Browsing by Subject "innate immunity"

Now showing 1 - 4 of 4
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    The functional impact of Retinoic acid and RIP140 in macrophages: from chromatin to physiology
    (2016-08) Lee, Bomi
    Innate immunity consists of two systems; humoral and cellular systems. The humoral system includes anti-microbial peptides and opsonins while the cellular system involves specialized cells including phagocytes. The major functions of phagocytes are scavenging toxic compounds and producing inflammatory mediators to destroy infectious organisms and to transfer signals to other immune cells. Dysregulation of the phagocytic system by various conditions including the defect of immune cells and insufficient nutrition can lead to inflammatory diseases. Therefore, understanding the characteristics of phagocytes and the molecular mechanism in response to extracellular stimulations is critical for the development of therapeutics for inflammatory diseases. The focus of my thesis was to evaluate cellular signaling and its pathophysiological relationship in one type of phagocytes, macrophages. All-trans retinoic acid (RA) and its derivatives have been proved as potent therapeutics for inflammatory diseases, but the molecular mechanism of RA action in macrophages was not well established. In order to shed light on the functional role of RA in macrophages, I first found that topical application of RA significantly improved wound healing and the co-stimulation with RA and IL-4 synergistically activated Arginase-1 (Arg1), a critical gene for tissue repair, in macrophages. This involves feed forward regulation of Raldh2, a rate-limiting enzyme for RA biosynthesis, and requires Med25 to remodel the +1 nucleosome of Arg1 for transcription initiation and to facilitate transcriptional initiation-elongation coupling by recruiting elongation factor TFIIS. This study demonstrated RA’s modulatory activity in IL-4-induced anti-inflammatory macrophages, which involves synergistic activation of Arg1 by RA and IL-4 and a functional role of Med25 in chromatin remodeling of this gene promoter. In macrophage activation, there are two well-established phenotypes; classically activated (M1, pro-inflammatory) and alternatively activated (M2, anti-inflammatory) macrophages. The switch from M1 to M2 is critical for the control of inflammatory responses including wound repair. Previously, it has been found that Receptor-interacting Protein 140 (RIP140) is an enhancer of M1 by acting as a co-activator for NF-κB. Related to this, my research has uncovered that RIP140 delays the wound healing process by suppressing the macrophage phenotype switch from M1 to M2. With regards to mechanism, IL-4 treatment stimulates RIP140 export from the nucleus to the cytoplasm to form a complex with calpain regulatory subunit (CAPNS1) to activate calpain1/2 that enhances the activity of PTP1B, a negative regulator for STAT6 in M2 macrophages. Together, these results have established a new modulatory role of RIP140 in macrophage phenotype switch during wound healing by regulating both M1 and M2 activations (enhancing M1 and suppressing M2 activation). Another new finding I discovered about RIP140 was its repressive effect on osteoclast (OC) differentiation. OCs are derived from monocyte/macrophage lineage of hematopoietic cells and are responsible for bone resorptive activity. OCs maintain a balance in bone remodeling with osteoblasts (OB) that are involved in bone formation. RIP140 forms a complex with orphan nuclear receptor TR4 in pre-osteoclastic cells to suppress OC differentiation. Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL) induces RIP140 protein degradation and represses TR4 mRNA level, which terminates the repressive activity of TR4/RIP140 complex in OC differentiation. In vivo micro CT analysis of macrophage/monocyte-specific RIP140 KD (mϕRIP140KD) mice showed an osteopenia phenotype with reduced OB function and increased OC activity, indicating uncoupling between OC and OB. This study demonstrated RIP140’s additional role in OC differentiation and bone diseases such as osteoporosis. Taken all together, these studies have established fine-tuning molecular mechanisms in macrophages, including their phenotypic switch and polarization/maturation. Specifically, we uncovered additional pathways of signal inputs and stimuli that regulate these processes such as RA, IL-4 and RANKL, and determined their physiological relevance in wound healing, inflammation and osteoclastogenesis. Differential activation of macrophages by these biological cues further confirms the plastic nature of macrophages. These findings contribute to our understanding of signaling mechanisms in macrophage polarization and their impact on diseases.
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    In vivo functions of intestinal dendritic cells
    (2014-09) Welty, Nathan
    Dendritic cells (DCs) in the intestinal lamina propria (LP) are composed of two CD103+ subsets that differ in CD11b expression. We report here that langerin is expressed by human LP DCs and that transgenic human langerin drives expression in CD103+ CD11b+ LP DCs in mice. This subset was ablated in huLangerin-DTA mice, resulting in reduced LP Th17 cells without affecting Th1 or T reg cells. Notably, cognate DC-T cell interactions were not required for Th17 development, as this response was intact in huLangerin-Cre I-Ab flox mice. In contrast, responses to intestinal infection or flagellin administration were unaffected by the absence of CD103+ CD11b+ DCs. huLangerin-DTA x BatF3-/- mice lacked both CD103+ LP DC subsets, resulting in defective gut homing and fewer LP T reg cells. Despite these defects in LP DCs and resident T cells, we did not observe alterations of intestinal microbial communities. Thus, CD103+ LP DC subsets control T cell homeostasis through both non-redundant and overlapping mechanisms.
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    Innate immune control of virus replication and transmission
    (2020-05) Fay, Elizabeth
    The activation of innate immune pathways is a critical step in the response to virus infection. The failure of infected cells to control virus replication can lead to massive destruction of tissue, resulting in severe illness or death of the host and spread to new hosts. The ongoing coronavirus pandemic highlights the critical need to understand the mechanisms by which infected cells activate the innate immune response following virus infection, and how failure to activate this response leads to virus spread and cross-species transmission. Here, I describe two model systems used to understand the innate immune response to viruses. First, I use genetically engineered reporter influenza A viruses to identify infected cells and characterize the early response in vivo. I have found distinct responses based on the magnitude and round of infection, as well as cell type- and stage-specific antiviral signatures. In the second model system, I aim to understand the dynamics of how viruses transmit between hosts. I leveraged a model whereby pet store mice—which harbor a myriad of mouse pathogens—are co-housed with clean laboratory mice. This ‘dirty’ mouse model offers a platform for studying the acute transmission of viruses between hosts via natural mechanisms—through direct contact, air, and saliva and other fluids. I co-housed pet store mice with wild type laboratory mice and mice deficient in interferon receptors to characterize the role of these important innate immune pathways. Finally, I have co-housed laboratory mice with the bedding of pet store rats to analyze immune and non-immune species barriers to transmission. Overall, the findings of these studies will help elucidate mechanisms of innate immune activation by viruses.
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    Local And Systemic Innate Immunity In Viral Infection And Transmission At Barrier Surfaces
    (2023-03) Roach, Shanley
    Viral infections are a source of significant morbidity and mortality. According to the World Health Organization, lower respiratory infections were the fourth leading cause of death globally from 2000-2019. Activation of the innate immune response is an essential step in combating viral infection. Failure of the immune response to control the infection can lead to widespread inflammation and damage within the host as well as transmission to new hosts. Understanding how viruses and hosts interact, both directly and indirectly during infection, is necessary to develop new treatments, understand intra- and inter-species transmission, and prepare for future zoonotic emergences. Furthermore, studying the broader implications of infection beyond the initial site of infection will help discern how highly pathogenic viruses cause more severe disease. Here, I describe two systems in which I explore local and systemic innate immune responses to viral infection. First, I discuss how respiratory influenza virus infection alters intestinal epithelial and innate lymphoid cell homeostasis. I found that infection drives increases in both tuft cells and type 1 and 2 innate lymphoid cells, with the type 2 increase being tuft cell-dependent and independent of the microbiome. Second, I leverage a natural rodent model where pet store animals – which harbor myriad of natural rodent pathogens – are cohoused with laboratory animals to study acute virus transmission, dissemination, and evolution. Using both wildtype and interferon-deficient animals, I evaluate the role of innate immunity in mitigating transmission and within host dissemination of viruses from a variety of viral families. I also report how this model can also be used to study cross-species transmission – including dead-end transmission events, which are invisible to many existing models. Altogether, this model establishes a foundation for which questions about transmission, evolution, and pathogenicity of different viruses within a host, between the same species, and between different species can be studied. Overall, the findings from these studies help inform how both local and systemic innate immunity contribute to the host response to viral infections.