IL-6: a cytokine at the crossroads of autoimmunity

•IL-6 promotes development of Th17 and Tfh cells and suppresses induction of Treg.•IL-6 signals via three distinct mechanisms: classical, trans signaling and cluster signaling.•IL-6/IL-6R axis is dysregulated in autoimmunity.•Targeting the IL-6 pathway has proven to be therapeutic in autoimmunity.