Latin name: Bromus inermis
Source material: Pollen
Family: Poaceae (Gramineae)
Sub family: Pooideae
Common names: Brome grass, Bromegrass, Smooth Brome, Rescue grass, Hungarian brome
Not to be confused with Bromus arvensis - Field Brome, a cool-season bunchgrass introduced from Europe into the USA in the late 1920s and used as a cover crop and for green manure in parts of the north-eastern and north-central regions.
Other common species of the genus include
A grass species producing pollen, which may induce hay fever, asthma and conjunctivitis in sensitised individuals.
The genus Bromus comprises about 60 species, of which two-thirds are native or naturalised to the United States (1). The Brome grasses may be either annual or perennial: the annual species, such as chess grass (B. secalinus) and ripgut grass (B. rigidus), tend to be grasses of little value, whereas the perennial species are valuable forage grasses (2).
Brome grass is native to Europe, China, Hungarian plains, Russian steppes and Siberia. It was introduced into North America in the 1880s, and has since been cultivated for pasturage and hay in the northern regions from Alaska and all the Canadian provinces, southern California and New Mexico, northern Oklahoma, and North Carolina. It extends from Northern Europe eastwards to China. It is also widely distributed in Argentina and elsewhere in South America (2).
Brome is a cool-season, perennial, sod-forming grass which resists trampling, making it excellent for grazing and soil conservation. It grows up to 1.5m tall. It is the only grass with a sealed sheath. In the middle of the leaf blade there is usually an impression of the letter ‘V’ or ‘W’, vertical on the leaf. The numerous dark green blades, both basal and from the stem, are flat but rolled in the bud-shoot, and are 4 to 13mm wide, 15 to 55cm long, flat, tapering to a sharp point, and with scabrous margins. It is strongly rhizomatous, with an extensive root system sometimes extending 1.5 m underground (2).
Brome grass has an erect, compound open panicle inflorescence from 6 to 17cm long, bearing 6- to 11-flowered spikelets 1.5 to 3 cm in length, that are pale green to slightly purple-tinged. In the Northern Hemisphere, Brome grass flowers in May to July in the USA, and June to September in Europe. The seeds ripen from August to September. The flowers are hermaphrodite (have both male and female organs) and are pollinated by wind. Brome grass reproduces by seed, rhizomes, and tillers, but spread by seed is weak.
Several brome grasses, including B. inermis and native California brome (B. carinatus) are considered significant inducers of hay fever in California, the Pacific Northwest, and the Midwestern USA (2).
Two principle types of Brome are recognised: the northern and the southern. The northern type is weakly rhizomatous, with leaves well up on the stem, and short glumes. A few northern cultivars are actually bunchgrasses. The southern type is strongly rhizomatous, with leaves near the base of the stem, and long glumes. Other notable differences are earlier spring growth of the southern type, and more even growth of the northern type through the growing season.
Brome grass is found in riparian zones, valley bottoms, and a variety of dryland sites.
The following allergen(s) have been characterised:
Bro i 7, a calcium binding protein (3, 4).
A lipid transfer protein has been isolated from the cells and seedlings (not pollen) of Brome grass after exposure to abiotic stresses. The LTP was up-regulated during active stages of cold acclimation. Severe drought stress induced the LTP gene; however, LTP expression doubled 3 days after re-hydration (5). The allergenic potential of this LTP was not evaluated.
Extensive cross-reactivity among the different individual species of the genus can be expected, and to a lesser degree among members of the subfamily Pooideae (6, 7).
The subfamily Pooideae (Festucoideae) of temperate pasture grasses contains five tribes, with over 2 000 species. Smooth brome is part of the tribe Poeae, which includes Kentucky bluegrass, fescue, and orchard grasses. Other Pooideae tribes are: Aveneae (oat and velvet grass), Phalarideae (canary and sweet vernal), Agrostideae (timothy, redtop, and foxtail) and Triticeae (western wheatgrass, wheat, rye, and barley) (2).
Pooideae grasses have marked homology of major allergen groups 1, 2/3, 4, and 5 (8-10). The resultant strong cross-reactivity between members demonstrates quantitative rather than qualitative differences (11). It has been suggested that testing and immunotherapy for Pooideae could be adequately covered by one or two members; however, because of lack of group 2 and 5 allergens in certain members (9, 11), there is much less cross-reactivity with southern grasses (2).
In an early study, Brome grass, Western Wheat, and Quack grasses demonstrated RAST inhibition patterns similar to the northern grasses (Timothy, Meadow grass, Rye, Redtop, Meadow Fescue, and Sweet Vernal grass) (12).
Inhibition studies of IgE antibody binding to Dac g 4 (Dactylis glomerata or Cocksfoot grass) with other pollen extracts confirmed the presence of cross-reactive allergens in Secale cereale (Cultivated Rye), Lolium perenne (Rye grass), Festuca elatior (Meadow Fescue), Holcus lanatus (Velvet grass), Bromus arvensis (Field Brome), Poa pratense (Meadow grass), Hordeum sativum (Barley), and Phleum pratense (Timothy grass) (13). Considering the presence of Group 4 allergens in Field Brome, the probability of a similar Group 4 allergen being present in Brome grass is high. Group 4 grass pollen allergens are glycoproteins with a molecular weight of 50 to 60 kDa, present in many grass species. Almost 75% of patients allergic to grass pollen display IgE reactivity to Group 4 allergens, which can hence be regarded as major grass pollen allergens (14). Further, Phl p 4 homologues with similar molecular weights were detected in Dactylis glomerata (Orchard grass), Festuca pratensis (Meadow Fescue), Holcus lanatus (Velvet grass), Poa pratensis (Meadow grass), and Lolium perenne (Rye grass). Group 4 homologues are present in the various grass extracts, but to varying extents (15).
As a result of the presence of a calcium binding protein, cross-reactivity between Brome grass and other grasses containing calcium binding proteins are possible but have not been evaluated yet (3, 4).
Anecdotal evidence suggests that Brome grass pollen can induce symptoms of asthma, allergic rhinitis and allergic conjunctivitis in sensitised individuals; however, few studies have been reported to date.
A 15-year-old Japanese boy was described whose allergic symptoms improved dramatically in the next season of grass pollens following rush-immunotherapy of grass-pollens (oats and brome grass), Japanese cedar, and ragweed. He had experienced erythema and oedema on his face, and serous rhinorrhoea when young, which had progressed to a choking sensation, dyspnoea, facial oedema, and asthma while at college. His symptoms deteriorated in summer and were ameliorated in winter. Serum-specific IgE for grass pollens was raised.
Brome grass pollen has been recorded as an aeroallergen in the Western Cape, South Africa (16).
Compiled by Dr Harris Steinman, developer of Allergy Advisor, http://allergyadvisor.com
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