Purification, biochemical, and immunological characterisation of a major food allergen: different immunoglobulin E recognition of the apo- and calcium-bound forms of carp parvalbumin

Background-Almost 4% of the population suffer from food allergy which is an adverse reaction to food with an underlying immunological mechanism. Aims-To characterise one of the most frequent IgE defined food allergens, f ish parvalbumin. Methods-Tissue and subcellular distribution of carp parvalbumin was analyse d by immunogold electron microscopy and cell fractionation. Parvalbumin was purified to homogeneity, analysed by mass spectrometry and circular dichro ism (CD) spectroscopy, and its allergenic activity was analysed by IgE bind ing and basophil histamine release tests. Results-The isoelectric point (pI) 4.7 form of carp parvalbumin, a three EF -hand calcium-binding protein, was purified to homogeneity. CD analysis rev ealed a remarkable stability and refolding capacity of calcium-bound parval bumin. This may explain why parvalbumin, despite cooking and exposure to th e gastrointestinal tract, can sensitise patients. Purified parvalbumin reac ted with IgE of more than 95% of individuals allergic to fish, induced dose -dependent basophil histamine release and contained, on average, 83% of the IgE epitopes present in other fish species. Calcium depletion reduced the IgE binding capacity of parvalbumin which, according to CD analysis, may be due to conformation-dependent IgE recognition. Conclusions-Purified carp parvalbumin represents an important cross reactiv e food allergen. It can be used for in vitro and in vivo diagnosis of fish- induced food allergy. Our finding that the ape-form of parvalbumin had a gr eatly reduced IgE binding capacity indicates that this form may be a candid ate for safe immunotherapy of fish-related food allergy.