IKKα negatively regulates ASC-dependent inflammasome activation.

The inflammasomes are multiprotein complexes that activate caspase-1 in response to infections and stress, resulting in the secretion of pro-inflammatory cytokines. Here we report that IκB kinase α (IKKα) is a critical negative regulator of apoptosis-associated specklike protein containing a C-terminal caspase-activation-andrecruitment (CARD) domain (ASC)-dependent inflammasomes. IKKα controls the inflammasome at the level of the adaptor ASC, which interacts with IKKα in the nucleus of resting macrophages in an IKKα kinase-dependent manner. Loss of IKKα kinase activity results in inflammasome hyperactivation. Mechanistically, the downstream nuclear effector IKK-related kinase (IKKi) facilitates translocation of ASC from the nucleus to the perinuclear area during inflammasome activation. ASC remains under the control of IKKα in the perinuclear area following translocation of the ASC/IKKα complex. Signal 2 of NLRP3 activation leads to inhibition of IKKα kinase activity through the recruitment of PP2A, allowing ASC to participate in NLRP3 inflammasome assembly. Taken together, these findings reveal a IKKi-IKKα-ASC axis that serves as a common regulatory mechanism for ASC-dependent inflammasomes

Interleukin-23-Independent IL-17 Production Regulates Intestinal Epithelial Permeability

SummaryWhether interleukin-17A (IL-17A) has pathogenic and/or protective roles in the gut mucosa is controversial and few studies have analyzed specific cell populations for protective functions within the inflamed colonic tissue. Here we have provided evidence for IL-17A-dependent regulation of the tight junction protein occludin during epithelial injury that limits excessive permeability and maintains barrier integrity. Analysis of epithelial cells showed that in the absence of signaling via the IL-17 receptor adaptor protein Act-1, the protective effect of IL-17A was abrogated and inflammation was enhanced. We have demonstrated that after acute intestinal injury, IL-23R+ γδ T cells in the colonic lamina propria were the primary producers of early, gut-protective IL-17A, and this production of IL-17A was IL-23 independent, leaving protective IL-17 intact in the absence of IL-23. These results suggest that IL-17-producing γδ T cells are important for the maintenance and protection of epithelial barriers in the intestinal mucosa

Signalling strength determines proapoptotic functions of STING

The cGAS/STING signalling pathway is responsible for sensing intracellular DNA and activating downstream inflammatory genes. Here the authors show mouse primary T cells and T leukaemia are hyperresponsive to STING agonist, and this strong STING signalling is associated with apoptosis induction

The essential role of single Ig IL-1 receptor-related molecule/Toll IL-1R8 in regulation of Th2 immune response

A novel cytokine IL-33, an IL-1 family member, signals via ST2 receptor and promotes T helper type 2 (Th2) responses, through the activation of NFκB and MAP kinases. Previous studies reported that SIGIRR (single immunoglobulin IL-1R-related molecule)/TIR8 (Toll IL-1R8) acts as negative regulator for TLR-IL-1R-mediated signaling. We now found that SIGIRR formed a complex with ST2 upon IL-33 stimulation and specifically inhibited IL-33/ST2-mediated signaling in cell culture model. Furthermore, IL-33-induced Th2 response was enhanced in SIGIRR-deficient mice compared to that in wild-type control mice, suggesting a negative regulatory role of SIGIRR in IL-33/ST2 signaling in vivo. Similar to ST2, SIGIRR was highly expressed in in vitro polarized Th2 cells, but not Th1 cells. SIGIRR-deficient Th2 cells produce higher levels of “Th2 cytokines”, including IL-5, IL-4 and IL-13 than that in wild-type cells. Moreover, SIGIRR-deficient mice developed stronger Th2 immune response in OVA-challenged asthma model. Taken together, our results suggest that SIGIRR plays an important role in the regulation of Th2 response in vivo, possibly through its impact on IL-33-ST2-mediated signaling

Mycobacterium tuberculosis Differentially Activates cGAS- and Inflammasome-Dependent Intracellular Immune Responses through ESX-1

Cytosolic detection of microbial products is essential for the initiation of an innate immune response against intracellular pathogens such as Mycobacterium tuberculosis (Mtb). During Mtb infection of macrophages, activation of cytosolic surveillance pathways is dependent on the mycobacterial ESX-1 secretion system and leads to type I interferon (IFN) and interleukin-1 beta (IL-1 beta) production. Whereas the inflammasome regulates IL-1 beta secretion, the receptor(s) responsible for the activation of type I IFNs has remained elusive. We demonstrate that the cytosolic DNA sensor cyclic GMP-AMP synthase (cGAS) is essential for initiating an IFN response to Mtb infection. cGAS associates with Mtb DNA in the cytosol to stimulate cyclic GAMP (cGAMP) synthesis. Notably, activation of cGAS-dependent cytosolic host responses can be uncoupled from inflammasome activation by modulating the secretion of ESX-1 substrates. Our findings identify cGAS as an innate sensor of Mtb and provide insight into how ESX-1 controls the activation of specific intracellular recognition pathways

m6A methylation potentiates cytosolic dsDNA recognition in a sequence-specific manner

Nucleic acid sensing through pattern recognition receptors is critical for immune recognition of microbial infections. Microbial DNA is frequently methylated at the N-6 position of adenines (m6A), a modification that is rare in mammalian host DNA. We show here how that m6A methylation of 5 '-GATC-3 ' motifs augments the immunogenicity of synthetic double-stranded (ds)DNA in murine macrophages and dendritic cells. Transfection with m6A-methylated DNA increased the expression of the activation markers CD69 and CD86, and of Ifn beta, iNos and Cxcl10 mRNA. Similar to unmethylated cytosolic dsDNA, recognition of m6A DNA occurs independently of TLR and RIG-I signalling, but requires the two key mediators of cytosolic DNA sensing, STING and cGAS. Intriguingly, the response to m6A DNA is sequence-specific. m6A is immunostimulatory in some motifs, but immunosuppressive in others, a feature that is conserved between mouse and human macrophages. In conclusion, epigenetic alterations of DNA depend on the context of the sequence and are differentially perceived by innate cells, a feature that could potentially be used for the design of immune-modulating therapeutics