The frequency of phospholipase A2 binding of basophilic granulocytes does not decrease during bee‐venom‐specific immunotherapy

BACKGROUND: The major allergenic component of bee venom is phospholipase A2 (PLA2). METHODS: In this study, PLA2 was used to analyze and enrich PLA2-binding cells from peripheral blood by high gradient magnetic cell sorting. RESULTS: In normal donors, the frequency of allergen (PLA2)-binding cells among peripheral blood mononuclear cells (PBMC) as determined by flow cytometry is below 0.1%, whereas in bee-venom-allergic patients, PLA2-binding cells are readily detectable at frequencies of up to 2.3%. In severely bee-venom-allergic patients, many basophilic granulocytes are present, as defined by anti-CD9, CD25, and CD38 mAb, comprising up to 95% of the PLA2-binding cells. From blood of allergic and normal donors, about equal absolute numbers of allergen-binding CD19/21-positive B cells can be enriched. Severe anaphylactic reactions (Mueller grade IV) and failure of or adverse reactions during immunotherapy are associated with high numbers of circulating allergen-binding basophils. Interestingly, in the patients studied, the number of PLA2-binding basophilic granulocytes did not markedly change during rush immunotherapy and up to 6 months of maintenance immunotherapy. CONCLUSIONS: The specific and reproducible enrichment of PLA2-binding cells provides a new tool for the analysis and monitoring of effector cells in bee-venom-allergic patients with immediate-type hypersensitivity.