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f85 Celery

Celery
Code f85
LOINC LP16943-0
Family Apiaceae
Genus Apium
Species graveolens
Route of Exposure Ingestion
Source Material Freeze-dried stem and root
Latin Name Apium graveolens
Other Names Stick celery, Celeriac, Celery root, Root celery, Celery tuber, Knob celery
Categories Food Of Plant Origin, Vegetables

Summary

Celery is a vegetable that is consumed globally in a variety of ways including raw, cooked and it is used in flavorings. Celery is native to Western and Northern Europe and the Middle East and is grown in Europe, East Asia, southern Africa and southeastern Oceania. Sensitization to celery allergens has been shown to be increasing in the general population from 3.5% to 6.3% from data published in 2010 and 2014, respectively. To date, six celery allergens have been identified with Api g 1 being the major celery allergen and a Fagales-related protein Bet v 1 homologue. Celery allergy is closely linked to birch and mugwort pollen sensitization and is often referred to as birch-mugwort-celery-syndrome. Since Api g 1 is a homologue of the major birch pollen (Bet v 1) cross-reactivity can be seen with related proteins found in other foods for example apples, stone fruits, carrots, hazelnuts and legumes. The clinical signs associated with celery allergy are often related to the oropharynx, known as oral allergy syndrome and 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. 

Allergen

Nature

Celery is an annual or biennial plant that belongs to the Apiaceae family (1). As a popular vegetable, it is grown mainly for the green leaf stalks. The celery plant grows to a height of between 30–40 cm (12–16 inches). Celery seeds are brown, ovoid, ridged and very small (approximately 1.3 mm in length). Celery is a commercially important seed spice (2). Celeriac (Apium graveolens rapaceum) is a root of a plant closely related to celery (3). 

Taxonomy

Celery belongs to the Apiaceae family. The Apiaceae family is one of the largest with around 4,000 species classified into 434 genera. There are several vegetable and spice crop species within this family with celery and carrot being the major representatives with respect to food allergy (1, 4). Apium graveolens has three different varieties. The variety (var.) known for crisp stalks and is popular in the USA and Western Europe is var. dulce. Celeriac which is grown for its edible hypocotyl is var. rapaceum, and celery leaves which are mainly cultivated in Asia is var. secalinum (5, 6).

Taxonomic tree of Celery
Domain Eukaryota
Kingdom Plantae
Order  Apiales
Family Apiaceae
Genus Apium
Species A. graveolens

Tissue

Allergens of Apium graveolens can be found in the celery stalk and celeriac tuber (4). 

Epidemiology

Worldwide distribution

Sensitization to celery allergens has been shown to be increasing in the general population from 3.5% to 6.3% from data published in 2010 and 2014, respectively (4). The prevalence of celery allergy in Europe is estimated to be between 2.8–11.1% from four epidemiological studies based on sensitization. One study in Taiwan reported a sensitization rate of 1.8% (7). Data from eight centers across Europe involved in the EuroPrevall project reported the prevalence of probable food allergy for 24 priority foods. Probable food allergy was defined as self-reported food allergy and matching IgE sensitization. Priority foods were either known to commonly cause allergic reactions or thought to be potentially important because of frequent consumption in one or more of the participating countries. The table below shows the prevalence of probable celery allergy per center for adults and children (aged 7–10 years) (8, 9).

 

  Zurich Madrid Reykjavik Lodz Utrecht Athens Vilnius Sofia
Adults 0.24 0.00 0.33 0.07 0.03 0.00 Ex Ex
Children (7-10 years) 0.14 0.00 0.00 1.24 0.00 0.00 0.00 Ex

Adapted from Lyons et al. 2019 and Lyons et al. 2020. Ex – excluded from analysis due to lack of cases.

Sensitization to celery has been reported in 30% and 40% of patients with a food allergy in France and Switzerland respectively (10). In Germany, 70% of patients with a pollen-associated food allergy were skin prick test (SPT) or enzyme allergosorbent positive. Sensitivity to food allergens in patients who have pollen allergy is well recognized (10). 

Environmental Characteristics

Worldwide distribution

Celery is native to Western and Northern Europe and the Middle East, and is grown in Europe, East Asia, southern Africa and southeastern Oceania (1). Celery grows well in mild climatic conditions in heavily manured, sandy loam soil (2). In India, France and the USA, celery is cultivated for seeds and are exported to continental countries such as Italy, Netherlands and Germany, and also Australia and New Zealand. India produces around 4,000 tons and exports an estimated 3,000 tons of celery per year (2). In 2017, approximately 79,000 tons of celery were produced in the USA and in the same year, the European Union produced almost 336,000 tons of celery and 526,000 tons of celeriac (5).

Route of Exposure

Main

Celery (Apium graveolens) is classified as a vegetable that is consumed globally (1). Celery and celeriac (celery root) can be consumed both raw and cooked (2). Celery seeds can be used in spice mixtures or as a ‘celery salt’ for flavoring (2). The use of celery salt or spice mixtures containing celery can lead to allergic reactions in susceptible individuals (4).

Many studies have researched the effect of heat on allergens with the results showing that the allergic capacity is increased in some and diminished in others (4). While studies involving thermal treatment have reported variable effects, drying may not affect the allergenicity of celery. Research has demonstrated that patients with an allergy to raw celery can have allergic reactions to celery spice highlighting that celery can remain allergenic despite being dried and powdered for use in spices (11).

Secondary

In addition to celery seeds being used in spice mixtures and celery salt, celery seed oil can be used as an ingredient in food and also in cosmetics (4). Celery seeds are also used for health benefits (2). 

Detection

The clinical signs of celery allergy are often associated with the oropharynx, referred to as oral allergy syndrome (OAS). Symptoms can range from aphthae, stomatitis, swelling of the lips or tongue and pharyngitis to more severe and systemic symptoms such as laryngeal edema, asthma, urticaria and anaphylaxis (4, 10, 12).   

Oral allergy symptoms

The main symptoms of OAS are itching and mild swelling of the lips, mouth and throat. Atypical symptoms can involve the hands, gastrointestinal tract, chest tightness and loss of consciousness (13). OAS is also known as ‘pollen-food allergy syndrome’ and occurs in 47–70% of patients with pollen allergy. Symptoms may vary according to the pollen season and are usually more evident during the associated pollen season and may continue for a few months after the season ends (13). 

Anaphylaxis

Risk factors for an anaphylactic response to food includes: a systemic response to the food; having a response to the cooked form of the food; a positive skin prick test to the food extract; a lack of sensitization to the associated pollen; and peach allergy (13). Celery is one of the foods associated with food-dependent exercise-induced anaphylaxis (FDEIA) (14). 

Cutaneous reactions

Patients with celery allergy may experience cutaneous reactions such as generalized pruritis and urticaria (10). A powerful photosensitizer, furano-coumarin bergapten is found in celery seeds, which can cause photodermatitis especially in people who routinely handle celery (15, 16).

Other topics

The IgE cross-reactivity which is commonly seen is not always associated with clinical relevance (4).

When assessing the clinical reactivity of celery cultivars, a study found that the Anita cultivar is better tolerated in allergic patients compared to Prinz (6). 

Diagnostic Sensitization

In vitro diagnostics

Specific celery allergens have different rates of sensitization with 75% for recombinant (r) Api g 1 and 42% for both rApi g 4 and native (n) Api g 5 (17). Diagnostic sensitivity increased from 67% to 88% using component-resolved diagnosis when compared to extract-based diagnosis (17).

Skin prick test

The use of raw plant foods for prick to prick testing is considered superior when compared to extract-based testing (4) .

Challenge tests

The preferred approach to determine IgE cross-reactivity and potentially rule out clinically silent cross-reactivity is to use food challenge tests (4).

Other topics

The typical diagnostic workup and results for patients who are allergic to celery is as follows (4):

  • Sensitization to mugwort pollen
  • Native food prick to prick test – positive
  • Celeriac extract test – negative

Molecular Aspects

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

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).

Compiled By

Author: RubyDuke Communications

Reviewer: Dr. Christian Fischer

 

Last reviewed: March 2021

References
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