IgA肾病患者血清IgA_1与正常人肾小球系膜细胞结合动力学研究

Study on the binding capacity of IgA_1 from patients with IgA nephropathy to human mesangial cells

目的 :观察IgA肾病 (IgAN)患者血清聚合IgA1(aIgA1)与体外培养的正常人肾小球系膜细胞 (HMC)结合动力学特征 ,明确HMC上是否存在特异性IgA1结合蛋白 ,比较IgAN患者及正常人血清aIgA1与HMC结合力的异同。方法 :亲和层析提取血清IgA1,加热聚合并用 [12 5I]标记 ,放射性配基结合法检测aIgA1与HMC结合力 ,用白蛋白、IgG及单体IgA1(mIgA1)作竞争抑制实验检测结合特异性 ,用正常人及IgAN患者aIgA1做交叉竞争抑制实验比较二者结合力。结果 :正常人及IgAN患者aIgA1与HMC的结合呈剂量依赖性和饱和性 ,这种结合不被白蛋白、IgG阻断 ,而被mIgA1部分阻断 ,二者解离常数Kd值分别为 (4 3± 1 2 )× 10 -7mol/L和 (8 9± 2 1)× 10 -8mol/L ,差异显著 (P<0 0 5 ) ,IgAN患者aIgA1竞争结合HMC的能力显著高于正常人aIgA1(P <0 0 1)。结论 :①HMC上存在特异性IgA1结合蛋白。②IgAN患者血清IgA1与HMC结合力高于正常人IgA1。

AIM: To examine and compare the ability of serum IgA 1, from both the patients with IgA nephropathy (IgAN) and the healthy control, to bind to human mesangial cells (HMC). METHODS: Serum IgA was isolated with jacalin column, heated to aggregated form (aIgA 1) and labeled with [ 125 I]. Binding capacity of aIgA 1 to primary HMC was evaluated by radioligant binding assay, specificity of binding was determined by competitive inhibition, and relative affinities was compared by cross competitive inhibition. RESULTS: Both aIgA 1 from normal control and patients with IgAN bound to MC in a dose-dependent, saturatable manner, but the binding of aIgA 1 from patients was saturated at approximately 200 pmol while that from healthy was at 400 pmol. The Scatchard analysis revealed a Kd of (8 9±2 1)×10 -8 mol/L for patient's aIgA 1 versus (4 3±1 2)×10 -7 mol/L for normal aIgA 1 ( P <0.05). Competition inhibition showed that both serum albumin and IgG could not block the binding of aIgA 1 to HMC while mIgA 1 could partially block that. Cross competition inhibition demonstrated that patient's aIgA 1 blocked normal aIgA 1 binding significantly ( P <0 01), however, normal aIgA 1 was unable to inhibit the binding of patient's aIgA 1. CONCLUSIONS: ①There are IgA binding proteins or receptors on mesangial cells. ②aIgA 1 from patients with IgAN has a higher binding capacity than that from healthy.