Interleukin-18 diagnostically distinguishes MAS
Interleukin-18 diagnostically distinguishes and pathogenically promotes human and murine macrophage activation syndrome
Weiss E.S., Girard-Guyonvarc’h C., Holzinger D., de Jesus A.A., Tariq Z., Picarsic J., Schiffrin E.J., Foell D., Grom A.A., Ammann S., Ehl S., Hoshino T., Goldbach-Mansky R., Gabay C., Canna S.W.
Hemophagocytic lymphohistiocytosis (HLH) and macrophage activation syndrome (MAS) are life-threatening hyperferritinemic systemic inflammatory disorders. Although profound cytotoxic impairment causes familial HLH (fHLH), the mechanisms driving non-fHLH and MAS are largely unknown. MAS occurs in patients with suspected rheumatic disease, but the mechanistic basis for its distinction is unclear. Recently, a syndrome of recurrent MAS with infantile enterocolitis caused by NLRC4 inflammasome hyperactivity highlighted the potential importance of interleukin-18 (IL-18). We tested this association in hyperferritinemic and autoinflammatory patients and found a dramatic correlation of MAS risk with chronic (sometimes lifelong) elevation of mature IL-18, particularly with IL-18 unbound by IL-18 binding protein, or free IL-18. In a mouse engineered to carry a disease-causing germ line NLRC4T337S mutation, we observed inflammasome-dependent, chronic IL-18 elevation. Surprisingly, this NLRC4T337S-induced systemic IL-18 elevation derived entirely from intestinal epithelia. NLRC4T337S intestines were histologically normal but showed increased epithelial turnover and upregulation of interferon-γ-induced genes. Assessing cellular and tissue expression, classical inflammasome components such as Il1b, Nlrp3, and Mefv predominated in neutrophils, whereas Nlrc4 and Il18 were distinctly epithelial. Demonstrating the importance of free IL-18, Il18transgenic mice exhibited free IL-18 elevation and more severe experimental MAS. NLRC4T337S mice, whose free IL-18 levels were normal, did not. Thus, we describe a unique connection between MAS risk and chronic IL-18, identify epithelial inflammasome hyperactivity as a potential source, and demonstrate the pathogenicity of free IL-18. These data suggest an IL-18-driven pathway, complementary to the cytotoxic impairment of fHLH, with potential as a distinguishing biomarker and therapeutic target in MAS.
Key idea/result:
We showed that IL-18 levels are elevated in patients with macrophage activation disease, more specifically in secondary forms that occur in presence of an inflammatory rheumatic disease such as adult onset Still’s disease and systemic onset juvenile idiopathic arthritis. This finding suggests that blocking IL-18 is to be considered in the management of patients with macrophage activation disease
Author:
Charlotte Girard-Guyonvarc’h is a clinician who is interested in inflammatory diseases and did her MD-PhD thesis in the laboratory on the role of IL-18 in inflammatory diseases in humans and mice.