Central Nervous System Parenchyma Research Articles

Immunohistochemical analysis of human neuronectin expression in normal, reactive, and neoplastic tissues.

Neuronectin (NEC1) is a human extracellular matrix protein of central nervous system (CNS) parenchyma found throughout the white matter of rostral brain segments (telencephalon, diencephalon, some areas of mesencephalon), but not in rostral CNS gray matter, most areas of mesencephalon, pons, cerebellum, medulla, spinal cord, or peripheral nerves. The present immunohistochemical study, using two monoclonal antibodies to distinct epitopes on the NEC1 molecule, examined NEC1 expression in normal non-neural tissues, malignant tumors of diverse histological types, non-malignant skin lesions, and dermal incision wounds. We show that (a) NEC1 is expressed in normal fetal precartilage blastemas and fetal and adult vascular and visceral smooth muscle, but not in most loose connective tissues and skeletal or cardiac muscle; (b) NEC1 is found along epithelial-mesenchymal junctions, with marked differences in prevalence and histological patterns in different organs; and (c) mesenchymal activation associated with wound healing, actinic keratosis, psoriasis, and neoplasia leads to strong induction of NEC1 expression. Parallel studies with cultured human cells suggest that region-specific NEC1 expression in normal developing tissues and localized induction in wound healing and disparate diseases is under the control of extrinsic signals provided by regulatory polypeptides.

Phosphosugars are potent inhibitors of central nervous system inflammation.

Adoptively transferred allergic encephalomyelitis can be inhibited by various phosphosugars, particularly mannose-6-phosphate. The sugar specificity suggests that inhibition may be due to depletion of lymphocyte cell-surface lysosomal enzymes, which are essential for the passage of lymphocytes across the vascular endothelium and the entry of lymphocytes into the central nervous system parenchyma.

Discrimination between Different Types of Neuroglial Cells in Rat Central Nervous System Using Combined Immuno- and Enzyme-Histochemical Methods

The central nervous system (CNS) contains several types of neuroglial cells. In the present study, we characterized different types of glial cells in rat CNS by using single and combined immuno- and enzyme-histochemical methods, and immunofluorescence techniques. Two recently developed monoclonal antibodies (mAbs) against rat macrophages-associated antigens appeared to recognize a subpopulation of glial cells in the CNS of normal adult rats. These ED4- and ED8-positive glial cells were predominately located in the white matter of adult rat CNS and shared morphological features with microglia. ED4 and ED8 were applied in a double staining combined with mAbs and an antiserum raised against galactocerebroside (GalC) to identify oligodendrocytes, or with anti-glial fibrillary acidic protein antiserum (GFA) to identify astrocytes. We also used a mAb against myelin basic protein (MBP) to identify oligodendrocytes. It appeared that ED4 and ED8 recognized a subpopulation of oligodendrocytes. MAbs against GalC and MBP recognized cells in an immunoperoxidase staining with a morphology identical to that of the ED8-positive cells and part of the ED4-positive cells. Frozen sections of Lewis rats CNS with acute experimental allergic encephalomyelitis (EAE) were investigated, where infiltrating brain macrophages could be found which stained positively with ED4 and ED8 as well as with the monocyte/macrophage mAbs ED1 and ED2. These brain macrophages did not stain when GalC, MBP and GFA markers were applied. Furthermore, ED4 +GalC + and ED8 +GalC + oligodendrocytes were present in the CNS white matter of EAE animals with similar appearance as in normal adult rats. With the currently used markers, we could not detect a third type of neuroglial cell, besides the astrocytes and oligodendrocytes. Thus, none of our anti-macrophage monoclonals recognized the presumptive microglia. Only under pathological conditions, e.g., in inflammatory infiltrates in the course of EAE, could brain macrophages be detected in the CNS parenchyma and only in the direct vicinity of blood vessels, indicating their hematogenous origin.

Interferon-γ and Ia antigen are present on astrocytes in active chronic multiple sclerosis lesions

Using immunocytochemical techniques, presence of interferon (IFN)-γ, IFN-α and Class II major histocompatibility (MHC) antigen (HLA-DR, Ia) was evaluated in active central nervous system (CNS) lesions of 11 patients with chronic multiple sclerosis (MS) and the findings were correlated with a detailed analysis of inflammatory cells. Both IFN-γ and Ia antigen were detectable on astrocytes at the edge of active chronic MS lesions and in the adjacent normal-appearing white matter, where CD4 + (helper/inducer) T cells and interleukin-2 receptor (IL-2R)-positive cells were also found. IFN-α was predominantly seen on Ia-positive macrophages and not on astrocytes. Astroglia in the inactive lesion center and in normal CNS parenchyma were unreactive for both types of IFN and Ia antigen. These findings suggested that similar to the situation in vitro, IFN-γ can also induce Ia-expression on astrocytes in vivo. Via local antigen presentation, IFN-γ might thus play an important role in the development of MS lesions, while IFN-γ might be involved in local immunosuppression.

A suppressor T-lymphocyte cell line for autoimmune encephalomyelitis

Experimental allergic encephalomyelitis (EAE) is a model for the in vitro and in vivo study of T-cell activation. It is an autoimmune disease mediated by T lymphocytes of the helper T-cell (Th) subset. After sensitization to guinea-pig myelin basic protein in complete Freund's adjuvant, Lewis rats develop an autoimmune response to central nervous system (CNS) myelin basic protein, manifested clinically as paralysis and histologically by a perivascular mononuclear cell infiltrate of the CNS parenchyma. Suppressor cell regulation of EAE has long been suspected because Lewis rats, which spontaneously recover from active disease, are resistant to reinduction of active EAE, even though effector T-cell lines can be rescued from these recovered rats. Using cyclosporin A, an immunosuppressive agent believed to inhibit Th cell function, suppressor T-cell (Ts) lines have now been generated from recovered Lewis rats. These Ts cells, when admixed with guinea pig myelin basic protein-specific Th cells, will prevent the adoptive transfer of EAE. The Ts cells appear to be CD4+, which explains previous observations that CD8+ lymphocytes are not important in the recovery of EAE in the rat. This is the first direct demonstration of Ts-cell regulation of EAE.

Absence of donor-type major histocompatibility complex class I antigen-bearing microglia in the rat central nervous system of radiation bone marrow chimeras

Localization of bone marrow-originated cells in the central nervous system (CNS) of the rat was investigated by using bone marrow chimeras. In order to do this, Lewis rats which carry major histocompatibility complex (MHC) class I antigens haplotype 1 (RT1.A 1) were reconstituted with (Lew × PVG)F 1 ( RT1.A 1 c bone marrow cells after lethal irradiation. Transferred bone marrow cells were detected by immunohistochemical staining using a monoclonal antibody, OX27, specific for haplotype c of rat MHC class I antigens (RT1.A c). The spleen and thymus of chimeric rats were fully reconstituted with transferred F 1 cells 4 weeks after bone marrow transplantation. At this stage, mononuclear cells in the subarachnoid space of the CNS expressed OX27 antigen indicating that they were of bone marrow origin. A few OX27-positive blood cells were scattered in the CNS parenchyma 4–12 weeks after reconstitution. Ramified microglia, however, remained OX27-negative. Bone marrow-derived microglia were not observed throughout the period of examination until 24 weeks. In addition, experimental allergic encephalomyelitis (EAE) was induced in chimeric rats in order to augment the expression of MHC class I antigens on microglia. Even under this condition, no OX27-positive microglia were observed. Taken together, ramified microglia might be of neuroectodermal origin and there is little possibility that the microglia are derived from the bone marrow. However, if the ramified microglia are derived from blood cells, the microglia may be expected to have characteristic cell kinetics from the following points: (1) the precursor cells of the microglia may enter the CNS only at the perinatal stage; and (2) even under the condition in which lymphocytes and macrophages enter the CNS as observed in EAE, the precursor cells of the microglia are not supplied from the blood.

Establishment of central nervous system infection by canine distemper virus: Breach of the blood-brain barrier and facilitation by antiviral antibody

Morphologic, immunologic and virologic data implicating antiviral antibody in promoting entry of canine distemper virus (CDV) into brain and reticuloendothelial tissues are reviewed. Infection of central nervous system (CNS) endothelium precedes invasion of virus-positive and -negative leukocytes into Virchow-Robin spaces and central nervous system (CNS) parenchyma by 1–3 days. Platelets are implicated in initiation of endothelial infection in that: CDV-infected dogs are thrombocytopenic; platelets from CDV-infected dogs contain IgG-virus complexes on their plasma membranes; platelet microthrombi were observed adjacent to foci of endothelial infection, and; CDV-susceptible ferrets rendered thrombocytopenic by antiplatelet antibody exhibit delayed viral entry into CNS tissues. Renal glomerular-bound IgG, IgM and occasionally CDV antigen were demonstrated in CDV-infected dogs by immunocytochemical techniques. Distemper-infected dogs with inherited C3 deficiency exhibited enhanced renal glomerular disease associated chiefly with deposition of IgM in mesengial regions vs. their homozygous normal CDV-infected littermates. Direct infusion of virus-positive leukocytes, plasma and platelets into the CNS capillary bed via the right carotid artery should establish the primacy of each in the initiation of CNS vascular endothelial infection by CDV.

Computed tomography demonstration of multiple parenchymal central nervous system nodules due to histiocytosis x

The computed tomography demonstration of multiple parenchymal brain lesions due to histiocytosis X is described. A comparison of follow-up computed tomography and magnetic resonance imaging studies is made.

Macrophages in the central nervous system of the rat

In an immunohistochemical study using monoclonal antibodies, which exclusively recognizecells of the monocyte-macrophage lineage, and monoclonal antibodies against the Ia-antigen, we describe the occurrence of macrophages in the developing and adult central nervous system (CNS). In normal adult brain, no macrophages could be detected in the CNS parenchyma; only inthe meninges and the choroid plexes were a few macrophages found. During ontogeny, numerous phagocytic cells infiltrated the CNS parenchyma; these cellswhich did not express Ia are blood-borne. About three weeks after birth, all macrophages had disappeared from the CNS. As microglia in adult and developing brain do not stain with the anti-macrophage antibodies, we suggest that microglial cells are not related to the mononuclear phagocyte system and do not have a hematogenous origin.

Immunohistochemical analysis of the rat central nervous system during experimental allergic encephalomyelitis, with special reference to Ia-positive cells with dendritic morphology.

The rat central nervous system (CNS) during experimental allergic encephalomyelitis (EAE) was analyzed immunohistochemically from the preclinical to recovery stage by using monoclonal antibodies specific for rat T lymphocyte subsets and Ia antigen. Through combination of the avidin-biotin technique and carefully selected fixative, cells with dendritic morphology (DC) and infiltrating mononuclear cells were clearly and intensely demonstrated in the CNS parenchyma during EAE. In normal and complete Freund's adjuvant (CFA)-injected controls, there were no inflammatory foci. Ia (OX3)-positive parenchymal cells were not detected, whereas W3/25 stained DC that were located mainly in the white matter and W3/13 stained axons. At the preclinical stage, 11 days after CNS/CFA sensitization, a few clusters of Ia+ DC were detected in some sections of the spinal cord. The number of Ia+ DC increased as clinical signs developed (P less than 0.001). In rats with a clinical score of 1 or 2, Ia+ DC were mainly located in the perivascular region and closely associated with infiltrating T lymphocytes. However, at moribund state (score 3), Ia+ DC were evenly distributed in gray and white matter on almost all sections of the spinal cord. In recovered rats, the numbers of inflammatory foci and Ia+ DC were less than those in clinical EAE rats (P less than 0.001). Rats without clinical signs throughout the course also contained a few clusters of Ia+ DC. Double immunofluorescent staining with OX3 and anti-glial fibrillary acidic protein (GFAP) antiserum demonstrated that Ia+ DC were negative for GFAP. Their morphology and distribution were similar to those of nucleoside diphosphatase-positive cells, suggesting that Ia+ DC are microglia. In contrast to DC, no astrocytes or endothelial cells express detectable levels of Ia antigen in control and clinical EAE rats. These findings suggest that brain cells other than Ia+ DC may not be involved in the local immune interaction. Ia+ DC may play a significant role in antigen presentation in the CNS with EAE.

Immunopathology of the lesion in chronic relapsing experimental autoimmune encephalomyelitis in the mouse

To analyze immunopathologic events within the central nervous system (CNS) during various stages of actively induced chronic relapsing EAE in SJL/J mice, animals were sampled at various timepoints post inoculation (PI) and T cells, T-cell subsets, Ia + cells and Ig + cells, albumin, and Ig deposits were localized in frozen sections by immunocytochemical techniques. Furthermore, sections were stained for the demonstration of Ia antigen, myelin basic protein (MBP), and galactocerebroside (GC) on endothelial cells and astrocytes. During the acute phase of the disease, large numbers of all types of inflammatory cells studied (Lyt-1.2 +, L3T4 +, Lyt-2 +, Ia +, Ig +) were randomly distributed throughout lesions, a finding similar to that described previously for acute EAE. A more distinct distribution pattern of infiltrating T cells was found during active chronic disease in that L3T4 + cells predominated within the CNS parenchyma, while Lyt-2 + cells were more numerous in meningeal and perivascular areas. During all chronic stages, a low-grade diffuse infiltration of the neuraxis by hematogeneous cells was present. Ia and myelin antigens were detectable on some endothelial cells and astrocytes. Damage to the blood-brain barrier, as indicated by albumin and Ig deposits, was more extensive during the acute than during chronic stages of the disease. Taken in concert, the results further support the possibility of local antigen presentation on endothelial and astroglial cells and an essential involvement of helper (L3T4 +) T cells in CNS lesion formation. These findings correlate well with events reported previously in acute and chronic multiple sclerosis lesions.

Acute experimental allergic encephalomyelitis in the mouse: Immunopathology of the developing lesion

To investigate the sequence of immunopathologic events during lesion formation in acute experimental allergic encephalomyelitis (EAE), SJL/J mice were inoculated with isogeneic spinal cord in complete Freund's adjuvant (CFA) and with Bordetella pertussis on Days 1 and 3 postinoculation (PI). Mice were sampled at different time points PI and T cells, T-cell subsets, Ia + cells, Ig + cells, albumin, and Ig deposits were localized in frozen sections by the avidinbiotin complex (ABC) method and direct fluorescence. Furthermore, samples were stained for Ia antigen, myelin basic protein (MBP), and galactocerebroside (GC) localization on endothelial cells by the ABC technique. Clinical and pathologic observations were correlated with the immunopathologic results. It was found that early in the disease process myelin and Ia-antigens were demonstrable on endothelial cells within the central nervous system (CNS). Simultaneously, damage to the blood-brain barrier was apparent, as indicated by albumin deposits, and small numbers of infiltrating T cells, T-cell subsets, and Ia + cells were found. With time PI, the density of infiltrating total T cells (Thy-1.2 +), helper/inducer (Lyt-1 +), and suppressor/cytotoxic (Lyt-2 +) T cells increased; Lyt-1 + and Lyt-2 + cells were detectable in meningeal as well as parenchymal infiltrates, while later on, Lyt-1 + cells showed some predilection for the CNS parenchyma and Lyt-2 + cells for meninges. Ia + cells (B cells, macrophages, activated T cells) were present in small numbers only. Ig + cells (B cells and macrophages) appeared shortly before onset of signs and persisted in moderate numbers. These results reconfirm the importance of early T-cell involvement for the development of EAE; they might also indicate a secondary role for Ig + cells and are consistent with the concept that presentation of myelin antigens to T cells might occur locally on Ia-bearing endothelial cells within the CNS.

Sarcoma metastatic to the central nervous system parenchyma: a review of the literature.

Sarcoma metastatic to cerebral parenchyma, although rare, occurs more frequently than generally recognized. With increased duration of survival due to multi-modal therapy, more CNS metastases are being found. A literature search occasioned by a patient with metastatic sarcoma has produced some interesting results.

The immunopathology of experimental allergic encephalomyelitis. I. Quantitative analysis of inflammatory cells in situ.

Acute experimental allergic encephalomyelitis (EAE) is a T cell-mediated, neurologic disease that is under immunogenetic control. We systematically analyzed the quantity and distribution of T cells, B cells, and macrophages in the central nervous system (CNS) of susceptible and resistant guinea (GP) with a panel of seven monoclonal antibodies by using the avidin-biotin complex (ABC) immunoperoxidase technique and alpha-naphthyl-butyrate esterase (ANBE) staining. Adult EAE-susceptible strain 13 GP immunized with isogeneic spinal cord homogenate (SC) or with myelin basic protein (MBP) developed clinical signs (paralysis, weight loss, etc.) in 2 to 3 wk. T cells were present in all CNS inflammatory foci and comprised 44% of the perivascular mononuclear cells. T cells diffusely infiltrated the neuropil away from inflammatory cell aggregates. These T cells were judged to be extravascular by the lack of an associated identifiable vessel in counter-stained sections, and by their persistence following exhaustive perfusion of the brains. In routine sections, mononuclear cells could be detected only in perivascular aggregates. IgM+ B cells comprised 9% of the perivascular infiltrates and did not diffusely infiltrate the parenchyma. ANBE+ macrophages comprised the remaining 47% of the identified perivascular cells. SC- and MBP-immunized GP showed equivalent numbers of inflammatory foci, T cells, and macrophages, but SC-immunized GP had more IgM+ cells in the meninges and choroid plexus (p less than 0.001, p less than 0.02, respectively). Virtually all cells in perivascular locations were Ia+. Ia+ mononuclear cells were also present in the neuropil. EAE-resistant strain 2 GP immunized with SC developed no clinical signs. These GP had fewer perivascular foci than strain 13 GP but, when present, the cellular composition, including the density of diffuse parenchymal T cell infiltrates, was indistinguishable. Significantly fewer parenchymal mononuclear cells in the strain 2 GP, however, displayed Ia, both in perivascular and diffuse infiltrates (p less than 0.001). We conclude that T cell migration into the CNS parenchyma is a characteristic feature of acute EAE in the GP, but that T cells can occur in this pattern without clinical signs of disease. The two features that distinguish susceptible and resistant strains were the frequency of perivascular infiltrates and the expression of Ia on parenchymal mononuclear cells, which probably reflects their enhanced immunologic activation in situ.

Blood-brain barrier in chronic relapsing experimental allergic encephalomyelitis: a correlative study between cerebrospinal fluid protein concentrations and tracer leakage in the central nervous system.

Blood-brain barrier (BBB) permeability in chronic relapsing experimental allergic encephalomyelitis was studied morphologically in tracer studies with horseradish peroxidase (HRP) as well as by quantitative determination of HRP, albumin, and IgG in serum and cerebrospinal fluid (CSF). BBB damage was found to be localized in demyelinating plaques and in blood vessels with vasculitis. Actively demyelinating lesions showed massive increase in BBB permeability, whereas in inactive or remyelinated lesions BBB damage was either minimal or absent. Determination of serum proteins in the CSF of animals with severe disease and a high incidence of actively demyelinating lesions showed evidence of BBB damage (reduction of Q-albumin) and an IgG-index in the normal range. In animals with only inactive lesions the Q-albumin was normal, the IgG index, however, was elevated. This finding indicates intrathecal IgG synthesis. A correlation between morphologically visualized tracer leakage in the central nervous system (CNS) with serum protein concentrations in the CSF revealed that elevated CSF albumin is a reliable indicator for BBB damage in lesions, located near the inner or outer surface of the brain and spinal cord. However, singular focal lesions with BBB damage located in the depth of the CNS parenchyma may not be accompanied by CSF protein alterations. The invariable presence of BBB damage in active inflammatory demyelinating lesions and its absence in inactive plaques or in the unaffected nervous tissue may be important in therapy, not only in experimental allergic encephalomyelitis but also in multiple sclerosis (MS).

Neurotoxicity of chemotherapeutic agents after blood-brain barrier modification: neuropathological studies.

We examined in 47 dogs the effects of 5-fluorouracil, Adriamycin (doxorubicin hydrochloride), cis-platinum (cis-diamminedichloroplatinum) cyclophosphamide, and bleomycin given in association with osmotic blood-brain barrier modification. The dose of drug ranged from 100% to as little as 5 to 10% of the conventional systemic dosage. Serial neurological observation and subsequent postmortem neuropathological evaluation at times varying from 2.5 hours to 52 days after drug administration showed that cis-platinum and Adriamycin were highly neurotoxic, as evidenced by neurological deficits and pathological changes in the central nervous system parenchyma; 5-fluorouracil and bleomycin had much less, but consequential neurotoxicity; and cyclophosphamide was not associated with substantial toxicity. Intracarotid cis-platinum, unlike the other drugs, damaged the blood-brain barrier and resulted in marked neurotoxicity in the absence of osmotic blood-brain barrier opening. The neural lesions produced by these agents were not specific but were manifested as foci of hemorrhagic necrosis and edema. In addition, secondary brainstem hemorrhage was observed in animals that developed transtentorial herniation. On the basis of these studies, of five drugs studied at a wide range of doses, only cyclophosphamide appears to be safe enough to evaluate in clinical trials that utilize blood-brain barrier modification to enhance drug delivery. These studies also suggest that the lack of neurotoxicity associated with the usual administration of most chemotherapeutic agents probably stems from limited entry of drug into the brain through an intact blood-brain barrier.

Acute experimental autoimmune encephalomyelitis: T- and B-cell distribution within the target organ

The sequence of T-cell events in the central nervous system (CNS) has been further studied during acute experimental autoimmune (allergic) encephalomyelitis (EAE). T cells were labeled by indirect fluorescence using a monoclonal antibody against guinea pig T cells. In addition, B cells, IgG, C 3, and albumin were localized by direct fluorescence. T cells were demonstrable as early as 5 days postinoculation (PI), well before the onset of signs and were predominantly found within the CNS parenchyma. B cells and macrophages appeared later (10 days PI) and were restricted to the meninges and perivascular spaces. IgG and albumin were found from day 5 PI onwards and were probably indicative of damage to the blood-brain barrier. C 3 was observed later and was distributed similar to IgG. These findings (a) further underline the primary involvement of T cells in this autoimmune condition, (b) indicate a difference in the migratory activity of T and B cells in the CNS, (c) suggest that suppression of clinical EAE with myelin basic protein can be correlated with a diminution of inflammatory cells within the CNS, and (d) represent an unambiguous demonstration of T cells in situ in the target organ in EAE.

Chronic relapsing experimental allergic encephalomyelitis: Identification and dynamics of T and B cells within the central nervous system

Using a monoclonal antibody against guinea pig T cells and anti-guinea pig immunoglobulins, T- and B-cell dynamics were studied by immunofluorescence in situ in the central nervous system (CNS) of animals with untreated and treated chronic relapsing experimental allergic encephalomyelitis (EAE). Treated animals were given a series of injections of either myelin basic protein (MBP) in incomplete Freund's adjuvant (IFA) or MBP and galactocerebroside in IFA. Within the CNS, T and B cells showed distinct distribution patterns in untreated chronic relapsing EAE, similar to that recently described in acute EAE. T cells were predominantly localized within the CNS parenchyma and B cells were mainly found in perivascular areas. B-cell infiltrates were more extensive than in acute EAE and, although most were centered around blood vessels, some were also detectable in the parenchyma. IgG, C 3, and albumin deposits were common. These observations suggest an age-dependent difference in the immune response. In treated chronic EAE, the disease process was apparently arrested and T- and B-cell infiltrates in the white matter were negligible. Therefore, it appears that the present treatment protocol prevents lymphocytes from entering the CNS parenchyma.

Neurological complications of infantile osteopetrosis.

Seven cases of infantile osteopetrosis are presented. Five of these were available for detailed clinical examination and 2 for retrospective review, including autopsy slides. Neurological deficits in these patients are reviewed. Involvement of the central nervous system parenchyma was suggested by observations of delayed development, ocular abnormalities, and reflex changes as well as radiographic and autopsy findings. Cerebral atrophy was present in several of our patients as well as some reported in the literature and may account for the ventricular enlargement found in many of these patients. Though hydrocephalus may be present, it is unclear that this is frequent or that it can occur without antecedent intracranial hemorrhage. The large head size is not accounted for by calvarial thickening or by hydrocephalus. Despite our patients' small stature, pituitary function appeared to be normal. Surgical decompression may stabilize cranial nerve function, particularly when the optic nerves are involved.

Hyperacute autoimmune encephalomyelitis induced by a synthetic autoantigen.

EXPERIMENTAL autoimmune encephalomyelitis (EAE) is an organ-specific autoimmune disease of the central nervous system (CNS) induced by immunisation with CNS tissue in complete Freund's adjuvant (CFA). It is generally regarded as an animal model of acute disseminated encephalomyelitis. In Lewis rats a hyperacute variant of EAE can be induced using appropriate CNS immunogen with Bordetella pertussis vaccine as adjuvant with or without CFA1–3. Hyperacute EAE (HEAE) differs from ordinary EAE clinically in its early onset and in its rapid and severe course, with high incidence of cerebral involvement and mortality. Histological lesions of HEAE are characterised by the presence in the CNS parenchyma of polymorphonuclear leukocytes, and necrosis, haemorrhage, oedema and fibrin1,2. Because HEAE and ordinary EAE overlap histopathologically and immunologically2 they provide experimental evidence supporting the concept that certain human demyelinating diseases represent a spectrum of autoimmunity ranging from chronic multiple sclerosis to acute haemorrhagic necrotising leukoencephalopathy, for which HEAE is a model1,2,4. We report here that the induction of HEAE is favoured by the absence of a methyl group in a sequence of 14 amino acids of the primary structure of the immunogen.