Isolation and characterization of a major allergen from the fish parasite Anisakis simplex.

BACKGROUND Ingestion of raw or undercooked fish can lead to infection of human subjects by the fish parasite Anisakis simplex, a disease known as anisakiasis or anisakidosis. Patients sensitized to this fish parasite show high levels of total and specific IgE. Cross-reactions seem to explain the fact that specific IgE antibodies are also found in a high number of normal subjects, as reported in other parasitoses. OBJECTIVE We sought to purify and characterize a major IgE-binding protein from the parasite. METHODS A protein was purified from the crude parasite extract by means of ethanol precipitation and reversed-phase HPLC. Its clinical relevance was tested on 20 parasite-positive sera by using IgE and IgG4 immunoblotting. A monospecific human serum was used to study its localization in the parasite body. RESULTS A 24-kd protein was purified, to which only 45% of the sera had specific IgG4, but 85% of sera had specific IgE. The protein was present only in the excretory gland, as shown by immunohistochemistry. N-terminal amino acid sequence (17 residues) showed no homology to previously described proteins. CONCLUSION A simplex contains a potent allergen in the excretory gland. This major parasite allergen, named Ani s 1, could have important clinical relevance, as shown by the high number of positive sera in the specific IgE immunoblotting.