Follicular Exclusion of Self Antigens Prevents Development of Autoantibodies

描述（由申请人提供）：越来越多的证据表明，脾脏边缘区巨噬细胞（MZMs）的失调在系统性红斑狼疮（SLE）等系统性自身免疫性疾病的发展中起作用。MZMs在捕获、加工和诱导对凋亡细胞（AC）抗原的耐受中起重要作用。狼疮耐受原性MZM反应失调的分子机制和触发这种失调的信号尚未阐明。提出的研究验证了以下假设：(1)狼疮耐受原性MZM反应失调的共同机制是MZMs中机械传感蛋白巨核细胞白血病-1 （MKL1）和相关丝状肌动蛋白组装表达的改变，影响MZMs吸收和维持对凋亡细胞抗原（AC-Ags）耐受性的能力；(2) SLE特征性事件可诱导MKL1表达的改变和f -肌动蛋白组装的破坏。I型干扰素（IFN）诱导MZ B细胞（表达膜淋巴毒素（mLT））从MZ到卵泡的“错定位”，从而导致MZMs上淋巴毒素受体（LT¿R）的信号丢失，从而诱导它们。值得注意的是，“干扰素信号”是人类SLE的一个标志，BXD2- IFN¿r-/-小鼠中1型IFN信号的缺乏消除了许多异常免疫MZM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感应慢性暴露于AC碎片和免疫复合物（ic）而诱导。这些假设将通过多种小鼠模型进行测试，这些模型通过广泛的合作、药理学破坏和最先进的共聚焦显微镜分析，有针对性地破坏相关通路。目的1将确定IFN¿诱导的mLT+ MZ B细胞的滤泡易位是否会导致ACs和ic对MZM的耐受性丧失。此外，BXD2和B6。TC自身免疫小鼠将用于确定MZM缺陷是否是狼疮的原发性早期缺陷。Aim 2将重点关注MKL1通路的LT¿R下游信号通路，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MZMs的生存中发挥作用。SLE和正常人脾脏的冷冻切片将用于确定SLE脾脏中MARCO+ MZMs的丢失是否与产生1-IFN型pDCs的高数量、LT+ B细胞的滤泡易位以及MKL1/肌动蛋白聚合失调有关。临床相关性。这些研究将提供狼疮的统一模型，表明I型IFNs的关键新致病机制，并确定狼疮中耐受原性巨噬细胞调节的新分子途径，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.