Mi-2

Mi-2

Diseases:
Polymyositis and Dermatomyositis

The Mi-2ß autoantigen (MW 221.3 kDa) belongs to a family of so-called chromodomain helicase-DNA-binding proteins; several isoforms of Mi-2 exist with molecular weights between 210 and 240 kDa. Biochemically, Mi-2ß is a component of the nucleosome remodeling and deacetylase (NuRD) complex, which seems to be involved in transcription regulation.

Autoantibodies targeting the Mi-2 nuclear antigen are a serologic feature of idiopathic inflammatory myopathies (IIM). In IIM Mi-2 antibodies are characterized by diagnostic sensitivity and specificity of approximately 4-18% and 98-100%, respectively. Furthermore, anti-Mi-2 antibodies are strongly associated with dermatomyositis (frequency up to 31%) and have a very high positive predictive value for such a disease subset. Anti-Mi-2 are the only defined myositis-specific autoantibodies clearly directed to a nuclear target. Another rather exceptional feature of Mi-2 antibodies relates to their frequency in children, which is comparable to that in adults.

Previously, only several recombinant Mi-2ß subfragments expressed in E.coli have been used in diagnostic applications. Recombinant, human Mi-2ß from DIARECT is a full-length, 220-kDa autoantigen, eukaryotically expressed in baculovirus-infected insect cells. DIARECT is the first commercial supplier offering a recombinant full-length Mi-2 antigen. 

相关疾病：多发性肌炎/皮肌炎 炎症性的肌病以骨骼肌炎症浸润为特征。这些原发性的肌病包含一系列的共有的和非共有的并发症。共同的亚类包含成人多发性肌炎（PM）和皮肌炎（DM），连同包含体肌炎，儿童肌病，恶性肿瘤相关的肌病和肌病重叠其他的自身免疫结缔组织病。在30%的肌炎病人血清中发现了氨酰基-tRNA合成酶的自身抗体。这些抗体紊乱有很高的特异性，并且与并发肺病高度相关。抗SRP抗体与坏死性心肌炎综合症有关，这种疾病很难治愈。Mi-2自身抗体是皮肌炎的特异性血清学标志物。在大约20%的肌炎患者血清中检测到，所以它可作为皮肌炎急性发作，预后良好和良好的治疗反应的标记物。Mi-2ß自身抗原（分子量 221.3 kDa）属于染色质域解旋酶DNA结合蛋白家族，Mi-2有几个亚型，分子量在210到240kDa之间。Mi-2ß是核小体重塑和脱乙酰基酶（NuRD）复合物的一个组分，可能参与转录调节。靶向Mi-2核抗原的自身抗体是自发性肌炎（IIM）存在的一个血清学特性。IIM Mi-2抗体以诊断灵敏性和各自约4-18%和98-100%的特异性为特征。此外，抗Mi-2的抗体与皮肌炎强烈相关（频率高达31%），对于这种疾病亚型有非常高的阳性预测价值。抗Mi-2抗体是直接指向核靶点的肌炎特异性自身抗体。Mi-2抗体另外一个较为罕见特性就是在儿童中出现的频率与在成人中出现的频率相当。

以前，只有少数在E.coli表达的重组Mi-2 ß亚片段可以应用于诊断。DIARECT生产的重组人Mi-2 ß是220kD全长的抗原，在杆状病毒感染的昆虫细胞中真核表达。DIARECT是第一个提供商业重组全长Mi-2抗原的公司。