Tree pollen allergens-an update from a molecular perspective

Abstract

It is estimated that pollen allergies affect approximately 40% of allergic individuals. In general, tree pollen allergies are mainly elicited by allergenic trees belonging to the orders Fagales, Lamiales, Proteales, and Pinales. Over 25 years ago, the gene encoding the major birch pollen allergen Bet v 1 was the first such gene to be cloned and its product characterized. Since that time, 53 tree pollen allergens have been identified and acknowledged by the WHO/IUIS allergen nomenclature subcommittee. Molecule-based profiling of allergic sensitization has helped to elucidate the immunological connections of allergen cross-reactivity, whereas advances in biochemistry have revealed structural and functional aspects of allergenic proteins. In this review, we provide a comprehensive overview of the present knowledge of the molecular aspects of tree pollen allergens. We analyze the geographic distribution of allergenic trees, discuss factors pivotal for allergic sensitization, and describe the role of tree pollen panallergens. Novel allergenic tree species as well as tree pollen allergens are continually being identified, making research in this field highly competitive and instrumental for clinical applications.

Keywords: allergen cross-reactivity; allergen exposure; molecular allergology; tree pollen allergy; tree pollen sensitization.

Figure 1

Phylogenetic tree of plant orders generated using the software phyloT a phylogenetic tree generator, based on NCBI taxonomy (http://phylot.biobyte.de/). Taxonomic orders containing species which have been acknowledged by the WHO/IUIS allergen nomenclature database (www.allergen.org) are highlighted in color (Pinales in green; Proteales in red; Lamiales in purple; Fagales in blue; and other in yellow). Photographs were obtained from Fotolia.

Figure 2

Schematic representation of tree pollen allergens clustered according to protein functions; major allergens are depicted in bold, minor allergens in regular font. Allergens of the Lamiales order are presented in purple, Proteales in red, Fagales in blue, Pinales in green, and other in black. Allergen structures were obtained from the RCSB PDB protein data bank (http://www.rcsb.org) and photographs from Fotolia.

Figure 3

Geographic distribution of allergenic Fagales, Lamiales, Proteales, and Pinales species. The distribution data were extracted from maps provided on www.eol.org. Photographs of florescences of members of the Fagales (birch Betula verrucosa), Proteales (plane tree Platanus acerifolia), Lamiales (lilac Syringa vulgaris and olive Olea europaea), and Pinales (mountain cedar Juniperus ashei and Japanese cedar Cryptomeria japonica) were obtained from Fotolia.