Horn beam

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Code: t209
Latin name: Carpinus betulus
Source material: Pollen
Family: Corylaceae
Common names: Horn beam, Hornbeam, European hornbeam

The Horn beam, Birch (Betula verrucosa), Alder (Alnus incana), and Hazel (Corylus avellana) all belong to the order Fagales.

Allergen Exposure

Geographical distribution
The Horn beam is a sturdy deciduous tree superficially resembling Beech. It is native to Britain and the temperate regions of Western, Central and Southern Europe, and it is found eastward as far as western Russia and the Ukraine.

The Horn beam grows15-25 m in height. The trunk is smooth and steel-grey, sometimes with a rippled, muscular appearance. The dark-green leaves are heavily textured, with deeply impressed veins. The leaves become golden-yellow to chartreuse in colour during autumn. The tree can reach 150 years in age.

Horn beam produces flowers from April to May. The flowers are monoecious (individual flowers are either male or female, but both sexes can be found on the same plant), and the male and female flowers appear in pendulous catkins in May after the leaves. The tree is wind-pollinated.

The fruit (seed) is a small 7-8 mm-long, light-brown, ribbed nutlet, partially surrounded by a 3-pointed leafy involucre 3-4 cm long. It ripens from October to November.

Horn beam grows in woodlands and hedgerows.

The tree produces extremely hard, white, close-grained wood.

To date, the following allergens have been characterised:

  • Car b 1, a 17 kD Bet v 1 homologue (1-7).
  • Car b 2, a profilin (3).
  • Car b CBP, a calcium-binding protein (3,8).

Potential cross-reactivity

An extensive cross-reactivity among the different individual species of the genus could be expected (9). Indeed, Birch (Betula verrucosa), Alder (Alnus glutinosa), Hazel (Corylus avellana), and Horn beam (Carpinus betulus) all belong to the order Fagales, and a high degree of homology of their 4 major allergens has been indicated (10). This is mostly due to pollen from these trees containing allergens that share IgE epitopes with Bet v 1 and Bet v 2 (3-4,6,11).

The deduced amino acid sequences in Car b 1 from Horn beam pollen show pronounced homology with Bet v 1, the major allergen from Betula verrucosa (White birch) pollen (2,7).

Homologues to Bet v 1, the major Birch pollen allergen, are also present in members of the Fagaceae, Rosaceae and Apiaceae families (12-14).

As Horn beam tree pollen contains profilin and calcium-binding proteins, cross-reactivity may occur with other pollens containing these panallergens (3,8).

The Horn beam tree contains an N-glycan carbohydrate structure. It is theorised that carbohydrate structures are another potential source of immunological cross-reaction among allergens such as Kentucky blue grass (Poa pratensis), Rye (Secale cerale), Rye grass (Lolium perenne), Short ragweed (Ambrosia elatior), Giant ragweed (Ambrosia trifida), Birch (Betula alba), Horse chestnut (Aesculus hippocastanum), Olive (Olea europaea) and snake-skin pine (Pinus leucodermis) pollen (15).

Patients with Type I allergy to Fagales pollens frequently show adverse reactions to fruits and vegetables, in particular to Apple and to Hazelnut (16).

Clinical Experience

IgE-mediated reactions
Anecdotal evidence suggests that asthma, allergic rhinitis and allergic conjunctivitis are possible following exposure to pollen from this tree; however, no specific studies have been reported to date.

Although the Horn beam is not as prevalent as other Fagales trees, i.e., Birch (Betula verrucosa), Alder (Alnus glutinosa), and Hazel (Corylus avellana), it should be borne in mind that these trees are highly cross-reactive (11-12). Similar clinical patterns can be expected with all members of the Fagales family. Fagales allergy can be found in Birch-free areas and can be caused by exposure to other Fagales species (17). Pollen from Horn beam can therefore be regarded as an important aeroallergen.

Compiled by Dr Harris Steinman, harris@zingsolutions.com.


  1. Gajhede M, Osmark P, Poulsen FM, Ipsen H, Larsen JN, et al. X-ray and NMR structure of Bet v 1, the origin of birch pollen allergy.
    Nat Struct Biol 1996;3(12):1040-5
  2. Larsen JN, Stroman P, Ipsen H. PCR based cloning and sequencing of isogenes encoding the tree pollen major allergen Car b I from Carpinus betulus, hornbeam.
    Mol Immunol 1992;29(6):703-11
  3. Niederberger V, Pauli G, Gronlund H, Froschl R,
    Rumpold H, et al. Recombinant birch pollen allergens (rBet v 1 and rBet v 2) contain most of the IgE epitopes present in birch, alder, hornbeam, hazel, and oak pollen: a quantitative IgE inhibition study with sera from different populations. J Allergy Clin Immunol 1998;102(4 Pt 1):579-91
  4. Hauser M, Klinglmayr E, Wopfner N, Mutschlechner S, Mari A, Bohle B, Briza P, Ferreira F, Wallner M. Cloning, purification and characterization of Bet v 1 homologues from hornbeam (Car b 1) and oak (Que a 1). (Poster) 2nd Int Symp Molecular Allergol, Rome, Italy 2007;April 22-24
  5. Ferreira F, Hirtenlehner K, Jilek A, Godnik-Cvar J, Breiteneder H, Grimm R, Hoffmann-Sommergruber K, et al. Dissection of immunoglobulin E and T lymphocyte reactivity of isoforms of the major birch pollen allergen Bet v 1: potential use of hypoallergenic isoforms for immunotherapy.
    J Exp Med 1996 Feb 1;183(2):599-609
  6. Ipsen H, Hansen OC. The NH2-terminal amino acid sequence of the immunochemically partial identical major allergens of Alder (Alnus glutinosa) Aln g I, birch (Betula verrucosa)
    Bet v I, hornbeam (Carpinus betulus) Car b I and oak (Quercus alba) Que a I pollens.
    Mol Immunol 1991;28(11):1279-88
  7. Breiteneder H, Ferreira F, Hoffmann-Sommergruber K, et al. Four recombinant isoforms of Cor a I, the major allergen of hazel pollen, show different IgE-binding properties. Eur J Biochem 1993;212(2):355-62.
  8. Wopfner N, Dissertori O, Ferreira F, Lackner P.
    Calcium-binding proteins and their role in allergic diseases. Immunol Allergy Clin North Am 2007 Feb;27(1):29-44
  9. Yman L. Botanical relations and immuno-logical cross-reactions in pollen allergy. 2nd ed. Pharmacia Diagnostics AB. Uppsala. Sweden. 1982: ISBN 91-970475-09
  10. Valenta R, Breiteneder H, Petternburger K,
    Breitenbach M, Rumpold H, Kraft D, Scheiner O. Homology of the major birch-pollen allergen, Bet v I, with the major pollen allergens of alder, hazel, and hornbeam at the nucleic acid level as determined by cross-hybridization.
    J Allergy Clin Immunol 1991;87(3):677-82
  11. Ferreira FD, Hoffmann-Sommergruber K,
    Breiteneder H, Pettenburger K, Ebner C, Sommergruber W, Steiner R, Bohle B, Sperr WR, Valent P, et al. Purification and characterization of recombinant Bet v I, the major birch pollen allergen. Immunological equivalence to natural Bet v I.
    J Biol Chem 1993;268(26):19574-80
  12. Hoffmann-Sommergruber K, Vanek-Krebitz M,
    Radauer C, Wen J, Ferreira F, Scheiner O, Breiteneder H. Genomic characterization of members of the Bet v 1 family: genes coding for allergens and pathogenesis-related proteins share intron positions.
    Gene 1997;197(1-2):91-100
  13. Ramirez J, Carpizo JA, Ipsen H, Carreira J, Lombardero M. Quantification in mass units of Bet v 1, the main allergen of Betula verrucosa pollen, by a monoclonal antibody based-ELISA. Clin Exp Allergy 1997;27(8):926-31
  14. Hoffmann-Sommergruber K, Susani M, Ferreira F, Jertschin P, Ahorn H, Steiner R, Kraft D, Scheiner O, Breiteneder H. High-level expression and purification of the major birch pollen allergen, Bet v 1.
    Protein Expr Purif 1997;9(1):33-9
  15. Wilson IB, Altmann F. Structural analysis of N-glycans from allergenic grass, ragweed and tree pollens: core alpha1,3-linked fucose and xylose present in all pollens examined. Glycoconj J 1998;15(11):1055-70
  16. Hirschwehr R, Valenta R, Ebner C, Ferreira F,
    Sperr WR, Valent P, Rohac M, et al. Identification of common allergenic structures in hazel pollen and hazelnuts: a possible explanation for sensitivity to hazelnuts in patients allergic to tree pollen. J Allergy Clin Immunol 1992;90(6 Pt 1):927-36
  17. Mari A, Wallner M, Ferreira F. Fagales pollen sensitization in a birch-free area: a respiratory cohort survey using Fagales pollen extracts and birch recombinant allergens (rBet v 1, rBet v 2, rBet v 4).
    Clin Exp Allergy 2003;33(10):1419-28


As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.