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).