Latency of human measles virus in hamster cells

L cell clone developing plaques upon infection with measles virus (Edmonston strain)

An L cell clone developing cytopathic plaques upon infection with measles virus (Edmonston strain) was obtained. The sensitivity as measured by the newly devised UV-Vero assay was not significantly different between plaque-forming and non-plaque-forming L cell clones. Cytopathogenicity and sensitivity to the virus infection appear to be under different host cell regulations.

The human CD46 molecule is a receptor for measles virus (Edmonston strain)

Measles virus normally causes disease in human beings, and the host range of this virus may be determined by a specific receptor on the surface of primate cells. Human-rodent somatic cell hybrids were tested for their ability to bind measles virus, and only cells that contained human chromosome 1 were capable of binding virus. A study of lymphocyte markers suggested that the complement regulator known either as membrane cofactor protein or CD46 was the measles virus receptor. We proved this hypothesis by demonstrating that hamster cell lines that expressed human CD46 could subsequently bind virus. Furthermore, infected CD46+ cells produced syncytia and viral proteins. Finally, polyclonal antisera against CD46 inhibited virus binding and infection. These results prove that human CD46 permits cells both to bind measles virus and to support infection.

Measles virus: evolution of a persistent infection in BGM cells

An African green monkey kidney cell line (BGM) persistently infected with measles virus (BGM/Hallé cells) has been studied during 3 years in culture. The early cell passages were characterized by slow growing cultures producing high yields of infections virus (10(6)--10(7) PFU/ml). These cells were gradually replaced by a population of cells multiplying at a similar rate as non-infected cells. During this evolution, the virus released from the cells changed from a large plaque variant, to a small plaque and eventually unlysed foci. Despite greater than or equal to 95 per cent of the cells being infected, the virus yield fell to the limits of detection. [35S]-methionine labelling of BGM/Hallé cultures at the 20th and 140th passage showed that in both cases all the measles virus structural proteins were synthesized. There were no changes in the apparent molecular sizes of the viral proteins during passage. Cell surface [125I]-labelling of BGM/Hallé cells indicates that viral envelope antigens are inserted into the membrane despite the diminution in virus yield. Several cell proteins not labelled in non-infected BGM cells are also labelled. These proteins could also be [125I]-labelled in clones of BGM/Hallé cells with had been "cured" of virus. Chase experiments of [125I]-pre-labelled BGM/Hallé cultures showed the radiolabelled antigen to be incorporated into virus particles. Non-infections virus particles released from the cells contained the same polypeptides as those released from a lytic infection.

Anesthetic action and virus replication: inhibition of measles virus replication in cells exposed to halothane

Replication of measles virus in BSC cells was studied in the presence of halothane, a commonly used volatile anesthetic. At clinical concentrations of the anesthetic, appearance of progeny virus was decreased in a dose-related manner. This inhibition was reversible as the removal of halothane allowed virus replication to be resumed. Studies attempting to elucidate the mechanism of action of the anesthetic inhibition of virus replication revealed that halothane did not directly inactivate the virus particle or prevent viral adsorption to the cell. Infectious virus and nucleocapsid production were decreased or stopped, depending on the anesthetic dosage used. Direct immunofluorescent staining for measles virus antigen was negative in cells treated at the higher concentrations of halothane. Recovery of nucleocapsid production started within a few hours after removal of halothane. Furthermore, the combined inhibitory effects on viral ribonucleic acid synthesis of 5-azacytidine and halothane were additive. This evidence suggests that inhibition of measles virus replication occurs at or before ribonucleic acid synthesis.

Measles virus-specified polypeptide synthesis in two persistently infected HeLa cell lines

Measles virus-directed protein synthesis was examined in two HeLa cell lines (K11 and K11A) that are persistently infected with wild-type measles virus. Four viral proteins (H, hemagglutination protein; P, nucleocapsid-associated protein; NP, the major nucleocapsid protein; and M, the matrix protein) were readily detected in both cell lines by immune precipitation of [(35)S]methionine-labeled cell extracts followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. When analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, three (H, NP, and M) of the four viral proteins in both K11 and K11A cells differed from the corresponding viral proteins synthesized in HeLa cells acutely infected with the parental wild-type virus. In addition, the M protein from K11A cells migrated significantly more slowly on sodium dodecyl sulfate-polyacrylamide gel electrophoresis than the M protein from K11 cells, and there appeared to be slight differences in the H and NP proteins between these two persistently infected cell lines. The altered viral proteins detected in K11 and K11A cells appeared to be the result of viral mutations rather than changes in the host cell, since virus recovered from these cells directed the synthesis of similar aberrant viral proteins in HeLa cells. Virus recovered from K11 cells and virus recovered from K11A cells were both temperature sensitive and grew more slowly than wild-type virus. HeLa cells infected with virus recovered from K11 cells readily became persistently infected, resembling the original persistently infected K11 cells. Thus, viral mutations are associated with persistent measles virus infections in cell cultures.

Role of virus variants and cells in maintenance of persistent infection by measles virus

Hamster embryo fibroblasts persistently infected with a derivative of the Schwarz vaccine strain of measles virus spontaneously released virus particles with an average buoyant density considerably lower than that of the parental virus. The released virus contained all of the measles virus structural proteins and interfered with replication of standard virus. All of the virus structural proteins were associated with a membrane-free cytoplasmic extract from the persistently infected cells. Membrane-free cytoplasmic extracts prepared from Vero cells lytically infected with Schwarz strain measles contained little or no virus envelope structural protein. Maintenance of persistent infection may involve both the presence of virus variants and a defect in the ability of the infected cell to replicate the virus efficiently.

Latent measles virus infection in Vero cells depending on a temperature-sensitive phenomenon

A latent infection by measles virus in a line of Vero cells could be maintained only at 37 degrees C. The conditions of temperature nonpermissiveness were associated with some block in virus production and/or release and with the establishment of an autointerference phenomenon. Reduction of the incubation temperature to 33.5 degrees C induced a rather rapid transition from the latent to a lytical infection with a recue of virus. The rescued virus exhibited a restricted capacity to grow at 37 degrees C.

In vitro studies on Borna virus. I. The use of cell cultures for the demonstration, titration and production of Borna virus

Borna virus produces non-lytic infections in a wide spectrum of primary cell cultures and cell lines. The sensitivity and virus yields vary with the different cell systems. Accurate virus titrations can be performed in the RK 13 cell line by counting immunoflourescent microfoci between the 5th and 10th day after infection. Since the virus is not released from the cells and does not spread via the culture medium, the use of a semisolid overlay in unnecessary in virus titrations. The cell line most productive for Borna virus is the CV 1 line. The conditions for optimum virus production include a prolonged cultivation period of at least two weeks with regular changes of medium, and an incubation temperature of 35 degrees C. Harvest of the virus requires thorough disruption of the infected cells, preferably by ultrasonication, since Borna virus seems to be closely associated with cellular structures.

Measles virus and its associated diseases

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Defective bud formation in human cells chronically infected with subacute sclerosing panencephalitis virus

Human prostate cells chronically infected with the Mantooth strain of subacute sclerosing panencephalitis (SSPE) virus multiply normally, fuse only occasionally to form giant cells, and yet have twisted intracytoplasmic nucleocapsids. These cells are able to support replication of vesicular stomatitis virus, although they release only small amounts of SSPE virus. To determine why carrier cells do not produce virus, they were examined with techniques for surface replication, freeze-fracturing, and immunoperoxidase labeling with SSPE antibody. The surface of carrier cells, like that of productive cells, is characterized by ridges crowned with viral antigens and devoid of the intramembrane particles revealed by freeze-fracture techniques. Since surface ridges form where nucleocapsids attach to the membrane, the shape and length of ridges are indicative of the shape and length of the underlying nucleocapsid. Whereas ridges on productive cells are serpentine in shape, those on carrier cells are typically straight or hairpin shaped, and the hairpin ridges are twice as long as serpentine ridges on productive cells. Furthermore, the spacing between ridges on carrier cells is never as small as that in productive infections, so that continuous sheets of viral membrane are never formed. The majority of carrier cells lack the round viral buds observed in productive cells but have, instead, many elongated processes attached to the cell surface. Each of these processes contains one or two hairpin ridges overlying hairpin-shaped nucleocapsids. These "hairpin buds" are restricted to a single region of the carrier cell surface, whereas viral buds are distributed over the entire surface of productive cells. Thus, there are several structural defects in carrier cells that depend on the specific interaction of a certain viral strain with a certain cell type. These defects prevent the deployment of viral antigen in some regions of the cell surface, the formation of nucleocapsids of normal length, the coiling of attached nucleocapsids, and the consolidation of sheets of viral membrane into spherical buds with the nucleocapsids coiled inside. These defects may account for the failure of carrier cells to shed infectious virus.

Persistent infection of tissue culture cells by RNA viruses

In this paper, the characteristics of cultured cells persistently infected with RNA viruses, other than leuko viruses are described. The roles that the host cell, interferon, virus mutants and defective interfering particles may play in the establishment and maintenance of persistent infection are discussed. It is proposed that the interaction of viruses with certain types of host cells can lead to persistent infection. The differences in virus-host interactions may be attributable to differences in membrane properties of various cells. Defective interfering particles may play a role in the establishment of persistent infections in cells which normally undergo lytic virus development. Mutant types of virus appear to be prominent in the virus released from persistently infected cells, but the role that various mutants play in the maintenance of persistent infections remains unclear.

Studies on a measles virus variant inducing persistent infections in cultured cells.I. Isolation and characterization of plaque purified virus clones

Attempts were made to characterized by a plaque assay two variants of the Edmonston strain of measles virus and to obtain plaque purified virus populations. The UP non-cytocidal variant, in all the examined cell systems, mainly produced small but also large plaques; the DP cytocidal variant always large plaques. Three clones, UP-SP4, UP-LP4 and DP-LP4, were derived by plaque purfication respectively of the UP small plaque, UP large plaque and DP large plaque forming particles. The virus populations of the clones could be distinguished by some other biological and physical characters: cytopathic effect in roller tube cultures, growth potential in HeLa cells, thermal stability at 45 degrees C, stability of the properties during serial passages at different input multiplicity. The hypothesis was supported that the typical properties of the UP and DP variants are host-independent and genetically controlled viral markers.

Induction of measles virus hemagglutinin in a persistently infected, nonvirogenic line of cells (BGM/MV)

BGM/MV cells carry measles virus antigens and nucleocapsid-like structures in their cytoplasm. There is no infectious virus demonstrable, and measles virus-induced cell surface changes detectable by hemadsorption (HAD) are absent. Treatment of cells with actinomycin D or cycloheximide or enucleation of cells with cytochalasin B induced surface changes in that the cells became HAD positive. 6-Azauridine treatment of cells did not inhibit the induction of HAD, suggesting that RNA synthesis was not required. Cycloheximide treatment of cells induced by enucleation inhibited the development of HAD, suggesting a requirement for protein synthesis.

Growth and genetic stability of the ts-1 mutant of respiratory syncytial virus at restrictive temperatures

An in vitro study was performed to define in greater detail those factors which favored the growth of the ts-1 mutant of respiratory syncytial virus under restrictive conditions and the emergence of genetically altered virus with decreased temperature sensitivity. Replication of ts-1 occurred at each of the restrictive temperatures of 37, 38, and 39 C, even through plaque formation was not observed. The level of virus growth under restrictive conditions was inversely related to the incubation temperature and directly related to the multiplicity of infection. These relationships appeared to reflect the effect of restrictive temperature in reducing the quantity of virus produced and released from an infected cell. Under restrictive conditions the production of genetically altered virus which exhibited reduced temperature sensitivity was directly related to the multiplicity of infection and inversely related to temperature. Production of genetically altered virus was not observed under permissive conditions.

Isolation and preliminary characterization of temperature-sensitive mutants of measles virus

Twenty-four genetically stable temperature-sensitive mutants of measles virus were isolated after mutangenesis by 5-azacytidine, 5 fluorouracil, or proflavine. The restricted replication of all mutants at 39 C was blocked subsequent to cell penetration and could not be attributed to heat inactivation of virus infectivity. Complementation analysis was made possible through the use of poly-L-ornithine. The members of one complementation group exhibited wild-type RNA synthesis at the nonpermissive temperature and induced the synthesis of virus antigens. These mutants were found defective in both hemolysin antigen synthesis and cell fusion "from within," supporting the unitary hypothesis for these functions. The members of the other two complementation groups synthesized neither virion RNA nor detectable virus antigens at the nonpermissive temperature.

Growth of measles virus in cultures of rat glioma cells

The interaction of measles virus with RG-6 cells derived from rat glioma was investigated. When a culture of RG-6 cells was infected with measles virus, the synthesis of viral antigens was detected in very few cells, at most 5%. The apparent resistance to measles virus infection was also repeatedly found in all of the subclonal cells derived form RG-6 cells. Although all of the virus-synthesizing cells had the ability to form plaques on Vero cells, they produced only a reduced amount of infectious virus, i.e., 0.1 plaque-forming units per cell. These results imply the existence of some mechanism that regulates growth of measles virus in cultures of RG-6 cells. The transmission of genetic material of measles virus from infected RG-6 cells to Vero cells was not inhibited in the presence of antiviral serum. This fact may provide a basis for interpretation of the persistence of virus, in the presence of antibody, in patients with subacute sclerosing panencephalitis.

Temperature-sensitive virus derived from BHK cells persistently infected with HVJ (Sendai virus)

BHK-HVJ cells, a cell line of baby hamster kidney cells persistantly infected with HVJ (Sendai virus), started to produce infectious virus by shifting down the incubation temperature from 38 to 32 C. The virus derived from BHK-HVJ cells, designated as HJV-pB, was effectively neutralized with antibody against wild-type virus (HVJ-W) which was used for the establishment of BHK-HVJ cells. HVJ-pB replicated in eggs at 32 C, but not at 38 C, while HVJ-W grew equally well at both temperatures. When BHK cells infected with HVJ-PB were incubated at 38 C, production of infectious virus, hemagglutinin, and neuraminidase was markedly restrained, whereas a considerable amount of viral nucleocapisid and envelope antigens was detected in the cells by complement fixation tests. These viral activities became detectable immediately after temperature shift-down from 38 to 32 C even at the later stage of infection. HVJ-pB was indistinguishable from HJV-W with respect to particle size, density, and morphological characteristics, but appeared to possess a higher neuraminidase activity and was inactivated more rapidly at 50 C than HVJ-W. HVJ-pB was less cytocidal and could easily cause latent infection in BHK and mouse L cells.

Persistent infection of BSC-1 cells by defective measles virus derived from subacute sclerosing panencephalitis

A line of cells (IP-3), persistently infected with defective measles virus, was developed from co-cultures of subacute sclerosing panencephalitis-derived brain cells with monkey kidney cells (BSC-1). The line, carried for more than 45 serial passages, produced neither infectious virus nor hemagglutinin. Cultures consistently displayed a cycling focal cytopathic pattern of infection characterized by formation of syncytia, necrosis, and plaques followed by healing. Fluorescent measles antigen was present in damaged areas only, especially in syncytia. The development of syncytia was suppressed by measles antibody. Syncytia were lysed by antibody plus rabbit complement. A variant noncytopathic subline (IP-3-Ca) was derived from the 16th passage. Infectious virus was not detected. Cells were minimally positive for hemadsorption. Fluorescent measles antigen was present in all cells. Co-cultures of IP-3-Ca cells with normal BSC-1 cells developed massive syncytia and extensive destruction. The IP-3-Ca cells multiplied in the presence of measles antibodies and were destroyed by antibodies plus complement. The possible relevance of these findings to the pathogenesis of subacute sclerosing panencephalitis is discussed.

Restricted replication of vesicular stomatitis virus in human lymphoblastoid cells

Replication of vesicular stomatitis virus (VSV) is restricted in one human lymphoblastoid cell line (Raji), but not in another similar cell line (Wil-2), compared with growth in HeLa cells. This restriction is characterized by a low proportion of cells yielding infectious virus and is associated with limited production of 42S virion RNA. Primary transcription of 13S and 26S VSV-specific RNA is not restricted in Raji cells, and the 13S RNA produced contains adenylate-rich sequences. This suggests that the block in Raji cells involves some step required for the replication of virion RNA.

Activation of a latent measles virus infection in hamster cells

The characteristics of infectious measles virus released from latently infected hamster embryo fibroblast cells are described. Low levels of virus were released spontaneously when the cultures were incubated at 37 C; this phenomenon was observed 19 passages after the cells had been exposed to the virus and has continued through cell passage 45. The virus yield could be significantly increased by cocultivation of the hamster cells with BSC-1 cells or incubation of the latently infected cells at 33.5 C rather than at 37 C. Measles virus released after cocultivation demonstrated increased cytopathology in cell culture and reduced temperature sensitivity when compared to the virus released at 33.5 C. After cell passage 45, there was an increase in spontaneous release of virus. However, the viruses recovered by cocultivation or temperature release after cell passage 45 were nearly identical. These observations suggest a possible mechanism for measles virus activation in cells latently infected with this virus.