Class I endochitinase containing a hevein domain is the causative allergen in latex-associated avocado allergy

Background In the medical literature immunoglobulin (Ig)E‐mediated sensitization to avocado is rarely reported. On the other hand, more than 50% of subjects having IgE‐mediated natural rubber latex allergy are sensitized to avocado fruit as demonstrated by skin‐prick testing and/or specific IgE measurements and about 10–20% report hypersensitivity reactions after ingesting avocado. Objective The underlying pathomechanism of latex‐associated avocado allergy is still unknown. The conserved hevein domain of the major latex allergen prohevein (Hev b 6.01) is a ubiquitous chitin‐binding protein structure that can be found in several plant proteins and may be responsible for the observed cross‐reactivity between latex and avocado fruit. Methods Chitin‐binding avocado proteins (CBAPs) were isolated by affinity‐chromatography and their IgE‐binding characteristics were studied by immunoblotting using the sera from 15 avocado‐sensitized latex patients. Inhibition experiments using isolated hevein and CBAPs as inhibitor solutions were performed to study the immunological cross‐reactivity between both protein species and to assess the role of the CBAPs as mediators in latex‐associated avocado allergy. Results In 80% of avocado‐sensitized subjects (n = 15), IgE antibodies directed against a 31‐kDa allergen were detected by immunoblotting. This IgE‐binding protein was identified by protein sequencing to be a class I endochitinase containing a hevein domain at the N‐terminus. Purified native and digested (using simulated gastric fluid) endochitinase were able to completely block all avocado‐specific IgE antibodies in six out of seven avocado patients. Conclusions Sensitization to endochitinase class I containing a hevein domain is the main underlying pathomechanism in latex‐mediated avocado allergy.