Basophil allergen threshold sensitivity to casein (casein-specific CD-sens) predicts allergic reactions at a milk challenge in most but not all patients.

BACKGROUND: The basophil activation test is an emerging clinical tool in the diagnosis of cow's milk allergy (CMA). The aim was to assess the association between the basophil allergen threshold sensitivity to the major milk protein casein (casein-specific CD-sens), the levels of milk- and casein-specific Immunoglobulin E antibodies (IgE-ab), and the severity of allergic reactions at milk challenges. METHODS: We enrolled 34 patients aged 5-15 (median 9) years who underwent a double-blind placebo-controlled milk-challenge (DBPCMC) as screening before inclusion in an oral immunotherapy study for CMA. The severity of the allergic reaction at the DBPCMC was graded using Sampson's severity score. Venous blood was drawn before the DBPCMC. Milk- and casein-specific IgE-ab were analyzed. Following in vitro stimulation of basophils with casein, casein-specific CD-sens, was determined. RESULTS: Thirty-three patients completed the DBPCMC. There were strong correlations between casein-specific CD-sens and IgE-ab to milk (rs = 0.682, p < .001), and between casein-specific CD-sens and IgE-ab to casein (rs = 0.823, p < .001). There was a correlation between the severity of the allergic reaction and casein-specific CD-sens level (rs = 0.395, p = .041) and an inverse correlation between casein-specific CD-sens level and the cumulative dose of milk protein to which the patient reacted at the DBPCMC (rs = -0.418, p = .027). Among the 30 patients with an allergic reaction at the DBPCMC, 67% had positive casein-specific CD-sens, 23% had negative casein-specific CD-sens, and 10% were declared non-responders. CONCLUSION: Two thirds of those reacting at the DBPMC had positive casein-specific CD-sens, but reactions also occurred despite negative casein-specific CD-sens. The association between casein-specific CD-sens and the severity of the allergic reaction and cumulative dose of milk protein, respectively, was moderate.

PD-L1- and IL-4-expressing basophils promote pathogenic accumulation of T follicular helper cells in lupus.

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by anti-nuclear autoantibodies whose production is promoted by autoreactive T follicular helper (TFH) cells. During SLE pathogenesis, basophils accumulate in secondary lymphoid organs (SLO), amplify autoantibody production and disease progression through mechanisms that remain to be defined. Here, we provide evidence for a direct functional relationship between TFH cells and basophils during lupus pathogenesis, both in humans and mice. PD-L1 upregulation on basophils and IL-4 production are associated with TFH and TFH2 cell expansions and with disease activity. Pathogenic TFH cell accumulation, maintenance, and function in SLO were dependent on PD-L1 and IL-4 in basophils, which induced a transcriptional program allowing TFH2 cell differentiation and function. Our study establishes a direct mechanistic link between basophils and TFH cells in SLE that promotes autoantibody production and lupus nephritis.

The association between expression of CD200 on B lymphocytes and the count of eosinophils and basophils in atopic dermatitis patients with and without dupilumab therapy - Pilot study.

BACKGROUND: Eosinophils and basophils are implicated in allergic reactions, and the molecule CD200 on B cells may have regulatory functions. Assessing the associations between the expression of CD200 on B lymphocytes and eosinophils and basophils helps unravel the complex immune interactions in atopic dermatitis, aiding in targeted therapeutic approaches. OBJECTIVE: The aim of our study is to evaluate the association between the count of eosinophils, basophils, CD16+ eosinophils, CD203+ basophils, the expression of activation marker CD200 on B cells and on their subsets in patients suffering from atopic dermatitis with and without dupilumab and in control group. MATERIALS AND METHODS: Altogether we examined 75 subjects: 45 patients suffering from atopic dermatitis -32 patients without dupilumab treatment, 13 patients with dupilumab treatment and 30 subjects as a control group. Immunophenotype was examined by flow cytometry in which monoclonal antibodies with fluorescent molecules were used. For statistical analysis we used non-parametric Kruskal-Wallis one-factor analysis of variance with post-hoc by Dunn's test with Bonferroni modification and the Spearman's rank correlation coefficient with calculation of R2 (%, percent of Variation Explained). RESULTS: In patients with dupilumab therapy we confirmed the association between absolute eosinophils and expression of molecule CD200 on total B lymphocytes (in 23.9 %), non-switched (in 27.2 %), naive (in 25 %) and memory (in 20.3 %) B lymphocytes and between relative eosinophils and expression of CD200 on total B lymphocytes (in 22.8 % %), non-switched (in 29 %), naive (in 21.3 %) and memory (in 22.3 %) B lymphocytes. This association is low in AD patients without dupilumab and even non linear in control healthy subjects. CONCLUSION: The higher association between eosinophils and expression of CD200 molecule on memory, naive and non switched B lymphocytes in AD patients under dupilumab therapy suggests that activation of B lymphocytes is caused by IL-4, whose production involves eosinophils and the CD200 molecule on B lymphocytes.

Basophil activation in insect venom allergy: comparison of an established test using liquid reagents with a test using 5-color tubes with dried antibody reagents.

BACKGROUND: Flow cytometry-based basophil activation tests (BAT) have been performed with various modifications, differing in the use of distinct identification and activation markers. Established tests use liquid reagents while a new development involves the use of tubes with dried antibody reagents. The aim of this pilot study was to compare these two techniques in patients with insect venom allergy. METHODS: Seventeen patients with an insect venom allergy were included in the study. The established "BAT 1" utilizes conventional antibody solutions of anti-CCR3 for basophil identification and anti-CD63 to assess basophil activation, whereas "BAT 2" uses dried anti-CD45, anti-CD3, anti-CRTH2, anti-203c and anti-CD63 for identification and activation measurement of basophils. Negative and positive controls as well as incubations with honey bee venom and yellow jacket venom at three concentrations were performed. RESULTS: Seven patients had to be excluded due to low basophil counts, high values in negative controls or negative positive controls. For the remaining 10 patients the overall mean (± SD) difference in activated basophils between the two tests was 0.2 (± 12.2) %P. In a Bland-Altman plot, the limit of agreement (LoA) ranged from 24.0 to -23.7. In the qualitative evaluation (value below/above cut-off) Cohen's kappa was 0.77 indicating substantial agreement. BAT 2 took longer to perform than BAT 1 and was more expensive. CONCLUSION: The BAT 2 technique represents an interesting innovation, however, it was found to be less suitable compared to an established BAT for the routine diagnosis of insect venom allergies.

Asparaginase-specific basophil recognition and activation predict Asparaginase hypersensitivity in mice.

Background: Asparaginase (ASNase) is a crucial part of acute leukemia treatment, but immune responses to the agent can reduce its effectiveness and increase the risk of relapse. Currently, no reliable and validated biomarker predicts ASNase-induced hypersensitivity reactions during therapy. We aimed to identify predictive biomarkers and determine immune cells responsible for anaphylaxis using a murine model of ASNase hypersensitivity. Methods: Our preclinical study uses a murine model to investigate predictive biomarkers of ASNase anaphylaxis, including anti-ASNase antibody responses, immune complex (IC) levels, ASNase-specific binding to leukocytes or basophils, and basophil activation. Results: Our results indicate that mice immunized to ASNase exhibited dynamic IgM, IgG, and IgE antibody responses. The severity of ASNase-induced anaphylaxis was found to be correlated with levels of IgG and IgE, but not IgM. Basophils from immunized mice were able to recognize and activate in response to ASNase ex vivo, and the extent of recognition and activation also correlated with the severity of anaphylaxis observed. Using a multivariable model that included all biomarkers significantly associated with anaphylaxis, independent predictors of ASNase-induced hypersensitivity reactions were found to be ASNase IC levels and ASNase-specific binding to leukocytes or basophils. Consistent with our multivariable analysis, we found that basophil depletion significantly protected mice from ASNase-induced hypersensitivity reactions, supporting that basophils are essential and can be used as a predictive marker of ASNase-induced anaphylaxis. Conclusions: Our study demonstrates the need for using tools that can detect both IC- and IgE-mediated hypersensitivity reactions to mitigate the risk of ASNase-induced hypersensitivity reactions during treatment.

Basophils are important for development of allergic skin inflammation.

BACKGROUND: Atopic dermatitis skin lesions exhibit increased infiltration by basophils. Basophils produce IL-4, which plays an important role in the pathogenesis of atopic dermatitis. OBJECTIVE: We sought to determine the role of basophils in a mouse model of antigen-driven allergic skin inflammation. METHODS: Wild-type mice, mice with selective and inducible depletion of basophils, and mice expressing Il4-driven enhanced green fluorescent protein were subjected to epicutaneous sensitization with ovalbumin or saline. Sensitized skin was examined by histology for epidermal thickening. Cells were analyzed for surface markers and intracellular expression of enhanced green fluorescent protein by flow cytometry. Gene expression was evaluated by real-time reverse transcription-quantitative PCR. RESULTS: Basophils were important for epidermal hyperplasia, dermal infiltration by CD4+ T cells, mast cells, and eosinophils in ovalbumin-sensitized mouse skin and for the local and systemic TH2 response to epicutaneous sensitization. Moreover, basophils were the major source of IL-4 in epicutaneous-sensitized mouse skin and promote the ability of dendritic cells to drive TH2 polarization of naive T cells. CONCLUSION: Basophils play an important role in the development of allergic skin inflammation induced by cutaneous exposure to antigen in mice.

Accurate determination of house dust mite sensitization in asthma and allergic rhinitis through cytometric detection of Der p 1 and Der p 2 binding on basophils (CytoBas).

BACKGROUND: House dust mite (HDM) is the most common allergen trigger globally for allergic rhinitis and atopic asthma. OBJECTIVES: To expedite accurate confirmation of allergen sensitization, we designed fluorescent allergen tetramers to directly stain specific IgE on basophils to detect specific allergen sensitization using the flow cytometric CytoBas assay. METHODS: Recombinant proteins of major HDM allergens (component), Der f 1, Der p 1, and Der p 2 were biotinylated and conjugated with fluorochrome streptavidins as tetramers. Blood samples from 64 patients who are HDM-allergic and 26 controls that are non-HDM-sensitized were incubated with allergen tetramers for evaluation of basophil binding (CytoBas) and activation (BAT) with flow cytometry. RESULTS: The tetramers effectively bound and activated basophils from patients who are allergic but not from controls who are nonsensitized. CytoBas with Der p 1 as a single allergen had comparable sensitivity and specificity (92% and 100%) to BAT (91% and 100%) in detecting allergen sensitization, as did CytoBas with Der p 2 (95% and 96%) to BAT (95% and 87%). A positive staining for Der p 1 and/or Der p 2 in CytoBas was 100% sensitive and 96% specific for HDM allergy. CONCLUSIONS: CytoBas has diagnostic accuracy for group 1 and group 2 HDM allergens that is comparable to BAT, but with additional advantages of multiple allergen components in a single tube and no requirement for in vitro basophil activation. These findings endorse a single, multiplex CytoBas assay for accurate and component-resolved diagnosis of aeroallergen sensitization in patients with allergic asthma and/or rhinitis.

Non-IgE-Mediated Immediate Drug-Induced Hypersensitivity Reactions.

Immediate drug-induced hypersensitivity reactions (IDHSRs) have conventionally been attributed to an immunoglobulin E (IgE)-mediated mechanism. Nevertheless, it has now been acknowledged that IDHSRs can also occur independently of IgE involvement. Non-IgE-mediated IDHSRs encompass the activation of effector cells, both mast cell-dependent and -independent and the initiation of inflammatory pathways through immunogenic and nonimmunogenic mechanisms. The IDHSRs involve inflammatory mediators beyond histamine, including the platelet-activating factor, which activates multiple cell types, including smooth muscle, endothelium, and MC, and evidence supports its importance in IgE-mediated reactions in humans. Clinically, distinguishing IgE from non-IgE mechanisms is crucial for future treatment strategies, including drug(s) restriction, readministration approaches, and pretreatment considerations. However, this presents significant challenges because certain drugs can trigger both mechanisms, and their presentations can appear similarly, ranging from mild to life-threatening symptoms. Thus, history alone is often inadequate for differentiation, and skin tests lack a standardized approach. Moreover, drug-specific IgE immunoassays have favorable specificity but low sensitivity, and the usefulness of the basophil activation test remains debatable. Lastly, no biomarker reliably differentiates between both mechanisms. Whereas non-IgE-mediated mechanisms likely predominate in IDHSRs, reclassifying most drug-related IDHSRs as non-IgE-mediated, with suggested prevention through dose administration adjustments, is premature and risky. Therefore, continued research and validated diagnostic tests are crucial to improving our capacity to distinguish between these mechanisms, ultimately enhancing patient care.

BTK signaling-a crucial link in the pathophysiology of chronic spontaneous urticaria.

Chronic spontaneous urticaria (CSU) is an inflammatory skin disorder that manifests with itchy wheals, angioedema, or both for more than 6 weeks. Mast cells and basophils are the key pathogenic drivers of CSU; their activation results in histamine and cytokine release with subsequent dermal inflammation. Two overlapping mechanisms of mast cell and basophil activation have been proposed in CSU: type I autoimmunity, also called autoallergy, which is mediated via IgE against various autoallergens, and type IIb autoimmunity, which is mediated predominantly via IgG directed against the IgE receptor FcεRI or FcεRI-bound IgE. Both mechanisms involve cross-linking of FcεRI and activation of downstream signaling pathways, and they may co-occur in the same patient. In addition, B-cell receptor signaling has been postulated to play a key role in CSU by generating autoreactive B cells and autoantibody production. A cornerstone of FcεRI and B-cell receptor signaling is Bruton tyrosine kinase (BTK), making BTK inhibition a clear therapeutic target in CSU. The potential application of early-generation BTK inhibitors, including ibrutinib, in allergic and autoimmune diseases is limited owing to their unfavorable benefit-risk profile. However, novel BTK inhibitors with improved selectivity and safety profiles have been developed and are under clinical investigation in autoimmune diseases, including CSU. In phase 2 trials, the BTK inhibitors remibrutinib and fenebrutinib have demonstrated rapid and sustained improvements in CSU disease activity. With phase 3 studies of remibrutinib ongoing, it is hoped that BTK inhibitors will present an effective, well-tolerated option for patients with antihistamine-refractory CSU, a phenotype that presents a considerable clinical challenge.

SARS-CoV-2 Induces Cytokine Responses in Human Basophils.

Basophils play a key role in the orientation of immune responses. Though the interaction of SARS-CoV-2 with various immune cells has been relatively well studied, the response of basophils to this pandemic virus is not characterized yet. In this study, we report that SARS-CoV-2 induces cytokine responses and in particular IL-13, in both resting and IL-3 primed basophils. The response was prominent under IL-3 primed condition. However, either SARS-CoV-2 or SARS-CoV-2-infected epithelial cells did not alter the expression of surface markers associated with the activation of basophils, such as CD69, CD13 and/or degranulation marker CD107a. We also validate that human basophils are not permissive to SARS-CoV-2 replication. Though increased expression of immune checkpoint molecule PD-L1 has been reported on the basophils from COVID-19 patients, we observed that SARS-CoV-2 does not induce PD-L1 on the basophils. Our data suggest that basophil cytokine responses to SARS-CoV-2 might help in reducing the inflammation and also to promote antibody responses to the virus.

Features of B Cell Responses Relevant to Allergic Disease.

This Brief Review delves into B cell responses in the context of allergy. The primary contribution of B cells to allergy is the production of IgE, the Ab isotype that triggers immediate hypersensitivity reactions through the release of mediators from mast cells and basophils. B cells may also have protective roles in allergy, such as through the production of IgG or as regulatory B cells. In this review, I focus on the basic principles of B cell differentiation and discuss features relevant to allergic immune responses. In particular, I discuss: (1) class-switch recombination; (2) plasma cell differentiation; (3) germinal centers and affinity maturation; and (4) memory B cells and recall responses, with an emphasis on IgE, IgG1, and IgG4. I also consider how B cells may contribute to allergic responses independent of Ab production-for example, by serving as APCs.

Alteration of Allergen Fold of Bos d 5 into a Hypoallergenic Vaccine for Immunotherapy of Cow's Milk Allergy.

BACKGROUND: Cow's milk allergy (CMA) is the most common IgE-mediated food allergy and Bos d 5 is the major allergen in cow's milk proteins. More than 60% of the patients with CMA are sensitized to this protein. METHODS AND RESULTS: A recombinant protein, encoded by a synthetic gene and consisting of reassembled Bos d 5 fragments, was expressed in E. coli strain BL21 (DE3) cells and purified to homogeneity. The B5M lacked relevant IgE-reactivity and allergenic activity compared with Bos d 5 in dot-blot and basophil activation assays. T-cell proliferation experiments demonstrated that B5M preserved the main T cell epitopes of Bos d 5. Immunization of rabbits with B5M induced protective IgG antibodies that blocked the binding of patients' IgE antibodies to the wild-type allergen and inhibited the degranulation of basophils induced by Bos d 5. CONCLUSION: Thus, we developed a new strategy, which was based on rational molecular reassembly for allergen-specific immunotherapy (AIT) of CMA and food allergy.

Targeting immunodominant Bet v 1 epitopes with monoclonal antibodies prevents the birch allergic response.

BACKGROUND: Blocking the major cat allergen, Fel d 1, with mAbs was effective in preventing an acute cat allergic response. OBJECTIVES: This study sought to extend the allergen-specific antibody approach and demonstrate that a combination of mAbs targeting Bet v 1, the immunodominant and most abundant allergenic protein in birch pollen, can prevent the birch allergic response. METHODS: Bet v 1-specific mAbs, REGN5713, REGN5714, and REGN5715, were isolated using the VelocImmune platform. Surface plasmon resonance, x-ray crystallography, and cryo-electron microscopy determined binding kinetics and structural data. Inhibition of IgE-binding, basophil activation, and mast cell degranulation were assessed via blocking ELISA, flow cytometry, and the passive cutaneous anaphylaxis mouse model. RESULTS: REGN5713, REGN5714, and REGN5715 bind with high affinity and noncompetitively to Bet v 1. A cocktail of all 3 antibodies, REGN5713/14/15, blocks IgE binding to Bet v 1 and inhibits Bet v 1- and birch pollen extract-induced basophil activation ex vivo and mast cell degranulation in vivo. Crystal structures of the complex of Bet v 1 with immunoglobulin antigen-binding fragments of REGN5713 or REGN5715 show distinct interaction sites on Bet v 1. Cryo-electron microscopy reveals a planar and roughly symmetrical complex formed by REGN5713/14/15 bound to Bet v 1. CONCLUSIONS: These data confirm the immunodominance of Bet v 1 in birch allergy and demonstrate blockade of the birch allergic response with REGN5713/14/15. Structural analyses show simultaneous binding of REGN5713, REGN5714, and REGN5715 with substantial areas of Bet v 1 exposed, suggesting that targeting specific epitopes is sufficient to block the allergic response.

Novel antibody cocktail targeting Bet v 1 rapidly and sustainably treats birch allergy symptoms in a phase 1 study.

BACKGROUND: The efficacy of an allergen-specific IgG cocktail to treat cat allergy suggests that allergen-specific IgG may be a major protective mechanism elicited by allergen immunotherapy. OBJECTIVES: Extending these findings, we tested a Bet v 1-specific antibody cocktail in birch-allergic subjects. METHODS: This was a phase 1, randomized, double-blind, study with 2 parts. Part A administered ascending doses of the Bet v 1-specific antibody cocktail REGN5713/14/15 (150-900 mg) in 32 healthy adults. Part B administered a single subcutaneous 900-mg dose or placebo in 64 birch-allergic subjects. Total nasal symptom score response to titrated birch extract nasal allergen challenge and skin prick test (SPT) with birch and alder allergen were assessed at screening and days 8, 29, 57, and 113 (SPT only); basophil activation tests (n = 26) were conducted. RESULTS: Single-dose REGN5713/14/15 significantly reduced total nasal symptom score following birch nasal allergen challenge relative to baseline. Differences in total nasal symptom score areas under the curve (0-1 hour) for subjects treated with REGN5713/14/15 versus those given placebo (day 8: -1.17, P = .001; day 29: -1.18, P = .001; day 57: -0.85, P = .024) and titration SPT with birch difference in area under the curve of mean wheal diameters for subjects treated with REGN5713/14/15 versus placebo (all P < .001) were sustained for ≥2 months; similar results were observed with alder SPT. REGN5713/14/15 was well tolerated. Basophil responsiveness to birch-related allergens was significantly decreased in subjects treated with REGN5713/14/15 versus those given placebo on days 8, 57, and 113 (all P < .01). CONCLUSIONS: Single-dose REGN5713/14/15 was well tolerated and provided a rapid (1 week) and durable (2 months) reduction in allergic symptoms after birch allergen nasal allergen challenge, potentially offering a new paradigm for the treatment of birch allergy symptoms.

Histamine in cancer immunology and immunotherapy. Current status and new perspectives.

Cancer is the second leading cause of death globally and its incidence and mortality are rapidly increasing worldwide. The dynamic interaction of immune cells and tumor cells determines the clinical outcome of cancer. Immunotherapy comes to the forefront of cancer treatments, resulting in impressive and durable responses but only in a fraction of patients. Thus, understanding the characteristics and profiles of immune cells in the tumor microenvironment (TME) is a necessary step to move forward in the design of new immunomodulatory strategies that can boost the immune system to fight cancer. Histamine produces a complex and fine-tuned regulation of the phenotype and functions of the different immune cells, participating in multiple regulatory responses of the innate and adaptive immunity. Considering the important actions of histamine-producing immune cells in the TME, in this review we first address the most important immunomodulatory roles of histamine and histamine receptors in the context of cancer development and progression. In addition, this review highlights the current progress and foundational developments in the field of cancer immunotherapy in combination with histamine and pharmacological compounds targeting histamine receptors.

Serum CD203c+ Extracellular Vesicle Serves as a Novel Diagnostic and Prognostic Biomarker for Succinylated Gelatin Induced Perioperative Hypersensitive Reaction.

Background: Perioperative hypersensitivity reaction (HR) is an IgE-FcϵRI-mediated hypersensitivity reaction with degranulation and activation of mast cells and basophils. Several studies have focused on assessing the degranulation and activation of mast cells and basophils to diagnose and predict the prognosis of drug induced HR. However, it is challenging to isolate sufficiently pure mast cells and basophils from human sources to investigate. Effective biomarkers to assess mast cells and basophils activation in vivo could potentially have high diagnostic and prognostic values. In the present study, we investigated EVs pelleted from serum in patients with succinylated gelatin induced HR. Methods: Extracellular vesicles (EVs) were isolated using a total exosome isolation kit and ultracentrifugation, characterized by Western blot, transmission electron microscopy, and nanoparticle tracking analysis. Basophils were isolated from fresh peripheral blood by negative selection using Basophil Isolation Kit II. Human mast cell line was stimulated with IL4. The expression levels of proteins related to the hypersensitive response were evaluated by Western blotting and flow Cytometer. Histamine and tryptase levels were tested using a commercial ELISA kit, and gene expression of inflammatory mediators was evaluated by qRT-PCR. The receiver operating characteristic (ROC) curve was used to evaluate the specificity and sensitivity of biomarker in predicting HR. Results: The concentration of EVs and protein expression level of CD63, FcϵRI, CD203c and tryptase were significantly (p< 0.05) increased in HR samples. The expression level of mast cell/basophil specific CD203c were significantly increased in EVs derived from serum and basophils of HR patients, and the CD203c+-EVs production in mast cells is dramatically increased in the presence of IL4, which positively correlated with histamine, tryptase and inflammatory mediators. Moreover, the ROC curve of EVs concentration and CD203c expression indicated that CD203c+-EVs had a strong diagnostic ability for HR. Conclusion: Serum CD203c+-EVs serves as a novel diagnostic and prognostic biomarker for HR.

What Basophil Testing Tells Us About CSU Patients - Results of the CORSA Study.

Basophil testing is the most effective single approach for diagnosing type-IIb autoimmune chronic spontaneous urticaria (TIIbaiCSU). A positive basophil test has been linked to long disease duration, higher disease activity, a poor response to antihistamines and omalizumab, and a better response to cyclosporine and fenebrutinib. As of now it is unclear what other features are connected to a positive basophil test in chronic spontaneous urticaria (CSU). We aimed to identify features of basophil test-positive CSU patients. We performed a cross-sectional study of 85 CSU patients. Basophil testing was done with the basophil activation test (BAT) and the basophil histamine release assay (BHRA). Data were analysed using SPSS: Student's t-test, Chi-square test, Odds Ratio, Spearman's correlation test. Of 85 CSU patients, 44% and 28% tested positive with the BAT and BHRA, respectively. These patients showed higher disease activity and impact, lower levels of disease control and total serum IgE, as well as higher rates of having a positive autologous serum skin test (ASST), angioedema, nocturnal symptoms, symptoms for >5 days/week, and thyroid autoantibodies. The ASST, by itself, was not a good predictor of basophil test results, but it predicted a positive basophil test in up to 100% of cases when combined with angioedema, thyroid autoantibodies or low IgE. In conclusion, a positive basophil test is linked to known features of TIIbaiCSU and novel characteristics including nocturnal symptoms. Further studies on basophil test-positive and -negative CSU patients can help to better understand CSU endotypes and to develop better management approaches.