Epitopes on Ki antigen and its association to autoantibody production.

我们已经克隆了一个核自身抗原Ki的cDNA，发现Ki的氨基酸序列与SV 40大T抗原核定位标志（SV 40 NLS）同源。我们研究了与SV 40 NMS同源的氨基酸序列是否为Ki抗原的表位之一，以及抗Ki抗体是否与SV 40大T抗原发生交叉反应。以重组Ki （bNAX）为抗原，采用酶联免疫吸附试验（ELISA）从250例系统性红斑狼疮（SLE）患者血清中筛选出49例抗Ki阳性血清。制备了与sv40 NLS （KILT）序列同源的16聚Ki合成肽。此外，根据Ki抗原的构象和水解性分析，制备了4种不同的合成肽（KISP1-4）。用ELISA法检测抗ki血清对合成肽的反应性。49种血清中有18种与KILT发生反应，但没有一种与KISP1-4发生强烈反应。KILT与抗ki血清特异性反应，但与其他核抗原（如U1 RNP、Sm、SS-A、SS-B、PCNA、Scl-70和Jo-1）自身抗体不发生反应。此外，抗ki抗体对KILT的反应性被bNAX特异性抑制。这些结果表明，KILT与抗ki抗体特异性反应。制备了与SV 40 NLS （LTSP）序列相同的7聚合成肽，用于检测Ki抗原与SV 40大T抗原之间的交叉反应性。49个血清中有8个与它反应，其中7个同时与LTSP和KILT反应。抗kilt阳性血清与LTSP反应的频率（38.8%）显著高于抗kilt阴性血清（3.2%）（P<0.01）。这些结果表明狼疮患者的抗Ki抗体识别与SV 40 NLS同源的氨基酸序列作为表位，Ki与SV 40大T抗原之间的分子相似性可能在自身抗体的产生中起作用。

A cDNA coding for a nuclear autoantigen, Ki, has been cloned previously and we have found that Ki has an amino acid sequence which is homologous to SV 40 large T antigen nuclear localization sign (SV 40 NLS). We studied whether the amino acid sequence which is homologous to SV 40 NMS is one of the epitopes on Ki antigen and anti-Ki antibody croos-react with SV 40 large T antigen.Forty-nine anti-Ki positive sera were selected from 250 patients with systemic lupus erythematosus (SLE) by enzyme-linked immunosorbent assay (ELISA) using recombinant Ki (bNAX) as an antigne. A 16-mer Ki synthetic peptide that had a sequence homologous to SV 40 NLS (KILT) was prepared. In addition, 4 different synthetic peptides (KISP1-4) were prepared based on the analysis of conformational profile and hydoropathy of Ki antigen. The reactivities of anti-Ki sera to those synthetic peptides were tested by ELISA.Eighteen out of 49 sera reacted with KILT but none of them strongly reacted with KISP1-4. The KILT specifically reacted with anti-Ki sera but did not react with autoantibodies to other nuclear antigens such as U1 RNP,Sm, SS-A,SS-B,PCNA,Scl-70 and Jo-1. In addition, the reactivity of anti-Ki antibodies to KILT was specifically inhibited by bNAX.Those results indicated that KILT specifically reacted with anti-Ki antibody. A 7-mer synthetic peptide that had the same sequence as that of SV 40 NLS (LTSP) was prepared to test the cross-reactivity between the Ki antigen and SV 40 large T antigen. Eight out of 49 sera reacted with it and 7 of them reacted with both LTSP and KILT.The frequency of sera reacted with LTSP in anti-KILT positive sera (38.8%) was significantly higher (P<0.01) compared with that in anti-KILT negative sera (3.2%). Those results suggest that anti-Ki antibodies from lupus patients recognize the amino acid sequence homologous to SV 40 NLS as an epitope and molecular mimicry between Ki and SV 40 large T antigen may play a possible role for autoantibody production.