Allergenicity of different apple cultivars assessed by means of skin prick test and sensitisation to recombinant allergens Mal d 1 and Mal d 3 in a group of Italian apple-allergic patients

Comparative analysis of allergen genes and pro-inflammatory factors in pollen and fruit of apple varieties

Allergy to freshly consumed apple fruits is often associated to pollinosis and manifested as oral allergy syndrome (OAS). The allergenic properties of apple varieties differ greatly, spanning from low allergenic to high allergenic varieties. The knowledge of the genetic determinants for allergenicity has been of great interest in scientific community for several years, but the molecular mechanisms involved are still little understood. Here, factors putatively involved in allergenicity were investigated at biochemical and molecular level in pollen and in fruits of apple varieties differing in their allergenic potential. Among putative sensitizing factors, transglutaminase (TGase) and phospholipase A₂ (PLA₂) were considered together with reactive oxygen species (ROS) and known apple allergen genes, with particular attention devoted to the Mal d 1 gene family, the most important one in sensitization. We found that the expression of some allergen genes and the activities of TGase, PLA₂ and ROS producing enzyme are lower in the hypo-allergenic variety 'Durello di Forlì' in comparison with the high-allergenic genotypes 'Gala' and 'Florina'. These results highlight correlations among allergen expressions, enzymatic activities and apple cultivars; these data underline the possibility that some of them could be used in the future as markers for allergenicity.

Old Apple (Malus domestica L. Borkh) Varieties with Hypoallergenic Properties: An Integrated Approach for Studying Apple Allergenicity

Freshly consumed apples (Malus domestica L. Borkh) can cause allergic reactions because of the presence of four classes of allergens. Knowledge of the genetic factors affecting the allergenic potential of apples would provide important information for the selection of hypoallergenic genotypes, which can be combined with the adoption of new agronomical practices to produce fruits with a reduced amount of allergens. In the present research, a multiple analytical approach was adopted to characterize the allergenic potential of 24 apple varieties released at different ages (pre- and post-green revolution). A specific workflow was set up including protein quantification by means of polyclonal antibodies, immunological analyses with sera of allergic subjects, enzymatic assays, clinical assessments on allergic patients, and gene expression assays on fruit samples. Taken as a whole, the results indicate that most of the less allergenic genotypes were found among those deriving from selection processes carried out prior to the so-called "green revolution".

A qRT-PCR assay for the expression of all Mal d 1 isoallergen genes

BACKGROUND

A considerable number of individuals suffer from oral allergy syndrome (OAS) to apple, resulting in the avoidance of apple consumption. Apple cultivars differ greatly in their allergenic properties, but knowledge of the causes for such differences is incomplete. Mal d 1 is considered the major apple allergen. For Mal d 1, a wide range of isoallergens and variants exist, and they are encoded by a large gene family. To identify the specific proteins/genes that are potentially involved in the allergy, we developed a PCR assay to monitor the expression of each individual Mal d 1 gene. Gene-specific primer pairs were designed for the exploitation of sequence differences among Mal d 1 genes. The specificity of these primers was validated using both in silico and in vitro techniques. Subsequently, this assay was applied to the peel and flesh of fruits from the two cultivars 'Florina' and 'Gala'.

RESULTS

We successfully developed gene-specific primer pairs for each of the 31 Mal d 1 genes and incorporated them into a qRT-PCR assay. The results from the application of the assay showed that 11 genes were not expressed in fruit. In addition, differential expression was observed among the Mal d 1 genes that were expressed in the fruit. Moreover, the expression levels were tissue and cultivar dependent.

CONCLUSION

The assay developed in this study facilitated the first characterisation of the expression levels of all known Mal d 1 genes in a gene-specific manner. Using this assay on different fruit tissues and cultivars, we obtained knowledge concerning gene relevance in allergenicity. This study provides new perspectives for research on both plant breeding and immunotherapy.

Genomic organisation of the Mal d 1 gene cluster on linkage group 16 in apple

European populations exhibit progressive sensitisation to food allergens, and apples are one of the foods for which sensitisation is observed most frequently. Apple cultivars vary greatly in their allergenic characteristics, and a better understanding of the genetic basis of low allergenicity may therefore allow allergic individuals to increase their fruit intake. Mal d 1 is considered to be a major apple allergen, and this protein is encoded by the most complex allergen gene family. Not all Mal d 1 members are likely to be involved in allergenicity. Therefore, additional knowledge about the existence and characteristics of the different Mal d 1 genes is required. In the present study, we investigated the genomic organisation of the Mal d 1 gene cluster in linkage group 16 of apple through the sequencing of two bacterial artificial chromosome clones. The results provided new information on the composition of this family with respect to the number and orientation of functional and pseudogenes and their physical distances. The results were compared with the apple and peach genome sequences that have recently been made available. A broad analysis of the whole apple genome revealed the presence of new genes in this family, and a complete list of the observed Mal d 1 genes is supplied. Thus, this study provides an important contribution towards a better understanding of the genetics of the Mal d 1 family and establishes the basis for further research on allelic diversity among cultivars in relation to variation in allergenicity. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11032-011-9588-4) contains supplementary material, which is available to authorized users.