Human intracellular ISG15 prevents interferon-a/ß over-amplification and auto-inflammation.

Nature

PubMedID: 25307056

Zhang X, Bogunovic D, Payelle-Brogard B, Francois-Newton V, Speer SD, Yuan C, Volpi S, Li Z, Sanal O, Mansouri D, Tezcan I, Rice GI, Chen C, Mansouri N, Mahdaviani SA, Itan Y, Boisson B, Okada S, Zeng L, Wang X, Jiang H, Liu W, Han T, Liu D, Ma T, Wang B, Liu M, Liu JY, Wang QK, Yalnizoglu D, Radoshevich L, Uzé G, Gros P, Rozenberg F, Zhang SY, Jouanguy E, Bustamante J, García-Sastre A, Abel L, Lebon P, Notarangelo LD, Crow YJ, Boisson-Dupuis S, Casanova JL, Pellegrini S. Human intracellular ISG15 prevents interferon-a/ß over-amplification and auto-inflammation. Nature. 2015;517(7532):89-93.
Intracellular ISG15 is an interferon (IFN)-a/ß-inducible ubiquitin-like modifier which can covalently bind other proteins in a process called ISGylation; it is an effector of IFN-a/ß-dependent antiviral immunity in mice. We previously published a study describing humans with inherited ISG15 deficiency but without unusually severe viral diseases. We showed that these patients were prone to mycobacterial disease and that human ISG15 was non-redundant as an extracellular IFN-?-inducing molecule. We show here that ISG15-deficient patients also display unanticipated cellular, immunological and clinical signs of enhanced IFN-a/ß immunity, reminiscent of the Mendelian autoinflammatory interferonopathies Aicardi-Goutières syndrome and spondyloenchondrodysplasia. We further show that an absence of intracellular ISG15 in the patients' cells prevents the accumulation of USP18, a potent negative regulator of IFN-a/ß signalling, resulting in the enhancement and amplification of IFN-a/ß responses. Human ISG15, therefore, is not only redundant for antiviral immunity, but is a key negative regulator of IFN-a/ß immunity. In humans, intracellular ISG15 is IFN-a/ß-inducible not to serve as a substrate for ISGylation-dependent antiviral immunity, but to ensure USP18-dependent regulation of IFN-a/ß and prevention of IFN-a/ß-dependent autoinflammation.