Japanese cedar

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Code: t17
Latin name: Cupressus japonica
Source material: Pollen
Family: Cupressaceae (old tax. Taxodiaceae)
Common names: Japanese cedar, Sugi tree (Japanese)

Synonym: Cupressus japonica

Japanese cedar tree should not be confused with the incense-cedar tree (Libocedrus decurrens) or with cedar trees of the genus Cedrus.

Allergen Exposure

Japanese cedar, also called sugi tree, is an evergreen growing 30 to 50 metres tall. Its needles shift from a pale opal in the summer to a bright red towards autumn.

Japanese cedar is native to Japan and the coastal provinces of China, and is often cultivated in Europe and North America.

The male Japanese cedar tree flowers between February and April. However, Japanese children born during the winter months of November to January and exposed to Japanese cedar pollen within the first 6 months of life demonstrated an increased risk of sensitisation (and of especially severe sensitisation) to this pollen, as determined by IgE antibodies. (1) As male sugi flowers disperse a small amount of pollen in early January, some Japanese cedar pollinosis patients will experience allergic symptoms as early as January. (2)

Japanese cedar grows in woods, often in pure stands, favouring rich, deep soils in places sheltered from strong winds. It is the most important timber tree in Japan, where about a third of the area under cultivation is devoted to it.

Allergen Description

Thirty-one C. japonica pollen allergenic proteins have been identified which show higher IgE-binding frequency than that of the previously characterised Cry j 2. (3) In addition to these and the allergens characterised to date, a number of other antigenic proteins have been isolated but not characterised, including proteins of 7, 15 and 20 kDa. (4)

The following allergens have been characterised:

Cry j 1, a 45-50 kDa protein, a pectate lyase, a major allergen. (5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)

Cry j 2, a polygalacturonase, a major allergen. (4, 19, 20, 21, 22, 23, 24)

Cry j 3, a 27 kDa protein, a thaumatin, a PR-5 protein. (25, 26, 27, 28)

Cry j 4, a calcium-binding protein. (29)

Cry j IFR, an isoflavone reductase. (27, 30)

Cry j Chitinase, a class IV chitinase. (27, 31)

Cry j Asp, an aspartic protease. (3, 32)

Cry j LTP, also known as CJP-8, a lipid transfer protein. (33)

Cry j CPA9, a serine protease. (3)

Cry j 1 and Cry j 2 are major allergens. However, concentrations of these allergens vary greatly in pollen from different individual Japanese cedar trees. (19) Most basically, there are 2 varieties of Japanese cedar trees: the popular diploid and the less popular triploid. These trees are not very different morphologically. In a comparison of the major allergens Cry j 1 and Cry j 2, the triploid tree pollen extract was shown to have lower concentrations of both. The pollen from this variety may thus be less allergenic. (34)

The IgE-binding frequency of Cry j 3 in the sera of patients allergic to Japanese cedar pollen was estimated at 27% (27/100). Cry j 3 may play a crucial role in cross-reactivity and oral allergy syndrome. (24)

Cry j IFR, an isoflavone reductase-like protein, has similarity to the birch pollen allergen Bet v 6 (previously known as Bet v 5). However, in contrast to Bet v 6, which has been reported to be a minor allergen, recombinant Cry j IFR exhibited 76% IgE binding frequency (19/25) in Japanese cedar pollen-allergic patients. (29)

A class IV chitinase has been isolated from Japanese cedar pollen. The purified protein displayed the ability to bind IgE from all patients tested (31/31). (30)

Cry j CPA9, a serine protease shows a significant sequence identity with plant subtilisin-like serine protease family members, including melon major allergen Cuc m 1; and shows a high IgE-binding frequency (88.5% of 26 subjects), and IgE cross-reactivity with melon extract.  (3)

Potential Cross-Reactivity

Japanese cedar (Cry j 1) has been shown to be very similar to the major allergens of mountain cedar (Jun a 1), Japanese cypress (Cha o 1) and Cupressus arizonica (Cup a 1), and this is thought to throw light on the cross-reactivity of conifer pollens. (35, 36, 37) These results have been confirmed by specific IgE inhibition assays.

In Japan, many patients with pollinosis have IgE antibodies to pollen of both Japanese cypress and Japanese cedar. The sequences of Cha o 1 and Cry j 1, the major allergens of Japanese cypress and Japanese cedar pollens, respectively, are 80% identical. (7) The presence of both T cells reactive to T cell epitopes common to Cha o 1 and Cry j 1, and T cells specific to T cell epitopes unique to Cha o 1 in patients with pollinosis, contributes to symptoms continuing after the cedar pollen season in March and into the cypress pollen season in April. (38)

Jun a 1 is a glycoprotein highly homologous with Japanese cedar pollen glycoallergen Cry j 1. (10)

Since it is unlikely that many patients in the United States were sensitised through Japanese cedar, they were probably sensitised with similar tree pollen allergens such as Cup s 1 and Jun a 1, which cross-reacted with Cry j 1. A study investigated human IgE epitopes of Cry j 1 and succeeded in identifying a common linear epitope. (39)

Cry j 2, a polygalacturonase, has a high sequence identity with Cha o 2 from Japanese cypress tree. (40, 41) Data suggests that conserved homologues of Cry j 2 confer cross-allergenicity among Taxodiaceae and Cupressaceae. (20)

Japanese cedar pollinosis is one of the most widespread diseases in Japan. Cross-reactivity between Japanese cedar pollen and tomato fruit was demonstrated through inhibition studies. (42) A potential allergen responsible may be Cry j 2, a polygalacturonase, which has a 40% identity with the polygalacturonase from tomatoes.

A class IV chitinase was isolated from Japanese cedar pollen. It may result in various degrees of cross-reactivity with other plants containing this allergen, e.g. latex. (30)

The lipid transfer protein (LTP) allergen (CJP-8) also cross-reacts with other LTP allergens from peach (Pru p 3) and Parietaria judaica pollen (Par j 1). (33)

The IFR allergen (CJP-6) is homologous to birch pollen allergen Bet v 5 (43) and pear allergen Pyr c 5. (30, cited in 3)

Cross-reactivity has also been demonstrated between the pollen of Cupressus sempervirens (Italian funeral cypress tree t23) and that of Japanese cedar. (44)

Clinical Experience

IgE mediated reactions

Japanese cedar pollen is the most common allergen causing seasonal pollen allergy in Japan. (45, 46, 47, 48, 49, 50, 51) It is the most common cause of seasonal allergic rhinitis (49, 52, 53) and contributes significantly to sinusitis (54) and rhinoconjunctivitis during spring. (55, 56) It is a risk factor for bronchial asthma in Japanese adult asthmatics. (57) Pollen from this tree also affects the severity of atopic dermatitis (58, 59) and is an important factor in oral allergy syndrome. (60, 61)

Population-based surveys in Japan in 2004 yielded a prediction that the prevalence of Japanese cedar pollen allergy among adolescents was 28.7% in metropolitan areas and 24.5% in the general population of urban areas. The prevalence increased 2.6-fold between 1980 and 2000, and the prevalence differed considerably according to age and degree of urbanisation. (62) In a nationwide Japanese epidemiological survey of allergic rhinitis through questionnaires mailed to 9 471 otorhinolaryngologists and their families (17 301 subjects), cedar pollen allergy was found to be 17.3%. The prevalence was higher on the Pacific coast and in the central districts of Japan, compared to districts on the Sea of Japan and the Inland Sea, and the prevalence was lower at both high and low altitudes. Morbidity was highest in the suburbs, followed by urban residential areas and downtown locations. (63) Based on another nationwide survey (conducted shortly after the peak pollen season) of 10 920 subjects from 12 regions in Japan, the estimated prevalence of Japanese cedar pollen allergy was 13.1%. Nasal symptoms were more severe than eye symptoms, and 62.5% of the respondents had severe or moderate interference with daily activities. (64)

In a more recent study in Wakayama Prefecture in Japan, among 759 first-year university students the prevalence of various allergic diseases was found to be 37.9%. The prevalence of rhinitis, including pollinosis, was 31.0%, while that of atopic dermatitis was 26.2% and that of bronchial asthma was 11.3%. The rate for IgE antibodies against Japanese cedar pollen was 48.6%, compared to 44.2%, 29.6%, and 28.9% for Dermatophagoides farinae, Timothy grass and house dust, respectively. (44)

Measurements in the Japanese population of IgE antibodies to Japanese cedar pollen indicate high levels of sensitisation, with a prevalence of 30.9% when a serum level of 0.7 kU/L or higher was considered positive. The prevalence was higher in males and highest in the 20-29 years age group. (65) The number of patients with Japanese cedar pollinosis was reported to be increasing, having extended up to about 15% of the Japanese population. (66, 67)

A study that investigated the prevalence of sensitisation to Japanese cedar pollen in allergic and non-allergic children from infancy to adolescence found that of 243 children with allergic diseases and 137 children without allergic diseases, 47.1% with allergic diseases and 19.9% without allergic diseases had IgE antibodies to Japanese cedar pollen (> or = 2). The youngest child sensitised to this pollen was a 23-month-old boy with atopic dermatitis. The proportion of children who were born from January to March was significantly higher in the Japanese cedar pollen-sensitised group than in the non-sensitised group. (68)

Further studies have confirmed the high rate of sensitisation to this pollen. (69) Among 226 children visiting a Japanese paediatric allergy clinic from 1996 to 1999, 53.1% were sensitised to Japanese cedar pollen, and sensitisation was higher in children aged 12 or more (68.8%). (70)

The highest frequency of Japanese cedar pollen allergy appears to occur among residents living alongside roads with heavy automobile traffic. This has been attributed to the elution of Japanese cedar pollen allergens from pollen grains and their adsorptive concentration onto hydrophobic and hydrophilic substances such as pollution from cars. (71)

Japanese cedar pollen is the most common causative allergen for seasonal allergic rhinitis in Japan. (72) It occurs in spring, causing the typical symptoms of seasonal allergic rhinitis. Furthermore, pollen counts of Japanese cedar are increasing. (73) Significant increases in the sensitisation to Japanese cedar pollen have occurred over the last 30 years, from 12.5% to 54.4% in asthma patients, and from 35.1% to 81.5% in allergic rhinitis patients. (74) A questionnaire-based survey reported that the prevalence of Japanese cedar pollen allergy in patients with adult asthma might be up to 30-50%, suggesting higher rates than those previously reported. Moreover, 30% to 60% of adult asthmatic patients with concomitant pollen allergy have exacerbations of their asthma symptoms during the Japanese cedar pollen season. Japanese cedar pollen was shown to be a trigger factor for worsening asthma. In clinical practice, a number of Japanese patients with asthma are monosensitised to Japanese cedar pollen. (72)

Based on subjective symptoms, it has been documented that as many as 21 to 62% of patients with Japanese cedar pollinosis have pollinosis symptoms before the start of pollen season, but these reports may contain overestimates due to inaccurate diagnosis of Japanese cedar pollinosis. (75, 76) In a study measuring Japanese cedar-specific IgE of stored 15-year-old sera of 88 patients, and comparing the results with those from a similar group of 91 current patients, Japanese cedar-specific IgE of Class 2 or more was demonstrated in 65.9% of the current patient group, compared with 46.6% for the former group. There was no significant difference between these 2 groups for children aged 6 or younger. (77)

Among 76 Japanese children less than 6 years of age with symptoms of asthma and atopic dermatitis, 27.6% had IgE antibodies to Japanese cedar pollen, as measured with ImmunoCAP®. The youngest child was a 1-year-, 8-month-old boy. Of a further 27 children attending the otorhinolaryngology clinic with complaints of rhinorrhoea and/or eye symptoms, cough, snoring, or epistaxis, approximately 40% were found to be sensitised to Japanese cedar and/or Cupressaceae pollen alone. (78)

Other Japanese studies have contributed, suggesting that the prevalence of allergic rhinitis between 20 and 49 years of age had increased by nearly 10% during the 10 years prior to 2009. A study of the prevalence of sensitisation to 7 aeroallergens (n = 1 540) found that 56% were sensitised to Japanese cedar. (79) A survey a year earlier found that the average prevalence of Japanese cedar-pollen allergy in Japan was 26.5%, although there are great regional differences; and a subsequent study that investigated the causes of these regional differences in the 47 prefectures of the original study found that the prevalence of cedar-pollen allergy had the highest correlation with the pollen dispersal period, followed by the correlation with pollen count and relative humidity, in that order. (80)

Japanese cedar pollen is not only a cause of allergic rhinitis, but also of allergic conjunctivitis. Allergic rhinitis can interfere with cognitive function and impair work productivity, and may cause work absences. Authors have suggested that clinicians should pay more attention to ocular symptoms as well as nasal symptoms, and improve patients' quality of life in order to reduce productivity losses. (81) Among patients with allergy-like symptoms seen at an ophthalmology and otolaryngology department in a Japanese hospital in 2001, 134 (87%) had allergic conjunctivitis; and in 2002, the number was 126 (91%). Approximately 22% were shown to have IgE antibodies for Japanese cedar. (82) In another Japanese study evaluating the relationship between IgE antibodies to 12 inhalant allergens and allergic conjunctivitis in autumn and spring, it was found that the highest positive rate was 69%, for Japanese cedar pollen, followed by cypress pollen (59%) in the spring group. (83) A study of rhinoconjunctivitis in 641 patients with allergic rhinitis in Hakodate, Japan, reported that 21% of patients were sensitised to Japanese cedar pollen. (84)

In 267 patients with allergic rhinitis, 73.8% tested positive for Japanese cedar, as determined by specific IgE determination. (85)

In a study, the purified Cedar pollen allergen Cry j1 was instilled in the left eye of 9 patients with Japanese cedar pollinosis who had no nasal or ocular symptoms. The allergen provoked not only ocular symptoms but also nasal symptoms in 77.8% of patients. Symptoms were itching and hyperaemia of the palpebral conjunctiva, and the itching lasted for more than 5 hours. (52)

Japanese cedar pollen plays a role in atopic dermatitis. Among children with atopic dermatitis, a statistically significant correlation was demonstrated between the severity of atopic dermatitis and the presence of Japanese cedar pollen; i.e. those with CP tended to have more severe atopic dermatitis. (43, 86) In a study in the Yokohama region or Japan, of 337 outpatients with skin allergy, specific IgE for Japanese cedar was found in 73.7% (244 cases). (87) Atopy patch testing with Japanese cedar pollen extract was used to investigate patients with atopic dermatitis whose condition is exacerbated by contact with Japanese cedar pollen. In a study of 74 patients with atopic dermatitis and 5 patients with Japanese cedar pollinosis, 21 of the 74 patients (30%) had a history of exacerbation every spring after contact with Japanese cedar. Of these patients, 68% were sensitised to Japanese cedar pollen. The authors suggested that atopy patch-testing with Japanese cedar pollen extract appears to be a useful method for investigating trigger factors for eczematous skin lesions in a subgroup of patients with atopic dermatitis. (55)

Among 97 patients with atopic dermatitis, 48.5% showed aggravation of dermatitis during the pollination season, and 85% of them had Japanese cedar pollinosis. This particular study suggested that some other factors (e.g. Japanese cedar pollen-specific T cells) might play an important role, in addition to Japanese cedar pollen-specific IgE. (88)

A study also suggested that Japanese cedar pollens play an important role in the aggravation of infantile atopic dermatitis in spring, by inducing IL-5 production. (89)

Airborne contact dermatitis after contact with Japanese cedar pollen has also been reported. A scratch-patch test, scratch test and specific IgE were performed in 13 patients with skin symptoms suspected to be of Japanese cedar pollen origin, and 5 patients with Japanese cedar pollinosis. All 13 patients with contact dermatitis showed a positive scratch-patch reaction to Japanese cedar pollen extract, compared to 20% of the patients with Japanese cedar pollinosis but no eruptions. (90)

Oral allergy syndrome may be associated with Japanese cedar tree pollen allergy, but less with Japanese cedar than with orchard grass, short ragweed and alder tree pollen. Furthermore, in Japanese studies of Japanese cedar, childhood oral allergy syndrome does not consistently accompany pollen allergy, compared to the pattern seen in adults. Among the frequent food allergens is kiwi fruit, followed by tomato, orange and melon. (91) In a study of 23 patients with Japanese cedar pollen allergy and oral allergy syndrome, with ages ranging from 5 to 62, the responsible fruits included melon, apple, peach, and kiwi fruit. Most patients with OAS exhibited hypersensitivity to more than 2 foods. Significantly, 13 of 20 patients were shown to have IgE antibodies to apple, whereas 17 patients had no IgE antibodies to melon, and only 2 patients had IgE antibodies to kiwi and 1 patient to peach. The study concluded that evaluation of IgE antibodies to birch pollen and apple may be useful for diagnosing oral allergy syndrome in patients with Japanese cedar pollinosis. (57)

Japanese cedar pollen is also a common sensitising allergen in other areas where the tree is grown. A Korean study reported a 10% sensitisation rate in the urban population and a 1.3% sensitisation rate in the rural population, (92) but variable prevalence has been reported. (93) An earlier Korean study of skin-prick tests for 16 aeroallergens performed on 1 060 subjects from different research centres found the prevalence of atopy to be 52%. Sensitisation to Japanese cedar varied from 16% to 21%. Compared with previous reports, the prevalence of atopy and the sensitisation rates of house dust mite, cedar and outdoor moulds were shown to be increasing. (94)

Importantly, symptoms may persist even after the end of the pollen season. Cry j I was still detected in house dust collected 2 weeks after airborne Japanese cedar pollen had disappeared. The authors postulate that some late symptoms of Japanese cedar pollinosis may have been caused by pollen which had attached to clothes and been brought indoors. (95)

Japanese cedar is a prominent aeroallergen in Japan, and immunotherapy has been of benefit. (96, 97, 98, 99, 100)

Other reactions

A 42-year-old-man with Japanese cedar pollen allergy reported repeatedly experiencing dyspnoea after drinking tomato juice during the Japanese cedar pollen season. Swelling of the oral and nasal mucosa and congestion of the conjunctiva were observed. IgE antibody tests were positive for tomato and Japanese cedar pollen. A challenge test using tomato juice was positive. Common antigenicity was found between tomato and Japanese cedar pollen. The dyspnoea may have reflected the feeling of pharyngeal narrowing. (101)

Compiled by Dr Harris Steinman, harris@allergyadvisor.com


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As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.