IgA肾病患者血浆抗糖抗体的测定及其与临床病理指标的相关性

目的建立并改良血浆IgG型及IgA1型抗糖抗体检测方法体系,评价其在IgA肾病(IgAN)的发生、发展中的作用。方法分层随机法抽取2006年1月至2015年12月在北京大学第一医院肾脏内科IgAN规律随访队列患者中的170例;同时选取30例健康人群为对照组。酶联免疫吸附法(ELISA)测定患者及健康人群血浆铰链区O糖半乳糖缺失IgA1(Gd-IgA1)及针对血浆Gd-IgA1的特异性抗糖抗体(IgG型、IgA1型)水平。线性相关及多因素线性回归分析抗糖抗体与临床病理指标的相关性。运用受试者工作特征曲线(ROC)评估血浆抗糖抗体诊断IgAN的价值。结果IgAN组患者及健康对照组人群血浆中均可检测到可识别包含铰链区Fab段(Fab-HR)抗原的IgG型和IgA1型自身抗体,凝集素抑制试验显示其特异性识别的抗原表位为IgA1铰链区半乳糖缺失而暴露的N-乙酰半乳糖胺(GalNAc)残基。IgAN组与健康对照组间血浆IgG型抗糖抗体含量绝对值的差异无统计学意义(P=0.963),校正血浆IgG浓度后,IgAN组患者IgG型标准化抗糖抗体浓度(lnIgG抗糖抗体/IgG])显著高于健康对照组人群(0.58±0.31比0.37±0.11,P<0.01)。IgAN患者血浆标准化抗糖抗体浓度与肾活检时24h尿蛋白量呈正相关(r=0.183,P<0.05),且在校正基线临床和病理因素后仍与24h尿蛋白量显著相关(β=0.713,95%CI0.323~1.102,P<0.01)。标准化IgG型抗糖抗体诊断IgAN的ROC曲线下面积(AUC)为0.764(95%CI0.682~0.845,P<0.05),其截断值为0.396,诊断IgAN的敏感度为0.729,特异度为0.700。IgAN患者IgA1型抗糖抗体绝对值及标准化浓度与健康对照组间差异无统计学意义(均P>0.05)。结论IgAN患者和健康人体内均存在特异识别Gd-IgA1的抗糖抗体,部分IgAN患者血浆抗糖抗体浓度显著升高。推断抗糖抗体可能参与部分IgAN的发生和发展。

Determination of plasma antiglycan autoantibodies in patients with IgA nephropathy and the correlation with clinical characteristics

Objective To establish the measurement of IgA1 O-glycan-specific antiglycan autoantibodies in patients with IgA nephropathy (IgAN), and evaluate their role in the development and progression of IgAN. Methods In the IgAN regular follow-up cohort of Peking University Institute of Nephrology from January 2006 to December 2015, 170 patients drawn by stratified randomization were enrolled in this study. Enzyme-linked immunosorbent assay (ELISA) was used to determine the levels of plasma galactose-deficient IgA1 (Gd-IgA1) and antiglycan autoantibody (IgG and IgA1). The correlation between antiglycan autoantibodies and clinicopathological parameters was analyzed by linear correlation and multiple linear regression analysis. The receiver operating characteristic curve (ROC) was used to evaluate the value of plasma anti glycide antibodies in the diagnosis of IgAN. Results IgG and IgA1 antiglycan autoantibodies that specifically recognized Fab-hinge region (Fab-HR) antigens could be detected in both IgAN and healthy control group. Agglutinin inhibition test showed that the specific antigen epitope was N-acetylgalactosamine (GalNAc) residue exposed to galactose deficiency in IgA1 hinged region. There was no significant difference in the absolute levels of plasma IgG antiglycan autoantibodies between IgAN and healthy controls (P=0.963). After adjustment of the plasma level of IgG, the normalized antiglycan autoantibody (lnIgG antiglycan antibody/IgG]) in patients with IgAN was significantly higher than that in healthy controls (0.58±0.31 vs 0.37±0.11, P﹤0.01). The normalized level of IgG antiglycan autoantibody in IgAN patients was positively correlated with 24 h urine protein level during renal biopsy (Spearman r=0.183, P﹤0.05), and was also significantly correlated with 24 h urinary protein level after adjusting for baseline clinical and pathological factors (β=0.713, 95%CI 0.323-1.102, P﹤0.01). The area under ROC curve (AUC) of normalized IgG antiglycan autoantibody in the diagnosis of IgAN was 0.764 (95% CI 0.682-0.845, P﹤0.05). Using the cut-off value of 0.396, the sensitivity and specificity of normalized IgG antiglycan autoantibody for IgAN were 0.729 and 0.700 respectively. There was no significant difference in the absolute or normalized levels of IgA1 antiglycan autoantibodies between IgAN patients and healthy controls. Conclusions Gd-IgA1-specific antiglycan autoantibodies can be detected both in IgAN patients and healthy controls. They are elevated in some patients with IgAN and possibly involved in the development of IgAN.