Apple allergy T78.4

For the molecular diagnosis of malus domesticus (apple) the following "apple allergens" are included:

• Mal d 1 Pathogenesis-related protein: cross-allergen with reactivity to other members of the PR-10 family. The reactivity usually leads to local symptoms such as oral allergy syndrome.
• Mal d 2 Thaumatin-like protein
• Mal d 3 Non-specific lipid transfer protein type 1 (nsLTP1)
• Mal d 4 Profilin

The symptoms of apple allergy are manifold. While mainly mild symptoms are observed in Northern and Central Europe, apple allergy sufferers in Southern Europe often have severe reactions (cause: different allergens). Apple allergy sufferers in Northern and Central Europe mainly suffer from local reactions in the mouth and throat area ( oral allergy syndrome). This is caused by the heat-labile, apple-specific protein Mal d 1 (is formed during apple ripening). Mal d 1 has great molecular similarities to Bet v 1 (main allergen of birch pollen - see birch below), so that cross-reactions are frequent (about 50-75% of all birch pollen allergy sufferers in Northern and Central Europe are affected by an apple allergy at the same time). Thus, an apple allergy directed against Mal d 1 often develops via an already existing sensitisation to birch pollen (pollen-associated food allergy). The milder course of this food allergy is probably due to the instability of mal d 1 protein in the digestive tract.

In Southern Europe (where sensitisation to tree pollen is not relevant for the development of apple allergy), the allergic reactions are mainly caused by the apple allergen Mal d 3. Mal d 3 (nsLipidtransferprotein - LTP) is mainly located in the fruit peel. NsLTPs are widespread in the plant kingdom and play a role in the defence against bacterial and fungal infections. They are insensitive to enzymatic processes, low pH-values and above all to the effects of heat (heat-stable). Thus, allergic symptoms can also occur when eating processed apples. Cross-reactions to similar proteins of other fruits belonging to the rose family (Rosaceae) are possible. The most common cause is a simultaneous allergy to peach. Mal d 2 and mal d 4 are further allergens of the apple. They have a lower allergological significance than Mal d 1 and Mal d 3.

• Frequent cross-reactions with apple allergy:
  • Pollen of birch, hazel, alder.
• Other members of the Rosaceae family:
  • Apricot, pear, blackberry, strawberry, rose hip, wood apple, raspberry, cherry, cherry plum, loganberry, loquat, almond, medlar, peach, plum, pimpernel, sour cherry, blackthorn, plum.

Apple allergens are often inactivated by heating and/or enzymatic browning (crushing). Processed products such as apple compote, apple juice or apple pie are therefore often tolerated by apple allergy sufferers (see above). The allergenic potency of apples is strongly dependent on variety and degree of ripeness:

• Highly allergenic apple varieties: e.g. Cox orange, Golden Del., Granny Smith, Jonagold, Braeburn
• Weakly allergenic apple varieties: e.g. Boskop, Jamba, Gloster, Gravensteiner, Altländer, Hammerstein, Berlepsch, Goldparmäne

1. Gomez F et al.(2014) High prevalence of lipid transfer protein sensitization in apple allergicpatients
   with systemic symptoms PLoS One 9:e107304.
2. Kleine-Tebbe J et al (2016) Molecular allergy diagnostics with IgE single determinations (singleplex): Methodological and practical aspects In: Kleine-Tebbe JK et al (Hrsg) Molecular allergy diagnostics. Springer Publishing House GmbH S91-138
3. WHO/IUS Allergen Nomenclature Sub-Committee