Hevein-like protein domains as a possible cause for allergen cross-reactivity between latex and banana

Background: Patients allergic to natural rubber latex (NRL) frequently exhi bit immediate hypersensitivity reactions to banana, but the molecular basis of these putative cross-reactions is unknown. Objective: We wanted to examine whether proteins resembling hevein, a major NRL allergen, exist in banana and whether coexisting allergy to NRL and ba nana can be explained by IgE cross-reactivity to these proteins. Methods: Allergens in banana cross-reacting with hevein were identified by IgE immunoblot inhibition. The cross-reacting proteins were purified by rev ersed-phase chromatography and characterized by amino acid sequencing. Alle rgen cross-reactivity was further assessed by IgE ELISA, IgE ELISA inhibiti on, and skin prick testing. Results: In immunoblotting, 9 of 15 sera from patients allergic to NRL with IgE to hevein showed IgE binding to 32- and 33-kd banana proteins. These 2 protein bands were also targets to IgG from a hevein-immunized rabbit. IgE binding to both 32- and 33-kd protein hands was totally inhibited by hevei n (10 ng/mL) in all 5 sera from patients allergic to NRL sera studied. N-te rminal sequencing of the purified 32- and 33-kd proteins revealed 80% ident ity to the N-terminus of hevein. An internal peptide (19 amino acids) of th e 33-kd protein gave over 90% identity to endochitinases of several plants. In ELISA all IS sera from patients allergic to NRL had IgE to the purified 32-kd banana protein. In ELISA inhibition hevein (10 ng/mL) inhibited appr oximately 50% of IgE binding to the solid-phase 32-kd banana protein in a p ool of sera from patients allergic to NRL. Conclusion: These results suggest that the commonly occurring hypersensitiv ity to banana in patients allergic to NRL could be explained by cross-react ing IgE antibodies binding to epitopes in hevein and in a hevein-like domai n of a previously undescribed endochitinase in banana.