IL6 and systemic inflammatory response syndrome: The in vitro release of pro-inflammatory cytokines such as interleukin (IL)-1β, IL-6, IL-8, and tumor necrosis factor-α (TNF-α) have been reported to coincide with ATRA-induced differentiation of APL blasts, which may lead in vivo to a systemic inflammatory response syndrome (SIRS) [3, 7].