New light on an old syndrome: Role of Api g 7 in mugwort pollen–related celery allergy

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BackgroundCelery root is known to cause severe allergic reactions in patients sensitized to mugwort pollen. ObjectiveTo study clinically well-characterized patients with celery allergy by IgE testing with a comprehensive panel of celery allergens to disentangle the molecular basis of the “celery-mugwort-syndrome”. MethodsPatients with suspected food allergy to celery underwent a standardized interview. Main inclusion criteria were a positive food challenge with celery or an unambiguous case history of severe anaphylaxis. IgE to celery allergens (rApi g 1.01, rApi g 1.02, rApi g 2, rApi g 4, nApi g 5, rApi g 6, rApi g 7), and to mugwort allergens (rArt v 1, rArt v 3, rArt v 4) were determined by ImmunoCAP. IgE levels ≥ 0.35kUA/L were regarded positive. ResultsSeventy-nine patients with allergy to celery were included. Thirty patients suffered from mild oral or rhino-conjunctival symptoms and 49 from systemic reactions. Sixty-eight % had IgE to celery extract, 80% to birch pollen and 77% to mugwort pollen. A combination of Api g 1.01, 1.02, 4, 5, and 7 increased diagnostic sensitivity for celery allergy to 92%. The LTPs Api g 2 and Api g 6 were not relevant in our celery allergic population. IgE to Api g 7, detected in 52% of patients, correlated closely (r=0.86) to Art v 1 from mugwort pollen. Eleven out of 12 patients with monosensitization to Api g 7 were IgE negative to celery extract. The odds ratio for developing a severe anaphylactic reaction rather than only mild oral symptoms was about 6 times greater (odds ratio 5.87; 95% CI 1.08-32.0, p=0.0410) for Api g 7 sensitized versus Api g 7 non-sensitized subjects. ConclusionThere is an urgent need for routine diagnostic tests to assess sensitization to Api g 7 not only to increase test sensitivity, but also to identify celery allergic patients at risk of a severe allergic reaction to celery.