f348 Litchi

Food

A food, which may result in allergy symptoms in sensitised individuals.

Allergen Exposure

Litchi is a member of the family Sapindaceae, which also contains 2 related species: rambutan (Nephelium lappaceum) and longan (Euphoira longana). These fruits are similar in appearance and taste.

The litchi tree is native to Southeast Asia, in particular to southern China, where it flourishes, especially along rivers and near the seacoast. It spread initially through other parts of Asia, and in the nineteenth century to the New World. However, China is still the leader in litchi-fruit production.

The litchi tree is a dense, round-topped, slow-growing tree with smooth grey bark, growing (though rarely) up to 14 m high. The leathery leaves are reddish when young, becoming shiny and bright green later. The flowers are abundant, tiny, petal-less, and yellowish-green. The fruit is covered by a leathery rind, which is pink to strawberry-red in colour and rough in texture. The fruit is oval, heart-shaped or nearly round, 2.5 to 5 cm in length and 7 to 12 cm in diameter. The rind separates from the flesh readily. The edible portion or aril is white to translucent, firm and juicy. The flavour is sweet and fragrant. Inside the aril is a single seed that varies considerably in size.

Strictly speaking, these are nuts and not fruits. Their closest non-tropical relatives are the walnut, cashew nut and pistachio nut of the Anacardiaceae family.

Litchis are increasingly well known and available in the West. They are usually eaten fresh, out of the hand. Peeled and pitted, they are often added to fruit cups and fruit salads. They can also serve as garnishes, hors d’oeuvres, and ingredients in a variety of desserts, including sherbet.

Litchis, being low in phenols and non-astringent in all stages of maturity, are canned with the addition of tartaric or citric acid to prevent browning.

They are also occasionally spiced, pickled, or made into sauces, syrups, jams, jellies or wine. The flesh of dried litchis is eaten like raisins. Litchis can also be frozen, but after thawing they spoil quickly. In China, honey from hives near litchi groves is prized.

Litchis and their seeds, and decoctions of the peel, root, bark and flowers, are used in traditional medicine to treat coughing and other throat aliments, intestinal complaints, neuralgia, and tumours. However, the Chinese believe that excessive consumption of raw litchis causes fever and nosebleed.

Allergen Description

Among 7 litchi varieties, no significant differences in allergenicity have been demonstrated. In a study of 38 litchi-allergic patients, 34 were shown to have specific IgE to a 55 kDa allergen. Proteins of 14, 20, 30, 40, 42, and >= 67 kDa were characterised. Significant differences in allergens were detected between the peel and flesh of the litchi. The peel contained 16, 18, 22, 40, 50, 80 and 100 kDa proteins. The pericarp showed a higher allergenic activity. No profilin was found in the peel, but 4 profilins were detected in the aril of the litchi. A sequence homology of 89% between a 40 kDa allergen from the aril and the glyceraldehyde-3-phosphate dehydrogenase from white mustard was demonstrated. The allergens were shown to be very heat-stable. Canned litchi demonstrated stable proteins of 14, 40, 42, 55 and 94 kDa, which remained stable even after a storage time of 12 months. Freezing did not alter the allergens. Only the 14 and 55 kDa allergens were resistant to simulated gastric digestion. While no more bands were visible in the immunoblot, remaining allergic potential could be proven by EAST-inhibition. (1)

In a study of 2 patients, both of them sensitised to Compositae pollen and sunflower seed, who developed anaphylaxis after ingesting litchi for the first time, allergens from litchi, Artemisia pollen and sunflower seed were characterised and protein bands in the 24-70 kDa range isolated in the 3 extracts. A protein band of approximately 70 kDa was recognised by serum IgE antibodies of both patients in litchi, Artemisia pollen and sunflower seed extracts, and was considered to be a possible candidate for cross-reactivity. (2)

The following allergens have been characterised:

Lit c 1, a 16 kDa protein, a profilin (3, 4, 5, 6) (previously known as Lit c 4).

Lit c IFR, a 35 kDa protein, an isoflavone reductase. (7, 8, 9)

Lit c TPI, a triose-phosphate isomerise, a major allergen. (10)

A Bet v 6-related food allergen, a phenylcoumaran benzylic ether reductase (PCBER). (11)

IgE reactivity of recombinant Lit c 1 was shown to bind to serum-specific IgE in 5 out of 15 litchi-allergic patients tested. (6)

Unlike other profilin proteins, Litchi profilin appears to be quite thermostable; skin-specific IgE was detected to pasteurised litchi (90 degrees C for 10-15 minutes). (3)

Lit c TPI bound to specific IgE in 67% of litchi-allergic patients. (10)

An extensive cross-reactivity among the different individual species of the family (litchi, ackee fruit, longan and rambutan) could be expected but has not been documented. (12)

Broad cross-reactivity between litchi fruit and other plants has been reported, and profilin has been identified as the protein responsible. (3) A high degree of cross-reactivity between litchi profilin and birch profilin was found in sera from litchi-allergic patients. (6)

The presence of an isoflavone reductase panallergen may result in cross-reactivity between this fruit and other plants containing this allergen, e.g. birch pollen, mango, apple, pear, orange, banana and carrot. (7, 9)

A homologous allergen to the birch pollen allergen Bet v 6, a phenylcoumaran benzylic ether reductase (PCBER), has been shown to be present in litchi, and may result in cross-reactivity with homologous allergens present in many foods such as apple, peach, orange, strawberry, persimmon, zucchini, and carrot. (11, 13)

Cross-reactivity between litchi, Artemisia pollen and sunflower seed as a result of the presence of a 70 kDa allergen has been suggested. (2)

Cross-reactivity of litchi with latex has been demonstrated through inhibition experiments. (14)

Among birch pollen-allergic individuals, 10-15% have specific IgE to the 35 kDa minor birch pollen allergen, and there is cross-reactivity with proteins of comparable size from litchi, mango, banana, orange, apple, pear and carrot. The 35 kDa protein is immunologically independent of the major birch pollen allergen Bet v 1; IgE binding to a 34 kDa structure, which appears to be a Bet v 1 dimer, has also been observed. (15)

IgE-mediated reactions

Litchi may induce symptoms of food allergy, including anaphylaxis, in sensitised individuals. (4, 16, 17, 18 19, 20) As exotic fruits enter new Western markets, the prevalence of allergy to this fruit is bound to increase, as demonstrated by a study of 38 litchi-allergic patients. (1)

A 12-year-old girl developed swelling of the lips, pruritus, generalised urticaria and dyspnoea 30 minutes after eating a raw litchi. A second event occurred 10 minutes after eating a piece of cake covered with a fruit cocktail, resulting in generalised urticaria and pruritis, rhinoconjunctivitis and dyspnoea. Restlessness, flush, generalised urticaria and inspiratory stridor occurred 50 minutes after eating half a litchi. Skin-specific IgE was detected to raw litchi, and a cellular allergen stimulation test was positive, but specific IgE in serum was – surprisingly – negative to litchi but positive to latex. Cross-reactivity of litchi to latex was shown by inhibition studies. (14)

Anaphylaxis to litchi (2, 4, 18, 19) has been described in a number of reports, including one of a 23-year-old woman with inhalant allergy to pollen from plants of the Compositae family, who experienced an acute episode of severe dyspnoea after eating 2 to 3 fresh litchis. She felt an itching in her mouth and throat a few minutes after eating the fruit. Five minutes later her lips and throat swelled, and she experienced severe dyspnoea. Skin-specific IgE to fresh and tinned litchi (pasteurised at 90 degrees C for 10 to 15 minutes) was found. Serum-specific IgE to litchi was detected. (4) Anaphylaxis was reported in a 21-year-old woman, who developed urticaria, angioedema, swelling of the oral mucosa, and dyspnoea within 10 minutes of eating Litchi on an empty stomach, although she had eaten this fruit many times previously without adverse effects. Skin-specific IgE testing with the fresh fruit and rind was positive. A double-blind oral challenge resulted in urticaria. (18)

A 26-year-old man developed pruritus, generalised urticaria, and severe angioedema of his lips and tongue, followed by dyspnoea, within 15 minutes of ingesting a litchi. Litchi -specific IgE antibodies were not detected, but a basophil activation test (BAT) and a cellular antigen stimulation test (CAST) to litchi were both positive, as was a prick-to-prick test with fresh litchi. The individual also experienced oral allergy syndrome to parsley and was sensitised to mugwort but not to latex or profilin. The authors suggested that mugwort was the allergen responsible for the cross-reactivity, as no sensitisation to latex or profilin could be demonstrated. (19)

A report described 2 patients who developed anaphylaxis after ingesting litchi for the first time. Both had been previously diagnosed with respiratory allergy to Compositae pollen and food allergy to sunflower seed. Both were prick-to-prick test-positive for litchi fruit, Artemisia pollen, sunflower seed, pistachio nut and other pollens. Serum IgE was detected for litchi in 1 individual (0.45 kU/1). Cellular stimulation tests for litchi were positive in both, as well as for Artemisia pollen and sunflower seed. Protein bands in the 24-70 kDa range were isolated in the 3 extracts, with a common 70 kDa recognised in both patients’ serum. (2)

A 33-year-old non-atopic woman was described with multiple episodes of anaphylaxis after ingestion of apple, banana and litchi, fruits belonging to botanically disparate plant families. Five years previously, minutes after eating an apple, she had become breathless and developed widespread wheals, followed by respiratory arrest. Two years later, a similar but milder reaction occurred after she ate a banana, which resulted in extensive whealing, dyspnoea and tongue oedema, but no respiratory arrest. She avoided all fruits for the next 3 years, during which time she was symptom-free. A few months before being investigated, she ate litchi, which resulted in severe urticaria, angioedema of the eyelids and mild wheezing. Prick testing was positive for apple and banana. No obvious cross-reactive mechanisms appeared to be playing a role. (20)

Food-dependent exercise-induced anaphylaxis associated with litchi has been reported. (21)

Contact urticaria was described in a 34-year-old woman, who developed generalised urticaria and angioedema, associated with bronchospasm, shortly after eating litchi. Skin-specific IgE was detected using a scratch test with litchi extract. (22)