探討血液循環系統中轉糖鏈球菌之葡糖基轉移酶引發抗雙股去氧核糖核酸抗體生成之機制

Abstract

目前已知感染可能導致宿主產生自體免疫抗體並促進自體免疫疾病的發生。我們先前的研究發現若將人類口腔中常見的轉糖鏈球菌(Streptococcus mutans)從尾靜脈施打感染老鼠，則老鼠會產生抗雙股去氧核醣核酸抗體(anti-dsDNA antibody)。轉糖鏈球菌的表面蛋白葡糖基轉移酶B(glucosyltransferase B, GtfB)可透過刺激緣區B細胞 (marginal zone B)產生抗雙股去氧核醣核酸抗體。關於其中的詳細機制仍尚未研究透徹。在本篇研究中，我們發現由尾靜脈施打入葡糖基轉移酶C亦可同施打葡糖基轉移酶B般誘發BALB/c小鼠產生抗雙股去氧核醣核酸抗體。對老鼠施打缺乏各種葡糖基轉移酶的轉糖鏈球菌NHS1DD則無法誘導抗雙股去氧核醣核酸抗體產生，說明葡糖基轉移酶對誘發抗雙股去氧核醣核酸抗體產生相當重要。為確認哪一片段的葡糖基轉移酶B負責誘發抗雙股去氧核醣核酸抗體產生，我們生產並大量表現葡糖基轉移酶B的氨基端與羧基端及葡糖基轉移酶C的氨基端片段。實驗結果發現僅有葡糖基轉移酶B的氨基端可在活體中誘發抗雙股去氧核醣核酸抗體產生，並活化邊緣區B細胞以及濾泡B細胞(follicular B cell)使之生產抗雙股去氧核醣核酸抗體。專一性抗雙股去氧核醣核酸的抗體無法辨識葡糖基轉移酶B的氨基端，且葡糖基轉移酶B的氨基端上並無偵測到醣類成分，說明葡糖基轉移酶B的氨基端並未含有雙股去氧核醣核酸及醣類分子。總結而言，葡糖基轉移酶B的氨基端在轉糖鏈球菌感染引起的菌血症中扮演誘導抗雙股去氧核醣核酸抗體產生的重要角色，並可能進一步誘導自體抗體的產生與自體免疫疾病的發 生。

Infections may contribute to the development of autoantibodies production and the progression of autoimmune diseases. Our previous data showed that bacteremia caused by Streptococcus mutans, an oral commensal, induces autoantibody production in a murine model. The recombinant protein of glucosyltransferase B (GtfB), a surface protein of S.mutans, induces anti-dsDNA IgG production in the MZ B cells-dependent manner. The detailed mechanism remains unclear. Here, we demonstrated that intravascular injection of another glucosyltransferase, GtfC, also induces anti-dsDNA antibodies production in BALB/c mice. An isogenic strain deficient in Gtfs (NHS1DD) failed to induce anti-dsDNA antibody production, confirming the role of Gtfs. To identify which part of GtfB is responsible for antibody production, the recombinant proteins of N-terminal and C-terminal domain of GtfB and the N-terminal domain of GtfC were generated. N-terminal domain of GtfB, not N-terminal domain of GtfC and C-terminal domain of GtfB, induced anti-dsDNA antibodies production in vivo and activated MZ B cells and FO B cells to produce anti-dsDNA antibodies. The specific anti-dsDNA antibody cannot recognize the N-terminal domain of GtfB and no sugar component can be detected in N-terminal domain of GtfB, suggesting that N-terminal domain of GtfB did not contain dsDNA and sugar moieties. Taken together, the N-terminal domain of GtfB is, at least partially, responsible for induce the anti-dsDNA antibody production in S. mutans-induced bacteremia, which may contribute to autoantibody production in patients with autoimmune diseases.