Use of Cross-reacting Carbohydrate Determinants (CCD) in Specific IgE Detection

Abstract

RATIONALE: Anti-CCD reactivity is known to exist in patient sera, resulting in false-positive immunoassay results, particularly with foods of plant origin. In this study, we evaluated the use of three specific IgE allergens_horseradish peroxidase (HRPO), ascorbate oxidase (ASO), and bromelain (BRO)_as immunoassay tools to detect anti-CCD reactivity.METHODS: Suspected CCD-reactive patient samples were selected on the basis of a negative case history to glycoprotein-containing foods and positive skin prick tests to a variety of pollen allergens. Specific IgE to the three allergens (HRPO, ASO, BRO) was determined using the IMMULITE® 2000 3gAllergy™ Specific IgE assay (Diagnostic Products Corporation, Los Angeles). Prior to analysis, standardized inhibition studies to confirm CCD reactivity were performed by preincubating patient sera with native and periodate-treated (chemically deglycosylated) allergen extracts (HRPO, ASO or BRO).RESULTS: In vitro studies of IgE sensitization to CCD were measured by comparing inhibition results between native and deglycosylated forms of HRPO, ASO, and BRO. All three are known to contain glycoprotein, although the exact number of glycan structures in each allergen varies. Greater than 90% inhibition was measured in each case, whereas negligible inhibition was measured for periodate-treated extracts.CONCLUSIONS: These data demonstrate convincingly that CCD-specific IgE interacted with the carbohydrate moieties of these glycoallergens. These glycoprotein-containing allergens, either together or individually, offer the opportunity to analyze discrepancies between clinical history, skin prick test results and in vitro results. RATIONALE: Anti-CCD reactivity is known to exist in patient sera, resulting in false-positive immunoassay results, particularly with foods of plant origin. In this study, we evaluated the use of three specific IgE allergens_horseradish peroxidase (HRPO), ascorbate oxidase (ASO), and bromelain (BRO)_as immunoassay tools to detect anti-CCD reactivity. METHODS: Suspected CCD-reactive patient samples were selected on the basis of a negative case history to glycoprotein-containing foods and positive skin prick tests to a variety of pollen allergens. Specific IgE to the three allergens (HRPO, ASO, BRO) was determined using the IMMULITE® 2000 3gAllergy™ Specific IgE assay (Diagnostic Products Corporation, Los Angeles). Prior to analysis, standardized inhibition studies to confirm CCD reactivity were performed by preincubating patient sera with native and periodate-treated (chemically deglycosylated) allergen extracts (HRPO, ASO or BRO). RESULTS: In vitro studies of IgE sensitization to CCD were measured by comparing inhibition results between native and deglycosylated forms of HRPO, ASO, and BRO. All three are known to contain glycoprotein, although the exact number of glycan structures in each allergen varies. Greater than 90% inhibition was measured in each case, whereas negligible inhibition was measured for periodate-treated extracts. CONCLUSIONS: These data demonstrate convincingly that CCD-specific IgE interacted with the carbohydrate moieties of these glycoallergens. These glycoprotein-containing allergens, either together or individually, offer the opportunity to analyze discrepancies between clinical history, skin prick test results and in vitro results.