Caspase-6 mediates resistance against Burkholderia pseudomallei infection and influences the expression of detrimental cytokines

Caspase-6 is a member of the executioner caspases and known to play a role in innate and adaptive immune processes. However, its role in infectious diseases has rarely been addressed yet. We here examined the impact of caspase-6 in an in vivo infection model using the Gram-negative rod Burkholderia pseudomallei, causing the infectious disease melioidosis that is endemic in tropical and subtropical areas around the world. Caspase-6-/- and C57BL/6 wild type mice were challenged with B. pseudomallei for comparing mortality, bacterial burden and inflammatory cytokine expression. Bone-marrow derived macrophages were used to analyse the bactericidal activity in absence of caspase-6. Caspase-6 deficiency was associated with higher mortality and bacterial burden in vivo after B. pseudomallei infection. The bactericidal activity of caspase-6-/- macrophages was impaired compared to wild type cells. Caspase-6-/- mice showed higher expression of the IL-1β gene, known to be detrimental in murine melioidosis. Expression of the IL-10 gene was also increased in caspase-6-/- mice as early as 6 hours after infection. Treatment with exogenous IL-10 rendered mice more susceptible against B. pseudomallei challenge. Thus, caspase-6 seems to play a crucial role for determining resistance against the causative agent of melioidosis. To our knowledge this is the first report showing that caspase-6 is crucial for mediating resistance in an in vivo infection model. Caspase-6 influences the expression of detrimental cytokines and therefore seems to be important for achieving a well-balanced immune response that contributes for an efficient elimination of the pathogen.半胱天冬酶-6（Caspase-6）属于执行型半胱天冬酶家族，已知在固有免疫与适应性免疫过程中发挥调控作用，但其在感染性疾病中的功能却鲜有报道。本研究以革兰氏阴性杆状致病菌类鼻疽伯克霍尔德菌（Burkholderia pseudomallei）构建体内感染模型，探究Caspase-6在感染中的作用——该菌引发的类鼻疽（melioidosis）在全球热带及亚热带地区呈地方性流行态势。 我们对Caspase-6基因敲除（Caspase-6⁻/⁻）小鼠与C57BL/6野生型小鼠实施类鼻疽伯克霍尔德菌攻毒，对比两组小鼠的死亡率、细菌负荷与炎症细胞因子表达水平；同时分离骨髓来源巨噬细胞（bone-marrow derived macrophages），分析缺失Caspase-6时的细胞杀菌活性。 实验结果表明：类鼻疽伯克霍尔德菌感染后，Caspase-6⁻/⁻小鼠的死亡率与体内细菌负荷均显著升高；Caspase-6⁻/⁻巨噬细胞的杀菌活性相较野生型细胞明显受损。此外，Caspase-6⁻/⁻小鼠体内IL-1β（IL-1β）基因的表达水平显著上调——已知IL-1β在小鼠类鼻疽模型中具有致病危害；感染后6小时内，Caspase-6⁻/⁻小鼠的IL-10（IL-10）基因表达同样出现升高。进一步功能实验显示，外源性IL-10处理会加重小鼠对类鼻疽伯克霍尔德菌攻毒的易感性。 综上，Caspase-6在宿主对抗类鼻疽致病菌的抗性调控中发挥关键作用。据我们所知，本研究是首个报道Caspase-6可在体内感染模型中介导宿主抗性的研究。Caspase-6可通过调控致病细胞因子的表达，助力维持平衡的免疫应答，从而实现病原体的高效清除。