Effect of interferon treatment on vesicular stomatitis virus (VSV): release of unusual particles with low infectivity

VSV replication in neurons is inhibited by type I IFN at multiple stages of infection

Vesicular stomatitis virus (VSV) is a rhabdovirus which causes acute encephalitis in mice after intranasal infection. Because type I interferon (IFN) has been shown to be a potent inhibitor of VSV, we investigated the role of type I IFN in viral replication in neurons in culture. Pre-treatment of NB41A3 neuroblastoma cells or primary neuron cultures with IFN-beta or IFN-alpha strongly inhibits virus replication, with 1000-fold inhibition of infectious virus release occurring at 7 h post-infection, and maximum inhibition of 14,000-fold occurring at 14 h. Type I IFN inhibited both viral protein and RNA synthesis, but not enough to account for the inhibition of infectious virus yield. The influenza virus protein NS1 binds dsRNA and antagonizes induction of PKR activity, an IFN-inducible antiviral protein which phosphorylates and inactivates the elongation factor eIF-2alpha, resulting in cessation of translation. In NS1-expressing neuroblastoma cells, VSV replication was inhibited by IFN-beta as well as in control NB41A3 cells, and eIF-2alpha phosphorylation was blocked, suggesting that PKR activity was not involved in inhibition of viral protein synthesis. Similarly, inhibition of VSV by IFN-beta was not affected by addition of inhibitors of nitric oxide synthase, indicating that IFN-beta activity is not mediated by nitric oxide or superoxide. This contrasts with the essential role of NOS-1 in inhibition of VSV replication when neurons are treated with IFN-gamma. Analysis of cell culture supernatants revealed suppression of release of VSV particles from both NB41A3 cells and primary neurons treated with IFN. The inhibition of virion release closely matched the overall suppression of infectious VSV particle release, suggesting that type I IFN plays a role in inhibition of VSV assembly.

Expression of human and macaque type I IFN transgenes interferes with HSV-1 replication at the transcriptional and translational levels: IFN-beta is more potent than IFN-alpha 2

A study was undertaken to compare the efficacy of plasmid constructs encoding human IFN-alpha 2 and IFN-beta and macaque IFN-beta against herpes simplex virus type 1 in transfected cells. All type I IFN transgenes significantly reduced viral titers in transfected cells by 3 logs. Human IFN-alpha 2-transfected cells produced significantly more IFN (2274 pg/ml) in comparison to IFN-beta-transfected cells (134-165 pg/ml). Viral lytic gene transcript and viral protein levels were lower in IFN-beta- versus IFN-alpha 2-transfected cells, which coincided with elevated PKR and OAS transcript levels and increased total STAT1 and phosphorylated STAT1 (Y701) protein levels in the IFN-beta-transfected cells. Although comparable viral titers were recovered in IFN-alpha 2 and IFN-beta plasmid-transfected cells, IFN-alpha 2 plasmid-transfected cells exhibited significantly more cytopathic effect compared to the IFN-beta transgene-transfected cells. In addition, IFN-alpha 2 transgene-transfected, infected cells displayed a cell cycle profile similar to that of vector-transfected, infected cells, whereas IFN-beta plasmid-transfected cells displayed a profile similar to uninfected control. Collectively, the results indicate that human IFN-beta is superior to IFN-alpha 2 in antagonizing herpes simplex virus type 1 infection.

Mechanism of enhancement of the antiviral action of interferon against herpes simplex virus-1 by chloroquine

Using double immunofluorescence, we have shown previously that interferon (IFN) treatment inhibits the transport of herpes simplex virus-1 (HSV-1) gD from the Golgi complex to the plasma membrane in the virus infected and gD cDNA transfected LMtk-cells. In the present study, we quantitated the gD protein on the cell surface and localized the gD protein in the trans-Golgi network (TGN). The results showed 10-fold less fluorescence for the gD protein on the cell surface in IFN-treated LMtk-cells. Subcellular fractionation studies demonstrated that gD was associated with TGN-enriched membranes. Gold labeling for DAMP distribution using electron microscopy showed that IFN raised the pH of TGN. IFNs induced alkalinization of TGN may be related to the block in the transport of HSV-1 gD. Earlier we reported that a subeffective dose of chloroquine (CHL) or IFN does not change the pHi. However, both CHL and IFN together raise the pHi significantly. To study the biologic significance of the finding, the effect of these subeffective doses of IFN and CHL on the antiviral activity and the transport of the gD protein was studied. Results suggested that CHL enhance the antiviral activity of IFN against HSV-1 and concomitantly increase the inhibition of HSV-1 gD transport. This IFN-induced increase in pHi of the TGN may also explain the inhibitory effect of IFN reported on the terminal steps of some of the enveloped viruses.

Defective transport of herpes simplex virus glycoprotein in interferon-treated cells: role of intracellular pH

We have investigated the mechanism(s) of interferon (IFN)-induced inhibition of assembly steps of herpes simplex virus (HSV-1) in mouse LB cells. Data showed that physiological doses of mouse IFN-beta (10-100 IU/ml) significantly inhibited the infectivity (5- to 100-fold) of HSV-1; however, viral protein synthesis was marginally inhibited (2- to 5-fold). Immunofluorescence studies showed that most of the HSV-1gD glycoprotein accumulated intracellularly in IFN-treated LB and LMtk- cells transfected with gD cDNA, as compared to untreated controls, where most of the gD was localized on the plasma membrane. Double-immunofluorescence studies demonstrated that rhodamine-labeled wheat germ agglutinin (WGA) was co-localized with gD protein, suggesting the block was in the transport from the trans-Golgi to the plasma membrane. IFN treatment of LB and LMtk- cells raised the intracellular pH as measured by DAMP distribution and SNARF-1 using laser spectroscopy; this could play an important role in the inhibition of transport of HSV-1gD.

Loss of infectivity by progeny virus from alpha interferon-treated human immunodeficiency virus type 1-infected T cells is associated with defective assembly of envelope gp120

Levels of human immunodeficiency virus (HIV) DNA, RNA, or p24 antigen and reverse transcriptase activity in T-cell cultures treated with 500 IU of recombinant alpha interferon (rIFN alpha) per ml were comparable to those in control cultures. Radioimmunoprecipitation analysis of proteins in lysates of IFN-treated T cells documented a marked accumulation of HIV proteins. Localization of gp120 by immunofluorescence showed a diffuse pattern in IFN-treated cells quite distinct from the ring pattern in untreated control cells. That large quantities of gp120 in aberrant cell compartments might affect HIV morphogenesis was confirmed in infectivity studies: virions from IFN-treated cells were 100- to 1,000-fold less infectious than an equal number of virions from control cells. Direct examination of IFN-treated and control HIV-infected cells by transmission electron microscopy showed little difference in the number or distribution of viral particles. However, quantitation of gp120 by immunogold particle analysis revealed a marked depletion of envelope glycoprotein in virions released from IFN-treated cells. This defect in gp120 assembly onto mature viral particles provides a molecular basis for this loss of infectivity.

Use of Brefeldin A to localize block in intracellular transport of vesicular stomatitis virus G protein on interferon-treated cells

Brefeldin A (BFA) induced a rapid redistribution of vesicular stomatitis virus G protein (VSV-G) to the endoplasmatic reticulum (ER) in interferon (IFN)-pretreated cells. This result is consistent with accumulation of VSV-G in the trans-Golgi (GC) complex in cells pretreated with IFN and implies that IFN does not interfere with the ability of BFA to induce redistribution of proteins from GC to ER.

Heterogeneity of CD4-positive human T-cell clones which recognize the surface protein antigen of Rickettsia typhi

Immunity to the typhus group of rickettsiae is largely dependent on the effector function of several classes of T lymphocytes, including those which produce gamma interferon. Since the surface protein antigen (SPA) derived from typhus group rickettsiae has been shown to be an effective immunogen in animal models, human T-cell clones specific for the SPA of Rickettsia typhi were isolated and tested for their antigenic specificity, as well as for their ability to produce gamma interferon. Eighteen CD4-positive clones specific for the SPA of R. typhi exhibited considerable diversity in their response to the SPAs derived from two strains of Rickettsia prowazekii and from Rickettsia canada. The vast majority of clones also recognized the SPAs from R. prowazekii but not from R. canada. Two heteroclitic clones demonstrated significantly higher proliferative responses to the SPAs derived from one or both of the R. prowazekii strains than to the SPA of R. typhi, and one clone demonstrated a significantly higher response to the SPA of R. typhi than to the other SPAs. All 18 clones produced gamma interferon in response to SPA stimulation. We conclude that the SPAs from typhus group rickettsiae can elicit both a diverse T-cell response in humans and the efficient stimulation of gamma interferon-mediated immunity.

Effect of cloned human interferons on protein synthesis and morphogenesis of herpes simplex virus

Pretreatment of human fibroblast cells with 100 U of either cloned human alpha-2 or beta interferon per ml for 24 h reduced the release of infectious herpes simplex virus type 1 by more than 99%. This inhibition in infectivity correlated well with the total number of extracellular virus particles released from treated cells as determined by DNA dot blot hybridization analysis. Electron microscopic observations of interferon-treated human fibroblast cells clearly demonstrated typical assembly of nucleocapsids inside the nucleus, even though very few mature extracellular particles were seen. Analysis of virus-specific proteins by the immunoblot technique showed that neither species of interferon had a significant inhibitory effect on the synthesis of major nucleocapsid proteins. However, the synthesis of specific glycoproteins (D and B) was drastically reduced or delayed in beta-interferon-treated cells. The results presented in this communication suggest that cloned human interferons block herpes simplex virus morphogenesis at a late stage and inhibit the release of particles from the treated cells.

The calcium ionophore A23187 evokes and potentiates antiviral activity of interferon

Calcium ionophore A23187, which causes a rapid efflux of Ca2+ from cells, evokes an antiviral response in mouse LB, simian COS-1, Hela, human amniotic (U), baby hamster kidney (BHK), and VERO cells against Sindbis (SBV) and vesicular stomatitis (VSV) viruses. The degree of antiviral activity depends on the type of cell, virus, and the dose of A23187. A23187 inhibits the production of infectious VSV; however, VSV particle production was not significantly inhibited as measured by viral RNA and viral proteins. The VSV released from the A23187-treated cells is deficient in VSV glycoprotein (G) and membrane (M) protein. A23187 potentiates the antiviral activity of interferon (IFN) against SBV and VSV in mouse LB and human U cells. It is possible to postulate that a change in intracellular Ca2+ may play an important role in the antiviral activity of IFN.

Differential effect of interferon on glycoprotein and membrane protein of vesicular stomatitis virus released from murine and simian cells

Previous studies by Maheshwari et al. have indicated that vesicular stomatitis virus (VSV) released from interferon (IFN)-treated mouse L-929 (L) cells was structurally defective. Such virions had significantly smaller amounts of glycoprotein (G) and membrane protein (M). Olden et al. recently reported, however, that they were not able to repeat the findings of Maheshwari et al. We have examined the effect of IFN on VSV released from three different cell lines and observed that treatment of L-cells and secondary mouse embryo (ME) cells with an amount of mouse IFN that reduced infectious virus yield 100-fold, led to the release of VSV with reduced amounts of G and M proteins. However, at concentrations of IFN less than this concentration, this effect was not observed. In contrast, VSV released from human (Hu)IFN-treated primate BSC-1, cells showed no reduction in their G and M protein even at concentrations resulting in 400-fold decreases in infectious virus yield.

Effect of cloned human interferons on the replication of and cell fusion induced by herpes simplex virus

Human alpha- and beta-interferons, expressed from cloned genes, block the replication of, and cell fusion induced by herpes simplex viruses. This inhibition is neutralized by antiserum to interferon and demonstrates species specificity. The block in replication appears to be late in the replication cycle of herpes simplex virus, since similar levels of viral DNA are synthesized in both interferon-treated and untreated cells.

Low infectivity of vesicular stomatitis virus (VSV) particles released from interferon-treated cells is related to glycoprotein deficiency

We have investigated the mechanism for the low infectivity of vesicular stomatitis virus (VSV) released from interferon (IFN) -treated cells. With 10-30 units/ml of IFN there was an approximately 5-30 fold reduction in the production of virus particles, as measured by VSV proteins; however, the infectivity of the VSV released from IFN-treated mouse LB, JLS-V9R, or human GM2504 was drastically reduced (2 to 4 logs). The low infectivity of VSV was directly related to a deficiency in virion glycoprotein (G). IFN treatment did not change the specific infectivity of the VSV particles released by HeLa cells; their G protein was also not reduced. A further effect of IFN to reduce the amount of virion M protein appeared to be secondary and was probably not related to the reduced infectivity of VSV.

Effect of interferon on two human choriocarcinoma-derived cell lines

Two cell lines derived from human choriocarcinomas (HCCM-5 and BeWo) are resistant to several biological effects of human interferon such as inhibition of VSV multiplication and inhibition of cell growth, but they develop a normal antiviral activity against EMCV. Nevertheless, in both cell lines, 2-5A synthetase and protein kinase are induced by IFN. 2-5A-dependent endonuclease can be measured by two independent methods and 2-5A itself is detected at least in poly(rI):poly(rC)- and IFN-treated BeWo cells. This is another example of two cell lines that are partially, with respect to the antiviral effect toward VSV, and totally, with respect to the anticellular effect, refractory to IFN treatment, although all the known elements of the 2-5A system are present.

Tunicamycin enhances the antiviral and anticellular activity of interferon

The inhibitory effects of interferon on virus multiplication and cell growth are significantly enhanced by treatment with tunicamycin. Potentiation of antiviral activity was found only with enveloped viruses and not with nonbudding viruses. Changes in the plasma membrane of treated cells may account for this effect, since enveloped viruses bud from the cell surface as a terminal step.

Mediators of protection against lethal systemic vesicular stomatitis virus infection in hamsters: defective interfering particles, polyinosinate-polycytidylate, and interferon

Homologous defective interfering (DI) particles protected adult Syrian hamsters against lethal systemic infection with vesicular stomatitis virus (VSV) serotype Indiana. The DI particles had to be biologically active, but did not have to be administered at the same inoculation site as the infectious virus. Serum and tissue levels of VSV postinoculation were significantly lower in DI-protected animals than in unprotected controls, suggesting that true autointerference was occurring. However, some aspects of protection also must be mediated through nonspecific mechanisms, since susceptible hamsters could be protected against VSV Indiana by coinjection with heterologous DI particles prepared from VSV serotype New Jersey or by simultaneous administration of polyinosinic acid-polycytidylic acid. By measuring serum levels of putative hamster interferon (type 1), we found that animals coinjected with VSV and DI particles or polyinosinic acid-polycytidylic acid produced significant levels of interferon. Since similarly high serum levels of interferon were measured in recipients of VSV alone (animals that eventually died from infection), there appeared to be no correlation between protection against lethal disease and induced levels of serum interferon. Instead, serum interferon levels correlated positively with amounts of VSV PFU found in serum and tissues of infected animals, the lowest levels being found in serum of animals protected with homologous DI particles. The data are consistent with the hypothesis that autointerference by DI particles as well as various host defense mechanisms (possibly including induction of interferon) participates in protecting hamsters against lethal VSV infection.