Delta-like ligand 4 regulates central nervous system T cell accumulation during experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is a CD4(+) T cell-mediated inflammatory demyelinating disease of the CNS that serves as a model for multiple sclerosis. Notch receptor signaling in T lymphocytes has been shown to regulate thymic selection and peripheral differentiation. In the current study, we hypothesized that Notch ligand-receptor interaction affects EAE development by regulating encephalitogenic T cell trafficking. We demonstrate that CNS-infiltrating myeloid dendritic cells, macrophages, and resident microglia expressed Delta-like ligand 4 (DLL4) after EAE induction. Treatment of mice with a DLL4-specific blocking Ab significantly inhibited the development of clinical disease induced by active priming. Furthermore, the treatment resulted in decreased CNS accumulation of mononuclear cells in the CNS. Anti-DLL4 treatment did not significantly alter development of effector cytokine expression by Ag-specific T cells. In contrast, anti-DLL4 treatment reduced T cell mRNA and functional cell surface expression of the chemokine receptors CCR2 and CCR6. Adoptive transfer of Ag-specific T cells to mice treated with anti-DLL4 resulted in decreased clinical severity and diminished Ag-specific CD4(+) T cell accumulation in the CNS. These results suggest a role for DLL4 regulation of EAE pathogenesis through modulation of T cell chemokine receptor expression and migration to the CNS.     

Naringenin attenuates experimental autoimmune encephalomyelitis by protecting the intact of blood-brain barrier and controlling inflammatory cell migration

Targeting pathogenic immune cell trafficking poses an attractive opportunity to attenuate autoimmune disorders such as multiple sclerosis (MS). MS and its animal model, experimental autoimmune encephalomyelitis (EAE), are characterized by the immune cells-mediated demyelination and neurodegeneration of the central nervous system (CNS). Our previous study has proven that dietary naringenin ameliorates EAE clinical symptoms via reducing the CNS cell infiltration. The present study examined the beneficial effects of naringenin on maintaining the blood-brain barrier in EAE mice via dietary naringenin intervention. The results showed that naringenin-treated EAE mice had an intact blood-CNS barrier by increasing tight junction-associated factors and decreasing Evans Blue dye in the CNS. Naringenin decreased the accumulation and maturation of conventional dendritic cells (cDCs), CCL19, and CCR7 in the CNS. Also, naringenin blocked the chemotaxis and antigen-presenting function of cDCs that resulted in reducing T-cell secreting cytokines (IFN-γ, IL-17, and IL-6) in the spleen. Importantly, naringenin blocked pathogenic T cells infiltrated into the CNS and attenuates passive EAE. Therefore, by blocking chemokine-mediated migration of DCs and pathogenic T cells into the CNS, naringenin attenuates EAE pathogenesis and might be a potential candidate for the treatment of autoimmune diseases, such as MS and other chronic T-cell mediated autoimmune diseases.     

Critical roles of CXC chemokine ligand 16/scavenger receptor that binds phosphatidylserine and oxidized lipoprotein in the pathogenesis of both acute and adoptive transfer experimental autoimmune encephalomyelitis

The scavenger receptor that binds phosphatidylserine and oxidized lipoprotein (SR-PSOX)/CXCL16 is a chemokine expressed on macrophages and dendritic cells, while its receptor expresses on T and NK T cells. We investigated the role of SR-PSOX/CXCL16 on acute and adoptive experimental autoimmune encephalomyelitis (EAE), which is Th1-polarized T cell-mediated autoimmune disease of the CNS. Administration of mAb against SR-PSOX/CXCL16 around the primary immunization decreased disease incidence of acute EAE with associated reduced infiltration of mononuclear cells into the CNS. Its administration was also shown to inhibit elevation of serum IFN-gamma level at primary immune response, as well as subsequent generation of Ag-specific T cells. In adoptive transfer EAE, treatment of recipient mice with anti-SR-PSOX/CXCL16 mAb also induced not only decreased clinical disease incidence, but also diminished traffic of mononuclear cells into the CNS. In addition, histopathological analyses showed that clinical development of EAE correlates well with expression of SR-PSOX/CXCL16 in the CNS. All the results show that SR-PSOX/CXCL16 plays important roles in EAE by supporting generation of Ag-specific T cells, as well as recruitment of inflammatory mononuclear cells into the CNS.     

TLR-activated B cells suppress T cell-mediated autoimmunity

TLR sense microbial infections, and control activation of immune responses. Dendritic cells, macrophages, and B lymphocytes express TLR and the TLR-signaling adaptor protein MyD88. The impact of TLR-activated B cells on T cell-mediated inflammation is unknown. In this study, we have used mice carrying B cell-restricted deficiencies in MyD88 or in distinct TLR to examine the impact of TLR-activated B cells on a T cell-mediated autoimmune disease, experimental autoimmune encephalomyelitis (EAE). We demonstrate that TLR-signaling in B cells suppresses inflammatory T cell responses (both Th1 and Th17), and stimulates recovery from EAE. Only certain TLR are required on B cells for resolution of EAE, and these are dispensable for disease initiation, indicating that a category of TLR agonists preferentially triggers a suppressive function in B cells and thereby limits autoimmune disease. The TLR agonists controlling the regulatory function of B cells are provided by components of Mycobacterium tuberculosis present in the adjuvant. Thus, MyD88 signaling in B cells antagonizes MyD88 signaling in other cells, which drives differentiation of Th17 cells and is required for induction of EAE. Altogether, our data indicate that B cells link recognition of microbial products via TLR to suppression of a T cell-mediated autoimmune disease.     

Gamma delta T cells regulate the extent and duration of inflammation in the central nervous system by a Fas ligand-dependent mechanism

Gamma delta T cells have been shown to regulate immune responses associated with inflammation, but the mechanism of this regulation is largely unknown. Using the experimental autoimmune encephalomyelitis (EAE) model of the human CNS autoimmune disease multiple sclerosis, we demonstrate that gamma delta T cells are important regulators of CNS inflammation. This was shown using gamma delta T cell-deficient mice that were unable to recover from EAE. The chronic disease was accompanied by a prolonged presence of both macrophages and lymphocytes in the CNS. This extended inflammatory response was due to alterations in both cell proliferation and death. In mice lacking gamma delta T cells, proliferation of encephalitogenic T cells was 3-fold higher, and caspase activity, indicating apoptosis, was 2-fold lower compared with those in control mice recovering from EAE. gamma delta T cell-deficient mice reconstituted with wild-type gamma delta T cells recovered from EAE and resolved inflammation in the CNS, whereas mice reconstituted with Fas ligand-dysfunctional gamma delta T cells did not. Thus, gamma delta T cells regulate both inflammation in the CNS and disease recovery via Fas/Fas ligand-induced apoptosis of encephalitogenic T cells, and a quick resolution of inflammation in the CNS is essential to prevent permanent damage to the CNS resulting in chronic disease.     

Inhibition of autoimmune diabetes by TLR2 tolerance

We have reported that apoptotic β cells undergoing secondary necrosis, called "late apoptotic (LA) β cells," stimulated APCs and induced diabetogenic T cell priming through TLR2, which might be one of the initial events in autoimmune diabetes. Indeed, diabetogenic T cell priming and the development of autoimmune diabetes were significantly inhibited in TLR2-null NOD mice, suggesting the possibility that TLR2 blockade could be used to inhibit autoimmune diabetes. Because prolonged TLR stimulation can induce TLR tolerance, we investigated whether repeated TLR2 administration affects responses to LA β cells and inhibits autoimmune diabetes in NOD mice by inducing TLR2 tolerance. Treatment of primary peritoneal macrophages with a TLR2 agonist, Pam3CSK(4), suppressed cytokine release in response to LA insulinoma cells or further TLR2 stimulation. The expression of signal transducer IRAK-1 and -4 proteins was decreased by repeated TLR2 stimulation, whereas expression of IRAK-M, an inhibitory signal transducer, was enhanced. Chronic Pam3CSK(4) administration inhibited the development of diabetes in NOD mice. Diabetogenic T cell priming by dendritic cells and upregulation of costimulatory molecules on dendritic cells by in vitro stimulation were attenuated by Pam3CSK(4) administration in vivo. Pam3CSK(4) inhibited diabetes after adoptive transfer of diabetogenic T cells or recurrence of diabetes after islet transplantation by pre-existing sensitized T cells. These results showed that TLR2 tolerance can be achieved by prolonged treatment with TLR2 agonists, which could inhibit priming of naive T cells, as well as the activity of sensitized T cells. TLR2 modulation could be used as a novel therapeutic modality against autoimmune diabetes.     

The immunopathology of acute experimental allergic encephalomyelitis induced with myelin proteolipid protein. T cell receptors in inflammatory lesions.

To determine whether there is predominance of T cells expressing a particular TCR V beta chain in the inflammatory lesions of an autoimmune disease model, TCR expression was analyzed in central nervous system (CNS) tissues of mice with experimental allergic encephalomyelitis (EAE). Acute EAE was induced in SJL/J mice either by sensitization with a synthetic peptide corresponding to myelin proteolipid protein residues 139-151 or by adoptive transfer of myelin proteolipid protein peptide 139-151-specific encephalitogenic T cell clones. Mice were killed when they showed clinical signs of EAE or by 40 days after sensitization or T cell transfer. Cryostat CNS and lymphoid tissue sections were immunostained with a panel of mAb to T cell markers and proportions of stained cells were counted in inflammatory foci. In mice with both actively induced and adoptively transferred EAE, infiltrates consisted of many CD3+, TCR alpha beta+, and CD4+ cells, fewer CD8+ cells, and small numbers of TCR gamma delta+ cells. Approximately 30% of CD45+ leukocytes in the inflammatory foci were T cells. Cells expressing TCR V beta 2, 3, 4, 6, 7 and 14 were detected in the infiltrates, whereas TCR V beta 8 and 11, which that are deleted in SJL mice, were absent. When EAE was induced by transfer of T cell clones that use either V beta 2, 6, 10, or 17, there was also a heterogeneous accumulation of T cells in the lesions. Similar proportions of TCR V beta+ and gamma delta+ cells were detected in EAE lesions and in the spleens of the mice. Thus, at the time that clinical signs are present in acute EAE, peripherally derived, heterogeneous TCR V beta+ cells are found in CNS lesions, even when the immune response is initiated to a short peptide Ag or by a T cell clone using a single TCR V beta.     

Proinflammatory bacterial peptidoglycan as a cofactor for the development of central nervous system autoimmune disease

Upon stimulation by microbial products through TLR, dendritic cells (DC) acquire the capacity to prime naive T cells and to initiate a proinflammatory immune response. Recently, we have shown that APC within the CNS of multiple sclerosis (MS) patients contain peptidoglycan (PGN), a major cell wall component of Gram-positive bacteria, which signals through TLR and NOD. In this study, we report that Staphylococcus aureus PGN as a single component can support the induction of experimental autoimmune encephalomyelitis (EAE) in mice, an animal model for MS. Mice immunized with an encephalitogenic myelin oligodendrocyte glycoprotein peptide in IFA did not develop EAE. In contrast, addition of PGN to the emulsion was sufficient for priming of autoreactive Th1 cells and development of EAE. In vitro studies demonstrate that PGN stimulates DC-mediated processes, reflected by increased Ag uptake, DC maturation, Th1 cell expansion, activation, and proinflammatory cytokine production. These data indicate that PGN-mediated interactions result in proinflammatory stimulation of Ag-specific effector functions, which are important in the development of EAE. These PGN-mediated processes may occur both within the peripheral lymph nodes as well as in the CNS and likely involve recognition by TLR on DC. Thus, PGN may provide a physiological trigger of DC maturation, and in this way disrupt the normal tolerance to self Ag. As such, PGN signaling pathways may serve as novel targets for the treatment of MS.     

Sequence-specific potent induction of IFN-alpha by short interfering RNA in plasmacytoid dendritic cells through TLR7

Short interfering RNA (siRNA) is used in RNA interference technology to avoid non-target-related induction of type I interferon (IFN) typical for long double-stranded RNA. Here we show that in plasmacytoid dendritic cells (PDC), an immune cell subset specialized in the detection of viral nucleic acids and production of type I IFN, some siRNA sequences, independent of their GU content, are potent stimuli of IFN-alpha production. Localization of the immunostimulatory motif on the sense strand of a potent IFN-alpha-inducing siRNA allowed dissection of immunostimulation and target silencing. Injection into mice of immunostimulatory siRNA, when complexed with cationic liposomes, induced systemic immune responses in the same range as the TLR9 ligand CpG, including IFN-alpha in serum and activation of T cells and dendritic cells in spleen. Immunostimulation by siRNA was absent in TLR7-deficient mice. Thus sequence-specific TLR7-dependent immune recognition in PDC needs to be considered as an additional biological activity of siRNA, which then should be termed immunostimulatory RNA (isRNA).     

A novel IL-10-independent regulatory role for B cells in suppressing autoimmunity by maintenance of regulatory T cells via GITR ligand

B cells are important for the regulation of autoimmune responses. In experimental autoimmune encephalomyelitis (EAE), B cells are required for spontaneous recovery in acute models. Production of IL-10 by regulatory B cells has been shown to modulate the severity EAE and other autoimmune diseases. Previously, we suggested that B cells regulated the number of CD4(+)Foxp3(+) T regulatory cells (Treg) in the CNS during EAE. Because Treg suppress autoimmune responses, we asked whether B cells control autoimmunity by maintenance of Treg numbers. B cell deficiency achieved either genetically (μMT) or by depletion with anti-CD20 resulted in a significant reduction in the number of peripheral but not thymic Treg. Adoptive transfer of WT B cells into μMT mice restored both Treg numbers and recovery from EAE. When we investigated the mechanism whereby B cells induce the proliferation of Treg and EAE recovery, we found that glucocorticoid-induced TNF ligand, but not IL-10, expression by B cells was required. Of clinical significance is the finding that anti-CD20 depletion of B cells accelerated spontaneous EAE and colitis. Our results demonstrate that B cells play a major role in immune tolerance required for the prevention of autoimmunity by maintenance of Treg via their expression of glucocorticoid-induced TNFR ligand.     

IFN-inducible protein 10/CXC chemokine ligand 10-independent induction of experimental autoimmune encephalomyelitis

In multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE), autoaggressive T cells traffic into the CNS and induce disease. Infiltration of these pathogenic T cells into the CNS has been correlated with the expression of the chemokine IFN-inducible protein (IP)10/CXC chemokine ligand (CXCL)10, a chemoattractant for activated T cells, and its receptor CXCR3, in the CNS of both MS patients and mice with EAE. In the present study, we report that targeted deletion of IP-10 did not diminish the expression, severity, or histopathology of EAE induced by active immunization with 100 micro g of myelin oligodendrocyte glycoprotein peptide (MOG)p35-55. However, we found that IP-10-deficient mice had a lower threshold for expression of disease compared with wild-type littermates. EAE induced by immunization with 5 micro g of MOGp35-55 resulted in more severe disease characterized by a greater number of CNS lesions and infiltrating mononuclear cells in IP-10-deficient mice compared with wild-type controls. IP-10-deficient mice immunized with MOGp35-55 demonstrated increased levels of IFN-inducible T cell alpha-chemokine/CXCL11 mRNA in the CNS and decreased levels of monokine induced by IFN-gamma/CXCL9 mRNA in draining lymph nodes, suggesting differential compensation for loss of IP-10 in lymphoid vs parenchymal tissue compartments. EAE in IP-10-deficient mice induced by low-dose immunization was associated with enhanced Ag-specific Th1 responses in the draining lymph node, which corresponded with diminished lymph node TGF-beta1 expression. Our data demonstrated that IP-10 was not required for the trafficking of pathogenic T cells into the CNS in EAE but played an unexpected role in determining the threshold of disease susceptibility in the periphery.     

Mycobacterium bovis bacille Calmette-Guérin infection in the CNS suppresses experimental autoimmune encephalomyelitis and Th17 responses in an IFN-gamma-independent manner

Multiple sclerosis and an animal model resembling multiple sclerosis, experimental autoimmune encephalomyelitis (EAE), are inflammatory demyelinating diseases of the CNS that are suppressed by systemic mycobacterial infection in mice and BCG vaccination in humans. Host defense responses against Mycobacterium in mice are influenced by T lymphocytes and their cytokine products, particularly IFN-gamma, which plays a protective regulatory role in EAE. To analyze the counter-regulatory role of mycobacterial infection-induced IFN-gamma in the CNS on the function of the pathological Th17 cells and the clinical outcome of EAE, we induced EAE in mice that were intracerebrally infected with Mycobacterium bovis bacille Calmette-Guerin (BCG). In this study, we demonstrate that intracerebral (i.c.) BCG infection prevented inflammatory cell recruitment to the spinal cord and suppressed the development of EAE. Concomitantly, there was a significant decrease in the frequency of myelin oligodendrocyte glycoprotein-specific IFN-gamma-producing CD4(+) T cells in the CNS. IL-17(+)CD4(+) T cell responses were significantly suppressed in i.c. BCG-infected mice following EAE induction regardless of T cell specificity. The frequency of Foxp3(+)CD4(+) T cells in these mice was equivalent to that of control mice. Intracerebral BCG infection-induced protection of EAE and suppression of myelin oligodendrocyte glycoprotein-specific IL-17(+)CD4(+) T cell responses were similar in both wild-type and IFN-gamma-deficient mice. These data show that live BCG infection in the brain suppresses CNS autoimmunity. These findings also reveal that the regulation of Th17-mediated autoimmunity in the CNS can be independent of IFN-gamma-mediated mechanisms.     

Laquinimod, a quinoline-3-carboxamide, induces type II myeloid cells that modulate central nervous system autoimmunity

Laquinimod is a novel oral drug that is currently being evaluated for the treatment of relapsing-remitting (RR) multiple sclerosis (MS). Using the animal model for multiple sclerosis, experimental autoimmune encephalomyelitis (EAE), we examined how laquinimod promotes immune modulation. Oral laquinimod treatment reversed established RR-EAE and was associated with reduced central nervous system (CNS) inflammation, decreased Th1 and Th17 responses, and an increase in regulatory T cells (Treg). In vivo laquinimod treatment inhibited donor myelin-specific T cells from transferring EAE to naive recipient mice. In vivo laquinimod treatment altered subpopulations of myeloid antigen presenting cells (APC) that included a decrease in CD11c(+)CD11b(+)CD4(+) dendritic cells (DC) and an elevation of CD11b(hi)Gr1(hi) monocytes. CD11b(+) cells from these mice exhibited an anti-inflammatory type II phenotype characterized by reduced STAT1 phosphorylation, decreased production of IL-6, IL-12/23 and TNF, and increased IL-10. In adoptive transfer, donor type II monocytes from laquinimod-treated mice suppressed clinical and histologic disease in recipients with established EAE. As effects were observed in both APC and T cell compartments, we examined whether T cell immune modulation occurred as a direct effect of laquinimod on T cells, or as a consequence of altered APC function. Inhibition of Th1 and Th17 differentiation was observed only when type II monocytes or DC from laquinimod-treated mice were used as APC, regardless of whether myelin-specific T cells were obtained from laquinimod-treated or untreated mice. Thus, laquinimod modulates adaptive T cell immune responses via its effects on cells of the innate immune system, and may not influence T cells directly.     

In vivo regulation of experimental autoimmune encephalomyelitis by NK cells: alteration of primary adaptive responses

Innate immune responses provide the host with its first line of defense against infections. Signals generated by subsets of lymphocytes, including NK cells, NKT cells, and APC during this early host response determine the nature of downstream adaptive immune responses. In the present study, we have examined the role of innate NK cells in an autoimmune model through the use of primary immunization with the myelin oligodendrocyte glycoprotein peptide to induce experimental autoimmune encephalomyelitis (EAE). Our studies have shown that in vivo depletion of NK cells can affect the adaptive immune responses, because NK cells were found to regulate the degree of clinical paralysis and to alter immune adaptive responses to the myelin oligodendrocyte glycoprotein peptide. The requirement for NK cells was reflected by changes in the T cell responses and diminished clinical disease seen in mice treated with anti-NK1.1, anti-asialo GM1, and selected Ly49 subtype-depleted mice. In addition to alteration in T cell responses, the maturational status of dendritic cells in lymph nodes was altered both quantitatively and qualitatively. Finally, examination of TCR Vbeta usage of the brain lymphocytes from EAE mice indicated a spectra-type change in receptor expression in NK- depleted mice as compared with non-NK-depleted EAE mice. These findings further establish a recently postulated link between NK cells and the generation of autoreactive T cells.     

TLR ligands act directly upon T cells to restore proliferation in the absence of protein kinase C-theta signaling and promote autoimmune myocarditis

The serine/threonine kinase, protein kinase C-theta (PKC-theta), plays a central role in the activation and differentiation of Th2 cells while being redundant in CD4+ and CD8+ antiviral responses. Recent evidence indicates that PKC-theta may however be required for some T cell-driven autoimmune responses. We have investigated the role of PKC-theta in the induction of autoimmune myocarditis induced by either Coxsackie B3 virus infection or immunization with alpha-myosin/CFA (experimental autoimmune myocarditis (EAM)). PKC-theta-deficient mice did not develop EAM as shown by impaired inflammatory cell infiltration into the heart, reduced CD4+ T cell IL-17 production, and the absence of a myosin-specific Ab response. Comparatively, PKC-theta was not essential for both early and late-phase Coxsackie virus-induced myocarditis. We sought to find alternate pathways of immune stimulation that might reconcile the differential requirements for PKC-theta in these two disease models. We found systemic administration of the TLR ligand CpG restored EAM in PKC-theta-deficient mice. CpG could act directly upon TLR9-expressing T cells to restore proliferation and up-regulation of Bcl-x(L), but exogenous IL-6 and TGF-beta was required for Th17 cell differentiation. Taken together, these results indicate that TLR-mediated activation of T cells can directly overcome the requirement for PKC-theta signaling and, combined with the dendritic cell-derived cytokine milieu, can promote the development of autoimmunity.     

Suppression of experimental autoimmune encephalomyelitis by selective blockade of encephalitogenic T-cell infiltration of the central nervous system

Multiple sclerosis (MS) is a devastating neuroinflammatory disorder of the central nervous system (CNS) in which T cells that are reactive with major components of myelin sheaths have a central role. The receptor for advanced glycation end products (RAGE) is present on T cells, mononuclear phagocytes and endothelium. Its pro-inflammatory ligands, S100-calgranulins, are upregulated in MS and in the related rodent model, experimental autoimmune encephalomyelitis (EAE). Blockade of RAGE suppressed EAE when disease was induced by myelin basic protein (MBP) peptide or encephalitogenic T cells, or when EAE occurred spontaneously in T-cell receptor (TCR)-transgenic mice devoid of endogenous TCR-alpha and TCR-beta chains. Inhibition of RAGE markedly decreased infiltration of the CNS by immune and inflammatory cells. Transgenic mice with targeted overexpression of dominant-negative RAGE in CD4+ T cells were resistant to MBP-induced EAE. These data reinforce the importance of RAGE-ligand interactions in modulating properties of CD4+ T cells that infiltrate the CNS.     

Administration of agonistic anti-4-1BB monoclonal antibody leads to the amelioration of experimental autoimmune encephalomyelitis.

4-1BB, a member of the TNFR superfamily, is a costimulatory receptor primarily expressed on activated T cells. It has been shown that the administration of agonistic anti-4-1BB Abs enhances tumor immunity and allogenic immune responses. Paradoxically, we found that the administration of an agonistic anti-4-1BB mAb (2A) dramatically reduced the incidence and severity of experimental autoimmune encephalomyelitis (EAE). Adoptive transfer of T cells from such treated mice failed to induce EAE, whereas anti-4-1BB treatment following adoptive transfer of encephalitogenic T cells did not prevent EAE pathogenesis. These results suggest that anti-4-1BB treatment during the induction phase inhibits autoreactive T cell immune responses rather than preventing T cell trafficking into the CNS. This was substantiated by the observations that draining lymph node cells from anti-4-1BB-treated mice failed to respond to Ag stimulation in vitro. In addition, we found that such treatment initially promotes the activation and proliferation of Ag-specific CD4+ T cells but subsequently increases their probability of undergoing activation-induced cell death, thereby inhibiting effector T cell responses. More importantly, 2A treatment also inhibits the relapse of EAE in a clinically relevant murine model of multiple sclerosis. This study indicates that the agonistic Ab against 4-1BB can potentially be used as a novel immunotherapeutic agent for treating autoimmune diseases.     

Endogenous, or therapeutically induced, type I interferon responses differentially modulate Th1/Th17-mediated autoimmunity in the CNS

Different viruses trigger pattern recognition receptor systems, such as Toll-like receptors or cytosolic RIG-I like helicases (RLH), and thus induce early type I interferon (IFN-I) responses. Such responses may confer protection until adaptive immunity is activated to an extent that the pathogen can be eradicated. Interestingly, the same innate immune mechanisms that are relevant for early pathogen defense have a role in ameliorating experimental autoimmune encephalomyelitis (EAE), a rodent model of human multiple sclerosis. We and others found that mice devoid of a component of the IFN-I receptor (Ifnar1(-/-)) showed significantly enhanced autoimmune disease of the central nervous system (CNS). A detailed analysis revealed that in wild-type mice IFN-I triggering of myeloid cells was instrumental in reducing brain damage. A more recent study indicated that similar to Ifnar1(-/-) mice, RLH-signaling-deficient mice showed enhanced autoimmune disease of the CNS as well. Moreover, when peripherally treated with synthetic RLH ligands wild-type animals with EAE disease showed reduced clinical scores. Under such conditions, IFN-I receptor triggering of dendritic cells had a crucial role. The therapeutic effect of treatment with RLH ligands was associated with negative regulation of Th1 and Th17 T-cell responses within the CNS. These experiments are consistent with the hypothesis that spatiotemporal conditions of, and cell types involved in, disease-ameliorating IFN-I responses differ significantly, depending on whether they were endogenously induced in the context of EAE pathogenesis within the CNS or upon therapeutic RLH triggering in the periphery. It is attractive to speculate that RLH triggering represents a new strategy to treat multiple sclerosis by stimulating endogenous immunoregulatory IFN-I responses.     

Gamma delta T cell regulation of IFN-gamma production by central nervous system-infiltrating encephalitogenic T cells: correlation with recovery from experimental autoimmune encephalomyelitis

Interferon-gamma has been shown to be important for the resolution of inflammation associated with CNS autoimmunity. Because one of the roles of gamma delta T cells is the regulation of inflammation, we asked whether gamma delta T cells were able to regulate CNS inflammation using the autoimmune disease mouse model experimental autoimmune encephalomyelitis (EAE). We show that the presence of gamma delta T cells was needed to promote the production of IFN-gamma by both CD4 and CD8 T cells in the CNS before the onset of EAE. This regulation was shown to be independent of the ability of gamma delta T cells to produce IFN-gamma, and was specific to T cells in the CNS, as no alterations in IFN-gamma production were detectable in gamma delta T cell-deficient mice in the spleen and lymph nodes of mice with EAE or following immunization. Analysis of TCR gamma delta gene usage in the CNS showed that the only TCR delta V gene families present in the CNS before EAE onset are from the DV7s6 and DV105s1 gene families. We also show that the primary IFN-gamma-producing cells in the CNS are the encephalitogenic T cells, and that gamma delta T cell-deficient mice are unable to resolve EAE disease symptoms like control mice, thus exhibiting a long-term chronic disease course similar to that observed in IFN-gamma-deficient mice. These data suggest that CNS resident gamma delta T cells promote the production of IFN-gamma by encephalitogenic T cells in the CNS, which is ultimately required for the recovery from EAE.