Experimental Allergic Encephalomyelitis Lesions Research Articles

Magnetic Resonance Imaging Reveals Therapeutic Effects of Interferon-Beta on Cytokine-Induced Reactivation of Rat Model of Multiple Sclerosis

Interferon-β (IFN-β) drugs are considered to derive their beneficial effects on multiple sclerosis (MS) progression via their antiinflammatory properties, but the precise mechanism of action remains unclear. Here, we sought to discover how IFN-β impacts on inflammation-associated aggravation of MS-like lesions in rat. Animals with dormant focal experimental allergic encephalomyelitis (EAE) lesions were challenged intravenously with a replication-deficient adenovirus vector carrying interleukin (IL)-1β cDNA (AdIL-1β). Aggravation of inflammation and demyelination within the focal EAE lesion was observed after AdIL-1β injection with associated changes in tissue structure detected by diffusion and magnetization transfer imaging. Postgadolinium-DTPA T1-weighted images revealed contrast enhancement in the ipsilateral meninges, indicating breakdown of the blood-cerebrospinal fluid barrier, and increased left/right regional cerebral blood volume ratio was also observed after AdIL-1β injection. To determine the role of IFN-β on reactivation of the EAE lesion, rats were treated with therapeutic doses of IFN-β and focal EAE lesions showed significantly reduced reactivation in response to systemic AdIL-1β injection. In conclusion, these findings indicate a central role for peripheral IL-1β expression in the mechanism of MS lesion reactivation and that the therapeutic effects of IFN-β may, at least in part, reflect suppression of the effects of peripheral inflammation on MS lesion pathogenesis.

Estradiol inhibits ongoing autoimmune neuroinflammation and NFκB-dependent CCL2 expression in reactive astrocytes

Astroglial reactivity associated with increased production of NFkappaB-dependent proinflammatory molecules is an important component of the pathophysiology of chronic neurological disorders such as multiple sclerosis (MS). The use of estrogens as potential anti-inflammatory and neuroprotective drugs is a matter of debate. Using mouse experimental allergic encephalomyelitis (EAE) as a model of chronic neuroinflammation, we report that implants reproducing pregnancy levels of 17beta-estradiol (E2) alleviate ongoing disease and decrease astrocytic production of CCL2, a proinflammatory chemokine that drives the local recruitment of inflammatory myeloid cells. Immunohistochemistry and confocal imaging reveal that, in spinal cord white matter EAE lesions, reactive astrocytes express estrogen receptor (ER)alpha (and to a lesser extent ERbeta) with a preferential nuclear localization, whereas other cells including infiltrated leukocytes express ERs only in their membranes or cytosol. In cultured rodent astrocytes, E2 or an ERalpha agonist, but not an ERbeta agonist, inhibits TNFalpha-induced CCL2 expression at nanomolar concentrations, and the ER antagonist ICI 182,170 blocks this effect. We show that this anti-inflammatory action is not associated with inhibition of NFkappaB nuclear translocation but rather involves direct repression of NFkappaB-dependent transcription. Chromatin immunoprecipitation assays further indicate that estrogen suppresses TNFalpha-induced NFkappaB recruitment to the CCL2 enhancer. These data uncover reactive astrocytes as an important target for nuclear ERalpha inhibitory action on chemokine expression and suggest that targeting astrocytic nuclear NFkappaB activation with estrogen receptor alpha modulators may improve therapies of chronic neurodegenerative disorders involving astroglial neuroinflammation.

T lymphocytes impair P-glycoprotein function during neuroinflammation

The ATP-binding cassette (ABC) transporter P-glycoprotein (P-gp; ABCB1) is highly expressed at the blood–brain barrier (BBB). P-gp actively secretes and keeps the central nervous system (CNS) safe from body-born metabolites, but also from drugs and food components, emphasising the importance of its optimal function to maintain brain homeostasis. Here we demonstrate that vascular P-gp expression and function are strongly decreased during neuroinflammation. In vivo, the expression and function of brain endothelial P-gp in experimental allergic encephalomyelitis (EAE), an animal model for multiple sclerosis (MS), were significantly impaired. Strikingly, vascular P-gp expression was decreased in both MS and EAE lesions and its disappearance coincided with the presence of perivascular infiltrates consisting of lymphocytes. Our data strongly suggest that activated CD4 + T cells induce impaired function of brain endothelial P-gp. Notably, lymphocyte interaction through endothelial intracellular adhesion molecule −1 (ICAM-1) resulted in activation of a nuclear factor kappa B (NF-κB) signaling pathway, which resulted in endothelial P-gp malfunction. Our study provides first evidence that CD4 + T cells are able to affect endogenous molecular protection mechanisms of brain endothelium. Loss of vascular P-gp function during neuroinflammation may disturb brain homeostasis and thereby aggravate disease progression via exposure of vulnerable CNS cells to detrimental compounds.

MRI of acute experimental allergic encephalomyelitis: correlation with pathology

Objective To investigate the MR imaging findings of acute experimental allergic encephalomyelitis(EAE) in correlation with pathology. Methods An EAE model was induced by intradermal inoculation with guinea pig CNS homogenate in 6 female Lewis rats.Another 6 rats served as control.The clinical presentation and body weight of the animals were recorded daily. Routine MRI,Gd-enhanced MRI were performed when EAE animals showed the initial symptoms. Uhrasmall superparamagnetic iron oxide(USPIO) colloid solution was also administrated intravenously and MRI was performed again after 24 hours. The brain was removed instantly after the second MR imaging. The pathological exams including HE staining,myelin sheath staining and prussian staining were performed.The imaging findings were observed in correlation with pathological results. Results The EAE rats showed decrease of body weight on the 6th to 7th day after inoculation,and the clinical symptoms appeared on the 10th to 11th day after inoculation.Routine MRI did not show any definite abnormalities.The Gd-enhanced MRI found the diffuse thickening and enhancement of brain meninges.The USPIO-enhanced MRI showedareas of low signal intensity at white matter of medulla oblongata on T2WI,and high signal intensity was observed at the corresponding area on T1 WI. Gradient T2 * WI found more foci of low signal intensity in eerebellar white matter besides the lesions in the brain stem.The range of abnormal signal intensity was larger in animal with higher clinical scores than that with lower score.There were no abnormal findings in control animaL The pathological exam found perivascular cuff in the brain white matter in EAE animals,some accompanied with adjacent demyelinatian. The prussian staining found blue particles within the cytoplasm of the macrophages around the lesion,which corresponded to the area of low signal intensity on T2WI.Conclusion USPIO-enhanced MRI could reveal acute EAE lesions which were not capable of being shown on routine MRI and Gd-enhanced MRI.It can image the macrophages around the lesions in vivo.USPIO is important for future research and application in MS patients. Key words: Encephalomyelitis,autoimmuc,experimental; Magnetic resonance imaging; Pathology

Effects of amphetamine and cocaine on the development of acute experimental allergic encephalomyelitis in Lewis rats

The present experiment deals with the effects of amphetamine and cocaine on the development and course of experimental allergic encephalomyelitis (EAE) induced in Lewis rats. Rats were immunized at the age of eight weeks with purified myelin basic protein isolated from guinea pig brain in complete Freund's adjuvant. Drug administration and recording of EAE clinical signs was performed daily since day 1 post-immunization (PI). On day 14 and 28 PI, six rats per group were bled and sacrificed. Spinal cord was examined histologically for EAE lesions. In vivo administration of 0.5 and 1 mg/Kg of amphetamine or cocaine resulted in a dose-related enhancement of neurological and histological signs of acute EAE in comparison with control rats. Both drugs caused a reduction of latent period together with a delayed regression of neurological signs along with an increase in inflammation in the central nervous system in comparison with placebo. Human & Experimental Toxicology (2007) 26, 637-643.

Latent TGF-β1-transduced CD4+ T cells suppress the progression of allergic encephalomyelitis

Systemic injection of small amounts of transforming growth factor-beta (TGF-beta), a cytokine produced by lymphoid and other cells, has a profound effect in protecting mice from the inflammatory demyelinating lesions of experimental allergic encephalomyelitis (EAE; an animal model for multiple sclerosis). However, TGF-beta has side-effects, which might be avoided if the cells producing TGF-beta can be delivered to the affected site in the nervous system to insure its local release in small amounts. Myelin basic protein (MBP)-specific, cloned CD4+ T cells were engineered by retroviral transduction to produce latent TGF-beta. Studies about the spontaneous form of EAE in T cell receptor (TCR)-transgenic recombination-activating gene (RAG)-1(-/-) mice showed that essentially all of the MBP-specific, TCR-transgenic RAG-1(-/-) (BALB/cxB10.PL)F1 mice develop spontaneous EAE by the age of 11 weeks. By 12 weeks, 25-50% of the mice have died from disease. A single injection of TGF-beta1-transduced T helper cell type 1 (Th1) cells significantly protected the mice from EAE, and untransduced Th1 cells did not protect. MBP-specific BALB/c Th2 clones, transduced with TGF-beta1-internal ribosome entry site-green fluorescent protein (GFP) significantly reduced EAE induction by untransduced Th1 cells in RAG-1(-/-) B10.PL mice. Furthermore, the GFP+ TGF-beta1-producing Th2 cells were detectable in the spinal cords of the injected mice.

Imaging inflammation: direct visualization of perivascular cuffing in EAE by magnetic resonance microscopy.

To determine if the architectural features revealed by magnetic resonance microscopy (MRM) allow one to detect microscopic abnormalities associated with neuroinflammation in fixed brain sections from animals with experimental allergic encephalomyelitis (EAE), an animal model for multiple sclerosis (MS). Imaging was performed at the Center for In Vivo Microscopy (CIVM) using a 9.4-Tesla, 89-mm bore, superconducting magnet with actively shielded gradients capable of 850 mT/m. A number of MR contrasts and spatial resolutions were explored. The assessment of EAE brain showed that it is possible to visualize perivascular cuffing in vitro by MRM on three-dimensional T1 proton stains. Inflammatory cell infiltration is a prerequisite for the development of lesions in EAE and MS. Thus, the ability to directly detect individual perivascular cuffs of inflammation may provide a useful means of monitoring the time course of inflammatory events, as conventional histopathological scoring of perivascular cuffs is utilized, but in the absence of sectioning and staining.

2001 Dolph Adams Award and the State of the Journal

2001 Dolph Adams Award and the State of the Journal

Identification of Genetic Loci Controlling the Characteristics and Severity of Brain and Spinal Cord Lesions in Experimental Allergic Encephalomyelitis

Experimental allergic encephalomyelitis (EAE) is the principal genetically determined animal model for multiple sclerosis (MS), the major inflammatory disease of the central nervous system (CNS). Although genetics clearly play a role in susceptibility to MS, attempts to identify the underlying genes have been disappointing. Considerable variation exists between MS patients with regard to the severity of clinical signs, mechanism of demyelination, and location of CNS lesions, confounding the interpretation of genetic data. A mouse-human synteny mapping approach may allow the identification of candidate susceptibility loci for MS based on the location of EAE susceptibility loci. To date, 16 regions of the mouse genome have been identified that control susceptibility or clinical signs of EAE. In this work, we examined the genetic control of histopathological lesions of EAE in an F2 intercross population generated from the EAE susceptible SJL/J and EAE resistant B10.S/DvTe mouse strains. Composite interval mapping was used to identify 10 quantitative trait loci (QTL), including seven newly identified loci controlling the distribution and severity of CNS lesions associated with murine EAE. QTL on chromosome 10 control lesions in the brain, whereas QTL on chromosomes 3, 7, and 12 control lesions in the spinal cord. Furthermore, sexually dimorphic QTL on chromosomes 2, 9, and 11 control CNS lesions in females, whereas QTL on chromosomes 10, 11, 12, 16, and 19 control lesions in males. Our results suggest that the severity and location of CNS lesions in EAE are genetically controlled, and that the genetic component controlling the character and severity of the lesions can be influenced by sex.

Human nerve growth factor protects common marmosets against autoimmune encephalomyelitis by switching the balance of T helper cell type 1 and 2 cytokines within the central nervous system.

Multiple sclerosis is a demyelinating disorder of the central nervous system (CNS), in which an immune attack directed against myelin constituents causes myelin destruction and death of oligodendrocytes, the myelin-producing cells. Here, the efficacy of nerve growth factor (NGF), a growth factor for neurons and oligodendrocytes, in promoting myelin repair was evaluated using the demyelinating model of experimental allergic encephalomyelitis (EAE) in the common marmoset. Surprisingly, we found that NGF delayed the onset of clinical EAE and, pathologically, prevented the full development of EAE lesions. We demonstrate by immunocytochemistry that NGF exerts its antiinflammatory effect by downregulating the production of interferon gamma by T cells infiltrating the CNS, and upregulating the production of interleukin 10 by glial cells in both inflammatory lesions of EAE and normal-appearing CNS white matter. Thus, NGF, currently under investigation in human clinical trials as a neuronal trophic factor, may be an attractive candidate for therapy of autoimmune demyelinating disorders.

Adenoviral gene therapy with catalase suppresses experimental optic neuritis.

To determine if adenoviral-mediated transfer of the gene for catalase (CAT), the reactive oxygen species scavenger, suppresses experimental optic neuritis. Gene therapy with CAT delivered by an adeno-associated viral vector was previously shown to suppress experimental optic neuritis. Because the transduction of protein expression with recombinant adeno-associated viral vector is relatively slow, taking weeks to reach full levels, we studied the effects of replication-deficient adenovirus containing CAT in suppressing experimental optic neuritis. Transduction with adenovirus occurs within days of inoculation, thus, it may be more applicable for the treatment of patients with acute optic neuritis. Replication-deficient adenovirus containing CAT was injected above the right optic nerve heads of SJL/J mice that were simultaneously sensitized for experimental allergic encephalomyelitis. For controls, the left eyes were injected with the replication-deficient adenovirus without CAT or no virus. The histological effects of CAT on the lesions of experimental allergic encephalomyelitis were measured by computerized analysis of the myelin sheath area (for demyelination), optic disc area (for optic nerve head swelling), the extent of the cellular infiltrate, extravasated serum albumin labeled with immunogold (for disruption of the blood-brain barrier), and the in vivo hydrogen peroxide reaction product. After 1 month, cell-specific catalase activity, evaluated by the quantitation of catalase immunogold, was increased about 2-fold each in endothelia, oligodendroglia, astrocytes, and axons of the CAT-inoculated right optic nerves compared with the control left optic nerves. The increased cellular levels of catalase reduced demyelination by 30%, optic nerve head swelling by 25%, cellular infiltration by 26%, disruption of the blood-brain barrier by 61%, and in vivo levels of hydrogen peroxide by 81%. Adenoviral-mediated gene transfer increased catalase levels in all optic nerve cell types, and it persisted for 1 month after inoculation. The increased cellular levels of catalase suppressed demyelination and blood-brain barrier disruption at the foci in the optic nerve where prior magnetic resonance imaging and histopathologic studies have demonstrated the demyelinating inflammation of experimental and human optic neuritis. Together, they suggest that gene therapy with CAT may be helpful in the treatment of patients with optic neuritis.

Age Dependence of Clinical and Pathological Manifestations of Autoimmune Demyelination: Implications for Multiple Sclerosis

A prominent feature of the clinical spectrum of multiple sclerosis (MS) is its high incidence of onset in the third decade of life and the relative rarity of clinical manifestations during childhood and adolescence, features suggestive of age-related restriction of clinical expression. Experimental allergic encephalomyelitis (EAE), a model of central nervous system (CNS) autoimmune demyelination with many similarities to MS, has a uniform rapid onset and a high incidence of clinical and pathological disease in adult (mature) animals. Like MS, EAE is most commonly seen and studied in female adults. In this study, age-related resistance to clinical EAE has been examined with the adoptive transfer model of EAE in SJL mice that received myelin basic protein-sensitized cells from animals 10 days (sucklings) to 12 weeks (young adults) of age. A variable delay before expression of clinical EAE was observed between the different age groups. The preclinical period was longest in the younger (<14 days of age) animals, and shortest in animals 6 to 8 weeks old at time of transfer. Young animals initially resistant to EAE eventually expressed well-developed clinical signs by 6 to 7 weeks of age. This was followed by a remitting, relapsing clinical course. For each age at time of sensitization, increased susceptibility of females compared to males was observed. Examination of the CNS of younger animal groups during the preclinical period showed lesions of acute EAE. Older age groups developed onset of signs coincident with acute CNS lesions. This age-related resistance to clinical EAE in developing mice is reminiscent of an age-related characteristic of MS previously difficult to study in vivo. The associated subclinical CNS pathology and age-related immune functions found in young animals may be relevant to the increasing clinical expression of MS with maturation, and may allow study of factors associated with the known occasional poor correlation of CNS inflammation and demyelination and clinical changes in this disease.

Adeno-associated viral-mediated catalase expression suppresses optic neuritis in experimental allergic encephalomyelitis.

Suppression of oxidative injury by viral-mediated transfer of the human catalase gene was tested in the optic nerves of animals with experimental allergic encephalomyelitis (EAE). EAE is an inflammatory autoimmune disorder of primary central nervous system demyelination that has been frequently used as an animal model for the human disease multiple sclerosis (MS). The optic nerve is a frequent site of involvement common to both EAE and MS. Recombinant adeno-associated virus containing the human gene for catalase was injected over the right optic nerve heads of SJL/J mice that were simultaneously sensitized for EAE. After 1 month, cell-specific catalase activity, evaluated by quantitation of catalase immunogold, was increased approximately 2-fold each in endothelia, oligodendroglia, astrocytes, and axons of the optic nerve. Effects of catalase on the histologic lesions of EAE were measured by computerized analysis of the myelin sheath area (for demyelination), optic disc area (for optic nerve head swelling), extent of the cellular infiltrate, extravasated serum albumin labeled by immunogold (for blood-brain barrier disruption), and in vivo H2O2 reaction product. Relative to control, contralateral optic nerves injected with the recombinant virus without a therapeutic gene, catalase gene inoculation reduced demyelination by 38%, optic nerve head swelling by 29%, cellular infiltration by 34%, disruption of the blood-brain barrier by 64%, and in vivo levels of H2O2 by 61%. Because the efficacy of potential treatments for MS are usually initially tested in the EAE animal model, this study suggests that catalase gene delivery by using viral vectors may be a therapeutic strategy for suppression of MS.

The Fate of T Cells in the Brain: Veni, Vidi, Vici and Veni, Mori

Since the dawn of modern immunology, immune responses within the central nervous system (CNS) have puzzled immunologists. On one hand, the immune-privileged status of the CNS has been known for a long time; along with the eye, the gonads, and the placenta, the CNS is among the few organs that accept grafted foreign cells more readily than the rest of the body. 1 On the other hand, the CNS has been known to be particularly susceptible to autoimmune disease. The first and best characterized autoimmune model, experimental allergic encephalomyelitis (EAE), which resembles multiple sclerosis (MS), is the result of an autoimmune attack by T lymphocytes on the CNS. 2 A report on EAE in this issue 3 by Bauer et al provides data of exceptional clarity that should help in understanding this apparent contradiction. Neuroantigen-specific T cells, which can mount an autoimmune attack against the CNS, are detectable in healthy individuals. This is particularly well established for T cells that are specific for myelin basic protein (MBP), the best-characterized target antigen in the CNS. Studies using MBP-specific T cell receptor-transgenic mice suggested that these T cells normally ignore the autoantigen. 4-6 Like lymphocytes that have not encountered their antigen before, they retain a naive/resting phenotype. Such T cells dramatically change their behavior as soon as they become activated in the course of an immune response; they start to infiltrate the CNS and cause inflammatory damage there. In experimental models EAE is initiated either by immunization with a CNS antigen (for active EAE) or by in vitro injection of activated CNS antigen-specific T cells (for passive EAE, the model used by Bauer et al). In MS, infections with crossreactive microorganisms are thought to initiate the autoimmune attack. It remains unclear why activated myelin-reactive T cells “see” and attack the autoantigen that resting T cells with the same specificity had ignored. The information needed to promote resolution of this question pertains to the rules that govern the entry of lymphocytes into CNS tissue. This issue was addressed by Bauer et al. They injected into rats congenic T cells specific for either various CNS “self” antigens (Bauer et al, Table 1) or for the irrelevant “foreign” antigen ovalbumin (OVA). To distinguish clearly between injected T cells with a defined specificity and activation state and recruited host-derived T cells of unknown specificity and activation state, the authors took advantage of a TK-tsa-transgenic model. The detection of the TK-tsA transgene by in situ hybridization facilitated reliable discrimination of the injected T cells from those of the host.

Astrocytes induce hyporesponses of myelin basic protein-reactive T and B cell function

We have isolated infiltrating mononuclear cells (inMNC) and lymph node MNC (lnMNC) from Lewis rats with actively induced experimental allergic encephalomyelitis (EAE), and compared their responses to myelin basic protein (MBP). MBP-induced proliferation and MBP-specific IgG secreting cells were lower in inMNC compared to lnMNC, while MBP-reactive IFN- γ secreting cells in inMNC were higher. Using an in vitro culture system, we observed that astrocytes derived from newborn Lewis rats not only suppressed T cell proliferation and IFN- γ production but also reduced MBP-specific IgG production by B cells. Astrocyte-derived soluble factor (s), rather than direct cell-to-cell interactions, seems to be responsible for the inhibitory effect. Supernatants from IFN- γ-stimulated astrocytes exhibited stronger suppressive effects than supernatants from unstimulated astrocytes, whereas supernatants from microglia did not cause downregulation of T and B cell functions. These results indicate that astrocytes are major effector cells in inhibiting functions of MBP-reactive T and B cells. Astrocytes down-regulated expression of ICAM-1 and MHC class II in lnMNC, but did not induce apoptosis of lnMNC. The results in the present study do not exclude the possibility that astrocytes induce T cell apoptosis in a cognate fashion. Taken together, the inhibitory properties of astrocytes may contribute to the confinement of inflammatory lesions in multiple sclerosis and EAE. Our report compares immunoreactivities of inMNC and lnMNC in EAE and elucidates the role of astrocytes in the inactivation of MBP-reactive T and B cells.

Astrocytes and microglia express inducible nitric oxide synthase in mice with experimental allergic encephalomyelitis

Nitric oxide (NO), produced by inducible NO synthase (iNOS), may play a role in inflammatory demyelinating diseases of the central nervous system (CNS). We show upregulation of iNOS mRNA in CNS of SJL/J mice with experimental allergic encephalomyelitis (EAE). Using antibodies against mouse iNOS, GFAP (a marker for astrocytes) and Mac-1/CD11b (a marker for macrophages/microglia), both astrocytes and macrophages/microglia were identified as iNOS-expressing cells in situ in EAE lesions. GFAP+ astrocytes not associated with inflammatory infiltrates were also found to express iNOS. Because microglia rather than astrocytes are implicated in demyelinating pathology, we propose that microglial NO may be cytopathic whereas astrocyte-derived NO may be protective in EAE.

Nitric oxide via an inducible isoform of nitric oxide synthase is a possible factor to eliminate inflammatory cells from the central nervous system of mice with experimental allergic encephalomyelitis

We recently identified the inducible isoform of nitric oxide synthase (iNOS) in inflammatory lesions of the central nervous system (CNS) in mice with experimental allergic encephalomyelitis (EAE), a known animal model of multiple sclerosis (MS). In the present study, the role of excessive nitric oxide (NO) production via iNOS was investigated in mice with EAE using immunohistochemistry with antibodies to nitrotyrosine and iNOS, NADPH-diaphorase histochemistry, and the in situ terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) method to detect cell death, presumably through an apoptotic mechanism. NADPH-diaphorase histochemistry and immunohistochemistry for iNOS revealed an elevation of nitric oxide synthase (NOS) activity during the course of EAE, which came from iNOS. Nitrotyrosine was detected in infiltrated cells and some glial cells in the spinal cord lesions, where iNOS-positive inflammatory cells were present at the peak of EAE. The findings implied the generation of NO and peroxynitrite in the EAE lesions, which might damage structural and functional proteins. The TUNEL positive cells were mainly inflammatory ones, and most of them were located in close proximity to iNOS-positive cells, while some of them were iNOS-positive themselves. These results suggested that excessive NO via iNOS played an important role to eliminate inflammatory cells in the CNS of mice with EAE, possibly through an apoptotic mechanism.

Exon 2 containing myelin basic protein (MBP) transcripts are expressed in lesions of experimental allergic encephalomyelitis (EAE)

Exon 2 containing myelin basic protein (MBP) transcripts are expressed during developmental myelination in mice and humans, and during remyelination subsequent to virally induced demyelination in adult mice. Since remyelination characterizes CNS lesions during experimental allergic encephalomyelitis (EAE) and multiple sclerosis (MS), we investigated whether exon 2 containing isoforms of MBP are expressed in EAE lesions during relapsing disease. Exon 2 containing MBP transcripts were detected by in situ hybridization in 17 of 52 EAE mice and in 16 of 30 mice at the peak of the first or second episode of paralysis. Thus exon 2 containing MBP transcripts are expressed in lesions of the CNS during active phases of chronic relapsing autoimmune disease. Implications of these findings with respect to future therapies aimed toward enhancing remyelination in EAE and, possibly MS, are discussed.

The potential role of dendritic cells in immune-mediated inflammatory diseases in the central nervous system

Dendritic cells of the rat were studied immunohistochemically with MRC OX62 monoclonal antibody and using electron microscopy. In normal CNS, a small number of OX62+ cells were detected in the choroid plexus and meninges. These cells were absent from other CNS and peripheral nervous system sites studied. Dendritic cells were also studied in two models of immune-mediated inflammatory conditions in the CNS. These were: acute experimental allergic encephalomyelitis and aberrant delayed-type hypersensitivity lesions induced as a response to heat-killed bacillus Calmette Guérin sequestrated behind the blood–brain barrier. In addition, a group of animals with a delayed-type hypersensitivity response was treated with dexamethasone to assess the effect of steroid treatment on T-cells and OX62+ cells in CNS lesions. Dendritic cells were present in many but not all lesions in acute experimental allergic encephalomyelitis and their numbers were small. In experimental allergic encephalomyelitis lesions, dendritic cells were found predominantly in perivascular cuffs, where they constituted approximately 2% of a total number of major histocompatibility complex class II+ cells. Some of these cells were also detected in the CNS parenchyma, close to the perivascular cuff. In contrast, dendritic cells were present in all delayed-type hypersensitivity lesions studied. Their number in delayed-type hypersensitivity lesions was significantly higher than in experimental allergic encephalomyelitis lesions. Numerous OX62+ cells were found, even in three-month-old lesions. Electron microscopy studies revealed that these cells were often in close contact with lymphocytes. There was no significant change in the density of both OX62+ cells, IL2R+ cells and OX19+ T-cells in delayed-type hypersensitivity lesions after seven-day treatment with dexamethasone, although there was a considerable reduction in the number of CD45RA+ T-cells. The high numbers of dendritic cells found in the delayed-type hypersensitivity lesions may be important in contributing to the chronicity of the response. They may also initiate autoimmune responses to CNS antigens uncovered during bystander tissue damage which occurs as a consequence of aberrant delayed-type hypersensitivity responses.

Focal brain damage enhances experimental allergic encephalomyelitis in brain and spinal cord.

The immunological basis of multiple sclerosis (MS) is well recognized but the factors inducing MS lesions are unclear. In this study, we test the hypothesis that focal brain injury, inflicted during the pre-clinical stages of experimental allergic encephalomyelitis (EAE), will enhance the severity of immunological damage in the cerebral hemispheres and spinal cord. Acute EAE was induced in 30 Lewis rats by the injection of guinea pig spinal cord homogenate in complete Freund's adjuvant. A cryolesion to the surface of the left cerebral hemisphere was induced at 3 days (n = 6) or 8 days (n = 10) postinoculation (p.i.) and animals were killed at 15 days p.i. Control animals were EAE only (n = 9), cryolesion only (n = 4), EAE and sham cryolesion (n = 5) and normal animals (n = 3). Brain and spinal cord were stained by immunocytochemistry using W3/13 (T-lymphocytes) OX6 (MHC Class II) and GFAP (astrocytes) antibodies. The results showed a 2-fold increase in the number of EAE lesions in the brain with significant and widespread increase of MHC Class II antigen expression by microglia, in the cryolesion EAE 8 days p.i. when compared with EAE only animals. The pattern of enhancement suggests that it is due to (i) local spread of tissue or serum factors from the cryolesion; (ii) neural factors affecting remote regions of the CNS; (iii) stimulation of the immune system which may occur due to products of brain injury draining to regional cervical lymph nodes. Investigation of the mechanisms involved may prove fruitful in establishing factors which initiate, aggravate or ameliorate brain damage in multiple sclerosis.