Cross-reactivity between coconut and hazelnut proteins in a patient with coconut anaphylaxis

Background The medical literature reports few cases of severe allergic reactions to coconut. We encountered a patient with anaphylaxis to coconut and oral symptoms to tree nuts. Objective To identify cross-reactive antibodies between coconut and other tree nuts. Methods We performed commercial radioallergosorbent tests to coconut and various tree nuts using the patient's serum. Skin prick testing was performed to fresh coconut and commercial extracts of coconut, almond, Brazil nut, cashew, pecan, walnut, and hazelnut. Proteins from fresh coconut, commercial coconut extract, and tree nuts were extracted. Immunoblot and inhibition assays were performed to evaluate for cross-reacting IgE antibodies between similar-sized allergens in coconut and hazelnut. Results Positive skin test results occurred to the coconut and multiple tree nut extracts. In vitro serum specific IgE was present for coconut, hazelnut, Brazil nut, and cashew. Immunoblots demonstrated IgE binding to 35- and 50-kDa protein bands in the coconut and hazelnut extracts. Inhibition assays using coconut demonstrated complete inhibition of hazelnut specific IgE, but inhibition assays using hazelnut showed only partial inhibition of coconut specific IgE. Conclusions Our study demonstrates the presence of cross-reactive allergens between hazelnut (a tree nut) and coconut (a distantly related palm family member). Because there are many potentially cross-reactive allergens among the tree nuts, we recommend patients with coconut hypersensitivity be investigated for further tree nut allergies.