Browsing by Author "McDonald, Braedon"
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- ItemOpen AccessCharacterizing the Immunological Role of Pulmonary Stretch Receptors(2022-06-14) Fatehi Hassanabad, Mortaza; George Yipp, Bryan; Robert Gillrie, Mark; McDonald, Braedon; Altier, ChristopheBreathing and the resulting exchange of oxygen and carbon dioxide are normally accomplished by pressure changes within the lungs. As we inhale, chest and diaphragm muscles increase the size of our chest cavity, in turn expanding our lungs. This increase in lung volume results in a pressure gradient whereby air from higher pressure areas (i.e. the atmosphere) flows into and fills our lungs, which are at a lower pressure. Exhalation follows the reverse of this process, and so, our bodies effortlessly carry out this vital function more than 20,000 times per day. Lungs contain receptors that are highly sensitive to mechanical stimuli such as pressure changes, cyclic strain, and shear flow. Such receptors are especially relevant to the lung as it is an organ that is frequently exposed to mechanical forces during breathing. This diverse group of molecules, also known as mechanoreceptors, can be found on sensory neurons, epithelium, leukocytes, and numerous other tissues; however, their functions in the lung during infections and inflammation remain obscure. One such mechanosensitive ion channel is TRPV4 which is evolutionarily conserved across all mammalian species and has become increasingly associated with immunological function in recent years. In this body of work, we investigated how mechanoreceptors (and more specifically TRPV4) modify the pulmonary immune response during host defense and inflammation. We have found that mechanical forces affect lung architecture, capillary barrier function, and bacterial dissemination in our rodent models. Moreover, inhibiting TRPV4 using commercially available agents reduces mortality and improves clinical sickness scores during Staphylococcus aureus pneumonia. We have also observed improved immune cell viability and altered neuropeptide levels using these same compounds suggesting that there may be additional neuroimmune mechanisms at play. These findings enhance our current understanding of lung mechanoreceptors and may be useful for identifying future pharmacological interventions during bacterial pneumonia.
- ItemOpen AccessDevelopment and characterization of a fecal-induced peritonitis model of murine sepsis: results from a multi-laboratory study and iterative modification of experimental conditions(2023-07-17) Sharma, Neha; Chwastek, Damian; Dwivedi, Dhruva J.; Schlechte, Jared; Yu, Ian-Ling; McDonald, Braedon; Arora, Jaskirat; Cani, Erblin; Eng, Mikaela; Engelberts, Doreen; Kuhar, Eva; Medeiros, Sarah K.; Bourque, Stephane L.; Cepinskas, Gediminas; Gill, Sean E.; Jahandideh, Forough; Macala, Kimberly F.; Panahi, Sareh; Pape, Cynthia; Sontag, David; Sunohara-Neilson, Janet; Fergusson, Dean A.; Fox-Robichaud, Alison E.; Liaw, Patricia C.; Lalu, Manoj M.; Mendelson, Asher A.Abstract Background Preclinical sepsis models have been criticized for their inability to recapitulate human sepsis and suffer from methodological shortcomings that limit external validity and reproducibility. The National Preclinical Sepsis Platform (NPSP) is a consortium of basic science researchers, veterinarians, and stakeholders in Canada undertaking standardized multi-laboratory sepsis research to increase the efficacy and efficiency of bench-to-bedside translation. In this study, we aimed to develop and characterize a 72-h fecal-induced peritonitis (FIP) model of murine sepsis conducted in two independent laboratories. The experimental protocol was optimized by sequentially modifying dose of fecal slurry and timing of antibiotics in an iterative fashion, and then repeating the experimental series at site 1 and site 2. Results Escalating doses of fecal slurry (0.5–2.5 mg/g) resulted in increased disease severity, as assessed by the modified Murine Sepsis Score (MSS). However, the MSS was poorly associated with progression to death during the experiments, and mice were found dead without elevated MSS scores. Administration of early antibiotics within 4 h of inoculation rescued the animals from sepsis compared with late administration of antibiotics after 12 h, as evidenced by 100% survival and reduced bacterial load in peritoneum and blood in the early antibiotic group. Site 1 and site 2 had statistically significant differences in mortality (60% vs 88%; p < 0.05) for the same dose of fecal slurry (0.75 mg/g) and marked differences in body temperature between groups. Conclusions We demonstrate a systematic approach to optimizing a 72-h FIP model of murine sepsis for use in multi-laboratory studies. Alterations to experimental conditions, such as dose of fecal slurry and timing of antibiotics, have clear impact on outcomes. Differences in mortality between sites despite rigorous standardization warrants further investigations to better understand inter-laboratory variation and methodological design in preclinical studies.
- ItemOpen AccessGastrointestinal colonization by Candida albicans modulates host defence in sepsis(2024-05-07) Changirwa, Diana Kasoha; McDonald, Braedon; Arrieta, Marie Claire; Mody, ChristopherPathological dysbiosis of the intestinal microbiome can lead to defects in immune homeostasis and a breakdown in host defense that increases susceptibility to infection. This is particularly relevant in patients with sepsis, a disorder of infection-induced systemic immune dysregulation and multi-organ dysfunction, where dysbiosis of the bacterial microbiome in these patients has been associated with adverse clinical outcomes. However, the impact of the fungal microbiome on sepsis pathogenesis has not been characterized. Analysis of the gut fungal microbiome in critically ill patients with sepsis identified severe fungal dysbiosis driven by marked overgrowth of Candida. Based on these clinical observations, we sought to investigate the functional impact of intestinal Candida overgrowth on systemic inflammation and host defense using mouse models. We colonized the gastrointestinal tracts of antibiotic-conditioned SPF C57BL/6 mice with different strains of C. albicans (including hyphal and yeast morphotypes) for 10 days prior to infection/sepsis with a well-characterized model of S. aureus bloodstream infection. The data indicated that colonizing mice with a yeast-locked strain of C. albicans displayed reduced illness severity, reduced systemic inflammation, and enhanced protection against systemic pathogen dissemination compared to uncolonized mice. In contrast, mice colonized with hyphal/filamentous C. albicans displayed similar illness severity, systemic inflammation, and pathogen burden as uncolonized controls. Further analysis of the immune landscape with mass cytometry indicated that yeast colonized mice have increased liver neutrophils. To test the therapeutic applicability of these findings, we treated hyphal colonized with yeast C. albicans to determine if it could displace hyphal C. albicans and impart immunological benefits. We found that yeast-treated mice had hyphal C. albicans physically displaced from their gut compartment by yeast treatment, and these treated mice had reductions in systemic pathogen burden. To expand upon this, we determined that genetically yeast locked strains (flo8-/-) are also able to displace wild-type C. albicans (SC5314), suggesting that these findings are likely applicable to a diverse amount of yeast-locked strains. Together, this project determined the impact of C. albicans gut colonization on the systemic host response, while describing immune mechanisms mediating this response and identifying the therapeutic potential of treatment with yeast C. albicans.
- ItemOpen AccessImpact of age on the host response to sepsis in a murine model of fecal-induced peritonitis(2024-03-08) Sharma, Neha; Chen, Alex; Heinen, Leah; Liu, Ruth; Dwivedi, Dhruva J.; Zhou, Ji; Lalu, Manoj M.; Mendelson, Asher A.; McDonald, Braedon; Kretz, Colin A.; Fox-Robichaud, Alison E.; Liaw, Patricia C.Abstract Introduction Despite older adults being more vulnerable to sepsis, most preclinical research on sepsis has been conducted using young animals. This results in decreased scientific validity since age is an independent predictor of poor outcome. In this study, we explored the impact of aging on the host response to sepsis using the fecal-induced peritonitis (FIP) model developed by the National Preclinical Sepsis Platform (NPSP). Methods C57BL/6 mice (3 or 12 months old) were injected intraperitoneally with rat fecal slurry (0.75 mg/g) or a control vehicle. To investigate the early stage of sepsis, mice were culled at 4 h, 8 h, or 12 h to investigate disease severity, immunothrombosis biomarkers, and organ injury. Mice received buprenorphine at 4 h post-FIP. A separate cohort of FIP mice were studied for 72 h (with buprenorphine given at 4 h, 12 h, and then every 12 h post-FIP and antibiotics/fluids starting at 12 h post-FIP). Organs were harvested, plasma levels of Interleukin (IL)-6, IL-10, monocyte chemoattract protein (MCP-1)/CCL2, thrombin-antithrombin (TAT) complexes, cell-free DNA (CFDNA), and ADAMTS13 activity were quantified, and bacterial loads were measured. Results In the 12 h time course study, aged FIP mice demonstrated increased inflammation and injury to the lungs compared to young FIP mice. In the 72 h study, aged FIP mice exhibited a higher mortality rate (89%) compared to young FIP mice (42%) (p < 0.001). Aged FIP non-survivors also exhibited a trend towards elevated IL-6, TAT, CFDNA, CCL2, and decreased IL-10, and impaired bacterial clearance compared to young FIP non-survivors. Conclusion To our knowledge, this is the first study to investigate the impact of age on survival using the FIP model of sepsis. Our model includes clinically-relevant supportive therapies and inclusion of both sexes. The higher mortality rate in aged mice may reflect increased inflammation and worsened organ injury in the early stage of sepsis. We also observed trends in impaired bacterial clearance, increase in IL-6, TAT, CFDNA, CCL2, and decreased IL-10 and ADAMTS13 activity in aged septic non-survivors compared to young septic non-survivors. Our aging model may help to increase the scientific validity of preclinical research and may be useful for identifying mechanisms of age-related susceptibility to sepsis as well as age-specific treatment strategies.
- ItemOpen AccessInvestigating the Sexual Dimorphism of Disease Tolerance in Sepsis(2023-12-04) Dobson, Breenna; McDonald, Braedon; Jenne, Craig; Nasser, YasminSepsis is a dysregulated immune response to infection, with mortality rates as high as 30%, however, there are currently no disease-modifying treatments for this disease. One of the reasons why preclinical sepsis discoveries have failed to translate into effective human therapies is that interindividual heterogeneity has historically been neglected in preclinical sepsis research, including the fundamental contributions of biological sex on disease pathogenesis and treatment response. Epidemiologic studies have observed that males have a higher incidence, severity and mortality rate than females in sepsis, however, the mechanisms underlying this bias have not yet been established. This thesis aims to examine potential underlying mediators of the sexual dimorphism within sepsis illness severity. We investigated the impact of biological sex on host defence using a well-established mouse model of sepsis induced by fecal peritonitis. We used this model to study three principal mediators of sex- based immune response differences: the gut microbiota, sex chromosomes and sex hormones. To uncover differences in these mediators we used a transgenic and germ-free mouse model. Further, we aimed to understand the sex-based influence on infection tolerance and resistance. Lastly, we completed preliminary studies on sex-based differences in infection tolerance using a tetracycline antibiotic as a potentiator of mitochondrial tolerance. This project addressed a critical gap within sepsis research and revealed biological sex differences in infection tolerance and potential therapeutic implications.
- ItemOpen AccessMicrobiota-Immune Interactions and Host Defense in Sepsis(2023-04-18) Zucoloto, Amanda; McCoy, Kathy; McDonald, Braedon; Arrieta, Marie Claire; Yipp, BryanGut microbial dysbiosis is associated with increased susceptibility to infectious diseases, including systemic infection and sepsis. While the impact of the microbiota on intestinal homeostasis is well recognized, gut commensals also influence several processes in extraintestinal niches, including host defense against systemic infection. This thesis aimed to study the microbiota-immune interactions that promote host defense against bacterial sepsis at a cellular and molecular level. Using gnotobiotic mouse models and resonant scanning confocal intravital microscopy, I demonstrated that mice devoid of gut commensals show defective intravascular immune responses against staphylococcal sepsis. In germ-free mice, impaired Kupffer cell-mediated bacterial capture and neutrophil trafficking in the liver contribute to increased bacterial dissemination and host mortality. Gut microbiota-dependent regulation of intravascular immunity is dynamic and partly rescued by replenishing gut-derived D-lactate, indicating this bacterial metabolite mediates the crosstalk between the gut microbiota and the liver microenvironment. D-lactate enhances bacterial clearance by Kupffer cells and primes the liver endothelium to respond robustly to inflammatory stimuli, leading to increased neutrophil adherence after infection. Altogether, this thesis uncovers a line of communication between the gut microbiota and the liver microenvironment that is pivotal for intravascular immune defense against sepsis.
- ItemOpen AccessMolecular mechanisms of neutrophil recruitment in the liver microcirculation(2012) McDonald, Braedon; Kubes, Paul
- ItemOpen AccessNational Preclinical Sepsis Platform: developing a framework for accelerating innovation in Canadian sepsis research(2021-03-19) Mendelson, Asher A; Lansdell, Casey; Fox-Robichaud, Alison E; Liaw, Patricia; Arora, Jaskirat; Cailhier, Jean-François; Cepinskas, Gediminas; Charbonney, Emmanuel; dos Santos, Claudia; Dwivedi, Dhruva; Ellis, Christopher G; Fergusson, Dean; Fiest, Kirsten; Gill, Sean E; Hendrick, Kathryn; Hunniford, Victoria T; Kowalewska, Paulina M; Krewulak, Karla; Lehmann, Christian; Macala, Kimberly; Marshall, John C; Mawdsley, Laura; McDonald, Braedon; McDonald, Ellen; Medeiros, Sarah K; Muniz, Valdirene S; Osuchowski, Marcin; Presseau, Justin; Sharma, Neha; Sohrabipour, Sahar; Sunohara-Neilson, Janet; Vázquez-Grande, Gloria; Veldhuizen, Ruud A W; Welsh, Donald; Winston, Brent W; Zarychanski, Ryan; Zhang, Haibo; Zhou, Juan; Lalu, Manoj MAbstract Despite decades of preclinical research, no experimentally derived therapies for sepsis have been successfully adopted into routine clinical practice. Factors that contribute to this crisis of translation include poor representation by preclinical models of the complex human condition of sepsis, bias in preclinical studies, as well as limitations of single-laboratory methodology. To overcome some of these shortcomings, multicentre preclinical studies—defined as a research experiment conducted in two or more research laboratories with a common protocol and analysis—are expected to maximize transparency, improve reproducibility, and enhance generalizability. The ultimate objective is to increase the efficiency and efficacy of bench-to-bedside translation for preclinical sepsis research and improve outcomes for patients with life-threatening infection. To this end, we organized the first meeting of the National Preclinical Sepsis Platform (NPSP). This multicentre preclinical research collaboration of Canadian sepsis researchers and stakeholders was established to study the pathophysiology of sepsis and accelerate movement of promising therapeutics into early phase clinical trials. Integrated knowledge translation and shared decision-making were emphasized to ensure the goals of the platform align with clinical researchers and patient partners. 29 participants from 10 independent labs attended and discussed four main topics: (1) objectives of the platform; (2) animal models of sepsis; (3) multicentre methodology and (4) outcomes for evaluation. A PIRO model (predisposition, insult, response, organ dysfunction) for experimental design was proposed to strengthen linkages with interdisciplinary researchers and key stakeholders. This platform represents an important resource for maximizing translational impact of preclinical sepsis research.
- ItemEmbargoNeutrophil- and B cell-mediated host defense against viral and fungal respiratory infections(2024-03-21) Sarden, Nicole; Yipp, Bryan; Kelly, Margaret; McDonald, BraedonInfections of the lung continue to be a worldwide annual problem affecting millions of people. Fighting acute respiratory infections requires rapid and collaborative responses involving diverse immune cells. An interesting and unexplained clinical problem that sparked this thesis was the clinical observation that influenza A, a common respiratory virus, increases susceptibility to secondary infections with environmental fungi such as Aspergillus fumigatus (Af). By establishing a mouse model of viral-fungal co-infection and using clinical human samples, I discovered an essential collaboration between an underappreciated innate B lymphocyte, called B1a, which produced natural antibodies against Af, which tagged the fungi for elimination by neutrophils. Following influenza A infections, B1a cells died of apoptosis leading to diminished natural anti-Af antibodies and negating the ability of neutrophils to target and eliminate Af. Disruption of this axis explained susceptibility in viral- and steroid-associated infections. Delving deeper into the requirements of immune cell resistance to influenza and Af as individual infections, I discovered unique roles for neutrophils during influenza and innate B cells in aspergillosis. While there is ample research investigating neutrophils and their roles during infections with extracellular pathogens, it remained unclear how the neutrophil pool is affected following viral infections and subsequent functional outcomes. Additionally, it has been recently proposed that an interferon-responsive neutrophil state with unknown functions emerges following viral infections. In isolated viral infection, I found neutrophils adapt to an anti-viral phenotype which is spatially regulated, requires type I interferon licensing and sympathetic drive. On the other hand, using a genetically engineered mouse, we studied the specific roles of innate B1a cells during Aspergillus infection and found that this rare antibody producing cells was essential for host resistance against isolated Af infection. Moreover, I discovered key molecular requirements of the B1a cells that allow them to traffic and recruit properly in the lung, and I discovered that these cells can be amplified to improve host defense against Af. Altogether, this body of work uncovers neutrophils’ effects following isolated viral infection and during co-infection and demonstrates the tight interconnectedness between neutrophils and B lymphocytes which are critical for anti-fungal immunity.
- ItemOpen AccessSex-based analysis of treatment responses in animal models of sepsis: a preclinical systematic review protocol(2023-03-21) Zhang, MengQi; Fergusson, Dean A.; Sharma, Rahul; Khoo, Ciel; Mendelson, Asher A.; McDonald, Braedon; Macala, Kimberly F.; Sharma, Neha; Gill, Sean E.; Fiest, Kirsten M.; Lehmann, Christian; Shorr, Risa; Jahandideh, Forough; Bourque, Stephane L.; Liaw, Patricia C.; Fox-Robichaud, Alison; Lalu, Manoj M.Abstract Background The importance of investigating sex- and gender-dependent differences has been recently emphasized by major funding agencies. Notably, the influence of biological sex on clinical outcomes in sepsis is unclear, and observational studies suffer from the effect of confounding factors. The controlled experimental environment afforded by preclinical studies allows for clarification and mechanistic evaluation of sex-dependent differences. We propose a systematic review to assess the impact of biological sex on baseline responses to disease induction as well as treatment responses in animal models of sepsis. Given the lack of guidance surrounding sex-based analyses in preclinical systematic reviews, careful consideration of various factors is needed to understand how best to conduct analyses and communicate findings. Methods MEDLINE and Embase will be searched (2011-present) to identify preclinical studies of sepsis in which any intervention was administered and sex-stratified data reported. The primary outcome will be mortality. Secondary outcomes will include organ dysfunction, bacterial load, and IL-6 levels. Study selection will be conducted independently and in duplicate by two reviewers. Data extraction will be conducted by one reviewer and audited by a second independent reviewer. Data extracted from included studies will be pooled, and meta-analysis will be conducted using random effects modeling. Primary analyses will be stratified by animal age and will assess the impact of sex at the following time points: pre-intervention, in response to treatment, and post-intervention. Risk of bias will be assessed using the SYRCLE’s risk-of-bias tool. Illustrative examples of potential methods to analyze sex-based differences are provided in this protocol. Discussion Our systematic review will summarize the current state of knowledge on sex-dependent differences in sepsis. This will identify current knowledge gaps that future studies can address. Finally, this review will provide a framework for sex-based analysis in future preclinical systematic reviews. Systematic review registration PROSPERO CRD42022367726.
- ItemOpen AccessThymic Development of Microbe-Specific T Cells and Their Effects on Antimicrobial Antibody Responses(2022-03-24) Wilson, Kirsten; Geuking, Markus; Peters, Nathan; McDonald, BraedonThe body of literature surrounding interactions between the microbiota, T cells and B cells has grown substantially in recent years, but several questions remain. This thesis worked towards filling knowledge gaps in this field. Research from the Geuking lab has shown that mice primed with E. coli_gp61 produced a significantly greater E. coli-specific immunoglobulin (Ig) response compared to mice challenged with wild-type (WT) E. coli. My research has shown these antimicrobial antibodies to be T cell dependent with Class Switch Recombination (CSR) increasing bacterial specific IgM on day 7 and bacterial specific IgG on day 14. Following this finding, it was determined that in vitro fitness of E. coli is comparable between WT E. coli, E. coli_gp61 and E. coli_OmpC KO, but these bacteria display unique metabolic profiles with E. coli_gp61 and E. coli_OmpC KO displaying the most similarities. To test the effect of bacterial antigens in the thymus as well as the effect of metabolites on selection in the thymus, an organotypic thymic culture system was then utilized. Thymic slices were able to recognize pure peptide but were unable to independently process and present bacterial antigens. Intestinal-derived bacterial metabolites were able to reach the thymus and modulate negative selection and nTreg generation shown by GF mice producing more nTregs and having less CD4+CD8+ cells in response to self-peptide compared to sDMDMm2 or SPF mice. Finally, Recent Thymic Emigrants (RTEs) showed comparable thymic output in vivo between GF and SPF mice. Overall, these results show important differences between both thymic development of microbe-specific T cells and their effects on systemic antimicrobial antibody responses in GF and SPF mice, adding to our body of knowledge surrounding microbiota, T cell and B cell interactions.