The inter- and intra-individual variability and seasonal variation of IgE, and high (FcεRI)- and low-affinity (CD23) IgE receptor expression in blood of seasonal allergic rhinitis (SAR) subjects, is not well studied. Thirty-two otherwise healthy subjects with a history of SAR to birch pollen and a positive skin prick test to birch pollen were sampled three times out of the pollen season and three times during the pollen season. FcεRI and CD23 expressions were analysed using flow cytometry. Total IgE was analysed using ImmunoCAP(®) and free IgE was analysed with a novel customised research assay using an IgG-FcεRI-chimera protein coupled to ImmunoCAP as capture reagent, ImmunoCAP-specific IgE conjugate and ImmunoCAP IgE calibrators. The performance of the free IgE assay was compared well with the reference ImmunoCAP total IgE assay. The working range of the assay was 0.35-200 kU/l IgE. FcεRI expression on basophils and CD23 expression on B cells showed low intrasubject variability both in and out of the pollen season (<10% CV). There was a small seasonal difference with lower total IgE levels (120 versus 128 kU/l; P = 0.004) and FcεRI expression (283 versus 325 mean fluorescence intensity (MFI); P < 0.001) during the pollen season. IgE, FcεRI expression and CD23 expression fulfilled biomarker and assay requirements of variability, and allergen exposure affected the biomarkers only to a minor degree. The free IgE assay may be used for measurement of free IgE levels in patients after anti-IgE antibody treatment.
© 2015 John Wiley & Sons Ltd.