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

血纤维蛋白原渗漏进入中枢神经系统并转化为反应性纤维蛋白起着关键作用 在许多神经系统疾病中，包括多发性硬化症（MS），一种神经炎性疾病。纤维蛋白 通过与整联蛋白受体结合刺激巨噬细胞和小胶质细胞的促炎活性 CD 11b/CD 18（Mac-1; αMβ2）。然而，这种CD 11b/CD 18的促炎性模式由于我们的研究而变得复杂。 令人惊讶的发现，CD 11b/CD 18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表明， 人类CD 11b变异增加自身免疫性系统性红斑狼疮的风险。分子 CD 11b的配体结合特性赋予巨噬细胞/小胶质细胞不同的 炎症活性未知。该项目的总体目标是两方面的：（1）确定分子 CD 11b/CD 18配体结合赋予巨噬细胞和小胶质细胞不同炎症反应的基础 性质和（2）鉴定介导白细胞的病理或有益功能的特定白细胞亚群， 在我们的初步研究中，我们发现了一种新的CD 11b突变体，CD 11bKH，即 纤维蛋白结合缺陷的。表达CD 11bKH的敲入小鼠表现出正常的巨噬细胞浸润， 降低体内促炎活性。使用进行性MS的小鼠模型，我们发现CD 11bKH 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CD 11b缺陷小鼠中未观察到。我们的骨髓移植实验 表明骨髓来源的细胞上的CD 11b和常驻的小胶质细胞在细胞凋亡中起着不同的作用。 基于这些令人兴奋的初步结果，我们假设CD 11b/CD 18 以配体依赖性和细胞类型特异性方式调节MS的发病机制。为了验证这个假设， 我们将确定包括CD 11bKH在内的CD 11b突变体结合其相关的各种蛋白配体的能力， 我们还将确定负责CD 11b/CD 18纤维蛋白启动的关键信号通路。 促炎活性（Aim 1）。接下来我们将确定CD 11b/CD 18调节细胞凋亡的机制。 疾病进展和缓解。重要的是，我们将在骨髓来源的细胞上表达CD 11b， 使用我们新产生的CD 11b-floxed小鼠在疾病发展的特定阶段观察常驻小胶质细胞 并确定其对疾病发展的影响（目标2）。最后，我们将调查是否破坏了 CD 11b/CD 18-纤维蛋白途径将增强抗CD 20诱导的抗原特异性免疫抑制（目的3）。 该项目的完成将填补我们对CD 11 b/CD 18介导的细胞凋亡机制的认识上的差距。 配体结合决定了其炎症性质。重要的是，考虑到ocrelizumab（人源化抗CD 20抗体） mAb）是FDA批准的用于原发性进行性MS的唯一治疗，从该研究中获得的信息是 该项目可以帮助我们开发下一代基于抗CD 20的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.