Use of CD63 expression as marker of in vitro basophil activation in identifying the culprit in insect venom allergy

Background: The diagnosis of insect venom allergy and the indication for specific immunotherapy is based on history, skin tests and demonstration of hymenoptera venom specific I-E-antibodies. In cases with contradictory test results additional cellular tests are recommended. Objective: We evaluated the usefulness of a newly introduced test based on basophil CD63 expression as marker of activation in comparison with the basophil histamine release test (BHR) and the cellular antigen stimulation test (CAST) measuring leukotriene release. Methods: In 14 patients (10 males, 4 females; age: 12 to 67 years, mean: 42.5 +/- 15.1 years) with systemic reactions to hymenoptera stings in their history skin tests and determination of specific IgE-antibodies (CAP-RAST-FEIA) had shown inconsistent results: No demonstration of specific IgE-antibodies (n=4), one sting by an unknown insect together with positive skin test and/or positive RAST to both bee and wasp venom (n=4), several stings of partly unknown insects with positive skin test and/or demonstrable specific IgE-antibodies to more than one insect venom (n=4), uncertain history and divergent results in skin test and/or RAST (n=2). BHR, CAST and basophil activation test (BAT) were done according to the manufacturers with negative and positive controls and different concentrations of bee and wasp venom. The BAT is based on double staining with anti-IgE antibodies and anti-CD63 and subsequent determination of the percentage of activated basophils by flow cytometry. Results: BAT and skin test were concordant in 42.9%, BAT and RAST in 57.1 %. Concordance of all three cellular tests was seen in 57.1 %, of BAT and BHR in 69.1 %, of BAT and CAST in 78.6% and of BHR and CAST in 64.3%. In 6 cases where the three cellular tests (BHR, CAST, BAT) were not in accordance the addition of BAT led to a more reliable diagnostic result concerning the relevant insect in 3 cases and added no further information in 3 cases. BAT in controls always was negative. Correlation between CAST and BAT was higher than between CAST and BHR. Conclusions: In difficult cases of hymenoptera allergy, where history, skin tests and determination of specific antibodies do not allow a clear decision regarding the relevant insect species for immunotherapy, the additional performance of cellular tests (CAST and BAT) may be helpful.