Measles virus antigen in panencephalitis. An immunomorphological study stressing dendritic involvement in SSPE

Subacute Sclerosing Panencephalitis in Children: The Archetype of Non-Vaccination

Subacute sclerosing panencephalitis (SSPE) is a late complication of measles virus infection that occurs in previously healthy children. This disease has no specific cure and is associated with a high degree of disability and mortality. In recent years, there has been an increase in its incidence in relation to a reduction in vaccination adherence, accentuated by the COVID-19 pandemic. In this article, we take stock of the current evidence on SSPE and report our personal clinical experience. We emphasise that, to date, the only effective protection strategy against this disease is vaccination against the measles virus.

Diagnosis of inflammatory demyelination in biopsy specimens: a practical approach

Multiple sclerosis is the most frequent demyelinating disease in adults. It is characterized by demyelination, inflammation, gliosis and a variable loss of axons. Clinically and histologically, it shares features with other demyelinating and/or inflammatory CNS diseases. Diagnosis of an inflammatory demyelinating disease can be challenging, especially in small biopsy specimens. Here, we summarize the histological hallmarks and most important neuropathological differential diagnoses of early MS, and provide practical guidelines for the diagnosis of inflammatory demyelinating diseases.

Infection of human oligodendroglioma cells by a recombinant measles virus expressing enhanced green fluorescent protein

One of the hallmarks of the human CNS disease subacute sclerosing panencephalitis (SSPE) is a high level of measles virus (MV) infection of oligodendrocytes. It is therefore surprising that there is only one previous report of MV infection of rat oligodendrocytes in culture and no reports of human oligodendrocyte infection in culture. In an attempt to develop a model system to study MV infection of oligodendrocytes, time-lapse confocal microscopy, immunocytochemistry, and electron microscopy (EM) were used to study infection of the human oligodendroglioma cell line, MO3.13. A rat oligodendrocyte cell line, OLN-93, was also studied as a control. MO3.13 cells were shown to be highly susceptible to MV infection and virus budding was observed from the surface of infected MO3.13 cells by EM. Analysis of the infection in real time and by immunocytochemistry revealed that virus spread occurred by cell-to-cell fusion and was also facilitated by virus transport in cell processes. MO3.13 cells were shown to express CD46, a MV receptor, but were negative for the recently discovered MV receptor, signaling leucocyte activation molecule (SLAM). Immunohistochemical studies on SSPE tissue sections demonstrated that CD46 was also expressed on populations of human oligodendrocytes. SLAM expression was not detected on oligodendrocytes. These studies, which are the first to show MV infection of human oligodendrocytes in culture, show that the cells are highly susceptible to MV infection and this model cell line has been used to further our understanding of MV spread in the CNS.

Observation of measles virus cell-to-cell spread in astrocytoma cells by using a green fluorescent protein-expressing recombinant virus

A recombinant measles virus (MV) which expresses enhanced green fluorescent protein (EGFP) has been rescued. This virus, MVeGFP, expresses the reporter gene from an additional transcription unit which is located prior to the gene encoding the measles virus nucleocapsid protein. The recombinant virus was used to infect human astrocytoma cells (GCCM). Immunocytochemistry (ICC) together with EGFP autofluorescence showed that EGFP is both an early and very sensitive indicator of cell infection. Cells that were EGFP-positive and ICC-negative were frequently observed. Confocal microscopy was used to indirectly visualize MV infection of GCCM cells and to subsequently follow cell-to-cell spread in real time. These astrocytoma cells have extended processes, which in many cases are intimately associated. The processes appear to have an important role in cell-to-cell spread, and MVeGFP was observed to utilize them in the infection of surrounding cells. Heterogeneity was seen in cell-to-cell spread in what was expected to be a homogeneous monolayer. In tissue culture, physical constraints govern the integrity of the syncytia which are formed upon extensive cell fusion. When around 50 cells were fused, the syncytia rapidly disintegrated and many of the infected cells detached. Residual adherent EGFP-positive cells were seen to either continue to be involved in the infection of surrounding cells or to remain EGFP positive but no longer participate in the transmission of MV infection to neighboring cells.

Measles virus antigen in macrophage/microglial cells and astrocytes of subacute sclerosing panencephalitis

In two patients with subacute sclerosing panencephalitis (SSPE) of 10 and 25 months duration we demonstrated by immunohistochemistry the presence of measles-virus nucleocapsid antigen (MVNA) in CD68+ cells and astrocytes of brain tissues. In both cases, CD68+ hematogenous monocyte/ macrophages and perivascular microglial cells (Mphi) were found infiltrating the brain parenchyma, and often partially or completely invested by perivascular reactive astrocytes expressing glial fibrillary acidic protein (GFAP). Mphi with cytoplasmic MVNA were often seen in the Virchow-Robin spaces and in close association with perivascular astrocytes, which often also contained MVNA+ intracytoplasmic inclusions. Reactive astrocytosis was more severe in the patient with long-standing illness, and a correspondingly elevated number of strongly GFAP+ MVNA+ or MVNA- perivascular binucleated astrocytes was observed. An uptake of MVNA+ cell debris by reactive astrocytes was evident in areas of white matter displaying extensive demyelination and necrosis. Taken together, these observations seem to indicate that the brain infiltration by Mphi carrying measles virus could represent one pathway of virus entry and dissemination in the central nervous system. Virus transfer to perivascular astrocytes via cell-to-cell contacts with infected macrophages is also suggested.

Widespread, restricted low-level measles virus infection of brain in a case of subacute sclerosing panencephalitis

In situ reverse transcriptase-polymerase chain reaction amplification with labeled-probe hybridization (in situ RT-PCR/LPH) was used to detect measles virus RNA within formalin-fixed, paraffin-embedded brain tissue sections from a patient who died with subacute sclerosing panencephalitis (SSPE). Many more infected neurons and oligodendrocytes were detected by in situ RT-PCR/LPH than by immunohistochemistry or by in situ hybridization alone. In addition, infection of vascular endothelial cells was demonstrated only by in situ RT-PCR/LPH. The observation that many cells contained only a few copies of viral RNA without detectable antigen is consistent with a persistent viral infection of the central nervous system. In situ RT-PCR/LPH, combining the sensitivity of PCR with the tissue localization of in situ hybridization, should prove useful in further studies to detect nucleic acids in situ in the central nervous system.

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.

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.

Postmortem detection of measles virus in non-neural tissues in subacute sclerosing panencephalitis

Subacute sclerosing panencephalitis, a rare, progressive, fatal central nervous system disease of children, is caused by measles virus. Clinical signs occur months to several years after recovery from acute measles infection. It is not known where the virus persists while the disease is inapparent. Involvement of organs outside the central nervous system has rarely been documented. To search for possible peripheral reservoirs of measles virus we used in situ hybridization to probe for measles virus RNA and immunocytochemical studies to localize measles virus antigens ina variety of organs taken at autopsy from confirmed cases of subacute sclerosing panencephalitis. Seven of 9 cadavers were found to contain measles virus RNA or antigens, or both, in at least one location outside the central nervous system. These sites included lymphoid organs such as thymus, spleen, lymph nodes, and tonsil, suggesting a role for lymphocytes in disease pathogenesis. Virus was also detected in kidney, lung, and glandular tissues such as pancreas, adrenal, and pituitary. These reservoirs may provide the antigenic stimulus leading to the elevated response characteristic for subacute sclerosing panencephalitis.

Dendritic pathology: an overview of Golgi studies in man

Study of dendritic morphology through Golgi impregnation techniques has significantly furthered our understanding of neuronal development, maturation, and senescence. It has also provided insight into the pathogenesis of a wide spectrum of disease processes ranging from brain malformations to degenerative disorders. Golgi impregnation remains virtually the only method for demonstrating dendritic morphology. It delineates the profile of the individual neuron and its dendritic ramifications with unsurpassed clarity. Although it has been widely applied to experimental neuroscience involving animal tissue, its application to human material has been limited. This review summarizes the information on dendritic development and pathology in the human brain revealed by the use of the Golgi method.

Immunohistochemical and electron microscopic techniques in the diagnosis of viral encephalitides

Electron microscopy and in particular, immunohistochemical examination techniques have substantially improved the chances to attain an etiologic diagnosis in viral encephalitis. The application of these techniques is needed first of all in the examination of cerebral biopsy specimens, but they can contribute to the clearing of the etiology at post mortem study of the brain, too. This review outlines the basic techniques and their application fields. In immunohistochemistry beside the demonstration of specific viral antigens the analysis of the humoral and cellular immune reactions and the identification of the cell types involved by cell specific markers is also important. The second part of the review gives a synopsis of the results of electron microscopic and immunohistochemical studies in the most important acute, subacute and chronic encephalitides occurring in Europe.

Measles virus matrix protein detected by immune fluorescence with monoclonal antibodies in the brain of patients with subacute sclerosing panencephalitis

Brain materials from four cases of subacute sclerosing panencephalitis were examined by immune fluorescence with monoclonal antibodies against five structural components of measles virus. All five antigens including the matrix component were present in the brain tissues of all cases. A defective Vero cell-associated virus isolate from one of the cases produced all of the structural components except the matrix protein.

Demonstration of immunoglobulin in brains of ferrets inoculated with an SSPE strain of measles virus: use of protein A conjugated to horseradish peroxidase

Measles virus-specific immunoglobulin G (IgG) has been found in the brains of patients with subacute sclerosing panencephalitis (SSPE), a slowly progressing central nervous system (CNS) disease affecting children. IgG/albumin ratios indicate that the antibodies are probably synthesized in the CNS. In a ferret model system, protein A conjugated to horseradish peroxidase (PrAPx) was used to localize Ig's in brains of animals inoculated with a cell associated strain of SSPE. Ig's were found in plasma cells in various stages of antibody production both in perivascular inflammatory lesions and scattered throughout the cerebral cortex. These findings offer corroborative evidence that the Ig found in SSPE ferret brain and CSF is actively synthesized within the CNS. Antibody was also demonstrated in glial and neuronal cell bodies and processes and in postsynaptic profiles. These are the same sites where measles virus antigens are most frequently found and suggests the possibility of immune complex formation.

Measles encephalomyelitis: lack of evidence of viral invasion of the central nervous system and quantitative study of the nature of demyelination

Measles encephalomyelitis appears to be an immune-mediated parainfectious disorder, but it is unclear whether viral invasion of brain is an obligate step in its development. Immunocytochemical methods were used to search for virus antigen in formalin-fixed, paraffin-embedded central nervous system (CNS) tissues from 10 patients with measles encephalomyelitis and 12 patients who had died of measles without CNS involvement. All the CNS tissues studied were viral antigen negative. Similarly fixed CNS tissues from all of 6 patients with subacute sclerosing panencephalitis were viral antigen positive and served as controls. The pattern of perivenular demyelination was also determined in 4 cases of measles encephalomyelitis using antibodies to myelin associated glycoprotein and myelin basic protein and a Luxol fast blue stain. Areas of demyelination in serial sections were quantitated, and no morphometrical differences were found among tissues stained with the three stains. The data suggest the lack of virus replication in the CNS during encephalomyelitis or fatal measles without CNS symptoms. The pattern of loss of myelin associated glycoprotein and myelin basic protein in regions of perivenular demyelination resembles that reported in experimental allergic encephalomyelitis. This pattern of demyelination has been proposed to result from a primary attack on the myelin sheath rather than from direct involvement of the oligodendroglial cell.