BACKGROUND: Immunosenescence is accelerated by chronic infectious and autoimmune diseases and could contribute to the pathobiology of multiple sclerosis (MS). How MS and disease-modifying therapies (DMTs) impact age-sensitive immune biomarkers is only partially understood. METHODS: We analyzed 771 serum samples from 147 healthy controls and 289 people with MS (PwMS) by multiplex immunoassays. We determined cytomegalovirus (CMV) serostatus and collected retrospective clinical information. We performed unsupervised and multivariable analyses. FINDINGS: Unsupervised analyses revealed that MS immune profile was characterized by low relative levels of anti-inflammatory/neuroprotective factors IL-4, IL-10, TNF, and β-NGF but high levels of growth factors EGF and bFGF. Serum levels of IL-4, β-NGF, IL-27, BDNF, and leptin were significantly influenced by sex and/or CMV status. IL-4 and β-NGF levels were lower in untreated PwMS compared to controls, while EGF and bFGF levels were influenced by age and markedly elevated in PwMS in multivariable analysis. Samples from treated PwMS, but not untreated PwMS, showed lower levels of BDNF and TNF than controls. Initiation of high efficacy DMTs, but not low efficacy DMTs, was associated with reduced levels of bFGF and EGF. Samples associated with distinct DMTs exhibited specific profiles for age-sensitive immune markers. Finally, lower levels of IL-6, TNF, IL-10, and β-NGF were observed at baseline in PwMS who subsequently experienced clinical failure after DMTs initiation. INTERPRETATION: Age, sex, CMV status, and specific DMTs significantly influence levels of age-sensitive immune biomarkers associated with MS and must be considered when investigating inflammation-related biomarkers. FUNDING: This work was supported by a Grant for Multiple Sclerosis Innovation by Merck KGaA (ID: 10.12039/100009945).