Diane Sewell

Interleukin-6 promotes post-traumatic healing in the central nervous system

The central nervous system (CNS) is an immune-privileged site where the role of immune cells and mediators in traumatic brain injury is poorly understood. Previously we have demonstrated that interleukin (IL)-6, a cytokine that acts on a wide range of tissues influencing cell growth and differentiation, is an agonist for vascular endothelial growth factor (VEGF), in in vitro vascularization assays for brain microvessel endothelial cells. In this present work we focus on the role of IL-6 in promoting tissue repair in the CNS in vivo. An aseptic cerebral injury (ACI) was created in the right parietal cortex, using both wild type (C57Bl/6J) and IL-6-deficient (C57Bl/6J-IL-6-/-) mice to study the consequences of the absence of IL-6 on the pathology of brain injuries. We monitored the immediate, early, and late responses to this traumatic injury by characterizing several histologic features in the CNS at days 1, 4, 7 and 14 following injury. Acellular necrosis, cellular infiltration, and re-vascularization were characterized in the injured tissues, and each of these histologic features was individually graded and totaled to assign a healing index. IL-6-deficient mice were found to have a comparatively slower rate of recovery and healing. Furthermore, fluorescein isothiocyanate (FITC)-dextran intravenous injection demonstrated leaky vessels in IL-6-deficient but not in wild type animals following ACI. Additionally, chronic expression of IL-6 in the CNS using transgenic GFAP-IL-6 mice resulted in more rapid healing following ACI. The accelerated tissue repair in GFAP-IL-6 transgenic animals is primarily due to extensive re-vascularization as detected by endothelial cell markers. Combined, this data suggests an important role of IL-6 in tissue repair processes following traumatic injury in the CNS.

Activated/effector CD4+ T cells exacerbate acute damage in the central nervous system following traumatic injury

CD4(+) helper T cells (Th) have been demonstrated to participate in the chronic phase of traumatic injury repair in the central nervous system (CNS). Here, we show that CD4(+) T cells can also contribute to the severity of the acute phase of CNS traumatic injury. We compared the area of tissue damage and the level of cellular apoptosis in aseptic cerebral injury (ACI) sites of C57BL/6 wild type and RAG1(-/-) immunodeficient mice. We demonstrate that ACI is attenuated in RAG1(-/-) mice compared to C57BL/6 animals. Adoptive transfer of CD4(+)CD62L(low)CD44(high) activated/effector T cells 24 h prior to ACI into RAG1(-/-) mice resulted in a significantly enhanced acute ACI that was comparable to ACI in the C57BL/6 animals. Adoptive transfer of CD4(+)CD62L(high)CD44(low) naive/non-activated T cells did not increase ACI in the brains of RAG1(-/-) mice. T cell inhibitory agents, cyclosporin A (CsA) and FK506, significantly decreased ACI-induced acute damage in C57BL/6 mice. These results suggest a previously undescribed role for activated/effector CD4(+) T cells in exacerbating ACI-induced acute damage in the CNS and raise a novel possibility for acute treatment of sterile traumatic brain injury.

Infection with Mycobacterium bovis BCG Diverts Traffic of Myelin Oligodendroglial Glycoprotein Autoantigen-Specific T Cells Away from the Central Nervous System and Ameliorates Experimental Autoimmune Encephalomyelitis

ABSTRACT Infectious agents have been proposed to influence susceptibility to autoimmune diseases such as multiple sclerosis. We induced a Th1-mediated central nervous system (CNS) autoimmune disease, experimental autoimmune encephalomyelitis (EAE) in mice with an ongoing infection with Mycobacterium bovis strain bacillus Calmette-Guérin (BCG) to study this possibility. C57BL/6 mice infected with live BCG for 6 weeks were immunized with myelin oligodendroglial glycoprotein peptide (MOG35-55) to induce EAE. The clinical severity of EAE was reduced in BCG-infected mice in a BCG dose-dependent manner. Inflammatory-cell infiltration and demyelination of the spinal cord were significantly lessened in BCG-infected animals compared with uninfected EAE controls. ELISPOT and gamma interferon intracellular cytokine analysis of the frequency of antigen-specific CD4+ T cells in the CNS and in BCG-induced granulomas and adoptive transfer of MOG35-55-specific green fluorescent protein-expressing cells into BCG-infected animals indicated that nervous tissue-specific (MOG35-55) CD4+ T cells accumulate in the BCG-induced granuloma sites. These data suggest a novel mechanism for infection-mediated modulation of autoimmunity. We demonstrate that redirected trafficking of activated CNS antigen-specific CD4+ T cells to local inflammatory sites induced by BCG infection modulates the initiation and progression of a Th1-mediated CNS autoimmune disease.

Antigen-specific T cell trafficking into the central nervous system.

The initiation step of cell-mediated immune responses in the central nervous system (CNS) involves the trafficking of the antigen-specific T cells into the brain. To study this trafficking, we developed an in vivo system for studying antigen-specific responses in the CNS. In this assay, T cell receptor (TCR) transgenic mice having 95% of T cells specific for a defined antigen-pigeon cytochrome c (PCC) were cannulated intraventricularly for PCC antigen infusion and cerebrospinal fluid (CSF) sampling. Upon PCC infusion into the CNS, the number of alpha/beta TCR(+) Vbeta3(+) Mac1(-) cells in the CSF was characterized. We found that infusion of antigen into the CSF induced an increased number of antigen-specific T cells in the CNS and activation of antigen-specific T cells in the peripheral blood. Hence, the drainage of CNS antigen into the periphery might play an important role in sustaining autoimmune reactivity in CNS inflammatory diseases.

Traumatic brain injury increases TGFβRII expression on endothelial cells

Transforming growth factor beta (TGFβ) modulates a variety of growth related functions following traumatic injury. The cellular response to TGFβ is predominantly mediated through TGFβ receptor I (TGFβRI) and receptor II (TGFβRII) on the cell surface and SMAD proteins intracellularly. We investigated the expression of TGFβ receptors in the acute and chronic phases of a traumatic cerebral injury (TCI) by immunohistochemistry and in cultures of murine brain microvascular endothelial (EN) cells using cytofluorimetry. Here, we report that TGFβRII expression significantly increases on brain endothelial cells in the chronic phase of TCI. SMAD3 and SMAD4 protein expression were also upregulated suggesting the activation of TGFβ receptor intracellular signaling. When TGFβRI and TGFβRII expression was studied in in vitro cultures of murine brain microvessel EN cells, TGFβRII showed increased expression on proliferating cells that are incorporating BrdU. These data show a differential expression of TGFβRI and TGFβRII on brain microvessel EN cells in the acute and chronic phases of TCI that might be associated with EN proliferation following injury.