Critical requirement of CD11b (Mac-1) on T cells and accessory cells for development of experimental autoimmune encephalomyelitis

Enhanced microglial clearance of myelin debris in T cell-infiltrated central nervous system

Acute multiple sclerosis lesions are characterized by accumulation of T cells and macrophages, destruction of myelin and oligodendrocytes, and axonal damage. There is, however, limited information on neuroimmune interactions distal to sites of axonal damage in the T cell-infiltrated central nervous system. We investigated T-cell infiltration, myelin clearance, microglial activation, and phagocytic activity distal to sites of axonal transection through analysis of the perforant pathway deafferented dentate gyrus in SJL mice that had received T cells specific for myelin basic protein (TMBP) or ovalbumin (TOVA). The axonal lesion of TMBP-recipient mice resulted in lesion-specific recruitment of large numbers of T cells in contrast to very limited T-cell infiltration in TOVA-recipient and -naïve perforant pathway-deafferented mice. By double immunofluorescence and confocal microscopy, infiltration with TMBP but not TOVA enhanced the microglial response to axonal transection and microglial phagocytosis of myelin debris associated with the degenerating axons. Because myelin antigen-specific immune responses may provoke protective immunity, increased phagocytosis of myelin debris might enhance regeneration after a neural antigen-specific T cell-mediated immune response in multiple sclerosis.

Gammadelta T cells in EAE: early trafficking events and cytokine requirements

We have previously shown that gammadelta T cells traffic to the CNS during EAE with concurrently increased expression of beta(2)-integrins and production of IFN-gamma and TNF-alpha. To extend these studies, we transferred bioluminescent gammadelta T cells to WT mice and followed their movement through the acute stages of disease. We found that gammadelta T cells rapidly migrated to the site of myelin oligodendrocyte glycoprotein peptide injection and underwent massive expansion. Within 6 days after EAE induction, bioluminescent gammadelta T cells were found in the spinal cord and brain, peaking in number between days 10 and 12 and then rapidly declining by day 15. Reconstitution of gammadelta T cell(-/-) mice with gammadelta T cells derived from beta(2)-integrin-deficient mice (CD11a, -b or -c) demonstrated that gammadelta T-cell trafficking to the CNS during EAE is independent of this family of adhesion molecules. We also examined the role of gammadelta T-cell-produced IFN-gamma and TNF-alpha in EAE and found that production of both cytokines by gammadelta T cells was required for full development of EAE. These results indicate that gammadelta T cells are critical for the development of EAE and suggest a therapeutic target in demyelinating disease.

Peripheral dendritic cells are essential for both the innate and adaptive antiviral immune responses in the central nervous system

Intranasal application of vesicular stomatitis virus (VSV) causes acute infection of the central nervous system (CNS). However, VSV encephalitis is not invariably fatal, suggesting that the CNS may contain a professional antigen-presenting cell (APC) capable of inducing or propagating a protective antiviral immune response. To examine this possibility, we first characterized the cellular elements that infiltrate the brain as well as the activation status of resident microglia in the brains of normal and transgenic mice acutely ablated of peripheral dendritic cells (DCs) in vivo. VSV encephalitis was characterized by a pronounced infiltrate of myeloid cells (CD45(high)CD11b(+)) and CD8(+) T cells containing a subset that was specific for the immunodominant VSV nuclear protein epitope. This T cell response correlated temporally with a rapid and sustained upregulation of MHC class I expression on microglia, whereas class II expression was markedly delayed. Ablation of peripheral DCs profoundly inhibited the inflammatory response as well as infiltration of virus-specific CD8(+) T cells. Unexpectedly, the VSV-induced interferon-gamma (IFN-gamma) response in the CNS remained intact in DC-deficient mice. Thus, both the inflammatory and certain components of the adaptive primary antiviral immune response in the CNS are dependent on peripheral DCs in vivo.

Matrix metalloproteinase-12 deficiency worsens relapsing-remitting experimental autoimmune encephalomyelitis in association with cytokine and chemokine dysregulation

The elevation of several members of the matrix metalloproteinase (MMP) family promotes the pathophysiology of both multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE). Nonetheless, given the multiple activities of MMPs, it remains possible that increased levels of a particular MMP may have beneficial functions during disease progression. We reported previously that MMP-12(-/-) mice of the 129/SvEv strain had a poorer EAE outcome than wild-type controls. However, we did not determine further differences in disease profiles between these groups. Using the EAE model in 129/SvEv mice, we report that disease in both wild-type and MMP-12(-/-) mice follows a relapsing-remitting course. Although both mouse groups had similar clinical onsets, subsequent relapses were more severe in MMP-12(-/-) mice; their residual disability at remission was also higher compared with wild-type controls. The worsened relapses and remissions in MMP-12(-/-) mice occurred despite a deficiency of the antigen recall capacity of lymph node-derived cells as well as a reduction in the proportion of macrophages in the spinal cord during the chronic phase of EAE. Significantly, large increases of levels of chemokines and cytokines were found in the spinal cords of MMP-12(-/-) mice during chronic EAE. These results highlight MMP-12 as a beneficial enzyme in EAE and suggest that therapeutic interventions in multiple sclerosis should avoid targeting MMP-12.

Effector and suppressor roles for LFA-1 during the development of experimental autoimmune encephalomyelitis

LFA-1 (CD11a/CD18) is a member of the beta(2)-integrin family of adhesion molecules important in leukocyte trafficking and activation. Although LFA-1 is thought to contribute to the development of experimental autoimmune encephalomyelitis (EAE) primarily through its functions on effector T cells, its importance on other leukocyte populations remains unexplored. To address this question, we performed both adoptive transfer EAE experiments involving CD11a(-/-) mice and trafficking studies using bioluminescent T cells expressing luciferase under the control of a CD2 promoter (T-lux cells). Transfer of encephalitogenic CD11a(-/-) T cells to wild type mice resulted in a significant reduction in overall EAE severity compared to control transfers. We also observed, using in vivo imaging techniques, that CD11a(-/-) T-lux cells readily infiltrated lymph nodes and the CNS of wild type recipients with kinetics comparable to CD11a(+/+) transfers, although their overall numbers in these organs were reduced. Surprisingly, transfer of encephalitogenic wild type T cells to CD11a(-/-) mice induced a severe and sometimes fatal EAE disease course, associated with massive T cell infiltration and proliferation in the CNS. These data indicate that LFA-1 expression on leukocytes in recipient mice plays an important immunomodulatory role in EAE. Thus, LFA-1 acts as a key regulatory adhesion molecule during the development of EAE, serving both pro- and anti-inflammatory roles in disease pathogenesis.

The complement cascade: Yin-Yang in neuroinflammation--neuro-protection and -degeneration

The complement cascade has long been recognized to play a key role in inflammatory and degenerative diseases. It is a 'double edged' sword as it is necessary to maintain health, yet can have adverse effects when unregulated, often exacerbating disease. The contrasting effects of complement, depending on whether in a setting of health or disease, is the price paid to achieve flexibility in scope and degree of a protective response for the host from infection and injury. Loss or even decreased efficiency of critical regulatory control mechanisms can result in aggravated inflammation and destruction of self-tissue. The role of the complement cascade is poorly understood in the nervous system and neurological disorders. Novel studies have demonstrated that the expression of complement proteins in brain varies in different cell types and the effects of complement activation in various disease settings appear to differ. Understanding the functioning of this cascade is essential, as it has therapeutic implications. In this review, we will attempt to provide insight into how this complex cascade functions and to identify potential strategic targets for therapeutic intervention in chronic diseases as well as acute injury in the CNS.

Production of CCL2 by central nervous system cells regulates development of murine experimental autoimmune encephalomyelitis through the recruitment of TNF- and iNOS-expressing macrophages and myeloid dendritic cells

Experimental autoimmune encephalomyelitis is a T cell-mediated demyelinating disease of the CNS that serves as a model for the human disease multiple sclerosis. Increased expression of the chemokine CCL2 in the CNS has been demonstrated to be important in the development of demyelinating disease presumably by attracting inflammatory cells. However, the mechanism of how CCL2 regulates disease pathogenesis has not been fully elucidated. Using radiation bone marrow chimeric mice we demonstrated that optimum disease was achieved when CCL2 was glia derived. Furthermore, CNS production of CCL2 resulted in the accumulation of iNOS-producing CD11b(+)CD11c(+) dendritic cells and TNF-producing macrophages important for demyelination. Lack of glial-derived CCL2 production did not influence experimental autoimmune encephalomyelitis by altering either Th1 or Th17 cells, as there were no differences in these populations in the CNS or periphery between groups. These results demonstrate that the glial-derived CCL2 is important for the attraction of TNF- and iNOS-producing dendritic cells and effector macrophages to the CNS for development of subsequent autoimmune disease.

Deletion of both ICAM-1 and C3 enhances severity of experimental autoimmune encephalomyelitis compared to C3-deficient mice

Multiple sclerosis (MS) is an autoimmune disease characterized by central nervous system (CNS) inflammation and leukocyte infiltration, demyelination of neurons, and blood-brain barrier breakdown. The development of experimental autoimmune encephalomyelitis (EAE), the animal model for MS is dependent on a number of components of the immune system including complement and adhesion molecules. Previous studies in our lab have examined the role of C3, the central complement component, and intercellular adhesion molecule-1 (ICAM-1) a key cell adhesion molecule involved in leukocyte trafficking to sites of inflammation including the CNS. In these studies we demonstrated that myelin oligodendrocyte glycoprotein (MOG)-induced EAE is markedly attenuated in both ICAM-1(-/-) and C3(-/-) mice. Given the pivotal role that these proteins play in EAE, we hypothesized that EAE in ICAM-1(-/-) and C3(-/-) double mutant mice would likely fail to develop. Unexpectedly, EAE in ICAM-1(-/-)xC3(-/-) mice was only modestly attenuated compared to wild type mice and significantly worse than C3(-/-) mice. Leukocyte infiltration was commensurate with disease severity between the three groups of mice. Spinal cord T cells from ICAM-1(-/-)xC3(-/-) mice produced the highest levels of IFN-gamma and TNF-alpha, despite reduced disease severity compared to wild type mice. The mechanisms behind the elevated EAE severity in ICAM-1(-/-)xC3(-/-) mice may relate to altered homing of leukocytes or processing of self-antigens in the double mutant background.

Reduced arthritis in MIF deficient mice is associated with reduced T cell activation: down-regulation of ERK MAP kinase phosphorylation

Macrophage migration inhibitory factor (MIF) is a pleiotropic pro-inflammatory cytokine with many cellular targets in rheumatoid arthritis (RA). MIF has been reported to activate cells via mitogen-activated protein kinase and serine/threonine kinase (AKT or protein kinase B)-dependent signal transduction pathways. Its contribution to T cell activation and signalling in RA is not known. Using MIF -/- mice and a T cell-mediated model of RA, antigen-induced arthritis, we investigated the role of MIF in T cell activation and signalling. Arthritis severity was significantly reduced in MIF -/- mice compared with wildtype mice. This reduction was associated with decreased T cell activation parameters including footpad delayed type hypersensitivity, antigen-induced splenocyte proliferation and cytokine production. Splenocyte proliferation required extracellular signal-regulated kinase (ERK)1/2 phosphorylation, and decreased T cell activation in MIF -/- mice was associated with decreased phosphorylation of ERK1/2 but not AKT. Collectively, these data suggest that MIF promotes antigen-specific immune responses via regulation of ERK phosphorylation in T cells.

Differential expression of beta 2-integrins and cytokine production between gammadelta and alphabeta T cells in experimental autoimmune encephalomyelitis

The expression of beta 2-integrins on gammadelta T cells in naïve mice or those with experimental autoimmune encephalomyelitis (EAE) remains poorly characterized. We compared beta 2-integrin expression and cytokine production between gammadelta and alphabeta T cells over the acute course of EAE. We observed that unlike in alphabeta T cells, beta 2-integrin expression on gammadelta T cells increased significantly from baseline, peaked at Day 10, and remained unchanged in the draining lymph nodes or declined in the spleen and CNS by Day 15. In addition, IFN-gamma- and TNF-alpha-producing gammadelta T cells infiltrated the CNS rapidly and produced significantly more of these cytokines than alphabeta T cells throughout the course of EAE. These results suggest unique roles for beta 2-integrins in the trafficking of gammadelta versus alphabeta T cells during EAE and that gammadelta T cells infiltrate the CNS rapidly, producing cytokines, which modulate acute disease.

p150/95 (CD11c/CD18) expression is required for the development of experimental autoimmune encephalomyelitis

p150/95 (CD11c/CD18, CR4) is a member of the beta(2)-integrin family of adhesion molecules and is considered an important phagocytic receptor. The role of p150/95 in the development of central nervous system demyelinating diseases, including multiple sclerosis, remains unexplored. To determine p150/95-mediated mechanisms in experimental autoimmune encephalomyelitis (EAE), we performed EAE using CD11c-deficient (CD11c(-/-)) mice. EAE in CD11c(-/-) mice was significantly attenuated and characterized by markedly reduced spinal cord T-cell infiltration and interferon-gamma production by these cells. Adoptive transfer of antigen-restimulated T cells from wild-type to CD11c(-/-) mice produced significantly attenuated EAE, whereas transfer of CD11c(-/-) antigen-restimulated T cells to control mice induced a very mild, monophasic EAE. T cells from MOG(35-55) peptide-primed CD11c(-/-) mice displayed an unusual cytokine phenotype with elevated levels of interleukin (IL)-2, IL-4, and IL-12 but reduced levels of interferon-gamma, tumor necrosis factor-alpha, IL-10, IL-17, and transforming growth factor-beta compared with control mice. Overall, CD11c(-/-) T cells from primed mice proliferated comparably to that of control T cells on MOG(35-55) restimulation. Our results indicate that expression of p150/95 is critical on both T cells as well as other leukocytes for the development of demyelinating disease and may represent a novel therapeutic target for multiple sclerosis.

T cell-associated CD18 but not CD62L, ICAM-1, or PSGL-1 is required for the induction of chronic colitis

The induction and perpetuation of chronic colitis are thought to involve a complex set of adhesive interactions between T cells and endothelial cells located on the vasculature within secondary lymphoid tissue and the intestine. The objective of this study was to assess the roles of T cell-associated CD18, CD62L (L-selectin), ICAM-1, and P-selectin glycoprotein ligand-1 (PSGL-1) in the induction of chronic colitis in mice. CD4(+)CD25(-) T cells derived from either wild-type (WT), CD18-deficient [CD18 knockout (KO)], CD62L KO, ICAM-1 KO, or PSGL-1 KO mice were adoptively transferred into recombinase activating gene-1 (RAG-1)-deficient mice (RAG KO mice) to assess the potential of these T cells to induce chronic colitis. At 8-10 wk following T cell transfer, we observed moderate to severe colitis as assessed by increases in colon weight-to-length ratios and by blinded histopathological analysis. In contrast, we found that transfer of CD18 KO T cells into RAG KO recipients resulted in the significant attenuation of colonic inflammation in these mice. Furthermore, we observed fewer infiltrating CD4(+) T cells in the colonic lamina propria in the CD18 KO-->RAG KO group compared with the WT-->RAG KO group. Finally, message levels of colonic TNF-alpha, IL-1beta, and IFN-gamma were significantly reduced in CD18 KO-->RAG KO mice compared with colitic control animals. We conclude that T cell-associated CD18, but not CD62L, ICAM-1, or PSGL-1, is required for the development of chronic colitis.

Enhanced visualization of axonopathy in EAE using thy1-YFP transgenic mice

It is widely accepted that chronic disabilities in multiple sclerosis (MS) patients are due in part to neuronal damage. The central aim of this study was to characterize axonal disruption in the spinal cord of mice with myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis (MOG-EAE), a model of progressive MS. To accomplish this goal, we induced MOG-EAE in thy1-yellow fluorescent (thy-YFP)-transgenic mice in which all spinal motorneurons express the YFP reporter protein. We demonstrate that a build-up of YFP fluorescence occurs in profiles reminiscent of tortuous fragmented axons and axonal spheroids/globules as seen in various neurodegenerative/neuroinflammatory diseases. Approximately two-thirds of these damaged axons were decorated by the monoclonal antibody SMI 32, which recognizes hypophosphorylated neurofilament-H (hypoP-NF-H), an established marker of CNS axonal pathology. Unexpectedly, one third of damaged axons were hypoP-NF-H negative but could be visualized by their expression of the YFP transgene, whilst the remaining profiles were hypoP-NF-H positive but did not exhibit YFP fluorescence. Thus, using YFP transgenic mice in conjunction with hypoP-NF-H immunoreactivity provides a more comprehensive depiction of axonopathy in the ventral-lateral aspect of lumbosacral spinal cord in MOG-EAE. When YFP fluorescence was used in conjunction with a monoclonal antibody that recognizes CD11b; a marker of subsets of inflammatory cells, we were able to discern evidence of an early inflammatory attack on white matter axons. Finally, we show the accumulation of hyperphosphorylated neurofilament-H (hyperP-NF-H) expression in YFP+, lesioned WM areas and in a subpopulation of neuronal perikarya in the lumbar spinal cords of EAE mice.

Complement in experimental autoimmune encephalomyelitis revisited: C3 is required for development of maximal disease

Complement per se has been shown to play an important role in demyelinating disease but controversy remains regarding the role of C3 in the development and progression of experimental autoimmune encephalomyelitis (EAE), the animal model for multiple sclerosis. In this study, we used C3(-/-) mice to confirm previous findings that C3 is required for full development of EAE. Furthermore, C3(+/-) mice (with serum C3 levels 50% that of wild-type mice) developed EAE with a severity intermediate between wild-type and C3(-/-) mice. Importantly transfer of wild-type encephalitogenic T cells to C3(-/-) mice resulted in attenuated EAE. C3(-/-) mice with EAE had fewer CD4(+) and CD8(+) T cells in the CNS and 50% fewer of these cells produced IFN-gamma compared to wild-type mice. When treated with anti-CD3 antibody, CD4(+) T cells from wild-type and C3(-/-) mice had similar activation profiles as judged by IFN-gamma production and CD25 and CD69 expression, indicating there is no gross or intrinsic defect in T cells from C3(-/-) mice. T cells from primed C3(-/-) mice proliferated comparably to that of control T cells on re-stimulation with MOG peptide. Our results confirm a requirement for C3 for maximal development of EAE and suggest that receptors for C3-derived activation fragments might be a viable therapeutic target for prevention and treatment demyelinating disease.

Disruption of the beta2-integrin CD11d (alphaDbeta2) gene fails to protect against experimental autoimmune encephalomyelitis

The fourth member of the beta(2)-integrin family of adhesion molecules, CD11d (alpha(D)beta(2)), is expressed on a wide variety of immune cells, however its function in autoimmune diseases, including EAE remains unknown. We induced EAE in wild-type and CD11d(-/-) C57BL/6 mice using myelin oligodendrocyte glycoprotein (MOG(35-55)) peptide. The clinical course and histopathology of EAE were identical in both groups of mice throughout the disease course. There were no significant differences in the infiltration of leukocyte subsets into the central nervous system or in the production of cytokines from T cells isolated from the spleen or spinal cord from both groups of mice. Our data demonstrate that CD11d is not required for the development of EAE and, to date, is the only beta(2)-integrin molecule whose deletion does not result in attenuated disease.

Complement and demyelinating disease: no MAC needed?

It has long been accepted that the complement system participates in the onset, evolution, and exacerbation of demyelinating disease, and it is widely suspected that this is accomplished mainly via destruction of nervous tissue by membrane attack complex (MAC)-mediated lysis of oligodendrocytes and neurons. However, recent studies using mutant mice indicate the MAC may not be so important. For example, mice lacking C5 and mice lacking the C5a receptor both develop experimental autoimmune encephalomyelitis (EAE) with the same frequency and intensity as their wild type counterparts. Also, transgenic mice that express C5a exclusively in the central nervous system (CNS) develop EAE that is not remarkably different from that in non-transgenic littermates. Since C5 is required for formation of the MAC, development of fulminant EAE in the absence of this complement protein demonstrates that non-complement-mediated mechanisms of CNS damage are operating. Paradoxically, mice lacking C3, mice lacking the C3a receptor, and mice lacking the complement receptor type 3 develop attenuated EAE, while mice that express C3a exclusively in the CNS develop severe and often fulminant EAE. Based on these newer data, we posit that C3-derived biologically active fragments, rather than C5 and the MAC, are central players in the pathophysiology of complement in EAE.