Role of the bacterial gut microbiota and innate immunity in Campylobacter jejuni-enteritis: Investigations in gnotobiotic mouse models of inflammation

C.空肠炎是世界范围内最普遍的肠道疾病之一。在工业化国家，C.空肠感染最常见的特征是下肠道中的急性严重炎症反应，伴有水样腹泻，包括血便、发烧和腹痛。炎症是由粒细胞和巨噬细胞浸润肠粘膜引起的。这些先天性免疫细胞引发炎症反应并使组织破坏永久化，导致由健康粘膜提供的肠屏障功能严重紊乱，以防御天然肠道植物群的非致病性细菌。因此，不仅C.空肠以及其它移位的肠道细菌渗入粘膜下组织部位，并与免疫细胞直接接触，从而加重炎症。提示先天免疫系统和正常肠道植物群可能在C.通过参与炎症过程的调节而引起的免疫病理学。几项临床研究表明，在患有炎症性肠病的患者中，正常肠道植物群的非致病性肠道细菌可能是肠道炎症持续存在的关键组分。然而，这些方面的肠道生态和先天免疫尚未研究在C。到目前为止，细菌分子通过与Toll样受体（TLR）或NOD 2蛋白结合而加重或抑制炎症反应，Toll样受体或NOD 2蛋白均分别由先天免疫系统的细胞（例如粒细胞、巨噬细胞或潘氏细胞）以高水平表达。产生的信号转导事件启动促炎或抗炎细胞因子应答，调节先天性和适应性免疫（包括T细胞和B细胞）的反应性。本课题组和其他研究人员的实际研究表明，TLR和NOD 2在胃肠道急性和慢性炎症过程的调节中发挥重要作用。基于这些发现，我们推测肠道菌群和先天性免疫系统都有助于C。空肠肠炎我们将使用无菌小鼠模型来研究肠道菌群与C。空肠定殖和发病机制，并研究天然免疫在空肠弯曲菌中的作用。空肠肠炎宿主天然免疫对C.将在TLR 2、TLR 4、TLR 9或NOD 2基因以及编码信号转导蛋白MyD 88或TRIF的基因中具有明确缺陷的小鼠中研究空肠炎。相应的机制将在体外进一步表征。C.将在携带确定的肠道细菌或被细菌化合物攻击的无菌小鼠中研究空肠定殖和肠道炎症。随后将使用纯化的TLR-和/或NOD 2-配体对相应动物进行治疗，以满足Koch假设，并评估TLR-/NOD-激动剂/拮抗剂、确定的肠道细菌或肠道植物群的调节是否适合抑制免疫活化并减少C.空肠肠炎最后，我们的目的是确定肠道炎症反应对抗C。空肠在我们建立良好的回肠炎和结肠炎小鼠模型中。

Enteritis caused by C. jejuni is one of the most widespread diarrhoeal diseases worldwide. In industrialized nations, the clinical spectrum of C. jejuni-infection is most commonly characterized by acute severe inflammatory responses in the lower intestinal tract accom-panied by watery diarrhoea including bloody stools, fever and abdominal pain. The inflam-mation is initiated by infiltration of the intestinal mucosa with granulocytes and macropha-ges. These innate immune cells trigger inflammatory responses and perpetuate tissue de-struction leading to a severe disturbance of the intestinal barrier functions presented by the healthy mucosa to defend against non-pathogenic bacteria of the natural commensal inte-stinal flora. In consequence, not only C. jejuni but also other translocating gut bacteria infil-trate submucosal tissues sites and are coming in direct contact with immune cells thereby aggravating inflammation. This suggests that the innate immune system and the normal gut flora might play a key role in C. jejuni-induced immunopathology by taking part in the modulation of the inflammatory process. Several clinical studies have shown that in patients suffering from inflammatory bowel diseases non-pathogenic commensal bacteria of the normal intestinal flora might represent critical components in the perpetuation of intestinal inflammation. However, such aspects of intestinal ecology and innate immunity have not been studied in C. jejuni-enteritis so far. Bacterial molecules aggravate or sup-press inflammatory responses by binding to Toll-like receptors (TLRs) or the NOD2-pro-tein, both of which are expressed at high levels by cells of the innate immune system such as granulocytes, macrophages or Paneth cells, respectively. The resulting signal transduc-tion events initiate pro-inflammatory or anti-inflammatory cytokine responses modulating the reactivity of innate and adaptive immunity, including T- and B-cells. Actual research in our group and others has demonstrated that TLRs and NOD2 play important roles in the modulation of acute and chronic inflammatory processes in the gastrointestinal tract. Based upon these findings we hypothesize that both, the commensal bacterial gut micro-flora and the innate immune system, contribute to the perpetuation or suppression of C. jejuni-enteritis. We will use gnotobiotic mouse models to investigate the interplay of the intestinal microflora with C. jejuni colonization and pathogenesis and to study the role of innate immunity in C. jejuni-enteritis. The influences of host innate immunity on C. jejuni-enteritis will be studied in mice with well-defined defects in the TLR2, TLR4, TLR9, or NOD2 genes as well as genes coding for the signal-transducing proteins MyD88 or TRIF. The corres-ponding mechanisms will be further characterized in vitro. C. jejuni-colonization and intestinal inflammation will be investigated in gnotobiotic mice carrying defined gut bacteria or challenged by bacterial compounds. A subsequent treatment of the corresponding animals with purified TLR- and/or NOD2-ligands will be used in order to fulfil the Koch`s postulates and to evaluate if TLR-/NOD-agonists/ antagonists, defined gut bacteria, or modulation of the intestinal flora might be suitable to suppress immune activation and reduce acute inflammatory responses in the course of C. jejuni-enteritis. Finally, we aim to determine the influences of intestinal inflammatory responses on colonization resistance displayed against C. jejuni in our well-established mouse models for ileitis and colitis.