f84 Kiwi

Kiwifruit (Actinidia deliciosa) is a woody, climbing, and dioecious vine. The fruit is ovoid, contains green edible flesh, which is partly transparent, has black colored seeds and has a hairy outer cover of brown color. The leaves are large, 7.5-12.5 cm long, deep green, leathery, ovate, alternate, long-petioled, deciduous, and cordate at the base. The fruit tastes sweet, tart to acidic. It grows well in volcanic or drained soil. The plant bears fruit after 1 year and continues till 3 years, after which the rate of bearing fruits decreases.

The origin of kiwifruit is China. Presently, this fruit is cultivated and commercialized from China, Spain, Europe, Italy, New Zealand, , France, United States, India, and Australia. The fruit contains a high amount of vitamin C, E, polyphenols and bioactive compounds. It is also a good source of dietary fiber, protein, calcium, iron, various vitamins like B1, B2, B3, B6, B9, and K.

The severity of symptoms and sensitization patterns of kiwifruit allergy differs geographically. The sensitization is rising in western countries. European countries reported varied kiwifruit sensitization rates. Spain reported 1.8% of its total population being kiwifruit sensitized.

Green kiwifruit has 13 different allergens. Act d 1, Act d 2, Act d 8, Act d 11, and Act d 12 are the major allergens present in it. Patients allergic to kiwifruit should avoid ingestion at any cost. However, kiwifruit is consumed as kiwifruit juice, vinegar, dried slices, jam, wine, yogurt, and jelly.

Kiwifruit allergy is not a homogeneous disorder. Consumption of kiwifruit may lead to mild symptoms of hypersensitive reactions, oral allergy syndrome (OAS), and cross-reactivity with other fruits and pollens.

Tissue

Kiwifruit contains a high quantity of ascorbic acid (420 mg/100 g kiwifruit) and flavonoids. It also contains high levels of vitamin E and various minerals. It contains the cysteine protease actinidin and numerous rare proteins. It is also a natural source of carotenoids (e.g. provitamin A beta-carotene, lutein, and zeaxanthin) (4, 5). 

Worldwide distribution

Kiwifruit belonging to the genus Actinidia is a dioecious plant and is widely distributed in the Asian continent. Sensitization to kiwifruit has been a rising incidence in the western population and Europe reports different allergen sensitization patterns. (6). Denmark reports kiwifruit sensitization for Oral allergy syndrome (OAS) (3). A cross-sectional study based on questionnaire responses in Sweden showed that out of 32% of food hypersensitivity, 7.3% was due to kiwifruit sensitization (7). Similarly, Spain reported 1.8% of the total population being kiwifruit sensitized (8). A high quantity of sensitization to kiwifruit is found in other European countries such as Switzerland, the Netherlands, Poland, and Lithuania(9). Phase 1 of the EuroPrevall study conducted in 8 European countries, reported the prevalence of kiwifruit allergen and peach allergen to be the important causative allergen in most countries but predominantly in Madrid (9).

The severity of allergic symptoms and sensitization patterns of kiwifruit allergy varies geographically. The birch-free Mediterranean region reports more severe symptoms in sensitized patients than in central Europe (6). Sensitization to kiwifruit in the Mediterranean is because of primary sensitization, and partially due to lipid transfer protein (9). 

Risk factors

Ingestion of kiwifruit in any form is risky for kiwifruit sensitized patients (8). 

Pediatric issues

A multicenter case series observational study in Japan reported kiwifruit as one of the most common allergens in children (41.7%) of Japan (10).

A study including 182 children in France, reported 9% of the population is hypersensitive to kiwifruit (8). 

Living environment

The plant requires a warm, humid climate and drained soil for proper growth (1). The fresh kiwifruit degrades quickly (short shelf life) due to tissue softening and senescence (8). It is a polymorphic plant that is comprised of many varieties (6).

Worldwide distribution

Kiwifruit is cultivated commercially. It was introduced in New Zealand in the 19^th century but is native to China. China produces more than 50% of the world’s total kiwifruit production, thereby being the largest producer of kiwifruit. Mostly cultivated in the mountainous area upstream of the Yangtze River (1, 5).

Shaanxi province is the largest kiwifruit producing area in China (8). Apart from being consumed as fresh fruit, it is also consumed as juice, vinegar, dried slices, jam, wine, yogurt, and jelly (5).

It is grown in Italy, India, New Zealand, France, Greece, Japan and the United States, Japan, and north into southeastern Siberia (1, 4).

Commercially, it is cultivated in New Zealand, California, Italy, South Africa and Chile (1). 

Main

Exposure to Kiwifruit causes oral allergy syndrome

Direct sensitization by food allergens may only take place via the oral route (6). 

Secondary

The entry of food allergens causes cross-reactivity

Pollen–food cross-reactivity leads to IgE production. The symptoms may vary from being mild and localized to severe and systemic reactions, particularly in young children (6).

Environmental source

Kiwifruit originated in China. Presently, kiwifruits are produced worldwide in countries including China, Spain, Europe, Italy, New Zealand, , France, United States, India and Australia. Pathogenesis-related (PR-10), thaumatin-like proteins (TLPs), non-specific lipid transfer protein (nsLTPs), and profilins are four main kiwifruit allergen that induces allergic reactions (8).

Other diseases

Evidence has been provided that kiwifruit allergy is not a homogeneous disorder (6, 11). A study reported 62% of kiwifruit-allergic volunteers developing OAS, and 38% developing systemic allergenic reactions after kiwifruit consumption (8).

Consumption of kiwifruit sometimes leads to swelling, itching of the mouth, lips, tongue, and/or throat, basically leading to OAS (12). A survey conducted in a hospital reported kiwifruit as the cause of OAS in 25% of respondents (12). Clinical symptoms are restricted to the oral cavity. A study stated that the consumption of kiwifruit causes OAS in 35% of patients with Baker’s asthma (13).

Allergen immunotherapy

Allergen-immunotherapy focuses on increasing the level of tolerance to allergens of kiwifruit. This therapy slowly increases the quantity of the responsible allergens ingested by allergic patients. However, currently, there is no such immunotherapy available for kiwifruit allergy (8). Antihistamines and epinephrine injection can be given to patients depending upon the severity of symptoms (8).

Prevention strategies

Avoidance

People allergic to kiwifruit should completely avoid ingestion of kiwifruit in any form be it direct or indirect. Avoidance is difficult and confounding as cross-sensitization to potential allergens vary from patient to patient.  Kiwifruit has multiple allergenic proteins that potentially cross-react with different foods. However, sensitization to all potential allergens in kiwifruit is rare. Hence, one patient might only need to avoid fresh kiwifruit and others might need to avoid kiwifruit as well as all foods having cross-reactivity with kiwifruit (8).

One should always cross-check the ingredients added in various food products to avoid any risk (8). Modification of secondary and tertiary structures of conformational epitopes of some kiwifruit allergens by heating (for example by steam cooking, boiling, etc.) or enzymatic hydrolysis results in the loss of the potential IgE binding sites of these allergens. This prevents the triggering of allergic symptoms, thereby decreases kiwi fruit sensitization in kiwifruit allergic individuals (8).

Allergenic molecules

The following allergens have been characterized: (3, 14)

• Act d 1, is a 30 kDa protein, also known as actinidin, and belongs to the cysteine protease protein family.
• Act d 2, is a 24 kDa thaumatin-like protein.
• Act d 3, is a 40 kDa protein.
• Act d 4, is an 11 kDa protein, a phytocystatin, a cysteine protease inhibitor.
• Act d 5, also known as kiwellin, is a 28 kDa protein.
• Act d 6, a pectin methylesterase inhibitor, is an 18kDa protein.
• Act d 7, is a 50 kDa protein, a pectin methylesterase.
• Act d 8, a Bet v 1 homologue, Pathogenesis-related protein (PR-10), is a 17 kDa protein
• Act d 9, a profilin, is a 14 kDa protein.
• Act d 10, a lipid transfer protein, is 10 kDa.
• Act d 11, major latex protein/ripening-related protein (MLP/RRP), Bet v 1 family member, is a 17 kDa protein.
• Act d 12, cupin, 11S globulin, 50,207.304 Da (mass spectrometry), 6 peptide sequences.
• Act d 13, 2S albumin, 11,359,6 Da (mass spectrometry), 4 peptide sequences.

Green kiwifruit has 13 different allergens, and among these the “major allergens” allergens are Act d 1, Act d 2, Act d 8, Act d 11, and Act d 12 (8). Act d 1 is the major allergen present in kiwifruit. Other allergens are Act d 3, Act d 5, Act d 2 and Act d 4. The major cross-reactive components are Class I chitinases with an N-terminal hevein-like domain and latex hevein (3). 

Biomarkers of severity

Kiwifruit post-consumption allergy leads to an unusual immune reaction. Specific antibodies are released which activates the high-affinity IgE receptors on the surface of mast cells (8).

The severity of symptoms depends upon the route of sensitization. Patients sensitized directly to kiwifruit has the highest risk of life-threatening anaphylactic reactions (8). 

Cross-reactivity

Around 20% of the latex-fruit syndrome is based on the association of kiwifruit and latex allergy that affects up to 50% of latex-allergic patients (6). Cross-reactivity may occur with avocado, banana, peanut, and tree nuts (15). The reason is structural similarities of proteins from different sources (6).

Bet v 1, a PR-10 and the profilins are the major allergens involved for kiwifruit sensitization. Act d 8, Act c 8 and Act d 11 are the two Bet v 1 homologues identified in green and gold species of kiwifruit. Act d 9 is the profilin present in green kiwifruit (6). Pollen allergy patients often report oral allergy syndrome after consuming some fruits, nuts and vegetables. This pollen–food cross-reactive IgE antibodies have mild symptoms such as OAS. (6). A cohort study reported 39% of peanut-allergic patients also being sensitized to kiwifruit allergen (16).

Act d 8 belongs to PR-10 family of protein which greatly resembles the proteins found in cherry (Pru av 1), apricot (Pru ar 1), tomato (Sol al 4), pear (Pyr c 1), strawberry (Fra a 1), peach (Pru p 1), apple (Mal d 1), carrot (Dau c 1), celery (Api g 1), birch pollen (Bet v 1), and beech pollen (Fag s 1). Following four amino acid sequences: FKAFVLD, LEGDGGVGTIK, TFGEGS, and VKHRIDG are present in the allergens of these fruits and resemble kiwifruit allergen (8).

Kiwifruit has many allergenic proteins and potential cross-reactive allergens. Sensitization to all of them is unusual, hence one patient might be sensitized just to kiwifruit and other to all the potential allergens along with kiwifruit (8). 

Author: Turacoz Healthcare Solutions

Reviewer: Dr. Fabio Iachetti

Last reviewed: October  2020