Comparative analysis of virus-specific antibodies and immunoglobulins in serum and cerebrospinal fluid of subacute measles virus-induced encephalomyelitis (SAME) in rats and subacute sclerosing panencephalitis (SSPE)

Viliuisk encephalomyelitis: intrathecal synthesis of oligoclonal IgG

Viliuisk encephalomyelitis (VE) is a neurodegenerative disorder expressed as subacute meningo-encephalitis progressing to a more prolonged pan-encephalitic syndrome with a fatal outcome within 1 to 10 years. Some patients survive to a steady state of global dementia and severe spasticity that may last for over 20 years. Multiple micronecrotic foci surrounded by inflammatory infiltrates are observed throughout the cerebral cortex and other gray matter areas. Infectious etiology of VE is strongly suspected, but the causative agent has not been identified. We conducted a search for assays that might be helpful for VE diagnosis and established for the first time that the majority of patients with definite VE show evidence for intrathecal IgG synthesis correlating with the clinical manifestations of the disease. This indicates that the detection of oligoclonal IgG banding in the cerebrospinal fluid is a valuable diagnostic assay for VE. Implications of these findings for a possible etiology of VE are discussed.

CD4+ T cells are essential in overcoming experimental murine measles encephalitis

Clinical observations and experimental animal models have stressed the importance of the cellular immune response in the recovery from measles virus infection. However, the relative contribution of different T-cell subsets to viral elimination is controversial. The aim of the present study was to define the components of the immune system which contribute to the control of measles virus infection. For this purpose the effect of in vivo depletion of CD4+ and/or CD8+ T lymphocytes in the murine model of experimental acute measles encephalitis was monitored with respect to disease manifestation, survival, neuropathological changes, virus elimination from brain, and antiviral antibody titre. In measles virus-resistant BALB/c mice removal of the CD8+ T-cell subset did not interfere with the clearance of virus from the brain. In contrast, depletion of CD4+ T cells rendered BALB/c mice susceptible to infection. Also, in measles virus-susceptible C3H mice CD4+ T cells played a role in recovery from measles infection, but seemed not to be as effective as CD4+ T cells from resistant BALB/c mice. The data indicate that CD4+ T cells are essential for protection against measles virus-infection of the central nervous system.

Pathogenesis of virus-induced demyelination

Demyelination is a component of several viral diseases of humans. The best known of these are subacute sclerosing panencephalitis (SSPE) and progressive multifocal leukoencephalopathy (PML). There are a number of naturally occurring virus infections of animals that involve demyelination and many of these serve as instructive models for human demyelinating diseases. In addition to the naturally occurring diseases, many viruses have been shown to be capable of producing demyelination in experimental situations. In discussing virus-associated demyelinating disease, the chapter reviews the architecture and functional organization of the CNS and considers what is known of the interaction of viruses with CNS cells. It also discusses the immunology of the CNS that differs in several important aspects from that of the rest of the body. Experimental models of viral-induced demyelination have also been considered. Viruses capable of producing demyelinating disease have no common taxonomic features; they include both DNA and RNA viruses, enveloped and nonenveloped viruses. The chapter attempts to summarize the important factors influencing viral demyelination, their common features, and possible mechanisms.

The diagnostic significance of antibody specificity indices in multiple sclerosis and herpes virus induced diseases of the nervous system

The antibody specificity index (ASI) indicates the cerebrospinal fluid (CSF)/serum difference of antibody amounts per weight unit IgG (normal less than 1.5). It has proven to be the most sensitive inflammation parameter in CSF analysis so far, more sensitive than the Western blot, the "oligoclonal" response, and the empirical differentiation of CSF immunoglobulins. By this diagnostic criterion, several benign viral meningitis cases were found to be caused by the varicella/zoster virus. The diagnostic relevance of local zoster antibody synthesis was greatest in ganglionitis cases, e.g., in zoster oticus sine herpete (facial paresis) and acute radicular syndromes of the elderly. The diagnostic significance of the local immune response against measles, rubella, and zoster antigens (MRZ response) was ascertained further. Together with oligoclonal gamma-globulin fractionation, there is now only 1 out of 100 multiple sclerosis (MS) patients left who has been found to have a normal CSF.

Antibody-induced restriction of viral gene expression in measles encephalitis in rats

After infection with the neurotropic CAM/RBH measles virus (MV) strain, newborn Lewis rats succumb to an acute necrotizing encephalopathy. Passive transfer of neutralizing monoclonal antibodies directed against MV hemagglutinin prevented this disease process. Instead, either an antibody-induced acute or subacute measles encephalitis developed after a prolonged incubation period with a restricted expression of MV structural proteins. The molecular biological analysis of MV gene expression in brain tissue of rats treated with MV-neutralizing antibodies revealed a transcriptional restriction of viral mRNAs, particularly for the envelope proteins, leading to a steep expression gradient. Based on in situ hybridization, it was concluded that the efficiency of transcription of viral genes at the single-cell level is reduced compared with that of controls. Passive immunization with monoclonal antibodies directed against other MV structural proteins proved to be ineffective. Similar results were obtained in MV-infected weanling Brown Norway rats. These rats developed a clinically silent encephalitis in the presence of high titers of neutralizing antibodies. In such animals, a pronounced attenuation of the viral gene transcription was observed. These findings indicated that neutralizing antibodies directed against a restricted set of specific antigenic sites on the viral hemagglutinin protein expressed on cell membranes exert a modulating effect on the viral gene expression at the level of transcription. This phenomenon contributes to the switch from the acute cytopathic effect to a persistent infection in the central nervous system.

Restriction of measles virus gene expression in acute and subacute encephalitis of Lewis rats

Measles virus (MV) replication in brain tissue of Lewis rats with acute (AE) and subacute (SAME) encephalitis was characterized by biochemical techniques. Messenger RNAs specific for measles virus nucleocapsid (N), phospho (P)-, matrix (M), fusion (F), and haemagglutinin (H) protein were detected in all brain extracts examined. The quantity of the individual MV mRNA species was quite different in comparison to lytically infected Vero cells. A steep gradient of MV transcripts was found in brain tissue which is most likely due to strongly attenuated transcription of mRNAs along the viral genome, representing particularly low transcription of the glycoprotein genes. In addition, in vitro translation assays only revealed synthesis of N and P protein in consistent fashion. The mRNAs for the glycoproteins did not direct the synthesis of detectable viral proteins whereas the M mRNA revealed some activity in animals with AE. The data indicate a strong restriction of the MV envelope gene expression in infected brain tissue, which is independent of the incubation time and type of the central nervous system (CNS) disease. This phenomenon which is similar to the findings observed in measles inclusion body encephalitis and subacute sclerosing panencephalitis suggest that host factors may initially be responsible for the initiation of transcriptional and translational alterations.