Profilin is a protein found throughout the plant kingdom and in all eukaryotic cells. An allergy to this protein occurs when a person’s immune system overreacts to its presence. This reaction is a form of cross-reactive allergy, meaning the immune system mistakes the profilin in certain foods for profilin from pollen, to which it is already sensitized. This connection is why profilin allergies are frequently linked with pollen allergies, particularly hay fever.
Sources of Profilin
Profilin proteins are widespread panallergens, which are allergens present across various unrelated species. Their structural similarity allows the immune system to react to profilin from different sources after being sensitized to just one. This molecular mimicry is the foundation of pollen-food allergy syndrome (PFAS), or oral allergy syndrome (OAS), where a pollen allergy leads to reactions from eating certain plant-based foods.
The primary source of sensitization to profilin is airborne pollen. Common pollens that contain significant profilin allergens include birch, grass, and ragweed. Once the immune system has developed antibodies against profilin from pollen, it is primed to react when it encounters similar profilin proteins in various foods. This cross-reactivity explains why seasonal allergy sufferers might experience symptoms when consuming specific raw fruits and vegetables.
A wide variety of plant-based foods contain profilins that can trigger a reaction in a sensitized individual. Foods frequently associated with profilin allergy include:
- Melons like cantaloupe and watermelon
- Citrus fruits such as oranges
- Tomatoes
- Bananas
- Celery
- Kiwi
- Pineapple
- Certain nuts like peanuts and almonds
Profilin is also found in latex from the rubber tree, which can lead to cross-reactions between pollen, food, and latex products.
Profilin Allergy Symptoms
The most common manifestation of a profilin allergy is Oral Allergy Syndrome (OAS). This reaction is localized to the mouth and throat, occurring shortly after consuming the raw trigger food. Symptoms include itching of the lips, mouth, tongue, and throat, sometimes accompanied by mild swelling in these areas.
Reactions are confined to the oropharyngeal area because the proteins are often degraded during digestion. This process prevents them from entering the bloodstream and causing a more widespread reaction.
While most reactions are mild and localized, more systemic symptoms can occur, although this is less common. Individuals may experience hives (urticaria), angioedema (deeper swelling under the skin), or gastrointestinal discomfort. Rarely, a more severe, body-wide allergic reaction known as anaphylaxis can be triggered by profilin, particularly in individuals with high levels of sensitization or when certain co-factors are present.
Diagnosis and Testing
Identifying a profilin allergy begins with a detailed clinical history, where a healthcare professional will ask about symptoms related to both seasonal allergies and reactions to specific foods. If OAS is suspected based on symptoms like mouth itching after eating raw fruits or vegetables, further testing is often recommended to confirm the diagnosis.
Common methods for diagnosis include skin prick tests and blood tests. During a skin prick test, a small amount of a commercial allergen extract or even the fresh food itself is applied to the skin, which is then lightly pricked. A raised, red bump indicates a positive reaction. Blood tests measure the amount of specific Immunoglobulin E (sIgE) antibodies to particular allergens in the bloodstream.
A more advanced method called component-resolved diagnostics (CRD) can provide a more precise diagnosis. This specialized blood test can identify the exact protein molecule, such as profilin, that the IgE antibodies are targeting. By distinguishing between sensitization to profilin and other allergens, CRD helps confirm that cross-reactivity between pollens and foods is the cause of the symptoms.
Managing a Profilin Allergy
The primary approach to managing a profilin allergy involves avoiding the specific raw foods that trigger symptoms. An important characteristic of profilin is its instability when exposed to heat. This heat-labile nature means that many individuals can eat the trigger foods without a reaction if they are cooked, baked, canned, or pasteurized, as these processes denature the protein.
For mild symptoms of OAS, over-the-counter antihistamines can be effective in reducing itching and swelling. These medications work by blocking the action of histamine, a chemical released by the immune system during an allergic reaction. Taking an antihistamine shortly after a reaction begins can provide relief from the localized discomfort.
In instances where an individual has a history of more severe or systemic reactions, an allergist may prescribe an epinephrine auto-injector. This device is used to administer epinephrine, a medication that can rapidly reverse the symptoms of a severe allergic reaction. While anaphylaxis from profilin is uncommon, having an auto-injector on hand is a precautionary measure for those identified as being at higher risk.