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).