Lisa Osborne

Intestinal commensal microorganisms play a critical role in promoting host health, but these organisms must be carefully managed. Breakdowns in the host’s ability to regulate these commensals can at best result in the loss of these health-promoting functions, and at worst lead to severe inflammation and death.In contrast to host-encoded regulation of bacterial commensals, less is understood about regulation of viral commensals. The so-called virome is increasingly understood to influence host health in both similar and distinct ways to the bacterial microbiome. In this thesis, I utilize the model murine viral commensal MNV CR6 to study host-encoded regulation of viral commensals, as well as the consequences of a failure to regulate these infections.STAT1 has previously been identified as an important host-encoded factor for the regulation of CR6 and other viruses. Using STAT1-deficient mice, I characterize a CR6-induced disease which consists of hyperinflammatory innate and adaptive immune responses, multi-organ inflammatory necrosis, and severe clinical disease requiring euthanasia. STAT1 has previously been shown to protect the host from disease following pathogenic viral infection by limiting the magnitude of T cell responses. However, in CR6 infection, STAT1 instead protects the host from disease by limiting viral replication within responding innate immune cells. Following this, I characterize the complex inflammatory milieu which precedes hepatic necrosis in the absence of STAT1.Environmental perturbations also influence regulation of viral infections. In particular, antibiotic treatment of mice has previously been shown to suppress the generation of antiviral immune responses. While this effect has been ascribed to depletion of the bacterial microbiota, existing evidence also suggests the alternative mechanism of direct effects of antibiotics on host cells. Using germ-free mice, I demonstrate that antibiotic-mediated immunosuppression is microbiota-independent in the context of CR6 infection. Mice treated with an antibiotic cocktail fail to generate virus-specific CD8+ T cells, and my data suggest this effect is mediated though suppression of dendritic cell’s ability to activate T cells.Together, my data describe novel mechanisms influencing the ability of the host to regulate commensal viral infection, and characterizes the consequences of a breakdown in this ability.

View record

Multiple sclerosis (MS) is an autoimmune neurodegenerative disease caused by autoreactive T cells that invade the central nervous system (CNS). The cause of MS remains unknown, and particularly the environmental components of disease susceptibility remain poorly understood. Perturbations of the intestinal environment, whether through infection or by an altered gut microbiome, have demonstrated striking abilities to modulate MS-like disease in animal models, either in protective or pathogenic capacities. Here, we investigate three distinct modalities by which modulation of the intestinal ecosystem alters disease course of experimental autoimmune encephalomyelitis (EAE), a mouse model of MS.Dietary fibres are potent modulators of immune responses that can restrain inflammation in multiple disease contexts. I demonstrate a potent ability of the dietary fibre guar gum to delay disease and neuroinflammation in EAE. These findings reveal specificity in the host response to fibre sources and define a pathway of fibre-induced immunomodulation that protects against pathologic neuroinflammation.Both people of advanced age and people with MS exhibit alterations in the gut microbiome and its associated metabolites; however, the relationship between these observations is poorly characterized. Here, I establish an age-dependent mouse model of progressive MS, and adapt this model to test the effects of an age-associated microbiota on disease progression. These findings provide a framework for metabolite discovery associated with EAE disease chronicity and severity.The immune response to helminths is diametrically opposed to the immune response generated during inflammatory autoimmune diseases, which has provoked investigation into harnessing helminths as immunotherapy in MS. Here, I describe the ability of the helminth Trichinella spiralis to ameliorate EAE, both prophylactically and therapeutically. These findings highlight the therapeutic potential of helminth-evoked immune responses to reduce neuroinflammation in people with MS.Collectively, these findings highlight the diversity of mechanisms by which the immune system and development of neuroinflammatory disease can be altered by the intestinal environment. Each of the modalities evaluated here identify novel mechanisms that could be harnessed for therapeutic benefit in people with MS.

View record

The combination of diverse metabolism, large microbial community, and vast surface area make the intestines a complex immunological challenge. Mucosal immune responses must target infections while limiting disruptions to intestinal function or off-target reactions in the antigen-rich environment. Regulation of this balance, which is shaped locally by tissue-specific cues, and distally in secondary lymphoid organs, is not fully understood. Exploring these concepts promises insights into vaccine development and treatment of inflammatory digestive diseases. Intestinal epithelial cells (IECs) not only maintain a barrier between the external environment and host tissues, they are also active participants in local immune homeostasis. Based on prior observations that IEC-intrinsic canonical and non-canonical NF-κB activation via the kinases IKKβ and IKKα shape the inflammatory tone of immune responses to helminth and bacterial infections, I hypothesized that IEC-intrinsic NF-κB signalling may be a conserved mediator of inflammation elicited by enteric infections. However, in the context of acute or persistent intestinal murine norovirus (MNV strain CW3 or CR6) infection, there was no detectable effect on viral loads or antiviral CD8⁺ effector T cells in the absence of either IKKα or IKKβ in IECs. To assess how antiviral CD8⁺ T cell distribution along the length of the gastrointestinal (GI) tract is regulated, I used tissue microscopy and flow cytometry following infection with MNV CW3 and CR6. I found that the initial intestinal site of infection dictates which node of the mesenteric lymph node (MLN) complex hosts the earliest CD8⁺ T cell responses. However, later stages of T cell expansion and localization within the GI tract are driven by virus-specific behavior. My results suggest that in the absence of systemic infection, antiviral effector cells primed in the spleen are not equipped for intestinal access. Understanding how intestinal access is granted will be valuable in designing oral vaccines while methods of enforcing intestinal immune seclusion may provide a means of preventing or limiting flareups in people with inflammatory digestive diseases. This work outlines avenues of inquiry using MNV strains in a comparative model to contrast CD8⁺ T cell responses and delineate cues which influence the distribution and scale of immune responses.

View record