A role for alpha4-integrin in the pathology following Semliki Forest virus infection

Viral infections and multiple sclerosis

The etiology and pathogenesis of MS is likely to involve multiple factors interacting with each other, and the role of infectious and viral agents is still under debate, however a consistent amount of studies suggests that some viruses are associated with the disease. The strongest documentation has come from the detection of viral nucleic acid or antigen or of an anti-viral antibody response in MS patients. A further step for the study of the mechanism viruses might be involved in can be made using in vitro and in vivo models. While in vitro models, based on glial and neural cell lines from various sources are widely used, in vivo animal models present challenges. Indeed neurotropic animal viruses are currently used to study demyelination in well-established models, but animal models of demyelination by human virus infection have only recently been developed, using animal gammaherpesviruses closely related to Epstein Barr virus (EBV), or using marmosets expressing the specific viral receptor for Human Herpesvirus 6 (HHV-6). The present review will illustrate the main potential mechanisms of MS pathogenesis possibly associated with viral infections and viruses currently used to study demyelination in animal models. Then the viruses most strongly linked with MS will be discussed, in the perspective that more than one virus might have a role, with varying degrees of interaction, contributing to MS heterogeneity.

Beyond RGD: virus interactions with integrins

Viruses successfully infect host cells by initially binding to the surfaces of the cells, followed by an intricate entry process. As multifunctional heterodimeric cell-surface receptor molecules, integrins have been shown to usefully serve as entry receptors for a plethora of viruses. However, the exact role(s) of integrins in viral pathogen internalization has yet to be elaborately described. Notably, several viruses harbor integrin-recognition motifs displayed on viral envelope/capsid-associated proteins. The most common of these motifs is the minimal peptide sequence for binding integrins, RGD (Arg-Gly-Asp), which is known for its role in virus infection via its ability to interact with over half of the more than 20 known integrins. Not all virus-integrin interactions are RGD-dependent, however. Non-RGD-binding integrins have also been shown to effectively promote virus entry and infection as well. Such virus-integrin binding is shown to facilitate adhesion, cytoskeleton rearrangement, integrin activation, and increased intracellular signaling. Also, we have attempted to discuss the role of carbohydrate moieties in virus interactions with receptor-like host cell surface integrins that drive the process of internalization. As much as possible, this article examines the published literature regarding the role of integrins in terms of virus infection and virus-encoded glycosylated proteins that mediate interactions with integrins, and it explores the idea of targeting these receptors as a therapeutic treatment option.

Mouse models of alphavirus-induced inflammatory disease

Part of the Togaviridae family, alphaviruses are arthropod-borne viruses that are widely distributed throughout the globe. Alphaviruses are able to infect a variety of vertebrate hosts, but in humans, infection can result in extensive morbidity and mortality. Symptomatic infection can manifest as fever, an erythematous rash and/or significant inflammatory pathologies such as arthritis and encephalitis. Recent overwhelming outbreaks of alphaviral disease have highlighted the void in our understanding of alphavirus pathogenesis and the re-emergence of alphaviruses has given new impetus to anti-alphaviral drug design. In this review, the development of viable mouse models of Old Word and New World alphaviruses is examined. How mouse models that best replicate human disease have been used to elucidate the immunopathology of alphavirus pathogenesis and trial novel therapeutic discoveries is also discussed.

Concordance of preclinical and clinical pharmacology and toxicology of therapeutic monoclonal antibodies and fusion proteins: cell surface targets

Monoclonal antibodies (mAbs) and fusion proteins directed towards cell surface targets make an important contribution to the treatment of disease. The purpose of this review was to correlate the clinical and preclinical data on the 15 currently approved mAbs and fusion proteins targeted to the cell surface. The principal sources used to gather data were: the peer reviewed Literature; European Medicines Agency 'Scientific Discussions'; and the US Food and Drug Administration 'Pharmacology/Toxicology Reviews' and package inserts (United States Prescribing Information). Data on the 15 approved biopharmaceuticals were included: abatacept; abciximab; alefacept; alemtuzumab; basiliximab; cetuximab; daclizumab; efalizumab; ipilimumab; muromonab; natalizumab; panitumumab; rituximab; tocilizumab; and trastuzumab. For statistical analysis of concordance, data from these 15 were combined with data on the approved mAbs and fusion proteins directed towards soluble targets. Good concordance with human pharmacodynamics was found for mice receiving surrogates or non-human primates (NHPs) receiving the human pharmaceutical. In contrast, there was poor concordance for human pharmacodynamics in genetically deficient mice and for human adverse effects in all three test systems. No evidence that NHPs have superior predictive value was found.

Kit (W-sh) mice develop earlier and more severe experimental autoimmune encephalomyelitis due to absence of immune suppression

Mast cells (MCs) have been thought to play a pathogenic role in the development of autoimmune diseases, including experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. However, an immunoregulatory function of these cells has recently been suggested. We investigated the role of MCs in EAE using the W(-sh) mouse strain, which is MC deficient. W(-sh) mice developed earlier and more severe clinical and pathological disease with extensive demyelination and inflammation in the CNS. The inflammatory cells were mainly composed of CD4(+) T cells, monocyte/macrophages, neutrophils, and dendritic cells. Compared with wild-type mice, MC-deficient mice exhibited an increased level of MCP-1/CCR2 and CD44 expression on CD4(+) T cells in addition to decreased production of regulatory T cells, IL-4, IL-5, IL-27, and IL-10. We also found that levels of IL-17, IFN-γ, and GM-CSF were significantly increased in peripheral lymphocytes from immunized W(-sh) mice compared with those in peripheral lymphocytes from wild-type mice. Reconstitution of W(-sh) mice downregulated susceptibility to EAE, which correlated with MC recruitment and regulatory T cell activation in the CNS. These findings indicate that responsiveness is not required in the pathogenesis of inflammatory demyelination in the CNS and that, in the absence of MCs, increased MCP-1, CCR2, IL-17, IFN-γ, CD44, and other inflammatory molecules may be responsible for increased severity of EAE.

Neuropathogenesis of Theiler's murine encephalomyelitis virus infection, an animal model for multiple sclerosis

Theiler's murine encephalomyelitis virus (TMEV) infection of mice is an experimental model for multiple sclerosis (MS). TMEV induces a biphasic disease in susceptible mouse strains. During the acute phase, 1 week after infection, TMEV causes polioencephalomyelitis characterized by infection and apoptosis of neurons in the gray matter of the brain. During the chronic phase, about 1 month after infection, virus infects glial cells and macrophages, and induces inflammatory demyelination with oligodendrocyte apoptosis and axonal degeneration in the white matter of the spinal cord. Although antibody, CD4(+), and CD8(+) T cell responses against TMEV capsid proteins play important roles in neuropathogenesis, infectious virus with persistence is necessary to induce demyelination; in general, adoptive transfer of antibody or T cells alone did not induce central nervous system (CNS) disease. The TMEV model can be useful for testing new therapeutic strategies specifically as a viral model for MS. Therapies targeting adhesion molecules, axonal degeneration, and immunosuppression can be beneficial for pure autoimmune CNS demyelinating diseases, such as experimental autoimmune encephalomyelitis, but could be detrimental in virus-induced demyelinating diseases, such as progressive multifocal leukoencephalopathy.

Targeting the tetraspanin CD81 blocks monocyte transmigration and ameliorates EAE

Leukocyte infiltration is a key step in the development of demyelinating lesions in multiple sclerosis (MS), and molecules mediating leukocyte-endothelial interactions represent prime candidates for the development of therapeutic strategies. Here we studied the effects of blocking the integrin-associated tetraspanin CD81 in in vitro and in vivo models for MS. In an in vitro setting mAb against CD81 significantly reduced monocyte transmigration across brain endothelial cell monolayers, both in rodent and human models. Interestingly, leukocyte as well as endothelial CD81 was involved in this inhibitory effect. To assess their therapeutic potential, CD81 mAb were administered to mice suffering from experimental autoimmune encephalomyelitis (EAE). We found that Eat2, but not 2F7 mAb directed against mouse CD81 significantly reduced the development of neurological symptoms of EAE when using a preventive approach. Concomitantly, Eat2 treated animals showed reduced inflammation in the spinal cord. We conclude that CD81 represents a potential therapeutic target to interfere with leukocyte infiltration and ameliorate inflammatory neurological damage in MS.

Regulation of immune response and inflammatory reactions against viral infection by VCAM-1

The migration of activated antigen-specific immune cells to the target tissues of virus replication is controlled by the expression of adhesion molecules on the vascular endothelium that bind to ligands on circulating lymphocytes. Here, we demonstrate that the adhesion pathway mediated by vascular cell adhesion molecule 1 (VCAM-1) plays a role in regulating T-cell-mediated inflammation and pathology in nonlymphoid tissues, including the central nervous system (CNS) during viral infection. The ablation of VCAM-1 expression from endothelial and hematopoietic cells using a loxP-Cre recombination strategy had no major effect on the induction or overall tissue distribution of antigen-specific T cells during a systemic infection with lymphocytic choriomeningitis virus (LCMV), except in the case of lung tissue. However, enhanced resistance to lethal LCM and the significantly reduced magnitude and duration of footpad swelling observed in VCAM-1 mutant mice compared to B6 controls suggest a significant role for VCAM-1 in promoting successful local inflammatory reactions associated with efficient viral clearance and even life-threatening immunopathology under particular infection conditions. Interestingly, analysis of the infiltrating populations in the brains of intracerebrally infected mice revealed that VCAM-1 deletion significantly delayed migration into the CNS of antigen-presenting cells (macrophages and dendritic cells), which are critical for optimal stimulation of migrating virus-specific CD8(+) T cells initiating a pathological cascade. We propose that the impaired migration of these accessory cells in the brain may explain the improved clinical outcome of infection in VCAM-1 mutant mice. Thus, these results underscore the potential role of VCAM-1 in regulating the immune response and inflammatory reactions against viral infections.

Animal Models of Multiple Sclerosis

To determine whether an immunological or pharmaceutical product has potential for therapy in treating multiple sclerosis (MS), detailed animal models are required. To date many animal models for human MS have been described in mice, rats, rabbits, guinea pigs, marmosets, and rhesus monkeys. The most comprehensive studies have involved murine experimental allergic (or autoimmune) encephalomyelitis (EAE), Semliki Forest virus (SFV), mouse hepatitis virus (MHV), and Theiler’s murine encephalomyelitis virus (TMEV). Here, we describe in detail multispecies animal models of human MS, namely EAE, SFV, MHV, and TMEV, in addition to chemically induced demyelination. The validity and applicability of each of these models are critically evaluated.

Toll-like receptors in defense and damage of the central nervous system

Members of the Toll-like receptor (TLR) family play critical roles as regulators of innate and adaptive immune responses. TLRs function by recognizing diverse molecular patterns on the surface of invading pathogens. In the brain, microglial cells generate neuroimmune responses through production of proinflammatory mediators. The upregulation of cytokines and chemokines in response to microbial products and other stimuli has both beneficial and deleterious effects. Emerging evidence demonstrates a central role for TLRs expressed on microglia as a pivotal factor in generating these neuroimmune responses. Therefore, understanding the basis of TLR signaling in producing these responses may provide insights into how activated microglia attempt to strike a balance between defense against invading pathogens and inflicting irreparable brain damage. These insights may lead to innovative therapies for CNS infections and neuroinflammatory diseases based on the modulation of microglial cell activation through TLR signaling.

Immune cell migration as a means to control immune privilege: lessons from the CNS and tumors

Certain organs, such as the brain, eye, and gonads, are particularly sensitive to damage by inflammation. Therefore, these tissues have developed unique immunological properties that curtail inflammatory responses, a phenomenon termed immune privilege. In addition, by co-opting some of the regulatory cues operant in immune privilege in normal organs, tumors can evade immunosurveillance. While many different mechanisms contribute to immune privilege, there is evidence that leukocyte migration is an important checkpoint in its control. This hypothesis is based on the fact that leukocyte entry into these organs is restricted by physical barriers and that the collapse of these obstacles marks a critical step in the development of inflammatory/autoimmune disease at these sites. Numerous studies in a variety of experimental systems have characterized the molecular and cellular mechanisms involved in leukocyte homing to immune-privileged organs. Recently, two-photon microscopy has revealed critical insights into the events occurring in the extravascular space of immune-privileged organs, including locomotion patterns and interactive behavior of leukocytes in the interstitial space. Here, we review our current understanding of immune cell migration to and within immune-privileged organs and highlight how this knowledge may be exploited for immunotherapeutic purposes.

Biozzi mice: Of mice and human neurological diseases

In 1972 Guido Biozzi selectively bred mice to study the immunopathological mechanisms underlying polygenic diseases. One line, the Biozzi antibody high (AB/H) mouse (now designated the ABH strain) was later found to be highly susceptible to many experimentally induced diseases such as autoimmune encephalomyelitis, autoimmune neuritis, autoimmune uveitis, as well as virus-induced demyelination and has thus been a key mouse strain to study human inflammatory neurological diseases. In this paper we discuss the background of the Biozzi ABH mouse and review how studies with these mice have shed light on the pathogenic mechanisms operating in chronic neurological disease.

Antisense oligonucleotide blockade of alpha 4 integrin prevents and reverses clinical symptoms in murine experimental autoimmune encephalomyelitis

We investigated the use of an antisense oligonucleotide (ASO) specific for mRNA of the alpha chain (CD49d) of mouse VLA-4 to down-regulate VLA-4 expression and alter central nervous system (CNS) inflammation. ISIS 17044 potently and specifically reduced CD49d mRNA and protein in cell lines and in ex-vivo-treated primary mouse T cells. When administered prophylactically or therapeutically, ISIS 17044 reduced the incidence and severity of paralytic symptoms in a model of experimental autoimmune encephalomyelitis (EAE). This was accompanied by a significant decrease in the number of VLA-4+ cells, CD4(+) T cells, and macrophages present in spinal cord white matter of EAE mice. ISIS 17044 was found to accumulate in lymphoid tissue of mice, and oligonucleotide was also detected in endothelial cells and macrophage-like cells in the CNS, apparently due to disruption of the blood-brain barrier during EAE. These results demonstrate the potential utility of systemically administered antisense oligonucleotides for the treatment of central nervous system inflammation.

Semliki forest virus infection of laboratory mice: a model to study the pathogenesis of viral encephalitis

Semliki Forest virus (SFV) infection of the laboratory mouse provides an experimental system to study the pathogenesis of viral encephalitis. Following extraneural inoculation the virus is efficiently neuroinvasive and crosses the blood-brain barrier to initiate perivascular foci of infection in neurons and oligodendrocytes. The outcome of infection ranges from clinically unapparent mild encephalitis to fatal panencephalitis. SFV infections of the developing nervous system are always highly destructive and are generally fatal. In contrast, SFV infections of the mature nervous system can result in persistent infection with no apparent cell loss. This dramatic difference is attributable to developmental changes in the interactions between virus and CNS cells. Antibody responses clear the systemic infection and control the CNS infection. CD8+ T-cells are required to generate the lesions of inflammatory demyelination which can be a feature of the neuropathology. This article reviews the pathogenesis of SFV encephalitis, describing the neuropathology and the mechanisms which underlie it and which may be fundamental to many viral encephalitides.

Essential role of VLA-4/VCAM-1 pathway in the establishment of CD8+ T-cell-mediated Trypanosoma cruzi-elicited meningoencephalitis

Central nervous system (CNS) damage can occur during Trypanosoma cruzi infection, especially in immunosuppressed patients. The enhanced susceptibility of C3H/He mice to CD8-mediated acute meningoencephalitis is associated with higher up-regulation of vascular cell adhesion molecule-1 (VCAM-1) on CNS vascular endothelia than in the less susceptible C57BL/6. Further, in vitro adhesion of activated peripheral blood cells to CNS blood vessels was abrogated by anti-VLA-4 antibodies that also inhibited cell migration into the CNS of T. cruzi-infected mice. Lastly, the reactivation of meningoencephalitis in immunosuppressed chronically infected mice was associated with VCAM-1 up-regulation. Therefore, we hypothesize that VLA-4/VCAM-1 pathway plays a pivotal role in the establishment of T. cruzi-elicited encephalitis.

The chemokine system in neuroinflammation: an update

Chemokines and their receptors govern physiologic and pathologic leukocyte trafficking. The function of the chemokine system may be of particular interest for hematogenous leukocyte infiltration of the central nervous system (CNS) because of the distinct character of CNS inflammation and the exquisite specificity with which the chemokine system regulates cellular migration events. This review summarizes recent information about the expression and function of elements of the chemokine system in CNS inflammatory processes. Animal models of CNS demyelinating disease and the corresponding human disorder, multiple sclerosis are both considered.

ICAM-1 is crucial for protection from TMEV-induced neuronal damage but not demyelination

Previous work has suggested that the factors protecting mice from Theiler's murine encephalomyelitis virus (TMEV)-induced spinal cord demyelination are distinct from those involved in protection of the brain during the acute encephalitic phase. In this study, we examined the requirement for intercellular adhesion molecule-1 (ICAM-1) in both of these processes. During the acute phase of infection (days 7 to 10 after intracerebral infection with TMEV), no differences in brain or spinal cord pathology or virus burdens were observed between ICAM-1-knockout mice and the infected immunocompetent control mice of a similar background. Examination of brain pathology later in infection (that is, day 45 post infection [p.i.]) revealed that ICAM-1-deficient mice experienced increased levels of pathology in gray matter regions of the brain. We observed an increase in striatal damage and meningeal inflammation in the brains of TMEV-infected ICAM-1-knockout mice compared to C57BL/6J mice. Despite the increase in brain pathology, no immunoreactivity to viral antigens was detected, suggesting that the virus had been cleared by this time. Resistance to demyelination was similar in both groups, indicating that the resulting immune response was sufficient for protection of the spinal cord white matter.

VCAM-1-positive microglia target oligodendrocytes at the border of multiple sclerosis lesions

The distribution and lineage of vascular cell adhesion molecule-1 (VCAM-1)-positive cells was investigated in 43 lesions from the brain tissue of patients with multiple sclerosis (MS). Numerous VCAM-1-positive macrophages/microglia were detected at the edges of MS lesions. Quantitative analysis of 6 active, 7 chronic active, and 4 chronic inactive MS lesions identified most VCAM-1-positive cells at the actively demyelinating borders of active (102/mm3) and chronic active (29/mm3) lesions, but rarely in chronic inactive lesions (4/mm3). Further, approximately 17% of the VCAM-1-positive cells closely apposed or surrounded oligodendrocyte perikarya at the edges of active and chronic active lesions that were sites of ongoing demyelination. Endothelial cells were VCAM-1-negative in both lesion and non-lesion MS brain tissue. This report is the first to document direct microglial interaction with oligodendrocytes in MS.