London Plane Tree (Pla a 3) IgE Test · Blood

If you live in a city lined with London plane trees and you also notice mouth tingling, hives, or stomach trouble after eating peach, walnut, or peanut, this test can connect the dots. It measures a specific antibody to Pla a 3, a small protein in plane tree pollen that shares a structural family with proteins found in many plant foods.

Standard allergy testing using whole plane tree pollen extract can tell you whether you react to the tree at all. This component test goes further by telling you which exact protein your immune system has latched onto, which is the difference between knowing you have a pollen allergy and knowing whether you are at higher risk for systemic food reactions.

What Pla a 3 Actually Is

Pla a 3 (Platanus acerifolia allergen 3) is a non-specific lipid transfer protein, or nsLTP. nsLTPs are small, sturdy proteins that plants use to move fatty molecules around and to defend against stress. They are abundant in pollens, fruit skins, nuts, and seeds, and they survive heat and digestion, which is why allergies to them can produce reactions to cooked and processed foods, not just raw ones.

The test measures IgE (immunoglobulin E), the antibody type your immune system makes when it has been trained to react to a specific allergen. When you have IgE to Pla a 3, your body has identified this particular plane tree protein as a threat. Because nsLTPs across many plants look biochemically similar to each other, that same IgE can also recognize the nsLTPs in peach, walnut, peanut, and other plant foods. This is the cross-reactivity that makes Pla a 3 clinically useful.

Why This Test Exists

Plane trees line streets across southern Europe and other temperate cities, and plane tree pollen is one of the standard inhalant allergens screened in European clinical practice. In high-exposure regions like Barcelona, plane pollen is a common driver of seasonal respiratory symptoms and a meaningful share of pollen-allergic patients in these areas are sensitized to plane tree.

What makes the Pla a 3 component test specifically valuable is that not everyone allergic to plane tree pollen is allergic the same way. Some people react to other plane tree proteins and develop respiratory symptoms. Others react to Pla a 3 and end up with reactions when eating certain plant foods. The test sorts you into the right category.

What a Positive Result Suggests

In the largest study to date, which looked at 939 patients positive on a broad allergy microarray, 71.9 percent were sensitized to Pla a 3, 54.1 percent to Pla a 2, and 10.9 percent to Pla a 1. People who tested positive for Pla a 3 were more likely to have both local food reactions (such as itching or swelling in the mouth) and systemic food-induced reactions. They had fewer past respiratory symptoms than those positive for Pla a 2.

In a separate Italian cohort of 568 nsLTP-sensitized patients, Pla a 3 stood out alongside mugwort nsLTP (Art v 3) as one of only two nsLTPs clearly tied to respiratory symptoms. The same study found that Pla a 3 sensitization clustered with tree nut and peanut nsLTP sensitization, and that plane pollen extracts could block a substantial portion of IgE binding to certain food nsLTPs in laboratory testing. In plain terms, your plane tree reactivity and your nut or fruit reactivity are often part of the same underlying immune pattern.

Food Reactions and the LTP Syndrome

nsLTPs are a leading cause of plant-food allergy in Mediterranean countries, and the test sits at the center of what allergists call LTP syndrome. The hallmark is reactions to multiple unrelated plant foods, sometimes severe, sometimes triggered only when combined with cofactors like exercise, alcohol, or NSAIDs.

An earlier study of plane-allergic patients found that Pla a 3 was a major allergen in 63.8 percent of those who also had peach allergy, but only a minor allergen in 27.3 percent of plane-allergic patients without food allergy. The same study showed frequent but not universal cross-reactivity with the peach nsLTP, Pru p 3. If you have unexplained reactions to peach, walnut, peanut, or related foods and you also have any plane tree pollen exposure, this test helps clarify the mechanism.

Respiratory Allergy

Plane tree pollen is on the standard European skin-test panel for inhalant allergens used to evaluate rhinitis and asthma. Within the plane tree allergen family, Pla a 2 tends to be the main driver of respiratory symptoms, while Pla a 3 is more closely tied to food reactions. People with co-sensitization to both Pla a 2 and Pla a 3 actually had a lower rate of severe food reactions than people sensitized to Pla a 3 alone, suggesting that the combination of these two profiles shifts the clinical picture.

This is why a single test result is not the whole story. Knowing your Pla a 3 status alongside Pla a 2 and other components gives a clearer read on whether your immune system is set up for primarily respiratory disease, primarily food reactions, or a mix.

Reconciling the Mixed Findings

At first glance, the evidence looks contradictory. One study links Pla a 3 to respiratory symptoms; another links it more to food reactions. The framework that resolves this is straightforward. Pla a 3 is not a single-outcome marker. It is a phenotype indicator that places you somewhere on a spectrum from purely respiratory plane tree allergy to a broader nsLTP food allergy syndrome. Where you sit on that spectrum depends on your full sensitization pattern, your exposure history, and your symptoms, not on Pla a 3 alone.

Tracking Your Trend

A single IgE reading captures one moment in your immune system. Specific IgE levels can change over time, particularly with ongoing exposure, after starting allergen immunotherapy, or as allergic disease evolves. For a baseline read, one well-timed test is enough, but if you are making changes (avoidance strategies, immunotherapy, or evaluating new symptoms) repeat testing is what shows whether the trajectory is moving in the right direction.

A practical cadence: get a baseline, retest in 6 to 12 months if you are pursuing immunotherapy or changing your diet meaningfully, and then at least annually if you have ongoing symptoms. Watch the direction of change more than the absolute number. Outside of intervention, most people do not need more frequent testing.

What an Unexpected Result Should Prompt You to Do

If your Pla a 3 IgE comes back positive and you have plant-food reactions, the next step is a fuller nsLTP component panel. Testing peach (Pru p 3), walnut (Jug r 3), hazelnut (Cor a 8), and peanut (Ara h 9) clarifies which specific foods are most likely to drive reactions and helps map your personal cross-reactivity pattern. Pairing component results with a careful history of which foods, in which forms, and with which cofactors have caused trouble gives you the clearest picture.

If you have respiratory symptoms during plane tree pollen season, knowing your Pla a 2 status alongside Pla a 3 helps determine whether immunotherapy targeting plane tree is appropriate. An allergist or immunologist is the right specialist to interpret the full panel, recommend immunotherapy candidates, and prescribe emergency medication if your food reaction risk warrants it. A positive Pla a 3 result without symptoms is not by itself a diagnosis; it indicates sensitization, and the clinical picture is what matters.

When Results Can Be Misleading

Specific IgE testing is generally stable across short timeframes, but a few factors can distort interpretation:

• Sensitization without symptoms: a positive Pla a 3 IgE means your immune system has produced antibodies to this protein, but it does not always mean you will have clinical reactions. Treat the result as one piece of evidence alongside your symptom history.
• Cross-reactivity with related proteins: because nsLTPs across many plant species share structural features, IgE measured against Pla a 3 may partly reflect sensitization that started with a different nsLTP (such as peach). The lab number alone cannot tell you which protein was the original trigger.
• Age effects: total IgE tends to rise with age in allergic patients, while specific IgE to individual allergens can shift. Interpret a single reading in the context of your age and history.
• Specimen handling: improper blood handling can occasionally affect specific IgE assays. If a result is inconsistent with your clinical picture, a repeat draw is reasonable.