The study found that people with relapsing‑remitting multiple sclerosis have low levels of the peptide thymosin‑alpha‑1, and adding this peptide to immune cells in the lab lowered inflammatory signals while boosting anti‑inflammatory ones, especially by growing special B cells that produce IL‑10. This suggests thymosin‑alpha‑1 can shift the immune system toward a calmer state in MS patients.

B cells are key pathogenic effectors in multiple sclerosis (MS) and several therapies have been designed to restrain B cell abnormalities by directly targeting this lymphocyte population. Moving from our data showing a Toll-like receptor (TLR)7-driven dysregulation of B cell response in relapsing-remitting multiple sclerosis (RRMS) and having found a low serum level of Thymosin-α1 (Tα1) in patients, we investigated whether the addition of this molecule to peripheral blood mononuclear cells (PBMCs) would influence the expansion of regulatory B cell subsets, known to dampen autoimmune inflammation. Serum Tα1 level was measured by enzyme immunoassay. Cytokine expression was evaluated by Cytometric Bead Array (CBA), enzyme-linked immunosorbent assay (ELISA), and real-time reverse transcription polymerase chain reaction (RT-PCR). B cell subsets were analyzed by flow cytometry. Tα1 pre-treatment induces an anti-inflammatory status in TLR7-stimulated RRMS PBMC cultures, reducing the secretion of pro-inflammatory interleukin (IL)-6, IL-8, and IL-1β while significantly increasing the regulatory IL-10 and IL-35. Indeed, Tα1 treatment enhanced expansion of CD19⁺CD24⁺CD38^hi transitional-immature and CD24^low/negCD38^hi plasmablast-like regulatory B cell subsets, which likely inhibit both interferon (IFN)-γ and IL-17 production. Our study reveals a deficient ability of B cells from MS patients to differentiate into regulatory subsets and unveils a novel anti-inflammatory and repurposing potential for Tα1 in MS targeting B cell response.