The mechanism of action of ruxolitinib in HLH. Activated T cells, natural killer (NK) cells, macrophages, and antigen-presenting cells (APC) produce proinflammatory cytokines in HLH. Many of these cytokines (IFN-γ, IL-2, IL-6, IL-12) signal through the JAK/STAT pathway to induce changes in gene expression that lead to hyperinflammation and cytokine storm. Ruxolitinib, a JAK1/2 inhibitor, blocks this process. Professional illustration by Somersault18:24.