Donald T. Gracias

The microRNA miR-155 controls CD8 + T cell responses by regulating interferon signaling

We found upregulation of expression of the microRNA miR-155 in primary effector and effector memory CD8+ T cells, but low miR-155 expression in naive and central memory cells. Antiviral CD8+ T cell responses and viral clearance were impaired in miR-155-deficient mice, and this defect was intrinsic to CD8+ T cells, as miR-155-deficient CD8+ T cells mounted greatly diminished primary and memory responses. Conversely, miR-155 overexpression augmented antiviral CD8+ T cell responses in vivo. Gene-expression profiling showed that miR-155-deficient CD8+ T cells had enhanced type I interferon signaling and were more susceptible to interferons antiproliferative effect. Inhibition of the type I interferon–associated transcription factors STAT1 or IRF7 resulted in enhanced responses of miR-155-deficient CD8+ T cells in vivo. We have thus identified a previously unknown role for miR-155 in regulating responsiveness to interferon and CD8+ T cell responses to pathogens in vivo.

Type I interferon upregulates Bak and contributes to T cell loss during human immunodeficiency virus (HIV) infection.

The role of Type I interferon (IFN) during pathogenic HIV and SIV infections remains unclear, with conflicting observations suggesting protective versus immunopathological effects. We therefore examined the effect of IFNα/β on T cell death and viremia in HIV infection. Ex vivo analysis of eight pro- and anti-apoptotic molecules in chronic HIV-1 infection revealed that pro-apoptotic Bak was increased in CD4+ T cells and correlated directly with sensitivity to CD95/Fas-mediated apoptosis and inversely with CD4+ T cell counts. Apoptosis sensitivity and Bak expression were primarily increased in effector memory T cells. Knockdown of Bak by RNA interference inhibited CD95/Fas-induced death of T cells from HIV-1-infected individuals. In HIV-1-infected patients, IFNα-stimulated gene expression correlated positively with ex vivo T cell Bak levels, CD95/Fas-mediated apoptosis and viremia and negatively with CD4+ T cell counts. In vitro IFNα/β stimulation enhanced Bak expression, CD95/Fas expression and CD95/Fas-mediated apoptosis in healthy donor T cells and induced death of HIV-specific CD8+ T cells from HIV-1-infected patients. HIV-1 in vitro sensitized T cells to CD95/Fas-induced apoptosis and this was Toll-like receptor (TLR)7/9- and Type I IFN-dependent. This sensitization by HIV-1 was due to an indirect effect on T cells, as it occurred in peripheral blood mononuclear cell cultures but not purified CD4+ T cells. Finally, peak IFNα levels and viral loads correlated negatively during acute SIV infection suggesting a potential antiviral effect, but positively during chronic SIV infection indicating that either the virus drives IFNα production or IFNα may facilitate loss of viral control. The above findings indicate stage-specific opposing effects of Type I IFNs during HIV-1 infection and suggest a novel mechanism by which these cytokines contribute to T cell depletion, dysregulation of cellular immunity and disease progression.

MicroRNAs: key components of immune regulation.

The regulation of gene expression at the posttranscriptional level has revealed important control levels for genes important to the immune system. MicroRNAs (miRNAs) are small RNAs that regulate gene expression by inhibiting protein translation or by degrading the mRNA transcript. A single miRNA can potentially regulate the expression of multiple genes and the proteins encoded. MiRNA can influence molecular signaling pathways and regulate many biological processes including immune function. Although the role of miRNAs in development and oncogenesis has been well characterized, their role in the immune system has only begun to emerge. During the past few years, many miRNAs have been found to be important in the development, differentiation, survival, and function of B and T lymphocytes, dendritic cells, macrophages, and other immune cell types. We discuss here recent findings revealing important roles for miRNA in immunity and how miRNAs can regulate innate and adaptive immune responses.

Acute exposure to ZnO nanoparticles induces autophagic immune cell death

Abstract The increasing risk of incidental exposure to nanomaterials has led to mounting concerns regarding nanotoxicity. Zinc oxide nanoparticles (ZnO NPs) are produced in large quantities and have come under scrutiny due to their capacity to cause cytotoxicity in vitro and potential to cause harm in vivo. Recent evidence has indicated that ZnO NPs promote autophagy in cells; however, the signaling pathways and the role of ion release inducing toxicity remain unclear. In this study, we report that ZnO NPs are immunotoxic to primary and immortalized immune cells. Importantly, such immunotoxicity is observed in mice in vivo, since death of splenocytes is seen after intranasal exposure to ZnO NPs. We determined that ZnO NPs release free Zn2+ that can be taken up by immune cells, resulting in cell death. Inhibiting free Zn2+ ions in solution with EDTA or their uptake with CaCl2 abrogates ZnO NP-induced cell death. ZnO NP-mediated immune cell death was associated with increased levels of intracellular reactive oxygen species (ROS). ZnO NP death was not due to apoptosis, necroptosis or pyroptosis. Exposure of immune cells to ZnO NPs resulted in autophagic death and increased levels of LC3A, an essential component of autophagic vacuoles. Accordingly, ZnO NP-mediated upregulation of LC3A and induction of immune cell death were inhibited by blocking autophagy and ROS production. We conclude that release of Zn2+ from ZnO NPs triggers the production of excessive intracellular ROS, resulting in autophagic death of immune cells. Our findings suggest that exposure to ZnO NPs has the potential to impact host immunity.

Phosphatidylinositol 3-Kinase p110δ Isoform Regulates CD8+ T Cell Responses during Acute Viral and Intracellular Bacterial Infections

The p110δ isoform of PI3K is known to play an important role in immunity, yet its contribution to CTL responses has not been fully elucidated. Using murine p110δ-deficient CD8+ T cells, we demonstrated a critical role for the p110δ subunit in the generation of optimal primary and memory CD8+ T cell responses. This was demonstrated in both acute viral and intracellular bacterial infections in mice. We show that p110δ signaling is required for CD8+ T cell activation, proliferation and effector cytokine production. We provide evidence that the effects of p110δ signaling are mediated via Akt activation and through the regulation of TCR-activated oxidative phosphorylation and aerobic glycolysis. In light of recent clinical trials that employ drugs targeting p110δ in certain cancers and other diseases, our study suggests caution in using these drugs in patients, as they could potentially increase susceptibility to infectious diseases. These studies therefore reveal a novel and direct role for p110δ signaling in in vivo CD8+ T cell immunity to microbial pathogens.

Rapid evolution of the CD8+ TCR repertoire in neonatal mice

Currently, there is little consensus regarding the most appropriate animal model to study acute infection and the virus-specific CD8+ T cell (CTL) responses in neonates. TCRβ high-throughput sequencing in naive CTL of differently aged neonatal mice was performed, which demonstrated differential Vβ family gene usage. Using an acute influenza infection model, we examined the TCR repertoire of the CTL response in neonatal and adult mice infected with influenza type A virus. Three-day-old mice mounted a greatly reduced primary NP(366–374)–specific CTL response when compared with 7-d-old and adult mice, whereas secondary CTL responses were normal. Analysis of NP(366–374)-specific CTL TCR repertoire revealed different Vβ gene usage and greatly reduced public clonotypes in 3-d-old neonates. This could underlie the impaired CTL response in these neonates. To directly test this, we examined whether controlling the TCR would restore neonatal CTL responses. We performed adoptive transfers of both nontransgenic and TCR-transgenic OVA(257–264)-specific (OT-I) CD8+ T cells into influenza-infected hosts, which revealed that naive neonatal and adult OT-I cells expand equally well in neonatal and adult hosts. In contrast, nontransgenic neonatal CD8+ T cells when transferred into adults failed to expand. We further demonstrate that differences in TCR avidity may contribute to decreased expansion of the endogenous neonatal CTL. These studies highlight the rapid evolution of the neonatal TCR repertoire during the first week of life and show that impaired neonatal CTL immunity results from an immature TCR repertoire, rather than intrinsic signaling defects or a suppressive environment.

The Transcription Factor T-Bet Is Regulated by MicroRNA-155 in Murine Anti-Viral CD8+ T Cells via SHIP-1

We report here that the expression of the transcription factor T-bet, which is known to be required for effector cytotoxic CD8+ T lymphocytes (CTL) generation and effector memory cell formation, is regulated in CTL by microRNA-155 (miR-155). Importantly, we show that the proliferative effect of miR-155 on CD8+ T cells is mediated by T-bet. T-bet levels in CTL were controlled in vivo by miR-155 via SH2 (Src homology 2)-containing inositol phosphatase-1 (SHIP-1), a known direct target of miR-155, and SHIP-1 directly downregulated T-bet. Our studies reveal an important and unexpected signaling axis between miR-155, T-bet, and SHIP-1 in in vivo CTL responses and suggest an important signaling module that regulates effector CTL immunity.