Role of DOCK8 in B Cell Function

描述(由申请人提供)：鸟嘌呤核苷酸交换因子胞质分裂-8(DOCK8)基因的缺失导致常染色体隐性遗传性高IgE综合征，其特征是反复肺部感染、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反应不足。我们发现DOCK8缺陷患者的免疫球蛋白抗体反应受损，缺乏记忆性B细胞，边缘带(MZ)样B细胞和滤泡辅助细胞(TFH)数量减少。与正常受试者不同的是，他们会产生针对肺炎链球菌抗原的IgE抗体。我们还观察到DOCK8在B细胞中位于TLR9下游，是TLR9诱导的STAT3激活所必需的，而STAT3在B细胞分化为抗体产生细胞过程中起着重要作用，并证明DOCK8与B细胞中的MyD88和酪氨酸激酶PYK2结合，经历PYK2的磷酸化，在人和小鼠B细胞中TLR9连接后的Lyn-Syk-STAT3级联激活中起关键作用。我们建议检验DOCK8是B细胞活性的关键调节因子这一总体假设。我们将利用我们对DOCK8缺乏患者的大量人群、B细胞可复制患者缺陷的新构建的Dock8-/-小鼠以及携带条件性(牙线状)Dock8等位基因的小鼠的访问，来测试DOCK8促进保护性T细胞依赖性(TD)和II型T非依赖性(TI)抗体的假设。但抑制过敏性IgE抗体。B细胞的内在和外在机制的反应。我们将1)检验以下假设：与TLR9结合的配体在B细胞中招募并激活Tri-R9。 分子MyD88/DOCK8/Pyk2复合体，导致STAT3活化和B细胞分化。2)验证DOCK8细胞通过介导TLR9信号转导、促进T滤泡辅助细胞功能和推动MZ B细胞发育而在抗体应答中起关键作用的假说。3)检验DOCK8是IgE抗体产生的调节者，以及针对微生物抗原的IgE抗体增强对感染的敏感性的假设 DOCK8缺乏症。深入了解DOCK8在B细胞功能中的作用将有助于我们进一步了解DOCK8患者对感染的易感性。由于DOCK8缺乏易导致自身免疫、过敏和癌症，其研究可能为这些常见疾病的发病机制提供新的和重要的见解。

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.