DNA Repair Defects in IgA Deficiency

描述(申请人提供)：免疫球蛋白A缺乏症(IGAD)的DNA修复缺陷是人类最常见的原发免疫缺陷，其特征是血清中没有IgA，呼吸道和胃肠道细菌感染的频率增加。随着时间的推移，IGAD可能发展成一种更严重的抗体缺陷形式--共同变量免疫缺陷，这两种疾病甚至可以在同一家庭的不同成员中共存，这表明它们代表着相同潜在遗传缺陷的各个方面(S)。为了产生IgA，表达的重链抗体亚型必须交换为编码IgA的DNA序列。这种DNA水平的交易被称为类开关重组(CSR)，它发生在两个所谓的开关区域序列之间，这两个开关区域序列位于编码抗体重链恒定区的相应外显子的上游。最近的研究表明，CSR是由AID催化的DNA胞嘧啶脱氨反应启动的，由此产生的尿嘧啶残基被普遍存在的DNA修复系统识别和处理，如碱基切除修复、错配修复、非同源末端连接以及最近的单链退火(替代末端连接途径)。AID或尿嘧啶切除(UNG2)的缺陷会导致免疫缺陷，其特征是高水平的IgM，损害包括IgA在内的其他抗体同型。我们最近发现了错配修复基因MSH5中与IGAD和CVID相关的变异。我们实验室随后的初步研究发现了其他DNA修复基因的变异，这些基因也与CVID和/或IGAD有关。这一建议将建立在我们之前的研究基础上，直接检验多个DNA修复缺陷也会导致IGAD/CVID的假设。来自至少400名IGAD/CVID患者的已知DNA修复基因的完整谱系将通过一种名为大规模并行DNA测序或454焦测序的新技术进行测序。在计算分析之后，候选突变将通过重新测序和使用世界上最大的IGAD/CVID患者队列进行的家庭研究来验证。关键的疾病相关突变将在基于细胞的系统中进行检查，以寻找DNA修复和抗体基因多样化计划中的缺陷。总体而言，我们预计，通过展示IGAD/CVID中几个额外的DNA修复因子的参与，我们将在先前研究的基础上取得重大进展。公共卫生相关性：抗体是我们对细菌和病毒等病原体的免疫反应的重要组成部分。最近来自许多实验室的证据表明，普遍存在的DNA修复因子通过促进DNA水平的交易来帮助确保有效的抗体反应，而DNA水平的交易是产生多样化和强大的抗体谱系所必需的。这项提案将确定来自世界上最大的免疫缺陷疾病队列之一的400多名患者的完整DNA修复基因序列。我们预计会发现几个新的因素，这些因素对于对病原体产生强大的抗体反应是必不可少的。

DESCRIPTION (provided by applicant): DNA Repair Defects in IgA Deficiency Immunoglobulin A deficiency (IgAD) is the most common primary immunodeficiency in humans, and it is characterized by the absence of serum IgA and an increased frequency of bacterial infections in the respiratory and gastrointestinal tracts. IgAD may develop over time into a more severe form of antibody deficiency, common variable immunodeficiency (CVID), and the two diseases can even co-exist in different members of the same family suggesting that they represent facets of the same underlying genetic defect(s). In order for IgA to be produced, the expressed heavy chain antibody isotype must be swapped for DNA sequences that encode IgA. This DNA level transaction is called class switch recombination (CSR) and it occurs between two so-called switch region sequences that reside upstream of the respective exons that encode the constant region of the antibody heavy chain. Recent studies have demonstrated that CSR is initiated by AID-catalyzed DNA cytosine deamination events and that the resulting uracil residues are recognized and processed by ubiquitous DNA repair systems such as base excision repair, mismatch repair, non-homologous end-joining and, most recently, single-strand annealing (alternative end-joining pathway). Defects in AID or uracil excision (UNG2) cause an immunodeficiency characterized by high levels of IgM at the expense of other antibody isotypes including IgA. We recently discovered variations in the mismatch repair gene MSH5 that associate with IgAD and CVID. Subsequent preliminary studies in our laboratories have revealed variations in other DNA repair genes that also associate with CVID and/or IgAD. This proposal will build on our prior studies by directly testing the hypothesis that multiple DNA repair defects also contribute to IgAD/CVID. The complete repertoire of known DNA repair genes from a minimum of 400 IgAD/CVID patients will be sequenced by a new technology called massively parallel DNA sequencing or 454 pyrosequencing. After computational analyses, candidate mutations will be validated by re-sequencing and by family studies using the largest IgAD/CVID patient cohort in the world. Key disease-associated mutations will be examined in cell-based systems for defects in DNA repair and in antibody gene diversification program. Overall, we anticipate significantly building upon our prior studies by demonstrating the involvement of several additional DNA repair factors in IgAD/CVID. PUBLIC HEALTH RELEVANCE: Antibodies are a crucial part of our immune response to pathogens such as bacteria and viruses. Recent evidence from many laboratories indicates that ubiquitous DNA repair factors help ensure an effective antibody response by facilitating the DNA level transactions that are required to generate a diverse and strong antibody repertoire. This proposal will determine the complete set of DNA repair gene sequences for more than 400 patients from one of the largest immunodeficiency disease cohorts in the world. We anticipate discovering several new factors that are essential for a robust antibody responses to pathogens.