Scientists pinpoint key source of shellfish allergy

Oysters on a rock at low tide.
Image: Wikipedia

by Anne Crawford

Shellfish allergy is one of the most serious of all allergies, on a par in terms of severity with the life-threatening reactions experienced by people allergic to peanuts. Yet it is sometimes hard to diagnose and tell which type of shellfish is the problem.

Now, Monash University scientists have made a big step forward in diagnosis for allergies caused by molluscs, an important shellfish group. The scientists from the Allergy Lab (AIRmed and Immunology & Pathology), CCS, characterised for the first time allergens of four commonly eaten Asia-Pacific molluscs: Sydney Rock Oyster, Blue Mussel, Saucer Scallop and Southern Calamari.

Their study, published in the journal Molecular Nutrition & Food Research, may lead to better management of, and potential new treatment for mollusc allergy.

First author Emeritus Professor Jennifer Rolland said people who have an allergic reaction to shellfish might suspect shellfish was involved but often don’t know the exact trigger. Reactions for the one per cent of people with the allergy can range from mild mouth irritation, vomiting and diarrhoea to a severe anaphylactic reaction requiring adrenaline treatment.

Even tiny amounts of allergen can be dangerous, whether ingested  or even as proteins inhaled in food vapours.

“We wanted a really good blood test that can help pinpoint what these patients are allergic to,” Emeritus Professor Rolland said. “The study was also trying to figure out the cross-reactivity: ‘if I’ve had a reaction to oyster can I eat crab?’ So it’s trying to advise patients on what they can and can’t eat.

“The important thing is to define the allergic components or proteins within an organism.”

To do this the scientists used “immunoblotting” in which tissue from the organism is chopped up and made into a liquid extract then tested against the patient’s serum to see which proteins bind to the allergy antibodies (IgE). The test demonstrated that several proteins showed strong IgE reactivity. The most commonly recognised protein was a muscle protein called tropomyosin, which has been shown previously to be an allergen in crustaceans and other organisms including house dust mites.

Molecular biologists at James Cook University led by Professor Andreas Lopata then collaborated to clone the novel tropomyosin from Sydney Rock Oysters, and genetically sequenced the allergen.

“I think the paper’s very important for people with mollusc allergies. We’ve definitely shown that tropomyosin is an important allergen for a lot of patients,” Emeritus Professor Rolland said.

The Monash researchers also tested whether cooking destroyed the allergens but found that, interestingly, this increased IgE reactivity of many proteins.

Emeritus Professor Rolland, Co-Head of the Allergy Lab with senior author Professor Robyn O’Hehir AO, said identifying a panel of specific antigens was “the way of the future” for allergy diagnosis.

To this end the researchers identified four other putative allergens. “Tropomyosin affects maybe 60 per cent of patients so we need to identify other allergenic proteins as well and work out the best combination of raw and cooked allergens to include in a mollusc allergy diagnostic test,” she said.

“The big thing clinically is that this will help advise patients what they can and can’t eat.”

The research was supported by the ARC, NHMRC and Alfred Hospital Research Trust.

Rolland JM, Varese NP, Abramovitch JB, Anania J, Nugraha R, Kamath S, Hazard A, Lopata AL, O'Hehir RE. Effect of Heat Processing on IgE Reactivity and Cross-Reactivity of Tropomyosin and Other Allergens of Asia-Pacific Mollusc Species: Identification of Novel Sydney Rock Oyster Tropomyosin Sac g 1. Mol Nutr Food Res. 2018 May 14:e1800148. doi: 10.1002/mnfr.201800148. [Epub ahead of print]