In recent years, there has been an elevated consumption of seafood, especially shellfish. This has also led to an increase in adverse reactions such as shellfish allergy.

At present, approximately 2% of the general world population is estimated to suffer from shellfish allergy. Patients with seafood-induced immediate allergic responses can develop a variety of symptoms affecting the skin, respiratory tract, gastrointestinal tract, and cardiovascular system. In contrast to many other food allergies, shellfish allergy is not commonly outgrown and persists lifelong in the allergic person. (1)

The assessment for a patient with a possible shellfish food allergy begins with a thorough history and physical examination. If the clinical history indicates IgE-mediated allergy, skin prick tests or tests for specific IgE are required to confirm the diagnosis.

ALEX^2® covers a broad spectrum of shellfish allergens, including:

Pen m 1 (Tropomyosin)

• Major allergen - 60 % of patients with clinical allergy to crustaceans demonstrate specific IgE binding to tropomyosin. Hence, Pen m 1 was identified as a major allergen

• Important marker allergen for shrimp allergy

• Pen m 1 sensitisation can be associated with serious allergic reactions

• Pen m 1 is stable to heat and digestion and reactions to cooked foods are possible

• Panallergen (highly cross-reactive between different species, such as crabs, lobsters, and shrimps, which have amino acid identities of 95-100%).

• Tropomyosins are also cross-reactive beyond the shellfish family, e.g., Der p 10 from European house dust mite. 5-18% of house dust mite allergic patients have IgE antibodies against Pen m 1. Patients with IgE to Der p 10 potentially have a higher probability of allergic reactions to shellfish (crustaceans and molluscs), insects and parasites. (2, 3, 4) This should also be considered during SIT with house dust mite extracts due to strong cross-reactivity.

• Tropomyosins have also been detected in the species Blomia tropicalis (Blo t 10), the American cockroach (Per a 7) and Anisakis simplex (Ani s 3).

Pen m 2 (Arginine Kinase)

• Pen m 2 belongs to the arginine kinase allergen family

• Minor allergen

• Causes mainly mild reactions

• Highly cross-reactive

• Homologous proteins have also been described in shrimp, lobster, crab and spiny lobster, the European house dust mite (Der p 20) and German cockroach (Bla g 9). (5)

• Pen m 2 is not stable to heat and digestion and loses its allergenicity when boiled or fried

Pen m 3 (Myosin light chain 1 and 2)

• Minor allergen

• The degree of cross-reactivity between Pen m 3 and other members of the MLC allergen family is unknown, but probably high with other shrimp species and possible with chicken MLC

• Pen m 3 is stable to heat and probably also to digestion

Pen m 4 (Sarcoplasmatic Calcium Binding Protein allergen family)

• Minor allergen

• Indicator for shrimp sensitisation

• Important element in the diagnosis of shellfish allergy

• The degree of cross-reactivity with other members of the SPCBP allergen family is considered high

• It is still unclear whether Pen m 4 is stable to heat and digestion

Cra c 6 (Troponin C)

• Minor allergen

• Member of troponin C allergen family with high cross-reactivity among each other

• It is still unclear whether Cra c 6 is stable to heat and digestion

The combination of IgE-reactivity to both allergens (Pen m 1 and Pen m 4) might increase the sensitivity to detect clinically shellfish allergic patients. No species-specific allergens have been identified so far, making it difficult to precisely diagnose allergy to a single crustacean or mollusc species. Therefore, allergy test results based on molecular allergens must be compared to anamnestic data or oral challenge test results. Only then it is possible to indicate or rule out clinically relevant allergic reactions to certain shellfish species.

References

1. doi: 10.1007/s40629-016-0124-2
2. doi: 10.1046/j.1365-2222.2003.01722.x
3. doi: 10.1002/mnfr.201300584
4. doi: 10.1159/000113512
5. doi: 10.4049/jimmunol.170.1.445