Histopathology and electron microscopy of three cases of subacute sclerosing panencephalitis (SSPE)

Subacute sclerosing panencephalitis

Subacute sclerosing panencephalitis (SSPE) is a slowly progressive brain disorder caused by mutant measles virus. SSPE affects younger age groups. SSPE incidence is proportional to that of measles. High-income countries have seen substantial decline in SSPE incidence following universal vaccination against measles. SSPE virus differs from wild measles virus. Measles virus genome recovered from the autopsied brain tissues demonstrates clustered mutations in virus genome particularly in the M gene. These mutations destroy the structure and functioning of the encoded proteins. Complete infectious virus particle has rarely been recovered from the brain. Human neurons lack required receptor for entry of measles virus inside the neurons. Recent in vitro studies suggest that mutations in F protein confer hyperfusogenic properties to measles virus facilitating transneuronal viral spread. The inflammatory response in the brain leads to extensive tissue damage. Clinically, SSPE is characterized by florid panencephalitis. Clinically, SSPE is characterized by cognitive decline, periodic myoclonus, gait abnormalities, vision loss, and ultimately to a vegetative state. Chorioretinitis is a common ocular abnormality. Electroencephalography (EEG) shows characteristic periodic discharges. Neuroimaging demonstrates periventricular white matter signal abnormalities. In advanced stages, there is marked cerebral atrophy. Definitive diagnosis requires demonstration of elevated measles antibody titers in cerebrospinal fluid (CSF). Many drugs have been used to stabilize the course of the disease but without evidence from randomized clinical trials. Six percent of patients may experience prolonged spontaneous remission. Fusion inhibitor peptide may, in the future, be exploited to treat SSPE. A universal vaccination against measles is the only proven way to tackle this menace currently.

The nucleocapsid protein of measles virus blocks host interferon response

Measles virus (MV) belongs to the genus Morbillivirus of the family Paramyxoviridae. A number of paramyxoviruses inhibit host interferon (IFN) signaling pathways in host immune systems by various mechanisms. Inhibition mechanisms have been described for many paramyxoviruses. Although there are inconsistencies among previous reports concerning MV, it appears that P/V/C proteins interfere with the pathways. In this study, we confirmed the effects of MV P gene products of a wild MV strain on IFN pathways and examined that of other viral proteins on it. Interestingly, we found that N protein acts as an IFN-α/β and γ-antagonist as strong as P gene products. We further investigated the mechanisms of MV-N inhibition, and revealed that MV-N blocks the nuclear import of activated STAT without preventing STAT and Jak activation or STAT degradation, and that the nuclear translocation of MV-N is important for the inhibition. The inhibitory effect of the N protein was observed as a common feature of other morbilliviruses. The results presented in this report suggest that N protein of MV as well as P/V/C proteins is involved in the inhibition of host IFN signaling pathways.

Glial degeneration and reactive gliosis in alpha-synucleinopathies: the emerging concept of primary gliodegeneration

The concept of gliodegenerative diseases has not been widely established although there is accumulating evidence that glial cells may represent a primary target of degenerative disease processes. In the central nervous system (CNS), examples that provide a "proof of concept" include at least one alpha-synucleinopathy, multiple system atrophy (MSA), but this disease is conventionally discussed under the heading of "neurodegeneration". Additional evidence in support of primary glial affection has been reported in neurodegenerative disorders such as Parkinson's disease, Alzheimer's disease and transmissible spongiform encephalopathies. Based on biochemical, genetic and transcriptomic studies it is also becoming increasingly clear that the molecular changes measured in whole tissue extracts, e.g. obtained from Parkinson's disease brain, are not based on a purely neuronal contribution. This important evidence has been missed in cell culture or laser capture work focusing on the neuronal cell population. Studies of animal and in vitro models of disease pathogenesis additionally suggest glial accountability for some CNS degenerative processes. This review provides a critical analysis of the evidence available to date in support of the concept of gliodegeneration, which we propose to represent an essential although largely disregarded component of the spectrum of classical "neurodegeneration". Examples from the spectrum of alpha-synucleinopathies are presented.

Morbillivirus nucleoprotein possesses a novel nuclear localization signal and a CRM1-independent nuclear export signal

Morbilliviruses, which belong to the Mononegavirales, replicate its RNA genome in the cytoplasm of the host cell. However, they also form characteristic intranuclear inclusion bodies, consisting of nucleoprotein (N), in infected cells. To analyze the mechanisms of nucleocytoplasmic transport of N protein, we characterized the nuclear localization (NLS) and nuclear export (NES) signals of canine distemper virus (CDV) N protein by deletion mutation and alanine substitution of the protein. The NLS has a novel leucine/isoleucine-rich motif (TGILISIL) at positions 70-77, whereas the NES is composed of a leucine-rich motif (LLRSLTLF) at positions 4-11. The NLS and NES of the N proteins of other morbilliviruses, that is, measles virus (MV) and rinderpest virus (RPV), were also analyzed. The NLS of CDV-N protein is conserved at the same position in MV-N protein, whereas the NES of MV-N protein is located in the C-terminal region. The NES of RPV-N protein is also located at the same position as CDV-N protein, whereas the NLS motif is present not only at the same locus as CDV-N protein but also at other sites. Interestingly, the nuclear export of all these N proteins appears to proceed via a CRM1-independent pathway.

Brain endothelial cell infection in children with acute fatal measles

Neurologic diseases are important complications of measles. The role of virus infection of the central nervous system as well as the route of virus entry has been unclear. Five autopsied cases of individuals who died with severe acute measles 3-10 d after the onset of the rash were studied for evidence of viral involvement of the central nervous system. In all cases, in situ hybridization and RT-PCR in situ hybridization techniques showed endothelial cell infection. Immunoperoxidase staining with an anti-ferritin antibody revealed a reactive microgliosis. These data suggest that endothelial cells in the brain are frequently infected during acute fatal measles. This site of infection may provide a portal of entry for virus in individuals who subsequently develop subacute sclerosing panencephalitis or measles inclusion body encephalitis and a target for immunologic reactions in post-measles encephalomyelitis.

Morphometric study of the frontal cortex in subacute sclerosing panencephalitis

In biopsic material collected from the frontal cortex of 6 patients with subacute sclerosing panencephalitis (SSPE) and 5 patients with posterior fossa tumors, we estimated the neuronal and synaptic numerical densities as well as the mean volume of the neurons from layers II and III. The thickness of these layers was also determined. The evaluation of the layer's thickness suggested that there was no difference in the shrinkage in SSPE as compared to controls. No differences were found between the neuronal numerical densities and the neuronal soma sizes from SSPE and controls. Conversely the synaptic numerical density was reduced in SSPE. Given the maintenance of the neuronal numerical density in the frontal cortex of patients with SSPE, the presence of a decreased density of synapses must be regarded as a consequence of the dendritic and axonal degeneration that we previously described in this condition. It must then be borne in mind that SSPE's functional and behavioral changes might spring from alterations of the frontal cortex neuronal circuitry.

A fine structural study of Onuf's nucleus in sporadic amyotrophic lateral sclerosis

Onuf's nucleus of the second sacral spinal cord level was examined in twelve patients with sporadic amyotrophic lateral sclerosis (ALS). Under light-microscopic examination, the neurons of Onuf's nucleus were well-preserved in contrast with the severe neuronal depletion of the anterior horn cells. Ultrastructurally, however, substantial pathological changes such as Bunina bodies (BB), randomly arranged filaments associated with fine granules corresponding to Lewy body-like hyaline inclusions (LBHI) and bundles of tubular filaments corresponding to skein-like inclusions (SI) all of which are characteristic features of ALS, were demonstrated ubiquitously in the Onuf's nucleus in eleven of twelve patients. These changes may be of a reactive nature and represent an initial change of neuronal degeneration, since no definite cell destruction was observed in the nucleus. The changes in the Onuf's nucleus correlated with the changes observed in the anterior horns, although to a lesser degree. The more BB, LBHI and SI were observed in the anterior horns of patients with ALS, the more these inclusions were observed in Onuf's nucleus. Thus, we conclude that Onuf's nucleus is also affected by pathological changes in ALS.

Measles virus infection of cells in perivascular infiltrates in the brain in subacute sclerosing panencephalitis: confirmation by non-radioactive in situ hybridization, immunocytochemistry and electron microscopy

As part of continuing multidisciplinary studies on the neuropathogenesis of subacute sclerosing panencephalitis (SSPE), in situ hybridisation, immunocytochemistry and electron microscopy were used to detect measles virus nucleic acid, protein and nucleocapsids in brain perivascular infiltrates of three cases. Perivascular cuffing cells which contained measles virus nucleic acid and antigens were found in all cases. Infected cuffs occurred predominantly in areas of general parenchymal cell infection and in many of these a high proportion of the infiltrating cells were infected. Other cuffs in these areas were either uninfected or contained only a few infected cells. Occasional infected cells were also seen in cuffs in non-infected areas. In contrast, no specific immunocytochemical reactions or in situ hybridisation for measles virus was observed in brain tissue from a patient with herpes encephalitis. By electron microscopy viral nucleocapsid, consistent with measles virus, was found within the cytoplasm of plasma cells in the inflammatory cuffs in SSPE brain tissue. Possible explanations for our results are that infiltrates become infected on arrival in the CNS or alternatively, that the infected infiltrates reflect a generalised infection of the reticuloendothelial system. The frequent presence of uninfected cuffs favours the former explanation.

Intranuclear inclusions in paramyxovirus-induced encephalitis: evidence for altered nuclear body differentiation

Intranuclear inclusion bodies (INB) are frequently encountered in viral infections, where they are thought to be accumulations of viral particles. However, for RNA viruses replicating in the cytoplasm, this compartmentalization represents a paradox not consistent with the viral replication cycle. To define the basis for intranuclear paramyxoviral inclusion bodies in astrocytes, natural cases of canine distemper virus subacute encephalitis were examined by light and transmission electron microscopy, and by quantitative confocal immunofluorescence microscopy. Although INB were viral antigen positive, they were not composed of structurally recognizable paramyxoviral nucleocapsids. The structural basis for the INB was instead viral antigen-associated forms of nucleolar development known as nuclear bodies. Three variants of the light microscopic Cowdry type A INB were complex nuclear bodies, giant beaded nuclear bodies (sphaeridia), and nuclear body-associated granulofilamentous matrices. In the latter, the granulofilamentous matrix frequently filled the nucleus, resulting in a fourth morphological INB variant, and was associated with morphological evidence of nuclear degeneration. These findings suggest a novel mechanism of virus-induced cytopathology whereby intranuclear viral protein exerts deleterious effects upon nucleolar differentiation in infected cells and hence altered host cell RNA metabolism.

Nuclear bodies (sphaeridia) in Sertoli cells of a man with acquired immunodeficiency syndrome (AIDS) and testicular infection by cytomegalovirus

Histological and ultrastructural study of an adult man with acquired immunodeficiency syndrome (AIDS) revealed multiple testicular lesions. The seminiferous tubules varied from dilated tubules with hypospermatogenesis, to tubules with Sertoli cells and a few spermatogonia, to necrotic tubules. The testicular interstitium showed abundant inflammatory infiltrates, some of them forming microabscesses. The Sertoli cells exhibited spherical intranuclear inclusions corresponding to both cytomegalovirus and sphaeridia. Some sphaeridia stained intensely with EDTA as granular and fibrillar portions of the nucleolus; however, many sphaeridia stained weakly as nucleolar fibrillar centers. These observations suggest that a Sertoli cell response to cytomegalovirus is the proliferation of nucleolar organizing centers that in some instances may transform to give rise to more or less abnormally developed nucleoli.

The neuropathology of Alzheimer's disease: a review with pathogenetic, aetiological and therapeutic considerations

The neuropathology of Alzheimer's disease is reviewed in this paper emphasizing the morphological and morphometric changes that occur in the disease and their relationship to age and ageing. From this, a new hypothesis of pathogenesis is presented which accounts for the pattern of neuronal damage in Alzheimer's disease. This is that the pathogenesis of Alzheimer's disease begins with a leakage of a neurotoxin through a defective cortical blood brain barrier. This incites development of the senile plaque and later, via a retrograde transport of the same (or different) factors, intracellular neurofibrillary tangle formation and death of neurones within areas of cortex affected by plaques and in subcortical areas such as nucleus basalis of Meynert, locus caeruleus and dorsal raphe nuclei, all of which project to these same areas of cortex. Evidence consistent with this hypothesis is presented and the aetiological and therapeutic implications are discussed.

Nuclear inclusions following chronic ethanol administration. An electron-microscopic investigation of the rat parietal cortex

Wistar rats with an average initial body weight of 180 g received a 15% (v/v) ethanol-water solution over a period of 6 months. Neurons of the parietal cortex (area 3) showed a significant increase of nuclear inclusions which consisted of parallel filaments and tubular systems. Furthermore, we observed an augmentation of lipid droplets, nemetosomes, and straight filaments. The latter could not be identified in control animals. It is discussed whether the occurrence of these structures might be enhanced by an altered cellular metabolic activity during the chronic ethanol administration.

Nerve cell fusion in a case of subacute sclerosing panencephalitis

Evidence indicating cell membrane fusion among cells and their processes where subacute sclerosing panencephalitis (SSPE) virus is present is shown in an ultrastructural study of a brain biopsy. Virus budding from plasma membrane was not seen. These rare findings reinforce the hypothesis of cell-to-cell transmission as the most likely mechanism of SSPE virus infection. The presence of fused membranes between cell processes and cell soma probably explains the rapid spread of this virus throughout the nervous system.

Encephalitis after inhalation of measles virus: a pathogenetic study in hamsters

A neuroadapted strain of measles virus (HNT) was administered by inhalation to newborn hamsters. Primary replication of virus in the lung was followed by the transient appearance of virus in spleen within 7 to 9 days of inoculation. A terminal encephalitis occurred between 6 and 60 days in 31% of infected hamsters, and virus was recovered by explant culture of these brains. Virus could not be cultured directly from brain or tissue homogenates. At least 7% of hamsters that had survived the infection for two months had antibody to measles virus. The histopathological change in morbid animals was limited to the central nervous system (CNS) and consisted of small foci of necrosis, perivascular mononuclear cell infiltrates, intracytoplasmic and intranuclear inclusions, and vacuolated pyknotic neurons. Immunofluorescent studies disclosed measles antigen in the lungs and brain. This hamster model of measles encephalitis following a "natural" route of inoculation appears to represent a faithful reproduction of certain CNS complications of natural measles infection in humans, i.e., measles encephalitis and subacute sclerosing panencephalitis.

Nuclear inclusions in Alzheimer's disease

Biopsy samples of parietal cortex from seven patients undergoing atrio-ventricular shunt operations have been examined electron microscopically. Five were suffering from Alzheimer's disease, while two were subjects with normotensive hydrocephalus following previous head injuries. Intranuclear neuronal, inclusions of three types were found. Most frequent was the intranuclear rodlet, which was commonly observed in four of the patients with Alzheimer's disease, but in one block only from one of the hydrocephalus cases. The other two types, namely the spherical inclusion body and the vermicellar-like inclusion, were found less commonly and in only two cases. No inclusions were seen in glial nuclei.

Intranuclear filaments in a soft tissue sarcoma

Intranuclear filaments aggregating into rodlike structures were found in cells of an undifferentiated soft tissue sarcoma in a child. Similar structures have been uncommonly described in human neoplasms, and uncertainties exist concerning the nature of the inclusion bearing cells in previous reports. The filaments were found to be resistant to mild trypsin digestion. Review of the pertinent literature indicates that these structures may represent the structural manifestation of a highly specialized functional state, rather than a degenerative phenomenon or an artifact. A certain selectivity of occurrence has also been noted. It is therefore plausible to speculate that intranuclear filaments may eventually constitute a morphologic criterion of interest for new tumor classifications.

Subacute sclerosing panencephalitis with special reference to the ultrastructure of inclusions in the brain and lung

A 7-year-old boy, who was diagnosed as typical SSPE by clinical data and laboratory findings, was autopsied and observed by immunofluorescent techniques, light and electron microscope. The morphological characteristics in the brain were perivascular cuffings with plasma cells, lymphocytes and mononuclear cells, gliosis and a large number of intranuclear and intracytoplasmic inclusions in the neuroglias and nerve cells. Various kinds of intranuclear inclusions were elucidated by electron microscopy and the fin structures of these inclusions were described in detail. At least five types of intranuclear inclusions were regarded as specific in SSPE. The presence of intranuclear inclusions of mononuclear cells in the lungs resembling the inclusions in the neuroglias suggested that the disease was not localized in the brain but could be disseminated throughout the body.

Vacuolation of oligodendroglia in neoplastic perifocal edema

Vacuolation of oligodendroglia, a new type of cytopathological change, has been described. The change is observed frequently at the perifocally edematous cerebral white matter adjacent to the metastatic lesions of carcinoma from the lung in all three cases examined. It is also present occasionally in association with astrocytoma. This condition is characterized by swelling of oligodendroglias due to numerous cytoplasmic vacuolations which contain the material identical with that of the extracellular edema fluid. In such cells, the nucleus is displaced and deformed by vacuoles but the nuclear chromatin and envelopes are arranged normally. By occupation of numerous large vacuoles the cytoplasm is divided into small areas, but the individual organelles are only minimally altered. The oligodendroglial vacuolation seems to be a phagocytic response to the edema fluid which contains proteinous macromolecules derived from blood-borne protein and necrotic material of brain tissue and neoplastic cells. The vacuolation may result in some oligodendroglial dysfunction in maintenance of myelin and probably be related with diffuse loss of myelin sheath in the longstanding brain edema secondary to neoplastic invasion. The vacuolated cells can be identified with light and electron microscopes in Epon-embedded sections of surgically removed tissue but not in paraffin sections.

Ultrastructure of tubular inclusions in endothelial cells of pituitary tumors associated with acromegaly

Tubular inclusions were present in 13 out of 43 pituitary adenomas of acromegalic patients and in a single chromophobe pituitary adenoma. There were none in 76 other pituitary adenomas with differing endocrinological symptomatology. The arrays were usually located in the perinuclear cistern of capillary endothelial cells. The tubule diameter in osmium fixed material measured 19-26 nm and the light core averaged 6-11 nm. A longitudinal period of about 4.5 nm could be demonstrated with PTA block staining. Fixation with glutaraldehyde and block staining with ethidium bromide as well as permanganate fixation followed by RNAse treatment showed only the core of the tubules consisting of globular subunits. Several histochemical reactions (perchloric acid extraction, methenamine-silver staining, trypsin and DNAse digestion of frozen sections) suggested that the particles consist of a core of DNA coated with protein. No virus multiplication could be detected in cell cultures or in mice innoculated with fresh tumor material. No significant antibody titers against several virus antigens could be demonstrated.

Chronic progressive panencephalitis due to rubella virus simulating subacute sclerosing panencephalitis

Late-onset chronic progressive panencephalitis developed in a 12-year-old boy with congenital rubella syndrome from whose brain rubella virus was isolated. Progressive dementia began at eight, and ataxia, choreiform movements, myoclonic seizures, and fine perimacular pigmentation appeared at 11 years of age. The cerebrospinal fluid was minimally pleocytotic and had a total protein of 156 mg per deciliter, of which 52 per cent was gamma globulin. Electroencephalography demonstrated generalized medium and occasional high-voltage slowing without burst suppression. The antibody titer to rubella virus (hemagglutination inhibition) was 1:8192 in serum and 1:256 in cerebrospinal fluid. Antibody titer to measles virus (complement fixation) was less than 1:8 in serum. Microscopical study of biopsied brain tissue at the age of 11 disclosed panencephalitis similar to subacute sclerosing panencephalitis, but with perivascular deposits and without inclusion bodies. Rubella virus was isolated from the brain by cocultivation with CV-1 cells.

Analysis of a viral agent isolated from multiple sclerosis brain tissue: characterization as a parainfluenzavirus type 1

A virus originally isolated from cell cultures obtained by lysolecithin-induced fusion of human multiple sclerosis brain cells with CV-1 cells has been analyzed for its antigenic, RNA, and polypeptide compositions, and for selective biological properties. Our findings establish that this isolate, designated 6/94 virus, contains a 50S RNA genome and is, as yet, indistinguishable from Sendai virus in its antigenic and total polypeptide compositions. Despite these similarities, the 6/94 and Sendai viruses differ in certain phenotypic properties. 6/94 virus is markedly less cytocidal for chick fibroblasts, especially at 37 C and, after beta-propiolactone inactivation, it possesses a greater capacity for cell fusion and a lower toxicity than does comparably treated Sendai virus. In addition, 6/94 virus shows greater hemolytic activity.