Intracellular ISG15 is an interferon (IFN)-α/β-inducible ubiquitin-like modifier which can covalently bind other proteins in a process called ISGylation; it is an effector of IFN-α/β-dependent antiviral immunity in mice1,2,3,4. We previously published a study describing humans with inherited ISG15 deficiency but without unusually severe viral diseases5. We showed that these patients were prone to mycobacterial disease and that human ISG15 was non-redundant as an extracellular IFN-γ-inducing molecule. We show here that ISG15-deficient patients also display unanticipated cellular, immunological and clinical signs of enhanced IFN-α/β immunity, reminiscent of the Mendelian autoinflammatory interferonopathies Aicardi–Goutières syndrome and spondyloenchondrodysplasia6,7,8,9. We further show that an absence of intracellular ISG15 in the patients’ cells prevents the accumulation of USP1810,11, a potent negative regulator of IFN-α/β signalling, resulting in the enhancement and amplification of IFN-α/β responses. Human ISG15, therefore, is not only redundant for antiviral immunity, but is a key negative regulator of IFN-α/β immunity. In humans, intracellular ISG15 is IFN-α/β-inducible not to serve as a substrate for ISGylation-dependent antiviral immunity, but to ensure USP18-dependent regulation of IFN-α/β and prevention of IFN-α/β-dependent autoinflammation.
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The Laboratory of Human Genetics of Infectious Diseases is supported by grants from the French National Agency for Research (ANR), the EU grant HOMITB (HEALTH-F32008-200732), the St Giles Foundation, the National Center for Research Resources and the National Center for Advancing Sciences (NCATS), National Institutes of Health grant number 8UL1TR000043, the Rockefeller University, the National Institute of Allergy and Infectious Diseases grant number R37AI095983, Institut Merieux research grant and the Empire State Stem Cell fund through NYSDOH Contract #C023046 to Flow Cytometry Research Core at the Rockefeller University. The Cytokine Signaling Unit is supported by the Institut Pasteur, CNRS and INSERM. S.P. and G.U. received funding from the EU Seventh Framework Programme under grant agreement 223608. V.F.-N. was supported by the Ligue contre le Cancer. L.R. is a Human Frontier Science Program long-term fellow. L.D.N. was supported by the National Institute of Allergy and Infectious Diseases grant number 1PO1AI076210-01A1. Y.J.C. thanks the Manchester Biomedical Research Centre and the Greater Manchester Comprehensive Local Research Network, the European Union’s Seventh Framework Programme (FP7/2007-2013) under grant agreement 241779, and the European Research Council (GA 309449). A.G.-S. acknowledges NIAID grants U19AI083025 and P01AI090935 for support. We thank C. Daussy for technical assistance, E. Bianchi and F. Michel for discussions. We thank D. Zhang and the members of the Zhang laboratory for assistance, advice and discussions. This work was supported by Chinese National Natural Science Foundation grants (81000079, 81170165) to X.Z. D.B. is supported by the National Institute of Allergy and Infectious Diseases grant number R00AI106942-02.
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