Direct evidence for the presence of allergens in Rosaceae fruit tree pollen

Abstract

The allergen content of insect-carried fruit tree pollen is poorly investigated. A recent report on orange allergy indicates a possible co-sensitisation to fruits by digestion and inhalation, suggesting an alternative mechanism for allergy development. Allergy to Rosaceae fruits like apple, pear, peach and cherry has been described as cross-reactivity to the birch pollen allergen Bet v␣1. The expression of two major apple allergens Mal d 1 and Mal d 3 and their homologues in Rosaceae pollen was investigated. Transcript expression of five Mal d 1 isoforms and of Mal d 3 was examined by RT-PCR. A Mal d 1 specific ELISA was used to quantify the content of Mal d␣1 homologues in Pomoideae pollen. Polyclonal antibodies against Mal d 1 and Mal d 3 were used␣for allergen detection in pollen extracts in Western blots. The cross-reactivity of pollen allergens with patient sera was confirmed by IgE-Western blotting. Pollen counts were carried out by using Hirst-type volumetric samplers, revealing an intermittent Rosaceae fruit tree pollen load, without remarkable peaks across large parts of Europe. The expression of Mal d 1 was confirmed in pollen of all tested Rosaceae fruit tree species by ELISA, Western blot and RT-PCR. IgE-Western blots showed a strong cross-reactivity, particularly with Mal d 1 and Mal d 3 homologues in different Rosaceae pollen. Although the pollen load of Rosaceae is rather low as a rule, there is certified evidence for temporary peaks, indicating that allergen exposure for sensitized individuals is likely.