Ribwort plantain also identified as Plantago lanceolate is a very important species from the Plantaginaceae family. It is a perennial weed with high ecological plasticity. It grows abundantly mainly in regions such as humid meadows and beside roadsides. Plantain is one of the key reasons for pollinosis in temperate regions. Pla l 1 and Pla l 2 are the two registered allergens till date. Pla l 1 is primarily an indicative marker allergen responsible for the diagnosis of plantain pollen sensitization with high specificity. Pla l 2 is a profilin protein with a molecular weight of 12-15 kDa. It is a small actin-binding protein and is responsible for polysensitization. Plantain allergy is mainly responsible for seasonal allergic rhinitis, rhino-conjunctivitis and in some cases also asthma. Plantain allergen also shows cross-reactivity with pollens like grass, birch, ash, or olive pollen.

Nature

Ribwort plantain (Plantago lanceolata) is a perennial herb, which forms several rosettes. It has long thin oval to elliptical leaves. The stems grow to a height of 20-70 cm, and the tips have 3-5 cm long spikes. The flowers of plantain blossom slowly from base to spike. A Japanese study revealed that Plantain pollens dispersed from May to September and the sensitized patients generally suffered from aggravated symptoms between April to October(1). A study conducted in the US showed that plantain growth rates were higher in September than in July, increasing by 62% in the normal and 29% in the wet treatment. (2)

Habitat

Plantain is a common perennial weed of arable fields and grassland. It is originating from grassy places on neutral or basic soils and is found abundantly in the UK. It is commonly found in lawns but less common as compared to greater plantain(3). Plantain belongs to the Plantaginaceae family with a perennial cosmopolitan species which shows high ecological plasticity. It is naturally found in grassy areas on roadsides, in pastures and in crops as weeds. It has moderate demands regarding soil and climatic factors. It also resists well in drought as well as cold winters and it can tolerate maritime exposure (2).

Taxonomy

Worldwide distribution

A large population study was conducted in Germany for over 20 years with skin prick testing (SPT) for 6220 individuals to evaluate sensitizations towards weed pollen aeroallergen. The patients were suspected of allergic rhinoconjunctivitis. 26.6% of patients from 1998 to 2007, showed positive results on SPT for plantain. Between 2008 and 2017 this percentage increased to 50.5% (7).

A Japanese study was conducted on 160 individuals suffering from allergic rhinitis. Among these 141 patients were tested with RAST and 12.8% of these showed positive results to plantain(1).

A study in China analyzing aeroallergen sensitization in individuals (n=480) suffering from allergic rhinitis showed 29.8% of these patients reported positive to skin prick test for plantain(8).

In one study conducted in a city Porto of Portugal to check the sensitization of plantain in patients with respiratory allergy, the result showed that 31 percent of the patients showed sensitization for plantain pollen. Plantain was responsible for about 3 percent of the yearly pollen load in the air of Porto. Plantain was found to be the ninth most common pollen in the air of Porto (9).

Risk factors

A study conducted in the UK found that 28% of patients (n=82) with a history of seasonal respiratory allergy tested positive for skin prick test for plantain pollen extract. The study has also shown when a patient’s sera with seasonal respiratory allergies were subjected to RAST testing with plantain pollen 34%showed positive results(10).

Sensitization to pollen allergens varies between different regions of the world and is closely related to climatic conditions, degree of urbanization, and plant distribution. In the Mediterranean countries or those with such climate, airborne plantain pollen, along with grass pollen, olive pollen, cypress pollen, plane tree pollen, dust mites, is considered as one of the most common triggers of respiratory allergy. (9)

Pediatric issues

A study was done on a Pacific island in the pediatric population who had wheezing bronchitis. The bronchitis episodes commonly occurred in children less than 4 years of age. The results of the skin test and the serologic test showed that hypersensitivity reaction to plantain allergens was related to bronchitis episodes. (11)

Worldwide distribution

The genus Plantago includes about 250 species Plantain is considered an important cause of pollinosis in the temperate regions of North America, Australia, and Europe. (12) It is an exotic species in Japan. Besides, it possesses excellent reproductive power and has proliferated more than the naturally growing plantain in Japan. This species is distributed all over the world, including Europe, North America and Australia(1).

Main

Plantain pollen is generally considered a causative allergen for airborne allergy in Europe. (13)

Allergic rhinitis

Plantain is responsible for about 20 to 30 percent of all the episodes of seasonal allergic rhinitis in the western population. A study was conducted in Japan in about 160 patients with allergic rhinitis to find out the prevalence of plantain pollinosis. The results showed a plantain RAST-positive rate of 12.8 percentage(1).

Asthma

A study was conducted with 866 patients suffering from allergic rhinoconjunctivitis (ARC) and asthma using skin prick tests to evaluate seasonal allergy. Among these 38.79% were suffering from asthma and ARC. The study reported 45.7% showed positive skin prick test results towards plantain pollen allergen(14).

Prevention strategies

Avoidance

It is generally difficult to avoid pollens on daily bases. Some measures that can be taken are to wear, sunglasses and mask. Keep windows of an allergic individual’s house (especially if situated in a tall building) and in a moving car shut. One can also try to avoid walking over open grassy areas, especially during high pollen count (15). 

Allergenic molecules

A study on plantain pollen‘s IgE binding protein profile showed several molecular bands ranging from 70kDa to 13 kDa. The 1D gel electrophoresis showed 8 prominent groups of IgE-reactive allergens. The mass spectroscopy revealed several peptides, among these 2 immunoreactive proteins of around 39 kDa and 37 kDa, corresponding to fructose-bisphosphate aldolase and glyceraldehyde-3-phosphate dehydrogenase, respectively. Proteomic analysis revealed that these two peptides are known to work together in metabolic pathways such as glycolysis and were also recognized as IgE-binding proteins in ryegrass (Lolium perenne) pollen extracts. Another peptide Glyceraldehyde-3-phosphate dehydrogenase was also found to be a wheat (Triticum aestivum) food allergen. Other identified peptide is α-1,4-glucan-protein synthase is known to be involved in the synthesis of cellulose and shows allergenic activity in date palm (Phoenix dactylifera) pollen aldolase(9).

Allergen Pla l 1 in plantain pollen has been identified and purified. Other allergens identified as specific to plantain include a cytochrome c protein and a calcium-binding protein. (9).

Pla l 2 is the second allergen found in plantain. Pla l 2 is a profilin, with a molecular weight of 12-15 kDa, a small actin-binding protein. It is responsible for polysensitization. From its purified form, a total of four peptides are recognized which have similarities ranging from 73% to 86% with other pollen profilin. In a profilin diagnostic study, around 87.5% percent of the serum samples identified Pla l 2. (16)

Biomarkers of severity

Pla l 1 constitutes the only indicative marker allergen for the diagnosis of genuine plantain pollen sensitization. Without considering Pla l 1 as a marker molecule for genuine sensitization, most of the patients would have been diagnosed positive solely because of cross-reactivity to grass, olive, birch, or ash allergens. (17) The allergenic significance of Pla l 1 has been studied in vitro with sera of allergic patients sensitized to plantain. Of the 22 sera analyzed, 19 had IgE antibodies to Pla l 1. In addition, Pla l 1 was responsible for 80% of the total IgE-binding capacity of the whole extract, which was determined by competitive ELISA.(4).

Cross-reactivity

Patients with a true monosensitization to plantain are rarely found. The vast majority of the plantain pollen-sensitized patients show concomitant sensitizations and allergies to other pollen allergen sources, such as grass, birch, ash, or olive pollen. Recent studies showed a lack of IgE cross-reactivity of Pla l 1 with homologous allergens. However, plantain pollen also contains the panallergens such as profilin and polcalcin which are present in other pollen sources. (17).

Author: Turacoz Healthcare Solutions

Reviewer: Dr. Christian Fischer

Last reviewed: October  2020