Basophil sensitivity through CD63 or CD203c is a functional measure for specific immunotherapy

Patients (n = 18) starting subcutaneous SCIT for wasp allergy with an up dosing scheme of 7 to 11 weeks were enrolled. Heparinised blood samples were drawn at weeks 1-4, 7 and at the first maintenance visit. Basophils were stimulated at 7 log dilutions of V. vespula allergen for 15 min, and were stained with CD203c and CD63. Basophils were identified as CD203c+ leukocytes, and the proportion of CD63+ and CD203c+ cells were plotted against allergen concentration. A sigmoid curve was fitted to the points, and the allergen concentration at which half of the maximal activation was achieved, LC50, was calculated. In another series of experiments, LC50 calculated in whole blood (AP) was subtracted from LC50 calculated with basophils suspended in plasma from a nonatopic donor (HS) to determine the protective effect of soluble factors in blood of patients treated with SCIT.Heparin blood basophil activation was similar through CD63 and CD203c. Basophils were significantly more sensitized three weeks after initiation of SCIT compared to baseline (p < 0,01). The difference in LC50 increased by 1,04 LC50 units (p = 0,04) in patients that had just achieved maintenance dose compared with patients before initiating SCIT. When maintenance allergen concentrations had been reached, an increase in the protective plasma component was documented. Blood basophil concentration was marginally reduced by SCIT.Basophil activation is a versatile and sensitive tool that measures changes in the humoral immune response to allergen during SCIT.Allergy to insect venom can be life threatening, and leaves patients in a continuous state of anxiety [1]. Subcutaneous immunotherapy (SCIT) is able to modify the course of allergic disease, and is the only form of protection available against this allergy [2]. The efficacy of SCIT for venom allergy has been documented in a meta analysis [3]. SCIT induces cellular increase in IL-10 [4] and changes in the humeral immune system; a transient increase in free a