Witt, Lila T.

Abstract Description Neonatal sepsis caused by bacteria such as Escherichia coli affects 1.3 million infants a year. The immunological responses activated in neonates during neonatal sepsis are currently thought to overwhelm the infant. Understanding where to intervene in the inflammatory response could lead to the development of therapeutics. Using Nur77-GFP reporter mice and our established animal models of neonatal sepsis, we observed γδ T cells-innate-like lymphocytes- are activated in a TCR-dependent manner in response to pathogenic bloodstream E. coli infection in neonatal mice (post-natal day 5-7). We find a subset of γδ T cells show similar levels of TCR-dependent activation of following infection with either pathogenic or commensal E. coli. In pathogenic bloodstream E. coli infection, there is a significant release of pro-inflammatory cytokines IL-17 by these CCR6+ γδ T cells in addition to IL-6 in the serum compared to serum in commensal infection. We found that in neonatal mice, CCR6+ γδ T cells have high expression of IL-6 receptor, and preliminary data suggests IL-6 blockade reduces IL-17 production. In summary, this suggests that during an E. coli systemic infection, the IL-17 producing γδ T cells are being activated by IL-6 due to higher levels of IL-6 receptor. Further work will seek to understand how γδ T cells may detrimentally contribute to neonatal sepsis outcomes. Topic Categories Microbial, Parasitic, and Fungal Immunology (MPF)

Abstract Bacterial bloodstream infections (BSIs) remain a significant contributor to neonatal mortality, despite improved hygienic practices in the NICU. Although the understanding of the neonatal immune system has increased greatly over the past decade, why neonates, but not older infants, are susceptible to severe adverse immunopathology – sepsis – in response to bacteremia remains poorly understood. In the present study, we find that postnatal day 5 (P5) neonatal γδ T cells are highly inflammatory during a mouse model of E. coli BSI and are associated with mortality. Furthermore, γδ T cells in P5 mice rapidly produce pro-inflammatory cytokines, such as IFN-γ, IL-17A, and TNFα, and increase their expression of cytotoxic molecules such as granzyme and perforin. Interestingly, blockade of the γδ TCR in vivo is associated with increased survival and decreased pro-inflammatory cytokine production in P5 pups. Signaling and activation via the γδ TCR was confirmed using Nur77-GFP mice, with P5 γδ T cells significantly upregulating expression of Nur77 during in vivo infection. Intriguingly, E. coli BSI in P15 pups results in markedly different γδ T cells responses compared to neonates, despite similar systemic bacterial burden. During bacterial bloodstream infection, P15 pups do not experience mortality, and unergo minimal activation of γδ T cells and production of IFN-γ, IL-17A, and TNFα. Furthermore, BSI infection in P15 Nur77-GFP mice revealed lack of TCR signaling in P15 γδ T cells at this age. In conclusion, the present study reveals rapid age-dependent changes to γδ T cell responses during early life and suggests neonates may be uniquely susceptible to γδ T cell-mediated immunopathology during bacterial bloodstream infection. T32 AI170478-01

AbstractThe increasing incidence of food allergy remains a significant public health concern. Food allergy is partially due to a lack, or loss of tolerance to food allergens. Clinical outcomes surrounding early life practices, such as breastfeeding, antibiotic use and food allergen exposure, indicate the first year of life in children represents a unique time for shaping the immune system to reduce allergic outcomes. Animal models have identified distinctive aspects of when and where dietary antigens are delivered within the intestinal tract to promote oral tolerance prior to weaning. Additionally, animal models have identified contributions from maternal proteins from breast milk and bacterial products from the gut microbiota in regulating dietary antigen exposure and promoting oral tolerance, thus connecting decades of clinical observations on the benefits of breastfeeding, early food allergen introduction and antibiotic avoidance in the first year of life in reducing allergic outcomes. Here, we discuss how exposure to gut luminal antigens, including food allergens, is regulated in early life to generate protective tolerance and the implications of this process for preventing and treating food allergies.

Abstract Immunosuppression of unknown aetiology is a hallmark feature of glioblastoma and is characterized by decreased CD4 T-cell counts and downregulation of major histocompatibility complex class II expression on peripheral blood monocytes in patients. This immunosuppression is a critical barrier to the successful development of immunotherapies for glioblastoma. We recapitulated the immunosuppression observed in glioblastoma patients in the C57BL/6 mouse and investigated the aetiology of low CD4 T-cell counts. We determined that thymic involution was a hallmark feature of immunosuppression in three distinct models of brain cancer, including mice harbouring GL261 glioma, B16 melanoma, and in a spontaneous model of diffuse intrinsic pontine glioma. In addition to thymic involution, we determined that tumour growth in the brain induced significant splenic involution, reductions in peripheral T cells, reduced MHC II expression on blood leucocytes, and a modest increase in bone marrow resident CD4 T cells. Using parabiosis we report that thymic involution, declines in peripheral T-cell counts, and reduced major histocompatibility complex class II expression levels were mediated through circulating blood-derived factors. Conversely, T-cell sequestration in the bone marrow was not governed through circulating factors. Serum isolated from glioma-bearing mice potently inhibited proliferation and functions of T cells both in vitro and in vivo. Interestingly, the factor responsible for immunosuppression in serum is non-steroidal and of high molecular weight. Through further analysis of neurological disease models, we determined that the immunosuppression was not unique to cancer itself, but rather occurs in response to brain injury. Non-cancerous acute neurological insults also induced significant thymic involution and rendered serum immunosuppressive. Both thymic involution and serum-derived immunosuppression were reversible upon clearance of brain insults. These findings demonstrate that brain cancers cause multifaceted immunosuppression and pinpoint circulating factors as a target of intervention to restore immunity.

Abstract Theiler's murine encephalomyelitis virus (TMEV) infection of the CNS is cleared in C57BL/6 mice by a CD8 T cell response restricted by the MHC class I molecule H-2Db. The identity and function of the APC(s) involved in the priming of this T cell response is (are) poorly defined. To address this gap in knowledge, we developed an H-2Db LoxP-transgenic mouse system using otherwise MHC class I–deficient C57BL/6 mice, thereby conditionally ablating MHC class I–restricted Ag presentation in targeted APC subpopulations. We observed that CD11c+ APCs are critical for early priming of CD8 T cells against the immunodominant TMEV peptide VP2121-130. Loss of H-2Db on CD11c+ APCs mitigates the CD8 T cell response, preventing early viral clearance and immunopathology associated with CD8 T cell activity in the CNS. In contrast, animals with H-2Db–deficient LysM+ APCs retained early priming of Db:VP2121-130 epitope–specific CD8 T cells, although a modest reduction in immune cell entry into the CNS was observed. This work establishes a model enabling the critical dissection of H-2Db–restricted Ag presentation to CD8 T cells, revealing cell-specific and temporal features involved in the generation of CD8 T cell responses. Employing this novel system, we establish CD11c+ cells as pivotal to the establishment of acute antiviral CD8 T cell responses against the TMEV immunodominant epitope VP2121-130, with functional implications both for T cell–mediated viral control and immunopathology.