Development and function of murine B220+CD11c+NK1.1+ cells identify them as a subset of NK cells

Lymphoid organs contain a B220+CD11c+NK1.1+ cell population that was recently characterized as a novel dendritic cell (DC) subset that functionally overlaps with natural killer (NK) cells and plasmacytoid DCs (PDCs). Using Siglec-H and NK1.1 markers, we unambiguously dissected B220+CD11c+ cells and found that PDCs are the only professional interferon (IFN)-α–producing cells within this heterogeneous population. In contrast, B220+CD11c+NK1.1+ cells are a discrete NK cell subset capable of producing higher levels of IFN-γ than conventional NK cells. Unlike DCs, only a minute fraction of B220+CD11c+NK1.1+ cells in the spleen expressed major histocompatibility complex class II ex vivo or after stimulation with CpG. Consistent with being a NK cell subset, B220+CD11c+NK1.1+ cells depended primarily on interleukin 15 and common cytokine receptor γ chain signaling for their development. In terms of function, expression of distinctive cell surface receptors, and location in lymphoid organs, NK1.1+B220+CD11c+ appear to be the murine equivalent of human CD56bright NK cells

NAB2 is a novel immune stimulator of MDA-5 that promotes a strong type I interferon response

Novel adjuvants are needed to increase the efficacy of vaccine formulations and immune therapies for cancer and chronic infections. In particular, adjuvants that promote a strong type I IFN response are required, since this cytokine is crucial for the development of efficient anti-tumoral and anti-viral immunity. Nucleic acid band 2 (NAB2) is a double- stranded RNA molecule isolated from yeast and identified as an agonist of the pattern- recognition receptors TLR3 and MDA-5. We compared the ability of NAB2 to activate innate immunity with that of poly(I:C), a well-characterized TLR3 and MDA-5 agonist known for the induction of type I IFN. NAB2 promoted stronger IFN-α production and induced a higher activation state of both murine and human innate immune cells compared to poly(I:C). This correlated with a stronger activation of the signalling pathway downstream of MDA-5, and IFN-α induction was dependent on MDA-5. Upon injection, NAB2 induced higher levels of serum IFN-α in mice than poly(I:C). These results suggest that NAB2 has the potential to become an efficient adjuvant for the induction of type-I IFN responses in therapeutic immunization against cancer or infections

Virus-induced Interferon α Production by a Dendritic Cell Subset in the Absence of Feedback Signaling In Vivo

An effective type I interferon (IFN-α/β) response is critical for the control of many viral infections. Here we show that in vesicular stomatitis virus (VSV)-infected mouse embryonic fibroblasts (MEFs) the production of IFN-α is dependent on type I IFN receptor (IFNAR) triggering, whereas in infected mice early IFN-α production is IFNAR independent. In VSV-infected mice type I IFN is produced by few cells located in the marginal zone of the spleen. Unlike other dendritic cell (DC) subsets, FACS®-sorted CD11cintCD11b−GR-1+ DCs show high IFN-α expression, irrespective of whether they were isolated from VSV-infected IFNAR-competent or -deficient mice. Thus, VSV preferentially activates a specialized DC subset presumably located in the marginal zone to produce high-level IFN-α largely independent of IFNAR feedback signaling

Human T Regulatory Cells Can Use the Perforin Pathway to Cause Autologous Target Cell Death

AbstractCytotoxic T lymphocytes and natural killer cells use the perforin/granzyme pathway to kill virally infected cells and tumor cells. Mutations in genes important for this pathway are associated with several human diseases. CD4+ T regulatory (Treg) cells have emerged as important in the control of immunopathological processes. We have previously shown that human adaptive Treg cells preferentially express granzyme B and can kill allogeneic target cells in a perforin-dependent manner. Here, we demonstrate that activated human CD4+CD25+ natural Treg cells express granzyme A but very little granzyme B. Furthermore, both Treg subtypes display perforin-dependent cytotoxicity against autologous target cells, including activated CD4+ and CD8+ T cells, CD14+ monocytes, and both immature and mature dendritic cells. This cytotoxicity is dependent on CD18 adhesive interactions but is independent of Fas/FasL. Our findings suggest that the perforin/granzyme pathway is one of the mechanisms that Treg cells can use to control immune responses

Human TLR8 Senses RNA From Plasmodium falciparum-Infected Red Blood Cells Which Is Uniquely Required for the IFN-γ Response in NK Cells

During blood-stage malaria, the innate immune system initiates the production of pro-inflammatory cytokines, including IFN-γ, that are critical to host defense and responsible for severe disease. Nonetheless, the innate immune pathways activated during this process in human malaria remain poorly understood. Here, we identify TLR8 as an essential sensor of Plasmodium falciparum-infected red blood cells (iRBC). In human immune cells, iRBC and RNA purified from iRBC were detected by TLR8 but not TLR7 leading to IFN-γ induction in NK cells. While TLR7 and 9 have been shown to lead to IFN-γ in mice, our data demonstrate that TLR8 was the only TLR capable of inducing IFN-γ release in human immune cells. This unique capacity was mediated by the release of IL-12p70 and bioactive IL-18 from monocytes, the latter via a hitherto undescribed pathway. Altogether, our data are the first reported activation of TLR8 by protozoan RNA and demonstrate both the critical role of TLR8 in human blood-stage malaria and its unique functionality in the human immune system. Moreover, our study offers important evidence that mouse models alone may not be sufficient to describe the human innate immune response to malaria

Dissection of a Type I Interferon Pathway in Controlling Bacterial Intracellular Infection in Mice

Defense mechanisms against intracellular bacterial pathogens are incompletely understood. Our study characterizes a type I IFN-dependent cell-autonomous defense pathway directed against Legionella pneumophila, an intracellular model organism and frequent cause of pneumonia. We show that macrophages infected with L. pneumophila produced IFNβ in a STING- and IRF3- dependent manner. Paracrine type I IFNs stimulated up-regulation of IFN-stimulated genes and a cell-autonomous defense pathway acting on replicating and non-replicating Legionella within their specialized vacuole. Our infection experiments in mice lacking receptors for type I and/or II IFNs show that type I IFNs contribute to expression of IFN-stimulated genes and to bacterial clearance as well as resistance in L. pneumophila pneumonia in addition to type II IFN. Overall, our study shows that paracrine type I IFNs mediate defense against L. pneumophila, and demonstrates a protective role of type I IFNs in in vivo infections with intracellular bacteria

Ribose 2′-O-methylation provides a molecular signature for the distinction of self and non-self mRNA dependent on the RNA sensor Mda5

The 5'-cap-structures of higher eukaryote mRNAs are ribose 2'-O-methylated. Likewise, a number of viruses replicating in the cytoplasm of eukayotes have evolved 2'-O-methyltransferases to modify autonomously their mRNAs. However, a defined biological role of mRNA 2'-O-methylation remains elusive. Here we show that viral mRNA 2'-O-methylation is critically involved in subversion of type-I-interferon (IFN-I) induction. We demonstrate that human and murine coronavirus 2'-O-methyltransferase mutants induce increased IFN-I expression, and are highly IFN-I sensitive. Importantly, IFN-I induction by 2'-O-methyltransferase-deficient viruses is dependent on the cytoplasmic RNA sensor melanoma differentiation-associated gene 5 (MDA5). This link between MDA5-mediated sensing of viral RNA and mRNA 2'-O-methylation suggests that RNA modifications, such as 2'-O-methylation, provide a molecular signature for the discrimination of self and non-self mRNA

ATG16L1 orchestrates interleukin-22 signaling in the intestinal epithelium via cGAS-STING.

A coding variant of the inflammatory bowel disease (IBD) risk gene ATG16L1 has been associated with defective autophagy and deregulation of endoplasmic reticulum (ER) function. IL-22 is a barrier protective cytokine by inducing regeneration and antimicrobial responses in the intestinal mucosa. We show that ATG16L1 critically orchestrates IL-22 signaling in the intestinal epithelium. IL-22 stimulation physiologically leads to transient ER stress and subsequent activation of STING-dependent type I interferon (IFN-I) signaling, which is augmented in Atg16l1 ΔIEC intestinal organoids. IFN-I signals amplify epithelial TNF production downstream of IL-22 and contribute to necroptotic cell death. In vivo, IL-22 treatment in Atg16l1 ΔIEC and Atg16l1 ΔIEC/Xbp1 ΔIEC mice potentiates endogenous ileal inflammation and causes widespread necroptotic epithelial cell death. Therapeutic blockade of IFN-I signaling ameliorates IL-22-induced ileal inflammation in Atg16l1 ΔIEC mice. Our data demonstrate an unexpected role of ATG16L1 in coordinating the outcome of IL-22 signaling in the intestinal epithelium

Bacterial RNA and small antiviral compounds activate caspase-1 through cryopyrin/Nalp3

Missense mutations in the CIAS1 gene cause three autoinflammatory disorders: familial cold autoinflammatory syndrome, Muckle-Wells syndrome and neonatal-onset multiple-system inflammatory disease(1). Cryopyrin (also called Nalp3), the product of CIAS1, is a member of the NOD-LRR protein family that has been linked to the activation of intracellular host defence signalling pathways(2,3). Cryopyrin forms a multi-protein complex termed 'the inflammasome', which contains the apoptosis-associated speck-like protein (ASC) and caspase-1, and promotes caspase-1 activation and processing of pro-interleukin (IL)-1 beta (ref. 4). Here we show the effect of cryopyrin deficiency on inflammasome function and immune responses. Cryopyrin and ASC are essential for caspase-1 activation and IL-1 beta and IL-18 production in response to bacterial RNA and the imidazoquinoline compounds R837 and R848. In contrast, secretion of tumour-necrosis factor-alpha and IL-6, as well as activation of NF-kappa B and mitogen-activated protein kinases (MAPKs) were unaffected by cryopyrin deficiency. Furthermore, we show that Toll-like receptors and cryopyrin control the secretion of IL-1 beta and IL-18 through different intracellular pathways. These results reveal a critical role for cryopyrin in host defence through bacterial RNA-mediated activation of caspase-1, and provide insights regarding the pathogenesis of autoinflammatory syndromes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62569/1/nature04517.pd