Cypress Pollen-Peach Cross-Reactivity: The Emerging Role of Pru p 7 as a Marker of Severe Allergic Phenotypes

Abstract

Background: The peach allergen Pru p 7, a member of the Gibberellin-Regulated Protein (GRP) family, has emerged as a key marker of severe fruit-induced allergies. It is hypothesized to mediate cross-reactivity between fruit allergens and cypress pollen. Given the increasing prevalence of food allergies and the complex patterns of cross-sensitization, the role of Pru p 7 in clinical allergy diagnostics warrants further investigation. Objective: This study aims to characterize the sensitization profile to Pru p 7 in a cohort of patients with suspected fruit allergy and to assess its relationship with cypress pollen allergy, particularly to Cup s 7, a homologous GRP from Cupressus sempervirens. Methods: A retrospective analysis was conducted on 20 patients evaluated at the Allergy Unit of the Fondazione IRCCS Policlinico San Matteo. Specific IgE (sIgE) levels to peach extract, Pru p 7, and Cup a 1 (cypress extract) were assessed using the ImmunoCAP^® system (Thermo Fisher Scientific Inc., Waltham, MA, USA). Statistical associations between sensitizations were evaluated using chi-square tests and Spearman’s correlation. Results: Sensitization to peach extract, Pru p 7, and cypress pollen was detected in 38%, 30%, and 45% of patients, respectively. Significant associations were observed between peach and cypress (χ² = 8.80, p = 0.003), peach and Pru p 7 (χ² = 8.23, p = 0.004), and cypress and Pru p 7 (χ² = 6.55, p = 0.01). Notably, all patients sensitized to Pru p 7 also tested positive for both peach and cypress allergens, supporting the hypothesis of pollen–food cross-reactivity. Conclusions: Pru p 7 is a clinically relevant allergen that may account for severe allergic responses in patients not sensitized to classical peach allergens. Its cross-reactivity with Cupressaceae-derived GRPs, such as Cup s 7, highlights the importance of molecular diagnostics in evaluating food allergies, particularly in regions with significant exposure to cypress pollen.

1. Introduction

Food allergies have garnered increasing attention as a pressing public health concern, particularly in developed countries where environmental and lifestyle factors appear to contribute to their rising prevalence. This is particularly relevant in patients suffering from Chronic Obstructive Pulmonary Diseases (COPD) or asthma [1,2]. Among various food allergens, peach (Prunus persica) is a common trigger, especially in Southern Europe [3]. Well-known peach allergens such as Pru p 1 (a PR-10 protein), Pru p 3 (a lipid transfer protein, LTP), and Pru p 4 (a profilin) are well-established in clinical diagnostics and allergy management.

However, a subset of patients reports severe allergic reactions to peaches despite testing negative for these classical allergens. This diagnostic gap has led to the identification of Pru p 7, a novel allergen belonging to the gibberellin-regulated protein (GRP) family [4,5].

GRPs are highly conserved proteins that play a crucial role in plant development and environmental stress responses. The synthesis of GRPs is regulated by gibberellins, a class of phytohormones involved in plant development. These proteins are found in a wide variety of plants, including both food crops and allergenic plants. GRPs are particularly notable for their resilience to environmental degradation, including heat, digestive enzymes, and acidic conditions, which makes them more likely to trigger allergic reactions upon ingestion or inhalation.

Pru p 7, the first GRP identified in peach, has been implicated in severe systemic reactions, including anaphylaxis. Its robust molecular structure contributes to its allergenicity by maintaining IgE-binding capacity even after processing or cooking. This makes it a critical diagnostic target, particularly in patients with unexplained severe peach allergies [6,7].

Other GRPs—such as Cit s 7 (orange), Pru m 7 (Japanese apricot), and Pun g 7 (pomegranate)—share structural homology with Pru p 7 and demonstrate IgE cross-reactivity. These shared characteristics may account for multiple fruit sensitivities within and across botanical families. The allergenic potential of GRPs depends on factors including their molecular size, enzymatic resistance, and epitope recognition by specific IgE [8,9].

An additional complexity in diagnosing GRP-related allergies arises from cross-reactivity between food and inhalant allergens. Notably, the pollen of Cupressus sempervirens (cypress), prevalent in Mediterranean climates, contains a GRP known as Cup s 7. Its homology with Pru p 7 supports the hypothesis of cross-sensitization, wherein individuals sensitized to cypress pollen may also develop allergic responses to peach and related fruits. This phenomenon, part of the broader pollen-food syndrome, underscores the need to investigate environmental exposures in food allergy diagnostics [6,7,8,9]. This study aimed to evaluate the clinical significance of Pru p 7 sensitization in a cohort of allergic patients, with a particular focus on its association with cypress pollen allergy. We sought to clarify the sensitization patterns and potential cross-reactivity among these GRPs, and to propose diagnostic implications for clinical practice.

2. Materials and Methods

2.1. Study Population

This retrospective observational study was conducted at the Allergy Unit of the Fondazione IRCCS Policlinico San Matteo, Italy. The study cohort included 20 patients evaluated for suspected food or respiratory allergies. Patients included had either confirmed clinical reactions following peach ingestion or suggestive clinical histories indicating potential peach allergy, supported by physician evaluation. Ethical approval for the study was obtained from the local ethics committee (approval number 22253/2017), and written informed consent was collected from all participants.

2.2. Allergen Testing

Serum samples were retrospectively obtained from patients evaluated at our allergology outpatient clinic, referred for suspected food or respiratory allergies. Serum samples were analyzed for specific IgE (sIgE) to peach extract, Pru p 7, and Cup a 1 (cypress pollen extract) using the ImmunoCAP^® system (Thermo Fisher Scientific Inc., Waltham, MA, USA). Specific IgE levels ≥ 0.1 kUA/L were considered positive, following current recommendations for high-sensitivity allergen-specific IgE detection (Thermo Fisher Scientific DFU reference). Recombinant allergens were used to assess Pru p 7-specific IgE, providing a more refined evaluation of sensitization patterns.

2.3. Sample Handling and Assay Procedure

Serum aliquots were stored at 2–8 °C for up to one week prior to the assessment of specific IgE levels. All determinations were performed in separate analytical sessions using the Phadia™ 1000 instrument (Thermo Fisher Scientific Inc., Waltham, MA, USA), which fully automates all steps of the assay and provides printed results upon completion.

The assays were conducted on automated analyzers to enhance precision and reduce turnaround time. The total processing time is approximately 1 h and 45 min from the introduction of the first sample to the availability of results.

ImmunoCAP™ Specific IgE Calibrators or Calibrator Strips (Thermo Fisher Scientific Inc., Waltham, MA, USA) were run in duplicate to generate a calibration curve, which can be stored within the system. The Phadia™ software includes predefined acceptance criteria for both the calibration curve and associated control samples. Two curve controls (CC-1 and CC-2) were assessed in single determinations to verify the consistency of subsequent assays against the stored calibration curve. The calibration range for IgE quantification is 0–100 kU/L.

The IgE calibrators (Thermo Fisher Scientific Inc., Waltham, MA, USA) used in this procedure are traceable, via an unbroken chain of calibrations, to the 2nd International Reference Preparation (IRP 75/502) or the equivalent 3rd International Standard (11/234) for Human Serum Immunoglobulin E, established by the World Health Organization (WHO).

The assay is based on the Fluorescent Enzyme Immunoassay (FEIA) principle. The allergen of interest is covalently bound to the ImmunoCAP™ solid phase, a cellulose-based sponge matrix shaped into a small cap. When the patient serum is applied, specific IgE antibodies bind to the allergen. After washing away unbound and non-specific IgE, enzyme-labeled anti-IgE antibodies are added to form an immune complex.

Following an additional incubation and wash step to remove unbound reagents, a developing agent is introduced. The enzyme-substrate reaction produces a fluorescent signal, which is directly proportional to the amount of specific IgE present in the sample. The fluorescence intensity is then measured, and the results are interpreted using the calibration curve and instrument software.

2.4. Statistical Analysis

Statistical analyses were performed using MATLAB^® Statistical Toolbox (version R2024b). Associations between binary sensitization results were assessed using chi-square tests, while Spearman’s rank correlation was used to examine relationships between quantitative sIgE levels. A p-value of <0.05 was considered statistically significant.

3. Results

Among the 20 patients analyzed, sensitization was observed in 38% (n = 8) for peach extract, 30% (n = 6) for Pru p 7, and 45% (n = 9) for cypress pollen (Cup a 1). Notably, all patients who tested positive for Pru p 7 were also sensitized to both peach and cypress allergens, except for patient 7 (

Table 1. Individual patient-level specific IgE concentrations (kUA/L) for Cup a 1 (cypress pollen), peach extract, and Pru p 7, highlighting co-sensitization patterns and potential cross-reactivity among allergens.

Patients	Sex	Cypress	Peach	Pru p 7
1	M	0.0	0.6	0.0
2	M	1.2	0.3	0.2
3	F	0.0	0.0	0.0
4	F	0.3	0.1	0.1
5	F	0.0	0.0	0.0
6	F	0.0	0.0	0.0
7	F	0.1	0.0	0.1
8	F	0.0	0.0	0.0
9	F	0.3	0.1	0.0
10	F	0.0	0.0	0.0
11	F	0.0	0.0	0.0
12	F	0.2	0.2	0.2
13	F	0.0	0.0	0.0
14	F	0.0	0.0	0.0
15	F	1.2	0.4	0.5
16	M	0.1	0.0	0.0
17	M	0.2	0.1	0.1
18	F	0.0	0.0	0.0
19	F	0.0	0.0	0.0
20	F	0.5	2.3	0.0

).

This finding provides further evidence supporting the hypothesis of cross-reactivity between peach and cypress allergens, likely mediated by structurally homologous gibberellin-regulated proteins (GRPs).

Statistical analysis using chi-square tests confirmed significant associations among the tested allergens. Specifically, a strong association was observed between sensitization to Cypress and Peach (χ² = 8.80, p = 0.003), Cypress and Pru p 7 (χ² = 6.55, p = 0.01) and Peach and Pru p 7 (χ² = 8.23, p = 0.004).

These results underscore the close immunological relationship among peach allergy, cypress pollen sensitization, and Pru p 7 reactivity. They also suggest that individuals sensitized to Pru p 7 are highly likely to exhibit co-sensitization to both peach and cypress allergens, thereby reinforcing the concept of pollen–food cross-reactivity.

Pru p 7-specific IgE positivity was consistently accompanied by sensitization to both peach and cypress extracts. Notably, Pru p 7-specific IgE values were generally lower than those measured for the whole allergen extracts.

Furthermore, the quantitative data show that Pru p 7-specific IgE levels are, on average, equal to or lower than those observed for the whole extracts of peach and cypress [10]. This observation raises the hypothesis that sensitization to Pru p 7 may not be primarily driven by peach exposure. Further molecular-level investigations are warranted to determine whether patients sensitized to Pru p 7 are also reactive to the molecular component Cup a 1 from cypress pollen, thereby supporting the theory that primary sensitization to Pru p 7 could originate from cypress rather than fruit allergens.

4. Discussion

Our findings support the hypothesis that Pru p 7 plays a pivotal role in mediating cross-reactivity between peach and cypress pollen. The strong association observed between cypress and peach allergens in this patient cohort suggests that sensitization to one may be influenced by prior exposure to the other. This is consistent with the concept of pollen–food syndrome, in which inhalant allergens such as cypress pollen sensitize individuals to structurally homologous proteins found in foods.

GRPs such as Pru p 7 contribute to food allergy through their ability to trigger severe allergic reactions. Unlike many conventional food allergens, GRPs are resistant to heat and enzymatic degradation, which preserves their IgE-binding capacity even after cooking. This biochemical stability may explain the persistence of allergic symptoms in individuals consuming cooked fruits like peaches.

Implications for Allergy Diagnostics

The identification of Pru p 7 as a biomarker of severe peach allergy is particularly relevant for clinicians, especially when patients present with systemic reactions despite negative testing for major allergens like Pru p 1 and Pru p 3. In such cases, Pru p 7-specific IgE testing can reveal overlooked sensitizations. Moreover, the demonstrated cross-reactivity between Pru p 7 and Cup s 7 emphasizes the need to consider environmental exposures—such as cypress pollen—in the diagnostic workup of fruit allergies.

Accurate molecular diagnostics, including component-resolved diagnostics (CRD), are essential to identify at-risk individuals [11,12,13]. In areas with high environmental exposure to Cupressaceae, such as Southern Europe, incorporating GRP-specific tests into routine allergy panels may enhance diagnostic accuracy and facilitate tailored treatment strategies.

The clinical significance of these findings is substantial. Pru p 7, as a highly stable allergenic protein, provides insight into severe and complex allergic phenotypes, particularly when cross-reactivity with Cupressaceae GRPs is involved. GRP sensitization has been associated with systemic reactions, multispecies fruit allergies regardless of botanical family, and—less commonly—cofactor-dependent symptoms [14].

Patients with GRP allergy may present with distinctive clinical features, including laryngeal tightness and periorbital edema, especially eyelid swelling, which has been proposed as a predictive marker for Pru p 7 allergy. Situational cofactors—such as physical exercise, NSAID use, or proton pump inhibitors—may exacerbate symptoms. Additionally, a potential molecular cofactor mechanism has been hypothesized, given the structural cleft in GRPs that could bind ligands and modify their immunogenicity.

Sensitization to Pru p 7 appears to be particularly prevalent in areas with high exposure to cypress pollen [15]. It represents a risk factor for severe allergic reactions to fruit, with the severity of symptoms significantly correlated with specific IgE levels.

Regional pollen exposure profiles strongly influence allergenic sensitization patterns, with Mediterranean cypress being predominant in our geographic area. Indeed, in the Italian region, Mediterranean cypress is the primary contributor, and other cypress species are not clinically significant due to their lack of local pollination. This specificity guides the relevance and applicability of our findings.

Pru p 7 was the only peach allergen positively associated with severe peach allergy, highlighting its clinical relevance in diagnostic workup. Component-resolved diagnostics (CRD), including specific IgE testing for Pru p 7, can improve the accuracy of diagnosis, particularly in patients with unexplained or atypical reactions to peach. This is especially important in Mediterranean areas, where exposure to cypress pollen may act as a primary sensitizing agent. Given the potential for cofactor-enhanced reactions and the limitations of extract-based skin testing, incorporating molecular-based diagnostics may provide a more reliable identification of at-risk individuals and support tailored management strategies.

Earlier versions of serum IgE assays offered a limit of quantitation (LoQ) of 0.35 kilounits per liter (kUA/L), which then became, in a clinical setting, an established analytical cutoff level for considering a positive test result. Currently, serum IgE assays are capable of measuring IgE levels as low as 0.1 kUA/L. This might help in demonstrating the presence of sensitization in cases in which previous assays could not. Indeed, many clinical laboratories have replaced 0.35 kUA/L with 0.1 kUA/L as an analytical cutoff when reporting serum IgE results. It has to be specified that our laboratory as well reports sensitization to allergens when serum IgE levels were higher than 0.1 kUA/L. Although some specialists still prefer to use the 0.35 kUA/L level as a cutoff, IgE antibody levels between 0.1 and 0.35 kUA/L are now considered positive for sensitization and might help clinicians to investigate if this sensitization correlates with clinically evident allergic disease [16].

One limitation of this study is the absence of a healthy control group, which restricts our ability to generalize findings. Further research with appropriately matched controls will be required to strengthen these results.

5. Conclusions

Pru p 7 has emerged as a pivotal marker of severe fruit allergy and a key driver of respiratory-food cross-reactivity, particularly in individuals exposed to cypress pollen. Our findings reinforce the growing evidence that Cup s 7, through cross-reactive gibberellin-regulated proteins (GRPs), acts as the primary sensitizing allergen that ultimately predisposes patients to peach allergy. Accurate molecular diagnosis is therefore indispensable for identifying at-risk individuals and guiding personalized management strategies. As food allergies continue their global rise, the demand for advanced diagnostic tools and targeted therapies will only intensify, and a detailed understanding of allergens such as Pru p 7 will be essential for improving patient outcomes.

Because Cup s 7 and Pru p 7 share a high degree of structural homology, IgE antibodies directed against one antigen often recognize the other. This immunological cross-reactivity helps to explain why patients sensitized to cypress pollen may experience systemic reactions to peaches, apricots, and other related fruits [17,18]. This underscores the need to consider food-inhalant cross-sensitizations when interpreting in vitro diagnostic profiles and assigning clinical relevance to detected sensitizations.

CRD enhance food-allergy assessment by delineating individual sensitization patterns and stratifying the likelihood and severity of clinical reactions. Integrating CRD into routine practice will facilitate precision-medicine approaches and, ultimately, deliver better care for patients with complex allergy profiles.