IgE-mediated hypersensitivity to custard-apple

Characterization and gene cloning of an acidic thaumatin-like protein (TLP 1), an allergen from sapodilla fruit (Manilkara zapota)

BACKGROUND

Allergy to sapodilla (Manilkara zapota) fruit ingestion is rare. An independent study from our group has identified a basic thaumatin-like protein (TLP 2) as the major allergen. The present study was aimed at identifying and characterizing additional allergens from sapodilla.

METHODS

Allergic subjects were identified by case history, skin prick test (SPT) and allergen-specific IgE. Sapodilla extract was fractionated using SP-Sepharose into 3 components (SP1, SP2 and SP3) which were analyzed by native/SDS-PAGE, IgE-immunoblot, isoelectric focusing (IEF) and N-terminal sequencing. The conserved regions of plant TLPs and the N-terminal sequence were used to design primers for PCR.

RESULTS

SPT and ELISA confirmed a subject with oral allergy syndrome (OAS) to sapodilla and custard apple. Two proteins (26.9 and 24.5kDa; reducing conditions) were detected as allergens, of which the latter in SP2 has already been identified as basic TLP (TLP 2). The 26.9kDa protein present in SP1 was identified as an acidic TLP based on native PAGE, IEF and N-terminal sequencing. Presence of a basic β-1,3-glucanase in SP3 was inferred by zymography. Sequence analysis of the genomic clone of the acidic TLP gene revealed that it is intronless and non-glycosylated. Evolutionary relatedness to olive, grape and kiwi fruit allergenic TLPs were inferred by phylogenetic analysis.

CONCLUSIONS

An acidic TLP (TLP 1) was identified as a new allergen in sapodilla. TLP 1 is a single polypeptide (207 residues) belonging to the thaumatin family of the GH64-TLP-SF superfamily. Clinically, sapodilla should be considered in the list of fruits causing OAS.

Clinical features of cross-reactivity of food allergy caused by fruits

Fruits are increasingly recognized as a cause of food allergy. The wide cross-reactivity among these foods has been extensively studied. In this review we will focus on studies addressing the clinical relevance of cross-reactivity among fruits, the diagnostic management of patients complaining of reactions to multiple fruits, and adequate dietary recommendations.