旋毛虫感染经PD-1和LAG-3途径协同抑制小鼠胶原诱导性关节炎的作用及其机制

The co-evolution of helminths along with their hosts, which results in the worms being able to induce the hosts’ immune tolerance to promote parasite survival, may produce the benefit of protecting the hosts from pathological lesions arising from aberrant inflammatory responses that underlies autoimmune disorders. However, the mechanisms of helminth-induced immune modulation are not yet clarified. Rheumatoid arthritis (RA) is an autoimmune disease that primarily causes articular cartilage injury. Recent studies demonstrated that PD-1 and LAG-3 inhibitory co-receptors in T cell membrane act synergistically to prevent autoimmunity. Our preliminary experiments showed that Trichinella spiralis reduced the severity of collagen-induced arthritis and induced expression of PD-1 and LAG-3. We hereby propose the hypothesis that helminth infection may inhibit the occurrence and development of arthritis through inducing co-inhibitory molecule expression and subsequent immune tolerance. Here we design to investigate the synergistical roles of PD-1 and LAG-3 pathways in their inhibitory effects against collagen-induced arthritis by T. spiralis infection, as well as in the proliferation and function of effective T cells, regulatory T cells and APC impacted by T. spiralis infection. We intend to clarify the immune regulatory effects of T. spiralis infection via PD-1 and LAG-3. This study is expected to greatly add to the molecular mechanisms of helminth-based immune modulation and to provide further substantiation for its application in the treatment of RA and other immune-related disease by targeting PD-1 and LAG-3.

在蠕虫与宿主共进化历程中，蠕虫为逃避宿主免疫反应而诱导的免疫耐受有助于抑制宿主自身免疫性疾病的发生，但其作用机制尚不清楚。类风湿关节炎（RA）是一种以关节软骨破坏为主要表现的自身免疫性疾病。新近研究表明，T细胞膜表面具有免疫负调节作用的抑制性受体PD-1和LAG-3能协同抑制自身免疫性疾病的发生。我们前期研究发现，旋毛虫感染能有效抑制小鼠胶原诱导性关节炎的发生，同时也可诱导小鼠PD-1和LAG-3的表达。据此，我们提出的科学假说是，蠕虫抗原通过诱导宿主抑制性受体的表达建立免疫耐受，从而抑制宿主类风湿关节炎的发生。本研究拟观察PD-1及LAG-3途径在旋毛虫感染抑制小鼠胶原诱导性关节炎中的协同作用，及其对旋毛虫感染小鼠效应T细胞、调节性T细胞及DC细胞活化、增殖及功能的影响，为完善蠕虫免疫调节作用的分子机制，进而以PD-1和LAG-3作为靶点防治RA及其它免疫相关性疾病的策略提供理论依据。

蠕虫感染诱导的Th2型免疫反应及调节性免疫反应能抑制感染所致的过度的炎症反应以利于虫体在宿主体内的慢性感染，以此同时，也抑制自身免疫性疾病和过敏症等高反应性免疫性疾病。然而，这种调节炎症性疾病的分子机制仍有待阐明。程序性死亡分子-1（Programmed death 1，PD-1）是一种在慢性感染中维持宿主免疫平衡的重要的抑制性受体。本研究利用小鼠模型研究CD4+T细胞PD-1的表达在旋毛虫影响胶原诱导性关节炎中的作用。研究发现，旋毛虫感染可诱导小鼠脾淋巴细胞中CD4+T细胞高表达PD-1。预先2周感染旋毛虫可显著抑制小鼠II型胶原诱导的关节炎（collagen-induced arthritis，CIA）的发病率及病变程度。而利用抗-PD-1抗体体内阻断PD-1可显著逆转旋毛虫感染对小鼠CIA的抑制作用，且该作用与小鼠增强的Th1和Th17免疫反应以及减弱的Th2免疫反应有关。进一步利用PD-1基因缺失小鼠研究PD-1在旋毛虫感染调节CD4+T细胞分化和增殖中的作用。研究发现，PD-1基因缺失小鼠中旋毛虫感染促进的Th2和Treg分化以及抑制的Th1分化较野生小鼠显著削弱，主要表现为Th1型细胞因子的升高和Th2及调节性细胞因子的降低。而且，PD-1基因缺失小鼠中旋毛虫感染对CD4+T细胞增殖的抑制作用也较野生小鼠显著削弱。本研究首次证实PD-1经调节CD4+T细胞的功能在旋毛虫感染抑制小鼠CIA的效应中发挥关键作用。本研究为蠕虫在自身免疫性疾病中的免疫调节机制提供了新的理论基础。