).

CONCLUSIONS

HuRa-40 cells-which carry the human-rat chimeric IgE receptor-comprise a valuable reporter cell line for the EXiLE method. Their versatility extends to various applications and facilitates high-throughput screening of anti-allergy drugs.

The Role of Crosstalk of Immune Cells in Pathogenesis of Chronic Spontaneous Urticaria

Chronic spontaneous urticaria (CSU) is defined as recurrent episodes of spontaneous wheal development and/or angioedema for more than six weeks and at least twice a week. The core link in the pathogenesis of CSU is the activation of mast cells, T cells, eosinophils, and other immune cells infiltrating around the small venules of the lesion. Increased vascular permeability, vasodilatation, and recruitment of inflammatory cells directly depend on mast cell mediators’ release. Complex regulatory systems tightly influence the critical roles of mast cells in the local microenvironment. The bias toward Th2 inflammation and autoantibodies derived from B cells, histamine expressed by basophils, and initiation of the extrinsic coagulation pathway by eosinophils or monocytes exerts powerful modulatory influences on mast cells. Cell-to-cell interactions between mast cells and eosinophils/T cells also are regulators of their function and may involve CSU’s pathomechanism. This review summarizes up-to-date knowledge regarding the crosstalk between mast cells and other immune cells, providing the impetus to develop new research concepts and treatment strategies for CSU.

Development and Evaluation of an In-House ELISA to Detect Anti-FcεR1α IgG Autoantibodies in Chronic Spontaneous Urticaria Patients

Background

Association between chronic spontaneous urticaria (CSU) and autoimmunity has been well documented. Autologous serum skin testing could support the autoimmune etiology of CSU, whereas it is difficult to interpret and could not be performed on antihistamine omitted patients. It was found that immunoglobulin G (IgG) autoantibodies (autoAbs) against high-affinity IgE receptor (FcεR1) were suggested as a potential trigger in the pathogenesis of CSU. Although many ELISA protocols have been developed to detect these autoAbs, they lacked validation or a reliable cut-off point. We, therefore, aimed to develop a validated ELISA with a reliable cut-off point to quantitate IgG anti-FcεR1α autoAbs for CSU.

Methods

We developed an in-house ELISA to quantitate IgG anti-FcεR1α autoAbs. Sera from 233 CSU patients and 25 healthy people were used to test with ELISA. The cut-off point was obtained from the results subjected to analyze with receiver operating characteristic (ROC) analysis. ELISA was validated with 116 CSU patients and 150 healthy donors.

Results

ELISA revealed that healthy people had a basal level of IgG anti-FcεR1α autoAbs, whereas their levels were significantly lower than autoAbs levels in CSU patients. ROC analysis of ELISA determined the cut-off point at 936.7 ng/ml. Our ELISA was validated and provided excellent sensitivity and specificity at 98.28% and 92.67%, respectively.

Conclusion

Our ELISA could detect significant levels of IgG anti-FcεR1α autoAbs in CSU, supporting that these autoAbs were associated with CSU etiology. Our validated ELISA with the reliable cut-off point provided excellent accuracy at 95.11% (98.28% sensitivity and 92.67% specificity). Our ELISA could be an alternative test benefit for the patient who is unable to omit antihistamine treatment.

A novel detection method for cross-linking of IgE-receptors by autoantibodies in chronic spontaneous urticaria

BACKGROUND

Autoantibodies (AAbs) against immunoglobulin E (IgE) antibodies (Abs) and their high-affinity receptor alpha subunits (FcεRIα) are key factors in the elicitation of type IIb autoimmune chronic spontaneous urticaria (type IIb aiCSU). In this study, we aimed to develop a new method to detect functional anti-FcεRIα and anti-IgE AAbs, which can crosslink the plural FcεRІα molecules and IgE Abs on the surface of mast cells and basophils, in sera from aiCSU patients using the amplified luminescence proximity homogeneous assay (Alpha).

METHODS

Sera were obtained from 14 aiCSU patients, as diagnosed by recurrent chronic spontaneous urticaria episodes and positive results for the autologous serum skin test and/or histamine release test (HRT). The AAbs to FcεRIα and IgE Abs were determined in sera from aiCSU patients using enzyme-linked immunosorbent assay (ELISA) and Alpha by cross-linking (AlphaCL) of IgE Abs and/or FcεRІα.

RESULTS

Serum anti-FcεRIα and anti-IgE AAb levels were not significantly different between aiCSU patients and healthy subjects in ELISA. Anti-FcεRIα AAbs were detected in 10 of 14 aiCSU patients who displayed positive (5/5) and negative (5/9) results in the HRT for anti-FcεRIα AAbs by AlphaCL, whereas no signals were observed in healthy subjects. Additionally, anti-IgE AAbs were detected in two of four aiCSU patients who displayed positive results in the HRT for anti-IgE AAbs.

CONCLUSIONS

A new assay method using AlphaCL can detect anti-FcεRIα and anti-IgE AAbs with FcεRIα- and IgE-crosslinking abilities in sera from aiCSU patients. This simple and practical assay method may be available as a diagnostic tool for urticaria patients.

Autoimmunity, IgE and FcεRI-bearing cells

Antibody-mediated autoimmune diseases (AAID) involve several isotypes of autoreactive antibodies. In a growing number of AAID, autoreactive IgE are present with a significant prevalence and are often associated with the presence of IgG anti-IgE and/or anti-FcεRIα (high affinity IgE receptor α chain). FcεRI-bearing cells, such as basophils or mast cells, are key players in some of these AAID. Recent advances in the pathophysiology of these diseases led to the passed or current development of anti-IgE strategies that showed very potent effects in some of them. The present review centralizes the information on the relevance of autoreactive IgE and FcεRI-bearing cells in the pathophysiology of different AAID and the ones where the anti-IgE therapeutic strategy shows or may show some benefits for the patients.

Relationship between changes in the 7-day urticaria activity score after treatment with omalizumab and the responsiveness of basophils to FcεRI stimulation in patients with chronic spontaneous urticaria

Background

About one-half of all patients with chronic spontaneous urticaria have low or less reactivity of the basophils to FcεRI stimulation. However, the differences in the clinical characteristics between patients who show normal and attenuated basophil reactivities to FcεRI stimulation are still unclear. Furthermore, it also remains unknown as to what factors induce the poor reactivity of basophils to FcεRI stimulation.

Objective

The aim of the study is to investigate the differences in the clinical characteristics between patients who show normal and attenuated basophil reactivities to FcεRI stimulation.

Methods

We compared the clinical characteristics, including the autologous serum skin test-positive rates, serum concentrations of anti-IgE and anti-FcεRIα autoantibodies, and the FcεRI-crosslinking ability of these autoantibodies between patients with a negative basophil activation test (BAT) (≤10% CD203c^high basophils, n = 9) and positive BAT (>10% CD203c^high basophils, n = 13). We also monitored the changes in the 7-day urticaria activity scores after treatment with omalizumab, as compared to the score at the baseline, between the BAT-positive and BAT-negative patients.

Results

The BAT-negative patients showed a significantly higher urticaria control test score than the BAT-positive patients (p = 0.01). There were no significant differences in the autologous serum skin test-positive rates, concentrations of anti-IgE and anti-FcεRIα autoantibodies, and the FcεRI-crosslinking ability of these autoantibodies between the 2 groups. After treatment with omalizumab for 35 days, the score decreased to under 15 (corresponding to controlled or mild chronic spontaneous urticaria) in all of the BAT-negative patients, whereas in 6 out of the 13 BAT-positive patients, the scores remained over 16 (corresponding to moderate or severe chronic spontaneous urticaria).

Conclusions

The weak reactivity of basophils to FcεRI stimulation may not be due to the desensitization of basophils by anti-IgE or anti-FcεRIα autoantibodies. The time to response to omalizumab might differ between BAT-negative and BAT-positive patients with chronic spontaneous urticaria.

Acid Stripping of Surface IgE Antibodies Bound to FcεRI is Unsuitable for the Functional Assays that Require Long-Term Culture of Basophils and Entire Removal of Surface IgE

Basophils are rare granulocytes and dysregulated functions of these cells are associated with several atopic and non-atopic allergic diseases of skin, respiratory system and gastrointestinal tract. Both cytokines and immunoglobulin E (IgE) are implicated in mediating the basophil activation and pathogenesis of these disorders. Several reports have shown that healthy individuals, and patients with allergic disorders display IgG autoantibodies to IgE and hence functional characterization of these anti-IgE IgG autoantibodies is critical. In general, anti-IgE IgG autoantibodies modulate basophil activation irrespective of allergen specificity by interacting with constant domains of IgE. Therefore, an ideal solution to prove the functions of such anti-IgE IgG autoantibodies would be to completely eliminate type I high affinity immunoglobulin E receptor (FcɛRI)-bound IgE from the surface of basophils and to demonstrate in an unequivocal manner the role of anti-IgE IgG autoantibodies. In line with previous reports, our data show that FcɛRI on peripheral blood basophils are almost saturated with IgE. Further, acetic acid buffer (pH 4) efficiently removes these FcɛRI-bound IgE. Although immediately following acetic acid-elution of IgE had no repercussion on the viability of basophils, following 24 h culture with interleukin-3 (IL-3), the viability and yield of basophils were drastically reduced in acid-treated cells and had repercussion on the induction of activation markers. Lactic acid treatment on the other hand though had no adverse effects on the viability of basophils and IL-3-induced activation, it removed only a small fraction of the cell surface bound IgE. Thus, our results show that acid buffers could be used for the elution of FcɛRI-bound IgE on the basophil surface for the biochemical characterization of IgE antibodies or for the immediate use of basophils to determine their sensitivity to undergo degranulation by specific allergens. However, these methods are not utile for the functional assays of basophils that require longer duration of culture and entire removal of surface IgE to validate the role of anti-IgE IgG autoantibodies that interact with FcɛRI-bound IgE irrespective of allergen specificity.

New treatments for chronic urticaria

OBJECTIVE

Chronic urticaria (CU) is a common, heterogeneous, and debilitating disease. Antihistamines and omalizumab are the mainstay therapies of CU. Additional treatment options are needed. Here, we review the off and beyond label use of licensed drugs, novel treatments that are currently under development, and promising new targets.

DATA SOURCES

MEDLINE was searched for recent reports of the successful use of treatments in CU and promising targets for the development of novel treatment options. We also searched ClinicalTrials.gov for recent and ongoing randomized clinical trials in CU.

STUDY SELECTIONS

Relevant articles were selected and reviewed.

RESULTS

Omalizumab, the treatment of choice in patients with antihistamine-resistant chronic spontaneous urticaria (CSU), should be explored for use in chronic inducible urticaria in children younger than 12 years with CSU and at higher doses. The off-label use of dupilumab, reslizumab, mepolizumab, and benralizumab can be effective in CU. Ligelizumab and UB-221, 2 novel anti-IgE monoclonal antibodies, are in clinical trials for CU. Other promising drugs that are currently under development for CU are a chemoattractant receptor-homologous molecule expressed on T_H2 cell antagonist, a monoclonal antibody to Siglec-8 (AK002), Bruton tyrosine kinase inhibitors (fenebrutinib and Lou064), a spleen tyrosine kinase inhibitor, and dupilumab. Promising targets of future therapies include the Mas-related G-protein-coupled receptor X2; the histamine₄ receptor; C5a and its receptor; inhibitory mast cell receptors other than Siglec-8; interleukin 33, interleukin 25, and thymic stromal lymphopoietin, and stem cell factor.

CONCLUSION

Novel and better treatments for CU are very much needed. Some agents are in clinical trials already (eg, ligelizumab), and additional ones should be developed, making use of the many promising targets recently identified and characterized.