Detailed characterization of Act d 12 and Act d 13 from kiwi seeds: implication in IgE cross-reactivity with peanut and tree nuts

Background:Act d 12 (11S globulin) and Act d 13 (2S albumin) are two novel relevant allergens from kiwiseeds that might be useful to improve the diagnostic sensitivity and the management of kiwifruit-allergic patients. Objective:To perform a comprehensive structural and immunological characterization of purified Act d 12 and Act d 13 from kiwiseeds. Methods:Sera from 55 well-defined kiwifruit-allergic patients were used. Act d 12 and Act d 13 were purified by chromatographic procedures. Circular dichroism, mass spectrometry, concanavalin A detection, immunoblotting, enzyme-linked immunosorbent assays, basophil activationtests, and IgE-inhibition experiments were used. Results:Act d 12 and Act d 13 were purified from kiwiseeds to homogeneity by combining size-exclusion, ion-exchange, and RP-HPLC chromatographies. Both purified allergens preserve the structural integrity and display typical features of their homologous counterparts from the 11S globulin and 2S albumin protein families, respectively. These allergens are released from kiwiseeds after oral and gastric digestion of whole kiwifruit, demonstrating their bioavailability after ingestion. The allergens retain the capacity to bind serum IgE from kiwifruit-allergic patients, induce IgE cross-linking in effector-circulating basophils, and display in vitro IgE cross-reactivitywith homologous counterparts from peanut and tree nuts. Conclusion:Purified Act d 12 and Act d 13 from kiwiseeds are well-defined molecules involved in in vitro IgE cross-reactivitywith peanut and tree nuts. Their inclusion in component-resolved diagnosis of kiwifruit allergy might well contribute to improve the diagnostic sensitivity and the management of kiwifruit-allergic patients.