The ribonucleic acid (RNA) helicases retinoic acid-inducible gene-I (RIG-I) and melanoma differentiation–associated gene 5 (MDA5) recognize distinct viral and synthetic RNAs, leading to the production of interferons. Although 5′-triphosphate single-stranded RNA is a RIG-I ligand, the role of RIG-I and MDA5 in double-stranded (ds) RNA recognition remains to be characterized. In this study, we show that the length of dsRNA is important for differential recognition by RIG-I and MDA5. The MDA5 ligand, polyinosinic-polycytidylic acid, was converted to a RIG-I ligand after shortening of the dsRNA length. In addition, viral dsRNAs differentially activated RIG-I and MDA5, depending on their length. Vesicular stomatitis virus infection generated dsRNA, which is responsible for RIG-I–mediated recognition. Collectively, RIG-I detects dsRNAs without a 5′-triphosphate end, and RIG-I and MDA5 selectively recognize short and long dsRNAs, respectively.

Toll-like receptors (TLRs) recognize microbial components, and evoke inflammation and immune responses. TLR stimulation activates complex gene expression networks that regulate the magnitude and duration of the immune reaction. Here we identify the TLR-inducible gene Zc3h12a as an immune response modifier that has an essential role in preventing immune disorders. Zc3h12a-deficient mice suffered from severe anaemia, and most died within 12 weeks. Zc3h12a(-/-) mice also showed augmented serum immunoglobulin levels and autoantibody production, together with a greatly increased number of plasma cells, as well as infiltration of plasma cells to the lung. Most Zc3h12a(-/-) splenic T cells showed effector/memory characteristics and produced interferon-gamma in response to T-cell receptor stimulation. Macrophages from Zc3h12a(-/-) mice showed highly increased production of interleukin (IL)-6 and IL-12p40 (also known as IL12b), but not TNF, in response to TLR ligands. Although the activation of TLR signalling pathways was normal, Il6 messenger RNA decay was severely impaired in Zc3h12a(-/-) macrophages. Overexpression of Zc3h12a accelerated Il6 mRNA degradation via its 3'-untranslated region (UTR), and destabilized RNAs with 3'-UTRs for genes including Il6, Il12p40 and the calcitonin receptor gene Calcr. Zc3h12a contains a putative amino-terminal nuclease domain, and the expressed protein had RNase activity, consistent with a role in the decay of Il6 mRNA. Together, these results indicate that Zc3h12a is an essential RNase that prevents immune disorders by directly controlling the stability of a set of inflammatory genes.

Polarization of macrophages to M1 or M2 cells is important for mounting responses against bacterial and helminth infections, respectively. Jumonji domain containing-3 (Jmjd3), a histone 3 Lys27 (H3K27) demethylase, has been implicated in the activation of macrophages. Here we show that Jmjd3 is essential for M2 macrophage polarization in response to helminth infection and chitin, though Jmjd3 is dispensable for M1 responses. Furthermore, Jmjd3 (also known as Kdm6b) is essential for proper bone marrow macrophage differentiation, and this function depends on demethylase activity of Jmjd3. Jmjd3 deficiency affected trimethylation of H3K27 in only a limited number of genes. Among them, we identified Irf4 as encoding a key transcription factor that controls M2 macrophage polarization. Collectively, these results show that Jmjd3-mediated H3K27 demethylation is crucial for regulating M2 macrophage development leading to anti-helminth host responses.

RNA virus infection is recognized by retinoic acid-inducible gene (RIG)-I–like receptors (RLRs), RIG-I, and melanoma differentiation–associated gene 5 (MDA5) in the cytoplasm. RLRs are comprised of N-terminal caspase-recruitment domains (CARDs) and a DExD/H-box helicase domain. The third member of the RLR family, LGP2, lacks any CARDs and was originally identified as a negative regulator of RLR signaling. In the present study, we generated mice lacking LGP2 and found that LGP2 was required for RIG-I– and MDA5-mediated antiviral responses. In particular, LGP2 was essential for type I IFN production in response to picornaviridae infection. Overexpression of the CARDs from RIG-I and MDA5 in Lgp2 −/− fibroblasts activated the IFN-β promoter, suggesting that LGP2 acts upstream of RIG-I and MDA5. We further examined the role of the LGP2 helicase domain by generating mice harboring a point mutation of Lys-30 to Ala ( Lgp2 K30A/K30A ) that abrogated the LGP2 ATPase activity. Lgp2 K30A/K30A dendritic cells showed impaired IFN-β productions in response to various RNA viruses to extents similar to those of Lgp2 −/− cells. Lgp2 −/− and Lgp2 K30A/K30A mice were highly susceptible to encephalomyocarditis virus infection. Nevertheless, LGP2 and its ATPase activity were dispensable for the responses to synthetic RNA ligands for MDA5 and RIG-I. Taken together, the present data suggest that LGP2 facilitates viral RNA recognition by RIG-I and MDA5 through its ATPase domain.

Regnase-1 (also known as Zc3h12a and MCPIP1) is an RNase that destabilizes a set of mRNAs, including Il6 and Il12b, through cleavage of their 3' UTRs. Although Regnase-1 inactivation leads to development of an autoimmune disease characterized by T cell activation and hyperimmunoglobulinemia in mice, the mechanism of Regnase-1-mediated immune regulation has remained unclear. We show that Regnase-1 is essential for preventing aberrant effector CD4(+) T cell generation cell autonomously. Moreover, in T cells, Regnase-1 regulates the mRNAs of a set of genes, including c-Rel, Ox40, and Il2, through cleavage of their 3' UTRs. Interestingly, T cell receptor (TCR) stimulation leads to cleavage of Regnase-1 at R111 by Malt1/paracaspase, freeing T cells from Regnase-1-mediated suppression. Furthermore, Malt1 protease activity is critical for controlling the mRNA stability of T cell effector genes. Collectively, these results indicate that dynamic control of Regnase-1 expression in T cells is critical for controlling T cell activation.

Nitric oxide (NO) inhibits vascular inflammation, but the molecular basis for its anti-inflammatory properties is unknown. We show that NO inhibits exocytosis of Weibel-Palade bodies, endothelial granules that mediate vascular inflammation and thrombosis, by regulating the activity of N-ethylmaleimide-sensitive factor (NSF). NO inhibits NSF disassembly of soluble NSF attachment protein receptor (SNARE) complexes by nitrosylating critical cysteine residues of NSF. NO may regulate exocytosis in a variety of physiological processes, including vascular inflammation, neurotransmission, thrombosis, and cytotoxic T lymphocyte cell killing.

Members of the IRAK family of kinases mediate Toll-like receptor (TLR) signaling. Here we show that IRAK2 was essential for sustaining TLR-induced expression of genes encoding cytokines and activation of the transcription factor NF-kappaB, despite the fact that IRAK2 was dispensable for activation of the initial signaling cascades. IRAK2 was activated 'downstream' of IRAK4, like IRAK1, and TLR-induced cytokine production was abrogated in the absence of both IRAK1 and IRAK2. Whereas the kinase activity of IRAK1 decreased within 1 h of TLR2 stimulation, coincident with IRAK1 degradation, the kinase activity of IRAK2 was sustained and peaked at 8 h after stimulation. Thus, IRAK2 is critical in late-phase TLR responses, and IRAK1 and IRAK2 are essential for the initial responses to TLR stimulation.

During a genome-wide RNAi screen, we isolated CG8580 as a gene involved in the innate immune response of Drosophila. CG8580, which we named Akirin, acts in parallel with the NF-κB transcription factor downstream of the Imd pathway and was required for defense against Gram-negative bacteria. Akirin is highly conserved and the human genome contains two homologues, one of which was able to rescue the loss of function phenotype in Drosophila cells. Akirins had a strict nuclear localization. Knockout of both Akirin homologues in mice revealed that one had an essential function downstream of Toll-like receptor, tumor necrosis factor and interleukin 1-β (IL-1β) signaling pathways leading to the production of IL-6. Thus, Akirin is a conserved nuclear factor required for innate immune responses.The innate immune system shields all metazoans against invading microorganisms. This well conserved defense mechanism relies on host-pathogen interactions between nonclonally distributed pattern recognition receptors in the host and pathogen-associated molecular patterns in microbes (reviewed in1-4). In contrast, the acquired immune system, based on selection of lymphocytes and their antigen-specific receptors, is specific to vertebrates. Drosophila has become an attractive model organism for the study of the innate immune system due to its well-established genetics, the absence of an acquired immune system and the striking conservation between its immune system and many mammalian Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:http://www.nature.com/authors/editorial_policies/license.html#terms Correspondence should be addressed to J-MR (e-mail: JM.Reichhart@ibmc.u-strasbg.fr). 4 current address, Graduate School of Pharmaceutical Sciences, Tohoku University, Aramaki Aoba-ku, Sendai, 980-8578, Japan 5 AG and KM contributed equally to this work. AUTHOR CONTRIBUTIONS A.G., V.G., L.E.-C., and D.K. did the Drosophila experiments. K.M. and O.T. did the mouse experiments. S.A., M.B., O.T. and JM.R. conceived and directed the experiments, A.G., O.T., JA.H. and JM.R. wrote the paper. All authors contributed to manuscript criticism. Despite more than ten years of research since the initial discovery of the Imd mutation, the pathway that took its name is still not fully understood. We undertook a functional genome- (Fig. 1). The conservation is highest for the putative C and N-terminal domains. All sequences show a clear nuclear localization signal (NLS) located between residues 24 and 29 at the N-terminus ( Supplementary Fig. 1 online). We renamed the gene Akirin (Akirin1 and Akirin2 in the case of vertebrates) from the japanese `akiraka ni suru', which means `making things clear'. HHS Public Access RESULTS Identification of Drosophila and mice Akirin homologues Akirins are ubiquitously expressed nuclear proteinsMicroarray data in Flybase35 indicate that DmAkirin expression is ubiquitous. Similarly, an an...