Maple leaf sycamore, London plane Pollen
Summary
London plane tree (Platanus acerifolia) is a wind-pollinated, deciduous tree that can attain a height of around 30 m. It is also known by the name Platanus Hybrida, as it is a hybrid of tree species P. orientalis and P. occidentalis. This tree can be found in abundance as an ornamental tree around urban streets, parks, and avenues. It is especially prevalent in Europe, North America, West Asia, South Africa, Australia, and New Zealand. Exposure to plane tree pollen might induce allergic reactions like asthma, rhinitis, and conjunctivitis among sensitive individuals. The allergenic components Pla a 1, Pla a 2, and Pla a 3 have been identified from the London plane tree pollen and listed in the IUIS database. Pla a 1, Pla a 2, and Pla a 3 have been established as significant diagnostic markers in Platanus-allergic patients. London tree pollen has exhibited cross-reactivity with tree pollens (like hazel, alder, birch), grass pollens (like maize, American cotton), food (like peach, tomato, hazelnut, banana), and fungi (like Alternaria alternata).
Epidemiology
Worldwide distribution
The concentration of London plane tree (Platanus) pollen is high during the spring season in countries like Europe, North America, and Australia. In Sydney, often exposure to London Plane tree pollen is speculated to be linked with conditions like conjunctivitis, rhinitis, and respiratory irritations.
A Spanish aerobiological pollen sampling study confirmed 14.9% as total annual pollen count for Platanus (London plane) tree pollen in the air.
Reports published from 1994-2005 have indicated the prevalence of London plane tree pollen sensitization of up to 8.48% in Barcelona, Spain, 11.4% in Cova da Beira, Portugal, and 56% in Madrid, Spain.
In Mediterranean European regions, the prevalence of sensitization towards Platanus (London plane) tree pollen grains has been reported to range between 3% - 52%.
An Australia-based study reported a positive skin prick test (SPT) towards Platanus (London plane tree) in 23.6% (13/55) of atopic patients with respiratory symptoms.
Sensitization rate of 22% towards London plane tree (Platanus Acerifolia) pollen allergen was reported in a study conducted in South Africa on 50 allergic rhinitis patients.
Route Of Exposure
Main
The route of exposure for London tree plane tree pollen is through inhalation.
Clinical Relevance
According to a study, the concentration of aeroallergen (like pollen from the London tree plane) is claimed to be related to the symptoms of allergic disease. For certain sensitized patients, plane tree pollen-mediated clinical symptom of allergic diseases is evident with an exposure concentration of 16 pollen grains per of air (threshold value). While, for a majority of the sensitized patients, these clinical symptoms are evident with an exposure concentration of 91 pollen grains per of air.
Exposure to London tree pollen may induce allergic symptoms like rhinitis, conjunctivitis, and asthma.
Allergic rhinitis (AR)
An Australia-based study was conducted on 64 individuals with a history of seasonal rhinitis (speculated to be triggered by Platanus pollens). 23.4 % (15/64) individuals exhibited positive SPT towards Platanus (London plane tree) pollen extract.
A retrospective, descriptive study conducted on 100 patients diagnosed with AR exhibited nasal obstruction as a frequent symptom in 80% of the patients, postnasal drip in 21%, itching in 39%, sneezing in 40%, and rhinorrhea in 58%. Out of these, 25% (25/100) of the patients showed sensitivity towards London plane tree pollen allergen.
Allergic Rhino-Conjunctivitis (ARC)
A study was conducted on 47 Spanish patients with a history of perennial or seasonal rhinitis and/or asthma. 74% of patients exhibited positive SPT towards London plane tree (Platanus hybrida) pollen. Clinical manifestation of conjunctivitis was evident among 78% of the patients who exhibited a positive SPT (n=36) towards London plane (Platanus) tree pollen.
Asthma
A Spanish study conducted on 187 patients with rhinitis and/or asthma (seasonal) reported positive SPT in 56% of the patients. 3 out of 5 patients in the control group developed immediate weal-and-erythema (Skin test) and significant IgE-reactivity towards Platanus hybrida (London plane tree) pollen. Additionally, a significant correlation (p < 0.001) was also reported between Platanus pollen count and bronchial asthma among these 3 patients.
Prevention And Therapy
Prevention strategies
Avoidance
One of the main measures to be taken is to reduce the amount of pollen entering the respiratory system. During pollen season, allergic patients are suggested to stay indoors or wear a mask outdoors to keep away from pollen allergens. In worsening conditions, patients may be advised to move to a non-pollen area.
Cross-Reactivity
A study reported cross-reactivity between plane tree pollens and other tree pollens like chestnut, oak, hornbeam, hazel, alder, and birch.
A number of studies reported cross-reactivity between pollen from the genus Platanus and Chenopodiaceae, Artemisia, Poaceae, Plantago, Parietaria, Olea, Betula, and Cupressus species pollen.
ELISA inhibition testing on Platanus-allergic individuals’ sera has exhibited significant cross-reactivity with grasses.
As per protein homology study Pla a 2 demonstrated identical residues of polygalacturonase in pollens like Zea mays (maize; 43%), Gossypium hirsutum (American cotton; 48%), Brassica napus (rape; 49%), Oenothera organensis (evening primrose; 56%) and food like tomato (37%), apple (38%), kiwi (39%), peach (42%). Similar protein homology was also observed in Japanese cedar pollen allergen (Cry j 2; 34%).
Pollen from the plane tree (Pla a 3) is reported to be cross-reactive with hazelnut, banana, celery, and peanut.
LTP from Plane tree (Pla a 3) is reported to exhibit sequence similarity of 58.3% with peach LTP (Pru p 3)
Significant correlation between plane tree pollen allergen rPla a 2 and fungal allergens rAlt a 6 (Alternaria alternata; p = 0.008) and rCla h 8 (Cladosporium herbarum; p = 0.010) has been reported in a study. Further, rPla a 3 has exhibited significant association with rCla h 8 (p = 0.003).
References
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