Latin name: Quercus virginiana
Source material: Pollen
Common names: Virginia live oak, Southern Live Oak, Live oak, bay live oak, scrub live oak, plateau oak, plateau live oak, escarpment live oak, Encino
Oaks, making up the genus Quercus, are abundant hardy trees of deciduous forests in North America, Europe, and Asia. There are approximately 500 to 600 species worldwide, 250 in the Western Hemisphere, more than 150 in Mexico, and 70 in the United States and Canada (1-2).
Virginia live oak tree is native to the southeastern United States, from Virginia to Florida and west to Texas. It is also found in Cuba and in isolated locales in Mexico.
Live oak is a long-lived, nearly evergreen tree. It has a variety of forms, from shrubby or dwarfed to large and spreading, depending upon the site. It drops its leaves and grows new leaves within several weeks in the spring. In some areas it is in leaf all year. Trees grown in the open average 15 to 20 m in height. The bark is dark red-brown to grey and deeply furrowed longitudinally, with small surface scales, eventually becoming black and blocky. The 5 to 12.5 cm-long dark green leaves are thick, leathery and oval. The upper surface is lustrous, the lower pale and pubescent.
Virginia live oak tree flowers in early spring. The flowers, typical of Oaks, are on inconspicuous catkins, and are monoecious (individual flowers are either male or female, but both sexes can be found on the same plant). They are pollinated by wind. The countryside may become dusted with yellow pollen from this tree. Brownish-black acorns are produced, which are edible.
Virginia live oak is not as common as White oak. The natural habitat of the Live oak is woodlands.
The acorns are used for coffee, oil and food, and various parts of the tree have been used for medicinal purposes.
No allergens from this plant have yet been characterised.
As an extensive cross-reactivity among the different individual species of the genus could be expected (3), Virginia live oak may have allergens similar to those of White oak. Studies suggest that White oak pollen contains multiple proteins that are potentially allergenic (4). These include a group 1 Fagales protein, a calcium-binding protein and a profilin. See Oak tree t 7.
Moreover, probably not all species of Oak are equally allergenic:
Q. ilex pollen, although produced in considerable quantities, was not found to cause allergies in one study (5).
Some of the pollen allergens in the various species of Oak cross-react with each other, while others are unique to their own species. No studies to date have examined the cross-reactivity between Virginia live oak and other plants, but assuming that an extensive cross-reactivity among the different individual species of the genus could be expected (3), studies involving White oak tree (Q. alba) are relevant.
In Sapporo, Japan, many Birch pollen-allergic patients complained of typical symptoms after the Birch pollen season. This has been attributed to Birch pollen-allergic individuals being affected by Oak pollinosis due to cross-reactivity between Birch and Oak pollen (6).
Natural Birch, Alder, Horn beam, Hazel, and Oak pollen contain allergens that share IgE epitopes with recombinant Bet v 1 and recombinant Bet v 2. A combination of recombinant Bet v 1 and Bet v 2 accounted for 82% of tree pollen-specific IgE in a study. Most of the tree pollen-specific IgE was directed against rBet v 1 (7).
In inhibitory ELISA assays, IgE binding to ginkgo pollen was inhibited more than 80% by Oak, Rye grass, Mugwort, and Ragweed; and 34% by Japanese Hop; and 10% by rBet v 2 at 10 µg/ml (8).
On the evidence of these studies, American patients allergic to Virginia live oak pollen can be expected to be affected by Oak species found in Europe and other parts of the world.
Oak pollen is a major cause of asthma, allergic rhinitis and allergic conjunctivitis (9-12). Virginia live oak is not as common as White oak, but when it is grown in urban communities and near rural ones, it is an important allergen, and the prevalence of atopic sensitisation its pollen will be high.
Oak pollen affects sensitised individuals throughout the world. In Madrid, Spain, the highest level of airborne pollen from 1979 to 1993 was from the Quercus species (17%) (12), and in Salamanca, Spain, the highest quantity of pollen was from Holm oak (13). Oak pollen has also been shown to be significant in Zurich (14), Mexico City (15), Japan (16), Korea (17), Tampa, Florida (18), and Cape Town, South Africa (19).
Exposure to Oak dust may also lead to the development of sore throat and bronchial hyperresponsiveness (20).
Occupational asthma and rhinitis due to Oak wood dust have been demonstrated in wood workers (21-22).
Determination of IgE antibodies has been documented to be a useful investigation in the case of Oak-allergic individuals (23-24).
Compiled by Dr Harris Steinman, email@example.com.
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