Route Of Exposure

The genus Phaseolus includes many varieties of edible Beans. The Green bean, also known as the French bean or Common bean, has a long, slender green pod with small seeds inside. The entire pod is edible. The Wax bean is a pale yellow variety of Green bean. The pods are usually harvested when immature, before the seeds inside have grown too large. When the pods are left on the plant to mature fully, the ripe seeds can then be dried and used as Haricot beans.

The green pods are commonly used as a vegetable. The young leaves can be eaten raw or cooked as a potherb. The green or dried mature pods, or the seeds alone, are diuretic, hypoglycaemic and hypotensive. Ground into flour, the seeds are used as a homeopathic remedy.

Clinical Relevance

Allergen description

No allergens from this plant have yet been fully characterised.

A 32 kDa IgE-binding protein, a class I chitinase closely resembling the major Avocado allergen Prs a 1, has been isolated. This reactive component was strongly induced by ethylene treatment. Immunoblot inhibition assays demonstrated cross-reactivity between the 2 allergens. The purified allergen, designated PvChI, induced positive skin prick test responses in 7 of 8 patients with Latex-fruit allergy. This allergen was completely inactivated by heating.

Green bean probably contains heat-labile and heat-stable allergens. A 35 kDa protein, probably a novel allergen and not a chitinase, was detected in a 20-year-old girl who experienced anaphylaxis to Green bean. She reacted to boiled Green bean, which induced a stronger reaction than raw Green bean. That some allergens are differently sensitive to heat was demonstrated in a second study, in which boiling completely abolished skin reactivity. In 3 women who developed asthma and rhinitis after exposure to raw Green beans, but who tolerated ingestion of cooked Green beans, immunoblots of raw and cooked Green bean extract showed 2 IgE-binding bands with apparent molecular weights of 41.1 and 70.6 kDa. A 47 kDa IgE-binding protein was detected only in raw Green bean extracts.

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 does not occur frequently. In an in vitro study, the specific IgE binding by protein extracts of 11 food legumes was examined by IgE antibody determination and RAST inhibition. Cross-allergenicity was demonstrated to be frequent, and most marked between the extracts of Peanut, Garden pea, Chick pea, and Soybean. However, clinical studies have found that there is little cross-reactivity between members of the legume family.

Nevertheless, legumes are an important ingredient in the Mediterranean diet, and among Spanish children, sensitivity to legumes is the fifth most prevalent food allergy. Lentil and Chick pea are the most frequent causes of allergic reactions to legumes in Spanish children. A high degree of cross-reactivity has been demonstrated among Lentil, Chick pea, Pea and Peanut. Unlike in other populations, in Spanish children this phenomenon implies clinical sensitisation for many. In a study of 39 Spanish children challenged (open or simple blind) with 2 or more legumes, 82% reacted to 2 or more legumes: 43,5% to 3, 25,6% to 2, and 13% to 4 legumes. However, and surprisingly, the legumes White bean and Green bean and Soy were well tolerated by children allergic to other legumes. Therefore the diagnosis of legume allergy should not be based only on allergen specific IgE tests.

PvChI, a class I chitinase closely resembling the major Avocado allergen Prs a 1, was demonstrated through immunoblot inhibition assays to be cross-reactive.

A study investigated the in vitro cross-reactivity of allergens from Mesquite tree pollen (Honey Locust tree; Prosopis juliflora) and Lima bean (Phaseolus limensis/Phaseolus lunatus). Of 110 patients with asthma, rhinitis or both, as evaluated with intradermal skin test, 20 were highly positive to Mesquite pollen extract. Of these, 12 patients showed elevated IgE antibody levels to Mesquite pollen extract alone, and 4 to both Lima bean and pollen extract. Lima bean extract could inhibit IgE binding to Mesquite in a dose-dependent manner. Also, humoral and cellular cross-reactivity was demonstrated. Although cross-reactivity was not investigated between Mesquite and Green bean per se, cross-reactivity may exist between pollen from this tree and other species of Phaseolus.

Clinical Experience

IgE-mediated reactions

As a member of the legume family, the Green bean may often result in symptoms of food allergy. Allergic reactions caused by skin contact or by inhalation of vapor from raw or boiling Green bean have also been reported.

Asthma and rhinitis were reported in 3 women after exposure to raw Green bean (and 1 also when exposed to raw Chard). All women tolerated ingestion of cooked Green beans. Multiple episodes while handling these vegetables for cooking were reported. SPT and serum IgE antibody test were positive. Bronchial challenge tests with these allergens showed positive responses to raw but not cooked Green bean and Chard. Oral food challenges with Green bean (raw and cooked) and Chard were negative in all patients. Similar symptoms were reported in a homemaker, who experienced rhino-conjunctivitis, occupational asthma, and contact urticaria while trimming raw Green beans or inhaling vapour from boiling Green beans. She was able to eat and touch cooked Green beans without any ill effect and showed no reactivity to any other foods. Skin reactivity was detected to an allergen in raw Green beans, but not to boiled Green beans. Rubbing the raw Green bean on the patient's forearm elicited wheals and pruritus within 10 minutes. Bronchial provocation test with both Green bean extracts was positive and immediate. Basophil histamine release test was positive.

In an atopic housewife, rhino-conjunctivitis and acute asthma associated with unrelated family members, Green bean and Swiss Chard, have been reported. Skin tests, histamine release test, IgE antibody determination, and bronchial responses after specific bronchial challenges were positive for both.

Reactions may be severe. Anaphylaxis was described in a 20-year-old girl, which occurred 1 hour after ingestion of Green beans. Her symptoms included gastro-enteritis, generalised urticaria and collapse. SPT demonstrated a greater positivity to boiled Green bean, inducing a stronger reaction than raw Green bean.

A 7-year-old boy developed angioedema associated with inhalation of vapour from cooked White bean. SPT evaluated using a prick-by-prick method with White bean was positive. IgE antibody levels was raised for White bean and a closely related family member, Green bean. The patient developed angioedema after ingestion of cooked White bean.

Recurrent otitis media with effusion was reported to be associated with a variety of foods, including beans, but not specifically Green bean. Due to the close family relationship between these legumes, Green bean may in future be shown to be similarly responsible.

Other reactions

Infantile food protein-induced enterocolitis syndrome (FPIES) is a severe cell-mediated gastrointestinal food hypersensitivity typically provoked by Cow's milk or 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. Occupational contact dermatitis caused by the leaves of Phaseolus plants has been reported in a farmer