Carsten Tue Berg

Induction of endogenous Type I interferon within the central nervous system plays a protective role in experimental autoimmune encephalomyelitis

The Type I interferons (IFN), beta (IFN-β) and the alpha family (IFN-α), act through a common receptor and have anti-inflammatory effects. IFN-β is used to treat multiple sclerosis (MS) and is effective against experimental autoimmune encephalomyelitis (EAE), an animal model for MS. Mice with EAE show elevated levels of Type I IFNs in the central nervous system (CNS), suggesting a role for endogenous Type I IFN during inflammation. However, the therapeutic benefit of Type I IFN produced in the CNS remains to be established. The aim of this study was to examine whether experimentally induced CNS-endogenous Type I IFN influences EAE. Using IFN-β reporter mice, we showed that direct administration of polyinosinic–polycytidylic acid (poly I:C), a potent inducer of IFN-β, into the cerebrospinal fluid induced increased leukocyte numbers and transient upregulation of IFN-β in CD45/CD11b-positive cells located in the meninges and choroid plexus, as well as enhanced IFN-β expression by parenchymal microglial cells. Intrathecal injection of poly I:C to mice showing first symptoms of EAE substantially increased the normal disease-associated expression of IFN-α, IFN-β, interferon regulatory factor-7 and IL-10 in CNS, and disease worsening was prevented for as long as IFN-α/β was expressed. In contrast, there was no therapeutic effect on EAE in poly I:C-treated IFN receptor-deficient mice. IFN-dependent microglial and astrocyte response included production of the chemokine CXCL10. These results show that Type I IFN induced within the CNS can play a protective role in EAE and highlight the role of endogenous type I IFN in mediating neuroprotection.

Cerebrospinal fluid aquaporin-4-immunoglobulin G disrupts blood brain barrier

To clarify the significance of immunoglobulin G autoantibody specific for the astrocyte water channel aquaporin‐4 in cerebrospinal fluid, aquaporin‐4‐immunoglobulin G from a neuromyelitis optica patient was administered intrathecally to naïve mice, and the distribution and pathogenic impact was evaluated. A distinct distribution pattern of aquaporin‐4‐immunoglobulin G deposition was observed in the subarachnoid and subpial spaces where vessels penetrate the brain parenchyma, via a paravascular route with intraparenchymal perivascular deposition. Perivascular astrocyte‐destructive lesions were associated with blood‐borne horseradish peroxidase leakage indicating blood‐brain barrier breakdown. The cerebrospinal fluid aquaporin‐4‐immunoglobulin G therefore distributes widely in brain to initiate astrocytopathy and blood‐brain barrier breakdown.

Influence of type I IFN signaling on anti-MOG antibody-mediated demyelination

BackgroundAntibodies with specificity for myelin oligodendrocyte glycoprotein (MOG) are implicated in multiple sclerosis and related diseases. The pathogenic importance of anti-MOG antibody in primary demyelinating pathology remains poorly characterized.ObjectiveThe objective of this study is to investigate whether administration of anti-MOG antibody would be sufficient for demyelination and to determine if type I interferon (IFN) signaling plays a similar role in anti-MOG antibody-mediated pathology, as has been shown for neuromyelitis optica-like pathology.MethodsPurified IgG2a monoclonal anti-MOG antibody and mouse complement were stereotactically injected into the corpus callosum of wild-type and type I IFN receptor deficient mice (IFNAR1-KO) with and without pre-established experimental autoimmune encephalomyelitis (EAE).ResultsAnti-MOG induced complement-dependent demyelination in the corpus callosum of wild-type mice and did not occur in mice that received control IgG2a. Deposition of activated complement coincided with demyelination, and this was significantly reduced in IFNAR1-KO mice. Co-injection of anti-MOG and complement at onset of symptoms of EAE induced similar levels of callosal demyelination in wild-type and IFNAR1-KO mice.ConclusionsAnti-MOG antibody and complement was sufficient to induce callosal demyelination, and pathology was dependent on type I IFN. Induction of EAE in IFNAR1-KO mice overcame the dependence on type I IFN for anti-MOG and complement-mediated demyelination.

Hypersensitivity Responses in the Central Nervous System

Immune-mediated tissue damage or hypersensitivity can be mediated by autospecific IgG antibodies. Pathology results from activation of complement, and antibody-dependent cellular cytotoxicity, mediated by inflammatory effector leukocytes include macrophages, natural killer cells, and granulocytes. Antibodies and complement have been associated to demyelinating pathology in multiple sclerosis (MS) lesions, where macrophages predominate among infiltrating myeloid cells. Serum-derived autoantibodies with predominant specificity for the astrocyte water channel aquaporin-4 (AQP4) are implicated as inducers of pathology in neuromyelitis optica (NMO), a central nervous system (CNS) demyelinating disease where activated neutrophils infiltrate, unlike in MS. The most widely used model for MS, experimental autoimmune encephalomyelitis, is an autoantigen-immunized disease that can be transferred to naive animals with CD4+ T cells, but not with antibodies. By contrast, NMO-like astrocyte and myelin pathology can be transferred to mice with AQP4–IgG from NMO patients. This is dependent on complement, and does not require T cells. Consistent with clinical observations that interferon-beta is ineffective as a therapy for NMO, NMO-like pathology is significantly reduced in mice lacking the Type I IFN receptor. In MS, there is evidence for intrathecal synthesis of antibodies as well as blood–brain barrier (BBB) breakdown, whereas in NMO, IgG accesses the CNS from blood. Transfer models involve either direct injection of antibody and complement to the CNS, or experimental manipulations to induce BBB breakdown. We here review studies in MS and NMO that elucidate roles for IgG and complement in the induction of BBB breakdown, astrocytopathy, and demyelinating pathology. These studies point to significance of T-independent effector mechanisms in neuroinflammation.

Induction of type I interferon in the central nervous system plays a protective role in EAE

the evaluation of neutrophil immune response (fMLP receptor, TLR2), chemotaxis and migration (CXCR1, CD62L, CD43), regulation of complement (CD46, CD55, CD59), respiratory burst, phagocytosis and degranulation. Compared to healthy controls (HC), neutrophils in NMO and MS show an activated phenotype characterized by a higher expression of surface TLR2, CXCR1 and fMLP receptor. However, contrary to MS neutrophils, NMO neutrophils show reduced adhesion and migratory capacity as well as decreased respiratory burst and degranulation in both treated and untreated patients. In conclusion, we show that although neutrophils are primed in both NMO and MS compared to HC, their effector functions differ significantly, suggesting distinct involvement of neutrophils in these two diseases.

Mechanisms underlying induction of antibody-mediated demyelination in muliple sclerosis

Multiple sclerosis (MS) is associated with impaired function of regulatory immune cell subsets. A new immunoregulatory role for human CD56bright NK cells (CD56brNK) recently emerged, with in vitro demonstration that activation of NK cells with IL-27, IL-2 or anti-CD25 antibody induces suppressor function of CD56br NK toward autologous T cells with mechanisms not fully explained. IL12, over expressed by antigen-presenting cells in MS, also induces activation of NK cells and their expression of cytokines in vitro, in combination with IL-15. We therefore hypothesize that upon IL-12/ IL-15 stimulation, CD56brNK acquire T-cell suppressor function to regulate T-cell activation in inflammatory conditions. Through proliferation assay of CD3/CD28-stimulated T cells, we found that exposure to IL-12/IL-15 for 3 days induces a suppressor function of CD56brNK towards activated, but not resting, autologous CD4+ T cells. We postulated that killing was part of the suppressive mechanism, likely attributable to Granzyme B whose mRNA expression was selectively induced in stimulated CD56brNK. Using a FACS-based assay, we found that stimulated CD56brNK are able to kill autologous activated CD4+ T cells directly through degranulation. In order to assess which NK receptor(s) could be involved in Tcell suppression, we analyzed the proliferation of T cells co-cultured with CD56brNK in the presence of blocking NK receptor antibodies. We found that the selective inhibition of Natural Cytotoxicity Receptors (NCR: NKp30, NKp44, NKp46), but not other tested receptors, restored CD4+ T cell proliferation, suggesting that these receptors are primarily involved in CD56brNK immunoregulatory function. Taken together, these data, provide insights for the mechanism by which the CD56brNK regulate the activation of autologous CD4+ T cells. We investigated CD56brNK in patients with MS to determine whether or not this regulatory cell subset is impaired in MS. We could not detect differences in the proportion of CD56brNK; however, we observed that CD56brNK from MS patients are less able to suppress the proliferation of autologous CD4+ T cells and are apparently impaired in their expression of NCR. Thus, we clearly demonstrate that CD56brNK, whose immunoregulatory function is apparently impaired in MS, play an important role in regulating the immune response, in particular by suppressing the activation of autologous CD4+ T cells through triggering of a specific class of NK receptors, the NCR.