Family: Betulaceae.

(Not to be confused with the Box elder tree (Acer Negundo) or the Elder tree (Sambucus Nigra)

The Grey Alder tree is an important allergen in urbanised communities, and rural communities situated near woodlands where this tree is growing. In these places, the prevalence of atopic sensitisation to pollen from this tree is expected to be high.

Grey Alder is the most widely distributed Alder in western North America and Europe.

Grey Alder is a rapidly growing, deciduous, multi-stemmed shrub or small tree, which tends to form thickets. It has a long trunk and a narrow crown. The Alder typically grows between 2 and 5m in height, but may reach 12m. The tree matures at 60 years but may reach 150 years of age. The bark is thin, smooth, and green-grey, greyish-brown, or reddish-brown. Trees often produce adventitious roots from near the base of the stem, and these give additional support in unstable soils. The leaves are broadly elliptic or ovate, approximately 3 - 7cm long, dull green on both sides, with doubly dentate margins. Leaves remain green until they are dropped in the fall.

Flowering generally begins during March and April, with seeds ripening from September to November. The flowers occur in catkins and are monoecious (individual flowers are either male or female, but both sexes are found on the same plant). The drooping staminate catkins are about 3 - 10cm long. Alders are wind-pollinated and produce clouds of yellow pollen. The cones remain on the plants for about a year after the seeds are shed, aiding in identification during winter. The fruit is a small, single-seeded nutlet, with narrow lateral wings, which aid in dispersal by wind and water. Alder produces abundant seed, which is dispersed during fall and winter.

Grey Alder seldom grows away from water. It is typically found bordering streams, rivers and mountain springs, on moist lowlands and in swamps. It invades gaps and clearings in forests and thrives there.

Red alder is used for furniture, flooring, and firewood. The bark and leaves contain tannin and have been used in folk medicine to treat chills.

Grey alder sheds its leaves annually and grows up to 20 metres. It is common in barren landscapes, woods, and by lakes and streams; often in misty forests. It is used to enrich soil because of its ability to bind nitrogen.

Alder has figured in mythology and folk tradition. Goethe wrote a summary of many beliefs surrounding alder in Erlkönig, the Alder King.

Grey alder is found in both northern and central Europe though not Denmark, England or north-eastern Europe. A. glutinosa grows in southern Sweden and Denmark. A closely related species, Alnus glauca, occurs in eastern North America, down to the Andes in Peru, Chile and Argentina.

Grey alder has minuscule flowers and blooms in the early spring. Grey alder belongs to the same family (Betulaceae) as Birch (t3). For taxonomical reasons, common, shared allergens could be expected and have also been found in these two species.

Allergens/Function:

Allergens:
Aln g 1, the major allergen, a 17kD protein, a Bet v 1-homolog.
Aln g 4, a 9.4 kDa calcium-binding protein. (Hayek 1998 ref.6641 0)

Alg g 4 reacts with serum IgE from approximately 18% of pollen-allergic patients (n = 122). (Hayek 1998 ref.6641 0)

In a RAST study on patients with seasonal rhinitis, it was found that birch, beech, alder, hazel and oak pollens are most important as causes of springtime hay fever, whereas maple, poplar, elm, sallow and ash allergens more often gave negative or only weak positive test results. (Jung 1987 ref.3252 7)

Sampling over a three-year period indicated that birch, alder and poplar pollen and fungus spores are the major aeroallergens from early May to September in the Fairbanks area, Alaska. (Anderson 1984 ref.3253 6)

Positive tests in 92 patients, often of high intensity, were most often found with birch, alder, bog-myrtle, beech and hazel allergens, whereas oak, aspen, linden, elm, sallow, maple and poplar allergens more often gave negative or only weak positive test results. (Eriksson)

Adverse Reactions:

IGE AND IMMUNE:
Asthma, allergic rhinitis and allergic conjunctivitis occur in individuals sensitised to this pollen. (Wuthrich 1979 ref.5884 2) (Gilardi 1994 ref.4549 8)

Cross-reactivity between Grey alder and Oak has also been reported.

This study reports that winter respiratory symptoms were due to alder pollen in 10 patients and hazel pollen in 12 and not to infectious coryza. (Laurent 1994 ref.4747 8)

Grey Alder tree pollen is a frequent cause of allergic symptoms. In the southern part of Switzerland, in 503 patients with allergic rhinitis tested by skin-prick test for sensitisation to common allergens, 33% were sensitised to Alder tree pollen. (Gilardi 1994 ref.4549 8)

In central Italy, the pollination period stretches from February to mid-October. Pollen from the Alder is particularly high in the month of March. (Murgia 1983 ref.4736 2)

Alder pollen has also been shown to be a frequent aeroallergen in studies in Spain. (Silva Palacios 2000 ref.4732 2) (Hernandez Prieto 1998 ref.4568 3)

OCCUPATIONAL EXPOSURE:
Wood worker

In this study, work-related respiratory complaints among Swedish woodwork teachers was shown to be partially due to specific IgE to a tree, but also due to other mechanisms. (Ahman 1995 ref.4428 4)

NON IMMUNE:
Unknown or Nil