Mountain juniper

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Code: t6
Latin name: Juniperus sabinoides
Source material: Pollen
Family: Cupressaceae
Common names: Mountain juniper, Mountain cedar, Ashe juniper

Allergen Exposure

The genus Juniperus is widely distributed in the northern hemisphere. Mountain juniper is native to south-western North America, and is particularly common in Texas. It is found in north-eastern Mexico, and in the United States only as far north and east as southern Missouri. It colonises grasslands and becomes a pest.

Mountain juniper is a drought-tolerant, evergreen large shrub or small tree, growing up to about 6 metres in height. The feathery foliage grows in dense sprays and is bright green in colour. The 2-5 mm-long aromatic leaves are scale-like and produced on rounded shoots.

Mountain juniper flowers in winter (December and January). It is a dioecious species, with male pollens and female flowers occurring on different trees. The seed cones are globose to oblong, 3-6 mm long, soft, pulpy and berry-like; green at first, but becoming purple with maturity at about 8 months after pollination. Most species of juniper produce copious amounts of pollen that can be carried long distances by the wind. Juniper is among the most significant allergenic offenders in the cypress family. Juniper pollen is very buoyant and is smaller and more allergenic than pine pollen. A juniper with berries (a female tree) will not produce pollen.

Mountain juniper occurs in rocky soils in canyons and ravines, and around rim-rocks and breaks, and can live as long as 2 000 years. Its reddish-brown wood makes for long-lasting house exteriors.

Allergen Description

In addition to those in mountain juniper pollen, allergens have been detected in mountain juniper wood and berry. No allergen was detected in the leaves, and no allergen in smoke from burning male and female trees. (1)

The following major allergens have been characterised: 

Jun a 1, a 42 kDa protein, a pectate lyase, previously known as Jun s 1. (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)

Jun a 2, a 43 - 55.7 kDa protein, a polygalacturonase. (2, 15)

Jun a 3, a 30 kDa protein, a thaumatin-like PR-5 protein. (2, 8, 16, 17, 18, 19, 20)

The major mountain juniper allergen, Jun a 1, contains conformational as well as linear IgE epitopes. (2)

Jun a 3, a thaumatin-like protein, is a member of the pathogenesis-related plant protein family. These proteins are modulated by stress, and therefore variable levels of Jun a 3 may be produced and alter the allergenic potency of pollens produced under different environmental conditions. (19)

Potential Cross-Reactivity

A high degree of cross-reactivity could be expected among the different species of the family Cupressaceae, (21) in particular between mountain juniper tree, Italian funeral cypress tree and Arizona cypress tree. (22) But in Europe, juniper (J. communis) seldom causes sensitisation in atopic individuals.

Twelve Cupressaceae (including mountain juniper) and the Taxodiaceae member Japanese cedar were shown to be extensively cross-reactive. In particular, a mountain juniper major allergen, gp40 (Jun a 1), was shown to be cross-reactive with 40 to 42 kDa proteins of the other Cupressaceae, and with the Japanese cedar major allergen of 46 kDa. (23)

Jun a 1, a major mountain juniper allergen, is highly homologous with the major Japanese cedar allergen Cry j 1 (2, 9, 11, 21, 24) and other cedar major allergens, including Jun v 1 of eastern red cedar. (23) Although Jun a 1 and Jun v 1 are highly homologous and cross-reactive, another pair of allergens, Jun a 3 and Jun v 3, are not cross-reactive. (25, 26) Jun a 1 has an amino acid sequence similar to that of the major allergen Cha o 1 from Japanese cypress (Chamaecyparis obtusa). (2)

Jun a 2, another major allergen of mountain juniper pollen, is highly homologous to Cry j 2 (70.7 %) and Cha o 2 (82.0%), major allergens of Japanese cedar tree (Cryptomeria japonica) and Japanese cypress tree (Chamaecyparis obtuse) pollen respectively. IgE antibodies in sera of Japanese pollinosis patients bind not only to Cry j 2 and Cha o 2, but also to Jun a 2, strongly suggesting that Jun a 2 is an allergen of mountain cedar pollen and that allergenic epitopes of these 3 proteins are similar. (15)

Jun a 3, a thaumatin-like pathogenesis-related protein (PR-5), has a high homology with Cup a 3 from Arizona cypress tree. (27) Jun a 3 has also been shown to be closely related to a thaumatin-like protein in banana. (16, 28) In vitro cross-reactivity has been reported between Jun a 3 and thaumatin-like proteins in cherry (Pru av 2), apple (Mal d 2), and paprika or bell pepper (P23) and therefore sensitisation to Jun a 3 may result in symptoms of oral allergy syndrome in patients sensitised to mountain cedar tree (Jun a 3). (29, 30)

Osmotin protein is present in apple, tomato, peach, capsicum, kiwi fruit, and cypress. Osmotin has been shown to be resistant to digestion and heat treatment at 90°C for 1 hour. Osmotin has been shown to have significant IgE binding with sera of 22 of 117 patients sensitised to tomato and apple, thus indicating cross-reactivity among tomato, apple, and osmotin allergens. Further analysis demonstrated osmotin amino acid identity (75%) with kiwifruit allergen Act d 2, followed by Jun a 3 (64%) and Cry j 3.8 (63%) of Cryptomeria japonica. (31, 32)

Pollen allergens such as Hor v 4, Jun a 2, Pla a 2, Cry j 2, Bet v 7, and Tri a 25 have been reported to have homologues in fungi. This raises the interesting possibility that pollen and fungal allergens could cross-sensitise in a synergistic manner, giving rise to the complex interactions observed in thunderstorm asthma. (33)

Clinical Experience

IgE mediated reactions

Mountain juniper pollen causes asthma, hay fever and allergic conjunctivitis, in particular during winter months. (34, 35, 36, 37) Mountain juniper is the leading cause of respiratory allergy in South Texas, (23) and is also a significant aeroallergen in Tulsa, Oklahoma. (38) Sensitisation to mountain juniper may also result in symptoms of oral allergy syndrome. (29, 30)

In Tulsa, the pollen has been recorded during December and January over the past 20 years; the nearest upwind sources for this pollen are tree populations growing in southern Oklahoma and central Texas, at distances of 200 km and 600 km respectively. Researchers have argued that long-distance dispersal of J. ashei pollen into the Tulsa area showed a strong correlation with the trajectories of winds blowing across southern populations before travelling north towards eastern Oklahoma. (39) As individuals allergic to mountain juniper are often allergic to the close relative J. virginiana (eastern red cedar), the allergy symptoms starting in the winter may extend into spring, since the pollination of J. virginiana follows that of J. ashei.

In central Texas, where pollen from this tree causes severe respiratory tract allergy during the winter months, 34% of 234 unselected mountain juniper-allergic patients were found to be allergic only to mountain juniper, while 66% were allergic to mountain juniper and other aeroallergens. Sensitised individuals appear to require much longer exposure to juniper pollen before developing mountain juniper pollen allergy, and they develop allergic disease at a later age (39 years, on average) when compared to patients with multiple allergies. Significantly, the authors noted that many of the mountain juniper-allergic patients who had only allergic rhinitis were sensitive only to mountain juniper pollen. The authors suggested that mountain juniper pollen may be unique in causing allergic rhinitis in patients who have no other sensitivities. (30, 40) The authors suggested also that a possible explanation may lie in the carbohydrate nature of the main allergen of mountain juniper pollen, which may facilitate allergen transport through the respiratory tract mucosa and subsequent sensitisation. (33)

Aeroallergen sensitisation may occur at an earlier age than previously noted. A study attempting to identify which pollens cause early sensitisation in young children presenting with rhinitis symptoms investigated skin-test results of 2- to 8-year-old patients in Reno, Nevada, USA. Patients were tested to aeroallergens common to the Great Basin. Of 123 children less than 8 years of age, over 50% were sensitised to at least one aeroallergen. Chemopodaciae, Timothy grass, alfalfa, black walnut, olive, mountain cedar and willow were predominating sensitising aeroallergens, and these differed from those which had been predominately reported in other regions of the United States. Sensitisation to birch, cedar, mulberry, and maple was present in young children. Approximately 50% of children tested were sensitised to mountain cedar. (41)

A Texas study compared serum-specific IgE testing with skin-prick testing for 53 inhalant allergens using subjects > or = 18 years old, with chronic rhinitis, and who had at least 1 positive skin-test to a 53-inhalant allergen panel. For mountain cedar, 50% were positive by skin-prick testing, compared to 54% by serum-specific IgE. (42)

A number of studies in Mexico have examined the prevalence of sensitisation to allergens, including mountain cedar. In 181 atopic asthmatic adults, 12% were sensitised, with a male predominance of 19% compared to 9% of females. (43) In a study evaluating the prevalence of sensitisation to Ficus benjamina (weeping fig) on 89 patients with persistent moderate-severe allergic rhinitis, 10% were sensitised to Ficus benjamina and 35% to mountain cedar (J. sabinoide). (44) In a skin-prick test study conducted in Guadalajara metropolitan area of Mexico on 965 patients aged 16 to 78 years with allergic rhinitis, of which 78% had positive skin-prick tests, the most frequent outdoor allergens were Quercus sp. and Fraxinus sp. Of 752 patients 11% were sensitised to Juniperus sp. (45)

A study in Mashhad City, the second-largest city in Iran, with a semi-arid climate, evaluated the prevalence of positive skin-test to various common aeroallergens among 311 allergic rhinitis patients. Skin-prick tests were performed with 27 common regional aeroallergens. The overall rate of sensitisation to any allergen was 81%. Seventy-six per cent of patients were polysensitised, and weed and grass were the most prevalent allergens (77% and 62% respectively). Salsola kali was the most prevalent allergen (73%), with 17% being sensitised to juniper. (46)

Immunotherapy has been successfully applied in mountain juniper-allergic individuals, with evidence that extract with a high Jun a 1 content may significantly reduce nasal steroid consumption in patients allergic to European cypress. (47, 48)

Compiled by Dr Harris Steinman,


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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.