Route Of Exposure

Pea probably originated in south-western Asia, but it spread nearly throughout the world. Green peas are the number-one processed vegetable in the UK and the USA. The plant is an annual, dwarf or climbing, growing as high as 2 m. The Pea is a small, round, smooth or wrinkled seed, growing in pods.

There are many varieties of Pea, some grown to be eaten fresh, others to be used dried. (Dried Peas were the staple food of Europe during the Middle Ages.) Pod Peas are those that are eaten pod and all, namely the Snow pea and Sugar snap pea. Dried Peas are high in carbohydrate and fibre and low in fat, and an economical source of protein.

Green peas are marketed fresh, canned, or frozen. They can be cooked alone as a vegetable or added to other dishes. They can also be sprouted and added to salads, soups, etc. The mature seed may be dried and used whole or split (in which form it is often served as dhal), or ground into a powder and then used to enrich the protein content of flour. Roasted Peas can be a coffee substitute. The leaves and young shoots are cooked as a potherb. Peas, either whole or ground and extruded, are increasingly popular snack items.

Peas are reported to be contraceptive, fungistatic and spermacidal, and are said to have several other medicinal properties. The dried and powdered seed, for example, has been used as a poultice for skin complaints, including acne.

Clinical Relevance

Allergen description

Pea contains a number of allergens, of which a few have been characterised. In a study of 8 patients with adverse reactions after ingestion of foods from the legume family, IgE binding to a Pea 30-33 KDa protein region occurred in 7, and in 4 patients these were the major bands.

The following allergens from this plant have been characterised:

Two isoforms of Pis s 1, Pis s 1.0101 and Pis s 1.0102, have been characterised, and one of Pis s 2, Pis s 2.0101.

Immature Peas have low allergenicity compared to ripe Peas, as there are few storage albumin proteins at this stage. Allergens are expected to be found in the storage proteins. However, all levels of maturation of Green pea seeds show allergenicity and IgE-binding capacity, as do immature seeds, but total IgE-binding capacity rises with the progress of maturation. The highest allergenic potency is caused by the albumin fraction, but globulin and glutelin fractions also contribute to the allergenicity of Green pea.

The globulin storage protein accounts for 75-80% of the total seed protein, and albumin the remainder. The amount depends on the cultivar. Skin reactivity has not been detected to globulin extracts, whereas albumin retained its allergenicity even when heated at 60 °C for 30 minutes or boiled at 100 °C for 5 minutes. Autoclaving at 120 °C for 15 minutes significantly reduced allergenic activity. Although some studies have shown no skin reactivity to the globulin protein, a protein belonging to the vicilin (7S globulin) family has been isolated and may yet be shown to have allergenic potential, as a vicilin from English walnut kernel (Jug r 2) has been shown to be a major allergen. Indeed, in a study of 3 patients with a history of anaphylaxis to Pea who subsequently had symptoms after ingestion of Peanut, immunoblotting studies demonstrated strong IgE binding, mainly to vicilin in Pea extract and exclusively to Ara h 1 in crude Peanut extract. IgE binding to Peanut could be inhibited by Pea but not or only partially the other way around.

A common feature of most legume allergens is their natural resistance to thermal, chemical, and, in some respects, proteolytic denaturation.

Potential Cross Reactivity

An extensive cross-reactivity among the different individual species of the genus could be expected but in fact is not seen frequently. In an in vitro study, the IgE antibody binding to protein extracts of 11 food legumes was examined by IgE antibody determination and RAST inhibition. Cross-allergenicity was demonstrated to be most marked among the extracts of Peanut, Garden pea, Chick pea, and Soybean, and between Pea and Soybean. However, clinical studies have found that there is little cross-reactivity among members of the legume family.

Substantial clinical allergenic cross-reactivity exists among Lentil, Chick pea and Pea in the Mediterranean area, where these legumes are widely consumed, in contrast with the low clinical significance of legume cross-reactions (mainly between Peanut and Soybean) reported in the USA. Allergic reactions to Pea ingestion are frequently associated with Lentil allergy in the Spanish population. Vicilin and convicilin are potential major allergens from Pea seeds, and all of these proteins cross-react with the major Lentil allergen Len c 1, a vicillin.

In a study of Spanish children, evaluation of allergen-specific IgE demonstrated that most of the children were sensitised to more than 1 legume species. That a high degree of cross-reactivity existed among Lentil, Chick pea, Pea and Peanut was shown by inhibition studies. Thirty-nine patients were challenged with 2 or more legumes, and 32 (82%) reacted to 2 or more legumes: 43,5% to 3, 25,6% to 2, and 13% to 4 legumes. Seventy-three per cent of the patients challenged with Lentil and Pea had positive challenge to both, 69,4% to Lentil and Chick pea, 60% to Chick pea, and 64,3% to Lentil, Chick pea and Pea simultaneously. Peanut allergy was associated with allergy to Lentil, Chick pea and Pea, but less frequently. In this study, 82% of the children allergic to legumes were sensitised to pollen. Pea and Bean were the legumes with more in vitro cross-reactivity with Lolium perenne, Olea europea and Betula alba, probably as a result of common antigenic determinants or the coexistence of pollen and legume allergy. Panallergens as the cause seem to be less probable.

It is important to differentiate patients allergic to a legume from those only sensitised. This is demonstrated by a study of 8 patients with adverse reactions after ingestion of foods from the legume family. The majority had experienced symptoms with more than 1 legume (median 3 legumes), but sensitisation to other legumes without clinical symptoms also occurred (medium 5 legumes). Sensitisation and symptoms to 1 legume were observed only in 1 patient. IgE binding to a Pea 30-33 KDa protein region occurred in 7 out of 8 patients, and in 4 patients these were the major bands. Serum IgE to Pea was <0.35 kUA/l in 4 patients. For the Pea sensitised patients, immunoblotting assays with Chick pea and Bean detected numerous IgE binding proteins bands, but no predominant IgE binding pattern could be seen. This study thus demonstrated by in vivo and in vitro tests that most of the patients were sensitised to more than 1 food of the legume family.

In a Spanish study aimed at determining the prevalence of Lupin sensitisation in 1,160 subjects, using SPT evaluation, a 4,1% sensitisation rate (28 patients) was found, with a 75% co-sensitisation between Lupin and other legumes. Of the 28 patients, 7 were SPT positive to at least 1 legume: 9 to Fava bean, 8 to Soy, 13 to Chick pea, 8 to Pea, 12 to Peanut, 13 to Bean, 7 to Lentil (but 18 were not tested), 23 to at least 1 Pollen, 14 to grasses, 11 to Birch pollen, 15 to Mugwort, 10 to Olive and 8 to Latex.

An early study reported that the Ara h 1 from Peanut has significant homology of 60% to 65% with the vicilin seed storage protein found in Pea, and that there is homology of vicillin in most higher plants. In a more recent study of 3 patients with a history of anaphylaxis to Pea who subsequently had symptoms after ingestion of Peanut, immunoblotting revealed strong IgE binding, mainly to vicilin in Pea extract and exclusively to Ara h 1 in crude Peanut extract. Immunoblot and ELISA inhibition studies with crude extracts, as well as with purified proteins, showed that IgE binding to Peanut could be inhibited by Pea but not or only partially the other way around. Clinically relevant cross-reactivity between Pea and Peanut did not occur. Vicilin homologues in Pea and Peanut (Ara h 1) were thought to be the molecular basis for this cross-reactivity. Tri f 1 from Fenugreek is a vicilin-like globulin and has been shown to be similar to vicilins from Soy, Pea, Bean, Lentil, Chick pea, and Lupin, which all cross-reacted serologically with the IgE antibodies from Peanut allergic patients.

Ana o 1 from Cashew has a 52-62% similarity to proteins found in African oil palm, Macadamia nut, Pea, Soybean and English walnut. These proteins have been variously described as vicilin-like protein pre-cursors, sucrose-binding proteins and precursors, and 7S globulins.

The Soybean glycinin G1 acidic chain shares IgE epitopes with Peanut Ara h 3. The glycinins in Ara h 3, Soybean, and Pea have a sequence similarity of 62% to 72%.

The isoflavone reductase allergen detected in Pea has a 56-80% sequence identity with IFR homologue proteins from various plants, e.g., Birch, Apple, Pear, Orange, Mango, Litchi, Carrot, Banana, and Chick pea.

An association between grass pollinosis and sensitisation to Tomato, Potato, Pea, Peanut, Watermelon, Melon, Apple, Orange and Kiwi has been reported. A considerably high frequency of positive reactions to Tomato (39.2%), Peanut (22,5%), Pea (13.7%), and Wheat (11.7%) was observed in children with allergy to grass pollen.

Clinical Experience

IgE-mediated reactions

Legumes are among the most common foods causing allergic reactions in children and adults. Pea, a legume, may commonly induce symptoms of food allergy in sensitised individuals, and IgE antibodies to Pea have been detected in sensitised individuals. Symptoms reported include atopic dermatitis, asthma, rhinitis, angioedema, dermatitis, oral pruritis, nausea, vomiting, and diarrhoea.

In a study of 8 Spanish patients with adverse reactions after ingestion of foods from the legume family, the majority experienced symptoms with more than 1 legume (median 3 legumes), but sensitisation to other legumes without clinical symptoms also occurred (medium 5 legumes). Sensitisation and symptoms to 1 legume were observed only in 1 patient. The symptoms were urticaria; oral allergy syndrome; anaphylaxis; angioedema and asthma. Significantly, although IgE binding to a Pea protein occurred in 7 out of 8 patients, and in 4 patients these were the major bands. Serum IgE antibodies to Pea were <0.35 KUA/l in 4 patients. This study concluded that, according to in vivo and in vitro tests, most of these patients were sensitised to more than 1 food of the legume family. It is important, however, to differentiate patients allergic to a legume from those who are only sensitised. In the Mediterranean, where legume ingestion is high, clinical allergy is more common than in other Western countries such as the USA, where sensitisation may occur alone.

In this study in Delhi, the relevance of serum total and Pea-specific IgE were investigated in 216 asthmatics with food sensitisation. SPT was positive to Pea in 13. Food-induced anaphylaxis to Pea has been reported. Anaphylaxis to Pea has been reported in 3 patients who sub-sequently had symptoms after ingestion of Peanut. Although these patients were also affected by Peanut, clinically relevant cross-reactivity between Pea and Peanut did occur. Similarly, 5 patients with Peanut sensitivity had a history of adverse reactions to Pea.

A study reported on a 33-year-old woman who developed tongue swelling and burning and mouth itching minutes after eating baked beans. Similar symptoms occurred a day after ingesting Pea soup, and on another occasion within 15 minutes after eating a Bean burrito, and again 20 minutes after eating chilli containing Kidney and Pinto beans. SPT was positive to Red kidney and White bean but negative to Pea, Green and Lima beans. However, IgE antibodies were found to Pea, Red kidney, White and Pinto bean, and to Chick pea and Black-eyed pea.

In a study of 99 children with atopic dermatitis, Egg was the most common food allergen in children under 1 year of age. After that age, Apple, Carrot, Pea, and Soybean elicited positive reactions as often as Egg.

Pea has resulted in asthma following exposure to the cooking vapours. Occupational asthma has also been reported following exposure to Pea flour.

Other reactions

Infantile food protein-induced enterocolitis syndrome (FPIES) is a severe cell-mediated gastrointestinal food hypersensitivity typically provoked by Cow's milk and Soy. A study reported on other foods causing this syndrome: 14 infants with FPIES caused by grains (Rice, Oat, and Barley), vegetables (Sweet potato, Squash, String beans, Pea), or poultry (Chicken and Turkey) were identified. Typical symptoms of FPIES are delayed (median: 2 hours) and include vomiting, diarrhoea, and lethargy/dehydration. Eleven infants (78%) reacted to >1 food protein, including 7 (50%) who reacted to >1 grain. Nine (64%) of all patients with solid food FPIES also had Cow's milk and/or Soy FPIES. Initial presentation was severe in 79% of the patients, prompting sepsis evaluations (57%) and hospitalisation (64%) for dehydration or shock. None of the patients developed FPIES to maternally ingested foods while breastfeeding, unless the causal food was fed directly to the infant. Similarly, 6 patients (4 males, 2 females, aged 3-12 months) were diagnosed with FPIES triggered by foods other than Cow's milk and Soy: Chicken in 4, Turkey in 2, Pea in 1, and Lentils in 1. (Five patients reacted to more than 1 food type.) All reactions developed within 2 hours of ingestion of the allergenic food.