Origin of discordances between ImmunoCAP™ and NOVEOS
The 27 most divergent sIgE results from Figure 2A are shown in detail in Figure S3. As most discordant results concerned plant allergens (18/27), we investigated two possible causes. The first potential explanation is the spiking of ImmunoCAP™ but not NOVEOS hazelnut extract with Cor a 1, a member of the PR-10 MA family (22). Thus, we assayed the 53 hazelnut-sensitized samples for anti-Cor a 1 sIgE using the Cor a 1 NOVEOS reagent F428. Sera with high concentrations of anti-Cor a 1 sIgE (>10 kUA/L; range 11 to >100 kUA/L, n = 12) were excluded from new ROC curves calculation. The new AUC were 0.81 for ImmunoCAP™ and 0.84 for NOVEOS (data not shown), compared to previous values of 0.79 for ImmunoCAP™ and 0.82 for NOVEOS before removal of the anti-Cor a 1 sIgE-positive samples. Cut-off values were unchanged (16.7 for ImmunoCAP™ versus 3.6 for NOVEOS).
The second potential cause for discordant results resides in CCD displayed by plant allergens. We hypothesized that peanut or hazelnut positive results obtained using ImmunoCAP™ but not NOVEOS were related to IgE reactivity against CCD. We were able to test 11 samples (out of 25) for CCD IgE reactivity by using ImmunoCAP™ o214 reagent and found that 8/11 samples possessed anti-MUXF3 IgE. We then used a reagent blocking CCD antibody reactivity (MUXF3-HSA, ProGlyCan reagent from Hämosan) for the three samples which were the most discordant for peanut (1 patient) and hazelnut extracts (2 patients). CCD-blocker reagent abolished ImmunoCAP™ reactivity against peanut and hazelnut extracts for these three samples, while testing these same samples with NOVEOS revealed no reactivity to peanut or hazelnut extracts, without adding the CCD-blocker (Table 3). In order to confirm these results in a different setting, we selected MUXF3-positive samples from 8 adult patients with Hymenoptera venom sensitization but without a history of food allergy. All these samples showed sIgE reactivity against ImmunoCAP™ hazelnut extract, but no or very low reactivity against NOVEOS hazelnut extract. The ImmunoCAP™ reactivity was abolished or strongly reduced after addition of the CCD-blocker reagent (Table 3).