Characteristics of in vitro cytotoxic effects of myelin basic protein-reactive T cell lines on syngeneic oligodendrocytes

Suppressive effects of 4-acetylaminophenylacetic acid (actarit) on experimental autoimmune encephalomyelitis in rats

To elucidate the efficacy of 4-acetylaminophenylacetic acid (actarit), an anti-rheumatic drug, on neuroinflammatory diseases such as multiple sclerosis, the effects of actarit on both actively induced and adoptively transferred experimental autoimmune encephalomyelitis (EAE) were studied. Daily intraperitoneal administration of actarit during the effector phase of active EAE and transferred EAE suppressed the clinical manifestation and pathological findings of EAE at doses of 300 mg/kg or higher. The percentages of CD4 and CD25 positive cells in the infiltrating cells in the CNS were reduced by this treatment. Semi-quantitative cytokine analysis revealed that the mRNA expression of TNF-alpha and INF-gamma in spinal cords and spleens of actarit treated active EAE rats was significantly reduced compared with vehicle treated EAE rats. The mRNA expression of IL-10 on day 17 in spleens of actarit-treated EAE rats was significantly upregulated. Actarit is potentially useful for the treatment of neuroimmunological disorders, such as multiple sclerosis.

T cell response to two immunodominant proteolipid protein (PLP) peptides in multiple sclerosis patients and healthy controls

Multiple sclerosis (MS) is a demyelinating disease of the central nervous system in which autoimmune T lymphocytes reacting with myelin antigens are believed to play a pathogenic role. Since HLA binding is involved in the selection of T cell responses, we have examined PLP peptide binding to HLA DR2, an HLA allele frequently found in MS patients. Both PLP 40-60 and PLP 89-106 show significant, high affinity binding to HLA DR2. We then tested whether responses to PLP peptides 40-60 and 89-106 are elevated in multiple sclerosis patients compared to matched controls. We also analysed T cell responses to MBP 87-106, which is considered to be the immunodominant region of MBP in humans. Here we demonstrate heterogenous T cell responses to PLP 40-60, PLP 89-106 and MBP 87-106 in both MS patients and controls. The overall number of TCL and the HLA restriction of those TCL did not vary significantly in the two groups. PLP 40-60 specific cytolytic TCL were increased in MS patients, whereas healthy controls had increased percentages of cytolytic TCL responding to PLP 89-106 and MBP 87-106. Although the data presented here shows heterogenous responses in T cell numbers, differences in numbers and specificity of cytolytic cells could be involved in the pathogenesis of autoimmune demyelinating disease.

Inflammation in EAE: role of chemokine/cytokine expression by resident and infiltrating cells

Experimental allergic encephalomyelitis (EAE) is an inflammatory demyelinating disease of the central nervous system (CNS) which has many clinical and pathological features in common with multiple sclerosis (MS). Comparison of the histopathology of EAE and MS reveals a close similarity suggesting that these two diseases share common pathogenetic mechanisms. Immunologic processes are widely accepted to contribute to the initiation and continuation of the diseases and recent studies have indicated that microglia, astrocytes and the infiltrating immune cells have separate roles in the pathogenesis of the MS lesion. The role of cytokines as important regulatory elements in these immune processes has been well established in EAE and the presence of cytokines in cells at the edge of MS lesions has also been observed. However, the role of chemokines in the initial inflammatory process as well as in the unique demyelinating event associated with MS and EAE has only recently been examined. A few studies have detected the transient presence of selected chemokines at the earliest sign of leukocyte infiltration of CNS tissue and have suggested astrocytes as their cellular source. Based on these studies, chemokines have been postulated as a promising target for future therapy of CNS inflammation. This review summarized the events that occur during the inflammatory process in EAE and discusses the roles of cytokine and chemokine expression by the resident and infiltrating cells participating in the process.

Ciliary neurotrophic factor selectively protects human oligodendrocytes from tumor necrosis factor-mediated injury

Oligodendrocytes (OLs) and their myelin membranes are the apparent injury targets in the putative human autoimmune disease multiple sclerosis. The basis for this selective injury remains to be defined. OLs in vitro have been shown to be susceptible to both tumor necrosis factor (TNF) and non-TNF-dependent immune effector mechanisms. The former involves initial nuclear injury (apoptosis); the latter, when mediated by activated T cells, involves initial cell membrane injury (lysis). In the current study, we determined whether human adult CNS-derived OLs could be protected from the above immune effector mechanisms by selected neurotrophic factors (CNTF, BDNF, NGF, NT-3, and NT-4/5) or cytokines demonstrated to protect from human or experimental autoimmune demyelinating diseases (beta-interferon [IFN], IL-10, and TGF-beta). Nuclear injury was assessed in terms of DNA fragmentation using a DNA nick-end-labelling technique; cell membrane injury was assessed by lactate dehydrogenase or chromium 51 release. MTT and cell counting assays were used to assess cell viability and cell loss, respectively. Amongst the neurotrophic factors and cytokines tested, only CNTF significantly protected the OLs from TNF-mediated injury. CNTF also protected the OLs from serum deprivation-induced apoptosis. CNTF, however, did not protect the OLs from injury induced by activated CD4+ T cells. CNTF also did not protect human fetal cortical neurons from serum deprivation or TNF-induced DNA fragmentation, nor did it protect the U251 human glioma cell line from DNA fragmentation induced by a combination of TNF and reduced serum concentration in the culture media. Our results indicate that potential protective effects of neurotrophic factors or cytokines on neural cell populations can be selective both for cell type involved and mechanism of immune-mediated injury. CNTF is the protective factor selective for nuclear-directed injury of OLs.

Oligodendrocyte lysis by CD4+ T cells independent of tumor necrosis factor

The capacity of human CD4+ T cells to lyse heterologous human oligodendrocytes in an 18-hour chromium 51-release assay was compared to that of systemic blood-derived macrophages and central nervous system-derived microglia. CD4+ T cells, activated with either phytohemagglutinin, anti-CD3 antibody, or antigen (myelin basic protein), could induce lysis of the oligodendrocytes whereas macrophages and microglia, activated with interferon-gamma and lipopolysaccharide, could not. The CD4+ T-cell effect was not inhibited with an anti-tumor necrosis factor-alpha-neutralizing antibody. Both the CD4+ T cells and the macrophages could induce lysis of tumor necrosis factor-sensitive rodent cell lines, Wehi 164, and L929; these effects were inhibited with anti-tumor necrosis factor antibody. Pretreatment of the CD4+ T cells with cyclosporine or mitomycin C did not inhibit oligodendrocyte lysis. These results indicate that at least in vitro, CD4+ T cells can induce a form of oligodendrocyte injury that is not reproduced by macrophages or microglia or by tumor necrosis factor. The non-major histocompatibility complex (MHC)-restricted injury of oligodendrocytes induced by both myelin antigen-reactive and mitogen-stimulated T cells may provide a basis whereby cytotoxic CD4+ T cells could interact with a target cell that does not express MHC class II molecules. Our results suggest that immune-mediated oligodendrocyte/myelin injury, as is postulated to occur in the disease multiple sclerosis, may involve multiple effector mechanisms.

Enhancing effects of irrelevant lymphocytes on adoptive transferred experimental allergic encephalomyelitis

To help understand effector mechanisms in experimental allergic encephalomyelitis (EAE) we examined the effects of adding 'irrelevant' lymphocytes from non-EAE donors to major basic protein (MBP)-reactive lymphocytes in the adoptive transfer of EAE (Tr-EAE). The intravenous injection of tetanus toxoid-reactive lymphocytes (TT-cells) and phytohemagglutinin-stimulated lymphocytes on the same day or 2 days after intra-arterial injection of MBP-reactive lymphocytes enhanced the clinical and pathological expression of Tr-EAE. In lymphocyte trafficking studies there was significant accumulation of these injected TT-cells in the central nervous system during enhanced transfer of EAE. W3/25-positive cells were much more predominant in lesion of central nervous system when reinjected with TT cells along with MBP cells compared with lesions of rats injected with MBP cells alone. These findings suggest possible participation of lymphocytes other than MBP-reactive cells in the expression of EAE and provide a useful model to further explore effector mechanisms in the future.

In the presence of dexamethasone, gamma interferon induces rat oligodendrocytes to express major histocompatibility complex class II molecules

Cells that express major histocompatibility complex (MHC) class II molecules can interact directly with CD4 T lymphocytes and either activate immune reactions or become the targets of T-cell-mediated cytotoxic attack. Using rat optic nerve cultures combined with immunocytochemistry and in situ hybridization, we have shown that oligodendrocytes, the major myelin-forming cells of the central nervous system and the main casualty of the immune attacks associated with multiple sclerosis and experimental allergic encephalomyelitis, can be readily induced to express MHC class II mRNA and surface antigens in vitro by exposure to gamma interferon, provided the glucocorticoid dexamethasone is included in the culture medium. Oligodendrocytes exposed to gamma interferon without dexamethasone fail to express MHC class II molecules, which may account for the failure of previous attempts to induce expression in these cells. In the experiments reported here MHC class II expression can be demonstrated both on galactocerebroside-positive cells and on mature oligodendrocytes that express proteolipid protein. These findings expand possibilities for understanding immune-related oligodendrocyte killing and demyelination in human and experimental demyelinating diseases.

Non-specific oligodendrocyte cytotoxicity mediated by soluble products of activated T cell lines

Supernates from myelin basic protein (MBP)-reactive T cell lines have been tested by a battery of assays for cytotoxicity against oligodendrocytes in vitro. All supernates tested demonstrated cytotoxic activity in both a dose- and time-dependent manner that ranged from 29.1% to 55.8% after 48 h incubation. Oligodendrocyte cytotoxicity mediated by MBP-reactive T cell lines was not antigen specific since lines reactive with purified protein derivative (PPD) of tuberculin showed similar cytotoxicity. Supernates cytotoxic to oligodendrocytes were equally effective against syngeneic and non-syngeneic target cells, but had no effect upon astrocytes. Neutralization studies revealed that oligodendrocyte cytotoxicity mediated by MBP-reactive T cell supernates could only be partially attributed to lymphotoxin/tumor necrosis factor activity, and was not associated with perforin, serine proteinase or N-methyl-D-aspartate (NMDA) receptor agonists.

Apoptosis in the nervous system in experimental allergic encephalomyelitis

We report here for the first time the occurrence of apoptosis of cells in the spinal cord in experimental allergic encephalomyelitis (EAE), an autoimmune, T-cell-mediated demyelinating disease. Four different forms of EAE were studied in the Lewis rat: (i) acute EAE induced by inoculation with whole spinal cord and adjuvants; (ii) acute EAE induced by inoculation with myelin basic protein (MBP) and adjuvants; (iii) acute EAE induced by the passive transfer of MBP-sensitized spleen cells; (iv) chronic relapsing EAE induced by inoculation with whole spinal cord and adjuvants followed by treatment with low-dose cyclosporin A. Cells undergoing apoptosis were recognized at light and electron microscopy by the presence of either crescentic masses of condensed chromatin lying against the nuclear envelope or rounded masses of uniformly dense chromatin. They were found in both the white and grey matter of the spinal cord in all 4 forms of this disease. Although it was not possible to identify definitively the types of cells undergoing apoptosis, the size and location of some of the affected cells suggested that they were oligodendrocytes. As there is now a large body of evidence that T-cell-induced target cell death takes the form of apoptosis, it is attractive to hypothesize that oligodendrocyte apoptosis is occurring in EAE as a result of oligodendrocyte-directed T-cell cytotoxicity. However, other apoptotic cells were located within the myelin sheath, meninges and perivascular spaces and were clearly not oligodendrocytes but were most likely blood-derived mononuclear cells. The sparsity of their cytoplasm and the absence of phagocytosed material suggested that they were mainly lymphocytes rather than macrophages. Apoptosis has been shown to be involved in deleting autoreactive T-cells during the normal development of tolerance. Thus apoptotic deletion of myelin/oligodendrocyte-specific lymphocytes in the central nervous system in EAE might explain both the subsidence of inflammation and the acquisition of tolerance in this autoimmune disease.

Cytotoxic effects of myelin basic protein-reactive T cell hybridoma cells on oligodendrocytes

Cells of a rat/mouse T cell hybridoma reactive to the encephalitogenic peptide of myelin basic protein (MBP) was found to be cytotoxic to 51Cr-labelled rat oligodendrocytes (oligos) inducing 52 +/- 5% 51Cr release vs. 28 +/- 2% spontaneous 51Cr release from replicate oligos. The hybridoma cells were not toxic for rat astrocytes or concanavalin A-stimulated lymphoblasts. Hybridoma T cells reactive to an experimental allergic encephalomyelitis-irrelevant antigen (ovalbumin) were not cytotoxic to oligos. The cytotoxic reaction required cell-cell contact but did not require the in vitro presence of antigen-presenting cells MBP. The target antigen on the oligos is not yet defined. These studies suggest that MBP-reactive T cells can be directly cytotoxic to oligos in the absence of other cell populations.