James J A, Harley J B
Arthritis and Immunology Program, Oklahoma Medical Research Foundation, Oklahoma City 73104.
J Immunol. 1992 Apr 1;148(7):2074-9.
Autoantibodies binding the Sm B/B' peptides are commonly associated with SLE. IgG antibodies binding overlapping octapeptides of Sm B/B' have been evaluated in 10 patients with anti-Sm and anti-nRNP precipitins, 5 patients with other autoimmune serology, and 4 normal human sera. Neither normal controls nor patients without an anti-Sm precipitin significantly bind any of the Sm B/B' octapeptides. All sera tested containing an anti-Sm precipitin strongly bind octapeptides from eight regions of the Sm B/B' sequence. Three of these eight regions share the same octapeptide sequences (PPPGMRPP) that are consistently the most immunoreactive octapeptides from Sm B/B'. Binding of the similar PPPGIRGP, as well as binding to deletion and substitution peptides, suggest that the motif PPPG(I,M) (R,K) appears to best define this binding. Interestingly, PAPGMRPP in the nRNP C peptide is as antigenic as PPPGMRPP and may provide a partial explanation for the cross-reactivity shown between Sm and nRNP autoantibodies. However, the sequence, PPPGMIPP, from nRNP A is not antigenic. These data define the linear sequence autoantigenicity of the Sm B/B' protein. They also demonstrate that the predominant autoimmune epitope is a proline-rich sequence from which limited variance is permitted before antigenicity is destroyed.
与Sm B/B'肽段结合的自身抗体通常与系统性红斑狼疮（SLE）相关。已对10例有抗Sm和抗nRNP沉淀素的患者、5例有其他自身免疫血清学表现的患者以及4份正常人血清检测了结合Sm B/B'重叠八肽的IgG抗体。正常对照以及无抗Sm沉淀素的患者均未显著结合任何Sm B/B'八肽。所有检测的含抗Sm沉淀素的血清均强烈结合Sm B/B'序列八个区域的八肽。这八个区域中的三个区域共享相同的八肽序列（PPPGMRPP），该序列始终是Sm B/B'中免疫反应性最强的八肽。类似的PPPGIRGP的结合，以及与缺失和替代肽的结合，表明基序PPPG(I,M)(R,K)似乎最能界定这种结合。有趣的是，nRNP C肽中的PAPGMRPP与PPPGMRPP一样具有抗原性，这可能部分解释了Sm和nRNP自身抗体之间显示的交叉反应性。然而，nRNP A的序列PPPGMIPP没有抗原性。这些数据确定了Sm B/B'蛋白的线性序列自身抗原性。它们还表明，主要的自身免疫表位是一个富含脯氨酸的序列，在抗原性被破坏之前，该序列允许有限的变异。
