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Whole Allergen

g1 Sweet vernal grass

g1 Sweet vernal grass Scientific Information

Type:

Whole Allergen

Display Name:

Sweet vernal grass

Route of Exposure:

Inhalation

Family:

Poaceae (Gramineae)

Species:

Anthoxanthum odoratum

Latin Name:

Anthoxanthum odoratum

Other Names:

Large Sweet Vernal grass, Sweet grass, Spring grass, Buffalo grass, Holy grass, Scented Vernal grass, Sweet-scent Vernal grass, Vanilla grass

Summary

Sweet vernal grass is a fragrant, perennial, and tufted grass native to cold-temperature zones, mainly pollinating in the spring season. The leaves of this grass are pointed, and flower heads are crowded with spikelets. This species (Anthoxanthum odoratum) thrives across a variety of habitats like wetlands with medium to a high amount of nutrients, forest, roadsides, wastelands, dry grasslands, and sward. Individuals allergic to sweet vernal grass pollen may experience symptoms like allergic rhinitis and asthma after inhalation which is the main route of exposure. Ant o 1 is reported as the major allergenic component of sweet vernal grass. Cross-reactivity is evident within the Poodieae subfamily, including grasses like brome, fescue, ryegrass, June, timothy, orchard, sweet vernal, velvet, and canary. Clinical cross-reactivity between Anthoxanthum odoratum and Limonium sinuatum (lavender) has also been reported. Due to the conserved structure and ubiquitous distribution, polcalcin and profilin are also found to be cross-reactive. The cross-reactivity of Anthoxanthum odoratum (sweet vernal grass) is also observed with the wheat pollen (Triticum aestivum).

Allergen

Nature

Sweet vernal grass is a tufted, fragrant perennial grass, precisely indigenous to cold-temperature regions (1). Its usual height ranges between 10 to 100 cm with one to three noded culms. The leaves are hairy, brown in color, with pointed blades which possess a length of up to 30 cm and width of up to 10 mm (2). Sweet vernal grass flowers usually in the spring season, but occasionally flowers in autumn as well. However, it is also stated that the flowering season of this grass is well observed in the summer season until autumn. The flower arrangement is much branched in nature with a length of 1-12 cm and 6-15 mm wide. The spikelets consist of 3 florets, 2 of which on the lower side are basal and infertile, and 1 is a bisexual floret (2). The glumes of this species (Anthoxanthum odoratum) are persistent and are not of equal length, wherein the lower glume is nearly half of the upper glume lengthwise. Further, there is a presence of brown and hairy sterile lemmas, in which the lower lemma has a straight awn, and the upper one has a bent awn (2). An organic compound called coumarin imparts a characteristic sweet smell to the sweet vernal grass (1).

Habitat

Anthoxanthum odoratum is reported to grow across various geographical distributions, including the habitats like wetlands with a medium to a high amount of nutrients, forests, roadsides, wastelands, dry grasslands, and sward (3). It can survive in a wide range of soil having different nutrient levels (2), especially the nitrogen concentrations (3). The capability of the species to survive in different nutrient levels and ecological flexibility helps this species to thrive across many habitats (3). Hard grazing condition is claimed to be optimal for the survival of A. odoratum (2).

Taxonomy

Sweet vernal grass (A. odoratum) belongs to the Poaceae family and the genus Anthoxanthum. Anthoxanthum possesses two species, which include Anthoxanthum odoratum L. and Anthoxanthum nipponicum Honda (4).

 

Taxonomic tree of Sweet vernal grass  (5)  
Domain Eukaryota
Kingdom Plantae
Phylum Spermatophyta
Subphylum Angiospermae
Class Monocotyledonae
Order Cyperales
Family Poaceae
Genus Anthoxanthum
Species Anthoxanthum odoratum
Taxonomic tree of Sweet vernal grass  (5)  

 

Tissue

Sweet vernal grass pollens are spherical with a size between 26 to 50 µm. A single spheroid and annulate opening are located at the periphery with a pointed grain wall of less than 1 μm in height (6, 7). Dry pollens are irregular in shape with large infoldings (6). Ant o 1, a Beta-expansin, has been identified as an allergenic molecule from this pollen (8).

Epidemiology

Worldwide distribution

Around 20% of the general population and almost 40% of the atopic individuals are impacted by allergic sensitization due to grass pollens (9). Sweet vernal grass pollens mainly cause seasonal respiratory symptoms, such as asthma (10, 11), rhinitis (9, 11) and conjunctivitis (9).

Anthoxanthum spp. are considered one of the most widespread genera responsible for the manifestation of allergy in the Northern Hemisphere and adds to the broad spectra of allergy-causing pollens from grass (12).

According to a study conducted on 184 Costa Rican patients with allergic rhinitis (AR) (tested for sensitivity to Poaceae species), A. odoratum demonstrated 83.2% (highest percentage) of positive skin prick test reports (13).

Environmental Characteristics

Worldwide distribution

The temperate or tropical-alpine species of the genus Anthoxanthum L. grows in the regions including northern Eurasia (Europe to Japan), Ethiopia, tropical east Africa, southern Africa (including Madagascar), south-eastern Asia, and Central America (14).

Route of Exposure

Main

Inhalation is one of the exposure routes for the pollens belonging to the Poaceae family (12).

Clinical Relevance

Studies have reported that inhalation of airborne pollen adversely impacts the respiratory system of genetically predisposed individuals and individuals who later developed hypersensitivity. This further results in hypersensitivity disorders like AR and asthma (15).

Allergic rhinitis

Pollen from grasses belonging to the Poaceae family is reported to be a significant contributor to outdoor aeroallergen. Further, it is claimed that a greater number of individuals are sensitized to grass pollens compared to any other pollen type (16).

An Istanbul-based study on 2822 AR patients (aged: 2 to 18 years) demonstrated that 11.1% (314/2822) exhibited positive skin allergy tests towards sweet vernal grass allergens. Moreover, sweet vernal grass was also reported as the second susceptible category of allergen among children with AR (17).

Asthma

The pollutants present in the air adversely impact the lung function in asthmatic patients, specifically children. The ingression of inhaled allergens into the cells of the immune system is further accelerated by the impaired mucous membrane of the respiratory system, caused by air pollutants (12).

A Turkey-based study was conducted on 125 patients (with rhinitis and/or asthma) to estimate the incidence of sensitivity towards pollens. 100 patients exhibited allergy to a minimum of one pollen. 45% (45/100) of patients reported sensitivity towards A. odoratum. The Poaceae family was also reported as a frequent aeroallergen source among pollen sensitized individuals with asthma and/or rhinitis within the study region (11).

Prevention and Therapy

Prevention strategies

Avoidance

One of the main measures to be taken is to cut down the pollen amount in the respiratory system. During the pollen season, allergic patients are suggested to stay indoors or wear a mask outdoors to keep away from pollen allergens. In worsening conditions, patients might be advised to move to a pollen-free area (18).

Molecular Aspects

Allergenic molecules

Studies have utilized antisera/antibodies and immunoglobulin E (IgE) binding/inhibition experiments to confirm group 1, 2/3, 4, 5, or 6 allergens and profilin in various grass species pollen. The study confirmed the presence of allergens, which included Group 1 [Ant o +, molecular weight (MW): 25-35 kDa], Group 2/3 (Ant o +, MW: 10-12 kDa), Group 4 (Ant o +, MW: 40-60 kDa), Group 5 (Ant o +, MW: 25-35 kDa), Group 6 (Ant o +, MW:  ̴ 10 kDa), and Profilin (Ant o +, MW:  ̴ 14 kDa protein) (19).

Ant o 7 was reported as a polcalcin allergen from A. odoratum (20).

Additionally, Group 13 allergen was also reported by a study as a potential allergen from the Pooideae subfamily (like sweet vernal grass) (21).

According to WHO/IUIS, Ant o 1 (group 1) has been listed as an allergenic molecule from Anthoxanthum odoratum (sweet vernal grass) and is represented in the table below (8). 

Allergen Biochemical name Molecular Weight (kDa) Allergenicity
Ant o 1 Beta-expansin 25-35 Group 1 specific antiserum and IgE binding/inhibition experiments were used to confirm the presence of the component in the extract (8). 
Allergen Biochemical name Molecular Weight (kDa) Allergenicity

Cross-reactivity

Cross-reactivity has been observed between grasses of the Pooideae subfamily due to the remarkable homology of major allergen groups 1, 2/3, and 5. This group is prevalent in various members of the grass family like timothy, orchard, velvet, sweet vernal, ryegrass, June, brome, fescue, and canary grasses (22). The cross-reactivity of A. odoratum (sweet vernal grass) is also observed with the wheat pollen (Triticum aestivum) (23).

According to a study, a 42-year-old woman (owner of a greenhouse and floral shop) with no history of atopic diseases have reported dyspnea and wheezing while handling fresh Limonium sinuatum (lavender) flowers. On further investigation, the patient exhibited a positive skin test reaction towards A. odoratum pollen. Cross-reactive epitopes between A. odoratum and L. sinuatum might be responsible for the manifestation of respiratory allergies in this patient (24).

As per a study, the conserved structure and ubiquitous distribution of polcalcin and profilin are claimed to be responsible for exhibiting cross-reactivity in between these proteins (25).

Compiled By

Author: Turacoz Healthcare Solutions

Reviewer: Dr. Christian Fischer

 

Last reviewed: January 2021

References
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  2. Lambrechtsen. SOME ASPECTS OF THE BIOLOGY OF ANTHOXANTHUM ODORATUM L. A Thesis presented for the degree of Doctor of Philosophy in Botany in the University of Canterbury, Christchurch, New Zealand. 1968.
  3. Lawniczak AE. Response of Anthoxanthum odoratum and A. aristatumto different habitat types and nutrient concentrations in soil. Fresenius Environmental Bulletin 20(9A):2465-2474. 2011.
  4. Alm T. Scented grasses in Norway--identity and uses. J Ethnobiol Ethnomed. 2015;11:83.
  5. CABI. Anthoxanthum odoratum (sweet vernal grass). 2020 [23-12-2020]. Available from: https://www.cabi.org/isc/datasheet/93023.
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  10. Ullmann N. Unusual cause of dyspnoea. Arch Dis Child Educ Pract Ed. 2018;103(6):300-1.
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  12. Garcia-Mozo H. Poaceae pollen as the leading aeroallergen worldwide: A review. Allergy. 2017;72(12):1849-58.
  13. Riggioni O, Montiel M, Fonseca J, Jaramillo O, Carvajal E, Rosencwaig P, et al. [Type I hypersensitivity to gramineae pollen (by species) in allergic rhinitis patients]. Rev Biol Trop. 1994;42 Suppl 1:71-6, 20.
  14. Pimentel M, Sahuquillo E, Torrecilla Z, Popp M, Catalan P, Brochmann C. Hybridization and long-distance colonization at different time scales: towards resolution of long-term controversies in the sweet vernal grasses (Anthoxanthum). Ann Bot. 2013;112(6):1015-30.
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  19. Niederberger V, Laffer S, Froschl R, Kraft D, Rumpold H, Kapiotis S, et al. IgE antibodies to recombinant pollen allergens (Phl p 1, Phl p 2, Phl p 5, and Bet v 2) account for a high percentage of grass pollen-specific IgE. J Allergy Clin Immunol. 1998;101(2 Pt 1):258-64.
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