IL-26 confers proinflammatory properties to extracellular DNA

C Poli, JF Augusto, J Dauvé, C Adam… - The Journal of …, 2017 - journals.aai.org
C Poli, JF Augusto, J Dauvé, C Adam, L Preisser, V Larochette, P Pignon, A Savina…
The Journal of Immunology, 2017journals.aai.org
In physiological conditions, self-DNA released by dying cells is not detected by intracellular
DNA sensors. In chronic inflammatory disorders, unabated inflammation has been
associated with a break in innate immune tolerance to self-DNA. However, extracellular
DNA has to complex with DNA-binding molecules to gain access to intracellular DNA
sensors. IL-26 is a member of the IL-10 cytokine family, overexpressed in numerous chronic
inflammatory diseases, in which biological activity remains unclear. We demonstrate in this …
Abstract
In physiological conditions, self-DNA released by dying cells is not detected by intracellular DNA sensors. In chronic inflammatory disorders, unabated inflammation has been associated with a break in innate immune tolerance to self-DNA. However, extracellular DNA has to complex with DNA-binding molecules to gain access to intracellular DNA sensors. IL-26 is a member of the IL-10 cytokine family, overexpressed in numerous chronic inflammatory diseases, in which biological activity remains unclear. We demonstrate in this study that IL-26 binds to genomic DNA, mitochondrial DNA, and neutrophil extracellular traps, and shuttles them in the cytosol of human myeloid cells. As a consequence, IL-26 allows extracellular DNA to trigger proinflammatory cytokine secretion by monocytes, in a STING-and inflammasome-dependent manner. Supporting these biological properties, IL-10–based modeling predicts two DNA-binding domains, two amphipathic helices, and an in-plane membrane anchor in IL-26, which are structural features of cationic amphipathic cell-penetrating peptides. In line with these properties, patients with active autoantibody-associated vasculitis, a chronic relapsing autoimmune inflammatory disease associated with extensive cell death, exhibit high levels of both circulating IL-26 and IL-26–DNA complexes. Moreover, in patients with crescentic glomerulonephritis, IL-26 is expressed by renal arterial smooth muscle cells and deposits in necrotizing lesions. Accordingly, human primary smooth cells secrete IL-26 in response to proinflammatory cytokines. In conclusion, IL-26 is a unique cationic protein more similar to a soluble pattern recognition receptor than to conventional cytokines. IL-26 expressed in inflammatory lesions confers proinflammatory properties to DNA released by dying cells, setting up a positive amplification loop between extensive cell death and unabated inflammation.
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