Ruxolitinib Targets JAK-STAT Signaling to Modulate Neutrophil Activation in Refractory Macrophage Activation Syndrome Open Access

• Ruxolitinib alleviates systemic inflammation and induces remission in refractory AOSD-MAS.

• Ruxolitinib modulates neutrophil activation in MAS by broadly inhibiting JAK-STAT signaling.

Macrophage activation syndrome (MAS) is believed to be the result of inappropriate proliferation and activation of the mononuclear phagocytic system. Adult-onset Still's disease (AOSD) is characterized by neutrophil activation and a cytokine storm, which can lead to its severe and potentially life-threatening complication MAS. RNA sequencing revealed that neutrophils may play a distinct and enhanced role in innate immunity in AOSD patients with MAS (AOSD-MAS). In the CpG-induced secondary hemophagocytic lymphohistiocytosis (HLH) model, depletion of neutrophils significantly reduced cytokine levels, with effects comparable to monocyte depletion. Significant enrichment was observed in the type I/II interferon and JAK-STAT pathways in neutrophils from AOSD-MAS patients. Treatment of 10 refractory AOSD-MAS patients with ruxolitinib led to the resolution of inflammatory parameters and clinical symptoms. RNA sequencing and ex vivo assays confirmed that ruxolitinib suppressed aberrant NETosis and STAT3/STAT5 signaling. In vivo, PAD4 knockout further confirmed the pathogenic role of NETosis in secondary HLH model. Moreover, selective inhibition of STAT3 or STAT5 alleviated systemic inflammation. Ten functional variants were identified in genes related to the JAK-STAT pathway, although their clinical relevance requires further validation. These findings suggest the potential of ruxolitinib in achieving disease remission in refractory AOSD-MAS patients by broadly inhibiting JAK-STAT signaling and modulation of neutrophil activation and NETosis.