Comparison of two basophil activation markers CD63 and CD203c in the diagnosis of amoxicillin allergy

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Abstract
Background To confirm allergy to β‐lactam (BL), a basophil activation test in flow cytometry based on CD63 up‐regulation was described. CD203c is a more recent basophil activation marker and up to day there is no consensus about which marker is the more sensitive one. CD203c has not yet been evaluated in the diagnosis of BL allergy. Objective The aim of the study was to compare the reliability of CD203c to CD63 for the diagnosis of amoxicillin (AX) allergy, which is nowadays the most frequent BL allergy. Methods Twenty‐seven patients with an immediate positive skin test (ST) to AX, 20 had had anaphylaxis with AX and 7 had urticaria and/or angioedema, were compared with 14 controls with no allergy to BL and to six patients with delayed positive ST to AX. Results In the anaphylaxis group, AX induced up‐regulation of CD203c in the basophils of 12 patients out of 20 (60%) and of CD63 in four patients (20%) (P+ gated cells, by means of CD33, a marker of monocytes, a contamination up to 50% by monocytes was detected. In contrast to CD63, CD203c is an activation marker specific of basophils with a basal low‐level expression in resting basophils. Thus, IgE and CD203c double targeting of basophils avoids the contamination by monocytes. Conclusion CD203c seems to be a more sensitive activation marker of basophils than CD63 for the diagnosis of amoxicillin allergy.