Study of Human RIG-I Polymorphisms Identifies Two Variants with an Opposite Impact on the Antiviral Immune Response

International audienceBACKGROUND: RIG-I is a pivotal receptor that detects numerous RNA and DNA viruses. Thus, its defectiveness may strongly impair the host antiviral immunity. Remarkably, very little information is available on RIG-I single-nucleotide polymorphisms (SNPs) presenting a functional impact on the host response. METHODOLOGY/PRINCIPAL FINDINGS: Here, we studied all non-synonymous SNPs of RIG-I using biochemical and structural modeling approaches. We identified two important variants: (i) a frameshift mutation (P(229)fs) that generates a truncated, constitutively active receptor and (ii) a serine to isoleucine mutation (S(183)I), which drastically inhibits antiviral signaling and exerts a down-regulatory effect, due to unintended stable complexes of RIG-I with itself and with MAVS, a key downstream adapter protein. CONCLUSIONS/SIGNIFICANCE: Hence, this study characterized P(229)fs and S(183)I SNPs as major functional RIG-I variants and potential genetic determinants of viral susceptibility. This work also demonstrated that serine 183 is a residue that critically regulates RIG-I-induced antiviral signaling

Innate Sensing of HIV-Infected Cells

Cell-free HIV-1 virions are poor stimulators of type I interferon (IFN) production. We examined here how HIV-infected cells are recognized by plasmacytoid dendritic cells (pDCs) and by other cells. We show that infected lymphocytes are more potent inducers of IFN than virions. There are target cell-type differences in the recognition of infected lymphocytes. In primary pDCs and pDC-like cells, recognition occurs in large part through TLR7, as demonstrated by the use of inhibitors and by TLR7 silencing. Donor cells expressing replication-defective viruses, carrying mutated reverse transcriptase, integrase or nucleocapsid proteins induced IFN production by target cells as potently as wild-type virus. In contrast, Env-deleted or fusion defective HIV-1 mutants were less efficient, suggesting that in addition to TLR7, cytoplasmic cellular sensors may also mediate sensing of infected cells. Furthermore, in a model of TLR7-negative cells, we demonstrate that the IRF3 pathway, through a process requiring access of incoming viral material to the cytoplasm, allows sensing of HIV-infected lymphocytes. Therefore, detection of HIV-infected lymphocytes occurs through both endosomal and cytoplasmic pathways. Characterization of the mechanisms of innate recognition of HIV-infected cells allows a better understanding of the pathogenic and exacerbated immunologic events associated with HIV infection

Caractérisation moléculaire et rôle de deux rétrovirus "endogènes" murins impliqués dans la croissance tumorale in vivo

PARIS-BIUSJ-Thèses (751052125) / SudocCACHAN-ENS (940162301) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Cutting edge: innate immune response triggered by influenza A virus is negatively regulated by SOCS1 and SOCS3 through a RIG-I/IFNAR1-dependent pathway

International audienceInfluenza A virus (IAV) triggers a contagious respiratory disease that produces considerable lethality. Although this lethality is likely due to an excessive host inflammatory response, the negative feedback mechanisms aimed at regulating such a response are unknown. In this study, we investigated the role of the eight "suppressor of cytokine signaling" (SOCS) regulatory proteins in IAV-triggered cytokine expression in human respiratory epithelial cells. SOCS1 to SOCS7, but not cytokine-inducible Src homology 2-containing protein (CIS), are constitutively expressed in these cells and only SOCS1 and SOCS3 expressions are up-regulated upon IAV challenge. Using distinct approaches affecting the expression and/or the function of the IFNalphabeta receptor (IFNAR)1, the viral sensors TLR3 and retinoic acid-inducible gene I (RIG-I) as well as the mitochondrial antiviral signaling protein (MAVS, a RIG-I signaling intermediate), we demonstrated that SOCS1 and SOCS3 up-regulation requires a TLR3-independent, RIG-I/MAVS/IFNAR1-dependent pathway. Importantly, by using vectors overexpressing SOCS1 and SOCS3 we revealed that while both molecules inhibit antiviral responses, they differentially modulate inflammatory signaling pathways

Population variation in miRNAs and isomiRs and their impact on human immunity to infection

International audienceBackground: MicroRNAs (miRNAs) are key regulators of the immune system, yet their variation and contribution to intra-and inter-population differences in immune responses is poorly characterized. Results: We generate 977 miRNA-sequencing profiles from primary monocytes from individuals of African and European ancestry following activation of three TLR pathways (TLR4, TLR1/2, and TLR7/8) or infection with influenza A virus. We find that immune activation leads to important modifications in the miRNA and isomiR repertoire, particularly in response to viral challenges. These changes are much weaker than those observed for protein-coding genes, suggesting stronger selective constraints on the miRNA response to stimulation. This is supported by the limited genetic control of miRNA expression variability (miR-QTLs) and the lower occurrence of gene-environment interactions, in stark contrast with eQTLs that are largely context-dependent. We also detect marked differences in miRNA expression between populations, which are mostly driven by non-genetic factors. On average, miR-QTLs explain approximately 60% of population differences in expression of their cognate miRNAs and, in some cases, evolve adaptively, as shown in Europeans for a miRNA-rich cluster on chromosome 14. Finally, integrating miRNA and mRNA data from the same individuals, we provide evidence that the canonical model of miRNAdriven transcript degradation has a minor impact on miRNA-mRNA correlations, which are, in our setting, mainly driven by co-transcription. Conclusion: Together, our results shed new light onto the factors driving miRNA and isomiR diversity at the population level and constitute a useful resource for evaluating their role in host differences of immunity to infection

Cutting Edge: Influenza A Virus Activates TLR3-Dependent Inflammatory and RIG-I-Dependent Antiviral Responses in Human Lung Epithelial Cells

International audienceInfluenza A virus (IAV) triggers a contagious acute respiratory disease that causes considerable mortality annually. Recently, we established a role for the pattern-recognition TLR3 in the response of lung epithelial cells to IAV-derived dsRNA. However, additional nucleic acid-recognition proteins have lately been implicated as key viral sensors, including the RNA helicases retinoic acid-inducible gene-I (RIG-I) and melanoma differentiation-associated gene (MDA)-5. In this study, we investigated the respective role of TLR3 vs RIG-I/MDA-5 signaling in human respiratory epithelial cells infected by IAV using BEAS-2B cells transfected with vectors encoding either a dominantnegative form of TLR3 or of mitochondrial antiviral signaling protein (MAVS; a signaling intermediate of RIG-I and MDA-5), or with plasmids overexpressing functional RIG-I or MDA-5. We demonstrate that the sensing of IAV by TLR3 primarily regulates a proinflammatory response, whereas RIG-I (but not MDA-5) mediates both a type I IFN-dependent antiviral signaling and a proinflammatory response

PLA2G1B is involved in CD4 anergy and CD4 lymphopenia in HIV-infected patients.

The precise mechanism leading to profound immunodeficiency of HIV-infected patients is still only partially understood. Here, we show that more than 80% of CD4+ T cells from HIV-infected patients have morphological abnormalities. Their membranes exhibited numerous large abnormal membrane microdomains (aMMDs), which trap and inactivate physiological receptors, such as that for IL-7. In patient plasma, we identified phospholipase A2 group IB (PLA2G1B) as the key molecule responsible for the formation of aMMDs. At physiological concentrations, PLA2G1B synergized with the HIV gp41 envelope protein, which appears to be a driver that targets PLA2G1B to the CD4+ T cell surface. The PLA2G1B/gp41 pair induced CD4+ T cell unresponsiveness (anergy). At high concentrations in vitro, PLA2G1B acted alone, independently of gp41, and inhibited the IL-2, IL-4, and IL-7 responses, as well as TCR-mediated activation and proliferation, of CD4+ T cells. PLA2G1B also decreased CD4+ T cell survival in vitro, likely playing a role in CD4 lymphopenia in conjunction with its induced IL-7 receptor defects. The effects on CD4+ T cell anergy could be blocked by a PLA2G1B-specific neutralizing mAb in vitro and in vivo. The PLA2G1B/gp41 pair constitutes what we believe is a new mechanism of immune dysfunction and a compelling target for boosting immune responses in HIV-infected patients.This work was part of the ANRS programs EP20, EP33, and EP36 (J.F. Delfraissy, O. Lambotte). It was initially supported by the Institut Pasteur (PTR 424) and the Pasteur-Weizmann Foundation. We are grateful to P. Pouletty for continuous interest and support. We wish to thank U. Schwarz (Leica Microsystems, Mannheim), E. Perret, P. Roux, A. Salles, and S. Shorte (Imagopole, Institut Pasteur) for their microscopy expertise, as well as A.H. Pillet for her expertise in biochemistry and P. Bochet for data processing and Benoit Colsch (Laboratoire d’Etude du Métabolisme des Médicaments (LEMM), CEA, INRA, Université Paris Saclay, MetaboHUB) for lipidomics analysis by mass spectrometry of CD4+ and CD8+ T cells. We thank Yoann Madec and Fredj Tekaia for their help and expertise in statistics. We acknowledge SOLEIL for the provision of synchrotron radiation facilities and thank the staff of the PROXIMA-1 beamline for their assistance. We benefited greatly from help and numerous discussions with C. Abrial, L. Touqui, B. Colsch, D. Troisvallet, M.L. Gougeon, P. Bruhns, and J. Tiollier. We also gratefully acknowledge J.P. Routy and B. Malissen for their critical review of the manuscript.S

Type I IFN triggers RIG-I/TLR3/NLRP3-dependent inflammasome activation in influenza A virus infected cells.

International audienceInfluenza A virus (IAV) triggers a contagious and potentially lethal respiratory disease. A protective IL-1β response is mediated by innate receptors in macrophages and lung epithelial cells. NLRP3 is crucial in macrophages; however, which sensors elicit IL-1β secretion in lung epithelial cells remains undetermined. Here, we describe for the first time the relative roles of the host innate receptors RIG-I (DDX58), TLR3, and NLRP3 in the IL-1β response to IAV in primary lung epithelial cells. To activate IL-1β secretion, these cells employ partially redundant recognition mechanisms that differ from those described in macrophages. RIG-I had the strongest effect through a MAVS/TRIM25/Riplet-dependent type I IFN signaling pathway upstream of TLR3 and NLRP3. Notably, RIG-I also activated the inflammasome through interaction with caspase 1 and ASC in primary lung epithelial cells. Thus, NS1, an influenza virulence factor that inhibits the RIG-I/type I IFN pathway, strongly modulated the IL-1β response in lung epithelial cells and in ferrets. The NS1 protein derived from a highly pathogenic strain resulted in increased interaction with RIG-I and inhibited type I IFN and IL-1β responses compared to the least pathogenic virus strains. These findings demonstrate that in IAV-infected lung epithelial cells RIG-I activates the inflammasome both directly and through a type I IFN positive feedback loop