Role of DOCK8 in B Cell Function

描述（由申请方提供）：胞质分裂奉献因子-8（DOCK 8）基因（一种鸟嘌呤核苷酸交换因子）缺陷导致常染色体隐性高IgE综合征，其特征为复发性肺部感染、湿疹、皮肤病毒感染、血清IgE水平升高、食物过敏、T细胞数量减少和抗体应答缺陷。 我们已经发现DOCK 8缺陷患者具有受损的IgG抗体应答、记忆B细胞的缺乏、边缘区（MZ）样B细胞和滤泡辅助（TFH）细胞的数量减少。与正常人不同，他们对肺炎球菌抗原产生IgE抗体。我们还进行了新的观察，DOCK 8在B细胞中在TLR 9下游起作用，并且对于TLR 9诱导的STAT 3活化是必需的，STAT 3在B细胞分化为抗体产生细胞中起重要作用，并且证明DOCK 8与B细胞中的MyD 88和酪氨酸激酶Pyk 2相关，经历Pyk 2的磷酸化，并且对于人和小鼠B细胞中TLR 9连接后Lyn-Syk-STAT 3级联的激活至关重要。 我们建议测试DOCK 8是B细胞活性的关键调节因子的总体假设。我们将利用我们对大量DOCK 8缺陷患者、新构建的Dock 8-/-小鼠（其B细胞表型复制患者中的缺陷）和携带条件性（floxed）Dock 8等位基因的小鼠的访问来检验DOCK 8促进保护性T依赖性（TD）和II型T非依赖性（TI）Ab的假设。反应，但抑制过敏性IgE抗体。通过B细胞内在和外在机制的反应。我们将1）测试在B细胞中与TLR 9结合的配体募集并激活三- 分子MyD 88/DOCK 8/Pyk 2复合物，导致STAT 3活化和B细胞分化。 2)检验DOCK 8细胞通过介导TLR 9信号传导、促进T滤泡辅助细胞功能和驱动MZ B细胞发育在IgG抗体应答中发挥关键作用的假设。 3)测试DOCK 8是IgE抗体产生的调节剂以及IgE抗体对微生物抗原增强感染易感性的假设。 DOCK 8缺乏症 对DOCK 8在B细胞功能中的作用的更深入的了解将进一步我们对DOCK 8患者对感染的易感性的理解。由于DOCK 8缺乏易导致自身免疫、过敏和癌症，因此其研究可能为这些常见疾病的发病机制提供新的重要见解。

DESCRIPTION (provided by applicant): Deficiency in the dedicator of cytokinesis-8 (DOCK8) gene, a guanine nucleotide exchange factor, results in autosomal recessive Hyper-IgE syndrome characterized by recurrent pulmonary infections, eczema, cutaneous viral infections, elevated serum IgE levels, food allergy, low numbers of T cells, and deficient antibody responses. We have found that DOCK8 deficient patients have impaired IgG antibody responses, lack of memory B cells, reduced numbers of marginal zone (MZ)-like B cells and of follicular helper (TFH) cells. Unlike normal subjects, they make IgE antibodies to pneumococcal antigens. We also made the novel observation that DOCK8 functions downstream of TLR9 in B cells, and is essential for TLR9-induced activation of STAT3, which plays an important role in the differentiation of B cells into antibody producing cells, and demonstrated that DOCK8 associates with MyD88 and the tyrosine kinase Pyk2 in B cells, undergoes phosphorylation by Pyk2 and is critical for the activation of a Lyn-Syk-STAT3 cascade following TLR9 ligation in human and mouse B cells. We propose to test the overall hypothesis that DOCK8 is a key regulator of B cell activity. We will take advantage of our access to a large population of DOCK8 deficient patients, of newly constructed Dock8-/- mice whose B cells phenocopy the defects in the patients, and of mice that carry a conditional (floxed) Dock8 allele, to test the hypothesis tht DOCK8 promotes protective T dependent (TD) and type II T independent (TI) Ab. responses, but inhibits allergic IgE Ab. responses by mechanisms both intrinsic and extrinsic to B cells. We will 1) Test the hypothesis that ligand binding to TLR9 in B cells recruits and activates the tri- molecular MyD88/DOCK8/Pyk2 complex, resulting in STAT3 activation and B cell differentiation. 2) Test the hypothesis that DOCK8 cells plays a critical role in IgG antibody responses by mediating TLR9 signaling, promoting T follicular helper cell function and driving the development of MZ B cells. 3) Test the hypothesis that DOCK8 is a regulator of IgE antibody production and that IgE antibodies to microbial antigens enhance the susceptibility to infection in DOCK8 deficiency. A deeper knowledge of the role of DOCK8 in B cell function will further our understanding of the susceptibility of DOCK8 patients to infection. Since DOCK8 deficiency predisposes to autoimmunity, allergy and cancer, its study is likely to provide novel and important insights into the pathogenesis of these common conditions.