Identification of a 7S globulin as a novel coconut allergen.
BACKGROUND
Coconut (Cocos nucifera) is a monocotyledonous plant of the Arecaceae family. Allergy to coconut is infrequent, with only 5 cases reported so far in the medical literature.


OBJECTIVE
To identify coconut allergens in 2 patients allergic to this food.


METHODS
We describe 2 patients allergic to coconut: an adult pollen-allergic patient monosensitized to coconut who presented with severe oropharyngeal symptoms and a child with a previous allergy to walnut, not allergic to pollen, who developed anaphylaxis on coconut ingestion. Both patients had positive skin prick test results and serum specific IgE (CAP) to coconut. IgE sodium dodecyl sulfate-polyacrylamide gel electrophoresis immunoblotting was performed to identify the allergens involved, and a strong IgE binding band detected in both patients was further analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF MS). Stability to pepsin digestion of the coconut extract and its cross-reactivity with tree nuts were studied.


RESULTS
An immunoblot showed an almost identical profile of IgE binding proteins in the coconut extract in both patients who reacted strongly to a band of approximately 29 kDa. The peptide analysis by MALDI-TOF MS of this band obtained the sequence GHGKREDPEKR. The protein with the highest correlation with this peptide was found to be a 7S globulin from Elaeis guineensis, another oil palm species also belonging to the Arecaceae family. The 29-kDa band was digested by pepsin in less than 1 minute. Cross-reactivity among coconut, walnut, and hazelnut was demonstrated by CAP inhibition in patient 2.


CONCLUSIONS
We have identified a 7S storage protein as a novel coconut allergen.
Benito
Cristina
C
Laboratorio de Investigación, Fundación Hospital Alcorcón, Alcorcón, Spain.
González-Mancebo
Eloína
E
de Durana
M Dolores Alonso Díaz
MD
Tolón
Rosa M
RM
Fernández-Rivas
Montserrat
M
D000328:Adult; D000485:Allergens / Q000737:chemistry / Q000276:immunology*; D000595:Amino Acid Sequence; D015153:Blotting, Western; D002675:Child, Preschool; D003059:Cocos / Q000737:chemistry / Q000276:immunology*; D003429:Cross Reactions; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D005512:Food Hypersensitivity / Q000097:blood / Q000276:immunology*; D005916:Globulins / Q000737:chemistry / Q000276:immunology*; D006801:Humans; D007073:Immunoglobulin E / Q000097:blood; D008297:Male; D008969:Molecular Sequence Data; D012882:Skin Tests; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
D000485:Allergens; D005916:Globulins; D007073:Immunoglobulin E