Detection of Circulating Peanut Components in Serum after Ingestion.

INTRODUCTION: Detection of specific food allergens brought into circulation following ingestion is complicated by the minute amounts present in serum. We therefore aimed to assess the utility of selective removal of IgE against peanut components using ImmunoCAP combined with the basophil histamine release (HR) assay (BHRA) to identify the absorbed allergen components after ingestion of peanut. METHODS: Serum from six healthy individuals was drawn before and 1 h after ingestion of 100 g peanut. Serum from two peanut allergic patients was depleted for IgE against single allergen components by incubation with ImmunoCAPs coupled with either Ara h 1; 2; 3 or 6 before donor basophils were passively sensitized with the serum preparations. The sensitized cells were challenged with serum obtained from the six individuals before and after ingestion of peanut, and HR was measured after serum provocation. RESULTS: Ara h 2 and Ara h 6 were detected in serum 1 h after ingestion in 6/6 individuals by negative selection. Depletion of specific IgE against Ara h 2 or Ara h 6 almost completely abolished the response to serum provocation, indicating a sequence homology between the two allergen components in serum. Ara h 1 was demonstrated in 5/6 sera and Ara h 3 in 1/6 sera. CONCLUSION: This study is a proof of concept showing that passive sensitization of basophils with sera depleted of component-specific IgE can be used to identify food allergen components present in serum after ingestion.

PACAP38- and VIP-induced cluster headache attacks are not associated with changes of plasma CGRP or markers of mast cell activation.

BACKGROUND: Pituitary adenylate cyclase-activating polypeptide-38 (PACAP38) and vasoactive intestinal polypeptide can provoke cluster headache attacks in up to half of cluster headache patients in their active phase. At present, it is unknown whether provoked attacks are mediated via calcitonin gene-related peptide or mast cell activation. METHODS: All enrolled patients with cluster headache were randomly allocated to receive a continuous infusion of either PACAP38 (10 pmol/kg/min) or vasoactive intestinal polypeptide (8 pmol/kg/min) over 20 min. We collected clinical data and measured plasma levels of calcitonin gene-related peptide and markers of mast cell activation (tryptase and histamine) at fixed time points: at baseline (T0), at the end of the infusion (T20), 10 min after the infusion (T30), and 70 min after the infusion (T90). RESULTS: Blood was collected from episodic cluster headache patients in active phase (n = 14), episodic cluster headache patients in remission (n = 15), and chronic cluster headache patients (n = 15). At baseline, plasma levels of calcitonin gene-related peptide, tryptase, and histamine were not different among the three study groups. Plasma levels of calcitonin gene-related peptide (p = 0.7074), tryptase (p = 0.6673), or histamine (p = 0.4792) remained unchanged during provoked attacks compared to attack-free patients. CONCLUSION: Cluster headache attacks provoked by either PACAP38 or vasoactive intestinal polypeptide were not accompanied by alterations of plasma calcitonin gene-related peptide, tryptase or histamine. The provoked attacks may not be mediated by calcitonin gene-related peptide or mast cell activation.Trial Registration: The study is registered at ClinicalTrials.gov (NCT03814226).

The Skin Reservoir Model: A Tool for Evaluating Microdialysis Sampling of Large Biomarkers from Human Skin.

Microdialysis is a well-established technique for sampling of small molecules from the human skin, but larger molecules are more difficult to recover. Consequently, sampling feasibility must be evaluated before microdialysis is used in vivo. This report presents a tool for estimating the recovery of large biomarkers from human skin by microdialysis, using previously frozen human skin specimens as reservoirs for biomarker reference solutions. Recovery of the following 17 biomarkers was assessed: CCL27/CTACK, CXCL1/GROα, CXCL7/NAP-2, CXCL10/IP-10, EGF, GM-CSF, IFN-γ, IL-1α, IL-6, IL-8, IL-17, IL-22, IL-23, MIF, TNF-α, TSLP and VEGF. The relative skin recoveries of 13/17 biomarkers were successfully determined in the range 4.0-18.4%. Sampling in the skin reservoir model was not associated with probe leakage, as fluid recovery was stable, at between 80% and 110%. Furthermore, the skin reservoir model enabled studies and optimization of different parameters known to affect biomarker recovery, including flow rate and perfusate composition.

Pharmacological blockade of the mast cell MRGPRX2 receptor supports investigation of its relevance in skin disorders.

Introduction: Because MRGPRX2 is now recognized as the mast cell receptor for basic secretagogues, there is currently a tremendous interest in whether MRGRPX2 could play an important role in various pruritic dermatoses such as chronic spontaneous urticaria. Therefore, we sought to identify new potent and selective antagonists to pharmacologically characterize the biological role of MRGPRX2. Methods: Various relevant in vitro, ex vivo, and in vivo model systems were used to investigate the role of MRGPRX2. This included the study of freshly isolated human skin mast cells and human basophils as well as an ex vivo human skin microdialysis preparation. The additivity of MRGPRX2 and FcεR1-mediated degranulation was also investigated. Human MRGPRX2 knock-in mice were generated to interrogate pharmacokinetic/pharmacodynamic relationships because both antagonists studied were shown to be human specific. Results: Two novel and structurally distinct MRGPRX2 antagonists were identified with one, Compound B, being orally active and demonstrating high potency in blocking Substance P-mediated degranulation using freshly isolated human skin mast cells with half maximal inhibitory concentration (IC50) at 0.42 nM. Compound B also potently blocked Substance P-stimulated histamine release from resident mast cells in a human skin explant setup as well as blocking itch in an established behavioral scratching model using MRGPRX2 knock-in mice. Unlike human mast cells, Substance P failed to elicit a functional response in human basophils. Conclusion: These data fully support the investigation of MRGPRX2 receptor antagonists in mast cell-driven allergic skin disorders such as chronic spontaneous urticaria.

Intradermal substance P as a challenge agent in healthy individuals.

Pharmacological challenge models are deployed to evaluate drug effects during clinical development. Intradermal injection of Substance P (SP) neuropeptide, a potential challenge agent for investigating local mediators, is associated with wheal and flare response mediated by the MRGPRX2 receptor. Although dose-dependent data on SP effects exist, full characterization and information on potential carryover effect after repeated challenge are lacking. This open-label, two-part, prospective enabling study of SP intradermal challenge in healthy participants aimed to understand and distinguish between wheal and flare responses following various SP doses. Part 1 included one challenge visit to determine optimum SP dose range for evaluation in part 2, which determined variability in 20 participants and used intradermal microdialysis (IDM) for SP-challenged skin sampling. At 5, 15, 50, and 150 pmol doses, respectively, posterior median area under the curve (AUC; AUC0-2h ) was 4090.4, 5881.2, 8846.8, and 9212.8 mm2 /min, for wheal response, and 12020.9, 38154.3, 65470.6, and 67404.4 mm2 /min for flare response (SP-challenge visit 2). When the challenge was repeated ~2 weeks later, no carryover effect was observed. IDM histamine levels were relatively low, resulting in low confidence in the data to define temporal characteristics for histamine release following SP challenge. No safety concerns were identified using SP. Wheal and flare responses following intradermal SP challenge were dose-dependent and different. The results indicate that this challenge model is fit-for-purpose in future first-in-human studies and further assessment of novel drugs targeting dermal inflammatory disease responses, such as chronic spontaneous urticaria, chronic inducible urticaria, and pseudo-allergic reactions.

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.

In vitro prediction of in vivo pseudo-allergenic response via MRGPRX2.

In development of peptide therapeutics, rodents are commonly-used preclinical models when screening compounds for efficacy endpoints in the early stages of discovery projects. During the screening process, some peptides administered subcutaneously to rodents caused injection site reactions manifesting as localized swelling. Screening by postmortem evaluations of injection site swelling as a marker for local subcutaneous histamine release, were conducted in rats to select drug candidates without this adverse effect. Histological analysis of skin samples revealed that the injection site reactions were concurrent with mast cell degranulation, resulting in histamine release. Mast cell activation can be mediated by MRGPRX2, a GPCR that induces a pseudo-allergenic immune response. The present study demonstrates that a commercially-available cell-based MRGPRX2 assay reliably identifies compounds that induce histamine release or localized edema in ex vivo human and rodent skin samples. In vitro screening was subsequently implemented using the MRGPRX2 assay as a substitute for postmortem injection site evaluation, thus achieving a significant reduction in animal use. Thus, in cases where injection site reactions are encountered during in vivo screening, to enable faster screening during the early drug discovery process, an MRGPRX2 in vitro assay can be used as an efficient, more ethical tool with human translational value for the development of safer pharmacotherapies for patients.

Measuring Histamine and Cytokine Release from Basophils and Mast Cells.

Basophils and mast cells are known for their capability to release both preformed and newly synthesized inflammatory mediators. In this chapter, we describe how to stimulate and detect histamine released from basophils in whole blood, purified basophils, in vitro cultured mast cells, and in situ skin mast cells (the latter by microdialysis), using either a solid phase assay or flow cytometry. We also give an example of an activation protocol for basophil and mast cell cytokine release and discuss approaches for cytokine detection.

Skin microdialysis: methods, applications and future opportunities-an EAACI position paper.

Skin microdialysis (SMD) is a versatile sampling technique that can be used to recover soluble endogenous and exogenous molecules from the extracellular compartment of human skin. Due to its minimally invasive character, SMD can be applied in both clinical and preclinical settings. Despite being available since the 1990s, the technique has still not reached its full potential use as a tool to explore pathophysiological mechanisms of allergic and inflammatory reactions in the skin. Therefore, an EAACI Task Force on SMD was formed to disseminate knowledge about the technique and its many applications. This position paper from the task force provides an overview of the current use of SMD in the investigation of the pathogenesis of chronic inflammatory skin diseases, such as atopic dermatitis, chronic urticaria, psoriasis, and in studies of cutaneous events during type 1 hypersensitivity reactions. Furthermore, this paper covers drug hypersensitivity, UVB-induced- and neurogenic inflammation, and drug penetration investigated by SMD. The aim of this paper is to encourage the use of SMD and to make the technique easily accessible by providing an overview of methodology and applications, supported by standardized operating procedures for SMD in vivo and ex vivo.

Antiproliferative effects of TRPV1 ligands on nonspecific and enteroantigen-specific T cells from wild-type and Trpv1 KO mice.

BACKGROUND: Treatment with the TRPV1 agonist, capsaicin, was previously shown to protect against experimental colitis in the severe combined immunodeficiency (SCID) T-cell transfer model. Here, we investigate trpv1 gene expression in lymphoid organs and cells from SCID and BALB/c mice to identify a potential target for the anti-inflammatory effect of capsaicin. METHODS: The trpv1 expression was studied by real-time PCR in lymphoid tissues and gut of untreated and capsaicin-treated colitic SCID mice. Effects of capsaicin and a TRPV1 antagonist on T cells were studied in vitro. RESULTS: In contrast to BALB/c mice, spleen, lymph nodes, and rectum of colitic and noncolitic SCID mice express trpv1 mRNA. Capsaicin treatment in vivo attenuated T-cell transfer colitis and capsaicin in vitro also attenuated T-cell proliferation induced by enteroantigen, mitogen, and anti-CD3/CD28 beads in BALB/c, C57BL/6 mice, and B6.129X1-trpv1tm1Jul/J trpv1 knockout mice. Proliferation and cytokine secretion were fully comparable in mice with and without trpv1 expression. Likewise, enteroantigen- and mitogen-stimulated T cells from wild-type and trpv1 knockout mice were equally inhibited by capsaicin. Surprisingly, the TRPV1 antagonist BCTC also inhibited enteroantigen- and mitogen-induced T-cell proliferation. CONCLUSIONS: The trpv1 mRNA expression in lymphoid organs and the rectum of SCID mice suggests that the TRPV1 signaling in these organs could play a role in capsaicin-mediated attenuation of colitis. In addition, capsaicin-induced inhibition of T-cell proliferation of wild-type T cells lacking trpv1 expression suggests that capsaicin inhibits colitogenic T cells in a TRPV1 receptor-independent way, which might be linked to its anti-inflammatory effect.