CUHK study identifies 11 allergens in crabs for precision diagnosis of allergy and discovers a new allergen for king crab, which is not a “true crab”
Research team members include (from left) Professor Chu Ka-hou, Professor Emeritus of the School of Life Sciences at CUHK, Professor Leung Ting-fan, Alice Ho Miu Ling Nethersole Charity Foundation Professor of Paediatrics and Dr Christine Wai Yee-yan, Research Assistant Professor in the Department of Paediatrics of CU Medicine.
Crab allergy is the most common type of shellfish allergy among adults
Professor Leung Ting-fan
Crustacean allergy and mollusk allergy, grouped together as shellfish allergy, poses a significant health risk, affecting up to 2% of the world’s population, which includes shrimp, crab, scallop, mussel, clam, lobster, oyster and abalone. Shellfish allergy is also the food allergy most likely to cause anaphylaxis in Hong Kong adolescents and adults. Crab is the second most common type of shellfish allergy, after shrimp, but the most common among adults. Allergic reactions include urticaria, angioedema, wheezing, and, in severe cases, anaphylactic shock.
Professor Leung Ting-fan, Alice Ho Miu Ling Nethersole Charity Foundation Professor of Paediatrics in the Department of Paediatrics at CU Medicine, said: “Most people start to eat crab later than fish or shrimp and therefore crab allergy is usually noticed at an older age. Given that some individuals who are allergic to fish or shrimp may tolerate these types of seafood after they grow up, crab allergy is a more common type of shellfish allergy than shrimp among adult patients.”
Study identifies 11 allergens in crabs
The research team extracted proteins from the muscle tissue in the claws of six widely consumed edible crab species, Charybdis feriata, Portunus pelagicus, Scylla paramamosain, Chionoecetes opilio and Eriocheir sinensis, as well as the king crab, Paralithodes camtschaticus, and conducted IgE reactivity tests with 64 serum samples from crab-allergic patients[1]. The team identified 11 allergens in crabs with differential epitope[2] homologies and allergenicity, eight of which are new discoveries (please refer to the list below for details). Since king crab is not a “true crab”, the researchers conducted a separate IgE reactivity test and found a king crab-specific allergen, malate dehydrogenase (MDH), and registered it as a new shellfish allergen, Para c 11, in the WHO/IUIS Allergen Nomenclature Database.
The 11 confirmed crab allergens in the study (Newly discovered allergens are indicated with an asterisk)
- aldolase (ALD)*
- glycogen phosphorylase (GP)*
- hemocyanin (HC)*
- heat shock protein (HSP)*
- malate dehydrogenase (MDH)*
- myosin heavy chain (MHC)*
- phosphoglucomutase (PGM)*
- paramyosin (PM)*
- arginine kinase (AK)
- filamin C98 (FLNC)
- tropomyosin (TM)
Professor Chu Ka-hou
Professor Chu Ka-hou, Professor Emeritus of the School of Life Sciences at CUHK, explained: “King crab is not a true crab as it evolved from the ancestors of hermit crabs, belonging to the anomuran group. Therefore, its biological protein structure is different from that of true crabs. Although MDH is present in the muscle proteins of true crabs, we found that king crab displays a higher sensitisation rate of 41% compared with none in true crabs. This is the first time a unique allergen is found in king crabs.”
Dr Christine Wai
Dr Christine Wai Yee-yan, Research Assistant Professor in the Department of Paediatrics at CU Medicine, said: “Through systematic molecular analysis of crab muscle proteins, we found that 11 identified crab allergens showed similar expression across species. The major crab allergens arginine kinase and tropomyosin showed high epitope similarity of over 90%, while for specific crab allergens the epitope similarity was only 68%. It is also worth noting that the serum samples of each crab- allergic patient showed varying responses to different allergens that overall highlight specific crab allergies”
Professor Leung concluded: “Our paediatric allergy team has been a pioneer in the research of seafood allergy over the past decade, discovering a number of allergens in fish and shrimp. This study provided a comprehensive profile of allergens from six widely consumed species of crab which will further assist us in providing a precise and personalised diagnostic and treatment plan for seafood allergic patients and promoting appropriate food avoidance.”
The research was supported by the Research Grant Council (RGC), the Health and Medical Research Fund (HMRF) and other funds.
[1] “Crab-allergic patients” refers to those who have allergic reactions within two hours of ingesting crab.
[2] Epitope refers to the peptide sequence where the IgE antibody (a type of antibody that plays a key role in allergic reactions) binds.
Mercy is allergic to a certain types of fish since she was a child but had never experienced an allergic reaction to shellfish. During her travel in South Korea two month ago, she had her very first bite of marinated raw crab and appeared with severe allergic symptoms within five to 10 minutes after consumption, including swollen lips and throat, and dizziness. The CUHK team prescribed her an epinephrine auto-injector, often called a “rescue pen” (shown in the photo on the right), as emergency medical treatment for severe allergic reactions. Subsequently, her serum samples were used for a more detailed shellfish allergy testing, revealing that she had an antibody response to hemocyanin which is a protein commonly found in the roe of Charybdis feriata and Eriocheir sinensis.
This photo shows the epinephrine auto-injector, often called a “rescue pen”.
