t6 Mountain juniper

Allergens within Tree Pollens

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

Synonym:  J. ashei

Allergen Exposure


Geographical distribution
The genus Juniperus is widely distributed in the Northern Hemisphere. Mountain juniper is native to southwestern North America and is particularly common in Texas. It is found in northeastern 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, 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.

Environment
It 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 exteriors.

Allergens
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 (2-13).
  • Jun a 2, a 43 kDa protein, a polygalacturonase (2,14).
  • Jun a 3, a 30 kDa protein, a thaumatin-like PR-5 protein (2,8,15-19).

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 (18).

Potential cross-reactivity

A high degree of cross-reactivity could be expected among the different species of the family Cupressaceae (20), in particular among Mountain juniper tree, Italian funeral cypress tree and Arizona cypress tree (21). 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 (22).

Jun a 1, a major Mountain juniper allergen, is highly homologous with the major Japanese cedar allergen Cry j 1 (2,9,11,20,23) and other Cedar major allergens including Jun v 1 of eastern red cedar (22). 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 (24-25). 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 (14).

Jun a 3, a thaumatin-like pathogenesis-related protein (PR-5), has a high homology with Cup a 3 from Arizona cypress tree. (26) Jun a 3 has also been shown to be closely related to a thaumatin-like protein in Banana. The presence of these common epitopes offers a molecular basis for positing cross-reactivity between aeroallergens and fruit allergens containing this allergen (15,27).

Clinical Experience

IgE-mediated reactions
Mountain juniper pollen causes asthma, hayfever and allergic conjunctivitis, in particular during winter months (28-29). Mountain juniper is the leading cause of respiratory allergy in South Texas (22) and is also a significant aeroallergen in Tulsa, Oklahoma (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 (31). 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 (29,32). The authors suggested also that a possible explanation may lie in the carbohydrate nature of the main allergen of the Mountain juniper pollen, which may facilitate allergen transport through the respiratory tract mucosa and subsequent sensitisation (32).

Compiled by Dr Harris Steinman, harris@zingsolutions.com.

References:

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2008



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