Aging-dependent change in Th17 and cytokine response in multiple sclerosis

Abstract

Background: Multiple sclerosis (MS) is a chronic autoimmune disease damaging the central nervous system. Diminished inflammatory disease activity (DA) as people with MS (pwMS) age motivated randomized clinical trials assessing disease-modifying therapy (DMT) discontinuation in older pwMS given the concern for risks outweighing benefits. This study aims to examine whether peripheral production of Myelin Basic Protein (MBP)-driven cytokine responses mediate the aging-associated decline in MS inflammatory DA.

Methods: We included the clinical data of 669 adult pwMS between 2017 and 2022 who enrolled in a clinic-based prospective cohort. From a subset of 80 participants, we isolated fresh peripheral blood mononuclear cells (PBMCs) and cultured with 50 µg/ml of MBP (or heat-killed Candida) for 24 h. 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 response drives the association between age and ARR.

Results: Among 669 pwMS (mean age 51.7 ± 12.7 years, 80.7% women, 89.4% non-Hispanic White), ARR declined with age (β=-0.003, p < 0.001). Among the subgroup of 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 (24.6% in women, 15.3% in men). In exploratory analyses, 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), while certain cytokines (MCP-2, MDC) mediated whereas others negated the effect of age on ARR.

Conclusion: Diminished peripheral IL-17 response as a potential biological mechanism underlying the aging-dependent decline in MS inflammatory DA warrants further investigation.

Keywords: Aging; Inflammatory disease activity; Multiple sclerosis; Myelin basic protein; Relapse; Th17.

Fig. 1

Overall study design

Fig. 2

MBP-driven Th17 response was inversely associated with age in women but not in men with MS. PBMCs from pwMS were stimulated ex vivo with MBP for 24 h. IL-17 concentration in the supernatant was measured using ELISA and plotted against age as a continuous variable (A-C) and age as a binary variable (D-F) using the age threshold of ≥ 50 years versus < 50 years

Fig. 3

MBP-driven Th17 response was inversely associated with relapse rate in women but not in men with MS. PBMCs from pwMS were stimulated ex vivo with MBP for 24 h. IL-17 concentrations were plotted against annualized relapse rate (ARR) within ± 2 years of sample collection

Fig. 4

Levels of additional MBP-stimulated cytokines in relation to age. PBMCs from pwMS were stimulated ex vivo with MBP for 24 h. In exploratory analyses, concentrations of 57 additional cytokines in the supernatant were measured using the Luminex xMAP platform human cytokine/chemokine array. Patient-level Z-score transformed levels of all cytokines are shown (A). Seven cytokines with marginally significant association with age are highlighted (B). Each row represents a unique participant in ascending order of age

Fig. 5

Exploratory associations between age and the additional MBP-stimulated cytokines. The levels of the seven cytokines (from Fig. 4B) in relation to age as continuous variable are shown in scatter plots (left panels) and age as a binary variable using the age threshold of ≥ 50 years versus < 50 years are shown in violin plots (right panels)