Abstract
BACKGROUND AND OBJECTIVES: Neuromyelitis optica (NMO) is an autoimmune astrocytopathy mediated by anti-AQP4 antibody-producing B cells. Recently, a B-cell subset highly expressing CD11c and T-bet, originally identified as age-associated B cells, has been shown to be involved in the pathogenesis of various autoimmune diseases. The objective of this study was to determine the relationship between the frequency of CD11c(high) B cells per CD19(+) B cells in the peripheral blood of patients with NMO and the clinical profiles including the brain volume. METHODS: In this observational study, 45 patients with anti-AQP4 antibody-positive NMO in remission and 30 healthy control subjects (HCs) were enrolled. Freshly isolated peripheral blood mononuclear cells were analyzed for immune cell phenotypes. The frequency of CD11c(high) B cells per CD19(+) B cells was assessed by flow cytometry and was evaluated in association with the clinical profiles of patients. Brain MRI data from 26 patients were included in the study for the analysis on the correlation between CD11c(high) B-cell frequency and brain atrophy. RESULTS: We found that the frequency of CD11c(high) B cells in CD19(+) B cells was significantly increased in patients with NMO compared with HCs. The expansion of CD11c(high) B cells significantly correlated with EDSS, past relapse numbers, and disease duration. In addition, a higher frequency of CD11c(high) B cells negatively correlated with total brain, white matter, and gray matter volumes and positively correlated with T2/FLAIR high lesion volumes. When the past clinical relapse episodes of patients with or without the expansion of CD11c(high) B cells were compared, relapses in the brain occurred more frequently in patients with CD11c(high) B-cell expansion. CD11c(high) B cells had distinct features including expression of chemokine receptors associated with migration into peripheral inflammatory tissues and antigen presentation. CD11c(high) B-cell frequency was positively correlated with T peripheral helper-1 (Tph-1) cell frequency. DISCUSSION: Even during the relapse-free period, CD11c(high) B cells could expand in the long disease context, possibly through the interaction with Tph-1 cells. The increased frequency of CD11c(high) B cells associated with brain atrophy and disease severity, indicating that this cell population could be involved in chronic neuroinflammation in NMO.