巨噬细胞中大麻素受体CB2R在脓毒症免疫抑制中的作用及其机制研究

Sepsis is an immune response disorder syndrome caused by infectious and non-infectious diseases with high mortality and poor therapeutic effect. Lots of researches reported that sepsis showed the bidirectional characteristics of inflammatory immunity and severe immune suppression, and most of the deaths occurred in the stage of immunosuppression. Cannabinoid receptor 2 (CB2R) is mainly distributed in a variety of immune cells, and its role of sepsis immunosuppression in macrophages has not been studied. Preliminary experiments found that, under endotoxin stimulation, Macrophages lacking CB2R had stronger inflammatory immune response depending on Toll like receptors and was more sensitive to the programmed necroptosis which could further activate the inflammation. Meanwhile, CB2R conditional knockout mice in macrophages, treated with low dose of LPS via intraperitoneal injection, showed higher levels of proinflammatory factor IL-6 in plasma and enhanced inflammatory response than wild-type mice in vivo. So we speculate that CB2R conditional deficiency in macrophages can relieve partly sepsis immunosuppression by enhancing immune inflammation depending on Toll-like receptor and necropotosis to activate immune cells, which provides a potential target mechanism for the treatment of sepsis.

脓毒症是感染引起的免疫应答紊乱综合征，死亡率高，治疗效果差。研究表明，脓毒症具有炎性免疫过强和免疫抑制的双向特征，且大多数死亡是发生在免疫被严重抑制的阶段。大麻素受体2主要分布在多种免疫细胞中，其在巨噬细胞中对脓毒症的免疫抑制作用还未见报道。预实验发现，内毒素刺激导致大麻素受体2敲除的巨噬细胞依赖于TLR3及TLR4受体介导的炎性免疫更强，促进了巨噬细胞的活化，与此同时，CB2R缺失的巨噬细胞对程序性坏死更加敏感，而程序性坏死增强会进一步激活炎症反应。动物水平上，我们用低剂量LPS腹腔注射小鼠发现，与野生型小鼠相比，CB2R巨噬细胞特异性敲除小鼠血浆中促炎因子IL-6分泌水平更高，表明体内炎症响应部分增强。因此，我们认为大麻素受体2在巨噬细胞中缺失可通过增强Toll受体介导的炎症和程序性坏死来活化免疫细胞从而部分解除脓毒症中发生的免疫抑制，为脓毒症的治疗提供潜在的机制靶点。

脓毒症是当宿主抵御病原微生物感染时免疫反应失调引起的致命性的多器官功能障碍，脓毒症的发展是机体多细胞、多器官协同应对后的综合结果，过去大多数的研究都倾向于认为机体的“炎症因子风暴”是导致脓毒症患者病危的主要原因，有研究表明大麻素受体CB2R（又名CNR2）参与调控脓毒症相关的促炎免疫响应，但本项目研究发现大麻素受体2对免疫抑制相关因子IL-10的调控也具有关键作用。之前的研究通常是以大麻素受体2全身敲除小鼠作为主要研究对象，这往往不能明确具体某一类细胞在疾病中的贡献程度，因而具有一定的局限性。在本项目研究中我们以大麻素受体2特异性敲除小鼠为主要研究对象，从动物水平和细胞水平探索特异性敲除大麻素受体2的巨噬细胞、树突细胞和CD4+T细胞在脓毒症中的作用及其中机制。结果发现当大麻素受体2发生全身性激活时会降低脓毒症的生存率，此时促炎性因子IL-6分泌水平无显著意义变化，免疫抑制关键细胞因子IL-10则显著意义降低，表明大麻素受体2激活对免疫抑制有负调控作用，随后在脓毒症中对巨噬细胞、树突细胞和CD4+T细胞大麻素受体2特异性敲除小鼠的研究发现，CD4+T特异性敲除小鼠能通过恢复血浆中的IL-10的分泌水平来改善脓毒症，而巨噬细胞和树突细胞特异性敲除小鼠和野生型对照小鼠相比没有明显改善，该结果表明CD4+T细胞上是大麻素受体2响应脓毒症免疫调节的关键细胞亚群。上述结果提示我们可以将CD4+T细胞上的大麻素受体2作为治疗脓毒症的可能机制靶点。