Aging-dependent Change in Th17 and Cytokine Response in Multiple Sclerosis

Background Multiple sclerosis (MS) is a chronic autoimmune disease damaging the central nervous system. Diminished inflammatory disease activities (DAs) as people with MS (pwMS) age justified randomized clinical trials assessing disease-modifying therapy (DMT) discontinuation in older pwMS given the concern for risks outweighing benefits. Objective This study aims to examine the effect of age on DAs and the peripheral production of Myelin Basic Protein (MBP)-driven cytokine response in pwMS. Methods We included the clinical data of 368 adult pwMS between 2017 and 2021 who enrolled in a clinic-based prospective cohort. From 80 participants, we isolated fresh peripheral blood mononuclear cells (PBMCs) and cultured with 50μg/ml of MBP for 24 hours. We assayed cell culture supernatants for interleukin 17 (IL-17) and interferon gamma (IFN-γ) using Enzyme-Linked Immunosorbent Assay and a subset of the supernatant samples using a commercial human cytokine/chemokine array. We examined the associations between age and annualized relapse rate (ARR) as well as between age and MBP-stimulated cytokine production (by cultured PBMC) using covariate-adjusted linear regressions. We performed mediation analyses to determine the extent to which MBP-driven cytokine responses drive the association between age and ARR. Results Among the 386 pwMS (mean age 53.1±12.6 years, 79.9% women, 92.1% non-Hispanic White), ARR declined with age (β=-0.003, p<0.001). Among the 80 pwMS whose cultured PBMCs underwent ex vivo MBP stimulation, IL-17 production declined with age in women (β=-0.27, p=0.04) but not men (β=-0.1, p=0.73). MBP-driven IL-17 response partially mediated the association between older age and lower ARR (24.7% in women, 15.3% in men). In exploratory analysis, older pwMS (≥50 years) had marginally lower (IL-4, MCP-2, MCP-3, PDGF-AA, PDGF-AB/BB) and higher (Fractalkine, MDC) concentrations of several cytokines than younger pwMS (<50 years). Some cytokines (MCP-2, MDC) mediate while others negate the effect of age on ARR. Conclusion This study suggests some of the potential biological mechanisms driving aging-dependent decline in MS inflammatory DA that warrant further investigation. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study did not receive any funding ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The institutional review boards of the University of Pittsburgh gave ethical approval for this work (STUDY19080007). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Code for analysis and figures is available at <>. De-identified data are available upon request to the corresponding author and with permission from the participating institution.