Bruns A, Bläss S, Hausdorf G, Burmester G R, Hiepe F
Charité University Hospital, Berlin, Germany.
Arthritis Rheum. 2000 Oct;43(10):2307-15. doi: 10.1002/1529-0131(200010)43:10<2307::AID-ANR19>3.0.CO;2-J.
Double-stranded DNA (dsDNA) is a well-known target of autoantibodies in systemic lupus erythematosus (SLE). The majority of these autoantibodies are of the IgG isotype and show affinity maturation, both of which are known hallmarks of T cell help. T cell responses to autoantigens, including DNA, have been reported only incidentally in SLE patients. Nevertheless, in murine SLE, naked DNA and complexed DNA (nucleosomes) are known to be recognized by T cells. This study aimed to characterize the antinucleosome response and its clinical impact on human SLE.
Nucleosomes were prepared from chicken erythrocytes. Sera from SLE and control patients were investigated by enzyme-linked immunosorbent assay (ELISA) for nucleosome-specific antibody responses. Peripheral blood mononuclear cells (PBMC) from SLE and control patients were analyzed by a kinetic T cell proliferation assay. PBMC were subsequently analyzed for nucleosome-specific T cell proliferation.
Of 136 SLE patients, 56% were seropositive for antinucleosome antibodies. In contrast, only 3% of 309 control patients (with rheumatoid arthritis, mixed connective tissue disease, undifferentiated connective tissue disease, Lyme borreliosis, scleroderma, Sjögren's syndrome, ulcerative colitis, hepatitis B virus infection, or human immunodeficiency virus infection) were seropositive. Thus, the antinucleosome ELISA had a sensitivity of 56%, a specificity of 97%, and a diagnostic confidence of 90% when applied to SLE. It was therefore superior to an anti-DNA ELISA that demonstrated a 69% diagnostic confidence in the same population. Antinucleosome reactivity in SLE patients correlated significantly with disease activity (P < 0.0001), nephritis (P < 0.002), and psychosis (P < 0.02). When proliferation assays were applied, 14 of 26 SLE patients (54%) were positive for nucleosome-specific T cells that proliferated in response to their cognate antigen. A suppressed response was elicited in 3 SLE patients (12%); in these patients, the PBMC response to nucleosomes was lower than the proliferation of PBMC in the presence of culture medium only. PBMC from the remaining 9 SLE patients (35%) were nonresponsive to nucleosomes in either way. Responding, nonresponding, and suppressed populations differed from each other significantly (P < 0.0001). None of the PBMC from 7 healthy donors and 10 control patients could be stimulated with nucleosomal antigens.
We present evidence that nucleosomes are major autoantigens in human SLE and that antinucleosomal antibodies are highly specific for the disease. The antinucleosome ELISA has been shown to be superior to the anti-dsDNA ELISA and may thus be a significantly better tool for diagnosing SLE. Nucleosome-specific T cells in SLE patients may help B cells class switch to IgG and undergo affinity maturation.
双链DNA（dsDNA）是系统性红斑狼疮（SLE）中自身抗体的一个众所周知的靶点。这些自身抗体大多数是IgG同种型，并表现出亲和力成熟，这两者都是T细胞辅助的已知特征。在SLE患者中，对包括DNA在内的自身抗原的T细胞反应仅偶尔有报道。然而，在小鼠SLE中，已知裸DNA和复合DNA（核小体）可被T细胞识别。本研究旨在表征抗核小体反应及其对人类SLE的临床影响。
从鸡红细胞中制备核小体。通过酶联免疫吸附测定（ELISA）研究SLE患者和对照患者血清中的核小体特异性抗体反应。通过动态T细胞增殖试验分析SLE患者和对照患者的外周血单个核细胞（PBMC）。随后分析PBMC的核小体特异性T细胞增殖。
在136例SLE患者中，56%抗核小体抗体血清学阳性。相比之下，309例对照患者（患有类风湿关节炎、混合性结缔组织病、未分化结缔组织病、莱姆病、硬皮病、干燥综合征、溃疡性结肠炎、乙型肝炎病毒感染或人类免疫缺陷病毒感染）中只有3%血清学阳性。因此，抗核小体ELISA应用于SLE时，敏感性为56%，特异性为97%，诊断可信度为90%。因此，它优于抗DNA ELISA，后者在同一人群中的诊断可信度为69%。SLE患者的抗核小体反应性与疾病活动度（P<0.0001）、肾炎（P<0.002）和精神病（P<0.02）显著相关。当应用增殖试验时，26例SLE患者中有14例（54%）对核小体特异性T细胞呈阳性，这些T细胞因同源抗原而增殖。3例SLE患者（12%）出现反应受抑制；在这些患者中，PBMC对核小体的反应低于仅在培养基存在下PBMC的增殖。其余9例SLE患者（35%）的PBMC对核小体均无反应。反应性、无反应性和受抑制群体彼此之间差异显著（P<0.0001）。7名健康供体和10名对照患者的PBMC均不能被核小体抗原刺激。
我们提供的证据表明，核小体是人类SLE中的主要自身抗原，抗核小体抗体对该疾病具有高度特异性。抗核小体ELISA已被证明优于抗dsDNA ELISA，因此可能是诊断SLE的显著更好的工具。SLE患者中的核小体特异性T细胞可能有助于B细胞类别转换为IgG并经历亲和力成熟。
