Basophil activation tests: time for a reconsideration

Challenges in in vitro allergy diagnostics lie in the development of accessible and reliable assays allowing identification of all offending allergens and cross-reactive structures. Flow-assisted analysis and quantification of in vitro activated basophils serves as a diagnostic instrument with increasing applications developed over the years. From the earliest days it was clear that the test could constitute a diagnostic asset in basophil-mediated hypersensitivity. However, utility of the basophil activation test should be reassessed regarding difficulties with preparation, characterization and validation of allergen extracts; availability and the potential of more accessible diagnostics. Today, the added value mainly lies in diagnosis of immediate drug hypersensitivity. Other potential indications are monitoring venom-immunotherapy and follow-up of natural history of food allergies. However, results in these nondiagnostic applications are preliminary. We review the most relevant clinical applications of the basophil activation test. Some personal comments and views about perspectives and challenges about flow-assisted allergy diagnosis are made.     

Omalizumab therapy is associated with reduced circulating basophil populations in asthmatic children

Basophils have been implicated in promoting the early development of T_H2 cell responses in some murine models of T_H2 cytokine‐associated inflammation. However, the specific role of basophils in allergic asthma remains an active area of research. Recent studies in animal models and human subjects suggest that IgE may regulate the homeostasis of human basophil populations. Here, we examine basophil populations in children with severe asthma before and during therapy with the IgE‐directed monoclonal antibody omalizumab. Omalizumab therapy was associated with a significant reduction in circulating basophil numbers, a finding that was concurrent with improved clinical outcomes. The observation that circulating basophils are reduced following omalizumab therapy supports a mechanistic link between IgE levels and circulating basophil populations, and may provide new insights into one mechanism by which omalizumab improves asthma symptoms.     

Beef-Induced Anaphylaxis Confirmed by the Basophil Activation Test

Beef allergies are relatively rare, especially in adults. However, clinical manifestations can vary from urticaria, angioedema, anaphylaxis to gastrointestinal symptoms. Currently available tests, such as skin testing or in vitro determination of beef-specific immunoglobulin E (IgE), do not provide an accurate diagnosis of beef allergy. The recent development of the basophil activation test (BAT) presents a new opportunity for the diagnosis of food allergies. Here, we report a 37-year-old woman with a history of recurrent generalised urticaria, nausea, vomiting and hypotension after ingestion of beef, suggesting a beef allergy. Although the skin prick test and serum specific IgE to beef, pork and milk allergens showed negative results using commercial kits, the BAT showed significant upregulation of CD203c in a dose-dependent manner compared to both non-atopic and atopic controls. To our knowledge, this is the first case study of beef allergy consisting of a non-IgE-mediated reaction. The detection of food allergies using direct basophil activation is suggested to complement conventional diagnostic tests.     

Influence of Neuraminidase and N-Acetylneuraminic Acid on Basophil Histamine Release in Vitro

Since N-acetylneuraminic acid (NANA) in cell membrane glucocalyx mediates or modulates a variety of actions, such as mediator release, we examined a possible modulating role of this amino sugar in histamine release from human basophil leukocytes. Removal of NANA from the cell membrane by the enzyme neuraminidase caused a dose-dependent histamine release. Removal of smaller amounts of NANA enhanced histamine release induced by anti-IgE, Concanavalin A and the calcium ionophore A23187, and reduced the interval between addition of antigen and initiation of histamine release. Pretreatment with free NANA had the opposite effects, i.e. a diminished and delayed maximal histamine release. The hypothesis that NANA in the cell membrane modulates the cellular response to stimulation was further substantiated by demonstrating that the altered response was reflected by a change in the sensitivity of the cell to extracellular calcium. NANA in the cell membrane glucocalyx thus seems to modulate the basophil response to stimulation by modulating transmembraneous calcium transport.     

Clinical and Immunological Aspects of a Case of Monoclonal Hyper-IgE

A case of monoclonal IgE type lambda with IgE levels about 1 mg/ml has been followed for 6 years. Except for a slight asthma no signs of malignancies, parasitic infestations or other known diseases compatible with hyper-IgE have been found. By the combination of fractional ammonium sulphate precipitation, gel filtration, chromatofocusing, and subtraction affinity chromatography the IgE protein was isolated in an immunochemically pure and homogeneous form. Immunofluorescence of bone marrow cells showed about 1% IgE plasma cells. The amount of basophil bound IgE was 42 ng/10(6) cells, and histamine release from basophils challenged with anti-IgE was not different from that in atopic control persons, indicating a within-allergic-patients normal amount of IgE receptors. The protein-A reactivity was 0.4% equivalent to well-known IgE myeloma proteins. No antigen specificity of the IgE protein was found. Only a few cases of asymptomatic hyper-IgE are known, and it cannot be ruled out that this represents a premyeloma condition, since a similar case terminated in a malignant lymphoma.