Cellular interactions determine the rate and degree of interferon action

The rate and degree of interferon action on mouse embryo (ME), mouse L, and human amnion (WISH) cells were found to be dependent on the cell density. The most precipitous drop in interferon action occurred just below cell confluency. This effect was shown with both vesicular stomatitis virus and Sindbis virus and at both constant and variable input multiplicities of infection. At both "high" and "low" cell densities, cells attached to a surface develop viral resistance faster than suspended cells. These data indicate that either cell contact or close cell proximity is required for maximal interferon activity. These results are discussed in relation to interferon-induced transfer of viral resistance.

Lipid-saccharide intermediates and glycoprotein biosynthesis in a temperature-sensitive Chinese hamster cell mutant

The characterization of a temperature-sensitive Chinese hamster cell mutant has been continued with the aim of localizing the apparent defect in glycoprotein synthesis (Tenner et al., '77). Although the mutation is lethal, a demonstration of the ability of the mutant cells to support proliferation of Mengo virus at the nonpermissive temperature indicates that the general metabolic processes of the cells remain intact at a time when glycoprotein synthesis is severely depressed. A quantitative study of protein synthesis on membrane-associated polysomes suggests that the synthesis of the polypeptide portion of the glycoproteins at 40.8 degrees C may be normal. The investigation of lipid-saccharide molecules which have been implicated in the formation and transfer of the oligosaccharide "core" to polypeptide acceptors shows that mutant cells at the nonpermissive temperature are capable of synthesizing these lipid saccharides normally, and that the pool of the dolichyl oligosaccharides is maintained at a constant level independent of the temperature. The rate of formation of the lipid-oligosaccharide, however, is reduced in intact mutant cells at the nonpermissive temperature. Further investigations show this decreased rate to be the result of an increased half life of the lipid-oligosaccharide at 40.8 degrees C. These data indicate that the temperature-sensitive step in glycoprotein biosynthesis is the transfer of the oligosaccharide core from the lipid-oligosaccharide intermediates to the nascent polypeptide chain. The data presented also provide evidence that the lipid-saccharide intermediates, previously described mainly in in vitro systems, are in fact involved in the glycosylation of a majority, if not all, of the mannose-containing glycoproteins in intact, growing hamster cells.

Mechanisms of interferon induced transfer of viral resistance between animal cells

The sequence of events initiated by interferon and leading to the antiviral state were studied as possible sites for the cell-to-cell transfer of interferon induced viral resistance. The possible role of interferon produced by recipient cells was negated by the demonstration of transfer of resistance in the presence of anti-human interferon antibody and under conditions of a single cycle of VSV growth. Transfer of sensitivity of WISH cells to mouse interferon, possibly through transfer of a membrane receptor, seems unlikely since resistance was transferred in the absence of mouse interferon. From kinetic data and the fact that actinomycin D blocked resistance in human cells for 3 h longer than in mouse cells, it seems unlikely that the mouse antiviral protein itself or its mRNA alone is a likely candidate for the transfer of resistance. Thus, by a process of elimination, we suggest that secondary messenger molecules which transmit the interferon signal from the membrane to the nucleus are the effector substance(s) for the transfer process.

Noninfectious vesicular stomatitis virus particles deficient in the viral nucleocapsid

Several temperature-sensitive mutants of vesicular stomatitis virus in complementation group III produce, at nonpermissive temperature, noninfectious particles which contain the viral M (matrix) and G (glycoprotein) proteins but less than 10% of the normal proportion of N protein or RNA. Since group III mutants are thought to be defective in the structural gene for the virus M protein, these findings demonstrate that an interaction between M and the nucleocapsid is of importance in virus budding. Taken together with earlier results, they suggest that M is the key protein in bud formation.

Comparative analysis of interferon and antiviral protein messenger RNAs

A comparative analysis of interferon and antiviral protein messenger RNAs was carried out. Differences in their biological activities and sedimentation coefficients were found. In RNA preparations from superinduced cells (cells treated with poly(I).poly(C) and antimetabolites) and from cells treated with interferon, messenger RNAs possesing interferon and antiviral activities were detected. The results suggest the existence of two types of mRNA (for interferon and antiviral protein, respectively) and support the hypothetic model of interferon action via an antiviral protein.

Growth and maturation of a vesicular stomatitis virus temperature-sensitive mutant and its central nervous system isolate

A temperature-sensitive (ts) mutant of vesicular stomatitis virus (VSV), tsG31, produces a prolonged central nervous system disease in mice with pathological features similar to those of slow viral diseases. tsG31 and the subsequent virus recovered from the central nervous system (tsG31BP) of mice infected with tsG31 were compared with the parental wild-type (WT) VSV for plaque morphology, growth kinetics, thermal sensitivity of the virions, and viral protein synthesis and maturation. Several properties of the central nervous system isolate distinguished this virus from the original tsG31 and the WT VSV. The WT VSV produced clear plaques with complete cell lysis, and the tsG31 produced diffuse plaques and incomplete cell lysis, whereas the tsG31BP had clear plaques similar to those of the WT VSV. Although plaque morphology suggested that tsG31BP virus was a revertant to the WT, growth kinetics in either BHK-21 or neuroblastoma (N-18) cells indicated that this virus was similar to tsG31, with a productive cycle at 31 degrees C and no infectious virus at 39 degrees C. At 37 degrees C, however, the tsG31BP matured much slower than did the original tsG31 (and produced only 1% of the yield measured at 31 degrees C). WT VSV produced similar quantities of infectious virions at 31, 37, and 39 degrees C. The lack of infectious virions at 39 degrees C for the ts mutants was presumably not due to a greater rate of inactivation at 39 degrees C. Unlike WT VSV, which synthesized viral proteins equally well at all three temperatures, tsG31 had a reduced synthesis of all the structural proteins at 37 and 39 degrees C, compared with that at 31 degrees C; the formation of the M protein was most temperature sensitive. In addition, fractionation of the infected cells indicated that the incorporation of the M and N proteins into the cellular membranes was also disrupted at the higher, nonpermissive temperatures. Several characteristics of protein synthesis during tsG31BP infection at 39 degrees C distinguished this virus from tsG31: (i) no mature viral proteins were detected at 39 degrees C; (ii) several host proteins were [ill], suggesting that the virus was incapable of completely depressing host macromolecular synthesis; and (iii) a great proportion of the incorporated radioactivity was found in unusually high-molecular-weight proteins. In addition, at 37 degrees C, the tsG31BP virus showed a decreased synthesis of viral proteins and reduced assembly of the viral structural proteins.

Pseudotypes of vesicular stomatitis virus and Pichinde virus

Super-infection of Pichinde virus-infected cells with vesicular stomatitis virus (VSV) resulted in the production of pseudotype virus which was not neutralized by antiserum to VSV but which was neutralized by antiserum to Pichinde virus. Analysis of pseudotype virus production in relation to the kinetics of replication of Pichinde virus demonstrated that pseudotype virus production occurred when super-infection with VSV was initiated 8 h or more after infecting the cells with Pichinde virus. The quantities of pseudotype virus produced correlated with the quantities of Pichinde virus antigen detected on the surface of the cells both during acute infection and in cells chronically infected with Pichinde virus. The observations indicate that pseudotype of VSV and Pichinde virus are readily formed and that the formation of pseudotype virus may be used to examine the Pichinde virus antigens expressed on the surface of infected cells.

Morphological and biochemical characterization of viral particles produced by the tsO45 mutant of vesicular stomatitis virus at restrictive temperature

The growth at restrictive temperature of tsO45, a group V (glycoprotein) conditional lethal mutant of vesicular stomatitis virus (VSV), was demonstrated to result in the production of large numbers of noninfectious viral particles. The infectivity of these tsO45 particles could be enhanced by procedures known to promote membrane fusion. Morphologically and biochemically these particles differed from wild-type VSV by their lack of viral glycoprotein. The other structural proteins of VSV were present and indistinguishable by size and relative proportion from those of virus grown at the permissive temperature. Examination of glycoprotein maturation at the restrictive temperature (39.5 degrees C) in tsO45-infected cells demonstrated the synthesis of normal viral glycoprotein but failed to demonstrate the presence of this glycoprotein in either the cell membrane or the envelope of free virions. The further absence of soluble viral glycoprotein from the supernatants of such cells strongly suggests that viral glycoprotein may not be necessary for the successful budding of VSV.

Absence of interferon production in a newly established human cell line

A cell line established from human embryonic lung, HEL-R66, was demonstrated to be highly susceptible to herpes simplex virus types 1 and 2, vaccinia virus, Newcastle disease virus (NDV), Japanese encephalitis virus (JEV), western equine encephalitis (WEE) virus, Sindbis virus, vesicular stomatitis virus (VSV), and rabies virus. The maximal yields of NDV, JEV, WEE virus, and rabies virus in this cell line exceeded by 2--4 logs those in control human embryonic lung cells. Inability of this cell line to produce interferon upon treatment with native and UV-irradiated forms of virogenic and lentogenic strains of NDV and with poly I:C was revealed. A refractory state to challenging VSV did not develop in HEL-R66 cells treated with the inducers. Furthermore, pretreatment of HEL-R66 cells with interferon did not potentiate the capacity to produce interferon in response to the addition of poly I:C, whereas the same treatment enhanced the production of interferon in normal human embryonic lung cells.

Specific protein phosphorylation in interferon-treated uninfected and virus-infected mouse L929 cells: enhancement by double-stranded RNA

The enhanced phosphorylation of specific protein(s) observed in extracts from interferon-treated cells (in the presence of ATP and double-stranded [ds] RNA) was also seen in intact mouse L929 cells upon treatment with dsRNA, polyriboinosinic.polyribocytidylic acid [poly(rI.rC)] or reovirus dsRNA, using 32Pi as radiolabel. Labeling of a 65,000-dalton protein(s) with 32P was greatly increased in interferon-treated cells in the presence of added dsRNA, suggesting that the expression in vivo of the kinase activity involved is regulated by dsRNA. This was used as a test system to investigate whether the activity of interferon-induced enzyme(s) is stimulated following virus infection, possibly owing to the accumulation of dsRNA. No obvious increase in 32P-labeling of 65,000-dalton protein(s) was observed upon infection of interferon-treated cells with mengovirus or vesicular stomatitis virus. A basal level of 32P-labeling of the 65,000-dalton protein(s) was detected in interferon-treated cells in the absence of added dsRNA, indicating a basal level of expression of the kinase activity involved. The possible implications of these results are discussed.

Restricted replication of two alphaviruses in ricin-resistant mouse L cells with altered glycosyltransferase activities

Two mouse L cell variant lines (CL 3 and CL 6) selected for resistance to the toxic plant lectin ricin were restricted in their ability to replicate the two alphaviruses Sindbis virus and Semliki Forest virus. CL 3 cells have been shown to exhibit increased CMP-sialic acid:glycoprotein sialyltransferase and GM3 synthetase activities, whereas CL 6 cells have been shown to contain decreased UDPgalactose:glycoprotein galactosyltransferase and UDP-N-acetylglucosamine:glycoprotein N-acetylglucosaminyltransferase activities. The adsorption of Sindbis virus to CL 6 cells was considerably reduced, suggesting that the loss or inaccessibility of the receptors for Sindbis virus accounted for a major defect in virus production in these cells. In contrast, CL 3 synthesized Sindbis viral RNA and proteins but were unable to convert the precursor glycoprotein PE2 to the structural protein E2. The cleavage of PE2 to E2 was also blocked in both CL 3 and CL 6 cells infected with Semliki Forest virus.

The matrix (M) protein of vesicular stomatitis virus regulates transcription

Temperature-sensitive mutants of vesicular stomatitis virus (VSV) belonging to complementation group III contain a lesion in the matrix (M) protein. This results in a 2--5 fold increase in transcription at the nonpermissive temperature. Co-infection of cells with one of these mutants and wild-type virus reverses this mutant phenotype. Separation of the transcriptional and translational products from mutant-infected cells reveals an overall increase in each of the viral mRNA species concomitant with degradation of the M protein at the nonpermissive temperature. The increase in mRNA, however, does not lead to increased synthesis of viral proteins. Quantitation of individual mRNA species indicates that M protein acts as a direct inhibitor of transcription as well as an attenuator of sequential transcription.

Resistance of visna virus to interferon

Visna is a slow infection of sheep caused by a retrovirus. The persistence of virus despite the immune response of the host is best explained by restricted genetic expression of the virus and consequently prolonged periods of residence inside cells. The purpose of this investigation was to determine whether the restriction in genetic expression of visna virus is mediated by interferon. Sheep interferon induced by polyriboinosinic-polyribocytidylic acid in fetal lambs inhibited the growth of herpes simplex virus, vesicular stomatitis virus, and vaccinia virus, but even highly concentrated interferon did not affect the replication of visna virus in sheep choroid plexus cells. The same results were obtained whether the effects of interferon were assessed in single of multiple cycles of growth and when interferon was added at later times in the growth cycle of the virus. This unusual resistance of visna virus to interferon suggests that restriction of viral expression by the host is probably not mediated in this way.

Efficient transfer of interferon-induced virus resistance between human cells

The rate of development of interferon-induced virus resistance in a mixture of two human cell types (U and WISH) is determined by the cell type (WISH) in the mixture which responds first. This phenomenon has been shown with two types of interferon assay procedure, and with both vesicular stomatitis virus and Sindbis virus. The transfer of virus resistance from one human cell (WISH) to another (U) (homospecific transfer) is much more efficient than the transfer from mouse L cells to WISH cells (heterospecific transfer), as shown by a much lower ratio of donor to recipient cells required for maximum transfer as well as a more rapid transfer. Thus, virus protection afforded by the interferon system is amplified more efficiently in mixtures of different human cells than in mixtures of mouse and human cells. These results suggest that, in a mixed population of cells such as occurs in vivo, more slowly responding cells might be influenced by cells which respond more rapidly to interferon. A defensive role is suggested for this mechanism which amplifies protection due to interferon.

Viral superinfection in cells carrying an arenavirus and/or a togavirus

Four lines of the same L-cell clone were transferred 60 times in parallel: uninfected cells, a line carrying lymphocytic choriomeningitis virus (LCMV), another one carrying tick-borne encephalitis virus (TEV) and one carrying both viruses. In double persistency, LCM and TEV were suppressed and stimulated, respectively. Cell multiplication rates were comparable in all four lines. Single LCMV persistence caused marked resistance of L cells to superinfecting viruses from various taxonomic groups, but this phenomenon was abolished or even reversed to increased sensitivity in the cell line with co-persisting LCMV plus TEV.

Persistent infection of L cells with vesicular stomatitis virus: evolution of virus populations

A previous report (Youngner et al., J. Virol. 19:90-101, 1976) documented that noncytocidal persistent infection can be established with wild-type vesicular stomatitis virus (VSV) in mouse L cells at 37 degrees C and that a rapid selection of RNA(-), group I temperature-sensitive (ts) mutants consistently occurs in this system. To assess the selective advantage of the RNA(-)ts phenotype, evolution of the virus population was studied in persistent infections initiated in L cells by use of VSV ts 0 23 and ts 0 45, RNA(+) mutants belonging to complementation groups III and V. In L cells persistently infected with ts 0 23, the ts RNA(+) virus population was replaced gradually by viruses which had a ts RNA(-) phenotype. VSV ts 0 45 (V) has another marker in addition to reduced virus yield at 39.5 degrees C: a defective protein (G) which renders virion infectivity heat labile at 50 degrees C. Persistent infections initiated with this virus (ts, heat labile, RNA(+)) evolved into a virus population which was ts, heat resistant, and RNA(-). These findings suggest that the ts phenotype itself is not sufficient to stabilize the VSV population in persistently infected L cells and also indicate that the ts RNA(-) phenotype may have a unique selective advantage in this system. In addition to the selection of ts RNA(-) mutants, other mechanisms which also might operate in the maintenance of persistent VSV infections of L cells were explored. Whereas defective-interfering particles did not seem to mediate the carrier state, evidence was obtained that interferon may play a role in the regulation of persistent infections of L cells with VSV.

Virus-replicating T cells in the immune response of mice. III. Role of vesicular stomatitis virus-replicating T cells in the antibody response

The functional role of the T cell (Tv) which can replicate vesicular stomatitis virus (VSV) on activation by the antigen was investigated in antibody response in vitro. By the inoculation of VSV into the culture, marked augmentation of antibody response to sheep erythrocytes (SRBC) was observed in the culture of spleen cells taken more than 3 days after the immunization with SRBC, suggesting that the VSV-susceptible suppressor cells were included in these spleen cells and the activity was eliminated by the effect of VSV. Development of two distinct types of suppressor T cells was revealed in the spleen of mice after the priming with SRBC. First, nylon wool nonadherent (NAd) suppressor T cells found in the spleen cells taken 3 days after immunization, and second, nylon wool adherent (Ad) suppressor T cells found in the spleen cells taken approximately 1 wk after immunization. The activity of nylon Ad suppressor T cells was completely abolished by VSV-preinfection, whereas that of nylon NAd suppressor T cells was unaffected. It was also shown that the helper T-cell activity was not influenced by VSV-preinfection. These results provided direct evidence that nylon Ad suppressor T cell but not nylon NAd suppressor T cell nor helper T cell can actually replicate VSV after antigenic stimulation. Thus it was strongly suggested that Tv represents the nylon Ad suppressor T cells.

Comparison of interferon action in interferon resistant and sensitive L1210 cells

Translation inhibition, leu-tRNA aminoacylation and double-stranded RNA and ATP dependent phosphorylation were examined in interferon-treated and control cell-free lysates of leukaemic mouse L 1210 R and L 1210 S cells. No differences were observed between the respective interferon-treated and control cell-free extracts, except for the presence of an enhanced 67K dalton phosphoprotein fraction in interferon-treated L 1210 S cell-free extracts. In non-responding cell-free lysates, the lack of stimulation of a 67K dalton phosphoprotein fraction cannot be explained by the presence of an increased level of some inhibitory activity, such as a phosphatase.

Virus-replicating T cells in the immune response of mice. II. Characterization of T cells capable of replicating vesicular stomatitis virus

Immunocytological properties of the splenic T cell (Tv) which develop into virus plaque-forming cells in response to the antigenic challenge in vitro were investigated in relation to the properties of helper T cells and suppressor T cells in antibody response. Tv was observed in spleen around 1 wk after the intravenous injection of mice with 10(7) sheep erythrocytes. This contrasted with the finding that both helper T cells and suppressor T cells developed as early as 3 days after the immunization. Tv was proliferative in response to the antigenic stimulation, whereas helper T-cell activity could be expressed without cell division. Development of Tv to virus plaque-forming cells was much more dependent on macrophages than the generation of helper activity. Tv was found in nylon wool adherent fraction, whereas helper T cell was found in both nylon adherent and nonadherent fractions. Tv belongs to the short-lived and nonrecirculating T-cell population (T1), whereas the major part of helper T cells belongs to the long-lived and recirculating T-cell population (T2). These results strongly suggest that vesicular stomatitis virus infect and replicate in the different subset(s) of T cell(s) to which the major part of helper T cells belong.

Effect of serum on the antiviral and anticellular activities of mouse interferon

Fetal bovine serum markedly decreased the ability of mouse L-929 interferon preparations to inhibit the formation of L-929 clones, but did not affect their ability to inhibit vesicular stomatitis virus (VSV) plaque formation in these cells. This dissociation of effects by interferon preparations indicates that: 1. the mechanism of action of interferon for its anticlonal antiviral activities is different; or 2. the molecule responsible for the anticlonal activity is a separate growth inhibitory factor.