Pathogenesis Of Experimental Allergic Encephalomyelitis Research Articles

A role for Apolipoprotein A-I in the pathogenesis of multiple sclerosis.

Apolipoprotein A1 (Apo A-I), the most abundant component of high-density lipoprotein (HDL), is an anti-inflammatory molecule, yet its potential role in the pathogenesis of multiple sclerosis (MS) has not been fully investigated. In this study, Western blot analyses of human plasma showed differential Apo A-I expression in healthy controls compared to MS patients. Further, primary progressive MS patients had less plasma Apo A-I than other forms of MS. Using experimental allergic encephalomyelitis (EAE) as a model for MS, Apo A-I deficient mice exhibited worse clinical disease and more neurodegeneration concurrent with increased levels of pro-inflammatory cytokines compared to wild-type animals. These data suggest that Apo A-I plays a role in the pathogenesis of EAE, a model for MS, creating the possibility for agents that increase Apo A-I levels as potential therapies for MS.

PD-L1 is increased in the spinal cord and infiltrating lymphocytes in experimental allergic encephalomyelitis.

Experimental allergic encephalomyelitis is a mouse model of human multiple sclerosis with similar pathology and pathogenesis. Th1 cells play an important role in the pathogenesis of experimental allergic encephalomyelitis. This study determined the potential effect of programmed cell death 1 ligand 1 in the pathogenesis of experimental allergic encephalomyelitis induced by injecting myelin oligodendrocyte glycoprotein, complete Freund's adjuvant and Bordetella pertussis toxin into C57BL/6J mice. Experimental allergic encephalomyelitis mice developed disease and showed inflammatory changes in the central nervous system by hematoxylin-eosin staining of spinal cord pathological sections, demyelination by Luxol fast-blue staining and clinical manifestations. The expression of programmed cell death 1 ligand 1 in mice was detected by immunohistochemistry, flow cytometry and western blot analysis. The expression of programmed cell death 1 ligand 1 in the spinal cord and splenocytes of mice was significantly increased compared with normal mice. Our findings suggest the involvement of programmed cell death 1 ligand 1 in the pathogenesis of experimental allergic encephalomyelitis and suggest this should be studied in multiple sclerosis.

H1R expression by CD11B+ cells is not required for susceptibility to experimental allergic encephalomyelitis

The histamine H1 receptor (Hrh1/H1R) was identified as an autoimmune disease gene in experimental allergic encephalomyelitis (EAE), the principal autoimmune model of multiple sclerosis (MS). Previously, we showed that selective re-expression of H1R by endothelial cells or T cells in H1RKO mice significantly reduced or complemented EAE severity and cytokine responses, respectively. H1R regulates innate immune cells, which in turn influences peripheral and central nervous system CD4+ T cell effector responses. Therefore, we selectively re-expressed H1R in CD11b+ cells of H1RKO mice to test the hypothesis that H1R signaling in these cells contributes to EAE susceptibility. We demonstrate that transgenic re-expression of H1R by H1RKO-CD11b+ cells neither complements EAE susceptibility nor T cell cytokine responses highlighting the cell-specific effects of Hrh1 in the pathogenesis of EAE and MS, and the need for cell-specific targeting in optimizing therapeutic interventions based on such genes.

Genetics of experimental allergic encephalomyelitis supports the role of T helper cells in multiple sclerosis pathogenesis

The major histocompatibility complex (MHC) is the primary genetic contributor to multiple sclerosis (MS) and experimental allergic encephalomyelitis (EAE), but multiple additional interacting loci are required for genetic susceptibility. The identity of most of these non-MHC genes is unknown. In this report, we identify genes within evolutionarily conserved genetic pathways leading to MS and EAE. To identify non-MHC binary and quantitative trait loci (BTL/QTL) important in the pathogenesis of EAE, we generated phenotype-selected congenic mice using EAE-resistant B10.S and EAE-susceptible SJL mice. We hypothesized that genes linked to EAE BTL/QTL and MS-GWAS can be identified if they belong to common evolutionarily conserved pathways, which can be identified with a bioinformatic approach using Ingenuity software. Many known BTL/QTL were retained and linked to susceptibility during phenotype selection, the most significant being a region on chromosome 17 distal to H2 (Eae5). We show in pathway analysis that T helper (T(H))-cell differentiation genes are critical for both diseases. Bioinformatic analyses predicted that Eae5 is important in CD4 T-effector and/or Foxp3(+) T-regulatory cells (Tregs), and we found that B10.S-Eae5(SJL) congenic mice have significantly greater numbers of lymph node CD4 and Tregs than B10.S mice. These results support the polygenic model of MS/EAE, whereby MHC and multiple minor loci are required for full susceptibility, and confirm a critical genetic dependence on CD4 T(H)-cell differentiation and function in the pathogenesis of both diseases.

Functional Blocking Monoclonal Antibodies against IL-12p40 Homodimer Inhibit Adoptive Transfer of Experimental Allergic Encephalomyelitis

IL-12p70 (p40:p35) and IL-23 (p40:p19) are bioactive cytokines and their role in experimental allergic encephalomyelitis (EAE), an animal model for multiple sclerosis, are becoming clear. On the other hand, the IL-12p40 homodimer (p40(2)) was considered as an inactive or inhibitory molecule and its functions are poorly understood. To facilitate the studies on p40(2), we have recently generated neutralizing mAb against mouse p40(2). The present study demonstrates the effectiveness of p40(2) mAb in treating the disease process of relapsing-remitting EAE in female SJL/J mice. The p40(2) mAb ameliorated clinical symptoms and disease progression of EAE in recipient mice and suppressed the generation of encephalitogenic T cells in donor mice. Histological and blood-brain barrier (BBB) and blood-spinal cord barrier (BSB) permeability studies reveal that p40(2) mAb effectively inhibited the infiltration of mononuclear cells into brain and spinal cord and improved the integrity of BBB and BSB in EAE mice. Consequently, p40(2) mAb also suppressed the expression of proinflammatory molecules, normalized the expression of myelin genes, and blocked demyelination in the CNS of EAE mice. On the other hand, recombinant mouse p40(2) increased the infiltration of mononuclear cells into the CNS, enhanced the permeability through BBB and BSB, stimulated CNS expression of proinflammatory molecules, and aggravated the disease process of EAE. Taken together, our results suggest that p40(2) participates in the pathogenesis of EAE and that neutralization of p40(2) may be beneficial in multiple sclerosis patients.

15-Deoxy-Δ12,14-Prostaglandin J2 and Curcumin Modulate the Expression of Toll-like Receptors 4 and 9 in Autoimmune T Lymphocyte

Experimental allergic encephalomyelitis (EAE) is a T cell-mediated autoimmune disease model for multiple sclerosis (MS). We have shown earlier that 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) and curcumin ameliorate EAE by modulating inflammatory signaling pathways in T lymphocytes. Toll-like receptors (TLRs), expressed primarily in innate immune cells, play critical roles in the pathogenesis of EAE. T lymphocytes also express TLRs and function as costimulatory receptors to upregulate proliferation and cytokine production in response to specific agonists. In this study, we show that naïve CD4(+) and CD8(+) T cells express detectable levels of TLR4 and TLR9 and that increase after the induction of EAE in SJL/J and C57BL/6 mice by immunization with PLPp139-151 and MOGp35-55 antigen, respectively. It is interesting to note that in vivo treatment with 15d-PGJ2 or curcumin results in a significant decrease in TLR4 and TLR9 expression in CD4(+) and CD8(+) T cells in association with the amelioration of EAE. Although the exact mechanisms are not known, the modulation of TLR expression in T lymphocytes by 15d-PGJ(2) and curcumin suggests new therapeutic targets in the treatment of T cell-mediated autoimmune diseases.

Distinct roles of STAT4α and STAT4β in the pathogenesis of experimental allergic encephalomyelitis (B99)

Abstract Experimental allergic encephalomyelitis (EAE) is a T cell-mediated autoimmune disease model of multiple sclerosis (MS). Interleukin 12 (IL-12) and IL-23 are heterodimeric cytokines, which share common IL-12p40/IL-12Rb2 subunits and play distinct roles in the pathogenesis of EAE. Signaling through JAK-STAT pathway, IL-12 induces Th1 cell development, while IL-23 enhances ThIL17 cell differentiation. We and other have shown earlier that therapeutic intervention or targeted disruption of STAT4 was effective in ameliorating EAE. Recent studies have identified the expression of a full-length STAT4α and a truncated STAT4β, which lacks 44 amino acids at the C-terminus. In this study we show that the STAT4β transgenic mice, induced to develop EAE by immunization with MOGp35-55 peptide, develop an exacerbated EAE than the wild type littermates. However, the STAT4α transgenic mice remain resistant to EAE, as seen in STAT4 knockout mice. Further analyses, by real-time PCR, ELISA and Western blot, show that STAT4β transgenic mice express higher levels of IFNγ, IL-17, IL-12, IL-23 and IL-27 in the brain and spleen than STAT4α transgenic mice, which correlates with the clinical outcome of EAE. Although the distinct roles played by STAT4α and STAT4β in IL-12 and IL-23 signaling in EAE is not known, this study validates the use of STAT4β as a novel therapeutic target in the treatment of MS and other autoimmune diseases.

Loss of blood-brain barrier integrity in the spinal cord is common to experimental allergic encephalomyelitis in knockout mouse models.

Experimental allergic encephalomyelitis (EAE) is an inflammatory demyelinating disease of the CNS that is used to model certain parameters of multiple sclerosis. To establish the relative contributions of T cell reactivity, the loss of blood-brain barrier (BBB) integrity, CNS inflammation, and lesion formation toward the pathogenesis of EAE, we assessed the incidence of EAE and these parameters in mice lacking NF-kappaB, TNF-alpha, IFN-alphabeta receptors, IFN-gamma receptors, and inducible nitric oxide synthase. Although increased myelin oligodendrocyte glycoprotein-specific T cell reactivity was generally associated with a more rapid onset or increased disease severity, the loss of BBB integrity and cell accumulation in spinal cord tissues was invariably associated with the development of neurological disease signs. Histological and real-time RT-PCR analyses revealed differences in the nature of immune/inflammatory cell accumulation in the spinal cord tissues of the different mouse strains. On the other hand, disease severity during the acute phase of EAE directly correlated with the extent of BBB permeability. Thus, the loss of BBB integrity seems to be a requisite event in the development of EAE and can occur in the absence of important inflammatory mediators.

A Tumor Necrosis Factor Receptor 1-Dependent Conversation between Central Nervous System-Specific T Cells and the Central Nervous System Is Required for Inflammatory Infiltration of the Spinal Cord

We examined the role of tumor necrosis factor receptor 1 (TNFR1) in inflammation initiated by the adoptive transfer of central nervous system (CNS)-specific Th1 cells in experimental autoimmune encephalomyelitis, a murine model of multiple sclerosis. This adoptive transfer paradigm eliminates the confounding effects of bacterial adjuvants in the analysis of inflammation. We found that although T cells could reach the meninges and perivascular space in the absence of TNFR1, recruitment of other inflammatory cells from the blood was dramatically reduced. The reduction in the recruitment of CD11b(hi) cells correlated with a dramatic reduction in the production of the chemokines CCL2 (MCP-1) and CXLC2 (MIP-2) in TNFR1-deficient hosts. Bone marrow chimera experiments demonstrated that TNF can be effectively supplied by either the hematopoietic system or the CNS, but the essential TNFR1-responsive cells reside in the CNS. Previous work has demonstrated that microglia produce CCL2, and here we demonstrate that astrocytes and endothelial cells produced CXCL2 in the early stages of inflammation. Therefore, productive inflammation results from a conversation, or mutually responding signals, between the initiating T cells and cells in the parenchyma of the spinal cord.

Pathogenesis of some neurological immune ultrastructural and morphometrical observations on rat thymus

Numerous studies on neuro-immuno-modulation indicate that the thymus is involved in many neurological diseases, including experimental allergic encephalomyelitis (EAE). Twenty Lewis rats were induced for EAE. At X, XII, XX and XXX days post-inoculation the animals were killed, and the thymus was recovered and harvested. Specimens of thymus were submitted to morphological light microscopy analysis (1% toluidine blue) and ultra-structural analysis (transmission electron microscopy). Significant morphometric data were collected by examining the images quantitatively and by statistically analysing the values. Our results show that the microenvironment of the thymus is severally involved in acute EAE. Thymocytes and reticular epithelial cells show many changes which are closely related to the pathogenesis of EAE. In particular we observed: (1) inside the cell an increase in intra-cytoplasmic vacuoles, and changes in the thickness of the nuclear membrane, mitochondria, rough endoplasmic reticulum, cellular inter-digitations and cellular electron-density; (2) outside the cell an increase in pericellular translucent halo, intercellular spaces, intercellular contacts and apoptotic and necrotic figures. The evidence of a thymic role in MS may suggest the intriguing therapeutic concept of thymectomy in the management of this neurological disease.

The role of iron in the pathogenesis of experimental allergic encephalomyelitis and multiple sclerosis.

Multiple sclerosis (MS) and its animal model, experimental allergic encephalomyelitis (EAE), are autoimmune disorders resulting in demyelination in the central nervous system (CNS). Pathologically, the blood-brain barrier becomes damaged, macrophages and T cells enter into the CNS, oligodendrocytes and myelin are destroyed, astrocytes and microglia undergo gliosis, and axons become transected. Data from several biochemical and pharmacological studies indicate that free radicals participate in the pathogenesis of EAE, and iron has been implicated as the catalyst leading to their formation. The primary focus of this article is the examination of the role of iron in the pathogenesis of MS and EAE. Particular attention will be paid to the role and distribution of iron and proteins involved with iron metabolism (e.g., transferrin, ferritin, heme oxygenase-1, etc.) in normal and disease states of myelin. Furthermore, therapeutic interventions aimed at iron, iron-binding proteins, and substrates or products of iron-catalyzed reactions leading to free radical production will be discussed.

CD134 plays a crucial role in the pathogenesis of EAE and is upregulated in the CNS of patients with multiple sclerosis

We investigated the role of the CD134 (also named OX40) molecule in experimental allergic encephalomyelitis (EAE) and multiple sclerosis (MS). We examined the susceptibility of Cd134 −/− mice to EAE, an autoimmune murine model that is dependent on infiltrating CD4 + T lymphocytes reactive to myelin proteins. EAE induced by myelin oligodendrocyte glycoprotein (MOG) injection in Cd134 −/− mice showed less severe clinical signs of disease and markedly reduced inflammatory infiltrates within the central nervous system (CNS). Resistance was associated with a strong reduction of pathogenic IFNγ-producing T cells infiltrating the CNS of Cd134 −/− mice. Furthermore, analysis of CNS tissue sections from EAE animals and MS patients revealed the presence of CD134 + cells that were localized in active lesions, mainly in perivascular infiltrates. The presence of CD134-expressing T cells in brain tissue of MS patients and EAE affected mice, together with the functional evidence provided by the significant decrease in disease score obtained in Cd134 −/− mice, indicate that interfering with the CD134 molecule in T cells may be an appropriate target for therapeutic intervention in active MS.

The correlation between severity of paraparesis and reduced density of resident antigen-presenting cells implicates an unknown role for the spinal perivascular macrophages in experimental autoimmune encephalomyelitis in rats

To study alterations in the morphology of spinal perivascular macrophages (SPM) during experimental allergic encephalomyelitis (EAE), we labelled SPM by intracerebroventricular (icv) injection of horseradish peroxidase (HRP). As earlier electron microscopical analysis had shown severely damaged SPM, we suspected that each inflammatory process is accompanied by the death of SPM. To prove this hypothesis, we compared the numerical density of resident SPM (icv labelled in red by Fluoro-Ruby) with that of monocytes/macrophages recruited to the perivascular space (icv labelled in green by Fluoro-Emerald). At the peak of paraparesis, the density of resident SPM was reduced by 33%. Since this reduction contrasted sharply with earlier data indicating a massive increase in the density of SPM during EAE, we checked our findings after general or selective suppression of the immune response to myelin autoantigens with the drugs dexamethasone and copaxone, respectively. Dexamethasone treatment commenced after evident paraparesis accelerated recovery, but did not influence SPM density. Immunisation with copaxone completely prevented the occurrence of EAE (monitored by video-based motion analysis of tail motility); the subsequent histological analysis revealed no reduction in SPM density. Based on this inverse correlation between the severity of EAE and the density of resident macrophages, we conclude that SPM plays an important role in the pathogenesis of EAE.

Therapeutic intervention in experimental allergic encephalomyelitis by administration of uric acid precursors.

Uric acid (UA) is a purine metabolite that selectively inhibits peroxynitrite-mediated reactions implicated in the pathogenesis of multiple sclerosis (MS) and other neurodegenerative diseases. Serum UA levels are inversely associated with the incidence of MS in humans because MS patients have low serum UA levels and individuals with hyperuricemia (gout) rarely develop the disease. Moreover, the administration of UA is therapeutic in experimental allergic encephalomyelitis (EAE), an animal model of MS. Thus, raising serum UA levels in MS patients, by oral administration of a UA precursor such as inosine, may have therapeutic value. We have assessed the effects of inosine, as well as inosinic acid, on parameters relevant to the chemical reactivity of peroxynitrite and the pathogenesis of EAE. Both had no effect on chemical reactions associated with peroxynitrite, such as tyrosine nitration, or on the activation of inflammatory cells in vitro. Moreover, when mice treated with the urate oxidase inhibitor potassium oxonate were fed inosine or inosinic acid, serum UA levels were elevated markedly for a period of hours, whereas only a minor, transient increase in serum inosine was detected. Administration of inosinic acid suppressed the appearance of clinical signs of EAE and promoted recovery from ongoing disease. The therapeutic effect on animals with active EAE was associated with increased UA, but not inosine, levels in CNS tissue. We, therefore, conclude that the mode of action of inosine and inosinic acid in EAE is via their metabolism to UA.

Modulation of blood-brain barrier dysfunction and neurological deficits during acute experimental allergic encephalomyelitis by the N-methyl-D-aspartate receptor antagonist memantine.

Previous studies by us have strongly indicated a role for the N-methyl-D-aspartate (NMDA) receptor in the pathogenesis of experimental allergic encephalomyelitis (EAE) and, moreover, the loss of blood-brain barrier (BBB) integrity implicit in the disease. The current investigation has used the NMDA receptor antagonist memantine to modify the neurological course of EAE and, in particular, prevent BBB breakdown. Memantine was administered orally either semiprophylactically, from day 7 postinoculation (PI), or therapeutically, 10 to 11 days PI. Semiprophylactic administration of drug at 60 mg/kg b.wt. significantly restored BBB integrity, reduced symptoms, and limited inflammatory lesions (p < 0.05), when assessed 12 days PI. Higher concentrations of memantine did not notably advance disease improvements observed at 60 mg/kg b.wt., and 40-mg/kg b.wt. doses only reduced histological scores (p < 0.05). Therapeutic application of memantine was found to be as effective as semiprophylactic dosing. Administration of drug at 60 mg/kg b.wt. was demonstrated as the optimum dose, significantly reducing disease, BBB permeability, and lesions (p < 0.01). Extended studies revealed that, after cessation of memantine treatment using either dosing regime, any subsequent appearance of disease was suppressed in severity and duration. We have provided further strong evidence in support of a role for the NMDA receptor in the development of EAE and, in particular, the loss of BBB function and recruitment of inflammatory cells. Moreover, memantine is therapeutically efficacious, suggesting the NMDA receptor as a viable pharmacological target for future treatment of human neurological conditions such as multiple sclerosis.

Peroxisome proliferator-activated receptor-gamma agonists inhibit experimental allergic encephalomyelitis by blocking IL-12 production, IL-12 signaling and Th1 differentiation

Peroxisome proliferator-activated receptor-gamma (PPARgamma) is a nuclear receptor transcription factor that regulates adipocyte differentiation and glucose homeostasis. PPARgamma agonists are potent therapeutic agents for the treatment of type 2 diabetes and obesity. PPARgamma agonists also prevent inflammation in animal models, suggesting their use for the treatment of human inflammatory diseases. Experimental allergic encephalomyelitis (EAE) is a Th1 cell-mediated inflammatory demyelinating disease model of multiple sclerosis (MS) and IL-12 plays a crucial role in the pathogenesis of EAE and MS. In this study we have examined the effect of PPARgamma agonists on the pathogenesis of EAE. In vivo treatment of SJL/J mice with PPARgamma agonists, 15-deoxydelta(12,14) prostaglandin J2 or Ciglitazone, decreased the duration and clinical severity of active immunization and adoptive transfer models of EAE. PPARgamma agonists inhibited EAE in association with a decrease in IL-12 production and differentiation of neural antigen-specific Th1 cells. In vitro treatment of activated T cells with PPARgamma agonists inhibited IL-12-induced activation of JAK-STAT signaling pathway and Th1 differentiation. These findings highlight the fact that PPARgamma agonists regulate central nervous system inflammation and demyelination by inhibiting IL-12 production, IL-12 signaling and Th1 differentiation in EAE.

Role of poly(ADP-ribose) synthetase activation in the development of experimental allergic encephalomyelitis

Peroxynitrite formation has been demonstrated during experimental allergic encephalomyelitis (EAE). Furthermore, peroxynitrite has been identified as an activator of poly(ADP-ribose) synthetase (PARS), an enzyme implicated in neurotoxicity. In the current study, we examined the role of PARS activation in the development of EAE. Administration of the PARS inhibitor 5-iodo-6-amino-1,2-benzopyrone (INH 2BP) delayed the onset of EAE and reduced the incidence and severity of disease signs. Moreover, drug treatment lowered iNOS activity and decreased cell infiltration in cervical spinal tissues from EAE-sensitized animals. To conclude, the results of the present investigation suggest that PARS activity may contribute to the pathogenesis of EAE.

SIN-1, a nitric oxide donor, ameliorates experimental allergic encephalomyelitis in Lewis rats in the incipient phase: the importance of the time window.

NO is involved in the regulation of immune responses. The role of NO in the pathogenesis of experimental allergic encephalomyelitis (EAE) is controversial. In this study, 3-morpholinosydnonimine (SIN-1), an NO donor, was administered to Lewis rats on days 5-7 postimmunization, i.e., during the incipient phase of EAE. SIN-1 reduced clinical signs of EAE compared with those in PBS-treated control rats and was accompanied by reduced ED1(+) macrophages and CD4(+) T cell infiltration within the CNS. Blood mononuclear cells (MNC) obtained on day 14 postimmunization revealed that SIN-1 administration enhanced NO and IFN-gamma production by blood MNC and suppressed Ag- and mitogen-induced proliferative responses. MHC class II, B7-1 and B7-2 were down-regulated in SIN-1-treated EAE rats. Simultaneously, frequencies of apoptotic cells among blood MNC were increased. In vivo, SIN-1 is likely to behave as an NO donor. Administration of SIN-1 induced NO production, but did not affect superoxide and peroxynitrite formation. Enhanced NO production during the priming phase of EAE thus promotes apoptosis, down-regulates disease-promoting immune reactivities, and ameliorates clinical EAE, mainly through SIN-1-derived NO, without depending on NO synthase.

On the role of peripheral macrophages during active experimental allergic encephalomyelitis (EAE).

Summary. Experimental allergic encephalitis (EAE) is an experimental autoimmune inflammatory condition of the central nervous system (CNS) that serves as a disease model for multiple sclerosis (MS). The primary effector mechanisms of the immune system leading to tissue destruction during EAE remain still controversial. T-cells, microglia, and macrophages infiltrating the brain parenchyma are suggested to be involved. To clarify the role of these cells during disease Lewis rats were immunised with different immunisation protocols: Immunisation with myelin basic protein (MBP) in complete Freunds adjuvant (CFA) containing high dose of mycobacterial components induced severe disease, whereas immunisation with low dose of mycobacterial components induced only mild disease. Severely and mildly diseased animals were analysed with respect to infiltration of T-cells, macrophages and upregulation of MHC class II molecules on microglia in the brain.All immunised rats showed high T-cell infiltration accompanied by microglia activation. The degree of disease and the infiltration of macrophages varied with dose of adjuvant. Lowering the dose of adjuvant prevented the development of disease but also the influx of peripheral macrophages into the brain without affecting the peripheral T-cell response to the autoantigen. Thus, appearance of (autoreactive) T-cells in the brain and microglia activation were probably not sufficient for development of disease.It can be concluded that peripheral macrophages play an essential or even key role in the pathogenesis of active EAE.

Heme oxygenase-1 and NADPH cytochrome P450 reductase expression in experimental allergic encephalomyelitis: an expanded view of the stress response.

Oxidative stress is implicated in the pathogenesis of experimental allergic encephalomyelitis (EAE), a model for multiple sclerosis. Heme oxygenase-1 (HO-1) is a heat shock protein induced by oxidative stress. HO-1 metabolizes the pro-oxidant heme to the antioxidant biliverdin and CO. HO-1 requires electrons, donated by NADPH cytochrome P450 reductase (henceforth, reductase), for catalytic activity. EAE was induced with a peptide of proteolipid protein in SJL mice, and the expression of HO-1 and reductase in the hindbrain was analyzed. HO-1 protein levels were significantly increased in EAE animals compared with control mice. HO-1 expression was present in ameboid macrophages, reactive microglia, and astrocytes in white matter tracks. Bergmann glia and ameboid macrophages also were occasionally stained in the molecular layer of the cerebellum. Unlike HO-1, reductase protein levels decreased with disease severity. HO-1 and reductase were associated with each other in endoplasmic reticulum micelles, suggesting that the decrease in reductase does not interfere with its association with HO-1. In cells that express HO-1, the association of reductase with HO-1 should competitively inhibit the interaction of reductase with cytochrome P450 isozymes and thereby limit free radical production as the latter two enzymes act cooperatively to produce superoxide. The increase in HO-1 together with the decrease in reductase may be part of a common defense mechanism attempting to minimize tissue damage in several neurological conditions.