Summary
Pla l 1 is a major allergen of and marker of genuine sensitization to English plantain (Plantago lanceolata) pollen. Pla l 1 is a member of the Ole e 1-like pollen protein family but displays limited, clinically non relevant, cross-reactivity with other members of this family, most notably with Ole e 1 from olive pollen and Che a 1 from goosefoot pollen.
Epidemiology
Worldwide distribution
Plantago lanceolata is a frequent and increasing cause of weed pollinosis under temperate climate worldwide [1, 2].
Pla l 1 sensitization was initially observed in 86% of P. lanceolata-allergic patients [1]. Subsequent studies reported variable levels, from 92% [3] to 33% - 34% [4, 5] in patients with evocative symptoms and P. lanceolata whole allergen extract sensitization, depending on the methodology of subject inclusion, the geographical area, the relative frequency of pollen multisensitization and the contribution of other plantain allergens [2-5].
This variation is also seen in epidemiological studies addressing subjects referred with a suspicion of allergy, which report locally relevant values of Pla l 1 sensitization, ranging from 0.3 to 7% in Germany [6] and up to 9.6% of pollen-sensitized subjects in the Czech Republic [7].
Environmental Characteristics
Source and tissue
Pla l 1 was identified as the dominant major allergen of P. lanceolata pollen [1].
Pla l 1 is present in P. lanceolata pollen, but not in other tissues, localized mainly in the cytoplasm of the vegetative cell [8]. Levels and temporal peaks of airborne Pla l 1 were reportedly ill-correlated with those of Plantago pollen counts, suggesting the contribution of additional sources of Pla l 1 [9].
Risk factors
The main risk factor for developing sensitization to Pla l 1 is exposure to P. lanceolata pollen [10]. Genetic susceptibility might also be involved, as a significant association was reported between Pla l 1 sensitization and the presence of the HLA class II allele DPB1*04:02 in a French adult cohort [11].
Clinical Relevance
Detailed information regarding P. lanceolata pollinosis, which manifests itself mainly as allergic rhinitis, rhinoconjunctivitis and asthma, is available in the whole allergen section.
Disease severity and prediction
In patients with a case history evocative of P. lanceolata pollinosis and sensitization to P. lanceolata whole allergen extract, the demonstration of Pla l 1 IgE confirms genuine sensitization to this pollen, thus assisting with correct classification of multisensitized patients [5, 10, 12]. .
Cross-reactive molecules
Pla l 1 exhibits limited and clinically irrelevant cross-reactivity with the major olive pollen allergen Ole e 1 and with Ole e 1-like allergens such as Phl p 11 from Phleum pratense, Che a 1 from Chenopodium album and Sal k 5 from Salsola kali [10, 13].
Molecular Aspects
Biochemistry
Pla l 1 is a polymorphic allergen belonging to a large protein family known as Ole e 1-like, broadly expressed in tree, weed, and grass pollen and sharing a beta-barrel fold with a potential ligand binding function [14, 15]. Pla l 1 is thermostable, with its conformation stabilized by the typical Ole e 1-like three intramolecular disulphide bridges and is N-glycosylated in its native form [14, 16]. Pla l 1 carries the major allergenic activity of P. lanceolata whole allergen extract, inhibiting 80% of its IgE-binding, and may form dimers under some conditions [1]. Its proposed biochemical function as a trypsin inhibitor has not been confirmed, especially as trypsin exposure rapidly denaturated Pla l 1 [15]. At the biological level, Ole e 1-like proteins are involved in pollen fertilization, i.e. pre-germination events controlling pollen tube development [17].
Isoforms, epitopes, antibodies
As of January 8, 2022, three isoallergens of Pla l 1 have been included in the World Health Organization (WHO) and International Union of Immunological Societies (IUIS) Allergen Nomenclature [18].
Cross-reactivity due to structural similarity
Pla l 1 shares limited sequence identity with other allergenic members of the Ole e 1-like pollen protein family, without clinically relevant cross-reactivity: 27% with Che a 1, the major allergen of the weed Chenopodium album [13], 26% with Sal k 5 from Salsola kali [14] and 38%-42% with Ole e 1 from Olea europaea pollen [16].
Diagnostic Relevance
Marker allergen for sensitization to P. lanceolata pollen
Pla l 1 sensitization confirms genuine sensitization to P. lanceolata pollen and is found in 33-92% of patients with P. lanceolata pollinosis, depending on the study population, the geographic area and local pollen exposure [3, 5, 10, 12]. In areas of concomitant sensitization to grass and other weed pollen and overlapping pollination seasons, Pla l 1 assists with the identification of the primary sensitizer [10].
Cross-Reactivity
Pla l 1 does not cross-react with Ole e 1 and Ole e 1-like allergens from other pollens (olive, grass, weeds) [10]. Importantly, even in patients exhibiting IgE to Ole e 1 and other Ole e 1-like allergens, IgE inhibition experiments confirmed true co-sensitization to Pla l 1 and the absence of cross-reactivity [15]. Therefore, Ole e 1 should not be used as a surrogate marker for sensitization to Pla l 1 [10].
Exposure
The main route of exposure is through inhalation of P. lanceolata pollen [10].
Compiled By
Author: Joana Vitte
Reviewer: Dr. Christian Fischer
Last reviewed:February 2022
