A novel mechanism of immunosuppression in sepsis: Depletion of monocytes and macrophages

脓毒症是一种危及生命的疾病，每年在美国影响100多万名患者。 越来越多的证据表明，免疫抑制是脓毒症死亡的主要驱动力。 巨噬细胞在病原体免疫应答中发挥着重要作用。此前的临床研究表明， 败血症患者外周血单核细胞通过细胞凋亡而耗尽。最近的体外研究表明， 细菌成分，鞭毛蛋白，III型分泌系统的杆状蛋白(T3SS)，或内毒素诱导 巨噬细胞通过激活炎性小体途径发生下垂。在这份提案中，我们提供 令人信服的证据表明，外周血单核细胞和组织巨噬细胞均因上睑下垂而耗尽 小鼠脓毒症模型包括盲肠结扎穿孔(CLP)模型。我们展示了静脉注射 注射鞭毛蛋白或杆状蛋白可引起组织中外周血单核细胞和巨噬细胞的耗竭。 我们进一步证明，在小鼠体内耗尽这些细胞会损害免疫反应，并增加 随后用大肠杆菌攻击的死亡率。重要的是，我们的数据表明组织因子释放 从嗜热性单核细胞和巨噬细胞中释放可引发弥散性血管内凝血(DIC)。因此，我们的 发现单核/巨噬细胞耗竭是免疫抑制和DIC的一种新机制 败血症。这项应用的目标是描绘单核/巨噬细胞的潜在机制。 脓毒症中的耗竭及其对免疫抑制的贡献。目标1是描述 脓毒症时嗜热单核细胞和巨噬细胞死亡。工作假说是炎症小体 脓毒症时激活和随后的下垂在单核/巨噬细胞耗尽中起关键作用。 Caspase-1、Caspase-11、Caspase-1/11 Double或GSDMD(全身和 巨噬细胞特异性)将被用来阐明炎症小体激活和 单核/巨噬细胞衰竭所致的下睑下垂。目标2是确定杆状蛋白和 鞭毛蛋白引起下垂，导致单核/巨噬细胞耗尽。我们最近发现了一种细胞内 EprJ的结合伙伴，巨噬细胞中的酰辅酶A脱氢酶家族成员9(ACAD9)。我们会 使用不同的方法来检验ACAD9依赖的途径有助于 巨噬细胞耗尽。目标3是确定单核/巨噬细胞耗竭对 脓毒症时的免疫抑制。我们将使用脓毒症模型的组合来研究 脓毒症时免疫抑制中的单核/巨噬细胞耗竭。脓毒症患者外周血单核细胞减少 患者也将接受调查。拟议研究的完成将揭示一种新的分子机制 革兰氏阴性菌引起的免疫抑制。这些发现将大大推进我们的 了解败血症的发病机制，并确定治疗这种致命疾病的新药物靶点。

Sepsis is a life-threatening condition that affects more than 1 million patients a year in the United States. Growing evidence indicates that immunosuppression is a major driving force for mortality in sepsis. Macrophages play essential roles in immune response to pathogens. Previous clinical studies have shown that peripheral monocytes are depleted in septic patients through apoptosis. Recent in vitro studies revealed that bacterial components, flagellin, the rod protein of the type III secretion system (T3SS), or LPS induce pyroptosis of macrophages through activation of inflammasome pathways. In this proposal, we provide convincing evidence that both peripheral monocytes and tissue macrophages are depleted due to pyroptosis in mouse sepsis models including the cecal ligation and puncture (CLP) model. We show that intravenous injection of flagellin or the rod proteins induced depletion of peripheral monocytes and macrophages in tissues. We further demonstrate that depletion of these cells in mice impaired immune response and increased mortality rate by subsequent challenged with E. coli. Importantly, our data indicate that tissue factor released from pyroptotic monocytes and macrophages triggers disseminated intravascular coagulation (DIC). Thus, our findings identified monocyte/macrophage depletion as a novel mechanism of immunosuppression and DIC in sepsis. The goal of this application is to delineate the underlying mechanisms of monocyte/macrophage depletion and its contribution to immunosuppression in sepsis. Aim 1 is to delineate the mechanisms of pyroptotic monocyte and macrophage death during sepsis. The working hypothesis is that inflammasome activation and subsequent pyroptosis play a critical role in monocyte/macrophage depletion during sepsis. Mouse models deficient in caspase-1, caspase-11, caspase-1/11 double, or GSDMD (whole-body and macrophage-specific) will be used to elucidate the detailed mechanism of inflammasome activation and pyroptosis in monocyte/macrophage depletion. Aim 2 is to identify the mechanism by which rod protein and flagellin induce pyroptosis leading to monocyte/macrophage depletion. We recently identified an intracellular binding partner of EprJ, the acyl-CoA dehydrogenase family member type 9 (ACAD9) in macrophages. We will use different approaches to test the hypothesis that the ACAD9-dependent pathway contributes to macrophage depletion. Aim 3 is to identify the contribution of monocyte/macrophage depletion to immunosuppression during sepsis. We will use a combination of sepsis models to investigate the role of monocyte/macrophage depletion in immunosuppression during sepsis. Peripheral monocyte depletion in septic patients will also be investigated. Completion of the proposed studies will reveal a novel molecular mechanism of immunosuppression induced by Gram-negative bacteria. Such findings will significantly advance our understanding about the pathogenesis of sepsis and identify new drug targets for this deadly disease.