D2.03 - Cofactor-Dependent Anaphylaxis to Rosaceae and Citrus Fruits: Molecular Characterization Reveals High-Molecular-Weight Allergens Beyond Classical Panallergens

Rosaceae and citrus fruits are well-recognized triggers of food allergy, typically mediated by PR-10 proteins, profilins or lipid transfer proteins (nsLTPs). However, a subset of patients exhibits severe cofactor-dependent reactions despite negative or low molecular IgE to classical plant panallergens. In such cases, direct molecular characterization of the native food extracts is essential to identify less common or previously uncharacterized allergenic proteins.

A polysensitized adult with uncontrolled allergic rhinitis and asthma experienced recurrent anaphylaxis to a wide range of Rosaceae (peach, apple, apricot, cherry, pear) and citrus fruits (orange, lemon, mandarin), frequently precipitated by cofactors such as exercise, alcohol, cannabis and hormonal variation..Protein extracts from peach, apple, lemon and orange were prepared using validated protocols. Antigenic and allergenic profiling was performed by SDS-PAGE and IgE–Western blot under reducing and non-reducing conditions using the patient’s serum.

ALEX testing showed strong sensitization to Cupressaceae and Platanus pectate lyases, with no sensitization to nsLTPs, profilins or PR-10 proteins. Skin prick tests to fresh fruits were clearly positive. SDS-PAGE/IgE–Western blot revealed intense IgE binding under reducing conditions, with a dominant ~70 kDa band in peach and apple and no equivalent band in orange; lemon displayed a diffuse pattern with a predominant ~55 kDa band. No IgE-reactive low-molecular-weight bands were detected, ruling out nsLTPs, profilins and PR-10 proteins. The ~70 kDa band observed in peach is compatible with a high-molecular-weight allergen such as (R)-mandelonitrile lyase described in recent literature. The ~55 kDa lemon band is consistent with pectin-methylesterase, a highly abundant citrus enzyme (53–60 kDa depending on glycosylation) known to appear primarily under reducing conditions. Overall, the IgE-binding pattern matched the patient’s strong clinical reactivity to Rosaceae and citrus despite negative results for classical plant panallergens.

This case illustrates that severe cofactor-dependent anaphylaxis to fruits may be driven by high-molecular-weight allergens rather than nsLTPs or other ubiquitous plant panallergens. Molecular analysis identified putative allergens of ~70 kDa in Rosaceae and ~55 kDa in citrus, consistent with emerging candidates such as mandelonitrile lyase and pectin-methylesterase. These findings highlight the clinical relevance of performing direct extract-based immunoblotting when routine molecular diagnostics fail to explain severe reactions.