CHI3L1 and neuromyelitis optica: To further investigate the effects of CHI3L1 on myelin integrity, we developed an ex vivo organotypic culture model of NMO using vibratome-cut cerebellar slices — a method widely used to study myelination and white matter diseases (16) — and treated them with Ctrl-IgG, AQP4-IgG, or AQP4-IgG plus CHI3L1 (Figure 1C).