Abstract
BACKGROUND AND OBJECTIVES: To assess the molecular landscape of B-cell subpopulations across different compartments in patients with neuromyelitis optica spectrum disorder (NMOSD). METHODS: We performed B-cell transcriptomic profiles via single-cell RNA sequencing across CSF, blood, and bone marrow in patients with NMOSD. RESULTS: Across the tissue types tested, 4 major subpopulations of B cells with distinct signatures were identified: naive B cells, memory B cells, age-associated B cells, and antibody-secreting cells (ASCs). NMOSD B cells show proinflammatory activity and increased expression of chemokine receptor genes (CXCR3 and CXCR4). Circulating B cells display an increase of antigen presentation markers (CD40 and CD83), as well as activation signatures (FOS, CD69, and JUN). In contrast, the bone marrow B-cell population contains a large ASC fraction with increased oxidative and metabolic activity reflected by COX genes and ATP synthase genes. Typically, NMOSD B cells become hyperresponsive to type I interferon, which facilitates B-cell maturation and anti-aquaporin-4 autoantibody production. The pool of ASCs in blood and CSF were significantly elevated in NMOSD. Both CD19(-) and CD19(+) ASCs could be ablated by tocilizumab, but not rituximab treatment in NMOSD. DISCUSSION: B cells are compartmentally fine tuned toward autoreactivity in NMOSD and become hyperreactive to type I interferon. Inhibition of type I interferon pathway may provide a new therapeutic avenue for NMOSD.