Class I chitinases, the panallergens responsible for the latex-fruit syndrome, are induced by ethylene treatment and inactivated by heating

Background: Class I chitinases have been identified as the major panallerge ns in fruits associated with the latex-fruit syndrome, such as avocado, ban ana, and chestnut. However, other plant foods containing these enzymes have not been related to this syndrome. Objective: We sought out class I chitinases in the green bean, a legume tha t is known to express chitinases but is not associated with latex allergy, and examined whether the content or allergenic activity of chitinases can b e modified by physical or chemical treatments. Methods: IgE-binding proteins in untreated bean samples, as well as in ethy lene- and heat-treated samples, were detected by using a pool of sera from patients with latex-fruit allergy. Putative allergens were purified by cati on-exchange chromatography and characterized by N-terminal sequencing, enzy matic activity assays, immunodetection with sera and antichitinase antibodi es, and immunoblot inhibition tests, Skin prick tests with untreated and he ated purified allergens were also carried out. Results: An IgE-binding protein of 32 kd that was also recognized by antich itinase antibodies was detected in green bean extracts, This reactive compo nent was strongly induced by ethylene treatment. The protein, designated Pv ChI, was identified as a class I chitinase closely related to the major avo cado allergen Prs a 1. Immunoblot inhibition assays demonstrated crossreact ivity between both allergens. Purified PvChI induced positive skin prick te st responses in 7 of 8 patients with latex-fruit allergy. Heat treatment of both Prs a 1 and PvChI produced a full loss of their allergenic capacities both in vitro and in vivo. No IgE-binding component was detected in the wh ite mature bean in which the main isolated 32-kd protein corresponded to a nonreactive phytohemagglutinin. Conclusions: Ethylene treatment induces the expression of plant class I chi tinases. The allergenic activity of plant class I chitinases seems to be lo st by heating. This fact could explain why plant foods containing these put ative allergens that are consumed after cooking are not usually associated with the latex-fruit syndrome.