Measurement of peptide-specific IgE as an additional tool in identifying patients with clinical reactivity to peanuts.

BACKGROUND: Peanut allergy is one of the most common food allergies, often resulting in severe reactions. Diagnostic decision levels of food-specific IgE antibody concentrations have been described. However, many patients still need to undergo oral peanut challenges because their IgE levels are in the nondiagnostic level.
OBJECTIVE: The aim of this study was to determine whether differences exist in IgE-binding epitope recognition between sensitized children with and without symptomatic peanut allergy.
METHODS: Eight peptides representing the immunodominant sequential epitopes on Ara h 1, 2, and 3 were synthesized on SPOTs membranes. Individual patient labeling was performed with sera from 15 patients with symptomatic peanut allergy and 16 patients who were sensitized but tolerant. Ten of these 16 patients had "outgrown" their allergy.
RESULTS: Regardless of their peanut-specific IgE levels, most patients with symptomatic peanut allergy showed IgE binding to the 3 immunodominant epitopes on Ara h 2. In contrast, each of these epitopes was recognized by < 10% of the tolerant patients. In addition, tolerant patients did not recognize 2 immunodominant epitopes on Ara h 1. At least 93% of symptomatic, but only 12.5% of tolerant patients, recognized 1 of these "predictive" epitopes on Ara h 1 or 2. Moreover, the cumulative IgE binding to the peanut peptides was significantly higher in patients with peanut allergy than in tolerant patients. With up to 50% of patients with peanut-specific IgE levels below diagnostic decision levels still being clinically reactive, oral food challenges could be avoided in ~90% of these patients through determination of peptide-specific IgE.
CONCLUSIONS: Determination of epitope recognition provides an additional tool to diagnose symptomatic peanut allergy, especially in children with peanut-specific IgE below diagnostic decision levels.