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口腔内常在菌の中で, 歯周病原性の高いグラム陰性桿菌の免疫系に対する影響を検討する目的で, マウスにPorphyromonas gingivalisの菌体成分を投与したところ, 肝において新しいリンパ球分画の誘導が発見された。この細胞は, NK細胞のマーカーのNK1.1の発現が通常のNK細胞より高く(high), 丁細胞マーカーのCD3が中等度(intermediate)に発現しているという特徴(CD3^Int NK1.1^H)を有する。このCD3^Int NK1.1^H細胞は, E.coli菌体成分や, そのLPS成分の投与によっても同じく肝に強く誘導された。これらの細胞は非常に強い細胞障害活性(NK活性)を示し, その誘導機構を追求したところ, LPSによって産生が誘導されるIL-12の投与で肝に誘導されることがわかった。P.gingivalisやE.coli菌体成分およびLPSで誘導される細胞群も, IL-12で誘導される細胞群も, 全て, CD3^Int NK1.1^Hの形質をもち, CD4弱陽性, Vβ8陽性で細胞障害活性の強いリンパ球であることがわかった。そして, この細胞群の前駆細胞は, 今日知られているNK細胞と丁細胞の両形質をもつT_NK細胞と考えられ, 所謂, 胸腺外分化丁細胞の活性型であることが示唆された。

To investigate the pathogenic roles of grarn-negative rods in oral and periodontal tissues, sonicates of Porphyromonas gingivalis were injected venously in mice. At least 24 hrs later, the surface markers of lymphoid cells isolated from the liver, spleen, and peripheral blood were examined by immunofluorescence with monoclonal antibodies against CD3,NK1.1,and other antigens expressed on murine lymphoid cells. A specific increase in the percentages of cells positive intermediately for CD3 and highly for NK1.1(CD3^Int NK1.1^H)was identified as a new population of lymphoid cells, which has never been reported before.This population of CD31^Int NK1.1^H could also be induced by injection of Escherichia coli sonicates and the lipopolysaccharide fraction isolated from E. coli. Furthermore, the same lymphoid cell population was induced in the liver of mice treated with a new cytokine, interleukin 12 (IL-12), which was specifically induced in mice by LPS.These CD3^Int NK1.1^H populations induced by P.gingivalis, E.coli, LPS, and IL-12 share a quite similar profile of lymphoid cell markers (CD3^Int, NK1.1^H, CD4^+, CD8^-, Vβ8^+), which was also found in T_NK cells an intermediate population between T cells and NK cells.In conclusion when injected in mice, oral gram-nagative bacteria induced a lymphoid population in the liver.These cells may be an activated cell population of precursor cells, which might belong to the extrathymically generating lymphoid cell population T_NK.

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