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Interleukin-18 diagnostically distinguishes and pathogenically promotes human and murine macrophage activation syndrome

Eric S. Weiss, Charlotte Girard-Guyonvarc'h, Dirk Holzinger, Adriana A. de Jesus, Zeshan Tariq, Jennifer Picarsic, Eduardo J. Schiffrin, Dirk Foell, Alexei A. Grom, Sandra Ammann, Stephan Ehl, Tomoaki Hoshino, Raphaela Goldbach-Mansky, Cem Gabay and Scott W. Canna

Key points

  • IL-18 distinguishes susceptibility to Macrophage Activation Syndrome (MAS) amongst hyperferritinemic and autoinflammatory diseases.

  • Excess IL-18 in NLRC4 gain-of-function mice derives from intestinal epithelia, and free IL-18 promotes experimental MAS.

Abstract

Hemophagocytic Lymphohistiocytosis (HLH) and Macrophage Activation Syndrome (MAS) are life-threatening hyperferritinemic systemic inflammatory disorders. Though 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 (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 germline 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 like Il1b, Nlrp3, and Mefv predominated in neutrophils, whereas Nlrc4 and Il18 were distinctly epithelial. Demonstrating the importance of free IL-18, Il18 transgenic 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.

  • Submitted December 11, 2017.
  • Accepted January 6, 2018.