g204 False oat-grass

Sub family: Pooideae
Tribe: Aveneae

There are two subspecies or varieties: one has swollen bases in the main shoots, resembling small onion bulbs, and is sometimes called 'Onion Couch'; the other lacks these swellings.

Pollen

A grass species producing pollen, which often induces hay fever, asthma and conjunctivitis in sensitised individuals.

Allergen Exposure

Geographical distribution

False Oat grass is native to Europe, and was brought to the United States early in the last century. It is now grown widely, for making hay and for grazing, in the central and northern states. World distribution includes the USSR, East Asia, and Africa.

False Oat grass is a hardy, upright, perennial bunchgrass growing up to 180cm high, with many leaves scattered along the stems. The seed head resembles that of Oats: hence the name. The leaf blades, rolled in the bud shoot, are flat, linear, up to 50cm long and 10mm wide, and sometimes sparsely hairy.

The inflorescence is a panicle, green to purple, shining, erect or nodding, oblong or ovate, contracted, and up to 35mm wide and 60cm long. The hermaphrodite (containing both male and female organs) florets number one to three per spikelet. Incomplete (male) florets also occur at the base of the inflorescence. False Oat grass flowers from November in the Southern Hemisphere and from May in the Northern Hemisphere.

Environment

Often found in dry meadows or pastures, but very seldom in the wild.

Allergen Description

The following allergens have been characterised:

• Arr e 1, a Group 1 Grass allergen (1, 2).
• Arr e 5, a ribonuclease, a Group 5 Grass allergen (3).

Extensive cross-reactivity among the different individual species of the genus may be expected, as well as to a certain degree among members of the family Poaceae, particularly in the tribe Aveneae (Sweet Vernal grass (g1), Cultivated Oat (g14), Velvet grass (g13), Canary grass (g71)) (4, 5).

Early studies of the antigens in Meadow grass (Kentucky bluegrass) pollen, compared with False oat grass and the combined extracts of Timothy, Orchard (cocksfoot), Velvet and Rye grasses, indicated that these grasses contain many cross-reactive antigens (6). Similarly, immunological partial identity between isolated major allergens of Timothy pollen and the corresponding pollen allergens of False oat, Orchard and Rye grass were demonstrated (7).

The presence of group 1 and 5 grass allergens may result in variable degrees of cross-reactivity with pollen from other grasses, weeds and trees, depending on the similarity of these panallergens with those found in this pollen (1, 6-8). However, these cross-reactions have not been fully elucidated yet (9).

For example, extensive IgE cross-reactivity has been observed between the allergens of the Pooideae grasses as a result of the presence of a group 1 grass allergen (8).

IgE-mediated reactions

Anecdotal evidence suggests that False Oat grass pollen may induce symptoms of asthma, allergic rhinitis and allergic conjunctivitis in sensitised individuals (3); however, no studies have been reported to date.