Circulating Proinflammatory Cytokines and Soluble Cytokine Receptors as Diagnostic Biomarkers in Multiple Sclerosis

Background: Circulating cytokines and their soluble receptors in body fluids have been implicated in the pathogenesis of multiple sclerosis (MS). Alterations in serum levels of pro- and anti-inflammatory cytokines and/or their soluble receptors can dysregulate central nervous system (CNS) signaling pathways and, therefore, may serve as potential biomarkers for the diagnosis of MS. Therefore, the primary end-point of this study is to investigate the utility of various cytokines and their soluble receptors as diagnostic biomarkers in MS. The secondary outcome is also to assess whether these cytokines are useful in differentiating the severity of MS. Methods: In this case-control study, we compared a panel of pro-inflammatory interleukins (ILs), including IL18 and tumor necrosis factor-alpha (TNFα), soluble IL receptors (sIL7Rα and sIL2Rα), and insulin-like growth factor-1 (IGF-1) in 45 MS patients and in 45 healthy control individuals matched for sex and age. Associations of these biomarkers with age, disease severity (Expanded Disability Status Scale [EDSS]), disease duration, and age at first MS symptom onset were also assessed. Results: Serum levels of cytokines and soluble IL receptors were elevated in MS patients compared to healthy controls. IGF-1 was lower (p < 0.001) in the MS patients than in the healthy individuals. The serum level of IGF-1 was higher (p < 0.01) in the remitting-relapsing phase compared to the primary progression and secondary progression stages. Similarly, only IGF-1 was more elevated (p < 0.01) in the mild stage compared to the moderate stage based on the EDSS score. Receiver operating characteristic (ROC) curve analysis demonstrated that IL18 had excellent discriminatory power for the diagnosis of MS (p < 0.001), with an area under the curve (AUC) of 0.96 ± 0.017, followed by IGF-1 (p < 0.001), which showed strong diagnostic performance (AUC = 0.873 ± 0.037). Soluble (s) IL2Rα exhibited fair diagnostic accuracy (p < 0.001; AUC = 0.717 ± 0.054). In contrast, sIL7Rα and TNFα showed poor discriminatory power despite statistical significance (p < 0.01), with AUC values of 0.675 ± 0.057 and 0.687 ± 0.056, respectively. Results of regression analysis revealed that EDSS, duration of disease, and use of any treatment had no impact on the cytokines. Similarly, no significant correlations were noted between these confounders and cytokines, except a moderate negative correlation (-0.418) between IGF-1 and EDSS. Conclusions: IL18 and IGF-1 have the potential to be used as biomarkers in distinguishing MS from healthy individuals. However, both biomarkers failed to demonstrate the discrimination between various phenotypic patterns of disease, limiting their utility for disease stratification. Future studies with larger, longitudinal cohorts and multi-marker panels are warranted to validate these results and to explore whether combining cytokines with imaging or genetic markers can improve prognostic precision.