In vitro allergy diagnosis: should we follow the flow?

Flow-assisted quantification of in vitro activated basophils in the diagnosis of wasp venom allergy and follow-up of wasp venom immunotherapy

BACKGROUND

Correct identification of the culprit venom is a prerequisite for specific venom immunotherapy (VIT). Despite the efficacy of VIT, issues as how to monitor treatment and when to discontinue maintenance therapy remain to be established.

METHODS

To evaluate diagnostic performances of the basophil activation test (BAT) in wasp venom allergy, 80 patients with a definite history of wasp venom anaphylaxis (systemic reactors) and 14 wasp-stung asymptomatic controls (stung controls) were enrolled. Venom-induced basophil activation was analyzed flow cytometrically by double-labeling with anti-IgE and anti-CD63. Results were compared to wasp IgE levels and results of a venom skin test (VST). To establish whether the BAT constitutes a candidate marker to monitor VIT, the BAT was repeated in 22 patients on the 5th day of a build-up course and after 6 months of maintenance VIT. Whether the BAT could contribute in the decision of discontinuing VIT was assessed in a cross-sectional analysis in 30 patients receiving treatment for 3 years.

RESULTS

Comparison between systemic reactors and stung controls revealed a sensitivity of 86.4% and specificity of 100% for venom IgE, and sensitivity of 81.8% for VST, respectively. In contrast to stung controls, patients demonstrated dose-dependent venom-induced basophil activation. The BAT attained a sensitivity of 83.8% and specificity of 100%. At the end of the build-up course, no effect of VIT on the BAT was demonstrable. When the BAT was repeated after 6 months of treatment, submaximal stimulation of the cells demonstrated a significant decreased CD63 expression (P < 0.04). Patients having VIT for 3 years also demonstrated significantly lower venom-induced CD63 expression (P < 0.001). After 3 years, 60% of the patients had a negative BAT for submaximal stimulation of the cells whereas only 17.9% of the patients had negativation of wasp IgE.

CONCLUSIONS

The BAT is a reliable instrument for the diagnosis of wasp venom anaphylaxis and might constitute an instrument to monitor wasp VIT.

Anaphylaxis from mandarin (Citrus reticulata): identification of potential responsible allergens

We report on a patient with anaphylaxis from mandarin. Temporal relationship between consumption of the fruit, the presence of positive specific IgE, the positive skin test and the basophil activation test for mandarin strongly supported the diagnosis of an IgE-mediated allergy from mandarin. The lipid transfer protein allergen from mandarin fruit was isolated and characterized. Specific IgE levels and IgE immunodetection data indicated the patient's sensitization to orange (Cit s 3) and mandarin (Cit r 3) lipid transfer protein allergens, as well as to germin-like (Cit s 1) allergen. These results were fully confirmed by skin prick test and basophil activation test (BAT) for lipid transfer proteins, and a BAT for Cit s 1. This case report has several particularities. First, in Central and Northern Europe, it is not widely appreciated that citrus fruits, particularly mandarin, can elicit anaphylaxis. Second, this case report re-emphasizes sensitization from lipid transfer proteins to predispose for severe allergic reactions. Finally, it provides an opportunity to summarize the applications of flow cytometry-assisted analysis and quantification of in vitro activated basophils in the diagnostic approach of anaphylaxis from food.

Expression of activation markers on basophils in a controlled model of anaphylaxis

BACKGROUND

Anaphylaxis has variable clinical presentations and lacks reliable biomarkers. Expression of activation markers on basophils has been useful in assessing sensitization in IgE-mediated diseases but has not been examined in vivo in anaphylaxis.

OBJECTIVE

The study's goals were to assess the baseline expression of activation markers on basophils in individuals with a sting reaction history, the degree of change in expression of these markers after intentional sting challenge, and the relationship between in vitro and in vivo activation marker expression.

METHODS

Patients allergic to insect venom were enrolled and grouped by clinical category defined by a history of a systemic or large local reaction and use of venom immunotherapy. Blood was collected before and after sting challenge. Enriched basophils were analyzed for activation marker expression. In select subjects, basophils were examined after in vitro stimulation with insect venom for activation marker expression and histamine release.

RESULTS

Of 35 sting-challenge participants, 21 provided adequate samples for analysis. Pre-sting basophil CD63 expression was significantly higher in systemic reactors on immunotherapy. Following sting challenge, the rise in basophil CD69 expression and CD203c was significantly higher in systemic reactors on immunotherapy. Levels of activation markers on basophils were greater after in vitro venom stimulation than after in vivo challenge.

CONCLUSION

Broader shifts in expression of basophil activation markers after in vivo challenge occurred among subjects with a history of in vivo systemic anaphylaxis despite venom immunotherapy.

CLINICAL IMPLICATIONS

Basophil activation markers may be potential biomarkers for anaphylaxis.

Measuring allergen-specific IgE: where have we been and where are we going?

About 40 yr ago, two groups of investigators identified a new class of immunoglobulins, IgE. By exchanging their results and reagents, they proved that the immunoglobulin responsible for immediate hypersensitivity was IgE. From that day forward the science of allergy was greatly advanced. Within a few years of the IgE discovery, an assay for IgE was developed. This test was named the radio allergosorbent test. The specific IgE testing methodology has matured in the last four decades. Different means of detecting IgE bound to allergen is the subject of this review. We have included methods for measuring specific IgE using the ImmunoCAP 1000 instrument. The methodology for measuring basophile histamine release is also detailed in this chapter.

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.

Serum-induced basophil CD63 expression by means of a tricolour flow cytometric method for the in vitro diagnosis of chronic urticaria

BACKGROUND

Functional autoantibodies against the alpha-chain of the high-affinity IgE receptor (FcepsilonRIalpha) identify a subset of patients with chronic urticaria (CU) due to autoreactivity, as assessed by an in vivo positive response to autologous serum skin test (ASST). We performed a study to standardize the serum-induced basophil activation assay by flow cytometry (FCM) using a new tricolour method, assessing the diagnostic performance of this test in discriminating between ASST+ and ASST- CU patients.

METHODS

Sera of 64 CU patients (22 ASST+ CU and 42 ASST- CU) and 10 healthy subjects were tested for their ability to induce basophil CD63 expression when incubated with whole blood of both atopic (DA) and non-atopic donors (DNA). Using a triple-labelled strategy with anti-CD123, anti-HLA-DR and anti-CD63 antibodies, CD63+ basophils were identified on a selected population of CD123+ HLA-DR- cells. In 3 ASST+ CU patients who underwent cyclosporine therapy, the assay was performed before and after treatment.

RESULTS

The ASST+ CU sera resulted in a significant higher induction of basophil CD63 expression compared with ASST- CU and healthy donors sera; when whole blood from DA was used, sensitivity and specificity of the assay were 95.5% and 90.5% respectively. ASST+ CU serum activity was significantly decreased during cyclosporine A treatment, in parallel with clinical remission.

CONCLUSIONS

Chronic urticaria serum-induced CD63 expression assay performed on DA whole blood by means of our tricolour FCM method could be the most useful tool for identification of a subset of patients with autoimmune CU and may become a promising tool also for monitoring treatment efficacy.

Molecular cloning and expression of icarapin, a novel IgE-binding bee venom protein

The 1045bp full-length cDNA sequence of a new bee venom component was obtained by rapid amplification of cDNA ends. The 672bp coding sequence corresponds to a protein with a signal peptide and multiple carbohydrate binding sites, and it was named icarapin. It has the new consensus sequence N-[TS]-T-S-[TV]-x-K-[VI](2)-[DN]-G-H-x-V-x-I-N-[ED]-T-x-Y-x-[DHK]-x(2,6)- [STA]-[VLFI]-x-[KR]-V-R-[VLI]-[IV]-[DN]-V-x-P. At least two transcript variants were found. Recombinant icarapin was tested for recognition by IgE antibodies and gave a positive dot blot with sera from 4 out of 5 bee venom allergic patients, all beekeepers. Indirect immunofluorescent staining localized the protein in the cuticular lining of the venom duct.

Flow-assisted diagnostic management of anaphylaxis from rocuronium bromide

BACKGROUND

Diagnosis of anaphylaxis from neuromuscular blocking agents (NMBA) is not always straightforward.

OBJECTIVES

To assess flow cytometric analysis of activated basophils (BAT) as a diagnostic instrument in anaphylaxis from rocuronium. To investigate whether the technique might help to identify cross-reactive and safe alternative compounds.

METHODS

For validation of the BAT, 14 patients with perioperative anaphylaxis demonstrating a positive skin test (ST) for rocuronium and eight individuals that tolerated rocuronium and a negative ST for this drug were enrolled. To confirm specificity of the BAT, five patients that tolerated atracurium or cisatracurium with a negative ST for rocuronium were tested. Basophil activation with rocuronium, vecuronium, atracurium, cisatracurium and suxamethonium was analysed flow cytometrically by labelling with anti-CD123/anti-HLADR/anti-CD63.

RESULTS

Sensitivity of BAT for rocuronium was 91.7% and specificity 100%. However, in two patients the BAT was lost as a diagnostic tool, as their cells were nonresponsive to positive control stimulation and allergen. Seven from the 12 responsive patients also demonstrated a clear basophilic activation for vecuronium. Moreover, according to ST and/or BAT cross-reactivity between rocuronium and vecuronium was suspected in 10/14 patients. Except one patient, all patients had negative BAT and ST investigations for atracurium and cisatracurium. Currently, five patients tolerated administration of cisatracurium. All control individuals demonstrated negative ST and BAT for all tested NMBA.

CONCLUSIONS

The BAT constitutes a reliable instrument to diagnose anaphylaxis from rocuronium. The technique also allows quick and simultaneous testing of different potential cross-reactive NMBA and to tailor a safe alternative.

Perioperative anaphylaxis from locally applied rifamycin SV and latex

A patient developed severe anaphylaxis during irrigation of a wound with rifamycin SV. The temporal relationship between application of rifamycin SV, the positive skin test and basophil activation test for rifamycin SV strongly supported diagnosis of anaphylaxis from the locally applied antibiotic. However, after operation the patient had two anaphylactic reactions with pruritus, urticaria and angio-oedema after routine care by a nurse, and these were probably caused by natural rubber latex. This case report has several messages. First, it is not widely appreciated that topically applied drugs and related compounds can elicit life-threatening anaphylaxis. Second, it illustrates patients can present with more than one allergy. Finally, it provides an opportunity to summarize the applications of flow cytometry-assisted quantification of in vitro activated basophils in diagnosing the cause of anaphylaxis during anaesthesia.

Diagnostic tests based on human basophils: potentials, pitfalls and perspectives

Human basophils are important tools for studying immediate-type hypersensitivity reactions since they release a variety of mediators (e.g., histamine, leukotriene C4, IL-4 and IL-13) following allergen triggering. Several diagnostic tools have been introduced that measure either leukotriene production or the upregulation of surface markers (CD63 and CD203c) from these cells after antigen stimulation. However, a broad variability in basophil activity exists between different basophil donors and different antigens within one donor. This manifests itself in terms of their reactivity (maximum secretory response), based on the intracellular signaling of the basophils studied, and in terms of their sensitivity. The latter is governed by the number of IgE receptors per basophil, the ratio of antigen-specific IgE to total IgE, and by the number of cell surface antigen-specific IgE molecules for half-maximal responses, termed 'intrinsic sensitivity'. These variables give rise to shifts in the dose-response curves which, in a diagnostic setting where only a single antigen concentration is employed, may produce false-negative data. Thus, in order to meaningfully utilize the current basophil activation tests for diagnostic purposes, each allergen should be pre-evaluated separately in order to determine a suitable stimulation range. Additionally, anti-IgE or anti-FcepsilonRIalpha antibodies should serve as positive controls, bearing in mind that 10-20% of basophil donors are not responsive to IgE-mediated stimulation. Diagnostic studies using CD63 or CD203c in hymenoptera, food and drug allergy are critically discussed. Basophil-based tests are indicated for allergy testing in selected cases but should only be performed by experienced laboratories.

Evaluation of basophil activation in food allergy: present and future applications

PURPOSE OF REVIEW

The diagnosis of immediate hypersensitivity relies on specific IgE and history. Because of low specificity, however, provocation challenges are often necessary. Furthermore, IgE testing does not predict features such as reaction severity; nor can it discriminate cross-reactivity from multiple sensitizations. Direct and passive basophil activation tests may address these needs. In addition, measuring basophil activation ex vivo may be useful for monitoring patients with food allergies.

RECENT FINDINGS

Several papers using basophil activation tests demonstrate comparable sensitivity and specificity to current testing for food allergy. Flow-based basophil activation tests have also been used to assess functional characteristics of patient IgE. Finally, several activation phenotypes have been identified as markers of allergic inflammation in vivo; these phenotypes appear to correspond to earlier reports of spontaneous histamine-releasing basophils in patients with active allergic inflammation.

SUMMARY

Although in their early stages, direct basophil activation tests may prove to be useful in the clinic. Indirect basophil activation studies are useful when applied to compare functional aspects of IgE. Identification of basophil activation ex vivo is a promising approach for monitoring allergic inflammation.

Evidence of in vivo basophil activation in chronic idiopathic urticaria

BACKGROUND

Approximately 40% of chronic idiopathic urticaria (CIU) subjects have autoantibodies to either FcepsilonRIalpha or IgE. The effect of such autoantibodies on circulating basophil activation status is unknown.

OBJECTIVE

The expression of cell surface activation markers on basophils from CIU, non-allergic, and allergic subjects were compared. Further, the relationship between marker expression and serum factors reported in CIU, such as histamine-releasing activity (HRA) and immunoreactivity to FcepsilonRIalpha were examined.

METHODS

Peripheral blood was obtained from CIU, allergic, and non-allergic donors and fractionated by density gradients. Enriched basophils (1-12%) were analysed by flow cytometry for expression of activation markers including CD63, CD69, and CD203c. Dilutions of serum (5-50%) were analysed for HRA on basophils from a normal donor. Serum was tested for immunoreactivity by western blotting to a standard cell lysate prepared from an RBL-SX38 cell line transfected with human FcepsilonRIalpha.

RESULTS

CIU subjects (n=9) and allergic subjects (n=8) exhibited enhanced expression of CD63 and CD69, as compared with non-allergic subjects (n=7); however, no difference was seen among groups for CD203c expression. Five CIU and two non-allergic subjects had evidence of significant serum HRA (>20%), whereas two CIU, two allergic, and three non-allergic subjects had evidence of serum immunoreactivity to FcepsilonRIalpha. Serum HRA and serum immunoreactivity to FcepsilonRIalpha were not associated with enhanced surface marker expression.

CONCLUSION

Basophil activation marker expression is increased in CIU subjects and is not associated with serum factors. In addition, serum HRA and FcepsilonRIalpha immunoreactivity are not unique to CIU, or related to enhanced circulating basophil marker expression.

Coriander anaphylaxis in a spice grinder with undetected occupational allergy

BACKGROUND

Anaphylaxis after ingestion of spices as a result from occupational sensitization remains anecdotal. We describe a patient, working in a spice factory, with anaphylaxis from coriander in a meal. He also demonstrated urticaria, angio-edema, rhinoconjunctivitis and bronchospasm during handling coriander and fenugreek.

OBJECTIVE

To determine the mechanism of the anaphylactic reaction and to evaluate cross-reactivity between both botanically unrelated spices.

METHODS

Investigations comprised quantification of total and specific IgE by Immuno-CAP FEIA, skin testing, basophil activation experiments by flow-assisted determination of CD63 expression in the patient and 3 healthy controls. Immuno-CAP inhibition experiments were applied to investigate cross-reactivity.

RESULTS

Specific IgE, skin tests and basophil activation tests were clearly positive in the patient, whereas they remained negative in controls. No cross-reactivity between fenugreek and coriander was demonstrable by inhibition experiments.

CONCLUSIONS

The clinical manifestations in temporal relationship to ingestion of coriander and handling of coriander and/or fenugreek, the positive specific IgE results, skin tests and basophil activation assays support the diagnosis of allergy to both spices. History suggests sensitization by occupational exposure.

Haemodialysis-associated anaphylactic and anaphylactoid reactions

Anaphylactic and anaphylactoid reactions related to haemodialysis have been increasingly described for almost 3 decades. The majority of these cases used to occur with ethylene oxide sterilized, and complement-activating cellulose membranes. However, a considerable number of publications have focused on polyacrylonitrile AN69 high flux membranes, angiotensin converting enzyme inhibitors and iron as other important causes of potentially severe haemodialysis-related anaphylactoid reactions. Clinical manifestations vary considerably and generally do not allow differentiation between IgE-mediated anaphylaxis and anaphylactoid reactions (e.g. from nonspecific mediator release). Successful management of these patients requires multidisciplinary approach and involves prompt recognition and treatment by the attending physician, and identification of the offending agent(s) with subsequent avoidance of the incriminated compound(s). This review focuses on some major causes of anaphylactoid and anaphylactic reactions during haemodialysis. Special consideration is given to the therapeutic and diagnostic approach.

NPP-type ectophosphodiesterases: unity in diversity

Nucleotide pyrophosphatase/phosphodiesterase (NPP)-type ectophosphodiesterases are found at the cell surface as type-I or type-II transmembrane proteins, but are also found extracellularly as secreted or shedded enzymes. They hydrolyze pyrophosphate or phosphodiester bonds in a variety of extracellular compounds including nucleotides, (lyso)phospholipids and choline phosphate esters. Despite their structurally related catalytic domain, each enzyme has well-defined substrate specificity. Catalysis by NPPs affects processes as diverse as cell proliferation and motility, angiogenesis, bone mineralization and digestion. In addition, there is emerging evidence for non-catalytic functions of NPPs in cell signaling. NPP-type ectophosphodiesterases are also implicated in the pathophysiology of cancer, insulin resistance and calcification diseases, and they hold great promise as easily accessible therapeutic targets.

Immediate-type allergy to drugs and related compounds: evaluation and management

Adverse drug reactions (ADR) constitute a major health issue in outpatient and inpatient clinical settings. An allergic drug reaction is an immunologically mediated adverse drug reaction that exhibits specificity and recurrence on re-exposure to the offending and/or cross-reactive compound(s). Diagnosis of drug allergy is difficult, as a broad spectrum of different drugs can elicit various immune-mediated diseases with distinct (sometimes unclear) pathomechanism, the exact structure (epitope) that causes the reaction is frequently unknown, the presence of an in vitro or in vivo test results might not be predictive of a clinical situation, and the gold standard or reference test for diagnosis, the drug challenge, is a complicated and sometimes dangerous endeavour. Nevertheless, during the past few years serious attempts have been made to standardise and validate in vitro and in vivo techniques for the diagnosis of drug allergy. New techniques, e.g. flow-assisted analysis of in vitro basophil activation, are replacing older ones like histamine release for immediate-type hypersensitivity reactions. However, additional comprehensive studies are required to further validate the technique and allow its entrance in mainstream diagnostic use, particularly for non-IgE-mediated hypersensitivity. This review attempts to summarize the major causes of immediate hypersensitivity reactions to drugs and related compounds. Special attention is paid to the diagnostic and therapeutic management of this common iatrogenic complication.

[Basophil activation tests in the diagnosis of drug reactions]

Over the past 10 years a number of studies on basophil activation tests (BAT) have been published which focus on their use as diagnostic methods in clarifying IgE-mediated hypersensitivity reactions to various allergens including drugs. These BAT are based on flow cytometric quantification of allergen- induced CD63 or CD203 expression or measurement of sulfo leukotriene release by ELISA. In the diagnosis of penicillin allergy, the combined use of the CD63-BAT and specific IgE increases sensitivity. The role of BAT in the diagnosis of non-IgE-mediated reactions to non-steroidal anti- inflammatory drugs remains to be clarified. This article focuses on (1) the principles of BAT, (2) technical aspects, (3) clinical applications and (4) recommendations for further development.

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.

Lysis with Saponin improves detection of the response through CD203c and CD63 in the basophil activation test after crosslinking of the high affinity IgE receptor FcepsilonRI

BACKGROUND

The basophil activation test (BAT), in which translocation of markers to the surface of blood basophils is measured in response to allergen by flow cytometry, is a rapid assay that is gaining popularity. Two markers are currently being evaluated for the BAT; CD63 and the lineage-specific CD203c. In a recent report, detection of CD203c after lysis with Saponin was shown to be superior to detection of CD63 after lysis with formic acid. We wanted to compare a) lysis with formic acid and lysis with Saponin, b) the response through CD203c and CD63, and c) the definition 10% activated cells above background with the probability binning metric T(chi) > 4, on sets of data generated with blood basophils stimulated with varying concentrations of anti-FcepsilonRI antibody.

METHODS

Blood from volunteers was incubated with serial logarithmic dilutions of anti-FcepsilonRI and subsequently with antibodies to CD203c PE and CD63 FITC. Sets of samples set up in parallel were lysed with either Saponin based Whole Blood Lysing reagent or with formic acid based Immunoprep/Q-prep. Samples were acquired on a FACS Calibur, but were compensated and analysed offline. Responders were defined as persons who had 10% or more activated basophils above background, or a T(chi) > 4, for two consecutive dilutions of anti-FcepsilonRI antibody.

RESULTS

More basophils (median 1164 vs. median 397) and better discrimination of upregulated CD203c and CD63 amongst responders were obtained after lysis with Saponin than after lysis with formic acid. We suggest that CD203c may be a more sensitive marker for the BAT than CD63, as 6/11 responders were found with CD203c, compared with 3/11 with CD63. Most responders (7/11) were identified with probability binning.

CONCLUSION

A combination of lysis with Saponin and the markers CD203c and CD63 computed by probability binning may be the most sensitive method of detecting activation of basophils after stimulation through FcepsilonRI.

The basophil activation test by flow cytometry: recent developments in clinical studies, standardization and emerging perspectives

The diagnosis of immediate allergy is mainly based upon an evocative clinical history, positive skin tests (gold standard) and, if available, detection of specific IgE. In some complicated cases, functional in vitro tests are necessary. The general concept of those tests is to mimic in vitro the contact between allergens and circulating basophils. The first approach to basophil functional responses was the histamine release test but this has remained controversial due to insufficient sensitivity and specificity. During recent years an increasing number of studies have demonstrated that flow cytometry is a reliable tool for monitoring basophil activation upon allergen challenge by detecting surface expression of degranulation/activation markers (CD63 or CD203c). This article reviews the recent improvements to the basophil activation test made possible by flow cytometry, focusing on the use of anti-CRTH2/DP2 antibodies for basophil recognition. On the basis of a new triple staining protocol, the basophil activation test has become a standardized tool for in vitro diagnosis of immediate allergy. It is also suitable for pharmacological studies on non-purified human basophils. Multicenter studies are now required for its clinical assessment in large patient populations and to define the cut-off values for clinical decision-making.

In vitro Analysis of Birch-Pollen-Associated Food Allergy by Use of Recombinant Allergens in the Basophil Activation Test

BACKGROUND

Basophil activation is associated with the expression of CD63. In birch-pollen-associated food allergy to celery, carrot and apple, Bet v 1, Api g 1, Dau c 1 and Mal d 1 are major allergens. Recombinant allergens have not yet been used in the CD63-based basophil activation test (BAT).

OBJECTIVE

To evaluate the feasibility of using recombinant allergens in the BAT in the diagnosis of allergy to apple, carrot and celery and to compare results with routine tests, i.e. skin prick tests (SPTs) and specific IgE.

METHODS

Thirty-two patients with an oral allergy syndrome induced by apple, carrot or celery and 22 controls were studied. SPTs were performed with native foods. Specific IgE was determined by the CAP method and basophil activation by flowcytometry upon double staining with anti-IgE/anti-CD63 monoclonal antibodies after incubating with purified recombinant Bet v 1, Bet v 2, Api g 1, Dau c 1 and Mal d 1.

RESULTS

By the combined use of the BAT and the CAP method, sensitization to Bet v 1 and Bet v 2 was detected in 100 and 25% of all subjects, respectively. Sensitivity of specific IgE for apple, carrot and celery was 60, 70 and 75% with corresponding specificities of 64, 86 and 82%. Sensitivity of the BAT for Mal d 1, Dau c 1 and Api g 1 was 75, 65 and 75% with corresponding specificities of 68, 100 and 77%.

CONCLUSIONS

The BAT using recombinant allergens provides a valuable new in vitro method for the detection of sensitization to foods. Although double-blind placebo-controlled food challenges remain the gold standard to confirm food allergy, the CD63-based BAT with recombinant allergens may supplement routine tests for allergy diagnosis.

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.

Anaphylaxis to an urethral lubricant: chlorhexidine as the "hidden" allergen

We report on a severe allergic reaction during urethral catheterisation, initially erroneously attributed to natural rubber latex (NRL). However, the negative investigations for latex, the uneventful further applications of NRL, the positive skin test and basophil activation test for chlorhexidine strongly support diagnosis of chlorhexidine anaphylaxis. This case illustrates that it is not widely appreciated that "innocent" products such as urethral lubricants may elicit serious life-threatening reactions. Careful inspection of the medical records is once again re-emphasised to be mandatory in order to avert subsequent anaphylaxis.

In vitro assays for the diagnosis of IgE-mediated disorders

Advances in technology have provided new laboratory tools for the quantitation of allergen-specific IgE antibodies in serum and on the surface of basophils. This review examines the evolution from qualitative IgE antibody assays of the late 1960s to the present-day, third-generation, automated and quantitative allergen-specific IgE assays. The latest technology trend is toward microarrays in which crude or purified native and recombinant allergens can be spotted in microdot arrays on silica chips to permit extensive panels of specific IgE measurements to be performed with small quantities of serum. Although these technologies hold promise, their diagnostic performance requires further assessment once their technical details have been optimized. Potential abuses of this newer IgE antibody technology include the use of allergosorbent specificities (eg, especially food and drugs) that lack validation, application of IgE antibody measurements in the diagnosis of non-IgE-dependent disorders (eg, aspirin sensitivity), and modification of IgE antibody assays to measure food-specific IgG antibody for which there is no clinical indication. Basophil mediator release assays have evolved to include flow cytometric methods that can quantitatively detect the presence of cell surface-bound allergen-specific IgE antibodies. Assays for histamine and leukotriene C 4 released after in vitro basophil activation are now more accurate and standardized. Current analytic methods for IgE antibodies provide more quantitative and reproducible measurements of IgE than ever before, although still with less sensitivity that traditional skin testing. The current challenge is to translate the quantitative IgE antibody results into a more accurate diagnosis of allergic disease.

Diagnostic methods for insect sting allergy

PURPOSE OF REVIEW

This review overviews advances from mid-2002 to the present in the validation and performance methods used in the diagnosis of Hymenoptera venom-induced immediate-type hypersensitivity.

RECENT FINDINGS

The general diagnostic algorithm for insect sting allergy is initially discussed with an examination of the AAAAI's 2003 revised practice parameter guidelines. Changes as a result of a greater recognition of skin test negative systemic reactors include repeat analysis of all testing and acceptance of serology as a complementary diagnostic test to the skin test. Original data examining concordance of venom-specific IgE results produced by the second-generation Pharmacia CAP System with the Johns Hopkins University radioallergosorbent test are presented. Diagnostic performance of honeybee venom-specific IgE assays used in clinical laboratories in North America is discussed using data from the Diagnostic Allergy Proficiency Survey conducted by the College of American Pathologists. Validity of venom-specific IgE antibody in postmortem blood specimens is demonstrated. The utility of alternative in-vivo (provocation) and in-vitro (basophil-based) diagnostic testing methods is critiqued.

SUMMARY

This overview supports the following conclusions. Improved practice parameter guidelines include serology and skin test as complementary in supporting a positive clinical history during the diagnostic process. Data are provided which support the analytical performance of commercially available venom-specific IgE antibody serology-based assays. Intentional sting challenge in-vivo provocation, in-vitro basophil flow cytometry (CD63, CD203c) based assays, and in-vitro basophil histamine and sulfidoleukotriene release assays have their utility in the study of difficult diagnostic cases, but their use will remain as supplementary, secondary diagnostic tests.