Role of IRAK-M in sepsis-induced immunosuppression

描述(由申请人提供)： 在脓毒症中幸存下来的患者仍然非常容易受到随后的医院感染，特别是细菌性肺炎。脓毒症后肺泡巨噬细胞功能受损，其特征是对内毒素的炎症反应减弱，抗菌活性降低。虽然单核/巨噬细胞失活是脓毒症诱导免疫抑制的关键特征之一，但在脓毒症过程中介导这一现象的确切细胞和分子途径尚不清楚。鉴于脓毒症巨噬细胞对内毒素的低反应性，脓毒症诱导的巨噬细胞失活的潜在机制之一可能涉及Toll样受体(TLR4)信号通路。白介素1受体相关激酶-M(IRAK-M)是多种TLRs的负调节因子，其中TLR4是脂多糖(LPS)的受体。这项提议中要检验的假设是，脓毒症引起的肺泡巨噬细胞TLR4信号通路的损害是由IRAK-M介导的。为了验证这一假设，这些研究将在野生型和IRAK-M基因敲除小鼠中使用多菌腹膜炎诱导的脓毒症小鼠模型[盲肠结扎和穿孔(CLP)模型]。本研究的具体目的是：1)评估CLP后TLR4、CD14和IRAK-M在肺泡巨噬细胞中的时间依赖性表达；2)确定IRAK-M在内毒素和脓毒症灭活肺泡巨噬细胞的效应细胞功能和内毒素信号转导通路中的功能意义；以及3)确定IRAK-M在脓毒症所致的体内肺细菌清除障碍中的作用。总之，这些研究将使我们能够确定IRAK-M是否是脓毒症诱导的巨噬细胞失活的相关介质，从而确定一个潜在的治疗靶点，以逆转脓毒症患者发生的免疫抑制。

DESCRIPTION (provided by applicant): Patients who survive sepsis remain highly susceptible to subsequent nosocomial infections, particularly bacterial pneumonia. Alveolar macrophages are functionally impaired following sepsis, characterized by diminished inflammatory responses to endotoxin and reduced antimicrobial activity. While monocyte/macrophage deactivation is one of the key features of sepsis-induced immunosuppression, the precise cellular and molecular pathways that mediate this phenomenon during sepsis are unclear. Given the hyporesponsiveness of septic macrophages to endotoxin, one of the potential mechanisms for sepsis-induced macrophage deactivation may involve the Toll-like receptor (TLR)4 signaling pathways. TLRs are critical for host recognition of microbial pathogens and the generation of an inflammatory innate immune response, lnterleukin-1 receptor associated kinase-M (IRAK-M) has been demonstrated to be a negative regulator of several TLRs, including TLR4, which is the receptor for lipopolysaccharide (LPS). The hypothesis to be tested in this proposal is that the sepsis-induced impairment of TLR4 signaling pathways in alveolar macrophages is mediated by IRAK-M. To test this hypothesis, these studies will employ a murine model of polymicrobial peritonitis-induced sepsis [cecal ligation and puncture (CLP) model] in both wildtype and IRAK-M knockout mice. The specific aims of this, proposal are to: 1) assess the time-dependent expression of TLR4, CD14, and IRAK-M in alveolar and pulmonary macrophages following CLP; 2) determine the functional significance of IRAK-M on effector cell function and LPS signaling pathways in endotoxin- and sepsis-deactivated alveolar macrophages in vitro; and 3) determine the contribution of IRAK-M to sepsis-induced impairment of lung bacterial clearance in-vivo. Collectively, these studies will enable us to determine if IRAK-M is a relevant mediator of sepsis-induced macrophage deactivation, thereby identifying a potential therapeutic target to reverse the immuno-suppression that occurs in patients with sepsis.