Zinc and metallothionein dysregulation in B cells in multiple sclerosis, with disease-specific CXCR3+/CXCR3⁻ divergence in blood.

INTRODUCTION: Multiple sclerosis (MS) is associated with compartmentalized B-cell responses in the cerebrospinal fluid (CSF), where CXCR3+ B cells contribute to intrathecal immune activity and tissue injury. Zinc is an important regulator of immune-cell function, but zinc homeostasis in pathogenic B-cell populations in MS remains poorly defined. METHODS: We reanalyzed two publicly available human single-cell RNA sequencing datasets containing CSF and peripheral blood (PB) B cells from healthy or non-MS controls and patients with clinically isolated syndrome or MS. Zinc transporter and metallothionein (Zn/MT) gene expression was examined in CXCR3+ and CXCR3- B-cell subsets, and a composite Zn/MT signature was calculated at the patient level. RESULTS: A composite Zn/MT signature was significantly elevated in MS relative to controls in both PB and CSF, and in both CXCR3+ and CXCR3- B cells, indicating a disease-associated feature of B cells broadly rather than one restricted to CXCR3+ cells. In CSF CXCR3+ B cells, this increase was driven by several zinc transporters, including SLC39A11 (ZIP11), SLC30A9 (ZnT9), and SLC39A6 (ZIP6), whereas no individual gene reached significance in PB. Direct comparison of CXCR3+ and CXCR3- B cells revealed a disease-specific divergence in PB, with a significantly higher Zn/MT signature in CXCR3+ cells from MS patients but not healthy controls. Five genes contributed to this effect. DISCUSSION: These findings identify altered zinc-homeostasis pathways as a disease-associated feature of B cells in MS and reveal a disease-specific divergence between CXCR3+ and CXCR3- B-cell subsets in peripheral blood. The results support further investigation of zinc-regulatory mechanisms in B cell-mediated neuroinflammation.