Zhang L Y, Lu Y P, Yang L, Luo G H, Song J, Li Y P
Transplantation Institute, West China Hospital, Chengdu, Sichuan, China.
Transplant Proc. 2009 Dec;41(10):4366-8. doi: 10.1016/j.transproceed.2009.08.071.
Citrate synthase (CS) is the one of the key enzymes in the citric acid cycle and an important mitochondrial autoantigen. The autoimmune responses against CS have not been studied in chronic allograft nephropathy (CAN). This study investigated the role of specific CS autoantibodies in rats bearing renal allografts affected with CAN.
Fisher344 rat renal grafts were orthotopically transplanted into Lewis rats following the procedure of Kamada with our modification. Lewis-to-Lewis and Fisher344-to-Fisher344 kidney transplantations were also performed as autologous control groups (each n = 9). All the allograft recipients given cyclosporine (10 mg/kg(-1)d(-1) x 10 d) were divided into four groups (each n = 9): (1) vehicle: normal saline orally; (2) cyclosporine: 6 mg/kg(-1)d(-1); (3)FK506: 0.15 mg/kg(-1)d(-1); (4) mycophenolate mofetil (MMF): 20 mg/ kg(-1)d(-1). At 4, 8, and 12 weeks posttransplantation, the animals were sacrificed to harvest sera and renal allografts. The serum creatinine (SCr) was measured and pathological changes assessed according to Banff 97 criteria. IgM and IgG isotypes of CS antibodies were detected in all recipient sera by enzyme linked immunosorbent assays.
Both IgM and IgG isotype CS autoantibodies were observed in the sera of all the recipients before and after transplantation, but the levels of IgM CS autoantibody were obviously higher than IgG isotype in all the blood samples. It was stable not only in autologous but also in allograft groups. In both autologous groups, the SCr and IgM and IgG isotype CS autoantibodies showed no obvious change before and after transplantation, and no typical CAN occurred. The values of IgG isotype of CS autoantibody (DeltaOD) at 4, 8 and 12 weeks were stable. At 4 weeks, the values of SCr, Banff score, and IgG isotype CS autoantibody (DeltaOD) were not significantly different (P > .05) among the allograft groups. At 8 and 12 weeks, with progression of CAN in vehicle, cyclosporine and FK506 groups' values of SCr, Banff score, and IgG (DeltaOD) also increased dramatically (P = .005) in all three groups when compared with the baseline and 4 week values, but the differences among the three groups were not significant (P > .05). At 8 and 12 weeks, the MMF group suffered mild-to-moderate CAN, but the values of SCr and Banff score were significantly lower than those in the other three groups. MMF significantly inhibited the formation of IgG (DeltaOD) when compared with the other three groups (P = .02).
This study suggested that the IgG isotype of CS autoantibody contributes to CAN after kidney transplantation. The IgM isotype is physiological. MMF significantly inhibited the formation of IgG isotype CS autoantibody, which may be related to its effects to alleviate CAN.
柠檬酸合酶（CS）是柠檬酸循环中的关键酶之一，也是一种重要的线粒体自身抗原。针对CS的自身免疫反应在慢性移植肾肾病（CAN）中尚未得到研究。本研究调查了特异性CS自身抗体在患有CAN的肾移植大鼠中的作用。
按照Kamada的方法并加以改进，将Fisher344大鼠肾移植到Lewis大鼠体内。Lewis大鼠之间和Fisher344大鼠之间的肾移植也作为自体对照组进行（每组n = 9）。所有接受环孢素（10 mg/kg⁻¹d⁻¹×10 d）的移植受体被分为四组（每组n = 9）：（1）载体：口服生理盐水；（2）环孢素：6 mg/kg⁻¹d⁻¹；（3）FK506：0.15 mg/kg⁻¹d⁻¹；（4）霉酚酸酯（MMF）：20 mg/kg⁻¹d⁻¹。在移植后4周、8周和12周，处死动物以采集血清和肾移植组织。测量血清肌酐（SCr），并根据Banff 97标准评估病理变化。通过酶联免疫吸附试验检测所有受体血清中CS抗体的IgM和IgG亚型。
在移植前后所有受体的血清中均观察到IgM和IgG亚型的CS自身抗体，但在所有血样中，IgM CS自身抗体水平明显高于IgG亚型。它不仅在自体组中稳定，在移植组中也稳定。在两个自体组中，移植前后SCr以及IgM和IgG亚型CS自身抗体均无明显变化，且未发生典型的CAN。CS自身抗体IgG亚型（ΔOD）在4周、8周和12周时的值稳定。在4周时，各移植组之间的SCr值、Banff评分和IgG亚型CS自身抗体（ΔOD）无显著差异（P > 0.05）。在8周和12周时，随着载体组、环孢素组和FK506组中CAN进展，与基线和4周时的值相比，这三组的SCr值、Banff评分和IgG（ΔOD）也显著增加（P = 0.005），但三组之间的差异不显著（P > 0.05）。在8周和12周时，MMF组发生轻至中度CAN，但其SCr值和Banff评分显著低于其他三组。与其他三组相比，MMF显著抑制了IgG（ΔOD）的形成（P = 0.02）。
本研究表明，CS自身抗体的IgG亚型在肾移植后导致CAN。IgM亚型是生理性的。MMF显著抑制了IgG亚型CS自身抗体的形成，这可能与其减轻CAN的作用有关。
