rApi g 1.01 PR-10, Celery

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Code: f417
Latin name: Apium graveolens
Common names: Group 1 Fagales-related protein (a Bet v 1 homologue).

Celery allergen components

Available ImmunoCAP®:

Summary

Celery is an herbaceous edible biennial plant in the family Apiaceae, native to the coasts of western and northern Europe, and to the Middle East. It was used by the ancient Greeks and Romans as a flavouring. The ancient Chinese used it as a medicinal plant.

The wild form of Celery is known as smallage. The stalks are furrowed and more stringy, the leaves are wedge-shaped, and the taste is rank and bitter. The most common commercial variety now sold is the Pascal variety, although gardeners can grow a range of cultivars under two classes, white and red.

Celery grows to 1 m tall, with pinnate to bipinnate leaves and rhombic leaflets 3-6 cm long and 2-4 cm broad. The edible Celery stalk is not a plant stem but a petiole, which is part of a leaf.

Celery stalks are not only consumed raw as fresh salad but also as a cooked vegetable and as a constituent of sauces and soups.

Celery seed is dried and used as a spice. When it is combined with salt, the resulting blend is called Celery salt. The furano-coumarin bergaptene, found in the seeds, is a potent photosensitiser and may cause photo-dermatitis, particularly in gardeners and field workers.

Celeriac (Apium graveolens rapaceum) is a species variety, forming a greatly enlarged, solid, globular body just below the soil surface. It is not used raw, but is especially suited for soups and stews.

The first case of allergic reaction to Celery root was reported in 1926 (1). Since then, a number of studies from across the world, and in particular from European countries, have documented the high prevalence of allergy to Celery, especially in association with cross-allergy to pollen (2-15).  IgE antibodies to Celery may occasionally be present in an individual’s sera without clinical sensitisation occurring (3).

In Switzerland, about 40% of patients with food allergy are sensitised to Celery, some experiencing severe anaphylactic reactions (13-14). Other studies have reported an even higher prevalence of allergy to Celery; in one study this was 42% (23); among the 69% of a group of 32 patients with a history of Celery allergy, DBPCFC resulted in systemic reactions in 50% (11/22) (4). In a study from 1978 to 1982, 173 cases of food allergy were diagnosed in patients (predominantly adults) attending the University of Zurich. The most frequent food allergens were found to be Celery in 40.5%, Carrots (20%), Green beans (6%), Hen’s egg (21%), Cow’s milk and other dairy products (20%) and fish (12%) (17).

In France, 30% of 580 patients with food allergy were sensitised to Celery, as determined by IgE antibodies. Sixty presented with severe, near-fatal reactions, in which the most common food implicated was Celery: 30% of severe anaphylactic reactions to food were thought to be due to Celery, according to patient histories (15).

In Germany, of 167 patients with a pollen-related food allergy, 70% were sensitised to Celery, as shown by skin test or allergen-specific IgE antibodies, and 14% reported clinical allergy to Celery (18).

Celery can cause oral symptoms (aphthae, stomatitis, swelling of the lips or tongue, pharyngitis, hoarseness and laryngeal oedema) and often also induces acute generalised symptoms, such as severe laryngeal oedema, bronchial asthma, urticaria and allergic shock (19). Oral allergy syndrome has been documented (20-21), and the symptoms have been reported to be more marked in severity compared to reactions to other vegetables (22).

Early allergen studies indicated the presence of IgE antibody binding to Celery proteins of molecular weight of around 14 kDa, 15 kDa, 16 kDa, and 17 kDa (2,23). Celery was also shown to contain at least 3 distinct cross-reacting allergens: a homologue of Bet v 1, a homologue of Birch profilin (Bet v 2), and a group of proteins with a molecular-weight range of 46 to 60 kDa (3). These allergens cross-reacted not only with Birch and Mugwort pollen, but also with a number of other fruits and vegetables (28). Early studies did not necessarily differentiate between Root celery (Celeriac) and Stick Celery, possibly presuming the allergens to be similar.

A number of allergens have been identified and characterised:

  • Api g 1, the major allergen, a 16 kDa protein and a Group 1 Fagales-related protein (a Bet v 1 homologue) (4,20,24-27,29-35).
     
  • Api g 1.0101 and Api g 1.0201, the isoforms of Api g 1 (27,36).
     
  • Api g 3, a chlorophyll Ab-binding Protein.
     
  • Api g 4, a 14.3 kDa protein, a profilin, a minor allergen (18,31-32,37-43).

Api g 5, isolated from the tuber, is a 60 kDa protein, a glycoprotein with homology to FAD-containing oxidases (44-45). This allergen carries carbohydrate determinants with cross-reactive structures (CCD); and importantly, convincing evidence that IgE directed to CCD is capable of eliciting allergic reactions in vivo has been reported (44-45).

A lipid transfer protein has also been detected (46-47).

The presence of CCDs (cross-reactive carbohydrate determinants) has been reported (36). Celery-allergic individuals have been shown to be monosensitised to CCDs, with exclusively CCD-specific IgE (37). A report stated that IgE specific for CCDs is common in Celery-allergic patients and can represent the major proportion of IgE against this food. Alpha 1, 3-fucose was shown to be an essential part of the IgE epitope, and immunoblotting inhibition indicated the presence of this carbohydrate determinant on multiple glycoproteins in Celery extract (5). Similarly, other studies have concluded that ubiquitous CCDs are important in allergy to Celery (and Zucchini) (4); and that, depending on the structure of the CCD-containing glycoproteins, CCDs can indeed be important epitopes for IgE; they may be clinically relevant allergens in certain patients and irrelevant in others (37).

One major allergen of Celery, possibly the lipid transfer protein, has been shown to be heat-stable. Heating Celery tuber for 30 minutes at 100 degrees C did not deplete the immunoreactivity of the major allergens (48). Other studies have concurred (49); Celery remained allergenic even after extended thermal treatment (430.5 min/100 °C), indicating that Celery spice (dried and powdered Celery) is allergenic for patients with an allergy to raw Celery (50). All patients undergoing DBPCFC with Celery spice reported reactions comparable to symptoms observed with raw Celery challenges (50).

Allergens from Apium graveolens listed by IUIS*

Api g 1 Api g 3 Api g 4
Api g 5    

*International Union of Immunological Societies (www.allergen.org) Jan. 2008.


f417 Api g 1.01

Recombinant non-glycosylated protein produced in an E. coli strain carrying a cloned cDNA encoding Apium graveolens allergen Api g 1.01

Common name: Bet v 1-homologous allergen, Group 1 Fagales-related protein, PR-10 protein
Biological function: Ribonuclease
Mw: 16 kDa

Allergen description

Api g 1 is a major Celery allergen and a Bet v 1-homologous protein (a Fagales-related protein) (35). Api g 1 has been shown to be a heat-labile protein, but stable upon exposure to high voltage, high pressure, gamma rays, drying and powdering, and therefore having allergenicity potential as a spice (18).

Api g 1 has had 2 isoforms characterised: Api g 1.0101 and Api g 1.0201, which share only a 52% sequence identity between each other and have approximately 40% identity with Bet v 1 (35). Compared with Api g 1.0201, Api g 1.0101 lacks Leu, and the negatively charged Glu is substituted for by the positively charged Lys (51).

In studies examining the prevalence of IgE antibodies against Api g 1, results varied from 59% of 22 patients who had positive DBPCFC to Celery (37), to 80% of 30 patients with pollen allergy reporting immediate allergy after ingestion of raw Celery (52), to 74% of a group of 23 patients with IgE mediated Celery allergy (3).

The Birch pollen allergen Bet v 1 plays a significant role in the cross-reactivity described. Celery Api g 1 has a 40% identity with (60% similarity to) the major allergen of Birch pollen, Bet v 1 (20), and Birch pollen-allergic individuals frequently develop IgE mediated reactions to Celery (53-54). A number of studies have demonstrated that cross-reactions among Birch pollen, Celery, Carrot, and various fruits and vegetables are based on allergens related to Bet v 1 and Art v 1, the major allergens of Birch and Mugwort pollen, respectively (26,32,54-55).

Considering that Api g 1, the major Celery allergen, is a homologue of the major Birch pollen allergen Bet v 1 (35), cross-reactivity with homologous proteins in Apples, stone fruits, Carrot, nuts, Soybean, Hazelnuts and pollens of several tree species can be expected to varying degrees (3, 56). Approximately 70% of patients who are allergic to Birch pollen may experience symptoms after consumption of foods from these groups (57).

The patterns may appear complex. For example, among sera of 61 patients with IgE antibodies to Mugwort pollen, 36 were positive for Celery and 23 had IgE antibodies to Birch pollen (23). Similarly, of 196 Birch pollen-hypersensitive patients with oral allergy syndrome (OAS), 195 had Apple and/or Hazelnut allergy, and 103 had Apiaceae sensitivity; only 1 patient had Apiaceae (Carrot, Celery, and Fennel) allergy alone. The study suggested that most Apiaceae determinants cross-react with Apple or Hazelnut determinants, whereas only some Apple or Hazelnut determinants cross-react with Apiaceae-allergenic determinants (58). Similarly, cross-reactivity has been reported between Celery and Zucchini, and it is stated that a specific association with Birch pollen allergy exists in allergy to Celery (mediated by Api g 1), but not in Zucchini allergy (4).

Nevertheless, epitope differences between Bet v 1-related food allergens exist, indicating different degrees of cross-reactivity among these allergens (59).

Similar results with other allergens have been reported: concurrent sensitisation to Mugwort and Birch pollen and to Camomile may occur, and binding was inhibited to varying degrees by extracts from Celery and Anise, and by pollen from Mugwort, Birch and Timothy grass. Profilins were not detected in the Camomile extracts (60).

In a study of the IgE antibody binding of 50 Bet v 1-positive patients’ sera to different food allergens, reactions with homologous Bet v 1 allergens were in the following proportions: 99% with Mal d 1 (Apple), 93% with Cor a 1 (Hazelnut), 59% with Api g 1 (Celery) and 38% with Dau c 1 (Carrot). Vice versa, patients with Birch pollen-related food allergy were predominantly sensitised to Bet v 1 homologues and less frequently recognised other allergens contained in both sources, e.g., profilins (56).

Individuals may be allergic to Celery without allergy or sensitisation to Birch tree pollen; 8% of Swiss patients allergic to Celery were not sensitised to rBet v 1 or rBet v 2 (61). Similarly, in a study of sera from 4 patients showing strong immediate systemic reactions after contact or ingestion of raw Carrot, all the patients had significant levels of IgE antibodies to Carrot allergen, Dau c 1, a Bet v 1 homologue, but no IgE antibodies to Birch pollen was detected in any. The sera contained a single band of around 18 kDa in raw Carrot and in Celery (with a weaker reaction), but no reactive band was found with Birch pollen. The Carrot IgE-binding protein’s N-terminal sequence was homologous to that of Bet v 1 and to allergens previously described in Celery and other foods. The 4 patients studied were not sensitised to Birch pollen, and 3 of them tolerated fruit ingestion. The study indicated that a sensitisation to Dau c 1 can induce IgE antibodies that do not cross-react with Birch pollen allergens (62).

Research has focused on the T cell response and epitope involvement influencing cross-reactivity between Birch pollen and Celery. In a study evaluating the T cell response to the major allergen Api g 1 in Celery, along with the cellular cross-reactivity with its homologous major allergen in Birch pollen, Bet v 1, the latter allergen was identified as the most important T cell epitope for cross-reactivity with Api g 1. The study concluded that the activation of Bet v 1-specific Th2 cells by Api g 1, in particular outside the pollen season, may have consequences for Birch pollen-allergic individuals (63). A study investigating the IgE-binding capacity of 2 cross-reactive allergens, Apg1.0101 from Celery and Pru av 1 from Cherry, showed that the IgE-binding epitopes are highly patient-specific (51, 64).

The influence of stronger IgE binding, and of the dissimilar sequence identity of rApi g 1.0101 compared to rApi g 1.0201, on clinical expression and cross-reactivity may be clarified in future studies using the 2 recombinant allergens.

Compiled by Dr Harris Steinman, harris@zingsolutions.com

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As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.