Comparison of the passive mast cell activation test with the basophil activation test for diagnosis of perioperative rocuronium hypersensitivity

BACKGROUND

Rocuronium is a major cause of perioperative hypersensitivity (POH). Skin tests (STs) and quantification of specific immunoglobulin E antibodies (sIgEs) can yield incongruent results. In such difficult cases, the basophil activation test (BAT) can be helpful. Here, we evaluated the passive mast cell activation test (pMAT) as a substitute of BAT as part of the diagnostic tests for rocuronium allergy.

METHODS

Sera from patients with a suspected POH reaction potentially related to rocuronium were included. All patients had a complete diagnostic investigation, including STs, quantification of sIgEs to morphine and rocuronium, and BAT. For execution of pMAT, human mast cells were generated from healthy donor peripheral blood CD34+ progenitor cells and sensitised overnight with patient sera.

RESULTS

In total, 90 sera were studied: 41 from ST+sIgE+ patients, 13 from ST-sIgE- patients, 20 from ST+sIgE- patients, and 16 from ST-sIgE+ patients. According to BAT results, patients were further allocated into subgroups. Of the 38 BAT+ patients, 25 (66%) showed a positive pMAT as well. Of the 44 BAT- patients, 43 (98%) also showed a negative pMAT. Mast cells that were not passively sensitised did not respond to rocuronium.

CONCLUSIONS

We show that the pMAT, in many cases, can substitute for BAT in the diagnosis of rocuronium hypersensitivity and advance diagnosis in difficult cases with uncertain ST or sIgE results when BAT is not locally available.

SIGLEC-5/14 Inhibits CD11b/CD18 Integrin Activation and Neutrophil-Mediated Tumor Cell Cytotoxicity

Since the successful introduction of checkpoint inhibitors targeting the adaptive immune system, monoclonal antibodies inhibiting CD47-SIRPα interaction have shown promise in enhancing anti-tumor treatment efficacy. Apart from SIRPα, neutrophils express a broad repertoire of inhibitory receptors, including several members of the sialic acid-binding receptor (SIGLEC) family. Here, we demonstrate that interaction between tumor cell-expressed sialic acids and SIGLEC-5/14 on neutrophils inhibits antibody-dependent cellular cytotoxicity (ADCC). We observed that conjugate formation and trogocytosis, both essential processes for neutrophil ADCC, were limited by the sialic acid-SIGLEC-5/14 interaction. During neutrophil-tumor cell conjugate formation, we found that inhibition of the interaction between tumor-expressed sialic acids and SIGLEC-5/14 on neutrophils increased the CD11b/CD18 high affinity conformation. By dynamic acoustic force measurement, the binding between tumor cells and neutrophils was assessed. The interaction between SIGLEC-5/14 and the sialic acids was shown to inhibit the CD11b/CD18-regulated binding between neutrophils and antibody-opsonized tumor cells. Moreover, the interaction between sialic acids and SIGLEC-5/14-consequently hindered trogocytosis and tumor cell killing. In summary, our results provide evidence that the sialic acid-SIGLEC-5/14 interaction is an additional target for innate checkpoint blockade in the tumor microenvironment.

Allergenic and Mas-Related G Protein-Coupled Receptor X2-Activating Properties of Drugs: Resolving the Two

Since the seminal description implicating occupation of the Mas-related G protein-coupled receptor X2 (MRGPRX2) in mast cell (MC) degranulation by drugs, many investigations have been undertaken into this potential new endotype of immediate drug hypersensitivity reaction. However, current evidence for this mechanism predominantly comes from (mutant) animal models or in vitro studies, and irrefutable clinical evidence in humans is still missing. Moreover, translation of these preclinical findings into clinical relevance in humans is difficult and should be critically interpreted. Starting from our clinical priorities and experience with flow-assisted functional analyses of basophils and cultured human MCs, the objectives of this rostrum are to identify some of these difficulties, emphasize the obstacles that might hamper translation from preclinical observations into the clinics, and highlight differences between IgE- and MRPGRX2-mediated reactions. Inevitably, as with any subject still beset by many questions, alternative interpretations, hypotheses, or explanations expressed here may not find universal acceptance. Nevertheless, we believe that for the time being, many questions remain unanswered. Finally, a theoretical mechanistic algorithm is proposed that might advance discrimination between MC degranulation from MRGPRX2 activation and cross-linking of membrane-bound drug-reactive IgE antibodies.

Mas-related G protein-coupled receptor MRGPRX2 in human basophils: Expression and functional studies

Background

Occupancy of MRGPRX2 heralds a new era in our understandings of immediate drug hypersensitivity reactions (IDHRs), but a constitutive expression of this receptor by basophils is debated.

Objective

To explore the expression and functionality of MRGPRX2 in and on basophils.

Methods

Basophils from patients with birch pollen allergy, IDHRs to moxifloxacin, and healthy controls were studied in different conditions, that is, in rest, after stimulation with anti-IgE, recombinant major birch pollen allergen (rBet v 1), moxifloxacin, fMLP, substance P (SP), or other potential basophil secretagogues. In a separate set of experiments, basophils were studied after purification and resuspension in different media.

Results

Resting whole blood basophils barely express MRGPRX2 on their surface and are unresponsive to SP or moxifloxacin. However, surface MRGPRX2 is quickly upregulated upon incubation with anti-IgE or fMLP. Pre-stimulation with anti-IgE can induce a synergic effect on basophil degranulation in IgE-responsive subjects after incubation with SP or moxifloxacin, provided that basophils have been obtained from patients who experienced an IDHR to moxifloxacin. Cell purification can trigger a "spontaneous" and functional upregulation of MRGPRX2 on basophils, not seen in whole blood cells, and its surface density can be influenced by distinct culture media.

Conclusion

Basophils barely express MRGPRX2 in resting conditions. However, the receptor can be quickly upregulated after stimulation with anti-IgE, fMLP, or after purification, making cells responsive to MRGPRX2 occupation. We anticipate that such "conditioned" basophils constitute a model to explore MRGPRX2 agonism or antagonism, including IDHRs originating from the occupation of this receptor.

Recent Knowledge and Insights on the Mechanisms of Immediate Hypersensitivity and Anaphylaxis: IgE/FcεRI- and Non-IgE/FcεRI-Dependent Anaphylaxis

Immediate hypersensitivity reactions can pose a clinical and diagnostic challenge, mainly because of the multifarious clinical presentation and distinct underlying - frequently uncertain - mechanisms. Anaphylaxis encompasses all rapidly developing and life-threatening signs and may cause death. Evidence has accumulated that immediate hypersensitivity and anaphylaxis do not necessarily involve an allergen-specific immune response with cross-linking of specific IgE (sIgE) antibodies bound to their high-affinity IgE receptor (FcεRI) on the surface of mast cells (MCs) and basophils. Immediate hypersensitivity and anaphylaxis can also result from alternative specific and nonspecific MC and basophils activation and degranulation, such as complementderived anaphylatoxins and off-target occupancy of MC and/or basophil surface receptors such as the Masrelated G protein-coupled receptor X2 (MRGPRX2). Degranulation of MCs and basophils results in the release of inflammatory mediators, which can be, depending on the underlying trigger, in a different spatiotemporal manner. In addition, hypersensitivity and anaphylaxis can occur entirely independently of MC and basophil degranulation, as observed in hypersensitivity to nonsteroidal anti-inflammatory drugs (NSAIDs) that divert normal arachidonic acid metabolism by inhibiting the cyclooxygenase (COX)-1 isoenzyme. Finally, one should remember that anaphylaxis might be part of the phenotype of particular - sometimes poorly recognizable - conditions such as clonal MC diseases (e.g. mastocytosis) and MC activation syndrome. This review provides a status update on the molecular mechanisms involved in both sIgE/FcεRI- and non-sIgE/FcεRI-dependent immediate hypersensitivity and anaphylaxis. In conclusion, there is increasing evidence for alternative pathophysiological hypersensitivity and anaphylaxis endotypes that are phenotypically and biologically indistinguishable, which are frequently difficult to diagnose, mainly because of uncertainties associated with diagnostic tests that might not enable to unveil the underlying mechanism.

Establishing diagnostic strategies for cannabis allergy

INTRODUCTION

Cannabis is the most widely consumed illicit drug in the world and carries a risk of severe IgE-mediated allergic reactions, requiring appropriate diagnostic management. Currently available diagnostics are still relatively limited and require careful interpretation of results to avoid harmful over- and underdiagnosis.

AREAS COVERED

This review focuses on the most up-to-date understandings of cannabis allergy diagnosis, starting with the main clinical features of the disease and the allergenic characteristics of Cannabis sativa, and then providing insights into in vivo, in vitro, and ex vivo diagnostic tests.

EXPERT OPINION

At present, the diagnosis of IgE-mediated cannabis allergy is based on a three-step approach that starts with accurate history taking and ends with a confirmation of sensitization to the whole extract and, finally, molecular components. Although much has been discovered since its first description in 1971, the diagnosis of cannabis allergy still has many unmet needs. The lack of commercial standardized and validated extracts and in vitro assays makes a harmonized workup of cannabis allergy difficult. Furthermore, the epidemiological characteristics, and clinical implications of sensitization to different molecular components are not yet fully known. Future research will complete the picture and likely result in an individualized and standardized approach.

Overexpression of FcεRI on Bone Marrow Mast Cells, but Not MRGPRX2, in Clonal Mast Cell Disorders With Wasp Venom Anaphylaxis

Background

Uncertainties remain about the molecular mechanisms governing clonal mast cell disorders (CMCD) and anaphylaxis.

Objective

This study aims at comparing the burden, phenotype and behavior of mast cells (MCs) and basophils in patients with CMCD with wasp venom anaphylaxis (CMCD/WVA⁺), CMCD patients without anaphylaxis (CMCD/ANA^-), patients with an elevated baseline serum tryptase (EBST), patients with wasp venom anaphylaxis without CMCD (WVA⁺) and patients with a non-mast cell haematological pathology (NMHP).

Methods

This study included 20 patients with CMCD/WVA⁺, 24 with CMCD/ANA^-, 19 with WVA⁺, 6 with EBST and 5 with NMHP. We immunophenotyped MCs and basophils and compared baseline serum tryptase (bST) and both total and venom specific IgE in the different groups. For basophil studies, 13 healthy controls were also included.

Results

Higher levels of bST were found in CMCD patients with wasp venom anaphylaxis, CMCD patients without anaphylaxis and EBST patients. Total IgE levels were highest in patients with wasp venom anaphylaxis with and without CMCD. Bone marrow MCs of patients with CMCD showed lower CD117 expression and higher expression of CD45, CD203c, CD63, CD300a and FcεRI. Within the CMCD population, patients with wasp venom anaphylaxis showed a higher expression of FcεRI as compared to patients without anaphylaxis. Expression of MRGPRX2 on MCs did not differ between the study populations. Basophils are phenotypically and functionally comparable between the different patient populations.

Conclusion

Patients with CMCD show an elevated burden of aberrant activated MCs with a significant overexpression of FcεRI in patients with a wasp venom anaphylaxis.

Novel Insights on MRGPRX2-Mediated Hypersensitivity to Neuromuscular Blocking Agents And Fluoroquinolones

Neuromuscular blocking agents (NMBAs) like atracurium and rocuronium as well as fluoroquinolones (FQs) cause mast cell-mediated anaphylaxis by activating Mas-related G protein-coupled receptor X2 (MRGPRX2), but many questions remain unanswered. Here, we address three of them, namely whether primary human mast cells show similar activation by these drugs as murine mast cells and mast cell lines, how sugammadex protects from atracurium-induced MRGPRX2-mediated mast cell activation, and why some but not all patients treated with rocuronium develop anaphylaxis. We used peripheral blood-derived cultured mast cells from healthy donors and patients, assessed mast cell activation and degranulation by quantifying intracellular calcium and CD63 expression, respectively, and made use of MRGPRX2-silencing, via electroporation with Dicer-substrate small interfering RNAs, and single cell flow cytometric analyses. Atracurium, ciprofloxacin, and levofloxacin activated and degranulated primary human mast cells, but only MRGPRX2-positive and not MRGPRX2-negative or -silenced mast cells. Sugammadex attenuated the atracurium-induced and MRGPRX2-mediated activation and degranulation of human mast cells by reducing free atracurium levels. The mast cells of patients with IgE-independent anaphylaxis to rocuronium were similar, in their MRGPRX2 expression and function, to those of patients with IgE-mediated anaphylaxis. These findings further improve our understanding of the role and relevance of MRGPRX2-driven mast cell activation in anaphylactic reactions to NMBAs and FQs and may help to improve their prediction, prevention, and treatment.

Mast cell activation tests by flow cytometry: A new diagnostic asset?

Since the late nineties, evidence has accumulated that flow-assisted basophil activation test (BAT) might be an accessible and reliable method to explore the mechanisms governing basophil degranulation and diagnostic allowing correct prediction of the clinical outcome following exposure to the offending allergen(s) and cross-reactive structures for different IgE-dependent allergies and particular forms of autoimmune urticaria. Although the BAT offers many advantages over mediator release tests, it is left with some weaknesses that hinder a wider application. It is preferable to perform the BAT analysis within 4 h of collection, and the technique does not advance diagnosis in patients with non-responsive cells. Besides, the BAT is difficult to standardize mainly because of the difficulty to perform large batch analyses that might span over several days. This article reviews the status of flow cytometric mast cell activation test (MAT) using passively sensitized mast cells (MCs) with patients' sera or plasma (henceforth indicated as passive MAT; pMAT) using both MC lines and cultured MCs in the diagnosis of IgE-dependent allergies. In addition, this paper provides guidance for generating human MCs from peripheral blood CD34⁺ progenitor cells (PBCMCs) and correct interpretation of flow cytometric analyses of activated and/or degranulating cells. With the recent recognition of the mas-related G protein-coupled receptor X2 (MRGPRX2) occupation as a putative mechanism of immediate drug hypersensitivity reactions (IDHRs), we also speculate how direct activation of MCs (dMAT)-that is direct activation by MRGPRX2 agonists without prior passive sensitization-could advance paradigms for this novel endotype of IDHRs.

Diagnosis of Primary Mast Cell Disorders in Anaphylaxis: Value of KIT D816V in Peripheral Blood

BACKGROUND

Anaphylaxis is frequent in patients suffering from primary mast cell disorders (PMCDs). In patients without mastocytosis in the skin (MIS) and a baseline serum tryptase (bST) less than 30 ng/mL, the diagnosis of PMCD is challenging. In these patients, detection of the KIT D816V mutation in peripheral blood (PB) has been suggested as screening tool for a PMCD.

OBJECTIVE

In this study, we investigated whether KIT D816V in PB can contribute to the decision to perform a bone marrow (BM) biopsy in patients with anaphylaxis without MIS and a bST less than 30 ng/mL.

METHODS

We selected 74 patients with severe anaphylaxis without MIS and a bST less than 30 ng/mL. All underwent a BM biopsy. KIT D816V mutation was quantified in both PB and BM using digital droplet polymerase chain reaction (ddPCR).

RESULTS

Diagnosis of a PMCD was established in 40 patients (54%). Median bST for patients with and without PMCD was, respectively, 9.5 ng/mL (range 4.2-27 ng/mL) and 4.9 ng/mL (range 2.2-20.3 ng/mL) (P <.001). KIT D816V in PB was detected in 16 out of 40 (40%) patients with PMCD. KIT D816V in BM was detected in 22 out of 40 (55%) patients with PMCD.

CONCLUSIONS

In patients without MIS and a bST less than < 30 ng/mL who experience anaphylaxis, determination of KIT D816V mutation in PB is of limited help in deciding when to proceed to a BM biopsy. Therefore, KIT D816V in PB mutation analysis should be interpreted together with scoring tools to make a better assessment in identifying patients who should undergo BM biopsy.

Basophil and mast cell activation tests by flow cytometry in immediate drug hypersensitivity: Diagnosis and beyond

Immediate drug hypersensitivity reactions (IDHRs) constitute a significant health issue with serious consequences of diagnostic error. The primary diagnostics to document IDHRs usually consists of quantification of drug-specific IgE (sIgE) antibodies and skin tests. Unfortunately, the positive predictive value (PPV) and negative predictive value (NPV) of these tests are not absolutely, which leaves room for new tests. Over the last two decades, the basophil activation test (BAT), in which ex vivo activation of individual basophils is quantified by flow cytometry, has emerged as a reliable complementary diagnostic to document IDHRs, to explore allergenic recognition, to study cross-reactivity and to monitor therapy. However, the BAT is technically challenging requiring specialized personnel and equipment, fresh samples and the technique is lost as a diagnostic in patients showing a non-responder status of their cells. By consequence, the BAT has still not entered mainstream application. In contrast, mast cell activation tests (MATs) use serum samples that can be frozen, stored, and shipped to a recognized reference centre experienced in mast cell (MC) lines and/or cultures and capable of offering batch testing with necessary quality controls. This review does not only highlight the use of the BAT and MAT as diagnostics in IDHRs, but also outlines the potential of both techniques in further exploring and unveiling the mechanisms that govern drug-induced basophil and MC activation and degranulation.

Mast Cell Activation During Suspected Perioperative Hypersensitivity: A Need for Paired Samples Analysis

BACKGROUND

Perioperative hypersensitivity (POH) reactions constitute a significant clinical and diagnostic challenge. A transient increase in serum tryptase during POH reflects mast cell activation (MCA) and helps to recognize an underlying hypersensitivity mechanism.

OBJECTIVE

To determine the diagnostic performance of different tryptase decision thresholds based on single and paired measurements to document MCA in suspected POH.

METHODS

Acute serum tryptase (aST) and baseline serum tryptase (bST) samples were obtained from patients referred to our outpatients clinic because of clinical POH. Tryptase samples from controls were obtained before induction (Tt₀) and 1.5 hours after induction (Tt₁) in uneventful anesthesia. Different cutoff points for tryptase increase over bST and the percentage increase in tryptase (%T) were calculated and compared with existing thresholds: aST > [1.2 × (bST) + 2] (consensus formula), aST higher than 11.4 ng/mL, and aST higher than 14 ng/mL.

RESULTS

Patients with POH had higher bST and aST levels compared with controls (respectively 5.15 vs 2.28 ng/mL for bST and 20.30 vs 1.92 ng/mL for aST). The consensus formula and a tryptase increase over bST of greater than or equal to 3.2 ng/mL held the highest accuracies to document MCA in POH (respectively 81% and 82%). A bST of higher than 8 ng/mL was present in 4% of controls, 5% of patients with grade 1 POH, 24% of patients with grade 2 POH, 15% of patients with grade 3 POH, and 17% of patients with grade 4 POH.

CONCLUSIONS

Our data endorse the consensus formula for detection of MCA in POH. Furthermore, it shows that a bST of higher than 8 ng/mL was associated with occurrence of anaphylaxis.

Peripheral blood cultured mast cells: Phenotypic and functional outcomes of different culture protocols

BACKGROUND

Mast cells (MCs) play a pivotal role in innate and adaptive immune responses. However, MCs are also involved in different pathologic conditions. Studies on the mechanisms that govern human MC functions are impeded by their limited and difficult recovery. Therefore, several research groups have developed protocols to culture human MCs from progenitor cells. These protocols vary with respect to culture duration and used maturation cytokines. How MCs obtained by different protocols differ in phenotype and functionality is currently unknown.

OBJECTIVE

To compare different protocols for the generation of human MCs from peripheral blood progenitors.

METHODS

Thirteen paired human MC cultures were investigated. MCs were cultured form CD34⁺ progenitors cells for 4 or 8 weeks and with or without the addition of IL-6. Phenotyping comprised staining for CD117, CD203c, FcεRI, MRGPRX2, CD300a and CD32. Functional studies included measurements of the up-regulation of CD63 and CD203c after allergen-specific cross-linking of sIgE/FcεRI complexes or ligation of MRGPRX2 with substance P and different drugs.

RESULTS

Cell cultures for 4 weeks in the presence of IL-6 consistently yielded the highest numbers of MCs. MCs cultured for 8 weeks with IL-6 showed more autofluorescence significantly impeding correct analyses of FcεRI and CD32. The density of FcεRI and CD32 was comparable between the different culture conditions. MRGPRX2 expression was significantly higher in the 8 week cultures. The density of CD300a was increased in the cultures with IL-6. Cells cultured for 8 weeks were more responsive to MRGPRX2 activation. In contrast, the 4-weeks cultures with IL-6 showed significantly higher allergen-specific activation.

CONCLUSION

Four weeks of culture with IL-6 are sufficient to generate sizeable numbers of human mast cells from blood progenitors, thereby enabling simultaneous exploration of allergen-specific sIgE/FcεRI cross-linking and non-specific activation via MRGPRX2.