Novel Biomarkers in Rheumatoid Arthritis

描述（由申请人提供）：本提案测试了类风湿关节炎（RA）病理生物学的一个新颖和创新的假设。具体来说，我们研究了补体C4B基因拷贝数变异（CNV）在RA发病机制中的作用，以及它与HLA-DRB1等位基因（如共享表位）在影响RA表型（疾病严重程度、B细胞多活性）中的相互作用。补体C4蛋白（C4A, C4B）在功能上由它们与靶标形成的共价键的性质来区分：氨基（C4A）和硫酯（C4B）。在它们的许多重要作用中，酸性C4A和碱性C4B对免疫复合物的清除很重要。C4A缺乏是一个公认的人类SLE的危险因素，但C4B缺乏的生理影响尚未得到充分研究。人类受试者的二倍体基因组包含0到4个C4B基因拷贝；血清C4B水平与C4B基因数量密切相关。在达特茅斯的RA人群中，我们观察到C4B缺乏症（0-1拷贝）存在于43%的血清阳性患者，31%的血清阴性RA患者和20%的非RA患者或健康对照（or从2.5到2.8）。我们假设C4B相对于C4A在RA中的特殊作用是通过其清除由抗瓜氨酸化蛋白抗体（ACPA）和瓜氨酸化抗原组成的免疫复合物的能力介导的。我们提出，这些复合物中存在去氨基精氨酸（即氨基数量减少的瓜氨酸）导致C4A清除能力降低。因此，C4B-硫酯羰基与底物羟基形成共价键以进行处置的能力使得C4B在清除acpa免疫复合物方面比C4A重要得多。因此，与C4B缺乏症相关的基于acpa的免疫复合物清除缺陷会特别增强和促进抗acpa反应的成熟，促进血清阳性RA和B细胞的过度活跃。假设：我们提出C4B缺乏独立于共享表位影响RA疾病的发病机制（Aim 1）。在Aim 2中，我们提出C4B缺乏影响RA表型和B细胞过度活跃（血清CXCL13、IgG和自身抗体水平）。

DESCRIPTION (provided by applicant): This proposal tests a novel and innovative hypothesis in Rheumatoid Arthritis (RA) pathobiology. Specifically, we examine the role of complement C4B gene copy number variation (CNV) on RA pathogenesis and its interaction with HLA-DRB1 alleles (e.g. the shared epitope) in influencing RA phenotype (disease severity, B cell hyperactivity). Complement C4 proteins (C4A, C4B) are functionally distinguished by the nature of the covalent linkage they form with their targets: amino (C4A) vs thioester (C4B). Among their many essential roles, the acidic C4A and the basic C4B are important for the clearance of immune complexes. A deficiency of C4A is a well-established risk factor for human SLE, but the physiologic impact of C4B deficiency is under-studied. A diploid genome of a human subject contains zero to four copies of the C4B gene; serum levels of C4B strongly correlate with the number of C4B genes. In a RA population at Dartmouth, we observed that C4B deficiency (0-1 copy) is present in 43% of the seropositive patients, 31% of seronegative RA patients and 20% of non-RA patients or healthy controls (OR from 2.5 to 2.8). We hypothesize a particular role for C4B relative to C4A in RA mediated by its ability to clear immune complexes made up of anti-citrullinated protein antibodies (ACPA) and citrullinated antigens. We propose that the presence of deiminated-Arginines (i.e. citrullines with decreased numbers of amino groups) in these complexes results in a reduced ability of C4A to contribute to their clearance. As a result, the ability of the C4B-thioester carbonyl group to form a covalent linkage with a hydroxyl group of substrates for disposal makes C4B of much greater importance than C4A in the clearance of ACPA-immune complexes. Thus, deficient ACPA-based immune complex clearance associated with C4B deficiency would particularly enhance and favor maturation of anti-ACPA responses, promoting both seropositive RA and B cell hyperactivity. Hypothesis: We propose that C4B deficiency influences RA disease pathogenesis independent of the shared epitope (Aim 1). In Aim 2, we propose that C4B deficiency shapes RA phenotype and B cell hyperactivity (serum CXCL13, IgG and autoantibody levels). PUBLIC HEALTH RELEVANCE: One of the ways humans differ from each other in their genetic makeup arises from the variations in how many copies they have of certain genes. We have determined that variations in the gene copy number of the complement C4 genes are associated with rheumatoid arthritis. We have also found that rheumatoid arthritis patients differ in their level of systemic B cell activation. We propose that understanding how these attributes lead to the development of rheumatoid arthritis as well as the shape its severity and response to treatment are of great importance to the public health, since this disorder affects 1% of the population worldwide.