Allergen Exposure

The Lupin is a member of the Legume family and the genus Lupinus, which includes 450 species. Four species are of agricultural interest: the White lupin (Lupinus albus), the Blue lupin (Lupinus angustifolius), the Yellow lupin (Lupinus luteus), and Lupinus mutabilis. A sulfur-rich transgenic variety is available for animal feed. Lupin flour is an excellent source of proteins, having a higher content of albumin (55.6%) than globulins (31.5%).

Lupin is cultivated globally, primarily for use as animal feed, but also to be ploughed under as a soil enhancer (1).

The Lupin is an annual growing to 1.2 m by 0.25 m, with conspicuous colourful flowers. It can grow wild, but has been cultivated for at least 2,000 years, probably starting in Egypt. It is a useful spring-sown green manure crop, especially on light soils.

It is important as a stock food. Up to the 1920s, when "Sweet lupin" crops were developed, the seeds required soaking before consumption to remove toxic alkaloids, but the new types are safe to eat without any processing.

The edible seeds (from cultivated varieties of the plant) are employed as a protein-rich vegetable or savoury dish in all of the ways that cooked beans are used. They can also be roasted or ground into a powder and mixed with cereal flours. They have also used as a thickener of food products. Edible oil is obtained from the seed and the roasted seed is used as a coffee substitute. The seed is high in protein. Dried Lupin (usually called "lupini" prepared by boiling Lupin seed, is a traditional snack (like Peanuts) in some Mediterranean countries.

Certain countries, e.g., France, allow Lupin flour to be added to ordinary food such as bread (2).

If the seed is bitter, this is due to the presence of toxic alkaloids, and the seed should be thoroughly leached by soaking it and then discarding the soak water.

The seeds, taken internally, are diuretic, emmenagogue, hypoglycaemic and vermifuge. When bruised and soaked in water, they are used as a poultice on ulcers, etc.

Allergen description

In an individual with allergy to Lupin, important allergenic proteins of 71, 59 and 34 kDa in size, along with less important 24 and 17 kDa proteins, were isolated (4). In another study of 2 individuals with Lupin allergy, strong differences in proteins in extracts of fresh and cooked seeds were demonstrated. Sensitisation to low-molecular-weight bands was demonstrated; a doublet of 9 and 10 kDa was found in raw and cooked seeds and was more clearly represented in skin than in pulp (5). A study reported the isolation of allergens that seemed to be in the 35 kDa to 55 kDa range and heat-stable, with a 21 kDa protein appearing to be a major protein (6).

Another study reported a reduction in allergenicity after autoclaving at 138 °C for 20 minutes. In the case of IgE antibodies from 2 individual sera that had recognised allergenic protein bands at 23 and 29 kDa in samples autoclaved at 138°C for 20 minutes, auto-claving for 30 min abolished the IgE binding to these 2 components. A previously undetected band at 70 kDa was recognised by an individual serum. The authors concluded that prolonged autoclaving might have an important effect on the allergenicity of Lupin for the majority of patients (7).

In a study that sought to identify allergens associated with Lupin allergy, 6 patients with a history of allergic reactions to Lupin flour were evaluated. Two patients allergic to Lupin but not to Peanut displayed IgE binding predominantly to proteins of approximately 66 kDa, and weak binding to 14 and 24 kDa proteins, whereas patients with both Peanut allergy and Lupin allergy showed weak binding to Lupin proteins of about 14 to 21 or 66 kDa (1). Similarly, in a study of 2 patients with oral allergic syndrome following Lupin ingestion, and no symptoms associated with Peanut or other legumes, sera IgE from both patients recognised proteins of approximately 34 kDa and in the 40-65 kDa range. The second patient's serum also recognised 7-15, 38, 77, 162 and 195 kDa proteins (8).

To date, the following allergens have been characterised:

• Lup a 11S Globulin (1,9-11).
• Lup a gamma Conglutin (9-14).
• Lup a beta Conglutin (1,9,11,13-14).
• Lup a Vicilin (1,11).
• Lup a LTP, a lipid transfer protein (15).

A 2S albumin has been isolated (10,16). The 2S albumin fraction appears to consist of a number of isoforms ranging from 4 to 11 kDa (16-17). However, the 2S albumin, unlike 2S albumins from other seeds, may be non-allergenic (10).

Plant stress was shown to activate a class-III chitinase, designated IF3. The protein was detected in the seed, leaves and roots. In healthy, nonstressed tissues of the plant a thaumatin-like protein was also detected, the presence of which researchers could not explain. Whether these proteins also occur in the pollen is unknown (18-19). Proteins that show similarity to PR-10 proteins have also been detected in the leaves (20). Although chitinase and thaumatin proteins have allergenic potential, their clinical significance in this plant has not been elucidated as yet.

A common feature of most legume allergens is their natural resistance to thermal, chemical, and in some ways proteolytic denaturation (21).

In an investigation of "hidden" Lupin seed in biscuits, chicken bouillon and a dehydrated chicken soup, a Lupin allergen with a molecular weight close to 14 kDa was detected (22).

Potential Cross Reactivity

An extensive cross-reactivity among the different individual species of the Fabaceae (legume family) could be expected but in fact does not occur frequently (23-24). In an in vitro study, the IgE 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 (25). However, clinical studies have found little cross-reactivity among members of the legume family, with the possible exception of cross-reactivity between Lupin seed and Peanut (26-27).

In a study of 6 Lupin-allergic individuals, 3 were co-sensitised to Peanut and Lupin (1). But in a study of 2 patients with oral allergic syndrome following Lupin ingestion, investigations supported the conclusion that Lupin is capable of inducing allergic sensitisation without cross-reactivity with Peanut (8). Significantly, individuals may have substantial levels of Peanut-specific IgE without being clinically allergic to Peanut (28).

A study of the legumes Peanut, Soybean, Green bean, Pea, and Lima bean demonstrated that clinical hypersensitivity to one legume does not warrant dietary elimination of all legumes. The authors pointed out that results of SPT should not become the basis of prolonged food restriction diets (26). However, legume sensitisation may be a dynamic process, as described in a patient whose symptoms started with reactions to only a single legume (Chick pea) and who then progressively developed sensitisation to Lentil, White bean, Lupin, and Pea (24).

Cross-allergic clinical reactions to other members of the legume family such as Soybean and Lentils occur in about 5% of Peanut-allergic patients, but cross-allergic reactions were found to be 68% between Peanut and Lupin (26). Among 24 Peanut-allergic patients, SPT to Lupin flour were positive in 11 (44%). Oral challenges with Lupin flour were positive in 7 of 8 subjects with the same dose as of Peanut. The major Lupin flour allergen, a 43 kDa protein, was found to be present in Peanuts. RAST inhibition and immunoblot tests showed cross-reactivity of Peanut with Lupin flour and pollen. The authors felt that the risk of cross-reactive Peanut-Lupin allergy is high, contrary to the risk with other legumes (29). Similar results have been reported by other researchers; one study reported that 68% of a group of Peanut-allergic patients showed positive reactions to Lupin flour when tested (6,30-31). Subjects with positive SPT to Lupin also reported a history of reactions to Green pea (6).

In a study of severe anaphylaxis to Almond, a 45 and a 30 kDa protein isolated from Almond showed a 60% homology to the conglutin gamma protein from Lupin seed and to the 7S globulin from Soybean respectively. Immunoblot inhibition experiments were performed, and IgE binding to Almond 2S albumin and conglutin gamma was detected in the presence of cross-reacting Walnut or Hazel nut antigens (32). The clinical relevance of this finding was not established. There were similar findings in other connections, with 2S albumin from Sunflower seeds being reported to be homologous with albumin from Lupin seeds (conglutin delta) (17). The full clinical significance of these cross-reactions will require further elucidation. However, the 2S albumin, unlike 2S albumins from other seeds, may be non-allergenic (10).

A study using computer-aided amino acid sequence comparison and 3-dimensional modelling of the suspected cross-reactive proteins to compare their molecular surfaces reported highly significant sequence homology and molecular similarity between allergen Ara h 8 of Peanut and pathogenesis-related protein PR-10 of White lupin. Another protein of Lupin, the beta-conglutin precursor, was found to be significantly homologous to the Ara h 1 allergen of Peanut. The molecular surfaces of Ara h 8 and PR-10 were remarkably similar (13). The full clinical significance of this was not elucidated.

Clinical Experience

IgE-mediated reactions

Lupin flour may commonly induce symptoms of food allergy, allergic rhinitis and asthma in sensitised individuals after ingestion of the food or inhalation of the flour (2,7,22,24,33-40). Lupin flour in food has also been reported to produce urticaria and anaphylaxis (24,36,41). Case reports of individuals experiencing oral allergy syndrome to Lupin have been made (1,8,42). Contact urticaria elicited by Lupin has been reported (43-44).

The eliciting dose of Lupin flour may be very small. In a study of 6 Lupin-allergic patients, the eliciting dose for subjective symptoms (oral allergy symptoms) was 3 mg or less, and 300 mg or more for objective symptoms (1).

Lupin allergy may arise either by primary sensitisation, or by clinical cross-reactivity in Peanut-allergic persons (8,28,45). The prevalence of allergic reactions to Lupin flour or seed appears to be increasing along with the practice of adding protein-rich flour to bread. Because Lupin flour has gained favour mainly in Europe, Lupin flour allergy has been reported mainly in European patients. These are known to commonly be allergic to other legumes, particularly Peanut, Soya and Pea (37). The prevalence of Lupin allergy has increased markedly in some countries, especially France, where the addition of Lupin flour to Wheat flour was first permitted in 1997 (2). The first report of Lupin anaphylaxis there was in 1999 (3). In 2002, Lupin was the fourth most frequent cause of severe food-associated anaphylaxis reported to the French Allergy Vigilance Network. Two instances of anaphylaxis resulted from a chocolate drink containing Lupin flour. Both children were also allergic to Peanuts, and the authors attributed these reactions to cross-reactivity mechanisms (36). In a recent Portuguese study aimed at determining the prevalence of Lupin sensitisation in 1,160 subjects and utilising, among other tests, SPT to Lupin, a sensitisation rate of 4.1% was found. A 75% co-sensitisation rate was found between Lupin and legumes, 82.1% co-sensitisation between Lupin and pollen, and 28.5% co-sensitisation between Lupin and Latex (46).

Lupin allergy may also occur in young children (47). A 5-year-old girl with Peanut allergy experienced urticaria and angioedema after ingesting spaghetti-like pasta fortified with Lupin flour (6). In a child who had experienced anaphylaxis to Lupin flour, SPT was positive and in vitro cross-reactivity with other legumes was demonstrated, but this was shown to not be clinically relevant in this instance (24).

An 8-year-old asthmatic child, with allergy to Peanut, suffered an asthma attack while playing with his brother, who had been eating Lupin seed as a snack. SPT was positive to Lupin extract, Peanut, Garbanzo bean, Navy bean, Pea, Green bean, Lentil, Soybean, and a number of pollens. The prick-by-prick tests both from dried seeds and those preserved in salt and water were strongly positive. Serum IgE antibody level to Lupine was 1.43 kUA/l, Peanut 4.32 kUA/l, Soy 2.15 kUA/l, Lentil 3.12 kUA/l and Garbanzo 0.7 kUA/l. A challenge with Lupin seeds resulted in asthma symptoms within 5 minutes of contact (35).

The first reported instance of an anaphylactic reaction caused by the ingestion of Lupin flour was that of a paediatric patient without a known Peanut allergy, an 8-year-old boy who developed nose and eye discharge followed by oedema of the face and difficulty breathing 30 minutes after eating a waffle containing Lupin flour. SPT was positive to Peanut, and a prick to prick test using Lupin flour was strongly positive. The IgE antibody level was raised for Lupin seed (20.8 kUA/l) and Peanuts (> 100 kUA/l) (28).

An interesting report was made of a 30-year-old technician who experienced repeated episodes of rhinitis, conjunctivitis and palpebral angiodema related to her handling of Lupin flour used for skin prick tests and oral challenges. She tolerated Peanuts (4).

Anaphylaxis was described in a 25-year-old Peanut-allergic woman after she ate a restaurant meal. During the meal, she developed pruritus of her mouth and lips, and her tongue started to swell. Fifteen minutes later she had difficulty in breathing and her throat had "narrowed". Lupin was identified as the cause and had been present in the onion ring batter she had consumed. She had not previously had allergic reactions to Lupin. SPT and IgE antibodies to Lupin were positive (37).

A description of 3 individuals who experienced adverse reactions to Lupin highlights potential consequences of Lupin allergy. The first, a 42-year-old woman, developed acute urticaria and angioedema, with throat tightness and cough, after a meal that included a bread roll. A more severe anaphylactic reaction, including marked breathlessness requiring oxygen and adrenaline, had occurred on another occasion following ingestion of the same type of bread roll. Lupin bran was a constituent of these rolls. SPT with saline extracts of the raw Lupin bran and of the baked bread roll were strongly positive, but negative for Soybean and Peanut. A mild generalised reaction followed ingestion of a specialty bread that was later found to contain Lupin bran. A second patient, a 42-year-old woman, was described who had developed acute abdominal discomfort, urticaria, facial oedema, cough and shortness of breath 10-15 minutes after eating a bread roll that contained Lupin bran. SPT was positive to an extract of Lupin bran. The third patient, a 26-year-old woman who had often eaten lupini (boiled and dried Lupin in the form of a snack food), on one occasion, after eating commercially prepared lupini from a jar, developed urticaria, angioedema and respiratory difficulty, requiring hospitalisation. Subsequently, a similar but less severe reaction occurred after she ingested a small portion of home-prepared, boiled and salted lupini. She had also experienced urticaria and angioedema after eating ginger biscuits, which were subsequently found to contain Lupin flour. SPT was strongly positive to a Lupin bran extract, and her IgE antibody level was 12.9 kUA/l (38).

A 24-year-old woman with Peanut allergy experienced acute swelling of the lips, urticaria and rhinoconjunctivitis on 4 separate occasions when eating a certain brand of hot dog bread containing Lupin flour (48).

A male patient reported several episodes of generalised angioedema after ingestion of snacks that included Lupin seeds. SPT was positive for a number of tree nuts as well as Sunflower seed. Skin reactivity was found against Lupin seed (both the skin and the pulp), and IgE antibodies was found to Lupin. The same report also described a female patient who had reported angioedema of the lip and generalised urticaria following ingestion of several Lupin seeds. She had previously eaten this snack on a number of occasions with no adverse effects. Skin reactivity was present for Maize flour, Hazel nut, Peanut, Walnut, Sunflower seed, Chestnut, Green bean, Tomato, Lettuce and Mustard. Skin reactivity was also found for Lupin seed (skin and pulp) and the Lupin IgE antibody level was raised (5).
A 52-year-old woman developed facial and mucosal oedema, followed by dizziness and shortness of breath, a few minutes after ingestion of a nut croissant containing Lupin flour; she required emergency care. The IgE antibody level for Lupin seed was 42.9 kUA/l. SPT using Lupin flour was strongly positive. No evidence of cross-reactivity with Peanut could be detected through in vitro or in vivo tests (49).

Further evidence for the close relationship between Peanut allergy and Lupin allergy was demonstrated in a study of 24 Peanut-allergic patients, in whom SPT for Lupin flour was positive in 11 (44%). Oral challenges using the same dose as used with Peanut were positive in 7 of 8 subjects (29). A study reported acute asthma in a patient with allergy to Peanuts. SPT to raw and cooked Lupin flour was positive. The level of allergen-specific IgE to Lupin flour was high. An oral challenge test induced acute asthma at a dose of 965 mg of Lupin flour, an amount that may be found in 100g of bread (31). Researchers have stated that cases of isolated allergy to Lupin flour, without pre-existence of Peanut allergy as well as workplace asthma by inhalation, are rarely seen (30).

Occupational allergy may occur to Lupin, particularly in mill workers. A study reports on 3 workers who showed allergic symptoms to Lupin flour following inhalation. Skin reactivity to Lupin seed flour extract was present in all 3 patients, and Lupin-specific IgE antibodies were detected in 2 (50)

Other reactions

The seeds of many Lupin species contain bitter-tasting toxic quinolizidine alkaloids, though there are often sweet varieties within the same species that are completely wholesome. The alkaloid profiles are rather constant (51). Taste is a very clear indicator. Lupin seed alkaloids appear to be toxic mainly to animals and non-toxic to humans, although not all researchers are in agreement about this (52). Anticholinergic toxicity associated with the ingestion of lupini beans was reported in a 46-year-old female of Italian descent, who presented with blurry vision, dry mouth, facial flushing, and confusion. Symptoms had begun quite suddenly over the course of about 30 minutes, 3 to 4 hours after ingesting lupini beans. Lupini beans derive their bitter flavour from the high levels of quinolizidine alkaloids they contain and must undergo a de-bittering process of washing with water, a process that normally takes 4 days. (Some authors state that these toxic alkaloids can be leeched out by soaking overnight and discarding the soak water. It may also be necessary to change the water once during cooking.) The patient had soaked her lupini beans for only 36 hours before she ate several handfuls of them (53).

The number, type, and level of alkaloids are highly variable among species. In Southern Europe and the Middle East, high-alkaloid Lupines or “Bitter lupins” are grown. The primary crop cultivated in Australia is low-alkaloid Lupin or “Sweet lupin”. The level of alkaloids remaining in European lupins after the de-bittering process is approximately 500 mg/kg, whereas the level of alkaloids in Sweet lupins is about 130 to 150 mg/kg (53).

Fungal toxins also readily invade the crushed seed and can cause chronic illness, usually in animals. Lupinosis is a mycotoxicosis caused by the ingestion of toxins produced by the fungus Phomopsis leptostromiformis, which grows on Lupine plants. Outbreaks of natural lupinosis may occur in lambs.

Ungerminated legume seeds (broad bean, Chick pea and Lupin) may contain biogenic amines. Tryptamine was the main biogenic amine detected, and its concentration increased considerably during germination. Beta-phenylethylamine was detected in small amounts, and its concentration slowly increased during germination. The concentration of tyramine showed a fluctuation pattern during germination in all tested legumes. Heat treatment seems to have little effect on the concentration of biogenic amines in legume sprouts (54).

A 7-year-old boy was operated on for intestinal obstruction due to a phytobezoar. He had eaten an exceptionally large amount of Lupin seeds a few hours before the onset of pain (55).

Last reviewed: June 2022.