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Systemic infections with Gram-negative bacteria are characterized by high mortality rates due to the "sepsis syndrome," a widespread and uncontrolled inflammatory response. Though it is well recognized that the immune response during Gram-negative bacterial infection is initiated after the recognition of endotoxin by Toll-like receptor 4, the molecular mechanisms underlying the detrimental inflammatory response during Gram-negative bacteremia remain poorly defined. Here, we identify a TRIF pathway that licenses NLRP3 inflammasome activation by all Gram-negative bacteria. By engaging TRIF, Gram-negative bacteria activate caspase-11. TRIF activates caspase-11 via type I IFN signaling, an event that is both necessary and sufficient for caspase-11 induction and autoactivation. Caspase-11 subsequently synergizes with the assembled NLRP3 inflammasome to regulate caspase-1 activation and leads to caspase-1-independent cell death. These events occur specifically during infection with Gram-negative, but not Gram-positive, bacteria. The identification of TRIF as a regulator of caspase-11 underscores the importance of TLRs as master regulators of inflammasomes during Gram-negative bacterial infection., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Abstract: DNA viruses are a significant contributor to human morbidity and mortality. The immune system protects against viral infections through coordinated innate and adaptive immune responses. While the antigen-specific adaptive mechanisms have been extensively studied, the critical contributions of innate immunity to anti-viral defenses have only been revealed in the very recent past. Central to these anti-viral defenses is the recognition of viral pathogens by a diverse set of germ-line encoded receptors that survey nearly all cellular compartments for the presence of pathogens. In this review, we discuss the recent advances in the innate immune sensing of DNA viruses and focus on the recognition mechanisms involved. [Copyright &y& Elsevier]

Type I Interferons are the hallmark cytokines deployed during infection to combat invading viruses. However, inflammatory cytokines such as Interleukin (IL)-1β and IL-18 also play important roles in anti-viral defenses. The activity of IL-1β and IL18 are regulated at the level of expression, processing, and secretion. Several classes of innate immune receptors control the expression of these cytokines, which must then be proteolytically processed via caspase-1. In this review, we provide an overview of how caspase-1-activating inflammasomes participate during viral infections and their role in regulating anti-viral immunity. [ABSTRACT FROM AUTHOR]

The article focuses on a research about the cytosolic nucleic acid-binding protein LRRFIP1 and its signal transducer β-catenin. It states that transcription of IFNB1 requires interferon-regulatory factors. It cites the use of a small interfering RNA (siRNA) screening approach in the study to target the Listeria monocytogenes-induced IFN-β response. Results show that LRRFIP1-specific RNA does not affect the activation of IRF3, NF-κB or mitogen-activated protein kinase during infection with L. monocytogenes.

Mycobacterium tuberculosis extracellular DNA gains access to the host cell cytosol via the ESX-1 secretion system. It is puzzling that this extracellular DNA of M. tuberculosis does not induce activation of the AIM2 inflammasome because AIM2 recognizes cytosolic DNA. In this study, we show that nonvirulent mycobacteria such as Mycobacterium smegmatis induce AIM2 inflammasome activation, which is dependent on their strong induction of IFN-β production. In contrast, M. tuberculosis, but not an ESX-1-deficient mutant, inhibits the AIM2 inflammasome activation induced by either M. smegmatis or transfected dsDNA. The inhibition does not involve changes in host cell AIM2 mRNA or protein levels but led to decreased activation of caspase-1. We furthermore demonstrate that M. tuberculosis inhibits IFN-β production and signaling, which was partially responsible for the inhibition of AIM2 activation. In conclusion, we report a novel immune evasion mechanism of M. tuberculosis that involves the ESX-1-dependent, direct or indirect, suppression of the host cell AIM2 inflammasome activation during infection. [ABSTRACT FROM AUTHOR]

Summary Inflammasome-activated caspase-1 cleaves gasdermin D to unmask its pore-forming activity, the predominant consequence of which is pyroptosis. Here, we report an additional biological role for gasdermin D in limiting cytosolic DNA surveillance. Cytosolic DNA is sensed by Aim2 and cyclic GMP-AMP synthase (cGAS) leading to inflammasome and type I interferon responses, respectively. We found that gasdermin D activated by the Aim2 inflammasome suppressed cGAS-driven type I interferon response to cytosolic DNA and Francisella novicida in macrophages. Similarly, interferon-β (IFN-β) response to F. novicida infection was elevated in gasdermin D-deficient mice. Gasdermin D-mediated negative regulation of IFN-β occurred in a pyroptosis-, interleukin-1 (IL-1)-, and IL-18-independent manner. Mechanistically, gasdermin D depleted intracellular potassium (K+) via membrane pores, and this K+ efflux was necessary and sufficient to inhibit cGAS-dependent IFN-β response. Thus, our findings have uncovered an additional interferon regulatory module involving gasdermin D and K+ efflux. Graphical Abstract Highlights • Inflammasome-activated gasdermin D limits type I interferon responses to cytosolic DNA • Gasdermin D targets cGAS activation to inhibit IFN-β response to cytosolic DNA • Depletion of intracellular K+ by gasdermin D is responsible for limiting cGAS signaling • K+ efflux is sufficient to inhibit cGAS-dependent type I interferon responses Gasdermin D is a pore-forming protein, which upon activation by inflammasome complexes mediates pyroptotic cell death and IL-1 release. Banerjee et al. demonstrate a previously unknown regulatory role for gasdermin D-driven K+ efflux in reining in cGAS-dependent type I interferon response to cytosolic DNA. [ABSTRACT FROM AUTHOR]