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，脾边缘区巨噬细胞（MZM）的失调在系统性自身免疫性疾病（包括系统性红斑狼疮（SLE））的发展中发挥作用。 MZM 在捕获、加工和诱导对凋亡细胞 (AC) 抗原的耐受性方面发挥着重要作用。狼疮中耐受性 MZM 反应失调的分子机制以及触发这种失调的信号尚未阐明。拟议的研究测试了以下假设：（1）狼疮中致耐受性 MZM 反应失调的一个常见机制是 MZM 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的表达改变，影响 MZM 吸收和维持对凋亡细胞抗原（AC-Ag）耐受的能力； (2) SLE 特征事件可诱导 MKL1 表达的改变和 F-肌动蛋白组装的破坏。它们可能是由于 I 型干扰素 (IFN) 诱导表达膜淋巴毒素 (mLT) 的 MZ B 细胞从 MZ 到滤泡的“错误定位”而导致 MZM 上淋巴毒素-¿ 受体 (LT¿R) 信号传导丧失而引起的。值得注意的是，“干扰素特征”是人类 SLE 的标志，BXD2-Ifn¿r-/- 小鼠中 1 型 IFN 信号的缺陷消除了许多异常的免疫 MZM 表型以及这些小鼠中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于 AC 碎片和免疫复合物 (IC) 来诱导。这些假设将使用多种小鼠模型进行测试，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途径。目标1将确定IFNτ诱导的mLT MZ B细胞的滤泡易位是否导致AC和IC的MZM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。目标 2 将重点关注 MKL1 途径的 LT¿R 下游信号传导，并在体内和体外测试 LT¿R/MLK1/肌动蛋白聚合途径是否在维持耐受性 MZM 的存活中发挥作用。 SLE 和正常人脾脏的冰冻切片将用于确定 SLE 脾脏中 MARCO MZM 的丢失是否与大量产生 1-IFN 的 pDC、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。这些研究将提供一个统一的狼疮模型，表明 I 型 IFN 的一种重要的新型致病机制，并确定 SLE 中耐受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.