A Glial Signature and Wnt7 Signaling Regulate Glioma-Vascular Interactions and Tumor Microenvironment

Gliomas comprise heterogeneous malignant glial and stromal cells. While blood vessel co-option is a potential mechanism to escape anti-angiogenic therapy, the relevance of glial phenotype in this process is unclear. We show that Olig2⁺ oligodendrocyte precursor-like glioma cells invade by single-cell vessel co-option and preserve the blood-brain barrier (BBB). Conversely, Olig2-negative glioma cells form dense perivascular collections and promote angiogenesis and BBB breakdown, leading to innate immune cell activation. Experimentally, Olig2 promotes Wnt7b expression, a finding that correlates in human glioma profiling. Targeted Wnt7a/7b deletion or pharmacologic Wnt inhibition blocks Olig2⁺ glioma single-cell vessel co-option and enhances responses to temozolomide. Finally, Olig2 and Wnt7 become upregulated after anti-VEGF treatment in preclinical models and patients. Thus, glial-encoded pathways regulate distinct glioma-vascular microenvironmental interactions.

The Microbiome-Gut-Behavior Axis: Crosstalk Between the Gut Microbiome and Oligodendrocytes Modulates Behavioral Responses

Environmental and dietary stimuli have always been implicated in brain development and behavioral responses. The gut, being the major portal of communication with the external environment, has recently been brought to the forefront of this interaction with the establishment of a gut-brain axis in health and disease. Moreover, recent breakthroughs in germ-free and antibiotic-treated mice have demonstrated the significant impact of the microbiome in modulating behavioral responses in mice and have established a more specific microbiome-gut-behavior axis. One of the mechanisms by which this axis affects social behavior is by regulating myelination at the prefrontal cortex, an important site for complex cognitive behavior planning and decision-making. The prefrontal cortex exhibits late myelination of its axonal projections that could extend into the third decade of life in humans, which make it susceptible to external influences, such as microbial metabolites. Changes in the gut microbiome were shown to alter the composition of the microbial metabolome affecting highly permeable bioactive compounds, such as p-cresol, which could impair oligodendrocyte differentiation. Dysregulated myelination in the prefrontal cortex is then able to affect behavioral responses in mice, shifting them towards social isolation. The reduced social interactions could then limit microbial exchange, which could otherwise pose a threat to the survival of the existing microbial community in the host and, thus, provide an evolutionary advantage to the specific microbial community. In this review, we will analyze the microbiome-gut-behavior axis, describe the interactions between the gut microbiome and oligodendrocytes and highlight their role in the modulation of social behavior.

Infectious agents and multiple sclerosis--are Chlamydia pneumoniae and human herpes virus 6 involved?

A good deal of evidence suggests an infectious component in the development of multiple sclerosis (MS) and, to date, some 20 bacteria and viruses have been associated with the disease. Recent independent sets of studies have implicated the respiratory bacterium Chlamydia pneumoniae and human herpes virus 6 (HHV-6) in the pathogenesis of MS. However, as is the case for essentially all earlier microbial associations, experimental evidence linking either this bacterium or this virus to MS is equivocal. We review the published reports concerning involvement of C. pneumoniae and HHV-6 in MS, and data relating to possession of the APOE epsilon 4 allele, which some studies indicate might influence how these or other pathogens affect disease genesis. Based on the large set of inconsistent observations available and given important new information regarding the neuropathology of MS, we contend that no conclusion is possible at this point regarding the potential role of either C. pneumoniae or HHV-6 in MS. We therefore propose future studies that should clarify whether, and if so how, these and other organisms function in the pathogenesis of this disease.

Infection of murine fetal brain cell cultures with Listeria monocytogenes

The uptake of Listeria monocytogenes by different brain cells was studied in primary dissociated brain cell cultures derived from murine fetuses. In respect to the supposed intraaxonal migration of Listeria monocytogenes in the pathogenesis of listeric focal brain stem encephalitis, it was examined whether the bacterium was internalized by neurons. Infection rates of distinct cell types were determined by double immunofluorescence with antibodies against cell type-specific markers and the bacterial pathogen. Because of the changing composition of the cultures and time-dependent expression of the oligodendrocyte marker galactocerebroside (GC), infections were carried out on day 4, 6, 8, and 15 in vitro. Listeria monocytogenes was detected predominantly within macrophages. Astrocytes, oligodendrocytes, and fibronectin-expressing cells were infected to a lesser extent. The lowest rates of infection were observed in neurons. A tropism of Listeria monocytogenes for neurons was not detected in vitro.

Neurotropism of human coronavirus 229E

The 299E prototype strain of human coronavirus (HCV-229E) has so far been mainly associated with infections of the respiratory tract. In the present study, we show evidence for infection of the central nervous system (CNS) by HCV-229E, both in vitro and in vivo. Various human cell lines of CNS origin were tested for their susceptibility to infection by HCV-229E. Production of viral antigens was monitored by indirect immunofluorescence with monoclonal antibodies and infectious progeny virions by plaque assay on the L132 human embryonic lung cell line. The SK-N-SH neuroblastoma and H4 neuroglioma cell lines were highly susceptible to infection. The U-87 MG and U-373 MG astrocytoma cell lines were also infectable by HCV-229E. We could also demonstrate infection of the MO3.13 cell line, which was established by fusion of human oligodendrocytes with a thioguanine-resistant mutant of the TE671 (RD) human rhabdomyosarcoma cell line. An apparently more extensive infection of the MO3.13 cells, when compared to the parental cells, supports the notion that human oligodendrocytes are differentially susceptible to infection by this virus. We also tested for HCV-229E gene expression in pathological brain specimens. For that purpose, we developed a reverse transcription-polymerase chain reaction (RT-PCR) assay to amplify a portion of the mRNA encoding the viral nucleocapsid protein. Using stringent laboratory conditions, viral RNA was detectable in brain tissue of 4 of 11 multiple sclerosis patients and none of 6 neurological and 5 normal controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of the infected target cell type in spongiform myeloencephalopathy induced by the neurotropic Cas-Br-E murine leukemia virus

The Cas-Br-E murine leukemia virus (MuLV) induces a progressive hindlimb paralysis accompanied by a spongiform myeloencephalopathy in susceptible mice. In order to better understand the pathological process leading to these neurodegenerative lesions, we have investigated the nature of the cell type(s) infected by the virus during the course of the disease in CFW/D and SWR/J mice. For this purpose, we used in situ hybridization with virus-specific probes in combination with cell-type-specific histochemical (lectin) and immunological markers as well as morphological assessment. In the early stage of infection, endothelial cells represented the main cell type expressing viral RNA in the central nervous system (CNS). With disease progression and the appearance of lesions, microglial cells became the major cell type infected, accounting for up to 65% of the total infected cell population in diseased areas. Morphologically, these cells appeared activated and were frequently found in clusters. Infection and activation of microglial cells were almost exclusively restricted to diseased regions of the CNS. Neurons in diseased regions were not discernibly infected with virus at either early or late times of disease progression. Similarly, the proportion of infected astrocytes was typically < 1%. Although some endothelial cells and oligodendrocytes were infected by the virus, their infection was not limited to diseased CNS regions. These results are consistent with a model of indirect motor neuron degeneration, subsequent to the infection of nonneuronal CNS cells and especially of microglial cells. Infected microglial cells may play a role in the disease process by releasing not only virions or viral env-gene-encoded gp70 proteins but also other factors which may be directly or indirectly toxic to neurons. Parallels between microglial cell infection by MuLV and by lentiviruses, and specifically by human immunodeficiency virus, are discussed.

Virulent and avirulent strains of Semliki Forest virus show similar cell tropism for the murine central nervous system but differ in the severity and rate of induction of cytolytic damage

The pathogenicity of the avirulent, demyelinating A7 strain of Semliki Forest virus (SFV) and the virulent SFV4 strain (derived from an infectious clone) for the central nervous system of adult BALB/c mice following intranasal infection was compared. The techniques used included immunocytochemistry using anti-SFV antibody and antibodies to cell markers, in situ hybridization (ISH) using a biotinylated cDNA probe specific for SFV, and immunocytochemistry/ISH double labelling. Whereas SFV4 was lethal at 4 days post-infection, A7-infected mice appeared normal at all times. Neuronal necrosis in the pyriform cortex was present in both infections, but developed sooner and was more severe following infection with SFV4 than with A7. Intact neurons and putative oligodendrocytes contained viral RNA and virus-specific antigen in SFV4 infected mice; viral RNA but not virus-specific antigen was detected in similar cells in A7-infected mice. These results confirm that SFV4 and A7 share similar cell tropisms for the murine central nervous system, but differ in the severity and rate of development of cytolytic damage. Intranasal infection is an efficient monitoring system for studies of the molecular basis of pathogenicity of SFV infection in mice.

Restricted canine distemper virus infection of oligodendrocytes

BACKGROUND

Canine distemper virus, a morbillivirus induces multifocal demyelination in the central nervous system. The acute demyelination correlates with virus replication in brain cells, especially astrocytes. Observations in vivo and in vitro demonstrated degeneration of oligodendrocytes, the myelin producing cells. However, the mechanism of oligodendroglial degeneration in distemper remained unexplained. Infection of the myelin producing cells, the most obvious explanation for the phenomenon of demyelination, could not be supported by extensive searches for viral particles or antigens in these cells neither in vivo nor in vitro.

EXPERIMENTAL DESIGN

In the present study, we combined in situ hybridization to visualize viral nucleic acid sequences with immunofluorescence for oligodendroglial antigens.

RESULTS

The nonradioactive in situ hybridization technique in combination with contrast enhanced video microscopy allowed us to unequivocally demonstrate the presence of canine distemper virus nucleic acid sequences in cultured oligodendrocytes. Many oligodendrocytes close to infected foci in the brain cell cultures were found to contain viral nucleic acid sequences. Only 1% of the viral nucleic acid sequences containing oligodendrocytes also contained viral antigen. Canine distemper virus replication in these cells is clearly restricted.

CONCLUSIONS

Different possibilities why oligodendrocytes do not support a productive virus infection and mechanisms by which such a restricted infection leads to oligodendroglial degeneration and ensuing demyelination are discussed. While our results have advanced our understanding of the pathogenesis of acute demyelination in distemper, they may also offer a possible explanation for the chronic progressive or even relapsing course of the disease. A restricted infection of the oligodendrocytes may be the mechanism by which canine distemper virus persists in the central nervous system. Virus persistence is probably a key event in many chronic viral induced inflammatory demyelinating diseases.

The restricted nature of HIV-1 tropism for cultured neural cells

Infection of the central nervous system by HIV-1, the agent of AIDS, is characterized by the presence of infected and giant microglial cells as well as astrocytosis, demyelination, and neuronal loss. To determine whether cells of neuroectoderm origin can be infected by HIV-1, we have inoculated primary cultures derived from adult human brain with a lymphotropic virus (LAV) or a neurotropic virus (Jr-FL) isolated from a patient with AIDS dementia. While Jr-FL invariably causes productive infection of cultured brain microglia, neither astrocytes nor oligodendrocytes became productively infected by these viral strains. Moreover, the cultured oligodendrocytes develop a normal network of processes and express differentiation antigens in the presence of an ongoing lytic infection of microglial cells. No HIV-1 proviral DNA was detected in primary astrocyte cultures devoid of microglial after inoculation of either HIV-1 strain. Similarly, the neuronal cell line HCN-1 in its differentiated state did not allow the virus to go through cycles of reverse transcription and replication. LAV, however, was able to replicate in undifferentiated HCN-1 cells. Thus, tropism of HIV-1 appears tightly restricted to only one type of differentiated cell in the CNS, the microglia.

Canine distemper virus-immune complexes induce bystander degeneration of oligodendrocytes

Demyelination in chronic canine distemper encephalitis may be the result of a bystander effect in which the antiviral immune response is involved. In the present report we demonstrate that canine distemper virus-antiviral antibody immune complexes induce oligodendroglial degeneration in mixed brain cell cultures, particularly at the level of the cell processes. The involvement of macrophages as effector cells in this process was confirmed by depletion of these cells from the cultures which prevented the immune complex-mediated oligodendroglial degeneration. Canine distemper virus-immune complex-induced oligodendroglial pathology is thought to be mediated by toxic factors released from stimulated macrophages, this bystander effect demonstrated here in vitro may be relevant to the mechanisms of demyelination in vivo, in which virus persistence plays an important role.

In situ analysis of proteolipid protein gene transcripts during persistent Theiler's virus infection

SJL/J mice inoculated intracranially with the DA strain of Theiler's virus exhibit a persistent demyelinating disease of the central nervous system. To investigate the effect of persistent infection of oligodendrocytes on the expression of myelin genes, we analyzed the level of PLP mRNA in infected as well as uninfected oligodendrocytes. This study was performed at the single-cell level using the simultaneous detection of viral antigens by immunocytochemistry and PLP mRNAs by in situ hybridization with 35S-labeled oligonucleotide probes. Our data indicate that viral infection of oligodendrocytes reduces the level of PLP mRNA by about 80%.

Infection by coronavirus JHM of rat neurons and oligodendrocyte-type-2 astrocyte lineage cells during distinct developmental stages

Primary telencephalic cultures derived from neonatal Wistar Furth rats were able to support the growth of coronavirus JHM if a viable neuronal population was maintained. This occurred under serum-free defined, but not serum-supplemented, growth conditions. The importance of neurons in establishing infections in mixed cultures was confirmed by immunocytochemical and electron microscopic studies. Glia, although more abundant than neurons in these cultures, were less frequently infected during the initial 48 h postinoculation. The two glial lineages present in mixed telencephalic cultures were separated into type-1 astrocytes and oligodendrocyte-type-2 astrocyte (O-2A) lineage cells and individually assessed for their ability to support virus growth. Infection could not be established in type-1 astrocytes regardless of the culture conditions employed, consistent with our previous study (S. Beushausen and S. Dales, Virology 141:89-101, 1985). In contrast, infections could be initiated in selected O-2A lineage cells grown in serum-free medium. Virus multiplication was however significantly reduced by preconditioning the medium with mixed telencephalic or enriched type-1 astrocyte cultures, suggesting that intercellular interactions mediated by soluble factor(s) can influence the infectious process in O-2A lineage cells. This presumption was supported by eliciting similar effects with basic fibroblast growth factor and platelet-derived growth factor, two central nervous system cytokines known to control O-2A differentiation. The presence of these cytokines, which synergistically block O-2A cells from differentiating into oligodendrocytes was correlated with specific and reversible resistance to JHM virus (JHMV) infection. These data, combined with our finding that accelerated terminal differentiation of the oligodendrocyte phenotype confers resistance to JHMV (Beushausen and Dales, Virology, 1985), suggest that the permissiveness of O-2A cells for JHMV is restricted to a discrete developmental stage.

Variation in resistance to herpes simplex virus type 1 of oligodendrocytes derived from inbred strains of mice

Primary oligodendrocyte (OL) cultures from three inbred strains of mice with known differences in resistance to herpes simplex virus type 1 (HSV-1) infection in vivo (A/J, susceptible; BALB/cByJ, moderately resistant; C57BL/6J, resistant), also display a similar pattern of resistance in vitro. The nature of the in vitro resistance at the cellular level was investigated. Virus production at different m.o.i.s indicated that the differences in HSV-1 replication are m.o.i.-dependent. Overall, virus yield from the OL cultures infected at a multiplicity of 1 increased 48 h post-infection (p.i.); no additional enhancement occurred 72 h p.i. However, the difference in the replication capacity of the three OL cultures observed at 24 h p.i. persisted at 48 and 72 h p.i. Serial electron microscopy studies on infected OL cultures derived from the different murine strains suggested that the resistance to HSV-1 infection occurs at different stages during the replicative cycle. Virus was detected at the nuclear membrane 5 min p.i. in A/J cells, but was not observed until 120 min p.i. in BALB/cByJ cells, whereas virus could not be detected at the nuclear membrane of C57BL/6J cells, even at 24 h p.i. Virus adsorption, determined by assay of residual non-adsorbed virus infectivity and cell-associated, radiolabelled HSV-1, did not differ in the OL cultures. The cumulative data suggest that A/J cells display the same replication pattern as permissive CV-1 cells, whereas the major replicative blocks in the other two murine strains occur at the level of the cytoplasmic membrane in C57BL/6J OLs, and at the level of the nuclear membrane in BALB/cByJ cells.

Fate of oligodendrocytes in HIV-1 infection

The brains of 22 HIV-1-infected cases and 11 controls, matched for age and sex, were studied with immunocytochemical reactions specific for oligodendrocytes, astrocytes, microglia and HIV-1. In HIV-1 infection, mild degrees of myelin damage were associated with an increase in oligodendrocyte numbers, a change that was reversed in the presence of severe damage. Severity of myelin damage correlated with the extent of astrocytic and microglial reactions expressed in a semi-quantitative manner. HIV-1 p24 antigen was detected in all cases with severe myelin damage and a smaller proportion of cases with lesser degrees of myelin damage. It is concluded that, in HIV-1 infection, oligodendrocytes undergo an initial reactive hyperplasia which may represent an attempt to repair myelin damage.

Cytotoxicity of Borrelia burgdorferi for cultured rat glial cells

A cytotoxic effect, as measured by 51Cr release, was detected after a 6-h incubation with two strains of Borrelia burgdorferi with neonatal rat primary brain cultures and with astroglial enriched cultures derived from the primary rat brain cells. A low-passage strain, J31, induced a significantly greater cytotoxic effect than did strain B31 in long-term in vitro culture. Live spirochetes and sonicates of both strains induced cytotoxicity, whereas heat-killed organisms did not. The degree of injury was greater in the primary brain than in the astroglial enriched cultures. Scanning electron microscopy revealed marked contraction of the membrane sheets and bleb production by the oligodendroglia of primary brain cultures after incubation with B. burgdorferi. The astroglial layer appeared unharmed.

Cytotropism of Theiler's murine encephalomyelitis viruses in oligodendrocyte-enriched cultures

The cytotropism of two strains, GDVII and DA, of Theiler's murine encephalomyelitis viruses (TMEV) was studied in the oligodendrocyte-enriched murine neural cell cultures. Both GDVII and DA caused cytopathic effects in the neural cell cultures, and double immunostaining for galactocerebroside (Gal-Cer), a marker molecule for oligodendrocyte, and viral antigens disclosed a dual expression of Gal-Cer and viral antigens in over 80% of cells in both cultures 24 h after infection with either GDVII or DA. The kinetics of cell-free and cell-associated infectivity were not significantly different between two cultures. These in vitro observations suggest that neither replication in oligodendrocyte nor cell-associated infectivity is a sole factor in discriminating those two subgroups of TMEV with regard to the demyelinating activity, and that virus cell binding may play an important role in virus persistence and TMEV-induced demyelination.

Specific infection of central nervous system white matter by a variant of gross murine leukemia virus

Exposure of neonatal Balb.B mice to a variant of Gross murine leukemia virus, termed WB91-GV, resulted in selective white matter infection within the central nervous system. Viral antigens were detected in brain sections of animals inoculated by either intracerebral or intraperitoneal routes, but were only seen in mice exposed within the first day after birth. This distinct tropism was confirmed by virus replication and gp70 expression in isolated glial cultures in vitro. Analysis of gp70 expression in highly enriched glial subpopulations indicated that oligodendrocytes and perhaps a subset of astrocytes were the targets of this infection.

Ligand binding to the cell surface receptor for reovirus type 3 stimulates galactocerebroside expression by developing oligodendrocytes

Viruses utilize normal cell surface structures as attachment sites. Interaction of viral components with these structures may alter target cell growth. In the present study, the expression and function of the cell surface receptor for reovirus type 3 (Reo3R) was studied in neonatal rat optic nerve glial cultures. The Reo3R is expressed by mature oligodendrocytes and astrocytes but not by O-2A progenitor cells. It appears at an early stage of oligodendrocyte development, coincident with the O4 marker but prior to galactocerebroside or myelin basic protein. Anti-Reo3R antibodies stimulate the expression of galactocerebroside by developing oligodendrocytes. Divalent Reo3R-binding peptides are similarly active. Maximal stimulation of galactocerebroside expression occurs with treatment as short as 4 hr, consistent with a receptor-mediated process. Cell surface structures used as an attachment site by reovirus type 3 may also play a role in the regulation of oligodendrocyte differentiation.

Human immunodeficiency virus-associated progressive multifocal leukoencephalopathy: apparent response to 3'-azido-3'-deoxythymidine

We present the case of a 26-year-old human immunodeficiency virus-seropositive man who developed progressive multifocal leukoencephalopathy as the initial manifestation of AIDS. He appears to have responded dramatically to therapy with 3'-azido-3'-deoxythymidine (AZT). His neurologic status deteriorated shortly after an AZT dose reduction. He has stabilized since resuming his previous AZT dose. Although it remains unclear whether AZT is useful in the treatment of JC virus infection, we think that all AIDS patients with progressive multifocal leukoencephalopathy should be offered treatment with AZT, especially in light of recent reports describing a possible potentiation of human immunodeficiency virus infection of the central nervous system in this setting.

Ultrastructural and biochemical findings in brain cell cultures infected with canine distemper virus

To study the pathomechanism of demyelination in canine distemper (CD), dog brain cell cultures were infected with virulent A75/17-CD virus (CDV) and examined ultrastructurally. Special attention was paid to the oligodendrocytes, which were specifically immunolabelled. In addition, cerebroside sulfotransferase (CST), an enzyme specific for oligodendrocyte activity was assayed during the course of the infection. Infection and maturation as well as CDV-induced changes were found in astrocytes and brain macrophages. Infection of oligodendrocytes was rarely seen, although CST activity of the culture markedly decreased and vacuolar degeneration of these cells occurred, resulting in their complete disappearance. We concluded that the degeneration of oligodendrocytes and demyelination is not due to direct virus-oligodendrocyte interaction, but due to CDV-induced events in other glial cells.

Cell type-specific expression of JC virus T antigen in primary and established cell lines from transgenic mice

The highly restricted host range of JC virus (JCV) has made it difficult to study the biology of this common human papovavirus. To increase our understanding of the tissue specificity of this virus, we have examined the expression of the T antigen (T-Ag) in primary and established cell lines from various tissues of transgenic mice containing the JCV early region. In contrast to earlier results from a simian virus 40-containing transgenic mouse, there was no T-Ag expression in mesenchymal fibroblasts derived from two lines of JCV-transgenic mice. Instead, we isolated T-Ag-positive (T-Ag+) cells that had characteristics consistent with a neural crest origin. Furthermore, primary brain cultures contained many T-Ag+ astrocytes, but no expression was detected in macrophages, epithelial cells, neuronal cells nor, surprisingly, in oligodendrocytes. Continued passage of these cultures resulted in vigorously growing glial fibrillary acidic protein-positive, T-Ag+ astrocytes. Thus, the strict tissue specificity of JCV expression was maintained, despite the fact that the viral genome pre-existed in every tissue of these transgenic mice and these constraints on expression were preserved even when cells were explanted in vitro.

Human and simian glial cells infected by human T-lymphotropic virus type I in culture

Although human T-lymphotropic virus type I (HTLV-I) has been implicated in the etiology of tropical spastic paraparesis (TSP) and HTLV-I associated myelopathy (HAM), the direct infectivity of the virus against constituent cells in the central nervous system remains undetermined. To investigate the neurotropism of HTLV-I, we exposed cultured human and simian glial cells to HTLV-I. Primary mixed glial cell cultures of astrocytes and oligodendrocytes were obtained from adult human and cynomolgus monkey (Macaca fascicularis) brains by an enzyme digestion-Percoll gradient method. After two weeks in vitro, the cells were co-cultured with irradiated MT-2 cells, an HTLV-I-producing T-cell line. Cultures were double stained with antibodies against cell-type specific markers and anti-HTLV-I p19 (gag) monoclonal antibody. The HTLV-I antigen was demonstrated in small numbers of glial fibrillary acidic protein-positive cells (astrocytes) and galactocerebroside-positive cells (oligodendrocytes) in both the human and simian cultures. Electron microscopy demonstrated the presence of type C virus-like particles in the cytoplasm of astrocytes. These results indicate that HTLV-I is capable of infecting human and simian glial cells in vitro.

Vulnerability of rat and mouse brain cells to murine hepatitis virus (JHM-strain): studies in vivo and in vitro

The pathogenicity and cell tropism of mouse hepatitis virus (MHV-JHM-strain) in the developing mouse (Balb/c) and rat (Wistar and Lewis) brain were analysed. Intracranial infection of Balb/c mice at postnatal day 5 induced a lethal encephalitis in all animals. Of Wistar rats infected at day 2 or 5 after birth, 30 to 70%, respectively, survived. The distribution of viral antigen was studied in frozen brain sections of animals that died after infection; astrocytes were found to be the major virus-infected cell type throughout the central nervous system. More than 75% of the surviving rat pups developed paralysis, but viral antigen was detected in only few brain cells and not in astrocytes. The cell tropism of MHV-JHM was examined further in virus-infected glial cell cultures derived from brains of rats or mice. In the glial cultures derived from Wistar rats, only oligodendrocytes were infected, whereas in cultures derived from mouse or Lewis rat brain viral antigen was detected in both astrocytes and oligodendrocytes. Infection of astrocytes led to the formation of syncytia and degradation of the cytoskeleton. Infected rat oligodendrocytes gradually disappeared from the cultures because of cell death. These phenomena indicate that, besides an indirect autoimmune response triggered by infected astrocytes, direct virus-induced injury to astrocytes or to oligodendrocytes can have a dominant role in the neuropathogenicity of mouse hepatitis virus. The present results underscore the importance of species and developmental stage of experimental animals in the neurotropism and pathogenicity of MHV-JHM.

Progressive multifocal leukoencephalopathy and retroviral encephalitis in acquired immunodeficiency syndrome

Antigens of human polyomaviruses, the etiologic agents of progressive multifocal leukoencephalopathy (PML), and of human immunodeficiency virus were localized in paraffin sections from brains of six patients who died with the acquired immunodeficiency syndrome. Immunostaining revealed polyomaviral antigens in oligodendrocytes and in some astrocytes. Human immunodeficiency (retro) virus antigens were immunostained in mononuclear macrophages, glial cells, and vascular endothelial cells. Both viral types were found ultrastructurally. The lesions of PML were more destructive than is usually seen in cases without the acquired immunodeficiency syndrome. The retroviral encephalitis could have occurred before the onset of PML. However, a secondary retroviral encephalitis could have resulted if the monocytes responding to an initial polyomaviral lesion were already infected with human immunodeficiency virus before they differentiated into macrophages.

Theiler's virus-associated antigens on the surfaces of cultured glial cells

Infection of the central nervous system by Theiler's murine encephalomyelitis virus (TMEV), a picornavirus, produces chronic demyelinating disease in susceptible mice. In this immunoelectron microscopic study of TMEV infection of neonatal mouse brain cells in culture, TMEV antigen was found on the surfaces of infected oligodendrocytes and astrocytes by labeling with hyperimmune serum from TMEV-infected mice or with rabbit antiserum to purified inactivated DA strain TMEV. Brain-derived macrophages had no TMEV-specific antigen on their surfaces and were not able to maintain productive TMEV infection, even though TMEV antigen was present in the cytoplasm. The presence of TMEV antigens on the surfaces of oligodendrocytes (myelin-producing cells) was unexpected because picornaviruses are nonenveloped viruses and do not bud from cell surfaces. The finding is consistent with the hypothesis that demyelination follows damage of infected oligodendrocytes by immune cells or immunoglobulins that recognize surface virus antigen.

Infection of human T-lymphotropic virus type I to astrocytes in vitro with induction of the class II major histocompatibility complex

To clarify the pathogenesis of human T-lymphotropic virus type I (HTLV-I)-associated myelopathy (HAM), we examined whether HTLV-I infects normal human glial cells in vitro with induction of the major histocompatibility complex (HMC) class II antigen by immunofluorescence method. It was found that about 10% of astrocytes were infected with HTLV-I with induction of class II MHC antigen. Fluorescence-conjugated HTLV-I was adsorbed to 10% of astrocytes. On the contrary, there was no class II MHC antigen expression and very few HTLV-I infection on oligodendrocytes. We speculated that in patients with HAM, HTLV-I-specific, MHC class II antigen restricted, activated CD4+ cells could damage the MHC class II antigen + HTLV-I-infected astrocytes, leading to the disturbance of blood-brain barrier and to the destructive lesion in the central nervous system.

In vivo and in vitro models of demyelinating disease: efficiency of virus spread and formation of infectious centers among glial cells is genetically determined by the murine host

Resistance or susceptibility of various mouse strains to central nervous system disease caused by different strains of coronavirus is well known. Data from the present study draw attention to an additional, genetically determined mechanism controlling CV infections. The resistance to A59 and JHM virus (JHMV) associated with SJL mice was maintained in explanted glial cultures which, by contrast, fully supported a productive infection by the serorelated mouse hepatitis virus type 3. A comparative analysis of the infectious process in glial cell explants from SJL and CD.1 mice helped to define the stage at which restriction is manifested. Cultures of oligodendrocytes and astrocytes from these strains of mice were challenged with JHMV or mouse hepatitis virus type 3, and cell-virus interactions were monitored, including adsorption, uptake of inoculum, transcription, and cell-to-cell dissemination. The sequence of early events from adsorption to genome activation occurred with about equal efficiency with both viruses and genetically different cells, indicating that SJL resistance is not due to any deficiency in specific receptors or penetration of the inoculum or general expression of viral functions. However, intercellular spread of the infection was restricted in SJL glial cells owing to an as yet undefined component. Since cells from (SJL x CD.1)F1 mice were fully susceptible to JHMV, resistance to virus spread must be due to a deficiency in some factor, perhaps a proteolytic activity necessary for dissemination.

A double-label method detects both early (T-antigen) and late (capsid) proteins of JC virus in progressive multifocal leukoencephalopathy brain tissue from AIDS and non-AIDS patients

A new double-label immunocytochemical method detects JC virus (JCV) early (T-antigen) and late (capsid) proteins simultaneously in cryostat sections of progressive multifocal leukoencephalopathy (PML) brain tissue from both acquired immunodeficiency syndrome (AIDS) and non-AIDS patients. T-antigen is detected with a monoclonal antibody (PAb 416) followed by goat anti-mouse IgG and mouse Clono-PAP, while capsid proteins are detected by a rabbit polyclonal antiserum to capsid proteins followed by biotinylated goat anti-rabbit IgG and streptavidin-alkaline phosphatase conjugate. The substrates are 3,3'-diaminobenzidine and Vector Red I, respectively. With this method some infected glial cells stain for late (capsid) antigens in the nucleus, while others show early protein (large T-antigen) immunoreactivity. The latter are likely to be astrocytes infected abortively or oligodendrocytes in the early stages of a productive JCV infection.

Mechanisms of virus-induced demyelination and remyelination

Viral models of demyelination and remyelination provide important clues to the pathogenesis of multiple sclerosis. Determining the precise viral polypeptides recognized by T cells during the demyelinating process will be important in understanding the mechanisms of viral-induced myelin destruction. Isolation, purification, and characterization of factors that promote remyelination and proliferation of oligodendrocytes may provide hope in the treatment of patients with chronic demyelinating disorders.

In vivo and in vitro models of demyelinating disease: activation of the adenylate cyclase system influences JHM virus expression in explanted rat oligodendrocytes

The specificity of JHM virus (JHMV) tropism for rat oligodendrocytes, as one of the primary host cells in the central nervous system, is maintained after explanation (S. Beushausen and S. Dales, Virology 141:89-101, 1985). The temporal correlation between onset of resistance to JHMV infection in vivo, completion of myelination, and maturation of the central nervous system can be simulated in vitro by inducers of oligodendrocyte differentiation (Beushausen and Dales, Virology, 1985). Stimulation of differentiation through the elevation of intracellular cyclic AMP (cAMP) levels suggests a possible connection between activation of the adenylate cyclase system and coronavirus expression. Chromatographic analysis of cAMP-dependent protein kinase activity in cytosol extracts prepared from astrocytes or oligodendrocytes revealed that both glial cell types were deficient in protein kinase I, indicating that expression of coronavirus in differentiated cells was not contingent upon the presence of protein kinase I. However, treatment with N6,2'-O-dibutyryladenosine-3',5'-cyclic monophosphate (dbcAMP) resulted in a severalfold enhancement of the free regulatory subunit (RI) in oligodendrocytes but not in astrocytes. The RII subunit in both neural cell types was relatively unaffected. Rapid increase in RI due to dbcAMP treatment was correlated with inhibition of JHMV expression. Other differentiation inducers, including 8-Br cAMP and forskolin which, by contrast, caused a decrease in detectable RI, also blocked JHMV expression. This apparent anomaly can be attributed to an increased turnover of RI due to destabilization of the molecule which occurs upon site-specific binding of the cyclic nucleotides. On the basis of these observations, we conclude that the state of oligodendrocyte differentiation manifested with the modulation of RI regulates JHMV expression. The differentiation process did not affect either virus adsorption or sequestration but appeared to inhibit the expression of viral RNA and proteins, implying that replication was inhibited at some step between penetration and initiation of genomic functions, perhaps at the stage of uncoating. We therefore examined the possibility that protein kinases and phosphatases, which influence cellular regulation during cAMP-induced differentiation, may be responsible for the phenomenon of coronavirus suppression in oligodendrocytes. Evidence was obtained indicating that normal processing of the phosphorylated nucleocapsid protein is inhibited in differentiated oligodendrocytes, consistent with the notion that JHMV replication might be arrested during uncoating.

Multiple neural cell types are infected in vitro by border disease virus

Border disease (BD) of sheep results from a congenitally acquired nonarbotogavirus infection which causes a highly selective central nervous system (CNS) pathological lesion consisting of diffuse decreased myelination without inflammation or neuronal destruction. Thus, a selective disruption of oligodendroglial function appears to occur. In order to investigate the in vitro cell tropism of BD virus, primary cultures derived from fetal and adult ovine CNS and peripheral nervous system were inoculated with BD virus. Infected cell types were determined by dual immunofluorescent labeling for viral and cell type specific antigens. Infection of all the major cell types represented in these cultures, including oligodendrocytes, astrocytes, fibroblasts, dorsal root ganglion neurons and Schwann cells was found. Oligodendrocytes were only infected earlier and appeared to remain infected longer than astrocytes and fibroblasts. Infectious virus was produced by all cultures and continued to be produced even after the disappearance of nearly all immunocytochemically detectable viral antigen within cells. These studies suggest that the selective dysfunction of the oligodendrocyte in BD is not based on a selective viral tropism.

Identification of Theiler's virus infected cells in the central nervous system of the mouse during demyelinating disease

Theiler's virus is a picornavirus responsible for a persistent, demyelinating infection of mouse central nervous system. We examined the nature of infected cells during the course of this disease using a simultaneous immunoperoxidase-in situ hybridization assay. Cell types were identified with antigenic markers and infected cells were recognized by the presence of viral RNA. We found that, depending on the animal, approximately 10% of infected cells were migroglia-macrophages, 5 to 10% were astrocytes and 25 to 40% were oligodendrocytes. Approximately half of the infected cells could not be identified.

Coronavirus mouse hepatitis virus (MHV)-A59 causes a persistent, productive infection in primary glial cell cultures

MHV-A59 causes a chronic demyelinating disease in mice which is accompanied by persistence of viral genome in white matter. As part of the investigation into the mechanism of viral persistence, infection of glial cells, probable targets for chronic infection, was studied by the use of mixed glial, enriched oligodendrocyte and enriched astrocyte cultures. Following MHV-A59 infection in vitro, approximately 10% of oligodendrocytes and 30% of astrocytes expressed viral antigens in the absence of overt cytopathic effect. All cultures released infectious virus for the lifetime of the cultures, for at least 45 days in the case of mixed glial cultures. Cultures derived from previously infected mice were similar to those infected in vitro with respect to percentage of cells expressing viral antigen and levels of infectious virus produced. These results show (1) that glial cells are early sites of infection in vivo as well as sites of infection in vitro cultures, and (2) that glial cells support a non-lytic but productive infection in vitro and thus may contribute to viral persistence in vivo.

Demyelinating, non-demyelinating and attenuated canine distemper virus strains induce oligodendroglial cytolysis in vitro

A virulent canine distemper virus (CDV) strain that causes demyelination in vivo has been shown to induce oligodendroglial degeneration in vitro. In order to investigate if this effect on oligodendrocytes is specific for demyelinating strains only, primary brain cell cultures were infected with either virulent demyelinating strains (A75/17 and CH84-CDV), a virulent non-demyelinating strain (SH-CDV) or a non-virulent strain (OP-CDV). All virulent viruses caused a persistent type infection with moderate cytolysis whereas the non-virulent strain was highly cytolytic. All strains induced a similar pattern of oligodendroglial degeneration. It was concluded that the ability to induce oligodendroglial degeneration, which is thought to be the in vitro correlate of demyelination in vivo, is inherent to CDV irrespective of the strain. The discrepancy between biological behaviour of CDV strains in brain cell cultures and in vivo can be explained by the more complex virus-cell interactions in vivo than in vitro.

Human immunodeficiency virus in brain biopsies of patients with AIDS and progressive encephalopathy

Human immunodeficiency virus (HIV) has been identified in patients with AIDS in their circulating and tissue lymphocytes and in their monocyte-macrophages, an arm of the cell-mediated immune system. We report our findings of HIV in brain biopsies. Virus was detected in oligodendroglial and astroglial cells. Virus was also present in the brain capillaries, both in lumens and at the endothelial gaps. Virus was also found in extracellular spaces. Budding forms of the developing virus and bar-shaped nucleoids of mature virus, the diagnostic hallmark of the HIV retrovirus, were identified in brain tissue of five of seven patients with AIDS studied. We believe that HIV may enter the the brain via the vascular capillaries (through the endothelial gaps), bind to brain cells containing T4 receptors, enter the cells, and replicate. There follows a reactive hyperplasia and degeneration of oligodendroglial and astroglial cells. The oligodendroglial cells are the myelin-forming cells, and thus, the result is myelin degeneration.

Tropism of border disease virus for oligodendrocytes in ovine fetal brain cell cultures

Primary dissociated ovine brain cell cultures prepared from 50- or 140-day-old fetuses were inoculated with border disease virus (BDV). The cells present in the cultures were identified, using immunofluorescence procedures and sera against various CNS cell-specific markers. These markers were glial fibrillary acidic protein, myelin basic protein, myelin-associated glycoprotein, neuron-specific enolase, neurofilament protein, and fibronectin. Double-labeling immunofluorescence techniques for visualization of BDV antigen and of the CNS cell markers were used to evaluate the pattern of individual cell susceptibility 48 hours after infection. In cultures from fetuses of both ages, about half of the infected cells were glial fibrillary acidic protein-positive astrocytes. Scattered myelin-associated glycoprotein-positive oligodendrocytes were positive for BDV antigen, but only in the infected cultures from the older fetuses. Fibronectin-positive cells were not infected with BDV. In infected and noninfected cultures, cells positive for neuron-specific enolase, myelin basic protein, or neurofilament protein were not seen. Therefore, the remaining infected cells in all the cultures were not identified by the cell-specific markers used. Results of these in vitro experiments indicate that BDV does not selectively infect oligodendrocytes, and that such a selective pattern of infection may not be the basis for the in vivo congenital hypomyelination in sheep with border disease.

Selective tropism of a neurotropic coronavirus for ependymal cells, neurons, and meningeal cells

The ability of a neurotropic virus, mouse hepatitis virus type 3 (MHV3), to invade the central nervous system (CNS) and to recognize cells selectively within the brain was investigated in vivo and in vitro. In vivo, MHV3 induced in C3H mice a genetically controlled infection of meningeal cells, ependymal cells, and neurons. In vitro, purified MHV3 bound to the surface of isolated ependymal cells and cultured cortical neurons but not to oligodendrocytes or cultured astrocytes. MHV3 replicated within cultured cortical neurons and neuroblastoma cells (NIE 115); infected cultured neurons nonetheless survived and matured normally for a 7-day period postinfection. On the other hand, MHV3 had a low affinity for cortical glial cells or glioma cells (C6 line), both of which appear to be morphologically unaltered by viral infection. Finally, MHV3 infected and disrupted cultured meningeal cells. This suggests that differences in the affinity of cells for MHV3 are determinants of the selective vulnerability of cellular subpopulations within the CNS. In vivo, a higher titer of virus was needed for CNS penetration in the genetically resistant (A/Jx) mice than in the susceptible (C57/BL6) mouse strain. However, in spite of viral invasion, no neuropathological lesions developed. In vitro viral binding to adult ependymal cells of susceptible and resistant strains of mice was identical. Genetic resistance to MHV3-CNS infection appeared to be mediated both by a peripheral mechanism limiting viral penetration into the CNS and by intra-CNS mechanisms, presumably at a stage after viral attachment to target cells.

In vivo and in vitro models of demyelinating diseases. XV. Differentiation influences the regulation of coronavirus infection in primary explants of mouse CNS

Mouse oligodendrocytes and astrocytes, in primary cerebral explant cultures, were infected with JHMV and MHV3 coronaviruses. Contrary to previous findings with neural cells from the rat (S. Beushausen and S. Dales, 1985, Virology 141, 89-101), these agents show no discrimination in the tropism and have the ability to replicate in either type of murine glial cell. Effects of the differentiation inducer dbcAMP on levels of the myelinspecific enzyme 2':3'-cyclic nucleotide-3'-phosphohydrolase (CNPase) activity and virus replication were determined. In the mouse system there was a gradual, continuous elevation of CNPase beyond 30 days whereas in comparable rat cell cultures maximum CNPase enhancement is elicited within 21 days (F. A. McMorris, 1983, J. Neurochem. 41, 506-515). After dbcAMP treatment replication of both coronaviruses was profoundly suppressed in murine oligodendrocytes, consistent with our findings on JHMV replication in treated rat oligodendrocytes. By contrast the replication of JHMV and MHV3 in dbcAMP-treated murine astrocytes was influenced only marginally. These findings provide further support for the hypothesis that susceptibility of rodents to CNS infection by coronaviruses is determined, in part, by the age-related maturation process of oligodendrocytes.

Mechanism of Theiler's virus-induced demyelination in nude mice

In its natural murine host, infection with Theiler's murine encephalomyelitis virus (TMEV) produces a chronic, progressive demyelinating disease. To help elucidate the role of host immune mechanisms involved in demyelination, we studied TMEV infection in Nude mice. These animals demonstrated rising titers of infectious virus within the central nervous system and failed to produce anti-TMEV antibody. Neurologic signs including the development of severe hind limb paralysis were evident approximately 2 weeks postinfection with most animals succumbing within the first month. Immunoperoxidase studies demonstrated viral antigen in the cytoplasm of neurons and glial cells for the entire period of observation. Plaques of demyelination associated with scanty inflammatory infiltrates were present in the spinal cord by 14 days postinfection. Electron microscopic studies of the involved white matter revealed numerous degenerating glial cells, many of which contained paracrystalline arrays of picornavirus within their cytoplasm. Some of the infected glial cells were identified as oligodendrocytes by demonstrating their myelin-plasma membrane connections. The studies indicate that in Nude mice TMEV causes a lytic infection of oligodendrocytes producing demyelination independent of the T lymphocyte immune system.

Theiler's virus in brain cell cultures: lysis of neurons and oligodendrocytes and persistence in astrocytes and macrophages

The mechanisms of persistence and of demyelination in Theiler's virus (TV)-induced chronic neurologic disease (a murine model for multiple sclerosis) are, as yet, disputed. We investigated the tropism and persistence of TV in brain cell culture to better understand the pathogenesis of this disease. Using anti-genic markers to identify specific cells in culture, we have demonstrated that TV infects, lytically, neurons and oligodendrocytes and persistently astrocytes and macrophages. These results suggest that host cell factors play a key role in the mechanism of demyelination and the persistence of TV in the nervous system.

Abilities of human oligodendroglial cells and mouse Schwann cells to phagocytose Mycobacterium leprae and other mycobacteria

Human oligodendroglial KG-1-C cells derived from human cerebral mixed glioma and mouse Schwann cells derived from dorsal root ganglion were studied with respect to their abilities to phagocytose various mycobacteria, especially Mycobacterium leprae, and other microorganisms. KG-1-C cells phagocytosed M. leprae at a markedly higher rate than BALB/3T3, BHK 21, HeLa S3, mKS-A TU-7, XC, TSV-5, N-18, and Schwann cells but at a lower rate than peritoneal macrophages. Schwann cells also exhibited substantial phagocytic ability against M. leprae, and their phagocytic rate against M. leprae was much higher than that of N-18 cells, derived from neurons. KG-1-C and Schwann cells phagocytosed mycobacteria other than M. leprae, and their phagocytic patterns with various mycobacteria were similar, thereby suggesting that their abilities to phagocytose mycobacteria were based on the same cellular mechanism. The time course of phagocytosis of M. leprae by KG-1-C cells markedly differed from that by macrophages, indicating differences in the cellular mechanisms of M. leprae phagocytosis. KG-1-C cells also ingested microorganisms other than acid-fast bacilli, such as Staphylococcus aureus, Listeria monocytogenes, Bacillus subtilis, and Escherichia coli but not Candida albicans. They also phagocytosed latex beads (0.8-micron diameter) but not sheep erythrocytes. Microscopically, most mycobacterial cells were ingested in the perikaryon of KG-1-C cells and Schwann cells.

Immunoenzymatic labelling of JC papovavirus T antigen in brains of patients with progressive multifocal leukoencephalopathy

Formalin-fixed, paraffin-embedded autopsy sections of brains from two patients with progressive multifocal leukoencephalopathy (PML) were stained by peroxidase-antiperoxidase methods for human papovavirus T antigen, a nonstructural protein expressed in cells lytically infected or transformed by JC, BK, and SV40 viruses. Adjacent sections were stained for papovavirus common structural antigen, a component of JC, BK, and SV40 virions which is synthesized in productively infected but not transformed cells. Intense immunoperoxidase labelling specific for T antigen was detected in large numbers of oligodendrocytes at the edges of demyelinated areas and in occasional oligodendrocytes within otherwise normal brain. Occasional morphologically normal astrocytic cells exhibited similar specific staining, but only rate atypical astrocytic cells contained detectable amounts of T antigen. Examination of adjacent sections stained with antisera to common structural antigen revealed an identical pattern of immunoenzymatic labelling, indicating that most of the cells expressing T antigen were also expressing viral structural proteins. The present study demonstrates that T antigen can be identified by immunoperoxidase methods in routinely processed autopsy material from cases of PML, but that detectable amounts of antigen are found almost exclusively in cells undergoing lytic infection.

Mechanisms of phagocytosis of Mycobacterium leprae and other mycobacteria by human oligodendroglial cells

The mechanisms by which human oligodendroglial cells, KG-1-C cells, phagocytose mycobacteria, especially Mycobacterium leprae, were studied. The ability of glial cells to phagocytose M. leprae was inhibited by azide, dinitrophenol (inhibitors of oxidative phosphorylation), and iodoacetamide but not fluoride (both are inhibitors of glycolysis). Thus, the energy metabolism dependency is somewhat different from that of peritoneal macrophages and polymorphonuclear leukocytes, the phagocytic capacities of which are mainly dependent on glycolysis. Phagocytosis of M. leprae by KG-1-C cells was markedly suppressed by a microfilament inhibitor (cytochalasin B) but not microtubule inhibitors (colchicine and vinblastine), as with macrophages. The phagocytosis of M. leprae by KG-1-C cells was dependent on the lipid and somewhat on the sugar ligands of the organism. Moreover, the phagocytosis of a given mycobacterium by KG-1-C cells correlated well with its hydrophobicity, thus revealing the importance of some lipid moieties on the surface of bacteria in the establishment of rigid binding interaction of bacteria with KG-1-C cells, before the onset of engulfment. Electric charge of a given microorganism did not correlate with its phagocytosis by KG-1-C cells.