The Role of the FCRL5 Protein in the Pathophysiology of Multiple Sclerosis and Response to Treatment

Multiple sclerosis (MS) is a chronic inflammatory and neurodegenerative disease of the central nervous system (CNS) and the leading non-traumatic cause of neurological disability in young adults. Historically considered a T-cell-mediated disease, the paradigm for MS has shifted thanks to the efficacy of therapies targeting B cells. The investigators recently identified FCRL5 as a B-cell-specific biomarker that is significantly elevated in the cerebrospinal fluid (CSF) of patients with relapsing-remitting MS and is independently associated with an increased risk of developing new MRI lesions within two years of diagnosis (ref. Deltombe et al., PMID: 41004694). This project aims to further explore FCRL5 as a prognostic biomarker, study the role of FCRL5-expressing B cells in MS pathogenesis and the effects of disease-modifying therapies on these subsets.

Inclusion Criteria: * For MS patients: * Male or female * Between 18 and 80 years of age * Diagnosed with MS according to the most recent McDonald criteria (2025) * Patients who are about to start a new MS treatment or switch treatments For healthy volunteers: * Men or women * Ages 18 to 80 * Healthy volunteers with no neurological conditions or autoimmune diseases For participants with Sjögren's syndrome: * Men or women * Ages 18 to 80 Exclusion Criteria: * For MS patients: * No recent relapse (during the 3 months prior to study enrollment) * Patients treated with corticosteroids (during the 3 months prior to study enrollment) * Patients receiving another immunosuppressive therapy unrelated to MS * Inability to sign the informed consent form For healthy volunteers: Subjects not receiving immunosuppressive therapy For subjects with Sjögren's syndrome: Subjects not receiving immunosuppressive therapy