Immunocap Cellulose Displays Cross-Reactive Carbohydrate Epitopes and Can Cause False-Positive Test Results in Patients with Anti-CCD IgE Antibodies
Monday, March 3, 2014: 2:30 PM
Room 15AB (Convention Center)
Wolfgang Hemmer, PhD, , ,
Rationale: Cross-reactive carbohydrate determinants (CCDs) in plant and insect venom extracts are a common cause of false-positive results during in vitro allergy diagnosis. We noticed, when using the Phadia ImmunoCAP system, that some CCD-positive sera deliver multiple positive results even when tested with CCD-free recombinant allergens.

Methods: ImmunoCAP IgE binding to selected recombinant allergens and to blank ImmunoCAPs (BIC) with no allergens coupled to the cellulose sponge was compared in CCD-positive sera before and after inhibition with a CCD inhibitor (ProGlycAn, Vienna, Austria).

Results: 30/45 (67%) CCD-positive sera (MUXF-CCD 1.01-59.6 kU/l) showed IgE-binding to BIC greater than 0.35 kU/l (0.41-6.66 kU/l). Among those with anti-CCD IgE levels >7.0 kU/l, 86% (24/28) were positive. IgE-binding to BIC correlated with IgE-binding to MUXF-CCD (r=0.66) and was completely abolished by serum pre-incubation with a CCD inhibitor (n=11). Binding scores with a second lot of BIC were lower but correlated strongly with the first lot (r=0.99). IgE-binding of seven highly CCD-reactive sera (14.0-52.5 kU/l) to the recombinant allergens rPhl p12, rFel d1, rAra h2, and rPru p3 was positive to all four components (up to 1.6 kU/l). Binding correlated strongly with antibody binding to MUXF-CCD and BIC (r=0.92) and could be completely blocked by the CCD inhibitor. Mass spectroscopic analysis confirmed the presence of MMXF glycans in unprocessed and processed cellulose.

Conclusions: Cellulose used as an allergen carrier in the ImmunoCAP system contains varying traces of CCDs itself, which can cause multiple false-positive results even to non-glycosylated recombinant components in patients with elevated levels of anti-CCD IgE antibodies.