LTP Allergy Follow-Up Study: Development of Allergy to New Plant Foods 10 Years Later

A systematic review of allergen cross-reactivity: Translating basic concepts into clinical relevance

Access to the molecular culprits of allergic reactions allows for the leveraging of molecular allergology as a new precision medicine approach-one built on interdisciplinary, basic, and clinical knowledge. Molecular allergology relies on the use of allergen molecules as in vitro tools for the diagnosis and management of allergic patients. It complements the conventional approach based on skin and in vitro allergen extract testing. Major applications of molecular allergology comprise accurate identification of the offending allergen thanks to discrimination between genuine sensitization and allergen cross-reactivity, evaluation of potential severity, patient-tailored choice of the adequate allergen immunotherapy, and prediction of its expected efficacy and safety. Allergen cross-reactivity, defined as the recognition of 2 or more allergen molecules by antibodies or T cells of the same specificity, frequently interferes with allergen extract testing. At the mechanistic level, allergen cross-reactivity depends on the allergen, the host's immune response, and the context of their interaction. The multiplicity of allergen molecules and families adds further difficulty. Understanding allergen cross-reactivity at the immunologic level and translating it into a daily tool for the management of allergic patients is further complicated by the ever-increasing number of characterized allergenic molecules, the lack of dedicated resources, and the need for a personalized, patient-centered approach. Conversely, knowledge sharing paves the way for improved clinical use, innovative diagnostic tools, and further interdisciplinary research. Here, we aimed to provide a comprehensive and unbiased state-of-the art systematic review on allergen cross-reactivity. To optimize learning, we enhanced the review with basic, translational, and clinical definitions, clinical vignettes, and an overview of online allergen databases.

Understanding of lipid transfer protein sensitization patterns and its clinical significance in children

Background: Lipid transfer proteins (LTP) are the most common food allergens in the Mediterranean region. Objective: The study aimed to investigate co-sensitization patterns and cluster relationships between LTP allergen molecules across a broad range of allergen-specific sensitization patterns, and clinical outcomes in eastern Mediterranean children. Methods: Among 496 children evaluated for multiple sensitizations with multiplex testing, 105 children (21%) with 16 different LTP sensitizations were analyzed. Clinical reactivity was examined based on clear-cut history of immunoglobulin E mediated symptoms (oral allergy syndrome [OAS], systemic reactions, and anaphylaxis). Results: All children included were sensitive to food LTPs, but 56% were sensitive to pollen LTPs. The number of children with OAS and clinical reactivity was 12 and 59, respectively, and no cofactors were reported. The most common sensitizations were Pru p 3 (74%) and Cor a 8 (66%). Significant correlations were observed in the heatmap between the LTP molecules other than Par j 2 and Tri a 14. Overall, clinical reactivity was associated with increased age and number of LTP molecule positivity. Conclusion: In the eastern Mediterranean region, 21% of children with multiple food and/or pollen sensitizations were found to have LTP sensitization; however, almost half reported clinical reactivity. The hierarchical pathway highlights that distinct LTP allergen molecules can act as primary sensitizers. Clinical reactivity is linked to increasing numbers of LTP molecule positivity and increasing age.

Sensitization to nsLTP: A Retrospective Study in An Italian Pediatric Population over the Last Decade

Background

Food allergy is common in the Mediterranean, especially concerning lipid transfer proteins (LTPs) allergy. LTPs are widespread plant food allergens in fruits, vegetables, nuts, pollen, and latex. Also, LTPs are prevalent food allergens in the Mediterranean area. They can sensitize via the gastrointestinal tract and cause a wide range of conditions: from mild reactions, such as oral allergy syndrome, to severe reactions, such as anaphylaxis. LTP allergy in the adult population is well described in the literature, concerning both the prevalence and clinical characteristics. However, there is poor knowledge about its prevalence and clinical manifestation in children living in the Mediterranean.

Materials and Methods

This study, including 800 children aged from 1 to 18 years, investigated the prevalence of 8 different molecules of nonspecific LTP over time in an Italian pediatric population visited over the last 11 years.

Results

About 52% of the test population was sensitized to at least one LTP molecule. For all the LTPs analyzed, sensitization increased over time. In particular, using the years 2010 through 2020 as a comparison, the major increases were observed for the LTPs of the English walnut Jug r 3, the peanut Ara h 9, and the plane tree Pla a 3 (about 50%); the increase of the LTP of the Hazelnut Cor a 8 was about 36%, and that of the LTP of the artemisia Art v 3 was approximately 30%.

Conclusions

The latest evidence in the literature indicates an increase in food allergy prevalence in the general population, including children. Therefore, the present survey represents an interesting perspective about the pediatric population of the Mediterranean area, exploring the trend of LTP allergy.

Hidden and Rare Food Allergens in Pediatric Age

In food allergy management, the avoidance of the allergen that caused the reaction plays a fundamental role. Nevertheless, that can be thwarted in case of accidental exposure to a rare or hidden allergen, causing the adoption of a monotonous diet and a consequent reduction in the quality of life of the patient and their family. The identification of a rare and hidden allergen is an important diagnostic challenge, taking into account that a significant proportion of all food reactions is in reality due to them. The aim of the present review is to provide the pediatric allergist an overview of the possible sources of rare and hidden food allergens, taking into consideration the routes of exposure to these potential allergens with the main examples published in the scientific literature and the distinction between types of direct or cross-contamination. The identification of the allergen responsible for the reaction and the provision of a dietary advice customized for the specific individual’s dietary habits is essential to improve quality of life of the familiar nucleus and to reduce the risk of further allergic reactions.

Combined LTP Sublingual and Oral Immunotherapy in LTP Syndrome: Efficacy and Safety

INTRODUCTION

SLIT for the treatment of plant food allergies has been demonstrated to be safe but less effective than OIT, but the latter is associated with more adverse reactions. The aim of the study was to evaluate the efficacy and safety of a new protocol starting with SLIT-peach followed by OIT with commercial peach juice in patients with LTP syndrome.

METHODS

This was a prospective, noncontrolled, open study on patients with LTP syndrome who are not sensitized to storage proteins. SLIT peach ALK was followed by OIT with Granini^® peach juice after 40 days of the SLIT maintenance phase. At home, the Granini^® juice dose was progressively increased during the 42 days until reaching 200 ml. After achieving the maximum dose, an open oral food challenge was carried out with the food that had caused the most severe reaction. If negative, the patient was instructed to progressively introduce the foods that were avoided before starting immunotherapy at home. Patients were reviewed 1 month later. The quality-of-life questionnaire FAQLQ-AF was completed at the beginning of the study and one month after the final challenge.

RESULTS

Forty-five patients were included, most of them with LTP anaphylaxis. Peach SLIT was well tolerated in 80.5%, and OIT with Granini^® was well tolerated in 85%, with no severe adverse reactions. The final provocation was successful in 39/45 (86.6%). One month after the final provocation, 42/45 (93.3%) patients had no dietary restrictions. FAQLA-AF was significantly reduced.

CONCLUSIONS

This combination of peach SLIT and OIT with commercial peach juice provides a new, fast, effective, and safe immunotherapy option for selected patients with LTP syndrome who are not allergic to storage proteins, improving their quality of life. This study suggests that cross-desensitization relative to the nsLTPs of several plant foods can be achieved by using Prup3.

Anaphylaxis across Europe: are pollen food syndrome and lipid transfer protein allergy so far apart?

PURPOSE OF REVIEW

Traditionally pollen-food syndrome (PFS) is considered to be a mild cross-reacting food allergy affecting only Northern Europe, with lipid transfer protein (LTP) allergy being more severe and mainly occurring in Southern Europe. This review seeks to update the reader on both types of plant food allergy and to determine whether the stereotypical presentations of these plant food allergies remain the same, with a particular focus on reaction severity.

RECENT FINDINGS

Recent findings suggest that both these types of plant food allergy occur in children and adults. Although it is true that PFS allergy is more prevalent in Northern Europe and LTP allergy is more well known in Southern Europe, these conditions are not hidebound by geography, and the increasing spread and allergenicity of pollen due to global warming continues to change their presentation. Both conditions have a spectrum of symptom severity, with PFS sometimes presenting with more severe symptoms, including anaphylaxis and LTP allergy with milder reactions.

SUMMARY

It is important to consider that in many parts of Europe, reactions to plant foods, especially fruits or vegetables, could be mediated either by pollen cross-reactivity or primary sensitization to LTP allergens. All those presenting with symptoms to plant foods will benefit from a detailed clinical history and appropriate tests so that an accurate diagnosis can be made, and correct management implemented.

Suitability of potyviral recombinant virus-like particles bearing a complete food allergen for immunotherapy vaccines

Virus-like particles (VLPs) have been gaining attention as potential platforms for delivery of cargos in nanomedicine. Although animal viruses are largely selected due to their immunostimulatory capacities, VLPs from plant viruses constitute a promising alternative to be considered. VLPs derived from Turnip mosaic virus (TuMV) have proven to present a tridimensional structure suited to display molecules of interest on their surface, making them interesting tools to be studied in theragnostic strategies. Here, we study their potential in the treatment of food allergy by genetically coupling TuMV-derived VLPs to Pru p 3, one of the most dominant allergens in Mediterranean climates. VLPs-Pru p 3 were generated by cloning a synthetic gene encoding the TuMV coat protein and Pru p 3, separated by a linker, into a transient high-expression vector, followed by agroinfiltration in Nicotiana benthamiana plants. The generated fusion protein self-assembled in planta to form the VLPs, which were purified by exclusion chromatography. Their elongated morphology was confirmed by electron microscopy and their size (~400 nm), and monodispersity was confirmed by dynamic light scattering. Initial in vitro characterization confirmed that they were able to induce proliferation of human immune cells. This proliferative capability was enhanced when coupled with the natural lipid ligand of Pru p 3. The resultant formulation, called VLP-Complex, was also able to be transported by intestinal epithelial cells, without affecting the monolayer integrity. In light of all these results, VLP-Complex was furtherly tested in a mouse model of food allergy. Sublingual administration of VLP-Complex could effectively reduce some serological markers associated with allergic responses in mice, such as anti-Pru p 3 sIgE and sIgG2a. Noteworthy, no associated macroscopic, nephritic, or hepatic toxicity was detected, as assessed by weight, blood urea nitrogen (BUN) and galectin-3 analyses, respectively. Our results highlight the standardized production of allergen-coated TuMV-VLPs in N. benthamiana plants. The resulting formula exerts notable immunomodulatory properties without the need for potentially hazardous adjuvants. Accordingly, no detectable toxicity associated to their administration was detected. As a result, we propose them as good candidates to be furtherly studied in the treatment of immune-based pathologies.

Differences in Linear Epitopes of Ara h 9 Recognition in Peanut Allergic and Tolerant, Peach Allergic Patients

Background

Peanut-allergic patients from the Mediterranean region are predominantly sensitized to the lipid transfer protein (LTP) Ara h 9, and the peach LTP Pru p 3 seems to be the primary sensitizer. However, LTP sensitization in peanut allergy is not a predictive marker for clinically relevant symptoms.

Objective

We aimed to identify sequential epitopes of IgE and IgG4 from Pru p 3 and Ara h 9 in peach-allergic patients sensitized to peanuts. We also sought to determine the differences in IgE and IgG4 binding between patients who had developed peanut allergy and those tolerating peanuts.

Methods

A total of 46 peach-allergic patients sensitized to peanuts were selected. A total of 35 patients were allergic to peanuts (peanut-allergic group) and 11 were tolerant to peanuts (peanut-tolerant group). We measured sIgE and sIgG4 in peanut, peach, and their recombinant allergen (Ara h 1, Ara h 2, Ara h 3, Ara h 8, and Ara h 9) with fluorescence enzyme immunoassay. We examined the IgE and IgG4 binding to sequential epitopes using a peptide microarray corresponding to linear sequences of the LTPs Ara h 9 and Pru p 3 with a library of overlapping peptides with a length of 20 amino acids (aa) and an offset of 3 aa.

Results

The frequency and the intensity of IgE recognition of Ara h 9 and Pru p 3 peptides were higher in the peanut-tolerant group than in the peanut-allergic group. We found four Ara h 9 peptides (p4, p14, p21, and p25) and four Pru p 3 peptides (p1, p3, p21, and p24) with a significantly elevated IgE recognition in peanut-tolerant patients. Only one peptide of Ara h 9 (p4) recognized by IgG4 was significantly elevated in the peanut-tolerant group. The IgG4/IgE ratio of Ara h 9 peptide 4 was significantly higher in peanut-tolerant patients than in peanut-allergic patients, while no significant differences were observed in the IgG4/IgE ratio of this peptide in Pru p 3.

Conclusion

Although we found significant differences in IgE and IgG4 recognition of Ara h 9 and Pru p 3 between peanut-tolerant and peanut-allergic patients (all of whom were allergic to peach), polyclonal IgE peptide recognition of both LTPs was observed in peach-allergic patients tolerating peanuts. However, the IgG4 blocking antibodies against Ara h 9 peptide 4 could provide an explanation for the absence of clinical reactivity in peanut-tolerant peach-allergic patients. Further studies are needed to validate the usefulness of IgG4 antibodies against Ara h 9 peptide 4 for peanut allergy diagnosis.

Epinephrine Auto-Injector Prescription and Use: A Retrospective Analysis and Clinical Risk Assessment of Adult Patients Sensitized to Lipid Transfer Protein

Lipid transfer proteins (LTPs) are widely widespread plant food allergens which represents the main cause of food allergy in adults living in the Mediterranean basin. The purpose of this study was to investigate in LTP patients the actual use of prescribed epinephrine auto-injector and appropriateness of its prescription. In addition, we investigated in these patients: (1) occurrence of new food reaction in the following three years after to diagnosis; (2) need and number of access to emergency services; (3) presence of possible predictive factors to further food reactions. One-hundred sixty-five adult patients sensitized to LTPs have been included. During follow-up, we recorded 68 further reactions, most of them (77.9%) characterized by local symptoms; rarely the patients required an emergency-department visits (16.1%) and only one patient (1.7%) used the epinephrine auto-injector. The patients with a previous history of anaphylaxis at baseline turned back to access to emergency services also during the follow-up (p = 0.006). The majority of patients with recorded systemic reactions (p = 0.004) and treated in an emergency room (p = 0.028) did not have any co-factor-enhanced at diagnosis. We noted an association between platanus pollen sensitization and severity of further reactions during the follow-up (p = 0.026). Epinephrine auto-injector were prescribed to 108/165 patients (65.5%) with an over-prescription rate of 25%. The unforeseeable clinical presentation of LTP allergic reactions and the eventual role played by the cofactor make necessary schedule a follow-up to monitor the patients over time and to assess the actual use of epinephrine auto injectors prescribed.

Lipid Ligands and Allergenic LTPs: Redefining the Paradigm of the Protein-Centered Vision in Allergy

Lipid Transfer Proteins (LTPs) have been described as one of the most prevalent and cross-reactive allergen families in the general population. They are widely distributed among the plant kingdom, as well as in different plant organs ranging from pollen to fruits. Thus, they can initiate allergic reactions with very different outcomes, such as asthma and food allergy. Several mouse models have been developed to unravel the mechanisms that lead LTPs to promote such strong sensitization patterns. Interestingly, the union of certain ligands can strengthen the allergenic capacity of LTPs, suggesting that not only is the protein relevant in the sensitization process, but also the ligands that LTPs carry in their cavity. In fact, different LTPs with pro-allergenic capacity have been shown to transport similar ligands, thus positioning lipids in a central role during the first stages of the allergic response. Here, we offer the latest advances in the use of experimental animals to study the topic, remarking differences among them and providing future researchers a tool to choose the most suitable model to achieve their goals. Also, recent results derived from metabolomic studies in humans are included, highlighting how allergic diseases alter the lipidic metabolism toward a pathogenic state in the individual. Altogether, this review offers a comprehensive body of work that sums up the background evidence supporting the role of lipids as modulators of allergic diseases. Studying the role of lipids during allergic sensitization might broaden our understanding of the molecular events leading to tolerance breakdown in the epithelium, thus helping us to understand how allergy is initiated and established in the individuals.

Rosaceae food allergy: a review

This review provides a global overview on Rosaceae allergy and details the particularities of each fruit allergy induced by ten Rosaceae species: almond/peach/cherry/apricot/plum (Amygdaleae), apple/pear (Maleae), and raspberry/blackberry/strawberry (Rosoideae). Data on clinical symptoms, prevalence, diagnosis, and immunotherapies for the treatment of Rosaceae allergy are herein stated. Allergen molecular characterization, cross-reactivity/co-sensitization phenomena, the impact of food processing and digestibility, and the methods currently available for the Rosaceae detection/quantification in foods are also described. Rosaceae allergy has a major impact in context to pollen-food allergy syndrome (PFAS) and lipid transfer protein (LTP) allergies, being greatly influenced by geography, environment, and presence of cofactors. Peach, apple, and almond allergies are probably the ones most affecting the quality of life of the allergic-patients, although allergies to other Rosaceae fruits cannot be overlooked. From patients' perspective, self-allergy management and an efficient avoidance of multiple fruits are often difficult to achieve, which might raise the risk for cross-reactivity and co-sensitization phenomena and increase the severity of the induced allergic responses with time. At this point, the absence of effective allergy diagnosis (lack of specific molecular markers) and studies advancing potential immunotherapies are some gaps that certainly will prompt the progress on novel strategies to manage Rosaceae food allergies.

Lipid transfer protein allergy: A review of current controversies

Sensitization to lipid transfer protein (LTP), the most frequent cause of food allergy in southern Europe, still shows several controversial, but also intriguing, aspects. Some of these include the degree of cross-reactivity between LTPs from botanically distant sources, the definition of risk factors, the role of some cofactors, clinical outcomes, geographical differences and the identification of the primary sensitizer in different areas. This review article tries to analyse and comment on these aspects point by point suggesting some explanatory hypotheses with the final scope to stimulate critical thoughts and elicit the scientific discussion about this issue in the readership.