Infection of different cell lines of neural origin with subacute sclerosing panencephalitis (SSPE) virus

Measles virus is the causative agent of subacute sclerosing panencephalitis (SSPE). The viruses isolated from brain cells of patients with SSPE (called SSPE viruses) are defective in cell-free virus production in vitro. To investigate the cell tropism of three strains of SSPE virus (Osaka-1, Osaka-2, Osaka-3), SSPE virus-infected cell cultures were treated with cytochalasin D to prepare virus-like particles (CD-VLPs). All CD-VLPs formed syncytia after infection in CHO cells expressing CD150 but not in those expressing CD46. In addition, an antibody to CD46 did not block the infection of Vero cells by SSPE CDVLPs. The results were consistent with our previous suggestion that one or more unidentified receptors might be involved in the entry process. Infection with the CD-VLPs from three SSPE strains was further examined in different human cell lines, including those of neural origin, and was found to induce syncytia in epithelial cells (HeLa and 293T) as well as neuroblastoma cells (IMR-32 and SK-N-SH) with varying efficiency. SSPE CD-VLPs also infected glioblastoma cells (A172) and astrocytoma cells (U-251) but syncytial formation was rarely induced. These epithelial and neural cell lines were not permissive for the replication of wild-type MV. Together with our previous observations, these results suggest that the cell entry receptor is the major factor determining the cell tropism of SSPE viruses. Further studies are necessary to identify other viral and/or cellular factors that might be involved in the replication of SSPE virus in specific neural cells and in the brain.     

Localization of measles virus antigens in subacute sclerosing panencephalitis in ferrets

Young adult male ferrets were inoculated intracerebrally (i.c.) with a cell-associated encephalitogenic subacute sclerosing panencephalitis (SSPE) virus strain to study the pathogenesis of the disease at the ultrastructural level. Most became acutely ill in 8-13 days. Areas of the brain were examined with indirect immunoperoxidase labeling techniques to detect measles antigen. None of these animals showed the characteristic viral nucleocapsids or marked inflammatory response associated with SSPE. However, all had positive immunolabeling of unstructured virus antigen, especially in post-synaptic regions in all areas of the brain that were examined. One ferret, immunized with measles vaccine 40 days prior to challenge with SSPE, became ill 18 days post inoculation (p.i.). Perivascular cuffings of inflammatory cells and large cytoplasmic inclusions of fuzzy nucleocapsids were found in the brain and spinal cord. The study indicates that ferrets which become acutely ill after inoculation with cell-associated SSPE virus do so before there is a marked cellular immune response or formation of virus nucleocapsids.     

Diversity of matrix protein in subacute sclerosing panencephalitis and measles virus-infected cells.

Expression of the viral matrix (M) proteins in Vero cells infected with 18 strains of subacute sclerosing panencephalitis (SSPE) virus and measles virus was examined by immunocytochemistry and Western blot analysis using an anti-M monospecific serum and two sera against the M protein specific synthetic peptides. By immunocytochemistry using the anti-M monospecific serum, M protein was detected in all of the virus-infected cells regardless of cell-free virus production. M proteins of the seven non-productive strains were found to vary significantly in their epitope, in their reactivity to different assay systems, and in their molecular weight, whereas M proteins of the other 11 productive strains were detected consistently. These results suggest diversification of M protein of the non-productive strains.     

Protective effect of measles virus inoculation on subacute sclerosing panencephalitis virus-infected mice

The Biken strain of subacute sclerosing panencephalitis (SSPE) virus caused a fatal neurologic disease in adult mice after intracerebral inoculation. However, the mice were completely protected from the disease when a high dose of measles virus was given intracerebrally after the SSPE virus infection. The measles virus inoculation induced interferon production and immune responses. An experiment with athymic nude mice showed that interferon and anti-measles antibody were able to prolong the incubation period of the disease but not to protect the SSPE virus-infected nude mice from death. For complete protection, T lymphocytes appeared to be essential. The present study suggested that the protective effect of measles virus inoculation is basically due to the induction of immune responses and that SSPE virus infection in mice is susceptible to immune reactions.     

Stimulation of lymphocytes from subacute sclerosing panencephalitis patients by defined measles virus antigens

The lymphoproliferative response of human peripheral blood mononuclear cells to different measles virus antigen preparations was studied with lymphocytes from 38 measlesseropositive healthy donors and 4 subacute sclerosing panencephalitis patients. The response was very weak or absent in all of the controls and in three of the subacute sclerosing panencephalitis patients. The fourth subacute sclerosing panencephalitis patient had fluctuating levels of lymphocyte stimulation by measles antigens. The response was very strong for several months and during this time the parameters of the test system were characterized. It was discovered that a membrane preparation of measles-infected cells caused stimulation equal to that of highly purified virions. Purified measles ribonucleoprotein also induced specific stimulation, although lower than that seen with other types of measles antigens. Results of experiments on stimulation kinetics and antigen dose responses were compatible with antigen-specific stimulation. Enriched T cells were more vigorously stimulated than unfractionated peripheral blood mononuclear cells suggesting that this transformation test is specific for T cells.     

Hemadsorption expressed by cloned H genes from subacute sclerosing panencephalitis (SSPE) viruses and their possible progenitor measles viruses isolated in Osaka, Japan

Most subacute sclerosing panencephalitis (SSPE) viruses, including our Osaka-1, -2, and -3 strains isolated in Osaka, have shown negative hemadsorption (HAD) by African green monkey red blood cells. This property has been thought to be characteristic of SSPE virus as compared to the positive reaction of the standard Edmonston strain of measles virus (MV). However, this assumption has become quite obscure because MV mutates frequently at the genetic level during its multiplication and also because recent field strains isolated by lymphoblastoid cell lines have shown negative HAD. To investigate the above issue, the nucleotide sequences of the hemagglutinin (H) genes from SSPE virus Osaka-1, -2, or -3 strains were compared to those of various MV field strains isolated in Osaka by Vero cells. The H gene sequences of three SSPE strains were relatively conserved without such biased hypermutation as had been observed in the matrix (M) gene of three SSPE strains. However, this analysis of the H gene sequence of the SSPE viruses enabled us to deduce possible progenitor MVs, which are in agreement with the deduction from the M gene analysis we reported previously. The HAD of Vero cells transfected with the cloned H cDNAs from the SSPE strains and their progenitors suggested that negative HAD of the SSPE viruses has been maintained as one of original properties of the progenitor MVs rather than having been acquired as an altered one during long-term persistent infection in the brains of patients with SSPE.     

Humoral and cellular immune responses to matrix protein of measles virus in subacute sclerosing panencephalitis.

The immune response to matrix (M) protein of measles virus was examined in patients with subacute sclerosing panencephalitis (SSPE) and controls. Antibodies specific for M and nucleocapsid (NC) proteins in 11 serum and 8 cerebrospinal fluid (CSF) samples from patients with SSPE were quantitated by enzyme-linked immunosorbent assay by using affinity-purified measles virus proteins. Geometric mean anti-NC antibody titers were higher in the serum (6.58 +/- 0.98 [mean +/- standard deviation]) and CSF (4.38 +/- 0.74) of SSPE patients compared with controls. Anti-M antibodies were present in the serum and CSF of all SSPE samples tested but in titers lower than those of anti-NC antibodies. Geometric mean anti-M antibody titer was 3.35 +/- 0.53 in sera from patients with SSPE compared with 3.05 +/- 0.66 in sera from patients with other neurological diseases and 3.12 +/- 0.74 in sera from healthy individuals. Geometric mean anti-M antibody titer was 2.59 +/- 0.86 in the CSF of eight patients with SSPE compared with a mean less than 1.00 for patients with other neurological disease (controls). Intrathecal synthesis of anti-M or anti-NC antibodies was established in four patients with SSPE. The cellular immune responses to M, F, HA, and NC proteins were examined in four of the patients with SSPE by lymphoproliferation and were not significantly different from those in five healthy controls. The results demonstrate humoral and cellular immune responses to M protein in patients with SSPE and indicate that it is unlikely that a defect in the immune response to this virus component accounts for the disease process in the patients studied.     

Expression of defective measles virus genes in brain tissues of patients with subacute sclerosing panencephalitis.

The persistence of measles virus in selected areas of the brains of four patients with subacute sclerosing panencephalitis (SSPE) was characterized by immunohistological and biochemical techniques. The five measles virus structural proteins were never simultaneously detectable in any of the brain sections. Nucleocapsid proteins and phosphoproteins were found in every diseased brain area, whereas hemagglutinin protein was detected in two cases, fusion protein was detected in three cases, and matrix protein was detected in only one case. Also, it could be shown that the amounts of measles virus RNA in the brains differed from patient to patient and in the different regions investigated. In all patients, plus-strand RNAs specific for these five viral genes could be detected. However, the amounts of fusion and hemagglutinin mRNAs were low compared with the amounts in lytically infected cells. The presence of particular measles virus RNAs in SSPE-infected brains did not always correlate with mRNA activity. In in vitro translations, the matrix protein was produced in only one case, and the hemagglutinin protein was produced in none. These results indicate that measles virus persistence in SSPE is correlated with different defects of several genes which probably prevent assembly of viral particles in SSPE-infected brain tissue.     

Partial C4 deficiency in subacute sclerosing panencephalitis

In an immunogenetic study, 23 subacute sclerosing panencephalitis (SSPE) patients and their families were studied for the HLA region markers HLA-A, B, C, DR, BF, C2, C4A, C4B, GLO I, and PGM3. In addition, C3, C4, and factor B serum levels were determined. A highly significant association of C4A^*QO with SSPE was found. Furthermore, two rare haplotypes, C4A*QOB*9QO, two C4ACh+ allotypes, and four Ch partial inhibitors were detected, which possibly impair the function of the C4 molecules. HLA-DR5 was increased. In addition, a number of rare HLA-A, C, B, DR haplotypes were observed. It is postulated that rare C4 molecular deficiency might be a predisposing factor in the pathogenesis of SSPE.     

Role of biased hypermutation in evolution of subacute sclerosing panencephalitis virus from progenitor acute measles virus.

We identified an acute measles virus (Nagahata strain) closely related to a defective virus (Biken strain) isolated from a patient with subacute sclerosing panencephalitis (SSPE). The proteins of Nagahata strain measles virus are antigenically and electrophoretically similar to the proteins of Edmonston strain measles virus. However, the nucleotide sequence of the Nagahata matrix (M) gene is significantly different from the M genes of all the acute measles virus strains studied to date. The Nagahata M gene is strikingly similar to the M gene of Biken strain SSPE virus isolated several years later in the same locale. Eighty percent of the nucleotide differences between the Nagahata and Biken M genes are uridine-to-cytosine transitions known as biased hypermutation, which has been postulated to be caused by a cellular RNA-modifying activity. These biased mutations account for all but one of the numerous missense genetic changes predicted to cause amino acid substitutions. As a result, the Biken virus M protein loses conformation-specific epitopes that are conserved in the M proteins of Nagahata and Edmonston strain acute measles viruses. These conformation-specific epitopes are also absent in the cryptic M proteins encoded by the hypermutated M genes of two other defective SSPE viruses (Niigata and Yamagata strains). Nagahata-like sequences are found in the M genes of at least five other SSPE viruses isolated from three continents. These data indicate that Biken strain SSPE virus is derived from a progenitor closely resembling Nagahata strain acute measles virus and that biased hypermutation is largely responsible for the structural defects in the Biken virus M protein.     

Multiple viral mutations rather than host factors cause defective measles virus gene expression in a subacute sclerosing panencephalitis cell line.

A measles virus (MV) genome originally derived from brain cells of a subacute sclerosing panencephalitis patient expressed in IP-3-Ca cells an unstable MV matrix protein and was unable to produce virus particles. Transfection of this MV genome into other cell lines did not relieve these defects, showing that they are ultimately encoded by viral mutations. However, these defects were partially relieved in a weakly infectious virus which emerged from IP-3-Ca cells and which produced a matrix protein of intermediate stability. The sequences of several cDNAs related to the unstable and intermediately stable matrix proteins showed many differences in comparison with a stable matrix protein sequence and even appreciable heterogeneity among themselves. Nevertheless, partial restoration of matrix protein stability could be ascribed to a single additional amino acid change. From an examination of additional genes, we estimated that, on average, each MV genome in IP-3-Ca cells differs from the others in 30 to 40 of its 16,000 bases. The role of extreme variability of RNA virus genomes in persistent viral infections is discussed in the context of the pathogenesis of subacute sclerosing panencephalitis and of other human diseases of suspected viral etiology.     

Elevated interleukin-12 and CXCL10 in subacute sclerosing panencephalitis

Immunosuppression associated with measles virus (MV) can be demonstrated by cytokine production failure in subacute sclerosing panencephalitis (SSPE) and may have implications on the pathogenesis of the disease. Cytokines (IL-12, IL-10, IL-4, IL-17, IL-18, IFN-alpha, IFN-gamma) and chemokines (CXCL8, CXCL10, CCL2 and CCL5) were measured in the cerebrospinal fluid (CSF) and serum samples from 60 patients with SSPE, 36 patients with infectious and/or inflammatory (IN) and 28 with other non-inflammatory (NIN) neurological diseases by ELISA. IL-12 p70+p40 was elevated in CSF and sera of SSPE when compared to the NIN group. However, the CSF levels of IL-12 p70 alone were not increased, indicating an increase of p40. The CSF of SSPE patients also showed relatively higher levels of IL-10 than that of the NIN group. CXCL10 levels in CSF were significantly higher in SSPE, whereas CXCL8 was increased in sera compared to NIN. No difference was detected in IFN-gamma, IFN-alpha, IL-17, IL-18, IL-4 or CCL2 and CCL5 levels. These results demonstrate that immune response against MV in SSPE may be impaired, although some T cell/Th1 inducing stimulations are present.     

Generation of recombinant adenovirus expressing siRNA against the L mRNA of measles virus and subacute sclerosing panencephalitis virus

Subacute sclerosing panencephalitis (SSPE) is a fatal neurodegenerative disease caused by prolonged persistent infection of the central nervous system with a measles virus (MV) mutant called SSPE virus. At present, there is no effective treatment to completely cure SSPE and development of a new therapeutic measure(s) against this fatal slow virus infection is needed. We previously reported that replication of MV and SSPE virus was effectively inhibited by small interfering RNA (siRNA), either chemically synthetic or plasmid-driven ones, that were targeted against different sequences of the mRNA for the L protein of MV. In this study, we have generated recombinant adenovirus expressing the siRNAs (rAd-siRNA-MV-L2, -L4 and -L5) and demonstrated that these rAd-siRNAs efficiently inhibited replication of MV and SSPE virus in a dose-dependent manner. Due to their high capacity for gene delivery to nerve cells and the potential to inhibit SSPE virus replication, the rAd-siRNAs could be a good candidate for a novel therapeutic measure against SSPE.     

Immune response in subacute sclerosing panencephalitis: reduced antibody response to the matrix protein of measles virus.

Immune precipitation was used to study the humoral immune response of patients with subacute sclerosing panencephalitis (SSPE). Patients with SSPE have a progressive infection of the CNS by measles or a measles variant despite high serum antibody levels to measles virus as measured by standard serologic techniques. However, when the antibody response to individual measles virus proteins was measured, we found a striking reduction in the ability of sera from patients with SSPE to precipitate the matrix (M) protein as compared to the precipitation of the M protein by sera from normal adults who had natural measles infection in childhood, or by convalescent sera obtained 3 to 5 weeks after a naturally occurring measles infection. The decreased antibody response to the M protein in sera from patients with SSPE occurred despite a vigorous antibody response to the other viral proteins, suggesting a selective defect in the production of antibody to a single viral protein. The reduced anti-M antibody in sera from patients with SSPE was demonstrated whether immune precipitation was performed with wild-type measles virus or SSPE virus proteins. These results suggest that in SSPE only small amounts of the M protein are produced. This result may help explain how measles virus persists in the central nervous system of patients with SSPE.