Type I interferon signature and cycling lymphocytes in macrophage activation syndrome

BACKGROUND: Macrophage activation syndrome (MAS) is a life-threatening complication of Still’s disease (SD) characterized by overt immune cell activation and cytokine storm. We aimed to further understand the immunologic landscape of SD and MAS. METHOD: We profiled PBMCs from people in a healthy control group and patients with SD with or without MAS using bulk RNA-Seq and single-cell RNA-Seq (scRNA-Seq). We validated and expanded the findings by mass cytometry, flow cytometry, and in vitro studies. RESULTS: Bulk RNA-Seq of PBMCs from patients with SD-associated MAS revealed strong expression of genes associated with type I interferon (IFN-I) signaling and cell proliferation, in addition to the expected IFN-γ signal, compared with people in the healthy control group and patients with SD without MAS. scRNA-Seq analysis of more than 65,000 total PBMCs confirmed IFN-I and IFN-γ signatures and localized the cell proliferation signature to cycling CD38(+)HLA-DR(+) cells within CD4(+) T cell, CD8(+) T cell, and NK cell populations. CD38(+)HLA-DR(+) lymphocytes exhibited prominent IFN-γ production, glycolysis, and mTOR signaling. Cell-cell interaction modeling suggested a network linking CD38(+)HLA-DR(+) lymphocytes with monocytes through IFN-γ signaling. Notably, the expansion of CD38(+)HLA-DR(+) lymphocytes in MAS was greater than in other systemic inflammatory conditions in children. In vitro stimulation of PBMCs demonstrated that IFN-I and IL-15 — both elevated in MAS patients — synergistically augmented the generation of CD38(+)HLA-DR(+) lymphocytes, while Janus kinase inhibition mitigated this response. CONCLUSION: MAS associated with SD is characterized by overproduction of IFN-I, which may act in synergy with IL-15 to generate CD38(+)HLA-DR(+) cycling lymphocytes that produce IFN-γ.