Gamma interferon expression and major histocompatibility complex induction during measles and vesicular stomatitis virus infections of the brain

Expressão do complexo de histocompatilidade principal de classe I (MHC I) no sistema nervoso central: plasticidade sináptica e regeneração

Foi demonstrado recentemente que o complexo de histocompatibilidade principal de classe I (MHC I), expresso no sistema nervoso central (SNC), não funciona somente como molécula com papel imunológico, mas também como parte de um mecanismo envolvido na plasticidade sináptica. A expressão de MHC I interfere na intensidade e seletividade da retração de sinapses em contato com neurônios que sofreram lesão e também influencia a reatividade das células gliais próximas a esses neurônios. A intensidade do rearranjo sináptico e resposta glial após lesão, ligadas à expressão de MHC I no SNC, repercute em diferenças na capacidade regenerativa e recuperação funcional em linhagens de camundongos isogênicos. Dessa forma, os novos aspectos sobre a função do MHC I no SNC direcionam futuras pesquisas no sentido de buscar o envolvimento do MHC I em doenças neurológicas e também o desenvolvimento de novas estratégias terapêuticas.

Correlations among measles virus-specific antibody, lymphoproliferation and Th1/Th2 cytokine responses following measles-mumps-rubella-II (MMR-II) vaccination

Immunity to measles is conferred by the interplay of humoral and cellular immune responses, the latter being critical in maintaining long-term recall response. Therefore, it is important to evaluate measles-specific humoral and cellular immunity in populations several years after vaccination and understand the correlations among these measures of immunity. We examined measles-specific antibodies, lymphoproliferation and the Th1/Th2 signature cytokines, interferon (IFN)-gamma and interleukin (IL)-4, in a population-based cohort of healthy children from Olmsted County, Minnesota after two doses of measles-mumps-rubella-II (MMR-II) vaccine. We detected positive measures of measles-specific cellular and humoral immunity in the majority of our study population. However, a small proportion of subjects demonstrated an immune response skewed towards the Th2 type, characterized by the presence of either IL-4 and/or measles-specific antibodies and a lack of IFN-gamma production. Further, we observed a significant positive correlation between lymphoproliferation and secretion of IFN-gamma (r = 0.20, P = 0.0002) and IL-4 (r = 0.15, P = 0.005). Measles antibody levels were correlated with lymphoproliferation (r = 0.12, P = 0.03), but lacked correlation to either cytokine type. In conclusion, we demonstrated the presence of both long-term cellular and humoral responses after MMR-II vaccination in a significant proportion of study subjects. Further, a positive correlation between lymphoproliferation and IL-4 and IFN-gamma suggests that immunity to measles may be maintained by both Th1 and Th2 cells. We speculate that the Th2 biased response observed in a subset of our subjects may be insufficient to provide long-term immunity against measles. Further examination of the determinants of Th1 versus Th2 skewing of the immune response and long-term follow-up is needed.

Involvement of quinolinic acid in AIDS dementia complex

Human immunodeficiency virus (HIV) infection is often complicated by the development of acquired immunodeficiency syndrome (AIDS) dementia complex (ADC). Quinolinic acid (QUIN) is an end product of tryptophan, metabolized through the kynurenine pathway (KP) that can act as an endogenous brain excitotoxin when produced and released by activated macrophages/microglia, the very cells that are prominent in the pathogenesis of ADC. This review examines QUIN's involvement in the features of ADC and its role in pathogenesis. We then synthesize these findings into a hypothetical model for the role played by QUIN in ADC, and discuss the implications of this model for ADC and other inflammatory brain diseases.

Identification of HLA a*0201 glioblastoma multiforme cell lines for immunotherapy by PCR-SSP and DNA sequencing

Most tumor specific antigens characterized to date are restricted by HLA a*0201, which is the major HLA subtype in many ethnic groups. Cancer cells that express tumor antigens in association with the HLA a*0201 subtype have been shown to be responsive to various immunotherapies. We therefore sought to identify glioma cell lines that also express this HLA subtype and determine whether they had the molecular properties needed for tumor-peptide presentation. The HLA a*0201 allele was identified with PCR using sequence-specific primers followed by DNA sequencing. With this method, we screened 15 glioma cell lines to determine if they were of the HLA a*0201 genotype. Glioma cell lines that express the HLA a*0201 subtype were further studied for the expression of MHC class I and beta-2-microglobulin (beta2m) molecules by flow cytometry, and peptide presentation molecules TAP-1, TAP-2, and tapasin by RT-PCR. We identified six out of fifteen cell lines that were of the HLA a*0201 subtype. These cell lines are U87, T98, U373, U138, CRL2365 and UMN-4. All these six cell lines exhibited high levels of MHC class I and beta2m molecules. In addition, these cell lines all expressed molecules required for peptide presentation as shown by the presence of peptide presentation-related molecules TAP-1, TAP-2 and tapasin. The identification of glioma cell lines that express the HLA a*0201 subtype along with the necessary molecules for peptide-presentation will enable their use in developing new immunotherapeutic approaches for treating brain tumors. The method used to identify HLA a*0201 glioma cells is rapid and inexpensive, and suitable for screening tumor cells.

Measles virus-specific T-cell immunity in rodent models

Measles virus (MV) infection still belongs to the most important infectious diseases world wide. To identify the components of the immune system that combat MV infection, infection models in rodents have been established. In rats and mice, the immune response to experimental MV infection is governed by the major histocombatibility complex (MHC). According to the MHC haplotype, the functional composition of the T-cell subsets determines the degree of susceptibility to experimental measles virus infection. CD4+ T-cells are the most important T-cell subset in combating experimental MV infection in rodents. However, the mechanism of action still remains to be elucidated.

Functional expression of chemokine receptor CCR5 on CD4(+) T cells during virus-induced central nervous system disease

Intracranial infection of C57BL/6 mice with mouse hepatitis virus (MHV) results in an acute encephalomyelitis followed by a demyelinating disease similar in pathology to the human disease multiple sclerosis (MS). CD4(+) T cells are important in amplifying demyelination by attracting macrophages into the central nervous system (CNS) following viral infection; however, the mechanisms governing the entry of these cells into the CNS are poorly understood. The role of chemokine receptor CCR5 in trafficking of virus-specific CD4(+) T cells into the CNS of MHV-infected mice was investigated. CD4(+) T cells from immunized CCR5(+/+) and CCR5(-/-) mice were expanded in the presence of the immunodominant epitope present in the MHV transmembrane (M) protein encompassing amino acids 133 to 147 (M133-147). Adoptive transfer of CCR5(+/+)-derived CD4(+) T cells to MHV-infected RAG1(-/-) mice resulted in CD4(+)-T-cell entry into the CNS and clearance of virus from the brain. These mice also displayed robust demyelination correlating with macrophage accumulation within the CNS. Conversely, CD4(+) T cells from CCR5(-/-) mice displayed an impaired ability to traffic into the CNS of MHV-infected RAG1(-/-) recipients, which correlated with increased viral titers, diminished macrophage accumulation, and limited demyelination. Analysis of chemokine receptor mRNA expression by M133-147-expanded CCR5(-/-)-derived CD4(+) T cells revealed reduced expression of CCR1, CCR2, and CXCR3, indicating that CCR5 signaling is important in increased expression of these receptors, which aid in trafficking of CD4(+) T cells into the CNS. Collectively these results demonstrate that CCR5 signaling is important to migration of CD4(+) T cells to the CNS following MHV infection.

The rainbow trout classical MHC class I molecule Onmy-UBA*501 is expressed in similar cell types as mammalian classical MHC class I molecules

Onmy-UBA is a polymorphic classical major histocompatibility (MHC) class I locus in rainbow trout (Oncorhynchus mykiss). A common allomorph is Onmy-UBA*501, which has been detected in several wildtype strains, in the clonal homozygous rainbow trout C25 and, in the current study, in the rainbow trout gonad cell line RTG-2. The extracellular domain of this allomorph was expressed in E. coli and a murine monoclonal antibody designated H9 was generated against the recombinant protein. In Western blot analysis Mab H9 specifically recognised an n-glycosylated protein of 45 kDa in leucocytes and erythrocytes of C25 fish and in RTG-2 cells. The level of Onmy-UBA*501 expression in erythrocytes was very low. Immunocytochemistry of isolated cells indicated expression in lymphocytes, macrophages, neutrophils, erythrocytes, RTG-2 cells and Onmy-UBA *501 transfected CHO cells, but not in untransfected CHO cells. Immunohistochemistry using frozen sections of C25 fish indicated that Onmy-UBA*501 expression is strong in the lymphoid organs (thymus, head kidney and spleen) and in the epithelia and endothelia of several organs. No significant expression was observed in muscle fibres, hepatocytes or neurons. These observations demonstrate that in jawed fish, the lowest phylogenetic group possessing an MHC system, the classical MHC class I molecules are expressed in similar cell types as in higher vertebrates.

Characterization of the inflammatory response during acute measles encephalitis in NSE-CD46 transgenic mice

Expression of the human measles virus receptor, CD46, in the murine central nervous system allows infection and replication by wild-type human measles virus (MV) strains (Rall, G.F., Manchester, M., Daniels L.R., Callahan, E., Belman, A., Oldstone, M.B.A., 1997. A transgenic mouse model for measles virus infection of the brain. Proc. Natl. Acad. Sci. U.S.A. 94, 2243-2248). MV replicates in neurons in focal lesions of the cortex, hippocampus and thalamus, leading to death of the animals. In MV-infected CD46 transgenic mice, infiltration of CD4+ and CD8+ T-lymphocytes, B-lymphocytes and macrophages was seen. Upregulation of MHC class I and class II molecules was observed, along with reactive astrocytosis and microgliosis. Increased chemokine mRNAs, especially RANTES and IP-10, and cytokine RNAs IL-6, TNF-alpha, and IL1-beta were observed. Apoptosis of neurons also was increased. No MV replication or inflammation was seen in similarly inoculated nontransgenic littermates. These results further characterize the MV-induced encephalitis in CD46 transgenic mice and highlight similarities to MV infection of the human CNS.

Measles virus in the brain

Measles virus can give three different forms of infections in the central nervous system. These are acute postinfectious encephalitis, acute progressive infectious encephalitis, and subacute sclerosing panencephalitis (SSPE). The postinfectious acute disease is interpreted to reflect an autoimmune reaction. The acute progressive form of brain disease, also referred to as inclusion body encephalitis, reflects a direct attack by the virus under conditions of yielding cellmediated immunity. The late progressive form of encephalitis (SSPE) has been extensively analyzed. Recent molecular genetic studies have unravelled a range of mechanisms by which a defective expression of either the matrix, the fusion, or the hemagglutinin proteins may lead to viral persistence in brain cells under conditions not allowing identification by immune surveillance mechanisms. Many aspects of virus-cell interactions have been examined by use of explant cultures of neuronal cells of human and animal origin. Some of the findings are reviewed. Experimental animals, in particular rodents, have been used to establish systems in which phenomena, pivotal to the evolution of acute as well as persistent measles virus infections in the brain, can be studied. A wide range of potentially important mechanisms has been highlighted and is discussed. More recently, mice with genetic defects in immune functions were used to evaluate consequences as to initiation and dissemination of virus infection in the brain.

Quinolinic acid production by macrophages stimulated with IFN-gamma, TNF-alpha, and IFN-alpha

Quinolinic acid (QUIN) has been associated with several inflammatory neurologic disorders, including AIDS dementia complex (ADC). Recent studies suggest that activation of macrophages with either HIV-1 or interferon-gamma (IFN-gamma) can lead to QUIN production. However, the importance of other cytokines, especially those related to the macrophage and that are especially important in ADC pathogenesis, remains unclear. We, therefore, sought to determine the role of tumor necrosis factor-alpha (TNF-alpha) and IFN-alpha in the production of QUIN. Primary human macrophages were stimulated with two different concentrations of these cytokines alone, in combination with each other, and with IFN-gamma. QUIN concentrations in the supernatants were then measured by mass spectrometry at 24, 48, and 72 hs. Results at 72 h showed significant increases in QUIN production in the cells stimulated with IFN-gamma (10297 +/- 170 nmol/L) and also in those stimulated with IFN-alpha (3600 +/- 113 nmol/L), whereas TNF-alpha-stimulated macrophages produced low levels of QUIN (1108 +/- 23 nmol/L). Macrophages stimulated with the cytokine combinations TNF-alpha and IFN-gamma, IFN-alpha, and IFN-gamma, and TNF-alpha and IFN-alpha also resulted in increases in QUIN production (11471 +/- 77.6 nmol/L, 16656 +/- 184 nmol/L, and 3369 +/- 120.5 nmol/L, respectively). The increases in QUIN production in all of the cytokine treatments approached or exceeded in vivo concentrations of QUIN that have been shown to be neurotoxic. These data further support a role for QUIN in cytokine-mediated neuronal death in inflammatory disorders of the brain, especially ADC.

Spread of measles virus through axonal pathways into limbic structures in the brain of TAP1 -/- mice

The spread of measles virus into the brain was studied exploiting the olfactory pathway, which represents an important route of neuroinvasion by viruses. The virus was injected into the main olfactory bulb of wild-type mice and mice with disrupted TAP1 gene (TAP refers to the Transporter associated with Antigen Presentation), which codes for products essential for the cell-mediated immune response. Virus invasion was monitored for 4 weeks by immunohistochemistry. The distribution of measles virus was found to be restricted to brain areas connected with the olfactory bulbs. However, in the wild-type mice there was a marked infiltration of lymphocytes in the infected brain structures, and the virus did not pass beyond the piriform cortex. In the TAP1 -/- mice the virus spread more extensively along olfactory projections into the limbic system and monoaminergic brainstem neurons. Infected mice of both types developed seizures, which may have been focally evoked from the piriform cortex. This study provides evidence that measles virus can spread through axonal pathways in the brain. The findings obtained in the gene-manipulated mice point out that a compromised immune state of the host may potentiate targeting of virus to the limbic system through olfactory projections.

Characterization of the cellular and cytokine response in the central nervous system following Semliki Forest virus infection

Cytokines are important mediators in the pathogenesis of central nervous system (CNS) inflammatory diseases including multiple sclerosis (MS), experimental allergic encephalomyelitis (EAE), viral encephalitis and virus induced demyelinating diseases. We have used immunohistochemical techniques to characterize the mononuclear cell infiltrate and cytokine profiles in the CNS following infection of mice with the demyelinating A7(74) strain of Semliki Forest virus (SFV), an important viral model of MS. Mononuclear cell infiltrates in the CNS, first observed at 3 days and maximal during clearance of infectious virus, were comprised predominantly of CD8+ lymphocytes. F4/80+ macrophage/microglia and CD45/B220+ B lymphocytes were most numerous during the subsequent phase of demyelination. CD4+ T-lymphocytes were observed at low levels throughout infection. By immunostaining MHC class I, IL-1beta , IL-3 and TGF beta1 were constitutively expressed in normal mice and were upregulated following infection. MHC class II, IL-1alpha, IL-2, IL-2R, TNF-alpha and IL-6 were strongly upregulated in the CNS of SFV-infected mice and mice with chronic relapsing EAE. The spatial and temporal distribution of these cytokines during the course of disease was analysed. Whereas IL-1alpha, IL-1beta, IL-10, and TGF beta1 were observed on day 3 following infection GMCSF, IL-2 and TNF alpha were first apparent at day 7 when the cellular infiltration in the CNS was most intense. In contrast IFN gamma and IL-6 were first observed on day 10 prior to the demyelination phase of disease. Cytokines in the lesions of demyelination suggest a role in the pathogeneisis of myelin damage. Based on cytokine profiles no clear bias of either a Th1 or Th2 response was observed in the CNS during infection.

Borna disease virus and the brain

Viruses with the ability to establish persistent infection in the central nervous system (CNS) can induce progressive neurologic disorders associated with diverse pathological manifestations. Clinical, epidemiological, and virological evidence supports the hypothesis that viruses contribute to human mental diseases whose etiology remains elusive. Therefore, the investigation of the mechanisms whereby viruses persist in the CNS and disturb normal brain function represents an area of research relevant to clinical and basic neurosciences. Borna disease virus (BDV) causes CNS disease in several vertebrate species characterized by behavioral abnormalities. Based on its unique features, BDV represents the prototype of a new virus family. BDV provides an important model for the investigation of the mechanisms and consequences of viral persistence in the CNS. The BDV paradigm is amenable to study virus-cell interactions in the CNS that can lead to neurodevelopmental abnormalities, immune-mediated damage, as well as alterations in cell differentiated functions that affect brain homeostasis. Moreover, seroepidemiological data and recent molecular studies indicate that BDV is associated with certain neuropsychiatric diseases. The potential role of BDV and of other yet to be uncovered BDV-related viruses in human mental health provides additional impetus for the investigation of this novel neurotropic infectious agent.

Interferon regulatory factor-2 physically interacts with NF-kappa B in vitro and inhibits NF-kappa B induction of major histocompatibility class I and beta 2-microglobulin gene expression in transfected human neuroblastoma cells

Most neural cells constitutively lack major histocompatibility complex (MHC) class I and beta 2-microglobulin gene expression. Cytokines and viruses may, however, induce expression of these genes in some neural cells, and this correlates with factor binding to the NF-kappa B and interferon stimulated response elements of these genes. Here, we demonstrate that NF-kappa B is capable of inducing MHC class I and beta 2-microglobulin gene expression when transiently co-transfected into CHP-126 neuroblastomas, and that IRF-2 represses this induction. Interferon regulatory factor-2 (IRF-2) repression of MHC class I and beta 2-microglobulin gene expression in CHP-126 neuroblastomas may demonstrate a mechanism by which virus persists in neural cells. We show here that IRF-2 physically interacts in vitro with NF-kappa B. This interaction may contribute to the repression of the expression of these genes. Our demonstration that IRF family members, in addition to IRF-2, physically interact in vitro with NF-kappa B (p50 and p65), provides a general mechanism by which these transcription factors may, in concert, regulate the expression of a variety of genes involved in immune responses in the brain.

NF kappa B and interferon regulatory factor 1 physically interact and synergistically induce major histocompatibility class I gene expression

Major histocompatibility (MHC) class I gene expression is synergistically induced by the cytokines TNF-alpha and IFN-gamma. However, the mechanism that results in synergistic activation of these genes has remained unclear. We demonstrated here that TNF-alpha induced binding of NF kappa B p50 and p65 to the NF kappa B-like element of the MHC class I promoter termed region I and IFN-gamma induced binding of IRF-1 to the adjacent interferon consensus sequence (ICS). We further demonstrated that NF kappa B and IRF-1 physically interacted with each other and cooperatively induced MHC class I gene expression when cotransfected into CHP-126 neuroblastomas. These results provide a molecular mechanism by which TNF-alpha and IFN-gamma synergistically induce the expression of a variety of genes involved in immune responses, including MHC class I.

Interpreting MHC class I expression and class I/class II reciprocity in the CNS: reconciling divergent findings

MHC-restricted T cells are thought to contribute to clinical demyelination in MS and other circumstances. The step-by-step mechanisms involved and ways of controlling them are still being defined. Identification of the MHC+ cells in the CNS in situ has been controversial. This chapter reviews MHC expression in neural tissue, including normal, pathological, experimental, and developing tissue in situ and isolated cells in vitro. A basic pattern is defined, in which MHC expression is limited to nonneural cells and strongest class I and II expression are on different cell types. Variations from the basic pattern are reviewed. Ways of reconciling divergent findings are discussed, including the use of "mock tissue" to help choose between technical and biological bases for divergent findings, the potential contribution of internal antigen to the in situ staining patterns, and the possibility that class I upregulation is actively suppressed in situ. Functional implications of the observed patterns of MHC expression and ways of confirming the function of each MHC+ cell type in situ are described. It is suggested that modulating MHC expression in different cell types at different times or in different directions might be desirable.

Effects of interferon gamma on the antibody response to Pseudomonas aeruginosa lipopolysaccharide in mice

Different strains of mice were examined for the capacity to produce an Ig subclass-specific antibody response to purified Pseudomonas aeruginosa lipopolysaccharide (PALPS). With the exception of the AKR strain, the predominant isotype for most of the strains tested was IgG3 whereas the least frequent isotype expressed was either IgG2b or IgG1. AKR mice were unique in that the predominant isotype produced was IgG2a, rather than IgG3; however, the administration of anti-interferon gamma antibody, at the time of immunization with PALPS caused a substantial decrease in the IgG2a antibody response. Selected B10 congenic strains were used to assess the relationship between the antibody responses and the major histocompatibility complex (MHC) genes. Here, the isotype-patterns for the antibody responses were essentially the same regardless of the MHC haplotype. Interestingly, an increase in IgG2a, with a concomitant decrease in IgM and IgG1 antibody was noted when C3H mice were given interferon gamma at the time of immunization. These studies indicate that, in general, the antibody response to PALPS consists of IgG3 antibody as the predominant isotype, and that the antibody response can be modified by interferon gamma.

Neuronal interferon-gamma immunoreactive molecule: bioactivities and purification

An interferon (IFN)-gamma immunoreactive molecule, localized to small neurons in peripheral sensory ganglia (N-IFN-gamma), has been detected with two mouse monoclonal antibodies (DB1 and DB16) directed against different epitopes of rat IFN-gamma. To define N-IFN-gamma with regard to its protein characteristics and bioactivities, DB1 and DB16 were used to purify N-IFN-gamma from rat trigeminal ganglia in a two-step sequential antibody-affinity procedure. Sodium dodecylsulfate polyacrylamide gel electrophoresis (PAGE) and silver staining of purified N-IFN-gamma displayed three bands with an approximate molecular mass of 66, 62 and 54 kDa. The N-IFN-gamma bioactivity was confined to the protein stained on gel when native material was run on PAGE. Biological effects of pure N-IFN-gamma were examined and compared with those of lymphocyte-derived recombinant IFN-gamma. N-IFN-gamma had antiviral effects in vitro and induced major histocompatibility complex class I and II antigens on macrophages and in cells in skeletal muscle cell cultures. N-IFN-gamma also stimulated myoblast proliferation and affected cholinergic receptor distribution on myotubes similar to recombinant IFN-gamma. Both molecules potently stimulated Trypanosoma brucei brucei growth. These data suggest that, although N-IFN-gamma is a protein distinct from lymphocyte-derived IFN-gamma, the two molecules have enough structural similarities to allow for antibody recognition of at least two epitopes, and action on similar target structures on both parasite and mammalian cells.

Central neuropathogenesis of vesicular stomatitis virus infection of immunodeficient mice

To determine whether central neuropathogenesis associated with vesicular stomatitis virus (VSV) infection is regulated by T cells, we have examined the effects of intranasal infection of mice lacking T cells. The mice examined were of two kinds: (i) thymus-deficient BALB/c nu/nu nice and (ii) BALB/c mice experimentally depleted of T cells by systemic infusions of a monoclonal antibody to the CD4 or CD8 cell surface molecules. These mice were infected intranasally with a single dose of replication-competent VSV. Brain tissue homogenates were analyzed for the presence of infectious virus. For each population of mice, infection-related mortality was assessed. In histological sections of brain, the distribution of viral antigens (Ags) was examined by immunocytochemistry. We found that recovery of infectious virus from homogenates of tissues obtained from athymic nu/nu animals was more than 10 times greater than that from samples from their euthymic littermates. With a single exception in a BALB/c nu/nu mouse, virus was not isolated from the spleen when it was administered intranasally. In these experimental infections, athymic mice succumbed 1 to 2 days before their euthymic littermates. A dose of virus that resulted in half of the nu/+ survival rate was uniformly lethal to nu/nu mice. In experiments with BALB/c mice depleted of either CD4+ or CD8+ T cells by in vivo antibody treatment, histological analysis revealed an increase in viral Ag distribution in comparison with control (medium-infused) infected mice. Necrosis and inflammation paralleled the extent of viral Ag expression. Viral Ags were detected in discrete areas that usually remain uninfected in immunocompetent mice. These areas include the neocortex and caudate putamen nuclei, the piriform cortex, and the lateral olfactory tract. Neuronal loss and necrosis were consistently found in the olfactory bulb and the horizontal/vertical band of Broca. In some of the T-cell depleted mice, necrosis was also evident in the hippocampus, fimbria, mammillary bodies, and hypothalamic nuclei. In the brain stem, perivascular cuffing was evident, but with little necrosis. Collectively, these data suggest that CD4+ and CD8+ T cells make only a minor contribution to the development of histopathology but rather function together to limit viral replication and transsynaptic or ventricular spread of virus, thus promoting recovery. The primary effectors of histopathology appear to be related more to the cytopathologic nature of the virus infection and non-T-cell-mediated mechanisms.

Mumps virus alters aggregation of acetylcholine receptors in cultured rat skeletal muscle cells

Cultured myoblasts, but not myotubes, from rat skeletal muscles were infected with the RW strain of mumps virus. Such myoblasts then fused to form myotubes containing viral antigen. The infected myotubes showed a significant decrease in the number of dorsal, linear acetylcholine receptor (AChR) aggregates as determined by FITC-conjugated alfa-bungarotoxin. Infected myotubes co-cultivated with spinal cord cells showed no increase in the number of dorsal, linear AChR aggregates, compared to normal, uninfected myotubes. In addition, an increased proliferation of the myoblasts, which remained uninfected in the infected cultures, was noted. This may indicate a release of a growth stimulating factor from the virus containing cells. This study shows that mumps virus infection can lead to an altered receptor organization in a morphologically preserved cell.

Viruses and behavioural changes: a review of clinical and experimental findings

This review focuses on behavioural neurovirology. Profound changes in behaviour are observed following infection of the central nervous system by some viruses. Irritability, insomnia, hyperactivity and learning disability are some of the behavioural disturbances that have been described in both humans and animals with central nervous system infection. The reticular core neurons which innervate the entire brain play an important role in regulating behaviour. Some of these neurons--locus coeruleus, raphe and diagonal bands--send projections to the olfactory bulbs and can be targets for exogenous agents attacking the olfactory epithelium. In infant rats, vesicular stomatitis virus is transported along the olfactory pathway by retrograde transport and reaches the reticular core neurons causing destruction of raphe, diagonal bands and, to a lesser extent, the locus coeruleus. As the neurons degenerate, the viral antigens disappear and the animals sustain severe deficits in neurotransmitter levels and behaviour. Such a "hit and run" effect of the virus suggests the possibility that a similar mechanism may be operating in some human disorders. Apart from their intrinsic interest as possible aetiological factors, viruses may provide valuable tools in experimental work seeking to correlate behaviour, morphology and neurotransmitter function.

Cell type-specific regulation of major histocompatibility complex (MHC) class I gene expression in astrocytes, oligodendrocytes, and neurons

Mechanisms of major histocompatibility complex (MHC) class I gene regulation in cells of the CNS have been studied in vitro. Astrocytes in primary cultures, but neither oligodendrocytes nor neurons, constitutively expressed cell surface MHC class I molecules. Interferon-gamma (IFN-gamma) treatment led to induction of MHC class I expression in astrocytes and oligodendrocytes but not in neurons. The conserved upstream sequence containing the juxtaposed nuclear factor (NF)-kappa B-like region I and IFN-response consensus sequence (ICS) constitutively enhanced MHC class I gene promoter activity in astrocytes, but not in oligodendrocytes or in neurons. Nuclear extracts from astrocytes, but not from oligodendrocytes and neurons, had a binding activity specific for the NF-kappa B-like region I sequence, indicating that constitutive expression of MHC class I genes is governed by the upstream region I enhancer and its binding factor. IFN-gamma treatment led to induction of MHC class I promoter activity in astrocytes and oligodendrocytes, but not in neurons. In accordance with this observation, a nuclear factor that binds to the ICS was induced in astrocytes and oligodendrocytes but not in neurons following IFN-gamma treatment. This study illustrates cell type-specific regulation of MHC class I genes in the CNS that correlates with the expression of DNA binding factors relevant to MHC class I gene transcription.

Effects of immune activation on quinolinic acid and neuroactive kynurenines in the mouse

Accumulation of quinolinic acid and neuroactive kynurenines derived from tryptophan are of potential significance in human neuropathologic diseases because of their neurotoxic and convulsant properties. Clinical studies have established that sustained elevations of quinolinic acid, L-kynurenine and kynurenic acid within the cerebrospinal fluid occur in patients with a broad spectrum of inflammatory diseases and correlate with markers of immune activation and interferon-gamma activity. The present study describes an animal model that replicates these clinical observations and investigates the role of interferon-gamma as a mediator between immune activation and increased kynurenine pathway metabolism. Marked elevations in quinolinic acid, L-kynurenine and 3-hydroxykynurenine as well as an increased ratio of quinolinic acid: kynurenic acid in brain occurred 24 h after systemic pokeweed mitogen administration to C57BL6 mice. In plasma, L-tryptophan and kynurenic acid levels were reduced by pokeweed mitogen, while the concentrations of L-kynurenine, 3-hydroxykynurenine and quinolinic acid were increased. Interferon-gamma, pokeweed mitogen and lipopolysaccharide induced indoleamine-2,3-dioxygenase, the first enzyme of the kynurenine pathway, and increased both L-kynurenine and quinolinic acid concentrations of brain and systemic tissues, particularly in the lung, gastrointestinal tract and spleen. In contrast, hepatic tryptophan-2,3-dioxygenase activity was either reduced or unaffected. Increases in kynurenine pathway metabolism were sustained in mice given daily injections of interferon-gamma for seven days and subsequent responses to interferon-gamma were further enhanced. In contrast, daily administration of lipopolysaccharide was associated with subsequent attenuated responsiveness (tolerance) to lipopolysaccharide, pokeweed mitogen and interferon-gamma. Systemic administration of a monoclonal antibody to mouse interferon-gamma either attenuated or abolished the responses of kynurenine pathway metabolism to pokeweed mitogen and interferon-gamma. We conclude that acute and chronic increases in quinolinic acid and neuroactive kynurenines follow immune stimulation in mice, and result from indoleamine-2,3-dioxygenase induction. The results demonstrate that interferon-gamma is an important mediator between immune stimulation and indoleamine-2,3-dioxygenase induction. These increases in kynurenine pathway metabolism closely parallel the responses documented in patients with a broad spectrum of inflammatory diseases. Mice treated with immune stimuli are a useful model to investigate the relationships between immune activation and kynurenine pathway metabolism.

A role for microglia in the maintenance of photoreceptors in retinal transplants lacking pigment epithelium

Studies on intact retina have pointed to a necessary role for retinal pigment epithelium in the maintenance of photoreceptor outer segments and for regeneration of visual pigment. However, it has been shown that when embryonic retinae are separated from the pigment epithelium and transplanted into the brain of neonatal rats, the transplanted photoreceptors develop outer segments and the retina responds to light in the apparent absence of pigment epithelial cells. We confirm that there are no retinal pigment epithelium cells associated with transplanted retinae in the present series of experiments and show that a row of cells, composed predominantly of microglia of host origin, border the graft. These cells can be seen to contain engulfed outer segments when they are apposed to the outer retina, suggesting that the microglia have assumed, at the least, the phagocytic function normally associated with retinal pigment epithelium. Microglial cells and their processes are also found within the transplant, but these cells are typically devoid of phagosomes, indicating an absence of phagocytic activity. The close physical association of these resting microglia with the transplant may facilitate their role in antigen presentation under specific conditions of immune provocation.

Interferon-gamma-like immunoreactivity in sensory neurons may influence the replication of Sendai and mumps viruses

Rat dorsal root ganglia in tissue culture, which contain an interferon-gamma (IFN-gamma)-like immunoreactive subpopulation of neurons, were infected with paramyxoviruses. Sendai virus caused a substantial neuronal lysis, while the RW strain of mumps virus caused a much less pronounced nerve cell loss. Early during infection, the subpopulation of IFN-gamma-like immunoreactive neurons was less susceptible to mumps virus. Virus antigen was rapidly lost from surviving IFN-gamma-like positive neurons infected with Sendai virus, while this remarkable self-curing effect occurred in both nerve cell populations at later time points after mumps virus infection. By quantitative enzyme-linked immunosorbent assay (ELISA) technique, increased levels of "neuronal IFN-gamma" were recorded at 10 hr and 30 hr after infection with Sendai and mumps virus, respectively. This study indicates a role for the neuronal IFN-gamma-like molecule in determining the outcome of a viral infection in sensory ganglia.