Detection of Galacto-Oligosaccharide Specific IgE in Vitro

Background: Anaphylaxis to galacto-oligosaccharide (GOS), a prebiotic, is an entity unique to the Asian region.  Despite being a pure carbohydrate, we have shown via skin prick (SPT) and basophil activation tests (BAT) that this reaction is IgE-mediated.  Our preliminary studies using biotinylation of GOS and streptavidin binding to solid phase to develop an in-vitroGOS specific IgE assay were unsuccessful.

Aim:We sought to develop an in vitro IgE assay to GOS for screening populations for GOS sensitization, and compare its accuracy to the BAT.

Methods:GOS (degree of polymerization≥4) was conjugated to human serum albumin (HSA) by means of Maillard reaction. Sera from 12 GOS allergic patients and 9 GOS SPT negative controls were studied.  In addition, sera from 14 GOS SPT positive volunteers who underwent oral GOS challenge (resulting in 7 positive challenges) were included. Sera were pre-absorbed with HSA prior to the detection of GOS-specific IgE using GOS conjugated HSA (GOS-HSA) by ELISA. The mean plus two standard deviation of the IgE level from 9 GOS SPT negative subjects was set as the cut of value to determine the positive or negative IgE response to GOS among the 28 tested sera. 

Results:In the GOS challenge cohort, the sensitivity of the GOS-HSA IgE assay was 14.3% (95% CI 0.8 – 58.0%) and specificity was 71.4% (95% CI 30.3 – 94.9%). Among 12 patients who had presented with GOS allergy, 8 had a positive GOS-HSA IgE assay result giving a sensitivity of 66.7% (95% CI 35.4 – 88.7%). In contrast, BAT had a sensitivity of 83.3% (95% CI 50.8 – 97.1%) and specificity of 100% in the GOS challenge cohort. All patients had a strongly positive BAT at GOS concentrations of 10 μg/ml or higher.

Conclusions: The GOS-HSA IgE assay is able to detect GOS specific IgE. However, the BAT assay is superior to this assay in terms of sensitivity and specificity.