Objectives Systemic autoimmune rheumatic diseases (SARDs) are characterized by chronic inflammation. Reliable biomarkers are crucial for diagnosis, monitoring disease progression and therapeutic responses. This study explores serum Syndecan-1 (SDC-1) as a biomarker for these conditions and its relationship with free light chain (FLC) levels. Methods A retrospective analysis was performed on sera from 60 patients with rheumatoid arthritis (RA) and from 60 with systemic lupus erythematosus (SLE), alongside 50 healthy donors (HD). Κ- and λ- FLCs were determined by turbidimetric assay, while SDC-1 levels by ELISA. Kruskal-Wallis test, Wilcoxon-Mann–Whitney U test, multivariable linear regression and Spearman’s correlation were employed to compare biomarker levels across groups and to explore correlations. Results SDC-1, κ-FLC, and λ-FLC were significantly increased in RA and SLE patients compared with HD (p< 0.001), while no significant differences in the κ/λ ratio were observed among the groups (p= 0.4). A significant difference in subject age was also identified. However, multivariate regression analysis indicated that RA and SLE are significantly associated with the levels of these markers, with minimal confounding by age. A significant correlation was observed separately in all groups between the FLC markers. Conversely, no correlation was detected between SDC-1 and FLCs, nor between these markers and age or disease activity indices. Conclusion Elevated serum levels of FLCs and SDC-1 in RA and SLE patients compared with HD underscore their potential as biomarkers for SARDs. The findings also suggest sustained plasma cell activation, supporting the multifaceted role of SDC-1 in the pathogenesis of SARDs.

中文翻译：

---

类风湿性关节炎和系统性红斑狼疮患者血清游离轻链和 syndecan-1 水平


目的 系统性自身免疫性风湿病 （SARDs） 以慢性炎症为特征。可靠的生物标志物对于诊断、监测疾病进展和治疗反应至关重要。本研究探讨了血清 Syndecan-1 （SDC-1） 作为这些情况的生物标志物及其与游离轻链 （FLC） 水平的关系。方法 对 60 例类风湿性关节炎 （RA） 患者和 60 例系统性红斑狼疮 （SLE） 患者的血清以及 50 例健康供体 （HD） 的血清进行回顾性分析。通过比浊法测定 κ- 和 λ- FLCs，而 SDC-1 水平通过 ELISA 测定。采用 Kruskal-Wallis 检验、 Wilcoxon-Mann-Whitney U 检验、多变量线性回归和 Spearman 相关性来比较各组生物标志物水平并探讨相关性。结果 与 HD 相比，RA 和 SLE 患者的 SDC-1 、 κ-FLC 和 λ-FLC 显著升高 （p< 0.001），而组间 κ/λ 比值无显著差异 （p= 0.4）。还确定了受试者年龄的显着差异。然而，多变量回归分析表明，RA 和 SLE 与这些标志物的水平显著相关，年龄混杂最小。在所有组中分别观察到 FLC 标志物之间的显著相关性。相反，在 SDC-1 和 FLCs 之间没有检测到相关性，这些标志物与年龄或疾病活动指数之间也没有检测到相关性。结论 与 HD 相比，RA 和 SLE 患者血清 FLCs 和 SDC-1 水平升高强调了它们作为 SARD 生物标志物的潜力。研究结果还表明持续的浆细胞活化，支持 SDC-1 在 SARD 发病机制中的多方面作用。