Prediction of disease severity in neuromyelitis optica by the levels of interleukin (IL)‐6 produced during remission phase

Summary T helper type 17 (Th17) cytokines have been implicated in the pathogenesis of neuromyelitis optica (NMO). As humanized anti‐interleukin (IL)‐6R (tocilizumab) immunoglobulin (Ig)G has been used as disease‐modifying therapy for NMO, the objective of our study was to investigate the role of endogenous IL‐6 on NMO‐derived CD4 + T cell behaviour. High production of IL‐6, IL‐17 and IL‐21 by CD4 + T‐cells was detected in NMO patients. Further, IL‐21 and IL‐6 levels were related directly to the level of neurological disabilities. The addition of anti‐IL‐6R IgG not only reduced directly the production of these cytokines, but also almost abolished the ability of activated autologous monocytes in enhancing IL‐6, IL‐17 and IL‐21 release by CD4 + T cells. In contrast, the production of IL‐10 was amplified in those cell cultures. Further, anti‐IL‐6R monoclonal antibodies (mAb) also potentiated the ability of glucocorticoid in reducing Th17 cytokines. Finally, the in‐vivo and in‐vitro IL‐6 levels were significantly higher among those patients who experienced clinical relapse during 2‐year follow‐up. In summary, our results suggest a deleterious role of IL‐6 in NMO by favouring, at least in part, the expansion of corticoid‐resistant Th17 cells.