GPD2 and systemic-onset juvenile idiopathic arthritis: Succinate, complex II, and GPD2 are critical for interleukin-1β (IL-1β) secretion from M1 macrophages (Langston et al., 2019, Mills et al., 2016, Tannahill et al., 2013), a cytokine important in both CD and Still's disease (Ruperto et al., 2012, Uhlig and Powrie, 2018).