ヒノキチオールの唾液分泌型IgA抗体産生に与える影響

ヒノキチオール（HNK）は，古くから細菌や真菌に対する抗菌作用を有し，生体に対してはストレス緩和作用という生理機能改善効果が知られ，現在，歯磨剤や整髪料，アロマ，食品に広く応用されている．だが，生体防御機構である免疫システムへのHNKが与える影響についてはほとんど知られていない．本研究では，HNKが粘膜免疫学的影響の一端を明らかにすることを目的に，マウス鼻腔からHNKを投与し，投与前・後の唾液中の分泌型IgA抗体（SIgA Ab）量の測定と，顎下唾液腺（SMG）における免疫細胞学的解析を行った．
BALB/cマウス（8週齢，メス）に，HNK 50 μgを毎週1回計4回経鼻投与し，各投与日の投与前および投与0.5時間後，1.5時間後，3時間後，6時間後の唾液採取を行い，唾液SIgA Abの定量を行った．さらに最終投与日（初回投与から21日目；Day 21）のHNK投与前・後のマウスSMGにおけるIgA Ab産生細胞（IgA AFCs）数を計測し，さらにIgA AFCsの生存・増殖能の測定を行った.
HNK各投与日におけるSIgA Ab分泌量は，投与1.5時間後が最大であり，投与6時間後で投与前と同レベルになることが認められた．興味深いことに，投与回数とSIgA Ab分泌量は正の相関傾向が認められた．Day 21のHNK投与前・後においては，SMGのIgA AFCs数に有意な差は認められなかったが，IgA AFCsの生存・増殖能はHNK投与0.5時間後と1.5時間後に有意な上昇が認められた．以上から，HNKの経鼻投与は，投与後1.5時間までのSMG IgA AFCsを活性化し，唾液SIgA Abの分泌を促進している可能性が示唆された.

Hinokitiol (HNK) is a well-known antimicrobial and antifungal agent, and is widely used in various formulations including tooth pastes, mouth rinses, aromatics, cosmetics, and food. There is limited information on the immunobiological activity of HNK. In the present study, we investigated the effects of interanasally administered HNK on salivary secretory-IgA antibody (SIgA Ab) secretion in mice. BALB/c (8 weeks old) mice were given 50 μg of HNK four times at weekly intervals (Days 0, 7, 14, and 21) via the nasal route. Saliva samples were collected prior to (−0 hour) and after (0.5, 1.5, 3, and 6 hours) the nasal administration of HNK on respective days, and the levels of salivary SIgA Ab were determined by ELISA. Furthermore, the numbers of SIgA Ab-producing cells (SIgA AFCs) in submandibular glands (SMG) were examined by ELISPOT, and proliferation responses of IgA+ B cells were measured by MTT assays based on the same schedule on Day 21.
On Days 0, 7, 14, and 21, the maximum level of SIgA Ab secretion in saliva occurred at 1.5 hours after the nasal administration of HNK. Interestingly, the number of doses of HNK and quantities of SIgA secretion showed a positive correlation. On Day 21, there were no significant differences between the number of SMG IgA AFCs prior to and after (0.5, 1.5, 3, and 6 hours) the nasal administration of HNK. However, significantly increased levels of IgA AFCs due to promotion of their proliferative activity were noted 0.5 and 1.5 hours after the nasal administration of HNK. Our results suggest that HNK has an impact on salivary SIgA Ab secretion immediately after nasal administration via elevating the proliferative activity of SMG IgA AFCs.