Follicular Exclusion of Self Antigens Prevents Development of Autoantibodies

描述(申请人提供)：越来越多的证据表明，脾边缘区巨噬细胞(MZM)的调节失调在系统性自身免疫性疾病(包括系统性红斑狼疮(SLE))的发展中发挥了作用。MZMS在捕获、加工和诱导对凋亡细胞(AC)抗原的耐受方面发挥着重要作用。狼疮耐受性MZM反应调节失调的分子机制以及触发这种调节失调的信号尚未阐明。拟议的研究验证了如下假设：(1)狼疮患者MZM耐受性反应失调的一个常见机制是MZM中机械感受蛋白巨核细胞白血病-1(MKL1)及相关的丝状肌动蛋白组装的表达发生变化，从而影响MZM摄取和维持对凋亡细胞抗原的耐受(AC-AGS)的能力；(2)SLE特有的事件可诱导MKL1表达的变化和F-肌动蛋白组装的中断。它们可以通过MZM上淋巴毒素受体(LT？R)信号的丢失而被诱导，这是由于I型干扰素(IFN)导致表达膜淋巴毒素(MLT)的MZ B细胞从MZ到毛囊的“错误定位”。值得注意的是，“干扰素信号”是人类系统性红斑狼疮的标志，Bxd2-干扰素-/-小鼠缺乏1型干扰素信号可以消除许多免疫MZM异常表型，以及这些小鼠自身抗体和症状性狼疮的产生。MKL1和肌动蛋白组装的改变也可以通过机械传感长期暴露在AC碎片和免疫复合体(IC)中而引起。这些假说将使用多个小鼠模型进行测试，通过广泛的合作、药理破坏和最先进的共聚焦显微镜分析获得相关通路的定向干扰。目的1确定干扰素诱导的MLT MZ B细胞的卵泡移位是否会导致ACS和ICS对MZM的耐受性丧失。此外，Bxd2和B6.TC自身免疫小鼠将被用来确定MZM缺陷是否是狼疮的原发早期缺陷。目的2将重点放在MKL1通路的LT？R下游信号通路上，并在体内和体外测试LT？R/MLK1/肌动蛋白聚合通路是否在维持耐受性MZM的生存中发挥作用。来自SLE和正常人脾的冰冻切片将被用来确定SLE脾中Marco MZM的丢失是否与产生I型干扰素的pDC的数量增加、LT B细胞的滤泡移位以及MKL1/肌动蛋白聚合的失调有关。临床相关性。这些研究将提供一个统一的狼疮模型，提示I型IFN的关键的新的致病机制，并确定SLE耐受巨噬细胞调控的新的分子途径，从而提出新的候选治疗靶点。

DESCRIPTION (provided by applicant): Accumulating evidence suggests that dysregulation of marginal zone macrophages (MZMs) of the spleen plays a role in the development of systemic autoimmune disease include systemic lupus erythematosus (SLE). The MZMs play an important role in trapping, processing, and inducing tolerance to apoptotic cell (AC) antigens. The molecular mechanisms underlying dysregulation of tolerogenic MZM responses in lupus and the signals that trigger this dysregulation have not been elucidated. The proposed studies test the hypotheses that: (1) A common mechanism underlying dysregulation of tolerogenic MZM responses in lupus is an alteration in the expression of a mechanosensing protein megakaryocytic leukemia-1 (MKL1) and associated filamentous actin assembly in MZMs that affects the ability of the MZMs to take up and maintain tolerance to apoptotic cell antigens (AC-Ags); (2) Alterations in expression of MKL1 and disruption of F-actin assembly can be induced by events that are characteristic of SLE. They can be induced by loss of signaling through the lymphotoxin- ¿ receptor (LT¿R) on the MZMs resulting from type I interferon (IFN) induced "mislocalization" of MZ B cells, which express membrane lymphotoxin (mLT), from the MZ to the follicle. Notably, the "interferon signature" is a hallmark of SLE in humans and deficiency of Type 1 IFN signals in BXD2- Ifn¿r-/- mice abrogates many of the abnormal immunologic MZM phenotypes as well as the production of autoantibodies and symptomatic lupus in these mice. The alterations in MKL1 and actin assembly also can be induced by chronic exposure to AC debris and immune complexes (ICs) through mechanosensing. These hypotheses will be tested using multiple mouse models with targeted disruption of pertinent pathways made available through extensive collaborations, pharmacological disruption, and state-of-the-art confocal microscopic analysis. Aim 1 will determine if IFN¿- induced follicular translocation of mLT+ MZ B cells leads to loss of MZM tolerance of ACs and ICs. In addition, BXD2 and B6.TC autoimmune mice will be used to determine if an MZM defect is a primary, early defect in lupus. Aim 2 will focus on the LT ¿R downstream signaling of MKL1 pathway and test in vivo and in vitro if the LT¿R/MLK1/actin polymerization pathways play a role in maintenance of the survival of tolerogenic MZMs. Frozen sections from SLE and normal human spleen will be used to determine if loss of MARCO+ MZMs in the SLE spleen is associated with high numbers of type 1-IFN producing pDCs, follicular translocation of LT+ B cells, and dysregulation of MKL1/actin polymerization. Clinical Relevance. The studies will provide a unified model of lupus, indicate a critical novel pathogenic mechanism of type I IFNs, and identify a new molecular pathway underlying regulation of tolerogenic macrophages in SLE thereby suggesting novel candidate therapeutic targets.