B细胞分泌的IgG抗体在cGVHD发病中的作用及机理研究

Chronic graft-versus-host disease (cGVHD) is a major cause of morbidity and mortality after allo-HCT. There has been little progress in prevention and treatment of cGVHD, due to the poor understanding of cGVHD pathogenesis. Recently it is reported that B cells play an important role in cGVHD, but the role of antibodies from B cells in the pathogenesis of cGVHD remains unclear. To answer this question is to distinguish between antibody-dependent and antibody-independent effects of B cells. We generated IgHμγ1 DBA/2 mice whose B cells have normal antigen-presentation and regulatory functions but cannot secrete antibodies. With a murine cGVHD model using DBA/2 donors and BALB/c recipients, we found that antibodies are required for persistence of cGVHD, but are not required to initiate cGVHD. Antibodies augment infiltration and expansion of Th17 cells in the skin and perpetuate cutaneous cGVHD. In this study, we explore the effects and mechanisms of antibodies on thymus, lymphoid and target tissue damage and T helper cells differentiation. In high dose IgHμγ1 DBA/2 to BALB/c transient cGVHD model, we explore the mechanisms that IgG antibodies perpetuate cutaneous cGVHD. In vitro and in vivo experiment, we explore the mechanisms that IgG antibodies mediate TGF-β1and PDGFR signaling and antibodies perpetuate cutaneous cGVHD by complement systems. This study will provide new insights into cGVHD pathogenesis and provide new scientific basis for developing novel therapy for cGVHD.

近年来B细胞在cGVHD中的作用受到广泛关注，早在1978年有学者提出B细胞分泌的抗体参与cGVHD发生，但至今仍有争议。解决这一争议的关键是区分抗体依赖性及抗体非依赖性B细胞的作用。基于此我们在前期研究中构建了有B细胞的抗原提呈及调节功能、但是不分泌抗体的IgHμγ1转基因DBA/2小鼠；在以DBA/2到BALB/c鼠的cGVHD模型中，研究提示：供者B细胞产生的抗体对于cGVHD的发生不是必须的，但是对于cGVHD的维持是必须的。为了进一步揭示抗体在cGVHD中的作用及机理，本项目拟开展：探讨抗体对胸腺、淋巴器官及靶器官的影响和对Th效应细胞分化的影响；探讨IgG抗体对TGF-β1及PDGFR通路的影响，揭示其导致cGVHD持续发生及皮肤纤维化的机制；探讨抗体是否通过补体系统导致cGVHD持续发生及机制。由此揭示抗体参与cGVHD持续发生的致病机理，为临床cGVHD的防治提供理论依据。

cGVHD是移植后最主要的死亡原因，近年来B细胞在cGVHD中的作用受到广泛关注。B细胞分泌的抗体在cGVHD发生发展中的作用，至今仍有争议。我们在前期研究中构建了有B细胞的抗原提呈及调节功能、但是不分泌抗体的IgHμγ1转基因DBA/2小鼠；在DBA/2到BALB/c鼠的cGVHD模型中，我们的研究发现：供者B细胞产生的抗体对于cGVHD的发生不是必须的，但是对于cGVHD的维持是必须的。IgG在胸腺及皮肤等靶组织沉积，进一步介导胸腺、外周淋巴器官的破坏。抗体诱导皮肤中的树突状细胞分泌IL-23,导致致病性Th17细胞在皮肤组织浸润，从而增强皮肤cGVHD的发生发展。且在cGVHD病人中，进一步证实了IgG1表达水平的增高，且与疾病严重程度呈正相关。此外，我们的研究首次在外周血中定义了循环滤泡外辅助性样的T细胞（circulating extrafollicular helper T like cells），该群细胞的扩增与cGVHD的严重程度呈正相关。cGVHD病人中，该群细胞诱导初始的B细胞向浆母细胞分化及分泌IgG1抗体的能力均增加。由此揭示抗体参与cGVHD持续发生的致病机理，为临床cGVHD的防治提供理论依据。