Berg Christoph P, Stein Gerburg M, Klein Reinhild, Pascu Maria, Berg Thomas, Kammer Winfried, Priemer Martin, Nordheim Alfred, Schulze-Osthoff Klaus, Gregor Michael, Wesselborg Sebastian, Berg Peter A
Department of Internal Medicine I, Medical Clinic, University of Tübingen, Tübingen, Germany.
Liver Int. 2006 Sep;26(7):846-55. doi: 10.1111/j.1478-3231.2006.01303.x.
Primary biliary cirrhosis (PBC) is characterized by the presence of antimitochondrial antibodies (AMA). Autoantibodies specific for the mitochondrial M4 antigen can be detected by a complement fixation test (CFT) but not by immunoblotting. The aim of this study was to elucidate the identity of the M4 antigen.
M4 proteins were purified by affinity chromatography using IgG fractions of PBC marker sera being CFT positive (n=5) or negative (n=5) and identified by Western blotting, silver staining and sequence analysis. Further, a cohort of 57 PBC patients was tested for the reactivity to M4 and pyruvate dehydrogenase complex (PDC).
Two AMA patterns of the marker sera were visualized: CFT-positive sera were defined as PDC-E2(+)/E1(+) and the CFT-negative sera as PDC-E2(+)/E1(-). The major proteins in the M4 fraction could be related to the PDC-E1 subunits. A clear-cut association between anti-M4 reactivity in the CFT and the reactivity to both PDC subunits could also be documented in the cohort of 57 PBC patients showing anti-PDC-E1alpha and E1beta antibodies at a frequency of 74% and 67%.
CFT reactivity against M4 antigens could be preferentially identified as a reaction against PDC-E1. As PDC-E1 subunits as compared with PDC-E2 lack lipoyl-binding sites, they probably have to be considered as an independent and important target.
原发性胆汁性肝硬化（PBC）的特征是存在抗线粒体抗体（AMA）。线粒体M4抗原特异性自身抗体可通过补体结合试验（CFT）检测到，但免疫印迹法无法检测到。本研究的目的是阐明M4抗原的身份。
使用CFT阳性（n = 5）或阴性（n = 5）的PBC标记血清的IgG组分通过亲和层析纯化M4蛋白，并通过蛋白质印迹、银染和序列分析进行鉴定。此外，对57例PBC患者进行队列研究，检测其对M4和丙酮酸脱氢酶复合物（PDC）的反应性。
标记血清呈现两种AMA模式：CFT阳性血清定义为PDC-E2(+)/E1(+)，CFT阴性血清定义为PDC-E2(+)/E1(-)。M4组分中的主要蛋白质可能与PDC-E1亚基有关。在57例PBC患者队列中也证实，CFT中的抗M4反应性与对两种PDC亚基的反应性之间存在明确关联，其中抗PDC-E1α和E1β抗体的出现频率分别为74%和67%。
针对M4抗原的CFT反应性可能优先被鉴定为针对PDC-E1的反应。由于与PDC-E2相比，PDC-E1亚基缺乏硫辛酰结合位点，它们可能必须被视为一个独立且重要的靶点。
