Peter C. Dowling

Cell death and birth in multiple sclerosis brain

The hallmark of the brain pathology in multiple sclerosis is the white matter plaque, characterized by myelin destruction and oligodendrocyte loss. To examine the role that cell death plays in the development of MS lesions, we used the in situ TUNEL technique, a method that sensitively detects DNA fragmentation associated with death at the single cell level. We found that patchy areas within acute MS lesions have massive numbers of inflammatory and glial cells undergoing cell death. The punched out areas of some long-standing chronic lesions also had labeled glial cells showing that the attack was not a single event. Immunocytochemical identification of the dying cells with glial specific marker co-labeling showed that 14-40% were the myelin-sustaining oligodendroglial cell. Confocal microscopic evaluation of fluorescein-labeled TUNEL positive cells revealed nuclei with morphologic characteristics of apoptosis, and electrophoresed MS brain DNA produced a ladder characteristic of apoptotic DNA cleavage confirming that substantial numbers of labeled cells, but not necessarily all, were dying by apoptotic mechanisms rather than cell necrosis. Companion studies using a marker for cell proliferation on MS lesions revealed that unexpectedly large populations of perivascular inflammatory cells and parenchymal glial cells had entered the cell proliferation cycle. These findings establish that two opposing glial cell responses - relentless cell death and coincident brisk cellular proliferation - are important features of MS pathology. In the end, however, glial cell loss prevails, and we suspect apoptosis may be the critical death mechanism responsible for the depletion of myelin observed in this condition.

Multiple sclerosis and viruses: An overview

The evidence for a viral etiology of MS has been reviewed. The strongest evidence favoring a virus is based primarily on epidemiologic considerations. Less convincing evidence comes from pathologic studies, serology, lymphocyte reactivity to viral antigens, and reports of identification of virus in MS tissues. Animal models of viral demyelination exist, which may provide insight into possible etiologic agents and pathogenetic mechanisms. Considering all the data, it is clear that no agent can be convincingly linked to MS at the present time. If a single virus causes the majority of cases of MS, then a morbilliform virus—canine distemper—is a leading contender, because this agent is consistent with the epidemiologic and serologic findings and is highly neurovirulent for animals ranging from mice to primates. Since no virus fulfills the usual criteria for linking an infectious agent to a disease, other possibilities must be considered. If MS is caused by a single virus, it may be a common virus not presently considered as being associated with MS, or an agent as yet unidentified. It is also conceivable that multiple agents, acting alone or in concert, initiate the MS process, perhaps through a common immune-mediated pathway. In this regard, another human demyelinating disease—the Guillain-Barré syndrome—which may in some instances become a chronic remitting and relapsing disorder, is thought to be initiated by multiple infectious agents but to have an immunologic pathogenesis.

Platelet‐derived growth factor‐α receptor‐positive oligodendroglia are frequent in multiple sclerosis lesions

Platelet‐derived growth factor (PDGF) ligand is a potent glial cell mitogen. When its cognate receptor (PDGF‐αR) is expressed on oligodendroglial lineage cells, such cells are considered capable of division, and the receptor thus serves as a phenotypic marker for oligodendrocyte precursor cells. Here we identify using immunohistochemistry a considerably enlarged, PDGF‐αR‐expressing oligodendrocyte cell population within multiple sclerosis (MS) white matter lesions compared to control brains. Numerous PDGF‐αR‐positive oligodendroglia also colabel heavily with the nuclear cell proliferation marker antibody Ki‐67. Our finding of large numbers of proliferating oligodendroglia in MS brains expressing up‐regulated PDGF‐αR suggests that these progenitor‐like cells represent an important source of regenerating cells for the healing MS lesion.

Beneficial effect of erythropoietin on experimental allergic encephalomyelitis

We have known for a long time that erythropoietin signaling plays a key role in bone marrow erythrocyte proliferation. However, recent studies have indicated that erythropoietin also may have protective effects on the nervous system. This unexpected role remains incompletely characterized. To investigate the potential neuroprotective role of erythropoietin in the central nervous system, we assessed its effects on a well‐characterized autoimmune demyelinating model of multiple sclerosis–myelin oligodendrocyte glycoprotein‐induced experimental autoimmune encephalomyelitis (EAE) in the mouse. We found that erythropoietin administered intravenously for 14 days after the onset of symptoms reduced both disease severity and duration of maximum impairment at dose levels as low as 50U/kg (p < 0.001). We assessed the neuropathology of diseased spinal cords and found that erythropoietin‐treated EAE animals had reduced axonal damage, inflammatory cell infiltration and demyelination, and diminished blood–brain barrier leakage when compared with saline‐treated EAE controls. Moreover, the pronounced upregulation of spinal cord major histocompatibility complex (MHC) class II expression found in saline‐treated EAE was significantly reduced in erythropoietin‐treated animals, a finding we replicated in vitro, using microglial cultures. The notion that short‐term erythropoietin therapy might be of clinical benefit in human autoimmune demyelinating diseases needs investigation. Ann Neurol 2004; 56: 767‒777

Up-regulated p75NTR neurotrophin receptor on glial cells in MS plaques.

Objective: To investigate the expression of the neurotrophin receptor p75NTR on glial cells within MS plaques. Background: In recent studies on the pathogenesis of MS white matter plaques, we found large populations of inflammatory and resident glial cells, including oligodendrocytes undergoing cell death, and identified increased expression of Fas receptor and ligand death pathway signaling molecules on the same glial cell types. In another study, the p75NTR was shown to induce apoptotic death of maturing oligodendrocytes when exposed to NGF in vitro. Methods: We used immunohistochemistry and in situ reverse-transcription PCR to detect p75NTR expression on inflammatory and resident glial cells in MS plaques and used TUNEL staining for fragmented DNA to detect cell death. Results: Up-regulated p75NTR messenger RNA and protein were demonstrated in both oligodendrocytes and microglia/macrophages in MS plaques but not in control white matter. However, only a fraction of p75NTR expressing oligodendrocytes was also stained by TUNEL. Conclusions: Glial cell expression of p75NTR receptor is up-regulated during MS plaque formation. The exact role of this receptor in glial cell death and/or survival in MS remains to be elucidated.

Measles virus L protein evidences elements of ancestral RNA polymerase

We have determined the nucleotide sequence of the measles virus (MV) L gene using a cDNA library encompassing the entire MV genome (J. Crowley et al. (1987) Intervirology, 28, 65-77). The L gene is 6639 nucleotides in length, and contains a single long open reading frame that could code for a protein of 247,611 kDa. Both the L gene and in particular the predicted L protein of MV bear substantial homology to their counterparts in Sendai virus and Newcastle disease virus, suggesting that the multifunctional nature of paramyxovirus L proteins imposes strong evolutionary constraints. The predicted MV L protein also contains distinct elements of a postulated ancestral RNA polymerase.

Declining incidence of multiple sclerosis in the Orkney Islands

The incidence of MS in the Orkney Islands has been updated from 1941 to September 21, 1983. Since 1965, MS incidence rates have fallen significantly when compared with those for 1941 to 1964. Alterations in age-specific prevalence, mean duration of illness, and mean age of the MS population are consistent with the decline in incidence of MS in recent years. Although the reason for the decreasing incidence is uncertain, it is consistent with the hypothesis that MS may be caused by canine distemper virus.

Erythropoietin: A Potent Inducer of Peripheral Immuno/Inflammatory Modulation in Autoimmune EAE

Background Beneficial effects of short-term erythropoietin (EPO) therapy have been demonstrated in several animal models of acute neurologic injury, including experimental autoimmune encephalomyelitis (EAE)-the animal model of multiple sclerosis. We have found that EPO treatment substantially reduces the acute clinical paralysis seen in EAE mice and this improvement is accompanied by a large reduction in the mononuclear cell infiltration and downregulation of glial MHC class II expression within the inflamed CNS. Other reports have recently indicated that peripherally generated anti-inflammatory CD4+Foxp3+ regulatory T cells (Tregs) and the IL17-producing CD4+ T helper cell (Th17) subpopulations play key antagonistic roles in EAE pathogenesis. However, no information regarding the effects of EPO therapy on the behavior of the general mononuclear-lymphocyte population, Tregs or Th17 cells in EAE has emerged. Methods and Findings We first determined in vivo that EPO therapy markedly suppressed MOG specific T cell proliferation and sharply reduced the number of reactive dendritic cells (CD11c positive) in EAE lymph nodes during both inductive and later symptomatic phases of MOG35–55 induced EAE. We then determined the effect in vivo of EPO on numbers of peripheral Treg cells and Th17 cells. We found that EPO treatment modulated immune balance in both the periphery and the inflamed spinal cord by promoting a large expansion in Treg cells, inhibiting Th17 polarization and abrogating proliferation of the antigen presenting dendritic cell population. Finally we utilized tissue culture assays to show that exposure to EPO in vitro similarly downregulated MOG-specific T cell proliferation and also greatly suppressed T cell production of pro-inflammatory cytokines. Conclusions Taken together, our findings reveal an important new locus whereby EPO induces substantial long-term tissue protection in the host through signaling to several critical subsets of immune cells that reside in the peripheral lymphatic system.

Spinal cord disease in children with HIV-1 infection: a combined molecular biological and neuropathological study*

An autopsy study was performed on spinal cords from 18 children who died with HIV‐1 infection, using standard histopathologic techniques as well as in situ hybridization and immunocytochemistry for HIV‐1. Of 16 spinal cords examined by histology, nine had inflammatory cell infiltrates and six had multinucleated cells; both types of lesion are associated with the presence of HIV‐1 in central nervous system tissue. HIV‐1 type lesions were often present in the spinal cord and brain from the same patient. Pallor of myelin in corticospinal tracts in the cord was present in half of the cases; this change correlated with diffuse myelin pallor in the corresponding brains, but not with the HIV‐1 associated changes in the cords. In situ hybridization for HIV‐1 nucleic acid sequences gave positive results in seven of 18 spinal cords, with hybridizing signal usually localized to inflammatory cell infiltrates and multinucleated cells. Positive in situ hybridization, on frozen sections, correlated with the presence of HIV‐1 associated changes on paraffin sections from the same cases. Immunocytochemistry for p25 core protein of HIV‐1, using a monoclonal antibody on frozen sections, was positive in multinucleated cells, macrophages, and microglia. In this series there were two cases of vacuolar myelopathy, one a 30–month‐old boy who had concomitant measles virus in the spinal cord grey matter, and the other nine‐year‐old girl who had severe HIV‐1 infection of the cord. Other than the single case of measles virus, there were no opportunistic infections in the cords in this series. HIV‐1 frequently involves the spinal cord in children with AIDS, while opportunistic infections are rare. Vacuolar myelopathy occurs in children with HIV‐1 infection, although its occurrence is much less frequent than in adults with AIDS.

Cytomegalovirus cornplement fixation antibody in Guillain‐Barré syndrome

Cytomegalovirus, measles, and adenovirus antibodies were measured in the sera of 92 Guillain-Barré patients and 120 controls. Thirty patients (33 percent) had markedly elevated levels of complement-fixing antibody to cytomegalovirus and in 21, a fourfold or more alteration in titer was demonstrated. Diagnostic falls in titer were seen in most instances and no significant elevation to the other viral agents was found. The serologic findings reported here suggest that cytomegalovirus may be a common agent involved in the pathogenesis of the Guillain-Barré syndrome.