All iodinated contrast media (CM) are known to cause both immediate (≤1 h) and nonimmediate (>1 h) hypersensitivity reactions. Although for most immediate reactions an allergic hypersensitivity cannot be demonstrated, recent studies indicate that the severe immediate reactions may be IgE‐mediated, while most of the nonimmediate exanthematous skin reactions, appear to be T‐cell mediated. Patients who experience such hypersensitivity reactions are therefore advised to undergo an allergologic evaluation. Several investigators have found skin testing to be useful in confirming a CM allergy, especially in patients with nonimmediate skin eruptions. If a patient with confirmed allergy to a CM needs a new CM exposure, a skin test negative CM should be chosen and premedication may be tried. However, none of these precautional measures is a guarantee against a repeat reaction. More research focusing on pathomechanisms, diagnostic testing and premedication is therefore clearly needed in order to prevent CM‐induced hypersensitivity reactions in the future.

For the diagnosis of allergy, cellular basophil activation tests (BAT), e.g. histamine or sulfidoleukotriene release tests, have long been introduced, but the expression of basophil activation markers such as CD63 and CD203c detected by flow cytometry has attracted more recent attention. A recent opinion paper in this Journal has stressed not only the potential but also the possible pitfalls of flow-cytometric BAT. We have applied clinical validation of various BAT in various ways for several years, and our experience shows that these new technologies have more potentials and perspectives than pitfalls. A comprehensive review of clinically validated studies on allergy to aeroallergens, insect venoms, latex, food allergens and drugs, e.g. myorelaxants, β-lactams, pyrazolones and non-steroidal anti-inflammatory drugs, as well as chronic urticaria shows clearly that even with different protocols, reproducible and meaningful results can be obtained. Although the available technologies may still be optimized and better standardized, there are no serious reasons to deprive allergic patients of clinically indicated BAT, which can be performed reliably by any laboratory with allergy and flow-cytometric capacity and expertise.

As compared to the clinical history and to the other parameters tested here, flow cytometry showed a high sensitivity and a high specificity. The excellent correlation observed between this method and the other cellular tests such as histamine and leukotriene release are in favour of the specificity of flow cytomery and in favour of the use of this method for venom allergy diagnosis.

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.

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Flow cytometry, as a popular method often used in the immunology and haematology departments of clinical laboratories may represent a new alternative for allergy diagnosis and basophil pharmacology.

IntroductionThe biological action of ultra high dilutions is controversial [1,2]. Inhibition of anti-IgE induced basophil degranulation by successive histamine dilutions is of interest, as it studies a chemically defined compound (histamine) which exerts a negative feed back effect via the histamine H 2 receptor. The biological activity is measured using the human basophil degranulation test, which is relatively simple to perform and does not require specialised equipment. Inhibition of basophil degranulation was observed with histamine dilutions ranging between the 15 th and 19 th centesimal dilutions. Since most data were originally obtained from only one laboratory, this study aimed to verify these results in a multi-centre trial. Materials and methods LaboratoriesFour independent laboratories agreed to participate in the trial. Prior to the start of the trial, participants underwent a training period and their results were verified by the French laboratory. Study protocolThe study was co-ordinated in Brussels and all histamine dilutions were coded randomly by the coordinator, who did not perform any of the tests. The dilutions were prepared in 3 separate laboratories, which did not participate in the trial. The samples were then posted to the trial laboratories. All reagents, including antibodies, histamine, staining solutions, microtitre plates etc., were from the same source. Data were returned to the co-ordinator and analysed independently by a biostatistician, who was not involved in any other part of the trial. Preparation of histamine dilutionsHistamine hydrochloride (50 mg, Sigma) was dissolved in distilled water (5 ml), diluted (1/10, v/v) in distilled water and vortexed for 15 s (full speed). To obtain the dilutions for the trial, this solution was serially diluted (1/100 v/v) up to 19 times, always with vortexing as described. The dilutions 15, 16, 17, 18 and 19 were coded by the coordinator. In parallel, dilutions of distilled water alone were prepared in an identical manner and coded (controls). On receipt of the dilutions, each participating laboratory stored them at 4°C. Prior to use, the solutions were made isotonic by dilution (1/10 v/v) in HEPES buffer (NaCl 127 mM, KCl 5 mM, HEPES 20 mM, pH 7.4). Human basophil degranulation testThe methods for the selection of volunteers, preincubation of cellular suspensions with the test dilutions and anti-IgE induced basophil degranulation have been described previously [3]. Cell suspensions (250 ml) were mixed with the test dilution (250 ml) and incubated at room temperature for 30 min. After mixing (3 s, medium vortex speed), aliquots (20 ml) were placed in the wells of a microtitre plate and mixed with anti-IgE (polyclonal anti-IgE affinity purified ATAB, USA, 20 ml; 1, 0.2, 0.04 mg/ml). The plates were then covered with a sealer tape (Dynatech Laboratories) and incubated for 30 min at 37°C. Thereafter, alcian blue (100 ml) was added to each well. Stained basophils (not activated) were counted using a haemocytometer (Fuchs Rosenthal). Approximately 80...

Anaphylactic shock accidents after allergen exposure are frequent. After immunization with ovalbumin (OVA), a common dietary constituent, we evaluated the efficacy of pretreatment with histamine-receptor or serotonin-receptor blockers administered alone or in combination with a nitric oxide synthase inhibitor (L-NAME) on OVA-induced anaphylactic shock in Brown Norway rats. Animals were allocated to the following groups (n = 6 each): control (0.9% saline); diphenydramine (15 mg kg(-1)); cimetidine (20 mg kg(-1)); diphenydramine + cimetidine; dihydroergotamine (50 microg kg(-1)); diphenydramine + cimetidine + dihydroergotamine; L-NAME (100 mg/kg) alone or associated with diphenydramine, cimetidine, diphenydramine + cimetidine, dihydroergotamine, or diphenydramine + cimetidine + dihydroergotamine. Mean arterial blood pressure (MABP), heart rate (HR), and survival time were monitored for 60 min following treatment. The shock was initiated with i.v. OVA. The MABP drop after i.v. OVA was worsened by diphenydramine and was modestly attenuated by cimetidine, dihydroergotamine, or both together. L-NAME potentiated slightly the effects of cimetidine and dihydroergotamine by lessening the initial MABP decrease, but this transient effect was not sufficient to prevent the final collapse or to improve survival time. Decreased vasodilatory (prostaglandins E2), increased vasoconstrictory (thromboxane B2) prostaglandins, and unchanged leukotriene C4 concentrations were contributory to the overall hemodynamic changes. Thus, the combined blockade of vasodilator mediators (histamine, serotonin, and nitric oxide) slowed the MABP drop in anaphylactic shock, but did not improve survival. More studies are needed to understand these discordant effects.