Characterization of peptidic and carbohydrate cross-reactive determinants in pollen polysensitization

Background Cross-reactivity may be due to protein sequence or domain homologies and/or the existence of cross-reactive carbohydrate determinants (CCDs). The clinical relevance of peptidic cross-reactivities is well known, whereas that of CCDs is still a question of debate. The aim of this study is to characterize the IgE specificity of various patients suffering from pollen polysensitization to identify both peptidic and carbohydrate cross-reactive determinants. Material and methods Rapeseed, grass and Arabidopsis proteins were separated by isoelectric focusing, followed by SDS-PAGE, and transferred to a nitrocellulose sheet. The sheets were incubated either with an individual serum from a birch+grass-sensitive patient, followed by anti-human IgE, or with labelled Concanavalin A (ConA). Binding inhibition was tested by incubation of the sera with a mixture of sugar residues. Results The results showed two different patterns of cross-reacting sera: a pattern that implies few proteins, not always glycosylated and known as allergens, and a pattern that implies numerous proteins with molecular masses over 30 kDa. This second pattern was very close to the ConA -binding pattern. The IgE binding was abolished by pre-incubation with sugar residues only in the case of the second pattern. Discussion This study shows that multiple pollen sensitizations could result from multiple sensitizations to specific proteins or from a cross-sensitization to a wide range of glycoproteins. Two-D blots allow to characterize a cross-sensitization due to carbohydrate determinants, and thus to improve the diagnosis of allergy and its medical treatment.