Table of Contents

Whole Allergen

w19 Wall pellitory

w19 Wall pellitory Scientific Information

Type:

Whole Allergen

Display Name:

Wall pellitory

Allergen code:

w19

Family:

Urticaceae

Species:

Parietaria officinalis

Route of Exposure:

Inhalation

Latin Name:

Parietaria officinalis

Other Names:

Pellitory-of-the-Wall, Parietaria, Pellitory, Parietaria erecta, Upright pellitory

WHO/ICD-11 code:

XM3LL8

(ICD-11 is currently under implementation by WHO and the ICD-11 codes displayed in the encyclopedia may not yet be available in all countries)

Allergen

Summary

Parietaria officinalis (P.officinalis), also known as wall pellitory, is a wind-pollinated, perennial plant that commonly grows in the shade of the walls with a height of about 30-100 cm. This species (Parietaria) possesses a prolonged pollination period, which starts during the beginning of spring and continues till summer. Additionally, a second shorter pollination period has also been reported, initiating from the end of August till October. The plant can grow in waste places and rocks. This weed pollen is predominantly found in Italy, Southern and Western Europe, North Africa, United States, Croatia, and Australia. P.officinalis pollen can trigger conditions like rhinitis, asthma, conjunctivitis, and seasonal hay fever. The allergen Par o 1 from P.officinalis pollen has been identified and listed in the IUIS database. P.officinalis pollen exhibits cross-reactivity with P. judaica, house-dust mites, birch, mugwort, and olive pollen.

Nature

Parietaria officinalis (P. officinalis) is also known as pellitory-of-the-wall (wall pellitory) as it is found to grow in the shade of the walls (1, 2). P. officinalis is a wind-pollinated, perennial plant that usually attains a height of around 30 -100 cm (1, 2). This plant is claimed to be slightly upright, bit-branched, and densely haired (2). The plant possesses several short-stalked leaves, which are found to be ovate-to-spear-shaped and 3-12 cm long. The flowers of the wall pellitory are reported to be axillary (at the junction between a leaf and the stem) (2). This species (Parietaria) has been found to possess an extensive pollination period, which initiates with the beginning of spring and continues up to summer. Moreover, a second pollination period (shorter) has also been observed, starting from the end of August till October (3). The leaves and stems of wall pellitory are found to be edible, nutrient-rich (due to extensively high calcium content), and therefore is used in soups and stews (4).

Habitat

The species Parietaria (such as P. officinalis) has been found to thrive in walls, waste places, and rocks (2). P. officinalis is found to sustain both mild winters and dry summers (3). High nitrogen level in soil has been reported to be favorable for the growth of the species belonging to Parietaria genus (5).

Taxonomy

P. officinalis belongs to the family of Urticaceae and genus Parietaria. Among the various species, P. officinalis is considered as one of the critical species due to its clinical relevance(1).

Taxonomic tree of Wall pellitory (6, 7)
Domain	Eukaryota
Kingdom	Plantae
Phylum	Spermatophyta
Subphylum	Magnoliophyta
Class	Magnoliopsida
Order	Urticales
Family	Urticaceae
Genus	Parietaria
Species	Parietaria officinalis

Tissue

The pollen size of Parietaria has been reported to be about 16-18 microns in diameter, which further eases the contact of each granule to the mucosal surface (8). The pollen grains of the Parietaria genus (such as P. officinalis) are mostly ellipsoidal and usually possess three pores (2); moreover, the pollen (from P. officinalis) bears fragments of coarse hair belonging to the leaves and the flowers (8). Par o 1 (15 kDa) has been identified as a potential allergenic molecule from the pollen of the P. officinalis plant and listed in the IUIS database (9).

Epidemiology

Worldwide distribution

Pollen from P. officinalis (wall pellitory) has been identified as one of the primary allergens responsible for pollinosis in western and southern Europe (10). A US-based prospective study identified 22.6% (31/137) as the frequency of positive response towards pellitory (weed) pollen among the study population (11). An Italy-based retrospective study on 793 respiratory allergic patients (6-85 years) confirmed 32.4% (108/333) of the patients were sensitized towards P. officinalis pollen (12). A cross-sectional study in Indonesia involving 106 respiratory allergic patients (19-59 years old) has reported 4.7% (5/106) of the study population to possess IgE-mediated sensitivity towards wall pellitory pollen (13). A retrospective Turkey-based study conducted on 7492 patients (with AR and/or asthma; 16-82 years) reported 2.4% (182/7492) as the prevalence of P. officinalis pollen-mediated sensitization among the study population (14).

Environmental Characteristics

Worldwide distribution

Wall pellitory (P. officinalis) is predominantly found in countries like Italy, Southern and Western Europe, North Africa (8), United States (US), Croatia, and Australia (3).

Route of Exposure

Main

The route of exposure for wall pellitory pollen is through inhalation (13).

Clinical Relevance

The pollination season of P. officinalis has been found to be usually prolonged, along with a high pollination level. Therefore, sensitive patients have been reported to experience severe symptoms during this period. (3). Exposure to P. officinalis weed pollen has been reported to elicit conditions such as rhinitis, asthma, conjunctivitis (12), and seasonal hay fever (15).

Rhinitis, asthma, and conjunctivitis

A retrospective study conducted on respiratory allergic patients revealed wall pellitory as one of the sensitizing allergens. As per the study, patients sensitized towards wall pellitory pollen exhibited conditions like rhinitis (39.9%; 114), asthma (78%; 223), and conjunctivitis (94.1%; 269) (12). A retrospective study reported 25% (71/284) of the allergic conjunctivitis patients to exhibit positive skin prick test towards P. officinalis pollen. The study further claimed that sensitization towards seasonal allergens like P. officinalis could lead to pollen-mediated allergies (16).

Prevention and Therapy

Avoidance

One of the main measures to be taken is to reduce the amount of pollen in 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 (17).

Allergen immunotherapy

In a study conducted on 26 allergic rhinitis patients, sublingual immunotherapy containing P. officinalis exhibited significant improvement in conditions like sneezing (p=0.005), nasal itching (p=0.003), rhinorrhoea (p=0.008), and nasal congestion (p=0.003) (18).

Molecular Aspects

Allergenic molecules

Par o 1 from P. officinalis (wall pellitory) pollen has been identified and listed in the IUIS database (9). The below table provides detailed information on the allergenic protein.

Allergen	Biochemical name	Molecular weight	Allergenicity
Par o 1	Non-specific lipid transfer protein type 1	15 kDa	A study conducted on 29 Parietaria allergic patients confirmed positive SPT to Par o 1 among all the patients. Most of the patients exhibited elevated levels of Par o 1 specific serum IgE antibody confirmed by RAST. (Oreste, Coscia (19).

SPT: skin prick test; RAST: radioallergosorbent test

Cross-reactivity

P. officinalis (wall pellitory) pollen has also been found to exhibit cross-reactivity with house-dust mites (D. farina, D. pteronyssinus), birch, mugwort, and olive pollen (10). Moreover, cross-reactivity between P. judaica and P. officinalis pollen extract has also been reported by a study (20).

Compiled By

Author: Turacoz Healthcare Solutions

Reviewer: Dr Christain Fisher

Last reviewed: August 2021

References

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