矢上 晶子

BACKGROUND: Immediate allergy caused by natto, a popular Japanese food prepared by fermenting soybeans with Bacillus subtilis var. natto, has been reported. Polygamma glutamic acid (PGA) in the sticky substance around natto beans has been reported to be a causative allergen of natto allergy. However, some of our patients with natto allergy were negative for PGA in the skin prick test (SPT). The sticky substance of natto beans contains a subtilisin family serine protease, nattokinase, along with PGA. In this study, we aimed to examine the antigenicity of nattokinase in natto allergy. METHODS: Eight patients, who developed symptoms after ingesting natto and positively reacted to natto (seven to the sticky substance in natto and one to the whole natto product) in their SPT, were enrolled in this study. To analyze IgE reactivity, we performed immunoblotting, ELISA, and SPT for natto (bean and sticky substance), and/or PGA, and/or nattokinase and/or cultured B. subtilis var. natto extract. RESULTS: In the SPT, four cases each were PGA-positive and PGA-negative. Immunoblotting of the sera from PGA-negative patients showed a protein band at 30 kDa, which was identified as nattokinase. Three PGA-negative cases, but not three PGA-positive cases, showed a positive reaction to nattokinase in the SPT and had a history of atopic dermatitis. The ELISA for nattokinase revealed a positive reaction of PGA-negative cases and negative reaction of PGA-positive cases in the SPT. CONCLUSIONS: We identified a subtilisin family serine protease, nattokinase, as a novel allergen in natto allergy patients unsensitized to PGA.

＜文献概要＞16歳,女性。モモ,イチジク摂取後にアナフィラキシー症状を発症した。複数の果物類摂取後にアレルギー症状を繰り返したとの臨床経過からgibberellin-regulated protein(GRP)抗原の関与を疑い,諸検査を施行した。その結果,プリックテストではイチジク(4+),モモ自体・モモGRPともに(3+)陽性であり,モモGRPの特異的IgEも陽性で,かつこの抗原はイチジク粗抗原で阻害されたため,自験例をGRPアレルギーと診断した。GRPは熱安定性および消化酵素抵抗性を有しているため当初はクラス1アレルゲンであると考えられていたが,近年はヒノキ花粉やスギ花粉中のGRP抗原との交差反応性に注目されており,今後同様の症例の発現に留意する必要がある。