New Ultrasensitive Test Developed for Peanut Allergies

Current peanut allergy tests are not very reliable when it comes to diagnosing the severity of an individual's allergic reaction, which can range from hives to life-threatening anaphylactic shock.

Severity of peanut allergies is linked to allergen-specific immunoglobulin E (IgE) antibodies in blood, but diagnostics from assays using glycoprotein allergen mixtures may be inaccurate. However measuring IgEs specific to individual peptide and carbohydrate epitopes of allergenic proteins is promising.

Chemists at the University of Connecticut (Storrs, CT, USA) are developing a more advanced peanut allergy test that, based on initial results, is many times more sensitive than current procedures. The new test is capable of determining the potential intensity of a patient's allergic reaction through just a few drops of blood.

In an allergic person who eats peanuts, their immune system releases an antibody protein known as IgE. These antibodies fight off peanut allergen molecules by binding to them and flushing them out of the body. The release of the antibodies causes tissue cells in the body to produce histamine, which in turn generates a variety of allergy symptoms such as itchy skin, runny nose, coughing, or wheezing. The more antibodies that are released, the more histamine is generated, the stronger the person's allergic response.

The scientists created an immunoarray for IgEs utilizing both peptide and carbohydrate epitopes. A surface plasmon resonance imaging (SPRi) microarray was equipped with peptide and β-xylosyl glycoside (BXG) epitopes from major peanut allergen glycoprotein Arachis hypogaea h2 (Ara-h2). A monoclonal anti-IgE antibody was included as positive control. IgEs were precaptured onto magnetic beads loaded with polyclonal anti-IgE antibodies to enhance sensitivity and minimize nonspecific binding.

The binding of IgE antibody to allergen epitopes was studied using a Surface Plasmon Resonance (SPR) imager (SPRimager II, GWC Technologies; Madison, WI, USA) interfaced with syringe pump and injection valve and sensor chip was assembled into the SPR imaging instrument. The chemists then injected blood serum from patients known to have peanut allergies into the array. As the blood serum floated over the samples, IgE antibodies were pulled down by the allergens and bound by them. They could then measure the quantity of antibodies to determine how strong a reaction a person would have to peanuts. To further refine the system, the team attached magnetic beads to the allergen samples. The beads captured the IgEs and amplified the final measurements, allowing them to detect concentrations of antibodies as low as 0.5 to 1 pg/mL.

James A. Rusling, PhD, a professor who led the study said, “A patient who has a serious allergy and gets exposed to an allergen protein will form antibodies in their body that should stay there for a while. Our theory is that the level of those antibodies can be used to predict how severe a patient's allergy is at any one point in time. Eventually, we'd like to use maybe five different peptides and carbohydrate samples to see how these IgEs bind to them. That way, we could determine a clear fingerprint of a patient's susceptibility to a specific allergen.” The study was originally published online on September 16, 2014, in the journal the Analyst.

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