The bacterium Mycobacterium tuberculosis (Mtb) causes tuberculosis (TB) and is responsible for more human mortality than any other single pathogen 1. Progression to active disease occurs in only a fraction of infected individuals and is predicted by an elevated type I interferon (IFN) response 2-7. Whether or how IFNs mediate susceptibility to Mtb has been difficult to study due to a lack of suitable mouse models 6-11. Here we examined B6.Sst1 S congenic mice that carry the "sensitive" allele of the Sst1 locus that confers susceptibility to Mtb 12-14. We found that enhanced production of type I IFNs was responsible for the susceptibility of B6.

The Stimulator of Interferon Genes (STING) pathway initiates potent immune responses upon recognition of DNA. To initiate signaling, serine 365 (S365) in the C-terminal tail (CTT) of STING is phosphorylated, leading to induction of type I interferons (IFNs). Additionally, evolutionary conserved responses such as autophagy also occur downstream of STING, but their relative importance during in vivo infections remains unclear. Here we report that mice harboring a serine 365-to-alanine (S365A) mutation in STING are unexpectedly resistant to Herpes Simplex Virus (HSV)-1, despite lacking STING-induced type I IFN responses. By contrast, resistance to HSV-1 is abolished in mice lacking the STING CTT, suggesting that the STING CTT initiates protective responses against HSV-1, independently of type I IFNs. Interestingly, we find that STING-induced autophagy is a CTT-and TBK1-dependent but IRF3independent process that is conserved in the STING S365A mice. Thus, interferonindependent functions of STING mediate STING-dependent antiviral responses in vivo.

Type I interferons (IFNs) are essential for anti-viral immunity, but often impair protective immune responses during bacterial infections. An important question is how type I IFNs are strongly induced during viral infections, and yet are appropriately restrained during bacterial infections. The Super susceptibility to tuberculosis 1 (Sst1) locus in mice confers resistance to diverse bacterial infections. Here we provide evidence that Sp140 is a gene encoded within the Sst1 locus that represses type I IFN transcription during bacterial infections. We generated Sp140-/- mice and find they are susceptible to infection by Legionella pneumophila and Mycobacterium tuberculosis. Susceptibility of Sp140-/- mice to bacterial infection was rescued by crosses to mice lacking the type I IFN receptor (Ifnar-/-). Our results implicate Sp140 as an important negative regulator of type I IFNs that is essential for resistance to bacterial infections.

Type I interferons (IFNs) are essential for anti-viral immunity, but often impair protective immune responses during bacterial infections. How type I IFNs are strongly induced during viral infections, and yet are appropriately restrained during bacterial infections, remains poorly understood. The Super susceptibility to tuberculosis 1 (Sst1) locus in mice confers resistance to many bacterial infections. Here we provide evidence that Sp140 is a gene encoded within the Sst1 locus that functions to repress the expression of type I IFNs during bacterial infections. We generated Sp140 -/mice and find they are susceptible to infection by diverse bacteria, including Listeria monocytogenes, Legionella pneumophila, and Mycobacterium tuberculosis. Susceptibility of Sp140-/mice to bacterial infection was rescued by crosses to mice lacking the type I IFN receptor (Ifnar -/-). Our results implicate Sp140 as an important repressor of type I IFNs that is essential for resistance to bacterial infections.

The Stimulator of Interferon Genes (STING) pathway initiates potent immune responses upon recognition of DNA derived from bacteria, viruses and tumors. To signal, the Cterminal tail (CTT) of STING recruits TBK1, a kinase that phosphorylates serine 365 (S365) in the CTT. Phospho-S365 acts as a docking site for IRF3, a transcription factor that is phosphorylated and activated by TBK1, leading to transcriptional induction of type I interferons (IFNs). IFNs are essential for antiviral immunity and are widely viewed as the primary output of STING signaling in mammals. However, other more evolutionarily ancestral responses, such as induction of NF-kB or autophagy, also occur downstream of STING. The relative importance of the various outputs of STING signaling during in vivo infections is unclear. Here we report that mice harboring a serine 365-to-alanine (S365A) point mutation in STING exhibit normal susceptibility to Mycobacterium tuberculosis infection but, unexpectedly, are resistant to Herpes Simplex Virus (HSV)-1, despite lacking STING-induced type I IFN responses. Likewise, we find Irf3 -/mice exhibit resistance to HSV-1. By contrast, resistance to HSV-1 is abolished in mice lacking the STING CTT or TBK1, suggesting that STING protects against HSV-1 upon TBK1 recruitment by the STING CTT, independent of IRF3 or type I IFNs. Interestingly, we find that STING-induced autophagy is a TBK1-dependent IRF3-independent process that is conserved in the STING S365A mice, and autophagy has previously been shown to be required for resistance to HSV-1. We thus propose that autophagy and perhaps other ancestral interferon-independent functions of STING are required for STING-dependent antiviral responses in vivo. Introduction 1 The immune response to pathogens is initiated upon detection of pathogen-2 associated molecular patterns (PAMPs) such as lipopolysaccharide, flagellin and nucleic 3 acids [1]. Double-stranded DNA (dsDNA) is an important PAMP for the detection of 4 many pathogens, including Mycobacterium tuberculosis and Herpes Simplex Virus-1 5 (HSV-1) [2-4]. In vertebrates, the intracellular presence of dsDNA is detected by cyclic-6 GMP-AMP Synthase (cGAS), a dsDNA-activated enzyme that produces a cyclic 7 dinucleotide (CDN) second messenger called 2′3′-cyclic-GMP-AMP (2′3′cGAMP) [5-8 10]. 2′3′cGAMP binds and activates the ER-resident transmembrane protein Stimulator 9 of Interferon Genes (STING). Transcriptional induction of type I IFNs is widely 10 presumed to be the primary output of STING signaling during antiviral defense. 11 However, STING is evolutionarily ancient, present even in bacteria [11] and in animals 12 such as the starlet sea anemone Nematostella vectensis and Drosophila melanogaster that 13 do not appear to encode type I interferons [12]. By contrast, autophagy and NF-κB 14 signaling are ancestral STING-induced signaling pathways, present in both N. vectensis 15 and D. melanogaster, raising the possibility that these pathways are the primary or 16 ancestral signaling outputs of STING [13-16]. 17 The ...

1The bacterium Mycobacterium tuberculosis (Mtb) causes tuberculosis (TB) and is 2 responsible for more human mortality than any other single pathogen 1 . Although ~1.7 3 billion people are infected with Mtb 2 , most infections are asymptomatic. Progression to 4 active disease occurs in ~10% of infected individuals and is predicted by an elevated type 5

In the version of this Letter originally published, in the key in Fig. 4b the red squares were mistakenly labelled B6.Sst1 S Il1rn-/-; they should have been labelled B6.Sst1 S Il1rn +/+. This has now been corrected.

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