RIG-I-Mediated STING Upregulation Restricts Herpes Simplex Virus 1 Infection.

UNLABELLED: STING has emerged in recent years as a key player in orchestrating innate immune responses to cytosolic DNA and RNA derived from pathogens. However, the regulation of STING still remains poorly defined. In the present study, we investigated the mechanism of the regulation of STING expression in relation to the RIG-I pathway. Our data show that signaling through RIG-I induces STING expression at both the transcriptional and protein levels in various cell types. STING induction by the RIG-I agonist 5'triphosphorylated RNA (5'pppRNA) was recognized to be a delayed event resulting from an autocrine/paracrine mechanism. Indeed, cotreatment with tumor necrosis factor alpha and type I/II interferon was found to have a synergistic effect on the regulation of STING expression and could be potently decreased by impairing NF-κB and/or STAT1/2 signaling. STING induction significantly contributed to sustainment of the immune signaling cascade following 5'pppRNA treatment. Physiologically, this cross talk between the RNA- and DNA-sensing pathways allowed 5'pppRNA to efficiently block infection by herpes simplex virus 1 (HSV-1) both in vitro and in vivo in a STING-dependent fashion. These observations demonstrate that STING induction by RIG-I signaling through the NF-κB and STAT1/2 cascades is essential for RIG-I agonist-mediated HSV-1 restriction. IMPORTANCE: The innate immune system represents the first line of defense against invading pathogens. The dysregulation of this system can result in failure to combat pathogens, inflammation, and autoimmune diseases. Thus, precise regulation at each level of the innate immune system is crucial. Recently, a number of studies have established STING to be a central molecule in the innate immune response to cytosolic DNA and RNA derived from pathogens. Here, we describe the regulation of STING via RIG-I-mediated innate immune sensing. We found that STING is synergistically induced via proinflammatory and antiviral cytokine cascades. In addition, we show that in vivo protection against herpes simplex virus 1 (HSV-1) by a RIG-I agonist required STING. Our study provides new insights into the cross talk between DNA and RNA pathogen-sensing systems via the control of STING.

Indoleamine 2,3-Dioxygenase-Expressing Aortic Plasmacytoid Dendritic Cells Protect against Atherosclerosis by Induction of Regulatory T Cells.

Plasmacytoid dendritic cells (pDCs) are unique bone-marrow-derived cells that produce large amounts of type I interferon in response to microbial stimulation. Furthermore, pDCs also promote T cell tolerance in sterile-inflammation conditions. However, the immunomodulatory role of aortic pDCs in atherosclerosis has been poorly understood. Here, we identified functional mouse and human pDCs in the aortic intima and showed that selective, inducible pDC depletion in mice exacerbates atherosclerosis. Aortic pDCs expressed CCR9 and indoleamine 2,3-dioxygenase 1 (IDO-1), an enzyme involved in driving the generation of regulatory T cells (Tregs). As a consequence, loss of pDCs resulted in decreased numbers of Tregs and reduced IL-10 levels in the aorta. Moreover, antigen presentation by pDCs expanded antigen-specific Tregs in the atherosclerotic aorta. Notably, Tregs ablation affected pDC homeostasis in diseased aorta. Accordingly, pDCs in human atherosclerotic aortas colocalized with Tregs. Collectively, we identified a mechanism of atheroprotection mediated by tolerogenic aortic pDCs.