Background: Kiwifruit is a popular fruit consumed worldwide and is also used as a cosmetic ingredient. However, it is known to cause allergic reactions in humans. Recent studies have suggested an association between food allergy and food allergens entering the body via the skin. However, percutaneously sensitizing kiwifruit allergens have not been identified in human studies or in animal models. Objective: This study aimed to identify kiwifruit proteins that percutaneously sensitized mice through the epidermal application of crude extracts from green and gold kiwifruit on the dorsal skin, and serum IgE and IgG1 levels were used as sensitization markers. Design: BALB/c mice were back-shaved and their skin was exposed to crude extracts from green and gold kiwifruit that contained sodium dodecyl sulfate. Specific IgE and IgG1 antibodies generated and secreted in response to antigens were measured using enzyme-linked immunosorbent assay or immunoblotting. Results: Skin exposure to kiwifruit extract induced an increase in the levels of kiwifruit-specific IgE and IgG1, which are helper T cell 2-related allergenic antibodies in mice. These antibodies reacted with 18, 23, and 24 kDa proteins found in both green and gold kiwifruits. Thus, three percutaneously sensitizing allergens were identified and purified. Their amino acid sequences partially matched with that of kiwellin (Act d 5). Discussion and conclusion: Kiwellin has been identified as a plant defense-related protein. Interestingly, many plant allergens are biodefense-related proteins belonging to the pathogenesis-related protein family. Kiwellin, which was discovered to be a transdermal sensitizing antigen, might also be categorized as a biodefense-related protein. This study is the first to identify kiwellin (Act d 5) as a percutaneously sensitizing kiwifruit allergen in a mouse model.

Al-Mg-Si 合金は強度と加工性のバランスに優れた合金であ り，近年自動車ボディパネル材への適用が進んでいる 1), 2) 。 自動車ボディパネルの製造工程では，本合金板材の溶体化処 理ならびに焼入れを行い，その後プレス成形および焼付塗装 熱処理(443 Kで1.2-3.6 ks 間)が行われる。溶体化処理はア ルミニウムメーカー，プレス成形および焼付け塗装は自動車 メーカーで施されるため 3) ，焼入れ後から焼付塗装熱処理を 施すまでの間，輸送等により本合金は一定期間室温で保管さ れる。本合金は析出強化型合金であり，焼入れ後直ちに 443 K 時効を施すと，強化相であるβ" 相が析出し硬度が著しく増 大する。しかし，焼入れ後の室温放置により，焼付塗装熱処 理時に時効硬化量が著しく減少する「二段時効の負の効 果」 4) 8) が生じ，実用上の問題となっている。この原因とし て，自然時効(以後，NA)中に形成されたクラスタが，後の 443 K 時効でβ" 相の析出を阻害するためと考えられてい る 2), 6), 9) 12) 。よって，NA中に形成されるクラスタを抑制する ことが求められる。 過去の報告 13) 17) より，Sn添加によってNA中の硬化が数日 間遅滞し，二段時効の負の効果が抑制されることが示され た。電気抵抗測定から，Sn 添加によってクラスタの形成が遅 滞し，クラスタ数密度が減少することが示唆された。この原 因として，Sn と空孔の強い結合エネルギーにより Sn が空孔 をトラップするため，溶質原子である Si 原子や Mg 原子が拡 散するのに必要な空孔が減少し，その結果 Si 原子と Mg 原子 の拡散速度が低下したためクラスタの形成割合が少なくなっ たと推察された 6), 14), 18) 24) 。また，Tuら 20) は3DAP (3-Dimensional Atom Probe)測定を用いて，NA 時間が 86.4 ks の場合 Mg/Si 比 の高いクラスタが形成され，これはβ" 相へと遷移しにくいと 推察した。一方で Banhart ら 25) や Liu ら 26) は，陽電子消滅法を 用いて Al-Mg-Si 合金における NA の進行に伴う陽電子寿命変 化に 4 つのステージが存在することを明らかにした。さらに Liuら 24) は，Sn添加によってステージⅡ p (陽電子寿命の減少) がおよそ 10 倍遅滞する一方，ステージⅢ p (陽電子寿命の増 加)がほとんど生じない実験結果を得た。しかし，Sn 添加に よってこのような陽電子寿命変化がなぜ生じるのか十分に明 確にはされておらず，過去の結果からの推測にとどまったま 1 兵庫県立大学 大学院工学研究科 材料・放射光工学専攻 大学院生(〒671-2280 兵庫県姫路市書写 2167) Graduate student,

This study investigated cluster formation in the early stages of natural aging in Al1.04 mass%Si0.55 mass%Mg alloys by soft X-ray XAFS measurements and first-principles calculation. XAFS measurements at the Mg-K and Si-K edges were carried out at the BL27SU beamline at SPring-8. It was found that the absorption edge energies changed as aging proceeded. Density functional theory (DFT) calculations were used to determine the valence electron densities near Si and Mg atoms and to simulate the Si-K and Mg-K edge spectra for some cluster models. On the basis of the results, it was demonstrated that Si and Mg atoms formed clusters in four stages (IIV) during natural aging. In stage I, Si-vacancy pairs, Mg-vacancy pairs, and a combination of both were formed. In stage II, vacancies were released from the clusters formed in stage I. In stage III, Mg-vacancy pairs were included in the clusters. In stage IV, the clusters coarsened through the release of vacancies. These results indicate that soft X-ray XAFS, which is capable of identifying individual elements, has the ability to provide information on such clusters.

This study investigated the cluster formation process in the early stages of 353 K aging in Al1.04 mass%Si0.55 mass%Mg alloys by means of soft X-ray absorption fine structure (XAFS) measurements and first-principles calculations. XAFS at the Si-K and Mg-K edges was carried out at the BL27SU beamline at SPring-8. To observe the structural changes in detail, an XAFS apparatus able to hold the sample at 353 K in a vacuum chamber and cool it rapidly to suppress the progress of clustering was developed. Density functional theory (DFT) calculations were used to simulate the Si-K and Mg-K edge spectra for various cluster models. Based on the results, the cluster formation process in the early stages of aging at 353 K was qualitatively clarified. Initially, MgVa (Va: vacancy) pairs and SiVa pairs were formed, then 2-MgVa clusters formed by bonding between MgVa pairs along (100); subsequently, L1 0 clusters were formed by Mg atoms ordered along (100), and then SiVapy clusters with Va adjacent to the first-nearest-neighbor atom of Si atoms and Si-py without adjacent Va were formed, in which MgVa pairs and SiVa pairs were individually united, respectively. Monolayer and multilayer structures then developed as aging proceeded, involving Mg and Si atoms ordered along (100), in which Mg and Si atoms were bonded.