Citations

Abstract Introduction The H-2Db class I restricted CD8 T cell response is critical for clearance of neurotropic Theiler’s virus encephalomyelitis virus (TMEV) infection. However, the key central nervous system cell types required to present H-2Db for CD8 T cell trafficking and expansion in the brain are not known. Mural cells are a critical cellular component of the neurovascular unit for maintaining vascular integrity which also express MHC class I molecules. However, the importance of mural cell antigen-restricted engagement by CD8 T cells has not been investigated. Methods To determine the function of mural cell MHC Class I antigen presentation, we crossed the Pdgfrβ-creERT2 mouse to our novel H-2Db LoxP mouse developed by our laboratory. This transgenic mouse approach enabled us to target mural cells during neuroinflammation. Results We observed robust knockdown of H-2Db on mural cells during acute TMEV infection. Conditional H-2Db knockdown in mural cells resulted in increased brain infiltration of CD8 T cells specific to the immunodominant Db:VP2 121-130 epitope of TMEV, demonstrating an important role of mural cells for immune cell recruitment. Conclusion To our knowledge, this is the first study demonstrating MHC class I antigen presentation by mural cells impacts CD8 T cell recruitment during neuroinflammation. Funding Source R01-NS103212, T32-AI170478 Topic Categories Neuroimmunology (NEUR)

Abstract Introduction CD8 T cells are key immune cells in viral clearance, targeting infected cells following recognition of MHC class I restricted antigen presentation. Previous work has determined that microglia and perivascular macrophages are essential for normal CD8 T cell responses against neurotropic viral infection, indicating that cells at the neurovascular unit can act as antigen-presenting cells. However, the specific importance of microglia MHC class I restricted antigen presentation to brain-infiltrating CD8 T cells has been difficult to define. Methods To address this question, our laboratory generated novel single MHC Class I conditional knockout mice in which H-2Kb or H-2Db can be deactivated specifically in Tmem119+ microglia with tamoxifen administration. Recombinant Theiler’s murine encephalomyelitis virus (TMEV) encoding the model OVA antigen enabled analysis of virus antigen-specific CD8 T cells restricted to H-2Kb class I molecules while Daniel’s strain TMEV H-2Db class I molecules enabled analysis of Db:VP2 specific CD8 T cells. Results Our results revealed profound differences in the response of CD8 T cells upon deletion of MHC class I molecules on microglia. Conditional knockout of H-2Kb in Tmem119+ microglia reduced Kb:OVA epitope specific CD8 T cells in the brain compared to Cre negative littermate controls, and BrdU staining revealed differences in T cell proliferation. Meanwhile, mice with deletion of Db in Tmem119+ microglia had reduced levels of perforin in Db:VP2 CD8 T cells. Furthermore, in a model of CNS vascular disease, the deletion of H-2Db of Tmem119+ microglia reduced CD8 T cell numbers in the brain, as well as the blood-brain barrier (BBB) breakdown observed by a FITC albumin assay. Conclusion These findings demonstrate discrete roles for specific MHC Class I molecules on microglia during CNS viral infection. This data will further our understanding of brain infiltrating CD8 T cell responses in neurologic diseases as well as the regulation of BBB by microglia. Funding Source R01 NS 103212 R01 NS122174 Topic Categories Neuroimmunology (NEUR)

Abstract Introduction The anatomical locations of generating adaptive immune responses to neurotropic viruses are still being investigated. Skull bone marrow (BM) has recently been identified as a pivotal immune site that can sense and respond to a local insult in the brain. Yet, there is a lack of understanding of the role of skull BM during viral encephalitis. We hypothesized that the skull BM is an important niche for antiviral CD8 T cells priming, expansion, and maintenance during Theiler’s murine encephalomyelitis virus infection. Methods Using peptide:MHC tetramer analysis, we determined that antiviral CD8 T cells are primed in the skull BM in early infection, at time points comparable to cervical lymph nodes. Employing MHC class I conditional knockout mice generated by our research group, we inactivated H-2Kb and H-2Db class I molecules on discrete antigen-presenting cell types. Results We determined using these transgenic mice that viral antigen presentation on dendritic cells (DCs) and endothelial cells is essential for the generation of virus-specific T cells in skull BM during acute viral encephalitis. However, antigen presentation by DCs is not required for long-lived antiviral CD8 T cells that reside in skull BM. Moreover, the use of FTY720 to block lymphocyte migration diminished skull antiviral CD8 T cell numbers, suggesting that peripheral trafficking is required for generating skull antiviral CD8 T cells. Conclusion We present compelling evidence for the importance of skull BM as a responsive site that is highly suitable for rapid generation of antiviral CD8 T cells during acute viral encephalitis. Skull BM also serves as a reservoir for memory T cells, long after the resolution of a neurotropic virus infection. This work sheds light on the skull as a potential target for further modulation of the immune response to viral infections in the brain. Funding Source NIH grants R01 NS5103212 and RF1 NS122174 Topic Categories Viral Immunology (VIR)

Abstract The impact of microglia antigen presentation on CNS infiltrating CD8 T cells responses during neurotropic virus infection remains undefined. Using Theiler’s murine encephalomyelitis virus (TMEV) infection of neurons as a model system, we generated H-2K b and H-2D b Tmem119 conditional knockout mice. During TMEV infection, we determined using Tmem119 K b cKO mice that microglia H-2K b contributes to antiviral CD8 T cell proliferation in the brain. Meanwhile, using Tmem119 D b cKO mice we determined that microglia H-2D b increased antiviral CD8 T cell perforin levels and the capacity to induce blood-brain barrier (BBB) disruption. Furthermore, microglial H-2D b was essential for antigen-specific reactivation of CD8 tissue resident memory (TRM) cell recall responses and BBB disruption long after virus had been cleared. These findings demonstrate discrete roles of individual MHC class I genes on microglia in CD8 T cell proliferation, effector functions, memory recall and neuropathology.

Hypoxia is a prevalent characteristic of neurological diseases, including ischemic injury, neurodegeneration and infectious disease complications. Concurrently, hypoxia shapes both protective and pathological responses within the central nervous system (CNS). Central to this process is hypoxia-inducible factor 1α (HIF1α), a transcription factor that regulates cellular adaptation to reduced oxygen availability through coordinated glycolytic, inflammatory and cell survival pathways. Under hypoxic conditions, HIF1α transcriptional activity influences microglial activation, mitochondrial quality control, and cytokine production, thereby modulating neuroinflammation and neuroprotection. Preclinical evidence points toward hypoxia preconditioning being neuroprotective through HIF1α-dependent mechanisms in a context-dependent matter. This review synthesizes the current understanding of the role of HIF1α across neurological disease contexts, highlighting the intersection of hypoxia, neuroinflammation and neuronal survival. Ultimately, defining the cell-specific and context-dependent involvement of HIF1α will be critical for targeted therapeutic approaches to alleviate neuronal death and slow disease progression.

Abstract Skull bone marrow (BM) is a recently identified site for immune activation responsive to CNS insults. The extent to which adaptive immunity is generated through skull BM is poorly understood. In this study, we evaluated how skull BM supports the early expansion of antiviral CD8 T cells during acute neurotropic virus infection. Virus antigen-specific CD8 T cells were rapidly identified in skull BM at a rate comparable to lymphoid compartments during acute Theiler’s murine encephalomyelitis viral (TMEV) infection. We therefore employed MHC class I conditional knockout mice and demonstrated the necessity of CD11c+ antigen-presenting cells (APCs) for the generation of various subsets of TMEV-specific CD8 T cells in skull BM. Importantly, the early expansion of skull BM-derived antiviral T cells was impeded by FTY720 treatment and restored upon shared circulation with a mouse exhibiting intact antigen presentation by CD11c+ APCs. Additionally, TMEV-specific CD8 T cells were retained in skull BM during both chronic CNS infection and long after infection has been resolved. Overall, we determined that skull BM responds to acute neurotropic viral infection through the rapid recruitment of virus-specific CD8 T cells primed in the periphery before serving as a reservoir for immunologic memory.

Abstract The impact of microglia antigen presentation on CNS infiltrating CD8 T cells responses during neurotropic virus infection has been difficult to define. Using Theiler’s murine encephalomyelitis virus (TMEV) infection of neurons as a model system, our laboratory has previously determined that H-2D b restricted, but not H-2K b restricted CD8 T cells are required for viral clearance, demonstrating the role of discrete MHC class I alleles. To determine the extent microglia antigen presentation impacts brain-infiltrating CD8 T cells, our laboratory generated novel single MHC class I conditional knockout mice in which H-2K b or H-2D b can be specifically deactivated in TMEM119+ microglia with tamoxifen administration. During TMEV infection, conditional knockout of H-2K b in microglia reduced antigen-specific CD8 T cell proliferation in the brain. Meanwhile, mice with deletion of D b in microglia had reduced levels of perforin in antigen-specific CD8 T cells. Furthermore, microglia specific deletion of H-2D b reduced CD8 T cell numbers in the brain and preserved blood-brain barrier (BBB) integrity. Microglial D b restricted antigen presentation was also essential for the reactivation of CD8 tissue resident memory (TRM) cells and BBB integrity during memory recall responses. These findings further our understanding of how brain infiltrating antiviral CD8 T cell responses are impacted by microglia, as well as define how this cellular interaction contributes to BBB disruption during neuroinflammation. These findings also have high significance to our understanding of how microglia impact CD8 TRM cell populations that reside in the brain long after virus infection is cleared. Graphical abstract

Abstract Description The importance of microglia class I restricted antigen presentation to brain-infiltrating CD8 T cells has been difficult to define. To address this question, our laboratory generated novel single MHC Class I conditional knockout mice in which H-2Kb or H-2Db can be deactivated specifically in Tmem119+ microglia with tamoxifen administration. Recombinant Theiler’s murine encephalomyelitis virus (TMEV) encoding the model antigen OVA enabled analysis of virus antigen-specific CD8 T cells restricted to Kb class I molecules while Daniel’s strain TMEV Db class I molecules enabled analysis of Db:VP2 specific CD8 T cells. Our results revealed profound differences between MHC class I molecules. Conditional knockout of Kb in Tmem119+ microglia reduced Kb:OVA epitope specific CD8 T cells in the brain compared to Cre negative littermate controls. Employing methodology using FTY720 and BrdU labeling, we determined that deletion of Kb in Tmem119+ microglia reduced proliferation and numbers of Kb:OVA specific CD8 T cells in the brain compared to Cre negative littermate controls. Meanwhile, mice with deletion of Db in Tmem119+ microglia had reduced levels of perforin in Db:VP2 CD8 T cells. These findings demonstrate there are discrete roles for specific MHC Class I molecules on microglia during CNS viral infection. These results plus transgenic mouse systems will help further our understanding of brain infiltrating CD8 T cell responses in neurologic disease. Funding Sources Supported by R01NS122174 and R01NS103212 Topic Categories Neuroimmunology (NEUR)

Abstract Description Tauopathies are a subset of neurological diseases associated with pathologic tau protein accumulation and the formation of neurofibrillary tangles in the brain. There is growing evidence of immune cell infiltration including T cells and an increase of inflammatory microglia in human brains from patients that have Tauopathies. However, the effect of T cells and how they interact with CNS-resident immune cells in these pathologies is not well understood. To answer this question, we developed a neurotropic AAV1 encoding human mutant P301L-Tau. AAV-Tau transduction of neurons in neonatal mice recapitulates features of Tauopathies found in human patients. As microglia are the predominant resident antigen presenting cells within the CNS, we hypothesized that CD8 T cells may be dependent on MHC class I presentation by microglia in mice with Tauopathy to achieve full infiltration and expansion in the brain. To address this hypothesis, we introduced AAV-Tau into our novel transgenic mice for which MHC class I antigen presentation by H-2Kb on microglia can be conditional ablated. We observed lower frequencies of CD8 T cell populations and less CD8 T cell CD69+CD103+ expression in mice with Tauopathy when MHC class I was ablated in microglia. We conclude that microglia class I restricted antigen presentation contributes to the expansion of resident memory CD8 T cells in experimental Tauopathy and therefore are an important driver of the immune response observed in this dementia model. Funding Sources NIH/NINDS: R01NS122174 Mayo Graduate School of Biomedical Sciences Topic Categories Neuroimmunology (NEUR)

Abstract Description Brain Barrier (BBB) disruption plays a role in various neurodegenerative diseases such as ALS, stroke, Huntington’s disease and Cerebral Malaria. In our laboratory, we aim to interrogate the immunological underpinnings associated with neuroinflammation and barrier leakage. In clinical studies, aging is associated with a decline in T cell production and a gradual shift to resident memory T cells in the brain characterized by reduced T cell repertoire diversity and weak activation. To model these clinical observations, we sought to define the effect of MHC class I restricted antigen presentation on endothelial cells of brain vasculature on CD8 T cell infiltration of the CNS. We conditionally ablated H-2Kb and H-2Db molecules on endothelial cells using Cdh5-Cre mice crossed with our novel Kb LoxP and Db LoxP mice generated by our research program. In these animals we studied CD8 T cell accumulation in the brain using Theiler’s Murine Endothelial Virus (TMEV) infection of young mice (<12 months) compared to old mice (>12 months). Our results indicate that the loss of endothelial cell Kb induces a defect in establishment of antigen experienced CD8 T cell populations in acute infection. These finding will allow us to further investigate the role of endothelial cell MHC Class I molecules in the immune response to chronic TMEV infection, as well as other neurologic disease models. Funding Sources NIH Grants R01 NS103212 and R01 NS122174 Topic Categories Neuroimmunology (NEUR)