t6 Mountain juniper Pollen

Nature

Mountain juniper or mountain cedar is known by the scientific Latin names Juniperus sabinoides and Juniperus ashei (J. ashei) and belongs to the Cupressaceae family (1). It is a dioecious, small-sized tree or a large-sized shrub that can grow up to 35-40 feet in height (2, 3). The tree has an open, irregular, column or pyramid-shaped crown and a spread of 15 to 25 feet (3) with grey to reddish-brown mature barks (2, 3). The leaves are green, scaled, triangle to oval-shaped with < 2 inches in length. It produces seeds of 2 mm in size (length) with a thick wood-like outer coating (2, 3).

 The species from the Cupressaceae family are capable of producing pollens in huge quantities, approximately 0.4 million pollen grains per male cone and 276 thousand million pollen grains per tree (4). The juniper pollen dispersion generally occurs during mild temperature conditions and avoids cold conditions (5). The pollination period of J. ashei usually occurs from December to March (winters) with high frequency and production quantity. The pollens may be airborne and transported over long distances, especially during the winter (4, 6). This tree is utilized mainly as an ornamental planting in the United States (US) as well as other countries (7, 8). 

Habitat

Juniperus species are observed to grow in natural areas and unmaintained farmlands (4). Mountain juniper tree is mainly prevalent in high altitude regions (8). They preferably grow on superficial calcareous soil in the eastern US to sharp hilly slopes of low to mid-level altitudes in the western US (9). It prefers bright sunlight, dry climatic region with negligible humidity for growth and is able to grow in well-drained soil with a varied composition like clay, loamy and sandy. This tree is drought tolerant and able to sustain in acidic or alkaline pH soil (3).

The pollen dispersal of J. ashei generally requires conditions like dry weather with mild temperatures (above 5 ºC) and <50% relative humidity persisting for 24 hours (10).

Taxonomy

Cupressaceae is a conifer family that is categorized into seven different subfamilies, 30 genera and close to 160 species. Mountain juniper is a tree that belongs to the family of Cupressaceae and genus juniper. Of interest, the genus juniper, along with the other four genera, i.e. Chamaecyparis, Hesperocyparis, Cupressus and Cryptomeria are considered to be the most essential taxa for allergic diseases (4). 

Tissue

Pollen from J. ashei (Mountain juniper), member of the Cupressaceae family, are recognized as highly allergenic in North America. Their pollens are not easily distinguishable among the same species by their morphological characteristics. The pollen from this tree is reported to have a size ranging between 19-22 µm (diameter) and a weight of 2.45 – 4.6 ng (12).

To date, Jun a 1, Jun a 2, Jun a 3 and Jun a 7 have been identified from the pollen of J. ashei (Mountain Juniper) and listed by the World Health Organization/International Union of Immunological Studies (WHO/IUIS) Allergen Nomenclature Sub-Committee (13).

Allergenic molecules

Major allergens such as Jun a 1, Jun a 2, Jun a 3 and Jun a 7 have been identified in various immunoblot analyses, which showed IgE binding to these proteins and listed in the WHO/IUIS database (13). 

kDa: kilodaltons, IgE: Immunoglobulin E, PR: Pathogenesis-related, ELISA: Enzyme Linked Immunosorbent Assay

Biomarkers of severity

Studies have identified Jun a 1 as the major marker allergen for mountain juniper allergy (22).

Cross-reactivity

Pollen-pollen cross-reactivity

Proteins from the pollen of 12 species of Cupressaceae, including mountain juniper and one Taxodiaceae member Japanese cedar, have exhibited extensive cross-reactivity. Jun a 1, a major allergen of mountain juniper, was responsible for the cross-reactivity with other allergens from Cupressaceae family (40 to 42 kDa), and Japanese cedar (46 kDa). Some of the species reported to be cross-reactive with mountain juniper include Port Orford Cypress (Chamaecyparis lawsonia), red cedar (J. virginiana), Italian cypress (C. sempervirens), Arizona cypress (C. arizonica), one-seed juniper (J. monosperma), redberry juniper (J. pinchotti) and other species of Juniperus (10, 25).

Jun a 1, a major allergen (pectate lyase) of mountain juniper (mountain cedar) was found highly cross-reactive with major allergens of Japanese cypress (Cha o 1), Japanese cedar (Cry j 1), and Arizona cypress (Cup a 1) (16, 20). This cross-reactivity may be attributed to homology (70%-95%) among the amino acid sequences of these proteins since they belong to the same family of tree species (24). A study has also reported high amino acid sequence similarity of 91% between Cup a 1 and Jun a 1 (26).

Further, Jun a 2 is also reported to be highly homologous to Cry j 2 (70.7 %) and Cha o 2 (82.0%), allergens of a Japanese cedar tree (Cryptomeria japonica) and Japanese cypress tree (Chamaecyparis obtuse) pollen respectively (23). Also, Cup s 3 from C. sempervirens species is revealed to have 95% sequence homology and strong cross-reactivity with Jun a 3 (PR-5 protein) (27). In addition, Jun a 7 was found to be 98% homologous to Cup s 7 (Cupressus sempervirens, Italian cypress) (24).

Pollen-food cross-reactivity

Jun a 1, Jun a 2 and Jun a 3 have been observed to have high homology with allergens in fruits. OAS was found in mountain juniper allergic patients due to cross-reactivity with tomato, banana, melon mix and apple. Jun a 2 (Polygalacturonase) was reported to be responsible for cross-reactivity with tomato allergen (Sola 14) (18).

Further, Jun a 3, a thaumatin-like pathogenesis-related protein (PR-5), is closely related to a thaumatin-like protein in bananas (28). Cross-reactivity is expected between Jun a 3 and thaumatin-like proteins in cherry (Pru av 2), apple (Mal d 2), and paprika or bell pepper (Cap a 1) and therefore, sensitization to Jun a 3 may induce symptoms of OAS in mountain juniper sensitized patients (Jun a 3) (29).

Additionally, osmotin (PR-5, thaumatin-like protein) homology has been reported in tomato (Lyc e NP24; 91.87%), kiwi fruit (Act c 2; 75%), cypress (Cup s 3; 61.3%), bell pepper, (Cap a 1; 88.16%), apple (Mal d 2; 40.65%) and mountain juniper (Jun a 3; 63.79%). This sequence homology may cause cross-reactivity between these species (30).

Further, Jun a 7 exhibiting 67% of sequence homology to Pru p 7 (peach) has also been reported in a study (24).

Pollen-Fungal Spores cross-reactivity

Fungi homologous allergens have been reported in allergens from pollen origin such as Jun a 2, Tri a 25 (Wheat), Bet v 7 (Birch), Cry j 2, Pla a 2 (London Plane tree), Hor v 4 (Barley).

This speculates the probability of cross-sensitization between fungi and pollen (31).