Induction of selected chemokines in glial cells infected with Theiler's virus

Critical role of TLR activation in viral replication, persistence, and pathogenicity of Theiler's virus

Theiler's murine encephalomyelitis virus (TMEV) establishes persistent viral infections in the central nervous system and induces chronic inflammatory demyelinating disease in susceptible mice. TMEV infects dendritic cells, macrophages, B cells, and glial cells. The state of TLR activation in the host plays a critical role in initial viral replication and persistence. The further activation of TLRs enhances viral replication and persistence, leading to the pathogenicity of TMEV-induced demyelinating disease. Various cytokines are produced via TLRs, and MDA-5 signals linked with NF-κB activation following TMEV infection. In turn, these signals further amplify TMEV replication and the persistence of virus-infected cells. The signals further elevate cytokine production, promoting the development of Th17 responses and preventing cellular apoptosis, which enables viral persistence. Excessive levels of cytokines, particularly IL-6 and IL-1β, facilitate the generation of pathogenic Th17 immune responses to viral antigens and autoantigens, leading to TMEV-induced demyelinating disease. These cytokines, together with TLR2 may prematurely generate functionally deficient CD25-FoxP3+ CD4⁺ T cells, which are subsequently converted to Th17 cells. Furthermore, IL-6 and IL-17 synergistically inhibit the apoptosis of virus-infected cells and the cytolytic function of CD8+ T lymphocytes, prolonging the survival of virus-infected cells. The inhibition of apoptosis leads to the persistent activation of NF-κB and TLRs, which continuously provides an environment of excessive cytokines and consequently promotes autoimmune responses. Persistent or repeated infections of other viruses such as COVID-19 may result in similar continuous TLR activation and cytokine production, leading to autoimmune diseases.

Excessive Innate Immunity Steers Pathogenic Adaptive Immunity in the Development of Theiler's Virus-Induced Demyelinating Disease

Several virus-induced models were used to study the underlying mechanisms of multiple sclerosis (MS). The infection of susceptible mice with Theiler’s murine encephalomyelitis virus (TMEV) establishes persistent viral infections and induces chronic inflammatory demyelinating disease. In this review, the innate and adaptive immune responses to TMEV are discussed to better understand the pathogenic mechanisms of viral infections. Professional (dendritic cells (DCs), macrophages, and B cells) and non-professional (microglia, astrocytes, and oligodendrocytes) antigen-presenting cells (APCs) are the major cell populations permissive to viral infection and involved in cytokine production. The levels of viral loads and cytokine production in the APCs correspond to the degrees of susceptibility of the mice to the TMEV-induced demyelinating diseases. TMEV infection leads to the activation of cytokine production via TLRs and MDA-5 coupled with NF-κB activation, which is required for TMEV replication. These activation signals further amplify the cytokine production and viral loads, promote the differentiation of pathogenic Th17 responses, and prevent cellular apoptosis, enabling viral persistence. Among the many chemokines and cytokines induced after viral infection, IFN α/β plays an essential role in the downstream expression of costimulatory molecules in APCs. The excessive levels of cytokine production after viral infection facilitate the pathogenesis of TMEV-induced demyelinating disease. In particular, IL-6 and IL-1β play critical roles in the development of pathogenic Th17 responses to viral antigens and autoantigens. These cytokines, together with TLR2, may preferentially generate deficient FoxP3⁺CD25^- regulatory cells converting to Th17. These cytokines also inhibit the apoptosis of TMEV-infected cells and cytolytic function of CD8⁺ T lymphocytes (CTLs) and prolong the survival of B cells reactive to viral and self-antigens, which preferentially stimulate Th17 responses.

Endothelin-1 contributes to the development of virus-induced demyelinating disease

Background

Experimental autoimmune encephalitis (EAE) and virally induced demyelinating disease are two major experimental model systems used to study human multiple sclerosis. Although endothelin-1 level elevation was previously observed in the CNS of mice with EAE and viral demyelinating disease, the potential role of endothelin-1 in the development of these demyelinating diseases is unknown.

Methods and results

In this study, the involvement of endothelin-1 in the development and progression of demyelinating diseases was investigated using these two experimental models. Administration of endothelin-1 significantly promoted the progression of both experimental diseases accompanied with elevated inflammatory T cell responses. In contrast, administration of specific endothelin-1 inhibitors (BQ610 and BQ788) significantly inhibited progression of these diseases accompanied with reduced T cell responses to the respective antigens.

Conclusions

These results strongly suggest that the level of endothelin-1 plays an important role in the pathogenesis of immune-mediated CNS demyelinating diseases by promoting immune responses.

Infection and Activation of B Cells by Theiler's Murine Encephalomyelitis Virus (TMEV) Leads to Autoantibody Production in an Infectious Model of Multiple Sclerosis

Theiler’s murine encephalomyelitis virus (TMEV) induces immune-mediated inflammatory demyelinating disease in susceptible mice that is similar to human multiple sclerosis (MS). In light of anti-CD20 therapies for MS, the susceptibility of B cells to TMEV infection is particularly important. In our study, direct viral exposure to macrophages and lymphocytes resulted in viral replication and cellular stimulation in the order of DCs, macrophages, B cells, and T cells. Notably, B cells produced viral proteins and expressed elevated levels of CD69, an activation marker. Similarly, the expression of major histocompatibility complex class II and costimulatory molecules in B cells was upregulated. Moreover, TMEV-infected B cells showed elevated levels of antigen-presenting function and antibody production. TMEV infection appeared to polyclonally activate B cells to produce autoantibodies and further T cell stimulation. Thus, the viral infection might potentially affect the outcome of autoimmune diseases, and/or the development of other chronic infections, including the protection and/or pathogenesis of TMEV-induced demyelinating disease.

Effects of Keratinocyte-Derived Cytokine (CXCL-1) on the Development of Theiler's Virus-Induced Demyelinating Disease

CXCL-1, also called keratinocyte-derived cytokine (KC), is a predominant chemokine produced in glial cells upon infection with Theiler's murine encephalomyelitis virus (TMEV). In this study, we assessed the role of KC in the development of TMEV-induced demyelinating disease by utilizing polyclonal anti-KC antibodies as well as KC-expressing recombinant TMEV. Our results indicate that the level of KC produced after infection with TMEV or stimulation with various TLRs is significantly higher in various cells from susceptible SJL mice compared to those in cells from resistant B6 mice. SJL mice treated with rabbit anti-KC antibodies displayed accelerated development of TMEV-induced demyelinating disease, elevated viral loads in the CNS and decreased antiviral T cell responses. In addition, infection of susceptible SJL mice with recombinant KC-TMEV produced biologically active KC, which resulted in the accelerated pathogenesis of demyelinating disease and elevated T cell responses to viral antigens compared to mice infected with control recombinant HEL-TMEV. These results strongly suggest that both the lack of KC during TMEV infection and the excessive presence of the chemokine promote the pathogenesis of demyelinating disease. Therefore, a balance in the level of KC during TMEV infection appears to be critically important in controlling the pathogenesis of demyelinating disease.

Prostaglandin E2 produced following infection with Theiler's virus promotes the pathogenesis of demyelinating disease

Infection of various cells with Theiler’s murine encephalomyelitis virus (TMEV) activates the TLR- and melanoma differentiation-associated gene 5 (MDA5)-dependent pathways, resulting in the production of IL-1β via the activation of caspase-1 upon assembly of the node-like receptor protein 3 (NLRP3) inflammasome. The role of IL-1β in the pathogenesis of TMEV-induced demyelinating disease was previously investigated. However, the signaling effects of prostaglandin E2 (PGE₂) downstream of the NLRP3 inflammasome on the immune responses to viral determinants and the pathogenesis of demyelinating disease are unknown. In this study, we investigated the levels of intermediate molecules leading to PGE₂ signaling and the effects of blocking PGE₂ signaling on the immune response to TMEV infection, viral persistence and the development of demyelinating disease. We demonstrate here that TMEV infection activates the NLRP3 inflammasome and PGE₂ signaling much more vigorously in dendritic cells (DCs) and CD11b⁺ cells from susceptible SJL mice than in cells from resistant B6 mice. Inhibition of virus-induced PGE₂ signaling using AH23848 resulted in decreased pathogenesis of demyelinating disease and viral loads in the central nervous system (CNS). In addition, AH23848 treatment caused the elevation of protective early IFN-γ-producing CD4⁺ and CD8⁺ T cell responses. Because the levels of IFN-β were lower in AH23848-treated mice but the level of IL-6 was similar, over-production of pathogenic IFN-β was modulated and the generation of IFN-γ-producing T cell responses was enhanced by the inhibition of PGE₂ signaling. These results strongly suggest that excessive activation of the NLRP3 inflammasome and downstream PGE₂ signaling contribute to the pathogenesis of TMEV-induced demyelinating disease.

RANTES: a genetic risk marker for multiple sclerosis

Regulated upon activation, normal T-cell expressed and secreted (RANTES) is a beta-chemokine and has been detected in brain lesions of multiple sclerosis (MS) patients. Considering its potential role in MS, we screened two functional polymorphisms in the proximal promoter region of the RANTES in MS patients versus controls. Methods: We examined 140 postmortem brain samples from subjects with a primary diagnosis of MS, and peripheral blood samples from 216 control subjects. The RANTES-28C/G and -403G/A promoter polymorphisms were examined. All subjects were non-Hispanic Caucasians. Results: MS cases differed from controls showing a significant association with the 403G/A polymorphism (odds ratio, 2.359, [1.465-3.799]; P-0.0001), but not the -28C/G (P-NS) polymorphism. There was a significant association of the -28G allele with both early onset (P-0.031) and longer survival (P-0.006). Conclusion: There is a significant but complex association of the RANTES gene with MS.

Theiler's virus infection provokes the overexpression of genes coding for the chemokine Ip10 (CXCL10) in SJL/J murine astrocytes, which can be inhibited by modulators of estrogen receptors

Theiler's murine encephalomyelitis virus (TMEV) induces demyelination in susceptible strains of mice (SJL/J) through an immunopathological process that is mediated by CD4(+) Th1 T cell. These T cells are chemoattracted to the central nervous system by chemokines. Hence, in this study, we focused on the production of the chemokine "interferon-gamma-inducible protein 10 kDa," or IP-10/CXCL10, by cultured SJL/J mouse astrocytes infected with the BeAn strain of TMEV and its capacity to attract activated T cells. The analysis of the whole murine genome by DNA hybridization with cRNAs from mock- and TMEV-infected cultures revealed the upregulation of six sequences that potentially encode for CXCL10. This increased CXCL10 expression was validated by PCR and qPCR. The presence of this chemokine was further demonstrated by enzyme-linked immunoassay (ELISA). Significantly, astrocytes from BALB/c mice, a strain resistant to demyelination, did not produce CXCL10. The secreted CXCL10 was biologically active, inducing chemoattraction of activated lymphocytes. The inflammatory cytokines, IL-1α, IFN-γ, and TNF-α, were strong inducers of CXCL10 in astrocytes. Serum from TMEV-infected SJL/J but not BALB/c mice contains CXCL10, the levels of which peak at the onset of the clinical disease. Finally, this in vitro inflammation model was fully inhibited by 17β-estradiol and four selective estrogen receptor modulators, as demonstrated by ELISA and qPCR.

Intrathecal humoral immunity to encephalitic RNA viruses

The nervous system is the target for acute encephalitic viral infections, as well as a reservoir for persisting viruses. Intrathecal antibody (Ab) synthesis is well documented in humans afflicted by infections associated with neurological complications, as well as the demyelinating disease, multiple sclerosis. This review focuses on the origin, recruitment, maintenance, and biological relevance of Ab-secreting cells (ASC) found in the central nervous system (CNS) following experimental neurotropic RNA virus infections. We will summarize evidence for a highly dynamic, evolving humoral response characterized by temporal alterations in B cell subsets, proliferation, and differentiation. Overall local Ab plays a beneficial role via complement-independent control of virus replication, although cross or self-reactive Ab to CNS antigens may contribute to immune-mediated pathogenesis during some infections. Importantly, protective Ab exert anti-viral activity not only by direct neutralization, but also by binding to cell surface-expressed viral glycoproteins. Ab engagement of viral glycoproteins blocks budding and mediates intracellular signaling leading to restored homeostatic and innate functions. The sustained Ab production by local ASC, as well as chemokines and cytokines associated with ASC recruitment and retention, are highlighted as critical components of immune control.

Infiltrating macrophages are key to the development of seizures following virus infection

Viral infections of the central nervous system (CNS) can trigger an antiviral immune response, which initiates an inflammatory cascade to control viral replication and dissemination. The extent of the proinflammatory response in the CNS and the timing of the release of proinflammatory cytokines can lead to neuronal excitability. Tumor necrosis factor alpha (TNF-α) and interleukin-6 (IL-6), two proinflammatory cytokines, have been linked to the development of acute seizures in Theiler's murine encephalomyelitis virus-induced encephalitis. It is unclear the extent to which the infiltrating macrophages versus resident CNS cells, such as microglia, contribute to acute seizures, as both cell types produce TNF-α and IL-6. In this study, we show that following infection a significantly higher number of microglia produced TNF-α than did infiltrating macrophages. In contrast, infiltrating macrophages produced significantly more IL-6. Mice treated with minocycline or wogonin, both of which limit infiltration of immune cells into the CNS and their activation, had significantly fewer macrophages infiltrating the brain, and significantly fewer mice had seizures. Therefore, our studies implicate infiltrating macrophages as an important source of IL-6 that contributes to the development of acute seizures.

Melanoma differentiation-associated gene 5 is critical for protection against Theiler's virus-induced demyelinating disease

Infection of dendritic and glial cells with Theiler's murine encephalomyelitis virus (TMEV) induces various cytokines via Toll-like receptor- and melanoma differentiation-associated gene 5 (MDA5)-dependent pathways. However, the involvement and role of MDA5 in cytokine gene activation and the pathogenesis of TMEV-induced demyelinating disease are largely unknown. In this study, we demonstrate that MDA5 plays a critical role in the production of TMEV-induced alpha interferon (IFN-α) during early viral infection and in protection against the development of virus-induced demyelinating disease. Our results indicate that MDA5-deficient 129SvJ mice display significantly higher viral loads and apparent demyelinating lesions in the central nerve system (CNS) accompanied by clinical symptoms compared with wild-type 129SvJ mice. During acute viral infection, MDA5-deficient mice produced elevated levels of chemokines, consistent with increased cellular infiltration, but reduced levels of IFN-α, known to control T cell responses and cellular infiltration. Additional studies with isolated CNS glial cells from these mice suggest that cells from MDA5-deficient mice are severely compromised in the production of IFN-α upon viral infection, which results in increased cellular infiltration and viral loads in the CNS. Despite inadequate stimulation, the overall T cell responses to the viral determinants were significantly elevated in MDA5-deficient mice, reflecting the increased cellular infiltration. Therefore, the lack of MDA5-mediated IFN-α production may facilitate a massive viral load and elevated cellular infiltration in the CNS during early viral infection, leading to the pathogenesis of demyelinating disease.

Interleukin-6, produced by resident cells of the central nervous system and infiltrating cells, contributes to the development of seizures following viral infection

Cells that can participate in an innate immune response within the central nervous system (CNS) include infiltrating cells (polymorphonuclear leukocytes [PMNs], macrophages, and natural killer [NK] cells) and resident cells (microglia and sometimes astrocytes). The proinflammatory cytokine interleukin-6 (IL-6) is produced by all of these cells and has been implicated in the development of behavioral seizures in the Theiler's murine encephalomyelitis virus (TMEV)-induced seizure model. The assessment, via PCR arrays, of the mRNA expression levels of a large number of chemokines (ligands and receptors) in TMEV-infected and mock-infected C57BL/6 mice both with and without seizures did not clearly demonstrate the involvement of PMNs, monocytes/macrophages, or NK cells in the development of seizures, possibly due to overlapping function of the chemokines. Additionally, C57BL/6 mice unable to recruit or depleted of infiltrating PMNs and NK cells had seizure rates comparable to those of controls following TMEV infection, and therefore PMNs and NK cells do not significantly contribute to seizure development. In contrast, C57BL/6 mice treated with minocycline, which affects monocytes/macrophages, microglial cells, and PMNs, had significantly fewer seizures than controls following TMEV infection, indicating monocytes/macrophages and resident microglial cells are important in seizure development. Irradiated bone marrow chimeric mice that were either IL-6-deficient mice reconstituted with wild-type bone marrow cells or wild-type mice reconstituted with IL-6-deficient bone marrow cells developed significantly fewer behavioral seizures following TMEV infection. Therefore, both resident CNS cells and infiltrating cells are necessary for seizure development.

Preferential induction of protective T cell responses to Theiler's virus in resistant (C57BL/6 x SJL)F1 mice

Infection of the central nervous system (CNS) with Theiler's murine encephalomyelitis virus (TMEV) induces an immune-mediated demyelinating disease in susceptible mouse strains such as SJL/J (H-2(s)) but not in strains such as C57BL/6 (H-2(b)). In addition, it has been shown that (C57BL/6 × SJL/J)F1 mice (F1 mice), which carry both resistant and susceptible MHC haplotypes (H-2(b/s)), are resistant to both viral persistence and TMEV-induced demyelinating disease. In this study, we further analyzed the immune responses underlying the resistance of F1 mice. Our study shows that the resistance of F1 mice is associated with a higher level of the initial virus-specific H-2(b)-restricted CD8(+) T cell responses than of the H-2(s)-restricted CD8(+) T cell responses. In contrast, pathogenic Th17 responses to viral epitopes are lower in F1 mice than in susceptible SJL/J mice. Dominant effects of resistant genes expressed in antigen-presenting cells of F1 mice on regulation of viral replication and induction of protective T cell responses appear to play a crucial role in disease resistance. Although the F1 mice are resistant to disease, the level of viral RNA in the CNS was intermediate between those of SJL/J and C57BL/6 mice, indicating the presence of a threshold of viral expression for pathogenesis.

Up-regulation of the vascular cell adhesion molecule-1 (VCAM-1) induced by Theiler's murine encephalomyelitis virus infection of murine brain astrocytes

The present article reports the up-regulation of the expression of the vascular cell adhesion molecule-1 (VCAM-1) by SJL/J mouse brain astrocytes infected with Theiler's murine encephalomyelitis virus (TMEV). Complementary RNA (cRNA) from mock- and TMEV-infected cells was hybridized to the Affymetrix whole murine genome U74v2 DNA microarray. Hybridization data analysis revealed background expression in untreated cells and the up-regulation of three sequences coding for VCAM-1, as described by the SCOP (Structural Classification Of Proteins) database. The authors further studied its regulation, confirming and validating their mRNA increase by reverse transcriptase-polymerase chain reaction (RT-PCR) and quantitative real-time RT-PCR. The presence of the 100-kDa VCAM-1 protein in mock- and TMEV-infected cells was demonstrated in the cell membrane by a specific cell-based enzyme-linked immunosorbent assay (ELISA), in addition to flow cytometry and confocal immunohistochemistry. Further, Western blots were used to quantify the amount of VCAM-1 molecules in cell extracts. All these data demonstrated a mean 75% increase in the expression of VCAM-1 on the surface of TMEV-infected cells. Three inflammatory cytokines, interleukin-1alpha (IL-1alpha), interferon gamma (IFNgumma), and specially tumor necrosis factor alpha (TNF-α), some of which are also induced by TMEV in astrocytes (IL-1alpha and TNF-alpha), were potent inducers of VCAM-1 expression. To demonstrate whether the VCAM-1 molecules were biologically active, mediating adhesion to other cells as the integrin alpha4-expressing CD4+ T lymphocytes, the authors used a cell adhesion test. It was also demonstrated by immunohistochemistry that in vivo VCAM-1 expression is enhanced after TMEV intracraneal infection. The present data show a small but statistically significant overexpression of VCAM-1 after astrocyte infection with TMEV that could play a significant role in vivo.

Theiler's virus infection induces a predominant pathogenic CD4+ T cell response to RNA polymerase in susceptible SJL/J mice

Theiler's murine encephalomyelitis virus (TMEV)-induced immune-mediated demyelinating disease in susceptible mouse strains has been extensively investigated as a relevant model for human multiple sclerosis. Previous investigations of antiviral T-cell responses focus on immune responses to viral capsid proteins, while virtually nothing is reported on immune responses to nonstructural proteins. In this study, we have identified noncapsid regions recognized by CD4(+) T cells from TMEV-infected mice using an overlapping peptide library. Interestingly, a greater number of CD4(+) T cells recognizing an epitope (3D(21-36)) of the 3D viral RNA polymerase, in contrast to capsid epitopes, were detected in the CNS of TMEV-infected SJL mice, whereas only a minor population of CD4(+) T cells from infected C57BL/6 mice recognized this region. The effects of preimmunization and tolerization with these epitopes on the development of demyelinating disease indicated that capsid-specific CD4(+) T cells are protective during the early stages of viral infection, whereas 3D(21-36)-specific CD4(+) T cells exacerbate disease development. Therefore, protective versus pathogenic CD4(+) T-cell responses directed to TMEV appear to be epitope dependent, and the differences in CD4(+) T-cell responses to these epitopes between susceptible and resistant mice may play an important role in the resistance or susceptibility to virally induced demyelinating disease.

Replication of Theiler's virus requires NF-kappa B-activation: higher viral replication and spreading in astrocytes from susceptible mice

To investigate viral replication and cell-cell spreading in astrocytes, recombinant Theiler's murine encephalomyelitis virus (TMEV) expressing green fluorescent protein (GFP) during the replication was generated. GFP and TMEV proteins were processed correctly in infected cells and production of viral proteins could be tracked by fluorescent microscopy. Viral replication of both wild-type TMEV and GFP-TMEV was dependent on the activation of NF-kappaB and partially MAP kinase, based on chemical inhibition studies. Viral replication was significantly reduced in primary astrocytes from NF-kappaB1 (p105)-deficient mice compared with that from wild-type control mice, whereas cytokine production was enhanced. These results suggest an association of canonical NF-kappaB subunits in viral replication, but not cytokine production. Viral replication was also suppressed in both IKKalpha and IKKbeta-deficient mouse embryonic fibroblasts (MEFs), compared with that in wild-type MEF. However, the inhibition was significantly greater in IKKbeta-deficient MEF, suggesting that IKKbeta plays a stronger role in supporting viral replication. Interestingly, viral replication and spreading in primary astrocytes from susceptible SJL/J mice were several-fold higher than those in astrocytes from resistant C57BL/6 mice, suggesting that higher viral replication levels in astrocytes may also contribute to the viral persistence in the central nervous system (CNS) of susceptible SJL/J mice. A relatively higher level of activated NF-kappaB was found in the nuclei of virus-infected SJL astrocytes compared with C57BL/6 astrocytes suggest that the NF-kappaB activation level affects on viral replication.

Astrocytes in multiple sclerosis: a product of their environment

It has long been thought that astrocytes, like other glial cells, simply provide a support mechanism for neuronal function in the healthy and inflamed central nervous system (CNS). However, recent evidence suggests that astrocytes play an active and dual role in CNS inflammatory diseases such as multiple sclerosis (MS). Astrocytes not only have the ability to enhance immune responses and inhibit myelin repair, but they can also be protective and limit CNS inflammation while supporting oligodendrocyte and axonal regeneration. The particular impact of these cells on the pathogenesis and repair of an inflammatory demyelinating process is dependent upon a number of factors, including the stage of the disease, the type and microenvironment of the lesion, and the interactions with other cell types and factors that influence their activation. In this review, we summarize recent data supporting the idea that astrocytes play a complex role in the regulation of CNS autoimmunity.

Differential virus replication, cytokine production, and antigen-presenting function by microglia from susceptible and resistant mice infected with Theiler's virus

Infection with Theiler's murine encephalomyelitis virus (TMEV) in the central nervous system (CNS) causes an immune system-mediated demyelinating disease similar to human multiple sclerosis in susceptible but not resistant strains of mice. To understand the underlying mechanisms of differential susceptibility, we analyzed viral replication, cytokine production, and costimulatory molecule expression levels in microglia and macrophages in the CNS of virus-infected resistant C57BL/6 (B6) and susceptible SJL/J (SJL) mice. Our results indicated that message levels of TMEV, tumor necrosis factor alpha, beta interferon, and interleukin-6 were consistently higher in microglia from virus-infected SJL mice than in those from B6 mice. However, the levels of costimulatory molecule expression, as well as the ability to stimulate allogeneic T cells, were significantly lower in TMEV-infected SJL mice than in B6 mice. In addition, microglia from uninfected naïve mice displayed differential viral replication, T-cell stimulation, and cytokine production, similar to those of microglia from infected mice. These results strongly suggest that different levels of intrinsic susceptibility to TMEV infection, cytokine production, and T-cell activation ability by microglia contribute to the levels of viral persistence and antiviral T-cell responses in the CNS, which are critical for the differential susceptibility to TMEV-induced demyelinating disease between SJL and B6 mice.

Oral administration of live virus protects susceptible mice from developing Theiler's virus-induced demyelinating disease

Intracerebral infection of susceptible mouse strains with Theiler's murine encephalomyelitis virus (TMEV) results in an immune-mediated demyelinating disease similar to human multiple sclerosis. TMEV infection is widely spread via fecal-oral routes among wild mouse populations, yet these infected mice rarely develop clinical disease. Oral vaccination has often been used to protect the host against many different infectious agents, although the underlying protective mechanism of prior oral exposure is still unknown. To understand the mechanisms involved in protection from demyelinating disease following previous oral infection, immune parameters and disease progression of mice perorally infected with TMEV were compared with those of mice immunized intraperitoneally following intracerebral infection. Mice infected perorally, but not intraperitoneally, prior to CNS viral infection showed lower chronic viral persistence in the CNS and reduced TMEV-induced demyelinating disease. However, a prolonged period of post-oral infection was necessary for effective protection. Mice orally pre-exposed to the virus displayed markedly elevated levels of antibody response to TMEV in the serum, although T cell responses to TMEV in the periphery were not significantly different between perorally and intraperitoneally immunized mice. In addition, orally vaccinated mice showed higher levels of early CNS-infiltration of B cells producing anti-TMEV antibody as well as virus-specific CD4(+) and CD8(+) T cells in the CNS compared to intraperitoneally immunized mice. Therefore, the generation of a sufficient level of protective immune responses appears to require a prolonged time period to confer protection from TMEV-induced demyelinating disease.

CCR2 regulates development of Theiler's murine encephalomyelitis virus-induced demyelinating disease

Theiler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease, a murine model for multiple sclerosis, involves recruitment of T cells and macrophages to the CNS after infection. We hypothesized that CCR2, the only known receptor for CCL2, would be required for TMEV-induced demyelinating disease development because of its role in macrophage recruitment. TMEV-infected SJL CCR2 knockout (KO) mice showed decreased long-term clinical disease severity and less demyelination compared with controls. Flow cytometric data indicated that macrophages (CD45(high) CD11b(+) ) in the CNS of TMEV-infected CCR2 KO mice were decreased compared with control mice throughout disease. CD4(+) and CD8(+) T cell percentages in the CNS of TMEV-infected control and CCR2 KO mice were similar over the course of disease. There were no apparent differences between CCR2 KO and control peripheral immune responses. The frequency of interferon-gamma-producing T cells in response to proteolipid protein 139-151 in the CNS was also similar during the autoimmunity stage of TMEV-induced demyelinating disease. These data suggest that CCR2 is important for development of clinical disease by regulating macrophage accumulation after TMEV infection.

Distinct roles of protein kinase R and toll-like receptor 3 in the activation of astrocytes by viral stimuli

Impaired immune surveillance and constitutive immunosuppressive properties make the central nervous system (CNS) a particular challenge to immune defense, and require that CNS-resident cells be capable of rapidly recognizing and responding to infection. We have previously shown that astrocytes respond to treatment with a TLR3 ligand, poly I:C, with the upregulation of innate immune functions. In the current study, we examine the activation of innate immune functions of astrocytes by Theiler's murine encephalomyelitis virus (TMEV), a picornavirus, which establishes a persistent infection in the CNS of susceptible strains of mice and leads to the development of an autoimmune demyelinating disease that resembles human multiple sclerosis. Astrocytes infected with TMEV are activated to produce type I interferons, the cytokine IL-6, and chemokines CCL2 and CXCL10. We further examined the mechanisms that are responsible for the activation of astrocytes in response to direct viral infection and treatment with poly I:C. We found that the cytoplasmic dsRNA-activated kinase PKR is important for innate immune responses to TMEV infection, but has no role in their induction by poly I:C delivered extracellularly. In contrast, we found that TLR3 has only a minor role in responses to TMEV infection, but is important for responses to poly I:C. These results highlight the differences between responses induced by direct, nonlytic virus infection and extracellular poly I:C. The activation of astrocytes through these different pathways has implications for the initiation and progression of viral encephalitis and demyelinating diseases such as multiple sclerosis.

Retinoic acid-inducible gene-I mediates RANTES/CCL5 expression in U373MG human astrocytoma cells stimulated with double-stranded RNA

Retinoic acid-inducible gene-I (RIG-I) mediates part of the cell signaling in response to viral infection. Polyinosinic-polycytidilic acid (poly IC) is a synthetic double-stranded RNA (dsRNA) and mimics viral infection when applied to cell cultures. The CC chemokine, RANTES (regulated on activation, normal T-cell expressed and secreted), is a potent attractant for inflammatory cells such as memory T-lymphocytes, monocytes and eosinophils. In the present study, we demonstrated that poly IC enhances the expression of RIG-I in U373MG human astrocytoma cells. The RNA interference of RIG-I resulted in the suppression of the poly IC-induced RANTES expression. Pretreatment of the cells with SB203580, an inhibitor of p38 mitogen-activated protein kinase, and dexamethasone inhibited the poly IC-induced expression of RIG-I. Furthermore, poly IC upregulated RIG-I in normal human astrocytes in culture and the in vivo injection of poly IC into the striatum of the mouse brain induced the expression of RIG-I in astrocytes. We conclude that RIG-I may be involved in immune reactions against viral infection, at least in part, through the regulation of RANTES expression in astrocytes.

Induction of the CXCL1 (KC) chemokine in mouse astrocytes by infection with the murine encephalomyelitis virus of Theiler

In the present study, we focused on the production of the chemokine CXCL1, also termed KC, by cultured Theiler murine encephalomyelitis virus (TMEV)-infected mouse astrocytes. cRNA from mock- and TMEV-infected cells was hybridized to the Affymetrix murine genome U74v2 DNA microarray. Hybridization data analysis demonstrated upregulation of two sequences coding for IL-8 and related to the GRO 1 oncogene MGSA. The murine counterpart of the above human genes has been reported to be the chemokine CXCL1 or KC, and therefore we studied its regulation, confirming its mRNA increase by Northern blots. The presence of CXCL1 in the supernatants of infected cells was further demonstrated by a specific ELISA and its intracellular accumulation by flow cytometry. This secreted CXCL1 was biologically active in a non species-specific way as it induces chemoattraction on human neutrophils and monocyte/macrophages, but not on CD3 positive lymphocytes. Its induction does not follow the MAP kinase pathway which transcripts are decrease in infected cells compared with uninfected astrocytes. Two inflammatory cytokines, IL-1alpha and TNF-alpha, which are also induced by TMEV in astrocytes, were potent inducers of CXCL1. Nevertheless, both mechanisms of induction follow different pathways as antibodies to both cytokines fail to inhibit TMEV-induced CXCL1 upregulation. Spinal cords but not brains from TMEV-infected SJL/J animals contain CXCL1 at the start of clinical signs of the disease. As no CXCL1 induction can be detected neither in cultured BALB/c astrocytes nor in nervous tissue, we propose an important role for CXCL1 in this experimental model of multiple sclerosis as a chemoattractant of destructive immune cells.

Initial capsid-specific CD4(+) T cell responses protect against Theiler's murine encephalomyelitisvirus-induced demyelinating disease

Central nervous system (CNS) infection by Theiler's murine encephalomyelitis virus (TMEV) causes an immune-mediated demyelinating disease similar to human multiple sclerosis in susceptible mice. To understand the pathogenic mechanisms, we analyzed the level, specificity, and function of CD4(+) Th cells in susceptible SJL/J and resistant C57BL/6 mice. Compared to resistant mice, susceptible mice have three- to fourfold higher levels of overall CNS-infiltrating CD4(+) T cells during acute infection. CD4(+) T cells in the CNS of both strains display various activation markers and produce high levels of IFN-gamma upon stimulation with anti-CD3 antibody. However, susceptible mice display significantly fewer (tenfold) IFN-gamma-producing Th1 cells specific for viral capsid epitopes as compared to resistant mice. Furthermore, preimmunization with capsid-epitope peptides significantly increased capsid-specific CD4(+) T cells in the CNS during the early stages of viral infection and delayed the development of demyelinating disease in SJL/J mice. This suggests a protective role of capsid-reactive Th cells during early viral infection. Therefore, a low level of the protective Th1 response to viral capsid proteins, in conjunction with Th1 responses to unknown epitopes may delay viral clearance in susceptible mice leading to pathogenesis of demyelination during acute infection, as compared to resistant mice.

Induction of chemokine and cytokine genes in astrocytes following infection with Theiler's murine encephalomyelitis virus is mediated by the Toll-like receptor 3

Theiler's murine encephalomyelitis virus (TMEV) infection in the central nervous system (CNS) induces a demyelinating disease similar to human multiple sclerosis. TMEV infection results in activation of various chemokine and cytokine genes that are important in the initiation of an inflammatory response. We have previously shown that the production of these chemokines and cytokines in astrocytes is induced via the NF-kappaB pathway following TMEV and Coxsackie virus infection. In this study, we investigated whether the NF-kappaB-dependent inflammatory responses after TMEV infection is triggered through TLR3 and/or TLR7. The activation of NF-kappaB or IRF/ISRE, as well as the production of both MCP-1/CCL2 and IL-8/CXCL8, was observed in only TLR3-transfected HEK 293 cells, but not in TLR7-tranfected cells. The potential involvement of TLR3 in mouse embryonic fibroblasts and primary astrocytes was further investigated following transfection with wildtype or dominant negative form of TLRs and MyD88, as well as astrocytes from TLR3- and MyD88-deficient mice. Similarly, the activation of transcription factors and chemokine genes is induced in these mouse cells through primarily TLR3 signaling pathway, but not TLR7 or other MyD88-mediated pathways following TMEV infection. However, the TLR3-mediated cellular activation does not appear to affect the level of viral replication in astrocytes. These results strongly suggest that TLR3-signaling by TMEV alone is sufficient to induce the initial inflammatory cytokine responses that could be very important for the outcome of virus-induced encephalitis and/or demyelinating diseases, such as multiple sclerosis.

Theiler's virus induces the MIP-2 chemokine (CXCL2) in astrocytes from genetically susceptible but not from resistant mouse strains

The murine encephalomyelitis virus of Theiler (TMEV) induces demyelination in susceptible strains of mice by a CD4(+) Th1 T cell mediated immunopathologic process. We focused on the production of one chemokine, the macrophage inflammatory protein-2 (MIP-2 or CXCL2), by cultured mouse astrocytes infected with the BeAn strain of TMEV. Analysis of a murine genome DNA hybridized with cRNA from mock- and TMEV-infected astrocytes, revealed up-regulation of three sequences encoding MIP-2. Northern blot analysis indicated increased MIP-2 mRNA expression. Levels of MIP-2 in the supernatants of infected cells as detected by ELISA, varied directly with the multiplicity of infection used. This secreted CXCL2 was biologically active inducing chemoattraction of neutrophils but not of lymphocytes. CXCL2 was specifically induced by TMEV infection, since induction was inhibited by anti TMEV antibodies. The inflammatory cytokines, IL-1alpha and TNF-alpha, which are also induced in astrocytes by TMEV, were very potent inducers of CXCL2. Nevertheless, both mechanisms of induction follows different pathways as antibodies to both cytokines fails to inhibit TMEV-induced CXCL2 up-regulation. Sera from TMEV-infected SJL/J mice with chronic demyelination, but not from BALB/c TMEV-resistant mice, revealed CXCL2 at the peak of clinical disease. Our main novel finding is the strain-dependent differences in CXCL2 expression both in vitro and in vivo. This suggest an role for this chemokine in attracting immune cells within the CNS, which in turn, might trigger demyelination in this experimental model of MS.

Differential effects of chemokines on oligodendrocyte precursor proliferation and myelin formation in vitro

Chemokines have recently been postulated to have important functions in the central nervous system (CNS) in addition to their principal role of directional migration of leukocytes. In particular, it has been shown that chemokines may play a role in the regulation of oligodendrocyte biology. Here, we have chosen to study the role of certain chemokines in regulating myelination. We have used the murine oligodendrocyte precursor-like cell line, Oli-neu, and primary mixed cortical cultures as experimental systems to assess their activities on oligodendrocyte precursor proliferation and developmental in vitro myelination. GRO-alpha, IL-8, SDF-1alpha and RANTES dose-dependently increased proliferation of this mouse A2B5 precursor-like cell line, while MCP-1 did not. Furthermore, the CXC chemokines GRO-alpha, IL-8 and SDF-1alpha stimulated myelin basic protein synthesis in a dose-dependent manner in primary myelinating cultures and enhanced myelin segment formation in this system, while the CC chemokines MCP-1 and RANTES did not. We also demonstrate that the receptor for SDF-1alpha, CXCR4, is expressed in mixed cortical cultures by PDGFalphaR positive oligodendrocyte precursors (OLPs) as well as by Oli-neu cells. SDF-1alpha induced proliferation in primary mixed cultures and the Oli-neu cell line was mediated through this receptor. We propose, therefore, that CXC chemokines and in particular SDF-1alpha regulates CNS myelination via their effects on cells of the oligodendrocyte lineage, specifically stimulation of OLP proliferation.

Double-stranded RNA stimulates chemokine expression in microglia through vacuolar pH-dependent activation of intracellular signaling pathways

During neurotropic virus infection, microglia act as a source of chemokines, thereby regulating the recruitment of peripheral leukocytes and the multicellular immune response within the CNS. Herein, we present a comprehensive study on the chemokine production by microglia in response to double-stranded RNA (dsRNA), a conserved molecular pattern of virus infection. Transcriptional analyses of chemokine genes revealed that dsRNA strongly induces the expression of CXC chemokine ligand 10 (CXCL10) and CC chemokine ligand 5 (CCL5) in microglia. We also observed that the dsRNA stimulation triggered the activation of signaling pathways mediated by nuclear factor kappaB (NF-kappaB) and mitogen-activated protein kinases (MAPK), including extracellular signal-regulated kinases 1 and 2 (ERK1/2), p38, and c-Jun N-terminal kinase (JNK). The microglial CXCL10 response to dsRNA was induced via NF-kappaB, p38, and JNK pathways, whereas the dsRNA-induced CCL5 production was dependent on JNK, but not on the other signal-transducing molecules tested. In addition, the acidic environment of intracellular vesicles was required for the activation of cellular signaling in response to dsRNA. Taken together, these results suggest that the recognition of dsRNA structure selectively induces the CXCL10 and CCL5 responses in microglia through vacuolar pH-dependent activation of NF-kappaB and MAPK signaling pathways.

Rabies virus-induced activation of mitogen-activated protein kinase and NF-kappaB signaling pathways regulates expression of CXC and CC chemokine ligands in microglia

Following virus infection of the central nervous system, microglia, the ontogenetic and functional equivalents of macrophages in somatic tissues, act as sources of chemokines, thereby recruiting peripheral leukocytes into the brain parenchyma. In the present study, we have systemically examined the growth characteristics of rabies virus (RV) in microglia and the activation of cellular signaling pathways leading to chemokine expression upon RV infection. In RV-inoculated microglia, the synthesis of the viral genome and the production of virus progenies were significantly impaired, while the expression of viral proteins was observed. Transcriptional analyses of the expression profiles of chemokine genes revealed that RV infection, but not exposure to inactivated virions, strongly induces the expression of CXC chemokine ligand 10 (CXCL10) and CC chemokine ligand 5 (CCL5) in microglia. RV infection triggered the activation of signaling pathways mediated by mitogen-activated protein kinases, including p38, extracellular signal-regulated kinases 1 and 2 (ERK1/2), and c-Jun N-terminal kinase, and nuclear factor kappaB (NF-kappaB). RV-induced expression of CXCL10 and CCL5 was achieved by the activation of p38 and NF-kappaB pathways. In contrast, the activation of ERK1/2 was found to down-regulate CCL5 expression in RV-infected microglia, despite the fact that it was involved in partial induction of CXCL10 expression. Furthermore, NF-kappaB signaling upon RV infection was augmented via a p38-mediated mechanism. Taken together, these results indicate that the strong induction of CXCL10 and CCL5 expression in microglia is precisely regulated by the activation of multiple signaling pathways through the recognition of RV infection.

Innate immune response induced by Theiler's murine encephalomyelitis virus infection

Although the causative agents of human multiple sclerosis (MS) are not known, it is suspected that a viral infection may be associated with the initiation of the disease. Several viral disease models in mice have been studied to understand the pathogenesis of demeylination. In particular, Theiler's murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD) has been extensively studied as a relevant model. Various cytokines and chemokines are produced upon viral infection by different cell types, including antigen-presenting cells (APCs) such as macrophages; dendritic cells (DCs); and glial cells, such as astrocytes, microglia, and oligoden-drocytes. The upregulation of the corresponding molecules are also found in MS and are likely to play an important role in the protection and/or pathogenesis of chronic inflammatory demyelinating disease. In this review, the type of cells and molecules, gene-activation mechanisms as well as their potential roles in protection and pathogenesis will be discussed.

Neutralization of chemokines RANTES and MIG increases virus antigen expression and spinal cord pathology during Theiler's virus infection

The role of chemokines during some viral infections is unpredictable because the inflammatory response regulated by these molecules can have two, contrasting effects—viral immunity and immunopathologic injury to host tissues. Using Theiler's virus infection of SJL mice as a model of this type of disease, we have investigated the roles of two chemokines—regulated on activation, normal T cell-expressed and secreted (RANTES) chemokine and monokine induced by IFN-γ (MIG)—by treating mice with antisera that block lymphocyte migration. Control, infected mice showed virus persistence, mild inflammation and a small degree of demyelination in the white matter of the spinal cord at 6 weeks post-infection. Treatment of mice with RANTES antiserum starting at 2 weeks post-infection increased both viral antigen expression and the severity of inflammatory demyelination at 6 weeks post-infection. MIG antiserum increased the spread of virus and the proportion of spinal cord white matter with demyelination. Overall, viral antigen levels correlated strongly with the extent of pathology. At the RNA level, high virus expression was associated with low IL-2 and high IL-10 levels, and RANTES antiserum decreased the IL-2/IL-10 ratio. Our results suggest that RANTES and MIG participate in an immune response that attempts to restrict viral expression while limiting immunopathology and that anti-chemokine treatment poses the risk of exacerbating both conditions in the long term.

Differential activation of astrocytes by innate and adaptive immune stimuli

The immunologic privilege of the central nervous system (CNS) makes it crucial that CNS resident cells be capable of responding rapidly to infection. Astrocytes have been reported to express Toll-like receptors (TLRs), hallmark pattern recognition receptors of the innate immune system, and respond to their ligation with cytokine production. Astrocytes have also been reported to respond to cytokines of the adaptive immune system with the induction of antigen presentation functions. Here we have compared the ability of TLR stimuli and the adaptive immune cytokines interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) to induce a variety of immunologic functions of astrocytes. We show that innate signals LPS- and poly I:C lead to stronger upregulation of TLRs and production of the cytokines IL-6 and TNF-alpha as well as innate immune effector molecules IFN-alpha4, IFN-beta, and iNOS compared with cytokine-stimulated astrocytes. Both innate stimulation and adaptive stimulation induce similar expression of the chemokines CCL2, CCL3, and CCL5, as well as similar enhancement of adhesion molecule ICAM-1 and VCAM-1 expression by astrocytes. Stimulation with adaptive immune cytokines, however, was unique in its ability to induce upregulation of MHC II and the functional ability of astrocytes to activate CD4(+) T cells. These results indicate potentially important and changing roles for astrocytes during the progression of CNS infection.

Upregulation of RANTES gene expression in neuroglia by Japanese encephalitis virus infection

Infection with Japanese encephalitis virus (JEV) causes cerebral inflammation and stimulates inflammatory cytokine expression. Glial cells orchestrate immunocyte recruitment to focal sites of viral infection within the central nervous system (CNS) and synchronize immune cell functions through a regulated network of cytokines and chemokines. Since immune cell infiltration is prominent, we investigated the production of a responding chemoattractant, RANTES (regulated upon activation, normal T-cell expressed and secreted), in response to JEV infection of glial cells. Infection with JEV was found to elicit the production of RANTES from primary neurons/glia, mixed glia, microglia, and astrocytes but not from neuron cultures. The production of RANTES did not seem to be directly responsible for JEV-induced neuronal death but instead contributed to the recruitment of immune cells. RANTES expression required viral replication and the activation of extracellular signal-regulated kinase (ERK) as well as transcription factors, including nuclear factor kappa B (NF-kappaB) and nuclear factor IL-6 (NF-IL-6). The induction of RANTES expression by JEV infection in glial cells needed the coordinate activation of NF-kappaB and NF-IL-6. Using enzymatic inhibitors, we demonstrated a strong correlation between the ERK signaling pathway and RANTES expression. However, JEV replication was not dependent on the activation of ERK, NF-kappaB, and NF-IL-6. Altogether, these results demonstrated that infection of glial cells by JEV provided the early ERK-, NF-kappaB-, and NF-IL-6-mediated signals that directly activated RANTES expression, which might be involved in the initiation and amplification of inflammatory responses in the CNS.

Chronic restraint stress during early Theiler's virus infection exacerbates the subsequent demyelinating disease in SJL mice

Chronic restraint stress, administered during early infection with Theiler's virus, was found to exacerbate the acute central nervous system (CNS) viral infection and the subsequent demyelinating phase of disease (an animal model of Multiple Sclerosis (MS)) in SJL male and female mice. During early infection, stressed mice displayed decreased body weights and spontaneous activity; while increased behavioral signs of illness and plasma corticosterone (CORT) levels. During the subsequent chronic demyelinating phase of disease, previously stressed mice had greater behavioral signs of the chronic phase, worsened rotarod performance, and increased inflammatory lesions of the spinal cord. In addition, mice developed autoantibodies to myelin basic protein (MBP), proteolipid protein peptide (PLP139-151), and myelin oligodendrocyte glycoprotein peptide (MOG33-55).

Alterations in chemokine expression following Theiler's virus infection and restraint stress

Restraint stress (RS) applied to mice during acute infection with Theiler's virus causes corticosterone-induced immunosuppression. This effect was further investigated by measuring chemokine changes in the spleen and central nervous system (CNS) using an RNase Protection Assay. mRNAs for lymphotactin (Ltn), interferon-induced protein-10 (IP-10), MIP-1 beta, monocyte chemoattractant protein-1 (MCP-1) and TCA-3 were detected in the spleen at day 2 pi, but not in the brain of CBA mice infected with Theiler's virus. Ltn, IP-10 and RANTES were elevated in both the spleen and the brain at day 7 pi, and were significantly decreased by RS in the brain. RS also resulted in decreased inflammation within the CNS.

Chemokines and glial cells: a complex network in the central nervous system

Chemokines are small secreted proteins that are essential for the recruitment and activation of specific leukocyte subsets at sites of inflammation and for the development and homeostasis of lymphoid and nonlymphoid tissues. During the past decade, chemokines and their receptors have also emerged as key signaling molecules in neuroinflammatory processes and in the development and functioning of the central nervous system. Neurons and glial cells, including astrocytes, oligodendrocytes, and microglia, have been identified as cellular sources and/or targets of chemokines produced in the central nervous system in physiological and pathological conditions. In this article, we provide an update of chemokines and chemokine receptors expressed by glial cells focusing on their biological functions and implications in neurological diseases.

Inducible nitric oxide synthase in chronic active multiple sclerosis plaques: distribution, cellular expression and association with myelin damage

Inducible nitric oxide synthase (iNOS) is an enzyme that produces nitric oxide (NO) and is thought to contribute to the pathogenesis of multiple sclerosis (MS). The extent of iNOS expression was examined using laser scanning confocal microscopy of 13 chronic active plaques from seven MS patients displaying both acute demyelination and active inflammation. iNOS expression in these plaques was substantial and diverse in cellular distribution. Expression of iNOS was observed in ependymal cells located in periventricular lesions, inflammatory cells, and occasionally in astrocytes. iNOS was found in microglial/macrophage cells that expressed CD64, the high affinity Fc gamma receptor associated with cells that have phagocytic function and participate in antibody-dependent cellular cytotoxicity (ADCC). Scavenger microglial/macrophage cells that expressed the marker CD14 were also present and may express iNOS. The markers for myelin damage, nitrotyrosine (an index of iNOS mediated damage via peroxynitrite formation), along with MBP fragments, were also observed associated with iNOS in MS plaques. Together, these findings support a central role for iNOS in the pathogenesis of multiple sclerosis.

Theiler's virus infection: a model for multiple sclerosis

Both genetic background and environmental factors, very probably viruses, appear to play a role in the etiology of multiple sclerosis (MS). Lessons from viral experimental models suggest that many different viruses may trigger inflammatory demyelinating diseases resembling MS. Theiler's virus, a picornavirus, induces in susceptible strains of mice early acute disease resembling encephalomyelitis followed by late chronic demyelinating disease, which is one of the best, if not the best, animal model for MS. During early acute disease the virus replicates in gray matter of the central nervous system but is eliminated to very low titers 2 weeks postinfection. Late chronic demyelinating disease becomes clinically apparent approximately 2 weeks later and is characterized by extensive demyelinating lesions and mononuclear cell infiltrates, progressive spinal cord atrophy, and axonal loss. Myelin damage is immunologically mediated, but it is not clear whether it is due to molecular mimicry or epitope spreading. Cytokines, nitric oxide/reactive nitrogen species, and costimulatory molecules are involved in the pathogenesis of both diseases. Close similarities between Theiler's virus-induced demyelinating disease in mice and MS in humans, include the following: major histocompatibility complex-dependent susceptibility; substantial similarities in neuropathology, including axonal damage and remyelination; and paucity of T-cell apoptosis in demyelinating disease. Both diseases are immunologically mediated. These common features emphasize the close similarities of Theiler's virus-induced demyelinating disease in mice and MS in humans.

Induction of chemokines in human astrocytes by picornavirus infection requires activation of both AP-1 and NF-kappa B

Infection with different picornaviruses can cause meningitis/encephalitis in humans and experimental animals. To investigate the mechanisms of such inflammatory diseases, potential chemokine gene activation in human astrocytes was investigated following infection with Theiler's murine encephalomyelitis virus (TMEV), coxsackievirus B3 (CVB3), or coxsackievirus B4 (CVB4). We report that all these viruses are potent inducers for the expression of interleukin‐8 (IL‐8) and monocyte chemoattractant protein‐1 (MCP‐1) genes in primary human astrocytes, as well as in an established astrocyte cell line (U‐373MG). Further studies indicated that both activator protein‐1 (AP‐1) and NF‐κB transcription factors are required in the activation of chemokine genes in human astrocytes infected with various picornaviruses. Interestingly, the pattern of activated chemokine genes in human astrocytes is quite restricted compared to that in mouse astrocytes infected with the same viruses, suggesting species differences in gene activation. This may result in potential differences in the pathogenic outcome in each species. © 2003 Wiley‐Liss, Inc.

Distinct roles for IP-10/CXCL10 in three animal models, Theiler's virus infection, EAE, and MHV infection, for multiple sclerosis: implication of differing roles for IP-10

Theiler's murine encephalomyelitis virus (TMEV) causes demyelination with inflammation of the central nervous system (CNS) in mice and is used as an animal model for multiple sclerosis (MS). Interferon-gamma inducible protein-10 kDa (IP-10) is a CXC chemokine and a chemoattractant for CXCR3+ T cells. IP-10 mRNA is expressed in the CNS during TMEV infection. However, administration of anti-IP-10 serum caused no difference in clinical signs, inflammation, demyelination, virus persistence or anti-virus antibody response in TMEV infection, while levels of virus specific and autoreactive lymphoproliferation increased. This likely reflects a difference in the pathogenesis of TMEV infection from that of two other animal models for MS, mouse hepatitis virus infection and experimental allergic encephalomyelitis (EAE), where blocking of IP-10 resulted in clinical and histological improvement with suppression of antigen specific lymphoproliferation. In this review, we compare and contrast the roles of IP-10 between the three animal models for MS, and discuss the relevance to MS patients with different clinical courses.

Infection with Theiler's murine encephalomyelitis virus directly induces proinflammatory cytokines in primary astrocytes via NF-kappaB activation: potential role for the initiation of demyelinating disease

Theiler's virus infection in the central nervous system (CNS) induces a demyelinating disease very similar to human multiple sclerosis. We have assessed cytokine gene activation upon Theiler's murine encephalomyelitis virus (TMEV) infection and potential mechanisms in order to delineate the early events in viral infection that lead to immune-mediated demyelinating disease. Infection of SJL/J primary astrocyte cultures induces selective proinflammatory cytokine genes (interleukin-12p40 [IL-12p40], IL-1, IL-6, tumor necrosis factor alpha, and beta interferon [IFN-beta]) important in the innate immune response to infection. We find that TMEV-induced cytokine gene expression is mediated by the NF-kappaB pathway based on the early nuclear NF-kappaB translocation and suppression of cytokine activation in the presence of specific inhibitors of the NF-kappaB pathway. Further studies show this to be partly independent of dsRNA-dependent protein kinase (PKR) and IFN-alpha/beta pathways. Altogether, these results demonstrate that infection of astrocytes and other CNS-resident cells by TMEV provides the early NF-kappaB-mediated signals that directly activate various proinflammatory cytokine genes involved in the initiation and amplification of inflammatory responses in the CNS known to be critical for the development of immune-mediated demyelination.

CXCL10 production from cytomegalovirus-stimulated microglia is regulated by both human and viral interleukin-10

Glial cells orchestrate immunocyte recruitment to focal areas of viral infection within the brain and synchronize immune cell functions through a regulated network of cytokines and chemokines. Since recruitment of T lymphocytes plays a critical role in resolving cytomegalovirus (CMV) infection, we investigated the production of a T-cell chemoattractant, CXCL10 (gamma interferon-inducible protein 10) in response to viral infection of human glial cells. Infection with CMV was found to elicit the production of CXCL10 from primary microglial cells but not from astrocytes. This CXCL10 expression was not dependent on secondary protein synthesis but did require the phosphorylation of p38 mitogen-activated protein (MAP) kinase. In addition, migration of activated lymphocytes toward supernatants from CMV-stimulated microglial cells was partially suppressed by anti-CXCL10 antibodies. Since regulation of central nervous system inflammation is essential to allow viral clearance without immunopathology, microglial cells were then treated with anti-inflammatory cytokines. CMV-induced CXCL10 production from microglial cells was suppressed following treatment with interleukin-10 (IL-10) and IL-4 but not following treatment with transforming growth factor beta. The IL-10-mediated inhibition of CXCL10 production was associated with decreased CMV-induced NF-kappa B activation but not decreased p38 MAP kinase phosphorylation. Finally, CMV infection of fully permissive astrocytes resulted in mRNA expression for the viral homologue to human IL-10 (i.e., cmvIL-10 [UL111a]) in its spliced form and conditioned medium from CMV-infected astrocytes inhibited virus-induced CXCL10 production from microglial cells through the IL-10 receptor. These findings present yet another mechanism through which CMV may subvert host immune responses.

Preferential induction of IL-10 in APC correlates with a switch from Th1 to Th2 response following infection with a low pathogenic variant of Theiler's virus

Theiler's murine encephalomyelitis virus induces immune-mediated demyelination in susceptible mice after intracerebral inoculation. A naturally occurring, low pathogenic Theiler's murine encephalomyelitis virus variant showed a single amino acid change within a predominant Th epitope from lysine to arginine at position 244 of VP1. This substitution is the only one present in the entire viral capsid proteins. In this paper, we demonstrate that the majority of T cells specific for VP1(233-250) and VP2(74-86) from wild-type virus-infected mice are Th1 type and these VP1-specific cells poorly recognize the variant VP1 epitope (VP1(K244R)) containing the substituted arginine. In contrast, the Th2-type T cell population specific for these epitopes predominates in variant virus-infected mice. Immunization with UV-inactivated virus or VP1 epitope peptides could not duplicate the preferential Th1/Th2 responses following viral infection. Interestingly, the major APC populations, such as dendritic cells and macrophages, produce IL-12 on exposure to the pathogenic wild-type virus, whereas they preferentially produce IL-10 in response to the low pathogenic variant virus. Thus, such a spontaneous mutant virus may have a profoundly different capability to induce Th-type responses via selective production of cytokines involved in T cell differentiation and the consequent pathogenicity of virally induced immune-mediated inflammatory diseases.

Critical role for a high-affinity chemokine-binding protein in gamma-herpesvirus-induced lethal meningitis

Chemokines are involved in recruitment and activation of hematopoietic cells in sites of infection and inflammation. The M3 gene of the gamma-herpesvirus gammaHV68 encodes an abundant secreted protein that binds CC chemokines with high affinity. We report here that this gene is essential for efficient induction of lethal meningitis by gammaHV68. An M3 mutant gammaHV68 (gammaHV68-M3.stop) was 100-fold less virulent than wild-type or marker rescue control (gammaHV68-M3.MR) viruses after intracerebral inoculation. After intracerebral inoculation, gammaHV68-M3.stop grew to lower titers than gammaHV68 or gammaHV68-M3.MR in the brain but spread to and grew normally in the spleen and lung. Expression of several CC chemokines was significantly induced in the CNS by gammaHV68 infection. Consistent with M3 acting by blockade of CC chemokine action, gammaHV68 induced a neutrophilic meningeal inflammatory infiltrate, while gammaHV68-M3.stop induced an infiltrate in which lymphocytes and macrophages predominated. In contrast to the important role of M3 in lethal meningitis, M3 was not required for establishment or reactivation from latent infection or induction of chronic arteritis. These data suggest a role for chemokines in the protection of the nervous system from viral infection and that the M3 protein acts in a tissue-specific fashion during acute but not chronic gammaHV68 infection to limit CC chemokine-induced inflammatory responses.