B cells in CNS autoimmunity

描述（由申请人提供）：B细胞可能在CNS自身免疫性疾病的发病机制中具有多种作用。虽然数据表明髓鞘特异性抗体（Ab）促进实验性自身免疫性脑脊髓炎（EAE）和MS中的脱髓鞘，但B细胞在CNS自身免疫性疾病中的抗原（Ag）呈递中的作用尚不清楚。当与其他APC群体相比时，当B细胞表达对由应答T细胞识别的Ag特异性的B细胞受体（BCR）时，它们是呈递蛋白Ag的有效APC。我们假设B细胞，特别是髓磷脂特异性B细胞在髓磷脂特异性T细胞的活化中具有作为APC的重要作用。我们建议（1）评估髓鞘特异性B细胞作为APC在EAE中的作用，并将这种功能与髓鞘特异性Ab在EAE中的作用区分开来。我们正在创建两种转基因（Tg）模型，一种含有仅表达膜MOG特异性BCR的B细胞，另一种含有表达膜MOG特异性BCR并可分泌MOG特异性IgM的B细胞。我们将比较这些小鼠与B细胞缺陷和MOG特异性BCR敲入小鼠的EAE易感性，后者可以分泌所有IG同种型。我们建议（2）研究B细胞MHC Ⅱ表达和髓鞘BCR特异性在EAE中髓鞘抗原呈递中的作用。我们假设B细胞，特别是髓磷脂特异性B细胞，在EAE和MS中作为APC在MHC II限制性Ag呈递和髓磷脂特异性T细胞的活化中具有关键作用。（a）我们将通过建立混合bm嵌合体小鼠来测试MHC II限制性B细胞Ag呈递给T细胞的作用，在所述混合bm嵌合体小鼠中，B细胞区室选择性缺乏MHC II表达，并比较MOG特异性T细胞的活化和对含有表达MHC II分子的B细胞的bm嵌合体小鼠的EAE易感性。(b)为了阐明BCR特异性在EAE中MHC II限制性抗原呈递中的作用，我们将研究混合bm嵌合体小鼠，其中B细胞表达MOG特异性BCR或硝基苯基（NP）特异性BCR，并表达或不表达MHC II分子。最近的临床结果表明，抗CD 20 B细胞耗竭可能是有效的MS治疗。我们的初步数据表明，B细胞耗竭在rMOG诱导的EAE中是有益的，但加剧了MOG p35- 55诱导的EAE。我们推测rMOG诱导的EAE的临床获益是由于B细胞Ag呈递减少或髓鞘特异性Ab分泌减少。我们还假设MOG p35-55诱导的EAE的恶化（一种较少依赖于B细胞和Ab的模型）代表调节性B细胞功能的丧失。为了评估这些可能性，我们将（3）检查抗CD 20 B细胞耗竭如何影响急性和慢性EAE中外周和CNS中的MOG特异性T细胞应答，并检查MOG特异性Ab应答是否与抗CD 20 B细胞耗竭小鼠的临床改善相关。这些研究应提供关于CNS自身免疫中B细胞耗竭的机制见解，并解决MS临床试验中不易解决的关于B细胞耗竭的问题。公共卫生相关性B淋巴细胞可能在多发性硬化症（MS）（一种中枢神经系统（CNS）自身免疫性疾病）的发病机制中发挥多种作用。我们在实验性自身免疫性脑脊髓炎（EAE），小鼠MS模型的研究，将评估和区分潜在的致病作用的B细胞在中枢神经系统自身免疫。我们的研究计划还将评估抗CD 20 B细胞耗竭（MS临床试验中正在研究的治疗方法）如何影响免疫调节。第5页

DESCRIPTION (provided by applicant): B cells may have multiple roles in pathogenesis of CNS autoimmune disease. While data indicate that myelin-specific antibodies (Ab) promote demyelination in experimental autoimmune encephalomyelitis (EAE) and MS, the role of B cells in antigen (Ag) presentation in CNS autoimmune disease is not clear. When compared to other APC populations, B cells are efficient APC in presentation of protein Ag when they express the B cell receptor (BCR) specific for the Ag recognized by responding T cells. We hypothesize that B cells, in particular, myelin-specific B cells have an important role as APC in activation of myelin-specific T cells. We propose (1) to evaluate the contribution of myelin-specific B cells as APC in EAE and distinguish this function from the role of myelin-specific Ab in EAE. We are creating two transgenic (Tg) models, one containing B cells that express membrane MOG-specific BCR only, and one containing B cells that express membrane MOG-specific BCR and can secrete MOG-specific IgM. We will compare EAE susceptibility in these mice to B cell-deficient and MOG-specific BCR knock-in mice that can secrete all Ig isotypes. We propose (2) to examine the roles of B cell MHC II expression and myelin BCR specificity in presentation of myelin Ag in EAE. We hypothesize that B cells, in particular myelin-specific B cells, have a key role as APC in MHC II-restricted Ag presentation and activation of myelin-specific T cells in EAE and MS. (a) We will test the role of MHC II-restricted B cell Ag presentation to T cells by creating mixed bm chimera mice in which the B cell compartment is selectively deficient in MHC II expression, and compare activation of MOG-specific T cells and EAE susceptibility to bm chimera mice containing B cells that express MHC II molecules. (b) To clarify the role of BCR specificity in MHC II-restricted Ag presentation in EAE, we will examine mixed bm chimera mice in which B cells express either the MOG-specific BCR or nitrophenyl (NP)-specific BCR and do, or do not, express MHC II molecules. Recent clinical results suggest that anti-CD20 B cell depletion may be effective in MS treatment. Our preliminary data suggest that B cell depletion is beneficial in rMOG-induced EAE, but exacerbates MOG p35- 55-induced EAE. We hypothesize that the clinical benefit in rMOG-induced EAE results from reduced B cell Ag presentation or decreased secretion of myelin-specific Ab. We also hypothesize that exacerbation of MOG p35-55-induced EAE, a model that is less dependent upon B cells and Ab, represents loss of regulatory B cell function. In order to evaluate these possibilities, we will (3) examine how anti-CD20 B cell depletion influences MOG-specific T cell responses in the periphery and in the CNS in acute and chronic EAE, and examine whether MOG-specific Ab responses correlate with clinical improvement in anti-CD20 B cell-depleted mice. These studies should provide mechanistic insight regarding B cell depletion in CNS autoimmunity and address questions regarding B cell depletion that are not easily approached in MS clinical trials. PUBLIC HEALTH RELEVANCE B lymphocytes may have multiple roles in the pathogenesis of multiple sclerosis (MS), a central nervous system (CNS) autoimmune disease. Our studies in experimental autoimmune encephalomyelitis (EAE), the murine MS model, will evaluate and distinguish potentially pathogenic roles of B cells in CNS autoimmunity. Our research program will also evaluate how anti-CD20 B cell depletion, a therapeutic approach being investigated in MS clinical trials, may influence immune regulation. Page 5