IL1B and systemic-onset juvenile idiopathic arthritis: In addition to this, sJIA can manifest in two main phenotypes, which may be explained by its pathogenesis: with predominantly systemic features, with a central role for the expression and signalling of IL-1β, as well as elevated expression of IL-18 and S100 proteins; and with predominantly active synovitis, mediated by further activation of the adaptive immune system, with participation of TNF-α [1, 4, 6, 7].