Lipid transfer protein. One of the allergen families. Cross reactions therefore seen with fruit (stoned fruit but also raspberry), nuts, seeds (eg linseed/flaxseed), pulses, even cereals, tomatoes, vegetables (lettuce! Cabbage!). You may also see reactions only to composite foods eg pizza, curry, due to multiple allergens being present, but only producing reaction due to co-factors.
A less common cause of Pollen food syndrome than PR10 allergy. Thought of as a Mediterranean thing but increasing reports from Northern and Western Europe. Plane tree and mugwort have LTP but not thought to be the usual cause for sensitisation (except maybe in China). In N/W Europe, often birch sensitised too but not to be confused with PR10 type PFS!
Important to identify because heat stable (so not affected by heat, processing, digestion etc in the way PR10 allergens are) and potential for severe reactions.
So do component testing if atypical (eg unusually severe) reactions to fruit.
LTP allergy also seems to be more likely to cause reactions of varying severity, compared with primary food allergy, with co-factors perhaps more important. Eating multiple different plant foods at the same time seems to be the most likely cause of co-factor associated severe reactions. Of course, co-factors can co-exist too (alcohol and dancing, for example). So some would advise:
- Avoid exercise for 2 hours before (more in same cases) and 4 hours after eating
- Avoid NSAIDs for 2 hours before and 2 hours after
- Avoid alcohol with food or after
- Eat cautiously if not had for many months
- (sleep deprivation, cannabis, stress, fasting, anti-reflux medication…)
Diagnosis
Danger that with LTP allergy you show sensitisation to multiple foods, and then you end up on a restricted diet without knowing whether there is allergy or not.
Peach allergen Pru p 3 is a good surrogate for LTP allergy, even if peach hasn’t been a problem! If not available, you could test with SPT reagent for peach that is rich in pru p 3 (but might be false positive due to other components being present. London plane and mugwort allergy would also support.
Wheat is a bit tricky – the wheat LTP Tri a 14 is only 45% homologous with Pru p 3 so may get missed. Given the co-factor issue, probably good to do Tri a 19 (omega 5 gliadin, as in exercise induced anaphylaxis) as well.
Where hay fever and atypical reactions to nuts, do the LTPs Ara h 9 (peanut), Cor a 8 (hazelnut), Jug r 3 (walnut). You would do the other components to exclude primary food allergy which can co-exist with LTP sensitisation.
Food challenges have limited use in this situation – if positive, unclear whether LTP is the cause, and if negative, perhaps because of co-factor issue! Exercise challenge?? May just need a bigger dose!
Management
Individualize, to balance risk of reaction against dietary restriction.
Safest fruit/veg appear to be potato, carrot/root vegetables, beans, peas, melon, cashew and pistachio. Avoid pips and skin. Banana is hit and miss.
Good results with Pru p 3 sublingual and oral peach juice immunotherapy in Spain and Portugal.