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.

The basophil activation test is a particularly useful technique in the diagnosis of patients with IgE-mediated allergy to betalactams and allows the identification of 50% of patients. Used in conjunction with CAP, it allows the identification of 65.5% of such patients.

Human interleukin 5 (IL-5), known as a selective colony-stimulating factor of the eosinophil lineage and activator of mature eosinophils, also profoundly influences the mediator release profile of human basophils. IL-5 by itself triggers neither granule release nor de novo synthesis of lipid mediators. However, at low concentrations (0.1-10 ng/ml), IL-5 rapidly primes basophils for enhanced histamine release and leukotriene C4 (LTC4) generation in response to all established basophil agonists. LTC4 generation is more strongly affected by IL-5 than histamine release. In particular, IL-5 renders basophils capable of producing large quantities of LTC4 in response to C5a, which, without the cytokine, induces histamine release only. Finally, IL-5 renders basophils responsive to agonists (neutrophil-activating peptide 1 and C3a), which are otherwise inefficient triggers for basophil mediator release. The effects are similar to the recently established bioactivity of IL-3 on basophils, with the exception of its influence on IgE-dependent basophil activation, which is less pronounced. Thus, IL-5 strongly modulates the function not only of eosinophils but also of basophils, the two major effector leukocyte types involved in allergic inflammatory processes, e.g., in asthma.

Basophils and mast cells are important effector cells of inflammation and in particular of acute allergic reactions. Basophils can be activated to release inflammatory mediators by IgE-dependent and IgE-independent stimuli (1-4). The mediator profile produced by basophils strongly depends upon the agonist used to activate the cells (4a) . For example, crosslinking ofhigh-affinity IgE-receptors by an antigen, anti-IgE or anti-receptor antibodies leads to the release of preformed mediators from granule stores, like histamine and proteolytic enzymes, and also results in the activation of enzymes (phospholipase[s] and 5-lipoxygenase) responsible for the generation of leukotriene C4 (LTC 4),' a very potent lipid mediator and smooth muscle contractant (6). Conversely, the anaphylatoxin C5a, which at low concentrations is a potent inducer of basophil degranulation, does not activate basophils to produce bioactive lipids . These observations clearly indicate that degranulation and the generation of the arachidonic acid metabolite LTC4 are dissociated events and therefore controlled by different mechanisms .Granulocyte/macrophage colony-stimulating factor (GM-CSF) is a pluripotent growth factor for myeloid bone marrow precursors (7,8), but more recent studies demonstrated that this cytokine also enhances the function (in particular cytotoxicity and oxygen radical release) of mature inflammatory effector cells, like monocytes, eosinophils, and neutrophils (PMN) (9-13). Studies from our laboratory demonstrated that PMN sequentially exposed to GM-CSF and the chemotactic peptides C5a or FMLP release relatively large amounts of LTB4 and LTB4 metabolites, while neither peptide alone triggers the formation of these lipid mediators (14). Preexposure of PMN to GM-CSF also results in a strong enhancement of chemotactic peptide-dependent generation ofplatelet-activating factor, another potent lipid mediator (15). From these experiments we concluded that GM-CSF not only enhances effector cell functions, but also qualitatively changes in the mediator profile of the neutrophils triggered by diverse agonists .These observations suggested that other growth-promoting cytokines may also modify the mediator profile of mature leukocytes, and we thus studied the effects of IL-3 on blood basophils. IL-3 stimulates the growth of early progenitor cells of

Complement component C3a is an anaphylatoxin known to induce plasma exudation and smooth muscle contraction in tissues. The effects on inflammatory effector leukocytes, however, are poorly defined and controversial, being at best weak and occurring at very high C3a concentrations. Here, we examined the effect of C3a upon mediator release from human basophils, with and without pretreatment with interleukin 3 (IL-3), a hematopoietic growth factor recently found to profoundly modify the basophil response to various cell agonists. In the absence of cytokines, C3a, even at a concentration of 1 FM, was ineffective or only weakly stimulatory for basophil mediator release. However, when basophils were pretreated with IL-3 at concentrations of only 0.01-1 unit/ml, they became responsive to C3a, releasing large amounts of histamine and also generating leukotrienes. Surprisingly, almost optimal effects occurred with even very low C3a concentrations (1 nM). Another hematopoietic growth factor, granulocyte/macrophage-colony-stimulating factor (GM-CSF), was also found to render basophils capable of responding to C3a, but the effect was weaker than that of IL-3. C3a-induced histamine release and leukotriene generation occurred rapidly in IL-3-primed cells, being complete after 0.5 and 2 min, respectively. The rapid and strong degraniulation response, occurring at very low concentrations of C3a, suggests the presence of a high-aitmity C3a receptor on basophils, which might be inducible by cytokines. Our results demonstrate that, depending on the presence of IL-3 or GM-CSF, C3a is a potent basophil activator, and such a phenomenon could be of relevance in various inflammatory processes, especially hypersensitivity reactions.

Background: We assessed whether nonsteroidal anti-inflammatory drugs (NSAIDs) may provoke blood basophil activation in vitro in aspirin- and NSAID-hypersensitive patients, as detected by a flowcytometric technique using the CD63 marker – flowcytometric basophil activation test (FAST) assay – in addition to the sulfidoleukotriene (sLT) release – the cellular allergen stimulation test (CAST). Methods: Sixty aspirin- and/or NSAID-hypersensitive patients were studied. Thirty control patients without history and negative provocation challenge were also included. The percentage of activated basophils after in vitro stimulation with NSAIDs at 3 different concentrations was evaluated by an anti-CD63 phycoerythrin conjugate (FAST assay) and the amount of sLTs released in the cell supernatant by ELISA (CAST assay). Results: For aspirin, the FAST indicated a sensitivity of 41.7%, a specificity of 100%, a positive predictive value of 100% and a negative predictive value of 99.4%; for paracetamol 11.7 and 100%, for metamizol 15 and 100%, for diclofenac 43.3 and 93.3%, and for naproxen 54.8 and 74.1%. Many patients showed positive tests to more than 1 NSAID. When considering the first 4 NSAIDs, the global sensitivity increased to 66.7%, while the specificity remained at 93.3%. The addition of the CAST results still increased the sensitivity up to 73.3%, but with a decrease of the specificity to 71.4%. Conclusions: The FAST shows a high percentage of positive reactions, which may reach 60–70% when 4 NSAIDs are tested and even 88% when the test is performed within 1 month of the last clinical drug exposure and reaction. The test has a high specificity above 90%. The addition of sLT determinations yields additional information in a few isolated cases. It is suggested that this test, when properly used, may help avoid some cumbersome and dangerous provocation challenges.

Flowcytometric determinations of basophil activation following stimulation with NSAIDs show a high sensitivity (60-70%) with specificity above 90%. So this test may help avoiding some cumbersome and dangerous provocation challenges.

The basophil activation test is a highly reliable technique in the diagnosis of allergy to inhalant allergens. The sensitivity of the basophil activation test was 93.3%, and its specificity 98.4%, when using a cut-off point of 15% activated basophils as positive result.