Ligand-dependent and cell type-specific functions of integrin CD11b/CD18 in multiple sclerosis

血纤维蛋白原渗入中枢神经系统并转化为反应性纤维蛋白起关键作用 在许多神经系统疾病中，包括多发性硬化症(MS)，一种神经炎症性疾病。纤维蛋白 通过与整合素受体结合刺激巨噬细胞和小胶质细胞的促炎活性 CD11b/CD18(Mac-1；αMβ2)。然而，CD11b/CD18的这种促炎范例被我们的 令人惊讶的发现CD11b/CD18在几种小鼠模型中具有抗炎特性 炎症性疾病。事实上，独立的全基因组关联研究已经将功能丧失联系起来 人类CD11b变异对自身免疫性系统性红斑狼疮风险增加的影响。分子 CD11b的配体结合特性使巨噬细胞/小胶质细胞具有不同的功能 炎症活动尚不清楚。本项目的总体目标有两个：(1)确定分子 CD11b/CD18配体结合使巨噬细胞和小胶质细胞发生不同炎症反应的基础 性质和(2)确定特定的白细胞亚群，以中介病理或有益的功能 在我们的初步研究中，我们发现了一个新的CD11b突变体CD11bKH，即CD11bKH 纤维蛋白结合有缺陷。表达CD11bKH的敲入小鼠表现出正常的巨噬细胞浸润，但 体内促炎活性降低。利用进行性多发性硬化症的小鼠模型，我们发现CD11bKH 小鼠出现了疾病的早期症状，但可以自发地逆转疾病的进展，这是一种独特的能力 在野生型或CD11b缺陷小鼠中未观察到。我们的骨髓移植实验进一步 研究表明，骨髓来源细胞和驻留小胶质细胞上的CD11b在急性髓系白血病中起着不同的作用。 MS的发病机制基于这些令人振奋的初步结果，我们假设CD11b/CD18 以配体依赖和细胞类型特异性的方式调节MS的发病。为了检验这一假设， 我们将确定包括CD11bKH在内的CD11b突变体与其相关蛋白配体结合的能力 我们还将与MS一起确定CD11b/CD18纤维蛋白启动的关键信号通路 促炎活动(目标1)。接下来，我们将确定CD11b/CD18的调制机制 疾病的进展和缓解。重要的是，我们将灭活骨髓来源细胞上的CD11b或 使用我们新产生的CD11b-FLOXED小鼠在疾病发展的特定阶段驻留小胶质细胞 并确定其对疾病发展的影响(目标2)。最后，我们将调查是否扰乱了 CD11b/CD18-纤维蛋白通路将增强抗CD20诱导的抗原特异性免疫抑制(AIM 3)。 该项目的完成将填补我们在CD11b/CD18机制方面的知识空白 配体结合决定了它的炎症性质。重要的是，鉴于ocriszumab(一种人性化的抗CD20 MAB)是FDA批准的治疗原发进展性MS的唯一方法，从这一点获得的信息 该项目可以帮助我们开发下一代基于CD20的抗CD20药物来治疗这种难治性疾病。

Leakage of blood fibrinogen into the central nerve system and its conversion into reactive fibrin plays a key role in many neurological diseases, including multiple sclerosis (MS), a neuroinflammatory disease. Fibrin stimulates the proinflammatory activity of macrophages and microglia by binding to the integrin receptor CD11b/CD18 (Mac-1; αMβ2). However, this proinflammatory paradigm of CD11b/CD18 is complicated by our surprising discovery that CD11b/CD18 possesses anti-inflammatory properties in several mouse models of inflammatory diseases. Indeed, independent genome-wide association studies have linked loss-of-function variants of human CD11b to increased risks of autoimmune systemic lupus erythematosus. The molecular mechanism by which ligand binding property of CD11b confers macrophages/microglia with distinct inflammatory activities is unknown. The overall goal of this project is two-fold: (1) to determine the molecular basis by which CD11b/CD18 ligand binding confers macrophages and microglia with different inflammatory properties and (2) to identify specific leukocyte subsets that mediate the pathological or beneficial functions of CD11b/CD18 in MS. In our preliminary studies, we discovered a novel CD11b mutant, CD11bKH, that is defective in fibrin binding. Knock-in mice expressing CD11bKH exhibited normal macrophage infiltration but reduced proinflammatory activity in vivo. Using a mouse model of progressive MS, we found that CD11bKH mice developed early signs of disease but could spontaneously reverse disease progression, a unique ability not observed in wild-type or CD11b-deficient mice. Our bone marrow transplantation experiments further demonstrated that CD11b on bone marrow-derived cells and resident microglia play distinct roles in the pathogenesis of MS. Based on these exciting preliminary results, we hypothesize that CD11b/CD18 modulates the pathogenesis of MS in a ligand-dependent and cell type-specific manner. To test this hypothesis, we will determine the ability of CD11b mutants including CD11bKH to bind its various protein ligands associated with MS. We will also identify key signaling pathways responsible for the CD11b/CD18-fibrin-initiated proinflammatory activities (Aim 1). We will next determine the mechanism by which CD11b/CD18 modulates disease progression and remission. Importantly, we will inactivate CD11b on bone marrow-derived cells or resident microglia at specific stages of disease development using our newly generated CD11b-floxed mice and determine their impact on disease development (Aim 2). Finally, we will investigate whether disrupting the CD11b/CD18-fibrin pathway will enhance anti-CD20-induced antigen-specific immunosuppression (Aim 3). Completion of this project will fill the gap in our knowledge regarding the mechanism by which CD11b/CD18 ligand binding dictates its inflammatory properties. Importantly, given that ocrelizumab (a humanized anti-CD20 mAb) is the only FDA-approved treatment for primary progressive MS, the information obtained from this project can help us develop next-generation anti-CD20-based drugs to treat this intractable form of the disease.