Speaker: Paolo Maria Matricardi
In 2008-2009, a project was initiated in Italy to investigate panallergens among a large population of allergic children through a network of pediatric clinical centres. The study aimed to explore the role of panallergens in childhood allergies. Five years later, the hypothesis of "panallergen X" emerged, suggesting the existence of an undetected panallergen. The third part of the study involved testing this hypothesis, while the fourth focused on its clinical implications and etiology. Panallergens, highly cross-reactive molecules found across various allergen sources, were a key focus. For example, grass pollen contains specific allergens (Phl p 1, Phl p 5) and panallergens (polcalcins, Phl p 7, Phl p 12). A diagnostic approach, presented in Venice in 2009, emphasized identifying relevant sensitizing molecules to better prescribe immunotherapy for polysensitized children. Profilins and polcalcins are consistently present in algorithms for diagnosing pollen allergies covering grasses, trees, and weeds.
The panallergenic X hypothesis emerged from observations of differing allergy patterns between Northern and Southern Europe. In Northern Europe, particularly Sweden, most allergic patients are sensitive to birch pollen, which also sensitizes them to related allergens. Conversely, Southern Europe, such as Italy, experiences multiple pollens simultaneously, leading to widespread polysensitization. Molecular allergology tests are thus more crucial in Southern Europe.
A significant study of 1,300 children revealed that approximately 50% were sensitized to over six pollen extracts and 82% to at least three, demonstrating the complexity of the allergy problem in Southern Europe. Another study highlighted the impact of advanced molecular testing on clinical practice. It showed that doctors altered their immunotherapy prescriptions in 50% of cases when provided molecular test results alongside traditional clinical history and skin tests. Further investigation revealed that many children with positive skin tests for birch pollen did not show expected IgE antibody responses to known birch pollen molecules (Bet v 1, Bet v 2, and Bet v 4). Specifically, out of 252 children, 146 were negative to Bet v 1, and only 71 had IgE antibodies against profilins or polcalcins, leaving 75 children's reactivity unexplained. This led to the panallergenic X hypothesis, proposing that other highly cross-reactive molecules might be influencing the results, a theory later published in the Journal of Allergy and Clinical Immunology (JACI) to explain these anomalies and suggest the need for further investigation into additional cross-reactive allergens.
The speaker highlighted a significant study on peanut allergy that explored the intriguing phenomenon where grass pollen extract appeared to inhibit unexpected peanut sensitization, focusing on the characterization of cyclophilin, particularly peanut RH 18, which was cloned and characterized. The finding suggested that cyclophilin might act as a panallergen, similar to profilin. Simultaneously, a clinical proposed that cyclophilin could be a third panallergen based on a single case. He noted the unclear frequency of IgE sensitization to cyclophilin in pollen allergy patients, thereby hypothesizing its relevance as a panallergen. Motivated by these insights, the research team decided to test this hypothesis despite the absence of clinical tests for pollen cyclophilin.
In May 2023, the team contacted Jonas Lidholm to use recombinant Bet v 7 in their population study. They tested a randomized sample of 253 patients to represent the global population, alongside 74 patients who were positive for birch pollen extract but negative for Bet v 1, Bet v 2, and Bet v 4. Additionally, 26 patients highly sensitive to Bet v 1 were studied.
The general population study revealed that 17% of the 253 participants had IgE antibodies against Bet v 7, indicating a significant sensitization rate. Notably, in the cohort at risk for panallergen sensitization, the prevalence jumped to 63%, a fourfold increase. This discovery suggested that cyclophilin could indeed elicit a robust IgE response comparable to other known panallergens. Further analysis showed a strong correlation between IgE levels to cyclophilin and the response to birch pollen extracts, with an R-squared value of 0.89. This quantitative and qualitative correlation emphasized the potential of cyclophilin as a significant allergen capable of provoking high IgE responses. This study's findings could have profound implications for understanding and managing peanut and pollen allergies.
The study presented explores the diagnostic and clinical relevance of IgE to cyclophilin, particularly its association with asthma and oral allergy syndrome (OAS). Initial findings showed a higher prevalence of asthma and OAS among patients with IgE to cyclophilin, suggesting a potential role in these conditions. However, further analysis revealed that the significance of this association diminishes when considering other highly cross-reactive molecules typically involved in pollen food syndrome (PFS). Specifically, a subset of 10 patients with IgE to cyclophilin but negative for other common allergens showed that 7 out of 10 had asthma but no OAS, indicating the complexity of cyclophilin's role. To further investigate, the study examined whether cyclophilin sensitization affects only birch pollen or extends to other pollen types. Inhibition tests on patients with positive responses to various pollens, such as plane tree and ragweed, but negative to common allergens, revealed high inhibition rates with cyclophilin. This indicates that cyclophilin reactivity is not limited to birch pollen but includes multiple relevant pollens, impacting the accuracy of pollen diagnoses.
The study's findings were quickly published in the Journal of Allergy and Clinical Immunology. It emphasizes that cyclophilin is almost as significant as profilin, with prevalence estimates suggesting it is 20% less common. For example, if profilin has a 7% prevalence in Sweden, cyclophilin's prevalence might be around 4%. Cyclophilin's relevance is noted to be higher in temperate climates due to the abundance of cyclophilin-inducing pollens. The biological importance of cyclophilins extends beyond allergenic reactions. Cyclophilins are crucial for various biological functions, including protein folding and viral interactions, such as with HIV. This ubiquitous molecule exists across fungi, vegetables, mammals, and insects. Its role as an allergen was first identified in the 1980s, with further recognition in 1995. The study underscores the need for further research to clone and characterize cyclophilins from various sources to better understand their potential links to asthma, OAS, and their broader biological and clinical implications.
Prominent studies were highlighted, such as the Ara H18 and research on fungal cyclophilins. Despite the recognized importance of cyclophilins, comparable to profilins, their testing remains limited. Currently, only one commercial test, Mala S6 from Malassezia fungi, is available, and it does not cross-react with pollen allergens, rendering it ineffective for pollen allergy testing.
The discussion emphasized the need for allergists to be well-versed in molecular allergology, referencing resources like the MAOG and the newly distributed pocket guide. The MAOG 2.0, specifically addressing grass pollen allergy, underscores the necessity of including cyclophilin testing. Preliminary findings from their research suggest that other groups need to test, verify, and reproduce these observations. Cyclophilins' relevance extends beyond grass pollen allergy, affecting general pollen allergies, atopic dermatitis, and other diseases. Questions were raised about the inducers of cyclophilin production, including grass and olive pollens. It was noted that the prevalence of cyclophilins varies geographically, with a higher prevalence in Italy compared to Sweden.
The homogeneity of plant cyclophilins was confirmed, showing that similar tests yield comparable results. However, testing for cyclophilins in pollen alone is insufficient for determining food allergies. Specific cyclophilins must be tested as they do not exhibit extensive cross-reactivity with pollen cyclophilins. Including at least one cyclophilin in multiplex tests is deemed necessary for a comprehensive assessment. Further studies are needed to understand the clinical implications, including cyclophilin concentrations in fruits and vegetables and their role in patient reactivity. This ongoing research aims to address these open questions and advance understanding in the field.
The discussion on human cyclophilins highlighted their potential relevance in cross-reactivity studies between human and fungal cyclophilins, especially in atopic dermatitis. The idea of cross-talk between external antigens and self-antigens, potentially involving IgE reactivity against fungal cyclophilins, could be significant for inflammation in atopic dermatitis. The topic warrants ongoing research to expand the understanding.
European Academy of Allergy and Clinical Immunology (EAACI), 2024 31st May-3rd June, Valencia