Naive B cells in neuromyelitis optica spectrum disorders: impact of steroid use and relapses.

Neuromyelitis optica spectrum disorders are a group of rare, but severe autoimmune diseases characterized by inflammation of the optic nerve(s) and/or spinal cord. Although naive B cells are considered key players by escaping central tolerance checkpoints, it remains unclear how their composition and outgrowth differ in patients with neuromyelitis optica spectrum disorders. Under complete treatment-naive circumstances, we found that naive mature/transitional B-cell ratios were reduced in the blood of 10 patients with aquaporin-4 immunoglobulin G-positive disease (neuromyelitis optica spectrum disorders) as compared to 11 both age- and gender-matched healthy controls, eight patients with myelin oligodendrocyte glycoprotein-immunoglobulin G-associated disorders and 10 patients with multiple sclerosis. This was the result of increased proportions of transitional B cells, which were the highest in patients with neuromyelitis optica spectrum disorders with relapses and strongly diminished in a separate group of nine patients with neuromyelitis optica spectrum disorders and myelin oligodendrocyte glycoprotein-immunoglobulin G-associated disorders who received corticosteroid treatment. These findings need to be confirmed in longitudinal studies. For purified naive mature B cells of seven patients with neuromyelitis optica spectrum disorders and myelin oligodendrocyte glycoprotein-immunoglobulin G-associated disorders with relapses, Toll-like receptor 9 ligand synergized with interferon-γ to enhance plasmablast formation during germinal centre-like cultures. This was not seen for 11 patients without relapses and nine healthy controls. In the neuromyelitis optica spectrum disorders group, plasmablast formation corresponded to total and anti-aquaporin-4 immunoglobulin G secretion, of which the latter was found only for relapsing cases. These data indicate that naive B-cell homoeostasis is different and selectively targeted by corticosteroids in patients with neuromyelitis optica spectrum disorders. This also supports further exploration of naive B cells for their use in Toll-like receptor 9-dependent platforms in order to predict the activity of neuromyelitis optica spectrum disorders.