B cells in CNS autoimmunity

描述(申请人提供)：B细胞在中枢神经系统自身免疫性疾病的发病机制中可能具有多种作用。在实验性自身免疫性脑脊髓炎(EAE)和多发性硬化症(MS)中，髓鞘特异性抗体(Ab)促进脱髓鞘，但在中枢神经系统自身免疫性疾病中B细胞在抗原(Ag)提呈中的作用尚不清楚。与其他APC群体相比，B细胞在表达反应性T细胞识别的抗原特异性B细胞受体(BCR)时，是高效的APC。我们假设B细胞，尤其是髓鞘特异的B细胞，在髓鞘特异的T细胞的活化中起着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，并将这一功能与髓鞘特异性抗体在EAE中的作用区分开来。我们正在创建两个转基因(TG)模型，一个包含仅表达膜MOG特异性BCR的B细胞，另一个包含表达膜MOG特异性BCR并能分泌MOG特异性IgM的B细胞。我们将把这些小鼠的EAE易感性与B细胞缺陷和MOG特异性bcr基因敲除小鼠进行比较，后者可以分泌所有Ig亚型。我们建议(2)研究B细胞MHC II表达和髓鞘BCR特异性在EAE中髓鞘抗原表达中的作用。我们假设B细胞，特别是髓鞘特异性B细胞，在MHC II限制性抗原提呈和EAE和MS中髓鞘特异性T细胞的激活中具有关键的APC作用。(A)我们将通过建立B细胞室选择性缺乏MHC II表达的混合BM嵌合体小鼠来测试MHC II限制性B细胞抗原提呈给T细胞的作用，并比较MOG特异性T细胞的激活和EAE对含有表达MHC II分子的B细胞的BM嵌合体小鼠的易感性。(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，在这些小鼠中，B细胞表达MOG特异性BCR或硝基苯基(NP)特异性BCR，并且不表达或不表达MHC II分子。最近的临床结果提示抗CD20B细胞去除对MS的治疗可能是有效的。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。我们假设，rMOG诱导的EAE的临床益处来自于B细胞抗原提呈减少或髓鞘特异性抗体分泌减少。我们还假设，MOG p35-55诱导的EAE的恶化代表着调节性B细胞功能的丧失。为了评估这些可能性，我们将(3)研究抗CD20B细胞耗竭如何影响急、慢性EAE患者外周和中枢神经系统的MOG特异性T细胞反应，以及抗CD20B细胞耗竭小鼠的MOG特异性抗体反应是否与临床改善相关。这些研究应该提供关于中枢神经系统自身免疫中B细胞耗竭的机械性见解，并解决在MS临床试验中不易解决的B细胞耗竭问题。

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.