Researchers characterize macadamia nut allergy

PHOENIX — Researchers for the first time sequenced the main allergen of macadamia nut and its cross-reactivity pattern with hazelnut, according to a poster presented at the American Academy of Allergy, Asthma & Immunology Annual Meeting.

The case report, presented by Ira Roibás Veiga of the allergy department at University Hospital Puerta de Hierro in Madrid, Spain, included data from two patients.

The first, a woman aged 45 years, had an aspirin allergy that had not previously been studied, in addition to gastric reflux. She also had allergic rhinoconjunctivitis and asthma for which she was receiving double immunotherapy due to her sensitization to Cupressus, grass and plantain pollen and dog epithelium. This patient experienced oral itching after eating hazelnut cream and hives after eating macadamia nuts.

The patient underwent skin prick test with positive result for Cupressus, grass, plantain and olive tree pollen, as well as for dog epithelium. She also showed positivity for peanut and chestnut. Radioallergosorbent testing (RAST) showed a total IgE of 232 kU/L with positivity to Cupressus, grass, plantain, olive tree, Fraxinus and dog epithelium. RAST also appeared positive for hazelnut, peanut, chestnut, walnut, pistachio and sunflower seeds, with negativity for Cor a 1.

“In order to address the hypothesis of the association of macadamia nut allergy through cross-sensitization to aeroallergens, in particular birch allergen, we tested the specific IgE with a negative result in our patient’s serum,” Roibás Veiga said during her presentation.

A prick by prick test with raw, unroasted macadamia nut showed a clear positive result, but a negative result for walnut, peanut, almond, hazelnut, pistachios, sunflower seeds and cashew.

The second patient was a man aged 45 years with a history of hyperuricemia and anaphylaxis due to naproxen. He consulted the allergy clinic after an episode of oral itching, abdominal pain, conjunctival hyperemia and facial swelling immediately after eating peanuts and macadamia nuts.

His SPT showed positive result to cat epithelium and tree pollens, including Cupressus, grass and plantain, as well as to peanut and chestnut. RAST was positive to Cupressus and plantain, but negative to all nuts, including Cor a 1, except peanut. A prick by prick test appeared positive to macadamia nuts.

Researchers then conducted electrophoretic analyses.

“We showed macadamia nuts have a different protein profile from either walnut, peanut or hazelnut, with the majority of the proteins being of low molecular mass. Both roasted and raw macadamia nut extracts had a similar protein profile,” Roibás Veiga said.

Western Blot analyses showed strong binding by IgE in both patients’ serum to two macadamia nut proteins, 12 and 17.4 kDa, as well as to the 17.4 kDa hazelnut protein.

Researchers then chose the second patient as a model to perform an inhibition of immunoblot with hazelnut at different concentrations, which led to the discovery that the 17.4 kDa protein was responsible for the cross-reactivity between macadamia nut and hazelnut, and that the 12 kDa protein is particular to macadamia nut.

By conducting a proteomic analysis and sequence of 12 kDa, researchers identified it as an antimicrobial peptide 1.

“Macadamia nut-allergic patients should only avoid hazelnut when they have symptoms from its consumption, and no cross-reactivity with peanuts has been detected,” Roibás Veiga said. “Unlike hazelnut, the acquisition of macadamia nut allergy in our patients has not occurred through cross-sensitization to birch allergen Bet v 1 and Mal d 1.

“We also want to underscore the importance of the prick by prick test as the gold standard technique when diagnosing macadamia nut allergy,” Roibás Veiga added.