In this study, we demonstrated that serum obtained from patients with KD prior to IVIG treatment exhibited a cytotoxic effect on HCAECs compared to that from healthy controls and patients with sJIA, in addition to triggering extracellular release of HMGB-1, up-regulating NF-κB-mediated inflammatory responses, and increasing IL-1β and TNF-α production. Here, HMGB1 is linked to systemic-onset juvenile idiopathic arthritis.