Human Herpesvirus 6B Downregulates Expression of Activating Ligands during Lytic Infection To Escape Elimination by Natural Killer Cells.

The Herpesviridae family consists of eight viruses, most of which infect a majority of the human population. One of the less-studied members is human herpesvirus 6 (HHV-6) (Roseolovirus), which causes a mild, well-characterized childhood disease. Primary HHV-6 infection is followed by lifelong latency. Reactivation frequently occurs in immunocompromised patients, such as those suffering from HIV infection or cancer or following transplantation, and causes potentially life-threatening complications. In this study, we investigated the mechanisms that HHV-6 utilizes to remain undetected by natural killer (NK) cells, which are key participants in the innate immune response to infections. We revealed viral mechanisms which downregulate ligands for two powerful activating NK cell receptors: ULBP1, ULBP3, and MICB, which trigger NKG2D, and B7-H6, which activates NKp30. Accordingly, this downregulation impaired the ability of NK cells to recognize HHV-6-infected cells. Thus, we describe for the first time immune evasion mechanisms of HHV-6 that protect lytically infected cells from NK elimination. IMPORTANCE: Human herpesvirus 6 (HHV-6) latently infects a large portion of the human population and can reactivate in humans lacking a functional immune system, such as cancer or AIDS patients. Under these conditions, it can cause life-threatening diseases. To date, the actions and interplay of immune cells, and particularly cells of the innate immune system, during HHV-6 infection are poorly defined. In this study, we aimed to understand how cells undergoing lytic HHV-6 infection interact with natural killer (NK) cells, innate lymphocytes constituting the first line of defense against viral intruders. We show that HHV-6 suppresses the expression of surface proteins that alert the immune cells by triggering two major receptors on NK cells, NKG2D and NKp30. As a consequence, HHV-6 can replicate undetected by the innate immune system and potentially spread infection throughout the body. This study advances the understanding of HHV-6 biology and the measures it uses to successfully escape immune elimination.

A systematic view on influenza induced host shutoff.

Host shutoff is a common strategy used by viruses to repress cellular mRNA translation and concomitantly allow the efficient translation of viral mRNAs. Here we use RNA-sequencing and ribosome profiling to explore the mechanisms that are being utilized by the Influenza A virus (IAV) to induce host shutoff. We show that viral transcripts are not preferentially translated and instead the decline in cellular protein synthesis is mediated by viral takeover on the mRNA pool. Our measurements also uncover strong variability in the levels of cellular transcripts reduction, revealing that short transcripts are less affected by IAV. Interestingly, these mRNAs that are refractory to IAV infection are enriched in cell maintenance processes such as oxidative phosphorylation. Furthermore, we show that the continuous oxidative phosphorylation activity is important for viral propagation. Our results advance our understanding of IAV-induced shutoff, and suggest a mechanism that facilitates the translation of genes with important housekeeping functions.

CEACAM1-Mediated Inhibition of Virus Production.

Cells in our body can induce hundreds of antiviral genes following virus sensing, many of which remain largely uncharacterized. CEACAM1 has been previously shown to be induced by various innate systems; however, the reason for such tight integration to innate sensing systems was not apparent. Here, we show that CEACAM1 is induced following detection of HCMV and influenza viruses by their respective DNA and RNA innate sensors, IFI16 and RIG-I. This induction is mediated by IRF3, which bound to an ISRE element present in the human, but not mouse, CEACAM1 promoter. Furthermore, we demonstrate that, upon induction, CEACAM1 suppresses both HCMV and influenza viruses in an SHP2-dependent process and achieves this broad antiviral efficacy by suppressing mTOR-mediated protein biosynthesis. Finally, we show that CEACAM1 also inhibits viral spread in ex vivo human decidua organ culture.

The RNA binding protein IMP3 facilitates tumor immune escape by downregulating the stress-induced ligands ULPB2 and MICB.

Expression of the stress-induced ligands MICA, MICB and ULBP 1-6 are up-regulated as a cellular response to DNA damage, excessive proliferation or viral infection; thereby, they enable recognition and annihilation by immune cells that express the powerful activating receptor NKG2D. This receptor is present not exclusively, but primarily on NK cells. Knowledge about the regulatory mechanisms controlling ULBP expression is still vague. In this study, we report a direct interaction of the oncogenic RNA binding protein (RBP) IMP3 with ULBP2 mRNA, leading to ULBP2 transcript destabilization and reduced ULBP2 surface expression in several human cell lines. We also discovered that IMP3 indirectly targets MICB with a mechanism functionally distinct from that of ULBP2. Importantly, IMP3-mediated regulation of stress-ligands leads to impaired NK cell recognition of transformed cells. Our findings shed new light on the regulation of NKG2D ligands and on the mechanism of action of a powerful oncogenic RBP, IMP3.

Endothelial cell recovery, acute thrombogenicity, and monocyte adhesion and activation on fluorinated copolymer and phosphorylcholine polymer stent coatings.

This study compares the effects of two polymers currently being marketed on commercially available drug-eluting stents, PVDF-HFP fluorinated copolymer (FP) and phosphorylcholine polymer (PC), on re-endothelialization, acute thrombogenicity, and monocyte adhesion and activity. Rabbit iliac arteries were implanted with cobalt-chromium stents coated with FP or PC polymer (without drug) and assessed for endothelialization at 14 days by confocal and scanning electron microscopy (SEM). Endothelialization was equivalent and near complete for FP and PC polymer-coated stents (>80% by SEM). Acute thrombogenicity was assessed in a Chandler loop model using porcine blood. Thrombus adherence was similar for both polymers as assessed by clot weight, thrombin-antithrombin III complex, and lactate dehydrogenase expression. In vitro cell adhesion assays were performed on FP and PC polymer-coated glass coupon surfaces using HUVECs, HCAECs, and THP-1 monocytes. The number of ECs adhered to FP and control surfaces were equivalent and significantly greater than on PC surfaces (p<0.05). There were no differences in THP-1 monocyte adhesion and cytokine (MCP-1, RANTES, IL-6, MIP-1alpha, MIP-1beta, G-CSF) expression. The data suggests that biological responses to both FP and PC polymer are similar, with no mechanistic indication that these polymers would be causative factors for delayed vessel healing in an acute timeframe.

Transcatheter injection-induced changes in human bone marrow-derived mesenchymal stem cells.

Human mesenchymal stem cells (hMSC) are being administered by direct intramyocardial (IM) injection into patients with myocardial dysfunction with an objective to improve clinical status. However, surprisingly little attention has been directed to qualifying hMSC functionality beyond simple viability. In particular, the transit of hMSCs through a small-caliber needle lumen, the final fluidic pathway for all IM injection devices, may be especially prone to inducing unwarranted effects on cell function. This study evaluated the changes in clonogenicity, gene expression, and cytokine secretion that may be induced in hMSC (20 million/ml) by injection through a 26-gauge Nitinol needle at two different flow rates compared to noninjected control samples. Results indicated that hMSC viability and colony forming unit (CFU) formation was not altered by changes in injection rate, although a trend toward lower titers was noted at the higher flow rate, for the specific batch of hMSCs studied. The gene expression and cytokine analysis data suggest that delivering a suspension of MSCs through narrow lumen needles may marginally alter certain gene expression programs, but that such in vitro effects are transient and not translated into measurable differences in protein production. Gene expression levels of four cytokines (bFGF, SDF-1, SCF, VEGF) were significantly different at 400 microl/min, and that of all cytokines were significantly different at 1600 microl/min when compared to controls (p < 0.05). These changes were less pronounced (statistically insignificant for most cases, p > 0.05) and, in certain instances directionally opposite, at 72 h. However, no differences in the amounts of secreted bFGF, VEGF, or TGF-beta were detectable at either of the two time points or flow rates. We infer that intramyocardial administration by transcatheter techniques is unlikely to interfere with the machinery required for cell replication or secretion of regulatory and other growth factors, which are the mainstays of MSC contribution to cardiac tissue repair and regeneration.