Researchers characterize macadamia nut allergy
February 26, 2022
2 minute read
Roibás Veiga I, et al. CA44. Presented at: AAAAI Annual Meeting; February 25-28, 2022; Phoenix (hybrid meeting).
Disclosures: The researchers do not report any relevant financial information.
PHOENIX – Researchers have sequenced the major macadamia nut allergen and its pattern of cross-reactivity with hazelnut for the first time, according to a poster presented at the annual meeting of the American Academy of Allergy, Asthma & Immunology.
The case report, presented by will go Roibas Veiga from the Allergy Department of Puerta de Hierro University Hospital in Madrid, Spain, included data from two patients.
The first, a 45-year-old woman, had a previously unstudied aspirin allergy, in addition to acid reflux. She also suffered from allergic rhinoconjunctivitis and asthma for which she was receiving dual immunotherapy due to her sensitization to VSuppressus, grass and plantain pollen and dog epithelium. This patient experienced itchy mouth after eating hazelnut cream and hives after eating macadamia nuts.
The patient underwent a skin test with a positive result for Cupressus, grasses, plantain and olive, as well as for the epithelium of the dog. She also showed positivity for peanut and chestnut. The radioallergosorbent test (RAST) showed a total IgE of 232 kU/L with a positivity at Cupressusgrass, 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.
“To address the hypothesis of the association of macadamia nut allergy with cross-sensitization to aeroallergens, in particular birch allergen, we tested specific IgE with a negative result in the serum of our patient,” Roibás Veiga said during his presentation.
A prick-by-prick test with raw, unroasted macadamia showed a clear positive result, but a negative result for walnut, peanut, almond, hazelnut, pistachio, sunflower seed and cashew nut.
The second patient was a 45-year-old man with a history of hyperuricemia and anaphylaxis due to naproxen. He visited the allergy clinic after an episode of itchy mouth, abdominal pain, conjunctival hyperemia and facial swelling immediately after eating peanuts and macadamia nuts.
His SPT tested positive for cat epithelium and tree pollens, including Cupressus, grass and plantain, as well as groundnut and chestnut. RAST was positive at Cupressus and plantain, but negative for all nuts, including Cor a 1, except groundnut. A prick-by-prick test came back positive for macadamia nuts.
The researchers then performed electrophoretic analyses.
“We have shown that macadamia nuts have a different protein profile than walnuts, peanuts or hazelnuts, with the majority of proteins being low molecular weight. Roasted and raw macadamia nut extracts had a similar protein profile,” said Roibás Veiga.
Western blot analyzes showed strong IgE binding in the serum of both patients to two macadamia nut proteins, 12 and 17.4 kDa, as well as to the 17.4 kDa hazelnut protein.
The researchers then chose the second patient as a model to perform an immunoblot inhibition 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 unique to macadamia nuts.
By performing proteomic analysis and a 12 kDa sequence, the researchers identified it as antimicrobial peptide 1.
“Patients allergic to macadamia nuts should only avoid hazelnuts when they experience symptoms related to its consumption, and no cross-reactivity with peanuts has been detected,” said Roibás Veiga. “Unlike hazelnut, the acquisition of macadamia nut allergy in our patients did not occur through cross-sensitization to birch allergens Bet v 1 and Mal d 1.
“We also want to highlight the importance of the prick-by-prick test as a gold standard when diagnosing macadamia nut allergy,” added Roibás Veiga.