Browsing by Author "Peters, Nathan C."

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    Antigen-specific CD4+ T-B cell interplay induces a robust, polyreactive systemic immunoglobulin response to commensal bacteremia.
    (2020-03-04) Koegler, Mia Elizabeth; Geuking, Markus B.; Peters, Nathan C.; Hirota, Simon Andrew; Jenne, Craig N.
    The impact of cognate CD4+ T cell help on the systemic antibody response during commensal bacteremia was assessed in detail in this thesis. To specifically evaluate cognate T cell-B cell interactions, we utilized a genetically modified commensal E. coli strain that expressed gp61, an additional T helper epitope, in its outer membrane ompC protein (E. coli ompC_gp61). Germ-free mice that were systemically primed with E. coli ompC_gp61 produced a significantly more robust E. coli-specific antibody response than mice that received the corresponding wild-type (WT) E. coli strain. The observed antibody response to E. coli ompC_gp61 appeared to be MHC II haplotype-dependent, as this phenomenon was reproducible in C57BL/6 mice (I-Ab) but not in BALB/c mice (I-Ad and I-Ed). Furthermore, mice adoptively transferred with gp61-specific SMARTA CD4+ T cells and later challenged with E. coli ompC_gp61 produced significantly more E. coli-specific IgM than recipient mice that were primed with WT E. coli. This finding suggests that the proportion of antigen-specific CD4+ T cells present during systemic immune priming may impact on class switch recombination and IgM+ memory formation. Finally, increasing gut microbiota complexity resulted in lower E. coli-specific antibody titers compared to germ-free mice in response to E. coli ompC_gp61 priming. However, non-primed mice with a more complex gut microbiota had higher total serum antibodies than their germ-free counterparts. Collectively, these data suggest that cognate CD4+ T cell help during commensal-induced bacteremia can orchestrate a potent, commensal-specific, and polyreactive antibody response. These findings shed new light on the systemic humoral immune response to bacteremia and could potentially be exploited to develop more effective and personalized vaccine strategies.
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    Defining How Entamoeba histolytica Modulates Macrophage Functions
    (2019-09-06) Begum, Sharmin; Chadee, Kris C.; McCafferty, Donna Marie; Peters, Nathan C.
    Entamoeba histolytica (Eh) colonizes the colonic mucus layer to establish asymptomatic infection and under certain circumstances not completely known, Eh breaches mucosal barriers to cause intestinal and extraintestinal amebiasis. Eh adherence and invasion to host cells triggers robust pro-inflammatory responses that are critical in disease pathogenesis. At present, it is unclear why there is an aggressive pro-inflammatory response that intensifies at the site of parasite invasion. In this study, I hypothesize that Eh contact with macrophages induces the release of the endogenous alarmin molecule HMGB1 to alert non-contacted cells of imminent Eh invasion to escalate innate host defenses. Preformed nuclear HMGB1 is a well-known alarmin protein that upon secretion plays critical roles in the pathogenesis of infectious inflammation. Eh in contact with macrophages induced rapid and early secretion of HMGB1. This was facilitated by Eh surface Gal-lectin mediated activation of PI3K and NF-κB signaling pathways and increased nuclear histone acetyltransferase activity that resulted in the acetylation of HMGB1 to cause active secretion without significant host cell death. In contrast to endotoxemia, Eh induced HMGB1 secretion was independent of caspase-1 mediated inflammasome activation and gasdermin D pores. Neutralization of HMGB1 in mice significantly inhibited Eh-induced pro-inflammatory responses in colonic loops, demonstrating a critical role for HMGB1 in shaping pro-inflammatory responses towards Eh. The second aim of this study was to investigate the role of autophagy associated protein ATG16L1 in response to Eh-induced pro-inflammatory responses. Autophagy maintains and regulates excessive inflammatory responses and tissue damage. Interestingly, Eh in contact with macrophages at the intercellular junction induced rapid degradation of ATG16L1 protein and dissociation of ATG5 from ATG12-ATG5 conjugates, which are essential components of immune regulatory autophagy processes. The cellular mechanism of ATG16L1 protein degradation was mediated by Eh induced activation of caspase-6. In vitro cleavage assays demonstrated that ATG16L1 protein was a potential proteolytic substrate for active caspase-6 and the presence of Eh increased ATG16L1 protein susceptibility towards degradation, which leads to dysregulation of immune regulatory processes with excessive inflammation. Taken together, these results revealed two distinct but novel interconnected outcomes following Eh interaction with macrophages at the intercellular junction 1), induction and secretion of the alarmin molecule HMGB1 to establish amplified pro-inflammatory responses and 2), caspase-6 activation that mediates proteolytic degradation of ATG16L1 to dysregulate immune responses to escalate the magnitude and duration of pro-inflammatory responses. Both these processes can play major roles in innate host defenses and/or disease pathogenesis in amebiasis.
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    Disentangling detrimental sand fly-mite interactions in a closed laboratory sand fly colony: implications for vector-borne disease studies and guidelines for overcoming severe mite infestations
    (2024-01-05) Nzelu, Chukwunonso O.; Meneses, Claudio; Bowhay, Christina; Coutinho-Abreu, Iliano V.; Bennett, Emily; Bahrami, Somayeh; Bonilla, Brian; Kamhawi, Shaden; Valenzuela, Jesus G.; Peters, Nathan C.
    Abstract Background Vector sand fly colonies are a critical component of studies aimed at improving the understanding of the neglected tropical disease leishmaniasis and alleviating its global impact. However, among laboratory-colonized arthropod vectors of infectious diseases, the labor-intensive nature of sand fly rearing coupled with the low number of colonies worldwide has generally discouraged the widespread use of sand flies in laboratory settings. Among the different factors associated with the low productivity of sand fly colonies, mite infestations are a significant factor. Sand fly colonies are prone to infestation by mites, and the physical interactions between sand flies and mites and metabolites have a negative impact on sand fly larval development. Methods Mites were collected from sand fly larval rearing pots and morphologically identified using taxonomic keys. Upon identification, they were photographed with a scanning electron microscope. Several mite control measures were adopted in two different laboratories, one at the Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases-National Institutes of Health (Rockville, MD, USA), and the other at the University of Calgary (Calgary, AB, Canada). Results The mite species associated with sand fly colonies in the two laboratories were morphologically identified as Tyrophagus sp. and Stratiolaelaps scimitus. While complete eradication of mites in sand fly colonies is considered unrealistic, drastically reducing their population has been associated with higher sand fly productivity. Conclusions We report a case of detrimental interaction between sand flies and Tyrophagus sp. and S. scimitus in a closed laboratory sand fly colony, discuss their impact on sand fly production and provide guidelines for limiting the mite population size in a closed laboratory colony leading to improved sand fly yields. Graphical abstract
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    Examining the Role of Non-Canonical NOD-like Receptors and Inflammasomes in Inflammation and Disease
    (2018-03-21) Platnich, Jaye Matthew; Muruve, Daniel A.; MacDonald, Justin Anthony; Power, Christopher; Duff, Henry J.; Peters, Nathan C.
    The NOD-like Receptors (NLRs) are a family of pattern recognition receptors known to regulate a variety of immune signaling pathways. A substantial portion of NLR research focuses on the pyrin domain-containing NLRP subfamily. The canonical NLRPs are inflammasome-forming proteins responsible for the activation of caspase-1 and the maturation and secretion of the pro-inflammatory cytokines IL-1β and IL-18. In contrast, the non-canonical inflammasome-independent NLRPs regulate a variety of other pathways, including MAPK and NF-κB, through the formation of non-inflammasome complexes. Interestingly, not all inflammasomes are nucleated by NLRPs. The recently characterized non-canonical caspase-4 (caspase-11 in mice) inflammasome is known to be a key driver of the innate immune response to intracellular pathogens (and the molecules associated with them), by triggering both inflammatory cell death and the activation of canonical inflammasomes. At the outset of this PhD work, the understanding of both non-inflammasome-forming NLRPs and the non-canonical caspase-4 inflammasome was poor and the studies were sparse. It was the goal of this thesis to characterize the expression, gene regulation, and function of the non-inflammasome-forming NLR protein NLRP6, both at the cellular and biochemical level. Furthermore, using a pathogen-associated molecular pattern (PAMP)-driven model of inflammation, we sought to elucidate the function of the non-canonical caspase-4 inflammasome, particularly as it pertains to the regulation of the canonical inflammasome and cell death. By studying the fundamental biology underlying these lesser-known mediators of the innate immune system, we hoped to better understand their contribution to the early immune response and their role in driving inflammatory disease with a view to, one day, ameliorating the condition of patients suffering from these afflictions through the development of targeted therapeutics.
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    Mechanisms of vaccine protection in pneumococcal pneumonia
    (2018-06-13) Schubert, Courtney Lynn; Yipp, Bryan G.; Leigh, Richard A.; Peters, Nathan C.
    Despite the overwhelming success of vaccination in reducing mortality due to infectious diseases, it is unknown what makes some vaccines protective while others are not. Multiple vaccine candidates have failed clinical trial regardless of the production of neutralizing antibodies, therefore there is a need to establish correlates of protection that are not antibody production. We began investigating the Pnuemovax-23 vaccine which provides well characterized protection in both mice and humans, in an attempt to determine the mechanism of vaccine protection. Instead of finding that Pneumovax-23 vaccination induces disease resistance against Streptococcus pneumoniae pneumonia through eradication of the bacteria, we found that vaccinated mice survive the pneumococcal infection via disease tolerance. Therefore, we began investigating how the survival of vaccinated mice is independent of bacterial clearance from the lungs and the spleen. The role of neutrophils was first explored since there was still robust neutrophil recruitment during infection in vaccinated mice, and neutrophils are known to regulate B cells in the spleen and produce B cell growth factors. Ultimately, we determined that despite ample neutrophil recruitment during infection, neutrophils are not mediating this disease tolerance to infection in vaccinated mice. Instead, we turned to investigate whether B cells were required for disease tolerance, where we found B1 innate B cells to be required for vaccinated mice to survive the infection. CD19-/- mice are deficient in innate cells, however still have conventional B cells and neutrophil recruitment during infection. Therefore, we have found a novel mechanism of how vaccination protects against infection, through disease tolerance of the bacterial infection. With further research into the exact mechanism of B1 cells, these findings can potentially alter the future of vaccine development for bacterial pathogens that do not yet have a protective vaccine.