Assays for measuring in vitro basophil activation induced by recombinant allergens

Expression and regulation of Siglec-6 (CD327) on human mast cells and basophils

BACKGROUND

Mast cells (MC) and basophils are effector cells of allergic reactions and display a number of activation-linked cell surface antigens. Of these antigens, however, only a few are functionally relevant and specifically expressed in these cells.

OBJECTIVE

We sought to identify MC- and basophil-specific surface molecules and to study their cellular distribution and regulation during cytokine-induced and IgE-dependent activation.

METHODS

Multicolor flow cytometry was performed to recognize surface antigens and to determine changes in antigen expression upon activation.

RESULTS

We identified Siglec-6 (CD327) as a differentially regulated surface antigen on human MC and basophils. In the bone marrow, Siglec-6 was expressed abundantly on MC in patients with mastocytosis and in reactive states, but it was not detected on other myeloid cells, with the exception of basophils and monocytes. In healthy individuals, allergic patients, and patients with chronic myeloid leukemia (CML), Siglec-6 was identified on CD203c⁺ blood basophils, a subset of CD19⁺ B lymphocytes, and few CD14⁺ monocytes, but not on other blood leukocytes. CML basophils expressed higher levels of Siglec-6 than normal basophils. IL-3 promoted Siglec-6 expression on normal and CML basophils, and stem cell factor increased the expression of Siglec-6 on tissue MC. Unexpectedly, IgE-dependent activation resulted in downregulation of Siglec-6 in IL-3-primed basophils, whereas in MC, IgE-dependent activation augmented stem cell factor-induced upregulation of Siglec-6.

CONCLUSIONS

Siglec-6 is a dynamically regulated marker of MC and basophils. Activated MC and basophils exhibit unique Siglec-6 responses, including cytokine-dependent upregulation and unique, cell-specific, responses to IgE-receptor cross-linking.

Interfacial pH Behavior at a Cell/Gate Insulator Nanogap Induced by Allergic Responses

In this paper, we clarify the interfacial pH behavior induced by allergic responses at a mast cell/gate insulator nanogap detected by laser scanning confocal fluorescence microscopy. In a previous work, the change in interfacial pH detected on the basis of allergic responses was monitored at a mast cell/gate insulator nanogap interface using a cell-cultured gate ion-sensitive field-effect transistor (ISFET), but the interfacial pH behavior at a mast cell/gate insulator nanogap has not been clarified using other methods. Here, the phospholipid fluorescein is employed as the extracellular pH indicator, which is fixed to the external side of the plasma membrane of mast cells cultured on a substrate. As a result, the interfacial pH at the mast cell/substrate nanogap increases after mast cells with IgE on their membrane are activated by the interaction between IgE and an allergen. This is due to the basicity of histamine molecules released from mast cells. Moreover, the change in the interfacial pH at the mast cell/substrate nanogap is larger than that at the mast cell/bulk solution interface. That is, molecules of substances secreted as a result of allergic responses are assumed to accumulate around the cell/substrate nanogap. The data obtained in this study support the idea that potentiometric ion sensors such as ISFETs can detect a cellular-function-induced change in pH at a cell/electrode nanogap in real time.

Recent advances in our understanding of mast cell activation - or should it be mast cell mediator disorders?

INTRODUCTION

An increasing number of patients present with multiple symptoms affecting many organs including the brain due to multiple mediators released by mast cells. These unique tissue immune cells are critical for allergic reactions triggered by immunoglobulin E (IgE), but are also stimulated (not activated) by immune, drug, environmental, food, infectious, and stress triggers, leading to secretion of multiple mediators often without histamine and tryptase. The presentation, diagnosis, and management of the spectrum of mast cell disorders are very confusing. As a result, neuropsychiatric symptoms have been left out, and diagnostic criteria made stricter excluding most patients. Areas covered: A literature search was performed on papers published between January 1990 and November 2018 using MEDLINE. Terms used were activation, antihistamines, atopy, autism, brain fog, heparin, KIT mutation, IgE, inflammation, IL-6, IL-31, IL-37, luteolin, mast cells, mastocytosis, mediators, mycotoxins, release, secretion, tetramethoxyluteolin, and tryptase. Expert opinion: Conditions associated with elevated serum or urine levels of any mast cell mediator, in the absence of comorbidities that could explain elevated levels, should be considered 'Mast Cell Mediator Disorders (MCMD).' Emphasis should be placed on the identification of unique mast cell mediators, and development of drugs or supplements that inhibit their release.

Proposed Diagnostic Algorithm for Patients with Suspected Mast Cell Activation Syndrome

Mast cell activation (MCA) accompanies diverse physiologic and pathologic processes and is one of the more frequently encountered conditions in medicine. MCA-related symptoms are usually mild and often transient. In such cases, histamine receptor blockers and other mediator-targeting drugs can usually control MCA. In severe cases, an MCA syndrome (MCAS) may be diagnosed. However, overt MCAS is an unusual condition, and many patients referred because of suspected MCAS are diagnosed with other diseases (autoimmune, neoplastic, or infectious) unrelated to MCA or suffer from MCA-related (eg, allergic) disorders and/or comorbidities without fulfilling criteria of an overt MCAS. These considerations are important as more and more patients are informed that they may have MCA or even MCAS without completing a thorough medical evaluation. In fact, in several instances, symptoms are misinterpreted as MCA/MCAS, and other clinically relevant conditions are not thoroughly pursued. The number of such referrals is increasing. To avoid such unnecessary referrals and to prevent misdiagnoses, we here propose a diagnostic algorithm through which a clinically relevant (systemic) MCA can be suspected and MCAS can subsequently be documented or excluded. In addition, the algorithm proposed should help guide the investigating care providers to consider the 2 principal diagnoses that may underlie MCAS, namely, severe allergy and systemic mastocytosis accompanied by severe MCA. Although validation is required, we anticipate that this algorithm will facilitate the management of patients with suspected MCAS.

Prueba de activación de basófilos: aspectos técnicos, metodológicos y su utilidad clínica

Introducción. La prueba de activación de basófilos (PAB) se considera una técnica confiable y segura para el diagnóstico de problemas alérgicos.Objetivo. Profundizar en el estado del arte de la PAB y su utilidad clínica.Materiales y métodos. Se realizó una revisión narrativa de la literatura mediante la búsqueda electrónica en las bases de datos y metabuscadores Ovid Medline, Google Scholar y PubMed, sin limitar la búsqueda por fecha, idioma o tipo de artículo. Se buscaron artículos sobre los detalles técnicos de la PAB y su utilidad clínica en el manejo de las enfermedades alérgicas.Resultados. De los marcadores de activación, CD63 ha sido el más estudiado y es el que mejor representa un evento de degranulación anafiláctica, mientras que CD203c es representativo de varias formas de degranulación. La superioridad de uno sobre otro como prueba diagnóstica depende del problema alérgico estudiado. En cuanto a los métodos de detección de basófilos, su selección con un único marcador, CCR3, se propone como una opción con buena relación de costo-efectividad.Conclusiones. La PAB es una herramienta prometedora para evaluar en clínica las reacciones alérgicas de forma segura. Es necesario una mayor estandarización de protocolos para obtener resultados más reproducibles.

BTK inhibition is a potent approach to block IgE-mediated histamine release in human basophils

Background

Recent data suggest that Bruton's tyrosine kinase (BTK) is an emerging therapeutic target in IgE receptor (IgER)‐cross‐linked basophils.

Methods

We examined the effects of four BTK inhibitors (ibrutinib, dasatinib, AVL‐292, and CNX‐774) on IgE‐dependent activation and histamine release in blood basophils obtained from allergic patients (n=11) and nonallergic donors (n=5). In addition, we examined the effects of these drugs on the growth of the human basophil cell line KU812 and the human mast cell line HMC‐1.

Results

All four BTK blockers were found to inhibit anti‐IgE‐induced histamine release from basophils in nonallergic subjects and allergen‐induced histamine liberation from basophils in allergic donors. Drug effects on allergen‐induced histamine release were dose dependent, with IC₅₀ values ranging between 0.001 and 0.5 μmol/L, and the following rank order of potency: ibrutinib>AVL‐292>dasatinib>CNX‐774. The basophil‐targeting effect of ibrutinib was confirmed by demonstrating that IgE‐dependent histamine release in ex vivo blood basophils is largely suppressed in a leukemia patient treated with ibrutinib. Dasatinib and ibrutinib were also found to counteract anti‐IgE‐induced and allergen‐induced upregulation of CD13, CD63, CD164, and CD203c on basophils, whereas AVL‐292 and CNX‐774 showed no significant effects. Whereas dasatinib and CNX‐774 were found to inhibit the growth of HMC‐1 cells and KU812 cells, no substantial effects were seen with ibrutinib or AVL‐292.

Conclusions

BTK‐targeting drugs are potent inhibitors of IgE‐dependent histamine release in human basophils. The clinical value of BTK inhibition in the context of allergic diseases remains to be determined.

A novel bispecific DARPin targeting FcγRIIB and FcεRI-bound IgE inhibits allergic responses

BACKGROUND

Binding of allergen-specific IgE to its high-affinity receptor FcεRI on basophils and mast cells is a central event in the development of allergies. Exposure of these cells to allergens induces the release of soluble mediators causing allergic symptoms. The inhibitory low-affinity IgG Fc-receptor FcγRIIB is co-expressed on allergic effector cells and has been implicated in negative regulation of immediate hypersensitivity responses. In order to harvest the inhibitory function of this receptor, we aimed to select specific binders against FcγRIIB and to generate a bispecific molecule simultaneously targeting FcγRIIB and FcεRI-bound IgE on the surface of allergic effector cells.

METHODS

We selected FcγRIIB-specific binding molecules from a library of designed ankyrin repeat proteins using ribosome display technology. The bispecific binding modality was generated by molecular cloning and recombinant protein expression. We determined binding characteristics on molecular and cellular levels using SPR, ELISA, and flow cytometry. The inhibitory potential of the newly described molecules was assessed in different cellular degranulation assays ex vivo and in a mouse model of passive systemic anaphylaxis.

RESULTS

We demonstrate that the selected DARPin^® proteins recognize FcγRIIB with high affinity. Furthermore, the bispecific binding protein successfully interferes with allergen-induced cell degranulation and efficiently inhibits systemic anaphylaxis in vivo. Mechanistically, we report that FcγRIIB-mediated inhibition of effector cell activation requires direct ligation to an activating FcεRI receptor.

CONCLUSION

The described bispecific DARPin protein has the ability to co-ligate FcγRIIB with FcεRI-bound IgE on allergic effector cells and represents an efficient dual-modality to interfere with allergic hypersensitivity reactions.

The basophil surface marker CD203c identifies Aspergillus species sensitization in patients with cystic fibrosis

BACKGROUND

Colonization by Aspergillus fumigatus in patients with cystic fibrosis (CF) can cause A fumigatus sensitization and/or allergic bronchopulmonary aspergillosis (ABPA), which affects pulmonary function and clinical outcomes. Recent studies show that specific allergens upregulate the surface-expressed basophil marker CD203c in sensitized subjects, a response that can be readily measured by using flow cytometry.

OBJECTIVE

We sought to identify A fumigatus sensitization in patients with CF by using the basophil activation test (BAT).

METHODS

Patients with CF attending Beaumont Hospital were screened for study inclusion. BAT was used to identify A fumigatus sensitization. Serologic (total and A fumigatus-specific IgE), pulmonary function, and body mass index measurements were performed.

RESULTS

The BAT discriminates A fumigatus-sensitized from nonsensitized patients with CF. Persistent isolation of A fumigatus in sputum is a significant risk factor for A fumigatus sensitization. Levels of the A fumigatus-stimulated basophil activation marker CD203c inversely correlated with pulmonary function and body mass index in A fumigatus-sensitized but not nonsensitized patients with CF. Total and A fumigatus-specific IgE, but not IgG, levels are increased in A fumigatus-sensitized patients with CF and ABPA when compared with those in A fumigatus-sensitized and nonsensitized patients with CF without ABPA. Itraconazole treatment did not affect A fumigatus sensitization.

CONCLUSION

Combining the BAT with routine serologic testing allows classification of patients with CF into 3 groups: nonsensitized, A fumigatus-sensitized, and ABPA. Accurate and prompt identification of A fumigatus-associated clinical status might allow early and targeted therapeutic intervention, potentially improving clinical outcomes.

Spectrum of mast cell activation disorders

Mast cell (MC) activation disorders present with multiple symptoms including flushing, pruritus, hypotension, gastrointestinal complaints, irritability, headaches, concentration/memory loss and neuropsychiatric issues. These disorders are classified as: cutaneous and systemic mastocytosis with a c-kit mutation and clonal MC activation disorder, allergies, urticarias and inflammatory disorders and mast cell activation syndrome (MCAS), idiopathic urticaria and angioedema. MCs are activated by IgE, but also by cytokines, environmental, food, infectious, drug and stress triggers, leading to secretion of multiple mediators. The symptom profile and comorbidities associated with these disorders, such as chronic fatigue syndrome and fibromyalgia, are confusing. We propose the use of the term 'spectrum' and highlight the main symptoms, useful diagnostic tests and treatment approaches.

Accelerated dissociation of IgE-FcεRI complexes by disruptive inhibitors actively desensitizes allergic effector cells

BACKGROUND

The remarkably stable interaction of IgE with its high-affinity receptor FcεRI on basophils and mast cells is critical for the induction of allergic hypersensitivity reactions. Because of the exceptionally slow dissociation rate of IgE-FcεRI complexes, such allergic effector cells permanently display allergen-specific IgE on their surface and immediately respond to allergen challenge by releasing inflammatory mediators. We have recently described a novel macromolecular inhibitor that actively promotes the dissociation of IgE from FcεRI through a molecular mechanism termed facilitated dissociation.

OBJECTIVE

Here we assessed the therapeutic potential of this non-immunoglobulin-based IgE inhibitor E2_79, a designed ankyrin repeat protein (DARPin), as well as a novel engineered biparatopic DARPin bi53_79, and directly compared them with the established anti-IgE antibody omalizumab.

METHODS

IgE-FcεRI complex dissociation was analyzed in vitro by using recombinant proteins in ELISA and surface plasmon resonance, ex vivo by using human primary basophils with flow cytometry, and in vivo by using human FcεRI α-chain transgenic mice in a functional passive cutaneous anaphylaxis test.

RESULTS

We show that E2_79-mediated removal of IgE from primary human basophils fully abrogates IgE-dependent cell activation and release of proinflammatory mediators ex vivo. Furthermore, we report that omalizumab also accelerates the dissociation of IgE from FcεRI, although much less efficiently than E2_79. Using the biparatopic IgE targeting approach, we further improved the disruptive potency of E2_79 by approximately 100-fold and show that disruptive IgE inhibitors efficiently prevent passive cutaneous anaphylaxis in mice expressing the human FcεRI α-chain.

CONCLUSION

Our findings highlight the potential of such novel IgE inhibitors as important diagnostic and therapeutic tools for management of allergic diseases.

Mast cell activation syndromes: definition and classification

Mast cell activation (MCA) occurs in a number of different clinical conditions, including IgE-dependent allergies, other inflammatory reactions, and mastocytosis. MCA-related symptoms may be mild, moderate, severe, or even life-threatening. The severity of MCA depends on a number of different factors, including genetic predisposition, the number and releasability of mast cells involved in the reaction, the type of allergen, presence of specific IgE, and presence of certain comorbidities. In severe reactions, MCA can be documented by a substantial increase in the serum tryptase level above baseline. When symptoms are recurrent, are accompanied by an increase in mast cell-derived mediators in biological fluids, and are responsive to treatment with mast cell-stabilizing or mediator-targeting drugs, the diagnosis of mast cell activation syndrome (MCAS) is appropriate. Based on the underlying condition, these patients can further be classified into i) primary MCAS where KIT-mutated, clonal mast cells are detected, ii) secondary MCAS where an underlying inflammatory disease, often in the form of an IgE-dependent allergy, but no KIT-mutated mast cells, is found, and iii) idiopathic MCAS, where neither an allergy or other underlying disease, nor KIT-mutated mast cells are detectable. It is important to note that in many patients with MCAS, several different factors act together to lead to severe or even life-threatening anaphylaxis. Detailed knowledge about the pathogenesis and complexity of MCAS, and thus establishing the exact final diagnosis, may greatly help in the management and therapy of these patients.

Detection of Allergen-Specific IgE Antibody Responses

Allergen-specific IgE production is the central event in the pathogenesis of atopic disorders and increases in specific IgE serum antibodies are an indicator of immediate hypersensitivity responses in humans and in animal models of allergy. Consequently, accurate and user-friendly methods are needed to measure serum levels of allergen-specific IgE. This review examines historical and recent developments in in vivo and in vitro methods for the detection of allergen-specific IgE in humans and in animal models. Routinely, in vitro methods such as enzyme-linked immunosorbant assays or radioallergosorbant tests and in vivo methods such as the skin prick test (SPT) for humans and the passive cutaneous anaphylaxis assay (PCA) used in animals are utilized to detect allergen-specific IgE. While in vivo assays are usually more accurate than in vitro assays since they provide a functional readout of IgE activity, they are relatively costly and require considerable expertise. On the other hand in vitro assays are limited by the fact that the amount of allergen-specific serum IgG exceeds IgE antibody by several orders of magnitude, resulting in competition for allergen binding. Consequently, methods that use allergen as a direct capture step are limited by the availability of free allergen binding sites for IgE. In order to circumvent this problem, in vitro methods usually require prior depletion of IgG or use high amounts of allergen in order to facilitate availability of free binding sites for IgE detection. Clearly, these approaches are limited for small sample volumes and allergens that are in short supply. New methods such as protein microarray could potentially overcome this problem by providing high allergen concentrations in a relatively small reaction volume. Currently, in vitro methods are rarely used in isolation for prognosis but are used primarily to complement the information obtained from in vivo assays. With the emergence of new technologies it is conceivable that in vitro assays may in the future replace in vivo assays, however until then in vivo assays remain the gold standard of allergen-specific IgE detection.

The PI3-kinase/mTOR-targeting drug NVP-BEZ235 inhibits growth and IgE-dependent activation of human mast cells and basophils

The phosphoinositide 3-kinase (PI3-kinase) and the mammalian target of rapamycin (mTOR) are two major signaling molecules involved in growth and activation of mast cells (MC) and basophils (BA). We examined the effects of the dual PI3-kinase/mTOR blocker NVP-BEZ235 on growth of normal and neoplastic BA and MC as well as immunoglobulin E (IgE)-dependent cell activation. Growth of MC and BA were determined by measuring ³H-thymidine uptake and apoptosis. Cell activation was determined in histamine release experiments and by measuring upregulation of CD63 and CD203c after challenging with IgE plus anti-IgE or allergen. We found that NVP-BEZ235 exerts profound inhibitory effects on growth of primary and cloned neoplastic MC. In the MC leukemia cell line HMC-1, NVP-BEZ235 showed similar IC₅₀ values in the HMC-1.1 subclone lacking KIT D816V (0.025 µM) and the HMC-1.2 subclone expressing KIT D816V (0.005 µM). Moreover, NVP-BEZ235 was found to exert strong growth-inhibitory effects on neoplastic MC in a xenotransplant-mouse model employing NMR1-Foxn1^nu mice. NVP-BEZ235 also exerted inhibitory effects on cytokine-dependent differentiation of normal BA and MC, but did not induce growth inhibition or apoptosis in mature MC or normal bone marrow cells. Finally, NVP-BEZ235 was found to inhibit IgE-dependent histamine release in BA and MC (IC₅₀ 0.5–1 µM) as well as anti-IgE-induced upregulation of CD203c in BA and IgE-dependent upregulation of CD63 in MC. In summary, NVP-BEZ235 produces growth-inhibitory effects in immature neoplastic MC and inhibits IgE-dependent activation of mature BA and MC. Whether these potentially beneficial drug effects have clinical implications is currently under investigation.

A strain of Lactobacillus casei inhibits the effector phase of immune inflammation

Some nonpathogenic bacteria were found to have protective effects in mouse models of allergic and autoimmune diseases. These "probiotics" are thought to interact with dendritic cells during Ag presentation, at the initiation of adaptive immune responses. Many other myeloid cells are the effector cells of immune responses. They are responsible for inflammation that accounts for symptoms in allergic and autoimmune diseases. We investigated in this study whether probiotics might affect allergic and autoimmune inflammation by acting at the effector phase of adaptive immune responses. The effects of one strain of Lactobacillus casei were investigated in vivo on IgE-induced passive systemic anaphylaxis and IgG-induced passive arthritis, two murine models of acute allergic and autoimmune inflammation, respectively, which bypass the induction phase of immune responses, in vitro on IgE- and IgG-induced mouse mast cell activation and ex vivo on IgE-dependent human basophil activation. L. casei protected from anaphylaxis and arthritis, and inhibited mouse mast cell and human basophil activation. Inhibition required contact between mast cells and bacteria, was reversible, and selectively affected the Lyn/Syk/linker for activation of T cells pathway induced on engagement of IgE receptors, leading to decreased MAPK activation, Ca(2+) mobilization, degranulation, and cytokine secretion. Also, adoptive anaphylaxis induced on Ag challenge in mice injected with IgE-sensitized mast cells was abrogated in mice injected with IgE-sensitized mast cells exposed to bacteria. These results demonstrate that probiotics can influence the effector phase of adaptive immunity in allergic and autoimmune diseases. They might, therefore, prevent inflammation in patients who have already synthesized specific IgE or autoantibodies.

Expression of a major plant allergen as membrane-anchored and secreted protein in human cells with preserved T cell and B cell epitopes

BACKGROUND

Expression of allergens in human cells is a prerequisite for the development of antigen-specific cell therapy in IgE-mediated allergy. We developed a strategy how the clinically relevant major grass pollen allergen Phl p 5 can be efficiently secreted or expressed on the surface of human cells with preserved allergenic activity.

METHODS

The cDNA of Phl p 5 was fused to a leader peptide with or without a transmembrane domain and both constructs were ligated into a mammalian expression vector. Transfection of these plasmids into human cells resulted in a membrane-anchored or secreted version of Phl p 5, respectively, as determined by ELISA or flow cytometric analysis.

RESULTS

Both the secreted and membrane-anchored Phl p 5 proteins bound IgE from allergic patients in an immunoblot assay and induced specific histamine release and CD203c upregulation in basophils of grass pollen-allergic patients. Proliferation of peripheral blood mononuclear cells from Phl p 5-allergic individuals was induced upon stimulation with both variants of Phl p 5 expressed in human cells similar to recombinant Phl p 5.

CONCLUSIONS

Secreted and membrane-anchored Phl p 5 expressed in human cells preserved B cell as well as T cell epitopes and may be used to develop and test various cell-based strategies for allergen-specific immunomodulation and to delineate the tolerance mechanisms involved therein.

Microarrayed recombinant allergens for diagnostic testing

The development of protein microarray-based immunoassays and the availability of recombinant allergens have, to a significant extent, emerged together over the past decade. Their long-anticipated wider application to allergy diagnosis has recently begun to accelerate. This review discusses some of the strengths and weaknesses of molecularly defined allergy testing and the microarray platform. Several recent applications of microarray assays to allergy testing are also summarized. Promising findings, particularly in the context of food and latex allergy, point to the potential for greater resolution between clinical reactivity and asymptomatic sensitization with this platform.

Clinical and laboratory parameters of mast cell activation as basis for the formulation of diagnostic criteria

Mast cell (MC) activation occurs in a number of different pathologic conditions. Acute activation is commonly seen in patients with allergic reactions, with consecutive massive release of vasoactive and proinflammatory mediator substances from MCs, leading to the clinical signs and symptoms of anaphylaxis. In these patients, serum tryptase concentrations usually increase subtantially above baseline levels. Chronic MC activation is more difficult to diagnose, especially when symptoms are mild or atypical, and no underlying disease is found. In these patients, serum tryptase levels usually are normal. In a smaller group of patients, tryptase levels are constantly elevated and may point to an occult form of mastocytosis. These patients have to be examined for MC monoclonality, other criteria of a primary MC disease, non-MC hematopoietic neoplasms, and reactive disorders producing chronic MC activation or MC accumulation. In most patients in whom MC activation is found, histamine-induced symptoms can be documented and usually respond to treatment with histamine receptor antagonists or MC stabilizers. If this is not the case, alternative explanations for symptoms and differential diagnoses have to be considered.

Inhibition of CD203c membrane up-regulation in human basophils by high dilutions of histamine: a controlled replication study

OBJECTIVE

Previous research suggests that human basophil activation may be inhibited by histamine even at extremely low doses (high dilutions). However, uncertainties about the nature of the phenomenon and its reproducibility mean that further, rigorously controlled studies are necessary.

METHODS

Serial 1:100 (v:v) histamine dilutions (centesimal dilutions, C) and water controls were tested on human basophil responsiveness to anti-IgE antibodies, using flow cytometry. Each dilution step was followed by vertical mechanical shaking (also designed as succussion) at 20 strokes/s. Basophil-enriched buffy coats from healthy blood donors were incubated with 10(-4) mol/l histamine (2C) and with serially diluted preparations from 10(-20) mol/l (10C) to 10(-32) mol/l (16C), then incubated for 30 min with 1 mug/ml goat monoclonal anti-human IgE and basophils stained for immunophenotyping.

RESULTS

Membrane up-regulation of CD203c, which in these experimental conditions proved to be a more consistent activation marker than CD63, was significantly inhibited in samples treated with histamine at the dilutions of 2C (P = 0.001), 12C (P = 0.047), 14C (P = 0.003), 15C (P = 0.036) and 16C (P = 0.009). Control water dilutions/succussions did not show any significant effect.

CONCLUSION

Using a strictly standardized flow cytometry protocol and a new dilution/succussion procedure, we have shown that low and high dilutions of histamine inhibit CD203c up-regulation in anti-IgE stimulated basophils.

Potential, pitfalls, and prospects of food allergy diagnostics with recombinant allergens or synthetic sequential epitopes

This article aims to critically review developments in food allergy diagnostics with regard to the verification of specific IgE antibodies and the identification of the responsible allergens. Results of IgE-binding tests with food extracts are hampered by cross-reactive proteins, low-quality test agents, or both. Specificity can be increased by defining adequate cutoff values, whereas sensitivity can be improved by using high-quality test agents. IgE-binding tests with purified allergens enabled reliable quantification of allergen-specific IgE titers, with higher levels found in individuals with food allergy compared with individuals without food allergy. However, the overlap in individual test reactivity between allergic and nonallergic subjects complicates interpretation. Recombinant allergens and synthetic sequential epitopes enabled detection of sensitization profiles, with IgE specific to several allergens and substructures now being suggested as markers of severity, persistence, or both. However, high-power quantitative studies with larger numbers of patients are required to confirm these markers. IgE-binding tests merely indicate sensitization, whereas the final proof of clinical relevance still relies on family/case history, physical examinations, and provocation tests. Novel technologies promise superior diagnostics. Microarray technology permits simultaneous measurement of multiple IgE reactivities regarding specificity, abundance, reactivity, or interaction. Improved functional tests might enable reliable estimation of the clinical relevance of IgE sensitizations at justifiable expenses.

Mediators of anaphylaxis

Anaphylaxis is a life-threatening condition closely linked to IgE activation of mast cells with subsequent release of preformed mediators, including histamine, neutral proteases (tryptase and chymase), and proteoglycans (eg, heparin) from intracellular granules. These factors participate in the development of classic symptoms involving the skin, respiratory tract, circulation, and gastrointestinal system. Release of these granules is followed quickly by increased synthesis from membrane arachidonic acid of prostaglandins and leukotrienes that have an additional role in clinical symptoms. Thereafter, mast cells release numerous chemokines and cytokines that initiate recruitment and activation of additional inflammatory cells, including basophils, eosinophils, and Th2 cells.

Gastro-duodenal digestion products of the major peanut allergen Ara h 1 retain an allergenic potential

BACKGROUND

The process of gastro-duodenal digestion may play a role in determining the allergenic properties of food proteins. The sensitizing and allergenic potential of digestion products of highly degraded allergens, such as the major peanut allergen Ara h 1, is currently under debate. We evaluated the effect of in vitro gastro-duodenal digestion of Ara h 1 on T cell reactivity and basophil histamine release.

METHODS

An in vitro model of gastro-duodenal digestion was used to investigate changes in the allergenic properties of Ara h 1 using in vitro assays monitoring T cell reactivity (proliferation, cytokine production) and histamine release of basophils from peanut allergic individuals. The digestion process was monitored using an SDS-PAGE gel.

RESULTS

In vitro gastric digestion led to rapid degradation of Ara h 1 into small fragments M(r) L5600. Gastric digestion did not affect the ability of Ara h 1 to stimulate cellular proliferation. Gastro-duodenal digestion significantly reduced its ability to stimulate clonal expansion (P<0,05; Wilxocon's signed rank test). The Th-2 type cytokine polarization of T cells from peanut allergic donors (IFN-gamma/IL-13 ratio and IFN-gamma/IL-4 ratio of CFSE(low) CD4(+) T cells) remained unchanged regardless of the level of digestion. Histamine release of basophils from peanut allergic individuals was induced to the same extent by native Ara h 1 and its digestion products.

CONCLUSION

Gastro-duodenal digestion fragments of Ara h 1 retain T cell stimulatory and IgE-binding and cross-linking properties of the intact protein.

Flow-assisted allergy diagnosis: current applications and future perspectives

Physicians predominantly rely upon quantification of serum-specific immunoglobulin E (IgE) and/or skin test to confirm clinically suspected IgE-mediated allergy. However, for various reasons, identification of the offending allergen(s) and potentially cross-reactive structures is not always straightforward. Flow-assisted allergy diagnosis relies upon quantification of alterations in the expression of particular basophilic activation markers. Actually, upon challenge with a specific allergen, basophils not only secrete quantifiable bioactive mediators but also upregulate the expression of different markers which can be detected efficiently by flow cytometry using specific monoclonal antibodies. Currently, the technique has been applied in the investigation of IgE-mediated allergy caused by classical inhalant allergens, food, Hevea latex, hymenoptera venoms and drugs. It is also appreciated; the technique proves valuable in the diagnosis of non-IgE-mediated (anaphylactoid) reactions such drug hypersensitivity and the detection of autoantibodies in certain forms of chronic urticaria. This review will not address immunologic features, characteristics and general pitfalls of flow-assisted analysis of in vitro-activated basophils as summarized elsewhere. After a recapitulation of the principles and some specific technical issues of flow-assisted analysis of in vitro-activated basophils, we principally focus on the current clinical and research applications of the basophil activation tests. Personal experience of both research groups is provided, where appropriate. Finally, a viewpoint on how the field might evolve in the following years is provided.

Analytical methodology for assessment of food allergens: Opportunities and challenges

This review summarizes the available in vitro, in vivo, and informatic methods designed to evaluate different aspects of the capacity of proteins to act as true food allergens. By now, there is no single method to fully assess the potential allergenicity of proteins. The characterization of many food allergens will help to uncover the sequential and structural motifs that determine the behaviour of proteins as food allergens.

Rational design of hypoallergens applied to the major cat allergen Fel d 1

BACKGROUND

Allergen-specific immunotherapy is the only treatment for allergic disease providing long-lasting symptom relief. Currently, it is mainly based on the use of crude allergen extracts. The treatment may be improved by the use of genetically engineered allergens, hypoallergens, aiming at a more effective and safer therapy.

OBJECTIVE

The aim of this study was to provide a rational design of hypoallergen candidates for immunotherapy by using structural information and knowledge of B and T cell epitopes of an allergen.

METHODS

The three-dimensional structure of the major cat allergen Fel d 1 was systematically altered by duplication of selected T cell epitopes and disruption of disulphide bonds. Seven Fel d 1 derivatives were generated and screened for allergenic reactivity in comparison with recombinant Fel d 1 in competition-ELISA. The allergenicity was further evaluated in basophil activation experiments and T cell reactivity was assessed in a lymphoproliferation assay.

RESULTS

Three out of seven Fel d 1 derivatives, with two duplicated T cell epitopes and one or two disulphide bonds disrupted, were carefully evaluated. The three derivatives displayed a strong reduction in allergenicity with 400-900 times lower IgE-binding capacity than recombinant Fel d 1. In addition, they induced a lower degree of basophil activation and similar or stronger T cell proliferation than recombinant Fel d 1.

CONCLUSION

By a rational approach, we have constructed three Fel d 1 hypoallergens with reduced IgE-binding capacities and retained T cell reactivities. This strategy may be applied to any well-characterized allergen to improve immunotherapy for allergic patients.

Flow cytometric analysis of in vitro activated basophils, specific IgE and skin tests in the diagnosis of pollen-associated food allergy

BACKGROUND

Specific immunoglobulin E (IgE) and commercially available skin prick tests have been demonstrated to be unreliable methods to diagnose pollen-associated food allergy. To evaluate the predictive value of the basophil activation test (BAT) in pollen-associated food allergy, the apple-mediated oral allergy syndrome (OAS) in patients with birch pollinosis was chosen as a representative model.

METHODS

Patients with birch pollen allergy and a history of apple-mediated OAS (OAS(+), n = 29), patients with birch allergic without OAS (OAS(-), n = 22), and healthy controls (HC, n = 10) without birch pollen allergy and OAS were included. Apple IgE was quantified by the CAP FEIA method. Skin prick tests were performed with a Jonagold apple extract. Flow cytometric analysis of basophils activated with the same Jonagold extract was based on double staining with anti-IgE/anti-CD63 monoclonal antibodies.

RESULTS

Comparison between OAS(+) subjects and HC showed sensitivities and specificities of 96% and 100% for apple IgE and 88% and 100% for the apple skin prick test, respectively. For the BAT, sensitivity and specificity were 100%. In contrast, when nonresponders on the BAT were considered, sensitivity decreased to 90%. In a separate analysis between OAS(+) and OAS(-) subjects, specificities decreased to 30% for apple IgE and to 80% for the apple skin test, respectively. The BAT reached a sensitivity of 88% and a specificity of 75%.

CONCLUSION

Flow cytometry-assisted quantification of in vitro basophil activation seems to be a reliable instrument in the diagnosis of this model of pollen-associated food allergy. In addition, this study reemphasizes that the specificity of diagnostic allergy tests decreases considerably when, apart from HC, control individuals with cross-reactive antibodies are included.