Overview of Pollen-Food Allergy Syndrome (PFAS)

  • Also known as oral allergy syndrome (OAS)
  • Class 2 (also known as type 2, incomplete, nonsensitizing elicitor) food allergens are postulated to lack the capacity to induce IgE sensitization via the GI tract due to their susceptibility to thermal processing (e.g. cooking, baking, heating, canning) and gastric digestion. These proteins are believed to elicit symptoms only after primary sensitization with cross-reactive inhalant allergens.


Pollen-Food Cross-reactivity Tables

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OAS_related_poll_fruits_edt.jpg

Spice_pollen_cross-reactivity.png


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Additions to above tables
  • Peanut Ara h 9 (LTP) shares 60-70% amino sequence identity with LTPs from a number of commonly consumed foods, including pear, lentils, sunflower, beans, and pomegranate (in addition to above table).
  • Mustard allergens
    • Sin a 1 (seed storage protein) and Sin a 2 involved in primary sensitization to mustard ingestion
    • Sin a 3 (LTP) and Sin a 4 (profilin) associated with OAS with likely initial sensitization to pollen
  • Soybean Gly m 4 (Bet v 1 homologue) retains allergenicity after heating (unlike other Bet v 1 homologues like apple, peach, cherry, etc)
  • Ragweed sensitization may cause symptoms with echinacea, chamomile tea
  • Phadia cross-reactivity chart



Distribution of Pollen-Food Allergens


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Latex-Fruit Syndrome



Diagnostic Testing


Fresh-food SPT (Prick-by-prick)

  • Performed by inserting the test device into the fruit, withdrawing, and then immediately pricking the patient's cleaned skin. It is important to prick all edible parts of the food (eg, both the outer skin and the flesh of fruits) with the testing device in order to recreate the allergen exposure that would result from eating these foods.
  • Performance (vs. commercial extracts)
    • For most foods implicated in PFAS, the FFPST method appears to be more sensitive than using commercial extracts
    • PFAS to foods containing stable allergens (peanut, hazelnut, and pea) may be best detected with commercial extracts
    • Commercial extracts may be preferred for foods that are difficult to prepare or irritating to the skin, such as spices
    • Patients with positive skin tests to commercial extracts may be more likely to experience systemic reactions than those with positive skin tests only to fresh extracts

OAS_test_comparison.png
  • One study demonstrated that FFSPT for birch oral allergy syndrome could be performed with fruits that are frozen and thawed

Phadia Allergen Component Resolved Diagnostic Testing

  • Peanut - Ara h 1, 2, 3, 8 and 9
    • IgE to Ara h 1, 2, 3 and 9 (LTP) are associated with peanut reactions, which in many cases can be severe.
    • IgE to Ara h 8 (PR-10) are usually associated with milder, local symptoms such as OAS, originating from birch sensitization.

  • Soy - Gly m 4, 5 and 6
    • IgE to Gly m 5 and 6 are associated with clinical reactions to soy.
    • Soy Gly m 5/peanut Ara h 1 and soy Gly m 6/peanut Ara h 3 share homologous structures.
    • IgE to Gly m 4 (PR-10) are usually associated with milder, local symptoms such as OAS, originating from birch sensitization.





Management (Nowak-Węgrzyn)

  • There are no established practice guidelines for the management of PFAS
Education
  • Inform patients of small, but definite risk for systemic reactions and the possibility of reacting to related foods with first exposure
  • Provide a printed list of cross-reactive foods that might also be expected to cause symptoms
  • The prognosis is favorable without evidence of progression to systemic symptoms in the majority of patients, but OAS tends to last life-long
Avoidance
  • Patients with symptoms limited to the oropharynx should avoid the raw fruits/vegetables (including shakes/juices and dehydrated forms) and any form of nuts (both raw and roasted) that cause symptoms
    • Note that the long-term consequences of continuing to ingest raw foods that cause PFAS are unknown
  • Patients with systemic symptoms should avoid any form of the responsible food (including cooked), unless patient history or OFC prove that the cooked food is tolerated
  • If a patient with severe symptoms wishes to start eating new foods that are cross-reactive, consider evaluating for allergy to the foods in question
  • If the patient wishes to continue eating other foods to which they test positive, but have not eaten recently, then consider an oral food challenge
Epinephrine indications
  • Patients with history of systemic or severe symptoms (e.g. dysphagia, significant throat discomfort, or worse) should carry epinephrine
  • Patients without systemic reactions should also carry epinephrine if any of the following are true:
    • Allergy to peach, peanut, tree nuts, or mustard (associated with higher rates of systemic reactions)
    • Reactions to foods in geographic regions where that food is often associated with systemic reactions (i.e. peach, apple in the Mediterranean)
    • The patient experienced an oropharyngeal or mild reaction to a cooked food
    • The patient had a positive SPT to a commercial extract for the culprit food
PPI/H2 blocker precautions
  • PPI/H2 blockers - limited evidence suggests that acid blocking medications may increase risk for more severe reactions in these patients, therefore more careful food avoidance should be recommended if these medications are required.
Unproven treatments
  • Prophylactic H1-antihistamines prior to eating foods
  • Subcutaneous immunotherapy for pollinosis; studies are mixed for birch, rhinitis may improve while OAS persists, might require higher doses for OAS to improve
  • Omalizumab
  • Oral desensitization
    • Build-up by ingesting doubling doses of fresh apple daily until a whole apple tolerated, then ingesting at least 3 apples/week for maintenance
    • Symptoms relapse if frequent apple ingestion is not maintained, and immunologic changes are not seen





References





Current Phadia PiRL Test Information