Browsing by Subject "Interferon-alpha"
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Item Characterization of the Antiviral Effector IFI6(2018-11-26) Richardson, Ryan Blake; Yan, Nan; Schoggins, John W.; Levine, Beth; Pfeiffer, Julie K.The innate immune response is a critical line of host defense against invading pathogens. The production of interferon (IFN) and the subsequent expression of interferon stimulated genes (ISGs) are major contributors to the innate immune response, which establish an antiviral state in the cell. Flaviviruses such as dengue virus, Zika virus, and West Nile virus rely intimately on host pathways for completing a replication cycle, and have developed strategies to overcome the inhibitory effect of the innate immune response. To identify host factors required during an IFN response to flavivirus infection, a genome-wide CRISPR screen was carried out. Two of the top hits from the screen were IFI6, a previously identified ISG long predicted to be antiviral, and BiP, a luminal chaperone in the endoplasmic reticulum (ER). I questioned whether IFI6 was important for the antiviral response to flaviviruses and sought to investigate its role during infection. I confirmed the results from the CRISPR screen and showed that cells lacking IFI6 were insensitive to IFN, suggesting a key role in the innate immune response to flaviviruses. This was complemented by overexpression studies which showed IFI6 is potently inhibitory to flavivirus infection. I further demonstrated that BiP is required for an intact IFN response and importantly mediates expression of IFI6, which it binds in a chaperone-dependent manner. I also showed that IFI6 is localized to the ER and is an integral membrane protein. Importantly, IFI6 acts during the flavivirus life cycle to inhibit replication and formation of replication complexes, which are formed by rearrangement of ER membranes. IFI6 specifically inhibits flaviviruses, since other viruses that replicate at the ER such as hepatitis C virus (HCV) are not affected by IFI6. I hypothesize the key to this specificity lies in the orientation of the replication complexes - HCV complexes extend outwards into the cytoplasm while flaviviruses bud inwards into the lumen. Taken together, these data support a model where IFI6 is sensitive to membrane alterations specifically induced by flaviviruses but not other viruses, which provides the innate immune response with a potent and specific ISG to block viral infection.Item Counter-Regulation of Human Cd4+ T Helper 2 Lymphocyte Development and Stability by Type I Interferon(2013-01-16) Huber, Jonathan Philip; Farrar, J. DavidInnate cytokines shape the differentiation of CD4+ T cells from naïve precursors into multiple functional subsets in order carry out effective adaptive immune responses to diverse immunological stimuli. Interleukin-12 controls the development of T helper 1 (Th1) cells, which fight infection by intracellular pathogens such as bacteria and viruses. Helminth parasites and allergens induce the production of IL-4, which drives differentiation to Th2. The IL-12 and IL-4 signaling pathways also counter-regulate each other, though this balance favors Th2 as IL-4 signaling overrides the effects of IL-12. In addition, IL-4 induces expression of the GATA3 transcription factor that stabilizes the Th2 phenotype through auto-regulatory maintenance of its own expression. A role for type I interferon (IFN-α/β), a major antiviral cytokine, has been described more recently in Th1 cells, but the potential role of IFN-α/β in counter-regulating Th2 development is poorly understood. My work reveals that IFN-α/β blocks IL-4-induced Th2 differentiation of human CD4+ T cells by inhibiting expression of GATA3. The loss of GATA3 in developing Th2 cells leads to reduced secretion of the Th2 cytokines, IL-4, IL-5, and IL-13, and reduced expression of chemoattractant receptor expressed in Th2 cells (CRTh2). IFN-α/β also suppresses GATA3 in committed Th2 cells, leading to a loss of the Th2 phenotype. GATA3 transcription utilizes two distinct first exons, exon 1A and 1B, which are controlled by separate promoters, but IL-4 signaling in Th2 cells leads to preferential utilization of the upstream exon 1A transcript. IFN-α specifically blocks expression of the 1A but not 1B transcript, indicating a specific regulation of Th2 cells. Furthermore, IFN-α appears to induce epigenetic silencing of an upstream conserved non-coding sequence I, which may be required for optimal exon 1A transcription in Th2 cells. This work reveals an unexpected role for IFN-α in selectively inhibiting Th2 but not Th1 differentiation, which may be important for ensuring appropriate development of antiviral immunity. In addition, the ability of IFN-α to suppress both developing Th2 cells and previously committed Th2 cells suggests that IFN-α may be useful as a novel therapeutic for atopic diseases.Item Reciprocal Regulation of CD4+ and CD8+ T Lymphocyte Effector and Memory Fates by Interleukin 12 and Type 1 Interferon(2009-06-18) Ramos, Hilario Jose; Farrar, J. DavidCytokine signaling networks play an important role in bridging the innate and adaptive immune responses. For example, the innate cytokines Interleukin-12 (IL-12) and type I interferon (IFN-a/b) are induced to high levels by intracellular bacterial and viral infections and have been shown to promote adaptive T lymphocyte responses to infection. While the role for IL-12 on the development of T lymphocyte effector responses has been well characterized, the exact role for IFN-a/b on these responses has been controversial. Therefore, the present study set forth to characterize the distinct roles for IL-12 and IFN-a/b on the development of effector and memory responses in human CD4+ and CD8+ T cells. My work has found that IL-12 drives the development of effector CD4+ and CD8+ T cells. In contrast, IFN-a/b was incapable of promoting these responses and this was due to a difference in the kinetics of activation of two downstream transcription factors STAT4 and T-bet. Further examination of CD8+ T cells revealed a distinct role for IFN-a/b in the development of a population of central memory T cells (TCM). Alternatively, IL-12 drove the development of effector memory cells (TEM). The variegated development of TCM and TEM was dictated by differential cytokine receptor expression and further, the strength of primary T cell receptor (TCR) activation determined the responsiveness to cytokine polarization. Finally, these studies uncovered a novel role for CD8+ T cell licensing of CTL activity through the costimulatory CD27/CD70 pathway. Therefore, taken together, these findings support a novel model in which TCR activation and costimulation act to shape the ability for IL-12 and IFN-a/b to differentially program the development of distinct classes of effector and memory CD8+ T lymphocytes. These studies have direct bearing on the design and development of effective therapeutics and vaccines and demonstrate a new understanding on the modulation of the adaptive immune response to intracellular infection.Item Regulation of Effector and Memory Development of Human CD4+ T Cells by Interleukin 12 and Type I Interferon(2009-01-09) Davis, Ann Marie; Farrar, J. DavidInnate cytokines induced at the onset of infection regulate the development of adaptive immune responses such as CD4+ T helper cell development. For instance, the innate cytokines interleukin 12 (IL-12) and type I interferon (IFN-alpha/beta) are produced in response to intracellular bacterial and viral infections. While the effects of IL-12 on CD4+ T cell differentiation are relatively well-understood, the role of IFN-alpha/beta, despite extensive study, has remained controversial. The present work seeks to clarify the effects of IFN-alpha/beta on CD4+ T cell development, effector functions, and memory generation. Previous reports had suggested that IFN-alpha, like IL-12, could promote Th1 development in human CD4+ T cells. However, my work demonstrates that IFN-alpha is insufficient to induce Th1 differentiation because of an inability to maintain stable STAT4 phosphorylation or T-bet expression. Furthermore, IL-12, but not IFN-alpha, induces the secretion of IFN-gamma and TNF-alpha from human CD4+ T cells. These two cytokines, in addition to promoting bacterial clearance, can directly participate in antiviral immunity via a signaling pathway which involves the type I IFN receptor. Finally, a combination of IL-12 and IFN-alpha influences memory CD4+ T cell function by strongly inducing IL-2 secretion from a subset of cells in a T-bet-independent manner. These IL-2-producing cells demonstrate both phenotypic and functional characteristics of long-lived and pluripotent central memory. Taken together, these data provide a new understanding of the role of innate cytokines in shaping adaptive CD4+ T cell responses. Given the numerous medical uses of IFN-alpha/beta, these findings could have a broad impact on the design of vaccines and antiviral therapeutics.Item [Southwestern News](2001-11-16) Wren, Worth, Jr.; Walker, WendyItem [Southwestern News](1993-04-30) Donovan, JenniferItem Type I Interferon Mediates Th2 Reprogramming and Acute Suppression of Effector Functions(2015-05-22) Gonzales-van Horn, Sarah Ruth; Niederkorn, Jerry Y.; Farrar, J. David; D'Orso, Iván; Gill, Michelle A.; van Oers, Nicolai S. C.The type I interferon (IFN-α/β) family is a pleiotropic set of cytokines that play a role in regulating many biological functions, including suppressing viral replication and modulating adaptive immune functions. Although IFN-α/β has been extensively studied regarding the activation of interferon sensitive genes, much less is known regarding its role as a negative regulator. Here, I demonstrate a role for IFN-α/β in the regulation of Th2 development as well as memory Th2 cell function. The Th2 master transcription factor GATA3, promotes its own expression through a positive regulatory loop, uncoupling the cell from the requirement of IL-4 signaling. IFN-α/β inhibits this process by inducing epigenetic modifications within the GATA3 locus that prevent this positive regulatory loop from being established. Reduced DNase hypersensitivity and enhanced H3K27me3 correlates with a reduction in GATA3 gene expression by targeting the IL-4-sensitive alternative transcript exon 1a for suppression. These results demonstrate that IFN-α/β interferes with IL-4-mediated programming and induction of GATA3 through the enhancement of gene-silencing histone modifications within the GATA locus. In addition to mediating chromatin modifications required for the long-term suppression of genes, IFN-α/β signaling also acutely suppresses gene expression in pre-committed Th2 cells. Here, I demonstrate the cellular and molecular pathways involved in suppressing the TCR-mediated expression of the human IL5 gene. IFN-α treatment potently suppressed IL5 and IL13 gene expression by reducing the rate of nascent transcription, independent of de novo expression of ISGs. Further, I show that IFN-α-mediated STAT4 activation is required to suppress gene expression. Furthermore, IFN-α/β-mediated acute suppression occurs in a species-specific manner, since murine Th2 cells are not regulated by IFN-α/β signaling in contrast to human Th2 cells. This robust suppression of acute IL5 and IL13 expression, paired with the suppression of Th2 development, provide further evidence that IFN-α/β is a candidate for the treatment of allergic disease.