Jeremiah McDole

Induction of Blood Brain Barrier Tight Junction Protein Alterations by CD8 T Cells

Disruption of the blood brain barrier (BBB) is a hallmark feature of immune-mediated neurological disorders as diverse as viral hemorrhagic fevers, cerebral malaria and acute hemorrhagic leukoencephalitis. Although current models hypothesize that immune cells promote vascular permeability in human disease, the role CD8 T cells play in BBB breakdown remains poorly defined. Our laboratory has developed a novel murine model of CD8 T cell mediated central nervous system (CNS) vascular permeability using a variation of the Theilers virus model of multiple sclerosis. In previous studies, we observed that MHC class II−/− (CD4 T cell deficient), IFN-γR−/−, TNF-α−/−, TNFR1−/−, TNFR2−/−, and TNFR1/TNFR2 double knockout mice as well as those with inhibition of IL-1 and LTβ activity were susceptible to CNS vascular permeability. Therefore, the objective of this study was to determine the extent immune effector proteins utilized by CD8 T cells, perforin and FasL, contributed to CNS vascular permeability. Using techniques such as fluorescent activated cell sorting (FACS), T1 gadolinium-enhanced magnetic resonance imaging (MRI), FITC-albumin leakage assays, microvessel isolation, western blotting and immunofluorescent microscopy, we show that in vivo stimulation of CNS infiltrating antigen-specific CD8 T cells initiates astrocyte activation, alteration of BBB tight junction proteins and increased CNS vascular permeability in a non-apoptotic manner. Using the aforementioned techniques, we found that despite having similar expansion of CD8 T cells in the brain as wildtype and Fas Ligand deficient animals, perforin deficient mice were resistant to tight junction alterations and CNS vascular permeability. To our knowledge, this study is the first to demonstrate that CNS infiltrating antigen-specific CD8 T cells have the capacity to initiate BBB tight junction disruption through a non-apoptotic perforin dependent mechanism and our model is one of few that are useful for studies in this field. These novel findings are highly relevant to the development of therapies designed to control immune mediated CNS vascular permeability.

The role of CD8+ T-cells in lesion formation and axonal dysfunction in multiple sclerosis

Abstract The etiology of multiple sclerosis (MS) remains unknown. However, both genetic and environmental factors play important roles in its pathogenesis. While demyelination of axons is a hallmark histological feature of MS, axonal and neuronal dysfunction may correlate better with clinical disability. All major immune cell types have been implicated in the pathogenesis of MS, with the CD4+ T-cells being the most commonly studied. In this review, we discuss the involvement of CD8+ T-cells in MS. In addition, we review the contribution of CD8+ T-cells to the pathogenesis of experimental autoimmune encephalitis (EAE) and Theilers murine encephalomyelitis virus (TMEV) mouse models of MS, including the concept of CD8+ T-cell mediated axonal damage.

CD8 T Cell-Initiated Vascular Endothelial Growth Factor Expression Promotes Central Nervous System Vascular Permeability under Neuroinflammatory Conditions

Dysregulation of the blood-brain barrier (BBB) is a hallmark feature of numerous neurologic disorders as diverse as multiple sclerosis, stroke, epilepsy, viral hemorrhagic fevers, cerebral malaria, and acute hemorrhagic leukoencephalitis. CD8 T cells are one immune cell type that have been implicated in promoting vascular permeability in these conditions. Our laboratory has created a murine model of CD8 T cell-mediated CNS vascular permeability using a variation of the Theiler’s murine encephalomyelitis virus system traditionally used to study multiple sclerosis. Previously, we demonstrated that CD8 T cells have the capacity to initiate astrocyte activation, cerebral endothelial cell tight junction protein alterations and CNS vascular permeability through a perforin-dependent process. To address the downstream mechanism by which CD8 T cells promote BBB dysregulation, in this study, we assess the role of vascular endothelial growth factor (VEGF) expression in this model. We demonstrate that neuronal expression of VEGF is significantly upregulated prior to, and coinciding with, CNS vascular permeability. Phosphorylation of fetal liver kinase-1 is significantly increased early in this process indicating activation of this receptor. Specific inhibition of neuropilin-1 significantly reduced CNS vascular permeability and fetal liver kinase-1 activation, and preserved levels of the cerebral endothelial cell tight junction protein occludin. Our data demonstrate that CD8 T cells initiate neuronal expression of VEGF in the CNS under neuroinflammatory conditions, and that VEGF may be a viable therapeutic target in neurologic disease characterized by inflammation-induced BBB disruption.

The CD8 T cell in multiple sclerosis: suppressor cell or mediator of neuropathology?

Multiple sclerosis (MS) is the most common human demyelinating disease of the central nervous system. It is universally accepted that the immune system plays a major role in the pathogenesis of MS. For decades, CD4 T cells have been considered the predominant mediator of neuropathology in MS. This perception was largely due to the similarity between MS and CD4 T-cell-driven experimental allergic encephalomyelitis, the most commonly studied murine model of MS. Over the last decade, several new observations in MS research imply an emerging role for CD8 T cells in neuropathogenesis. In certain experimental autoimmune encephalomyelitis (EAE) models, CD8 T cells are considered suppressors of pathology, whereas in other EAE models, neuropathology can be exacerbated by adoptive transfer of CD8 T cells. Studies using the Theilers murine encephalomyelitis virus (TMEV) model have demonstrated preservation of motor function and axonal integrity in animals deficient in CD8 T cells or their effector molecules. CD8 T cells have also been demonstrated to be important regulators of blood-brain barrier permeability. There is also an emerging role for CD8 T cells in human MS. Human genetic studies reveal an important role for HLA class I molecules in MS susceptibility. In addition, neuropathologic studies demonstrate that CD8 T cells are the most numerous inflammatory infiltrate in MS lesions at all stages of lesion development. CD8 T cells are also capable of damaging neurons and axons in vitro. In this chapter, we discuss the neuropathologic, genetic, and experimental evidence for a critical role of CD8 T cells in the pathogenesis of MS and its most frequently studied animal models. We also highlight important new avenues for future research.

Intracerebral hemorrhage leads to infiltration of several leukocyte populations with concomitant pathophysiological changes

Intracerebral hemorrhage (ICH) is a stroke subtype with high rates of mortality and morbidity. The immune system, particularly complement and cytokine signaling, has been implicated in brain injury after ICH. However, the cellular immunology associated with ICH has been understudied. In this report, we use flow cytometry to quantitatively profile immune cell populations that infiltrate the brain 1 and 4 days post-ICH. At 1 day CD45hi GR-1+ cells were increased 2.0-fold compared with saline controls (P ≤ 0.05); however, we did not observe changes in any other cell populations analyzed. At 4 days ICH mice presented with a 2.4-fold increase in CD45hi cells, a 1.9-fold increase in CD45hi GR-1 cells, a 3.4-fold increase in CD45hi GR-1+ cells, and most notably, a 1.7-fold increase in CD4+ cells (P ≤ 0.05 for all groups), compared with control mice. We did not observe changes in the numbers of CD8+ cells or CD45lo cells (P = 0.43 and 0.49, respectively). Thus, we have shown the first use of flow cytometry to analyze leukocyte infiltration in response to ICH. Our finding of a CD4 T-cell infiltrate is novel and suggests a role for the adaptive immune system in the response to ICH.

Rapid Formation of Extended Processes and Engagement of Theiler's Virus-Infected Neurons by CNS-Infiltrating CD8 T Cells

A fundamental question in neuroimmunology is the extent to which CD8 T cells actively engage virus-infected neurons. In the Theilers murine encephalomyelitis virus (TMEV) model of multiple sclerosis, an effective central nervous system (CNS)-infiltrating antiviral CD8 T cell response offers protection from this demyelinating disease. However, the specific CNS cell types engaged by these protective CD8 T cells in TMEV-resistant strains remains unknown. We used confocal microscopy to visualize the morphology, migration, and specific cellular interactions between adoptively transferred CD8 T cells and specific CNS cell types. Adoptively transferred GFP+ CD8+ splenocytes migrated to the brain and became 93% specific for the immunodominant virus epitope D(b):VP2(121-130). These CD8 T cells also polarized T cell receptor, CD8 protein, and granzyme B toward target neurons. Furthermore, we observed CD8 T cells forming cytoplasmic processes up to 45 μm in length. Using live tissue imaging, we determined that these T cell-extended processes (TCEPs) could be rapidly formed and were associated with migratory behavior through CNS tissues. These studies provide evidence that antiviral CD8 T cells have the capacity to engage virus-infected neurons in vivo and are the first to document and measure the rapid formation of TCEPs on these brain-infiltrating lymphocytes using live tissue imaging.

A translatable molecular approach to determining CD8 T-cell epitopes in TMEV infection

Defining the epitope specificity of CD8+ T cells is an important goal in autoimmune and immune-mediated disease research. We have developed a translational molecular approach to determine the epitope specificity of CD8+ T cells using the Theilers murine encephalomyelitis virus (TMEV) model of multiple sclerosis (MS). TMEV-specific CD8+ T cells were isolated from brains and spleens of 7-day TMEV-infected C57BL/6J mice and stimulated by Cos-7 cells that were co-transfected with expression vectors encoding the D(b) class I molecule along with overlapping segments of the TMEV genome. Both brain-infiltrating and spleen-derived CD8+ T cells expressed IFN-gamma when Cos-7 cells were co-transfected with D(b) class I molecule and the TMEV genomic segment that encoded the immunodominant TMEV epitope. This demonstrated that peripheral and brain-infiltrating CD8+ T-cell responses were focused on peptide epitope(s) encoded by the same region of the TMEV genome. We propose that a similar molecular approach could also be used to determine the antigen specificity of suppressor CD8 T cells by the measurement of transforming growth factor-beta (TGF-beta) production. In addition, with a randomly generated library and peripheral blood or isolated CSF CD8+ T cells, this would be an effective method of predicting the epitope specificity of CD8+ T cells in human inflammatory CNS diseases, in animal models of MS or other organ-specific inflammatory diseases with a protective or pathogenic role of CD8 T cells.