自己免疫性肝胆疾患の一つである原発性胆汁性胆管炎(Primary biliary cholangitis: PBC)は中高年の女性に好発し、比較的小型の肝内胆管が自己免疫学的機序により破壊され、慢性胆汁鬱滞から肝硬変に進展する難治疾患である。近年、診断技術や治療法の進歩もあり、その有病率は国内外で増加傾向にある。臨床的には血清ALPの上昇、抗ミトコンドリア抗体(AMA)の出現、IgM高値を特徴とする。AMAの主要対応抗原であるピルビン酸脱水素酵素複合体E2成分(PDC-E2)は種を越えて高率に保存されており、PBC患者のAMAや自己反応性T細胞が大腸菌やNovosphingobium aromaticivoransなどの微生物由来抗原と交差反応(molecular mimicry)を示すことから、特定の腸内細菌の病態への関与が示唆される。
本研究において、3名のPBC患者(P1, P2, P3)から採取した便をそれぞれ無菌マウス(n=4)に移植し、投与21日目に解剖を行い腸管、肝臓をはじめとする各臓器の免疫細胞の解析を行った。P1, P2の便を移植したマウスにおいて、便を移植しない無菌マウスと比較して各臓器における免疫応答に差を認めなかった一方、P3の便を移植したマウスにおいて肝臓のIFNg＋CD4 T 細胞 (Th1)の増加、および血清AMA抗体の上昇を認めた。興味深いことにP3は他の2名の患者と比較して血清AMAが上昇しており、特定の腸内細菌が肝臓のTh1免疫応答、AMA上昇を介してPBCの病態に直接寄与している可能性が示唆された。今後サンプル数を増やして上記結果の検証を行うと共に、腸間膜リンパ節や肝臓など腸管外へバクテリアルトランスロケーションした疾患特異的腸内細菌の同定を行う予定である。本研究の進展により、疾患特異的腸内細菌による自己抗体産生を介した胆管病変進展機序の解明が期待される。
Primary biliary cholangitis (PBC), one of the autoimmune hepatobiliary diseases, is an intractable disease that is more common in middle-aged and elderly women, in which relatively small intrahepatic bile ducts are destroyed by an autoimmune mechanism, leading to chronic bile stagnation and progression to cirrhosis. In recent years, the prevalence of this disease has been increasing both in Japan and abroad, partly due to advances in diagnostic techniques and treatment methods. Clinically, the disease is characterized by elevated serum ALP, the appearance of anti-mitochondrial antibodies (AMA), and high levels of IgM, and the major corresponding antigen of AMA, the pyruvate dehydrogenase complex E2 component (PDC-E2), is highly conserved across species, and AMA and autoreactive T cells from PBC patients are highly resistant to E. coli and The fact that AMA and autoreactive T cells from PBC patients cross-react (molecular mimicry) with antigens derived from microorganisms such as E. coli and Novosphingobium aromaticivorans suggests the involvement of specific intestinal bacteria in the pathogenesis of PBC.
In this study, stool samples from three PBC patients (P1, P2, and P3) were transplanted into sterile mice (n=4) and dissected on the 21st day of treatment to analyze immune cells in the intestinal tract, liver, and other organs. On the other hand, P3 transplanted mice showed an increase in IFNg+ CD4 T cells (Th1) in the liver and an increase in serum AMA antibodies. Interestingly, P3 had elevated serum AMA compared to the other two patients, suggesting that specific intestinal bacteria may directly contribute to the pathogenesis of PBC via Th1 immune response in the liver and elevated AMA. We plan to increase the number of samples to validate the above results and to identify disease-specific intestinal bacteria that have undergone bacterial translocation outside the intestinal tract, such as to mesenteric lymph nodes and the liver. The progress of this study is expected to elucidate the mechanism of bile duct lesion progression via autoantibody production by disease-specific intestinal bacteria.
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