Allergenic molecules
The biochemical names and molecular mass of the celery allergens are summarized in the table below (18).
Allergen |
Biochemical Name |
Molecular Weight (kDa) |
---|
Api g 1 |
Pathogenesis-related protein, PR-10, Bet v 1 family member |
16 |
Api g 2 |
Non-specific lipid-transfer protein (nsLTP) type 1 |
9 |
Api g 3 |
Chlorophyll a-b binding protein, chloroplast |
28 |
Api g 4 |
Profilin |
14 |
Api g 5 |
Flavin adenine dinucleotide (FAD) containing oxidase |
58 |
Api g 6 |
Non-specific lipid transfer protein (nsLTP) type 2 |
7 |
Allergen |
Biochemical Name |
Molecular Weight (kDa) |
---|
Adapted from the WHO/IUIS Allergen Database.
Currently, six celery allergens have been discovered, all which have been identified in the celeriac tuber except for Api g 2 which is found in the celery stalk (4).
Api g 1 is the major celery allergen with a molecular weight of 16 kDa and a Fagales-related protein Bet v 1 homologue (18-25). Bet v 1 belongs to the pathogenesis-related protein (PR-10) group (18, 25). Two isoforms of Api g 1 have been identified, Api g 1.0101 and Api g 1.0201 (26).
Api g 4 is considered to be a minor celery allergen and is a profilin protein with a molecular weight of 14 kDa (18, 23, 27-32).
Api g 5 is a celery allergen with homology to flavin adenine dinucleotide-containing (FAD) oxidase and has a molecular weight of 58 kDa (18, 23, 33, 34). The carbohydrate components of this enzyme appear to be pertinent for the IgE binding capacity (23).
Two non-specific lipid-transfer protein (nsLTP) allergens have been identified, Api g 2 and Api g 6. Api g 2 (nsLTP type 1) is located in celery stalks while Api g 6 (nsLTP type 2) is within the tuber. A study found that Api g 6-positive patients did not react to Api g 2 (35, 36).
Biomarkers of severity
Currently, no marker allergen has been discovered to help predict severe reactions in patients, however, severe reactions have been observed in patients who are mugwort sensitized (4, 10, 17).
Cross-reactivity
Allergic reactions to fruits and vegetables can be caused by cross-sensitization with pollen allergens or are due to food allergens (4). Patients who have celery allergies, cross-allergy to pollen is significant (19, 37-39). Celery allergy is closely linked to birch and mugwort pollen sensitization and it is often referred to as birch-mugwort-celery-syndrome (4).
With Api g 1 being the major celery allergen and because it is a homologue of the major birch pollen, Bet v 1 (22), cross-reactivity can been seen with related proteins found in other foods for example apples, stone fruits, carrots, hazelnuts and legumes (37, 40). It is estimated that around 70% of patients who are allergic to birch pollen could experience allergic reactions after eating such foods (40).
It has been shown that most Apiaceae allergen components can cross-react with apple or hazelnut components however, only some apple or hazelnut allergen components cross-react with Apiaceae components (41). Similarly, cross-reactivity has been determined between celery and courgette/zucchini, and although birch pollen allergy is present in patients who have celery allergy, this association is absent in relation to courgette/zucchini allergy (19).