Background: The cross-reactive allergen responsible for the so called "mugwort-celery-spice-syndrome", a pollen-food allergy that occurs in a minority of mugwort pollen-allergic patients, is still undefined.
Objective: To identify the allergen responsible for the cross-reactivity between mugwort pollen and plant-derived foods.
Methods: The serum from one index patient with both fennel and mugwort pollen allergy was used to identify IgE-reactive allergens by direct ELISA and Immunoblot analysis. Cross-reactivity between mugwort pollen and fennel was checked by cross-inhibition experiments. Fennel and mugwort allergens selected on the basis of IgE reactivity and inhibition tests were excised from SDS-PAGE gels and microsequenced. The amino acid sequences obtained were used to screen the NCBI database using the protein BLAST software.
Results: On ELISA inhibition experiments, serum absorption with fennel extract completely inhibited the IgE response to mugwort. On immmunoblot analysis periodate treatment caused the disappearance of all bands of IgE reactivity except one at about 60 kDa. The 60 kDa bands from both mugwort and fennel PAGE-SDS gels revealed the presence of distinct proteins. The N-terminal amino acid sequencing gave the same major amino acid sequence corresponding to an Api g 5-like allergen. The MS/MS spectra were analyzed and a provided evidence of a fennel-specific protein with sequence similarity to phosphoglyceromutase from Apium graveolens.
Conclusion: A 60 kDa allergen, highly homologous to Api g 5, was recognized in fennel by patient's IgE. Inhibition experiments showed a high degree of cross-reactivity between this fennel allergen and the homologous mugwort pollen allergen. This allergen might be responsible for the mugwort-celery-spice syndrome.