Novel Biomarkers in Rheumatoid Arthritis

描述(由申请人提供)：这项提案测试了类风湿性关节炎(RA)病理生物学中的一个新的和创新的假说。具体地说，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(例如共同表位)在影响RA表型(疾病严重程度、B细胞过度活动)方面的相互作用。补体C4蛋白(C4a，C4b)通过它们与靶分子氨基(C4a)和硫酯(C4b)形成的共价键的性质而在功能上有所区别。在它们的许多基本作用中，酸性C4a和碱性C4b对于清除免疫复合体是重要的。C4a缺乏是人类系统性红斑狼疮的一个公认的危险因素，但C4b缺乏对生理影响的研究还不够深入。人类的二倍体基因组包含零到四个C4b基因拷贝；血清C4b水平与C4b基因的数量密切相关。在达特茅斯的RA人群中，我们观察到C4b缺乏(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患者或健康对照中(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蛋白抗体(ACPA)和瓜氨酸化抗原组成的免疫复合体的能力来介导的。我们认为，在这些复合体中存在脱亚胺精氨酸(即氨基数量减少的瓜氨酸)会导致C4a促进其清除的能力降低。因此，C4b-硫代酯羰基与底物羟基形成共价键的能力使C4b在清除ACPA免疫复合体方面比C4a重要得多。因此，与C4b缺乏相关的基于ACPA的免疫复合物清除不足将特别增强和有利于抗ACPA反应的成熟，促进血清阳性RA和B细胞的过度活动。假设：我们提出C4b缺乏独立于共同表位影响RA疾病的发病机制(目标1)。在目标2中，我们提出C4b缺乏形成RA表型和B细胞过度活动(血清CXCL13、Ig G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).