Combined action of virus injection and local tumor irradiation on tumor growth in mice

The dynamics of SCCVII transplantable tumor growth in C3H/H mice was determined after local tumor irradiation and/or virus (NDV LaSota) i.p. injection. The virus applied alone significantly suppressed tumor growth, particularly until the 19th day after tumor transplantation. Local irradiation with 30 Gy resulted in tumor disappearance followed with its regrowth about 15 days later. However, if the virus was injected after the irradiation, there was no tumor growth until the end of the 31 day observation period. It should be noted that virus application prior to local irradiation did not have any additional influence on tumor growth. Thus, the pronounced efficacy of virus applied after tumor irradiation deserves attention. It is possible that the virus injected after irradiation induced a chain of cytokine production joining the action of tumor destruction induced by irradiation. This should be further studied in clarifying the approaches to combined tumor therapy with possible cell-free vaccine production.

Stimulation of human natural interferon-alpha response via paramyxovirus hemagglutinin lectin-cell interaction

A lectin-carbohydrate recognition event without enzymatic function is proposed as molecular basis for an important innate immune response to enveloped viruses. It involves the hemagglutinin-neuraminidase (HN) glycoprotein of Newcastle disease virus (NDV) and sialic acid expressing cellular receptors on human natural interferon (IFN) alpha producing cells. This conclusion is based on two types of experimental evidence: (a) strong UV irradiation of NDV, which destroyed the cell binding and hemadsorption (HAd) but not the neuraminidase (NA) activity of HN, also destroyed its IFN-alpha inducing activity; (b) DNA transfectants expressing HN mutant molecules with greatly reduced NA but not HAd activity induced IFN-alpha while transfectants expressing HN mutant molecules with greatly reduced NA and HAd activity were incapabable of inducing IFN-alpha in human peripheral blood mononuclear cells. The results clarify molecular mechanisms involved in pattern recognition during innate immune responses.

Cytopathic effect inhibition assay for canine interferon activity

Conditions for cytopathic effect (CPE) inhibition assay of canine interferon (IFN) activity in Madin-Darby canine kidney (MDCK) cells and in canine tumor cell line A72 was investigated using the New Jersey strain of vesicular stomatitis virus (VSV). The culture supernatant from canine splenocytes stimulated with ultraviolet-irradiated Newcastle disease viruses was used as reference IFN. MDCK cells were resistant for growth of VSV when the cells were confluent. Full CPE was observed only in a sparsely growing culture. Canine IFN activity could be assayed on less than 10(4) MDCK cells/well of a 96-well microplate, and more than 10(5) TCID50/ml of VSV was required. In A72 cells, VSV growth was not as dependent on cell density as in MDCK cells, requiring 10(3) TCID50/ml of VSV. MDCK-VSV system showed a higher IFN sensitivity than A72-VSV, whereas reproducibility was higher for the latter than the former. Based on these findings, A72-VSV system for canine IFN assay is recommended for practical use due to its easy handling characteristics.

Regulatory mechanisms of MuRantes and CRG-2 chemokine gene induction in central nervous system glial cells by virus

In this report we characterize the induction mechanisms of two chemokine genes, MuRantes and crg-2, the murine homologs of human RANTES and IP-10, respectively, in primary rat astrocytes and microglia by the neurotropic paramyxovirus, Newcastle Disease Virus (NDV). The time course for NDV induction of both MuRantes and crg-2 genes in astrocytes and microglia was similar, with peak mRNA expression at 10-12 h. Unlike crg-2, MuRantes mRNA was not induced by IFN-gamma. MuRantes and crg-2 are transcriptionally induced by noninfectious, UV-irradiated NDV in astrocytes and microglia, unlike TNFalpha gene transcription, which is induced only by live NDV. These data indicate that signals generated through virus-receptor interaction on the target cell surface suffice to initiate MuRantes and crg-2 gene transcription in the absence of viral replication. In astrocytes, MuRantes mRNA accumulation in response to NDV was completely blocked by tyrosine kinase inhibitors, and partially by PKC and PKA inhibitors, whereas crg-2 mRNA accumulation was significantly inhibited by PKC inhibitors, but minimally or not affected by inhibitors of tyrosine kinase or PKA activity. These kinase inhibitors also affected MuRantes and crg-2 gene transcription in similar patterns to those observed for mRNA levels, but did not reduce the mRNA stability. Therefore, the signals required for mRNA accumulation appear to operate at the level of transcription. Efficient transcription of MuRantes and crg-2 genes may require different sets of transcriptional proteins and enhancers that are regulated by different signaling pathways activated by NDV.

The effect of a mesogenic and a lentogenic Newcastle disease virus strain on Burkitt lymphoma Daudi cells

The destructive effect of Newcastle disease virus (NDV) strains on Burkitt lymphoma Daudi cells was investigated. Interaction of an active and UV-inactivated mesogenic strain (Roakin), as well as an active attenuated lentogenic strain (B1), grown in the allantoic sac of embryonated eggs, at high multiplicity, caused inhibition in cellular DNA synthesis and arrest in cell multiplication, eventually killing of the cells. The lentogenic strain cultivated in chicken fibroblasts exhibited only a moderate activity. The mechanism of the cytolytic effect is presumably linked to the increase in cell membrane permeability indicated by the elevation in 51Cr release. Thus it appears that the massive adsorption and/or penetration of viral particles, active or UV-inactivated (or possibly a toxic component that resides in the virion), damages the plasma membrane and may be responsible for the killing of the cells.

Complete regression of human neuroblastoma xenografts in athymic mice after local Newcastle disease virus therapy

BACKGROUND

Neuroblastoma is the most common pediatric extra-cranial solid cancer. Using conventional therapies, children older than 1 year of age with advanced neuroblastoma have a poor prognosis. The development of new approaches for treating such children with neuroblastoma continues to be one of the most important goals today in pediatric oncology. Despite numerous anecdotal reports of human tumor regression during viral infections, the use of viruses to directly lyse neuroblastoma cells has never been reported as a potential therapy. Newcastle disease virus (NDV) has been shown to replicate in and kill cultured human and rat neuroblastoma cells but not normal human fibroblasts.

PURPOSE

Our purpose was to determine if this selective killing of human neuroblastoma (IMR-32) cells is maintained during the in vivo treatment of established tumors.

METHODS

Two experiments were performed using NDV strain 73-T. Athymic mice with subcutaneous IMR-32 human neuroblastoma xenografts (6-12 mm) were treated intralesionally with live NDV, UV-inactivated NDV, or phosphate-buffered saline (PBS). To study virus replication in situ, mice were given intratumoral or intramuscular injections of NDV. These mice were then killed at various times, and the amount of infectious virus present in tumor or muscle was determined.

RESULTS

After one injection of live NDV, 17 of 18 tumors regressed completely, whereas rapid tumor growth occurred in all 18 mice treated with PBS and in all nine mice treated with UV-inactivated NDV (P < .0001). The one tumor that showed only a partial response to a single injection regressed completely after a second NDV treatment. Six months following virus-induced regression, only one tumor had recurred. No significant acute or chronic side effects of live NDV were noted in athymic mice given doses up to 500 times that used in this study. Virus levels increased more than 80-fold between 5 and 24 hours in virus-injected tumors (P < .04), while no infectious virus was produced in NDV-injected muscle tissue.

CONCLUSIONS

NDV 73-T appears to replicate selectively in human IMR-32 neuroblastoma xenografts, leading directly to a potent antitumor effect as demonstrated by long-lasting, complete tumor regression occurring after a single local injection of virus.

IMPLICATION

These experiments may provide an important step in the development of new therapeutic approaches to challenging cancers such as neuroblastoma.

Double-stranded ribonuclease coinduced with interferon

Double-stranded (ds) RNA and many viruses are inducers of interferon (IFN), the latter presumably because they contain, or can form, dsRNA. Concomitant with the induction of IFN in chicken embryo cells was the induction of a novel double-stranded ribonuclease (dsRNase), which was released into the medium and continued to accumulate long after IFN production ceased. Only avian cells (chicken, quail, turkey, or duck) expressed high levels of this dsRNase; mammalian, turtle, or fish cells did not. Production of the nuclease was inducer dose-dependent. Optimum pH and cation requirements distinguished it from other dsRNase activities. Degradation of dsRNA was endonucleolytic. Activity resided in a molecule of an Mr of approximately 34,500. Low levels of a single-stranded (ss) RNase activity were inseparable from the dsRNase. The role for a dsRNA-inducible dsRNase released from cells is unknown.

Purification and characterization of chick interferon induced by viruses

Chick interferon (IFN), produced in primary chick embryo (CE) cells stimulated by u.v.-irradiated Newcastle disease virus, was partially purified by two-step chromatography using both controlled pore glass and Blue Sepharose. The specific activity of the IFN increased about 500-fold by this method and the final recovery from starting material was more than 95%. The partially purified IFN was analysed by SDS-PAGE, and two peaks of IFN activity were observed. The molecular weight represented by the sharp peak was estimated to be 18 000 (18K) and a broad peak was found at 20K to 30K. Glycosidase treatment before SDS-PAGE resulted in disappearance of the broad peak and increased the activity of the 18K peak. Anti-CE IFN rabbit serum and a monoclonal antibody against the CE IFN neutralized the antiviral activity of all IFN samples prepared under various conditions.

Interferon induction by viruses. X. A model for interferon induction by Newcastle disease virus

Unirradiated Newcastle disease virus (NDV, strain AV) induced high levels of interferon (IFN) in primary chick embryo cells if the cells were 'aged' in vitro for 6 to 7 days. Dose (multiplicity)-response (IFN yield) curves, carried out in the presence of anti-NDV serum to prevent cycling infection, revealed that stocks of NDV-AV contain about sevenfold more IFN-inducing particles (IFP) than infectious particles (PFP). These non-infectious IFP were responsible for nearly all IFN induction in 'aged' cells, since PFP were determined to be incapable of inducing IFN. In contrast, with mouse L(Y) cells as hosts, about one-third the number of particles as there are PFP appeared to score as IFP. Heat and u.v. radiation (254 nm) inactivated NDV IFP and PFP activity at the same rate whether tested in chick or mouse cells, implying that virion-associated transcription is required to induce IFN. A model is proposed to account for the generation of IFN-inducing particles from infectious NDV following u.v. irradiation, and their subsequent inactivation at high doses of radiation. The model defines a series of u.v. targets in the NDV genome that regulate the expression of IFN-inducing particle activity in 'unaged' chick embryo cells.

Temperature-sensitive mutants of newcastle disease virus affecting interferon induction

Temperature-sensitive (ts) mutants of Newcastle disease virus (NDV) were isolated and studied for interferon (IFN) induction in primary chick embryo (CE) cells. At the non-permissive temperature (41 degrees C), there was no viral RNA synthesis or IFN induction by u.v.-treated virions except for ts-3 (RNA+), which did synthesize RNA at 41 degrees C, and whose u.v.-treated virions did induce IFN at this temperature. Another mutant (ts-4) induced IFN without irradiation, at the permissive temperature (37 degrees C). The minimum u.v. target size for IFN inducibility was unaffected by the mutation and corresponded to about 5% of the genome required for the expression of infectivity. These results support the hypothesis that the appearance of NDV RNA immediately after infection (primary transcription) plays a key role in IFN induction.

UV irradiation analysis of complementation between, and replication of, RNA-negative temperature-sensitive mutants of Newcastle disease virus

Random UV irradiation-induced lesions destroy the infectivity of Newcastle disease virus (NDV) by blocking downstream transcription from the single viral promoter. The nucleocapsid-associated polypeptides most likely to be involved in RNA synthesis are located at the extreme ends of the genome: NP and P are promoter proximal genes, and L is the most distal gene. We attempted to order the two temperature-sensitive (ts) RNA-negative (RNA-) mutant groups of NDV by determining the UV target sizes for the complementing abilities of mutants A1 and E1. After UV irradiation, E1 was unable to complement A1, a result compatible with the A mutation lying in the L gene. In contrast, after UV irradiation, A1 was able to complement E1 for both virus production and viral protein synthesis, with a target size most consistent with the E mutation lying in the P gene. UV-irradiated virus was unable to replicate as indicated by its absence in the yields of multiply infected cells, either as infectious virus or as particles with complementing activity. After irradiation, ts mutant B1 delta P, with a non-ts mutation affecting the electrophoretic mobility of the P protein, complemented E1 in a manner similar to A1, but it did not amplify the expression of delta P in infected cells. This too is consistent with irradiated virus being unable to replicate despite the presence of the components needed for replication of E1. At high UV doses, A1 was able to complement E1 in a different, UV-resistant manner, probably by direct donation of input polypeptides. Multiplicity reactivation has previously been observed at high-multiplicity infection by UV-irradiation paramyxoviruses. In this case, virions which are noninfectious because they lack a protein component may be activated by a protein from irradiation virions.

The in vitro effects of Newcastle disease virus on the metabolic and antibacterial functions of human neutrophils

Live Newcastle disease virus (NDV) was used to investigate the in vitro effects of a viral infection on phagocytosis, chemiluminescence generation, superoxide production, oxygen consumption, NADPH-oxidase activity, and intracellular killing of bacteria by Ficoll-Hypaque separated human neutrophils. Phagocytosis of oil red O particles by NDV-treated PMN was inhibited by 50%. Chemiluminescence by PMN was inhibited 79% after zymosan stimulation and 86% after tetradeconyl phorbol acetate stimulation. Superoxide generation was inhibited by 68%. Oxygen consumption was inhibited in the presence of NDV by 37% after stimulation with phorbol myristate acetate, while membrane-associated NADPH-enzyme activity was decreased by 19%. The percent of surviving intracellular S. aureus was significantly elevated in NDV-treated PMN after 60 and 120 min of incubation. Purified bacterial neuraminidase markedly suppressed chemiluminescence, while neuraminic acid blocked the effects of the virus. These observations suggest that infections with myxoviruses may suppress a number of vital neutrophil functions. It appears that the effects may be partly mediated by the interaction of viral neuraminidase with the external neutrophil membrane.

[The influence of artificial infrared radiation and microwaves upon mucopolysaccharides, protamine sulphate, and mucin in virus-infected organ cultures (author's transl)]

Infrared radiation and 1-2 micron microwaves influenced the infectivity of Newcastle Disease Virus (NDV) upon chick embryo tracheal tissue in such a way that the expected destruction of ciliated epithelium turned out to be incomplete or did not take place at all, respectively. Due to the fact that direct damaging of viruses following such radiation was not shown and that it was our intention to arrange the experimental set-up as if natural rhinolaryngeal conditions had induced the infection of the mucous membrane of the respiratory tract a study was performed in order to establish the radiation influence on mediator substances involved in the virus infection of mucous membranes. The mucopolysaccharides, chondroitine sulphate and hyaluronic acid, as well as mucin served as models; in addition protamine sulphate was used for reasons of comparison. The influence of the above substances upon NDV-infection in organ cultures and the effect of electromagnetic waves upon such influence were studied. By choosing a virus concentration of 10(-8)/ml on chick embryo tracheal tissue it was established that the application of infrared radiation (Osram Siccatherm Infrared Radiator,- 1-2 micron) and cm-waves (Klystron Raytheon Comp. Mass. USA, - 1.35 cm) for a length of 10 min. inhibited Newcastle Disease Virus (NDV) infectivity. The suspension fluid was treated with infrared and the tissue with cm-waves. Previous experiments revealed that direct radiation influence upon viruses cannot be taken for granted which is why the agents, chondroitine sulphate (polyanion) 5-10 microgram/ml, and hyaluronic acid (polyanion) 10-50 microgram/ml, were used in order to study such influence upon NDV-infected tracheal mucous membrane. In addition, protamine sulphate (polycation), 5-10 microgram/ml, and mucin were used. All the above mentioned substances influenced viral infectivity in organ cultures-expressed in terms of quotients: quotient 1 means no influence on the motility of the ciliated mucous membrane cells and quotient 0.01 means the complete destruction of the cells. Chondroitine sulphate inhibited strong but promoted weak virus infectivity, hyaluronic acid inhibited strong virus infectivity, protamine sulphate inhibited strong but promoted weak virus infectivity and mucin promoted weak virus infectivity in accordance with the used virus concentrations (Table 2). Under the influence of infrared radiation the mediator substances exercised a different influence upon viral infectivity: 25 times out of 32 experiments chondroitine sulphate was inhibited and hyaluronic acid increased in 8 out of 12 experiments (Table 2). The influence of protamine sulphate on viral infectivity was found to be increased 39 times and inhibited 14 times out of 54 experiments, mucin was inhibited 6 times. Furthermore, it is to be added that additional radiation with cm-waves increased the influence of infrared radiation (Table 1)...

Interferon production by individual L cells

Using a protected centre technique in which agarose prevents the diffusion of interferon from individual producing cells, we have shown that essentially every cell in a monolayer of mouse L cells can be induced to produce interferon by infection with Newcastle disease virus (NDV). The amount of interferon produced by individual cells appeared to be highly variable, even when cloned cells and viruses were used. U.v.-irradiated virus lost its capacity to induce interferon in L cells and to infect chick embryo fibroblasts at the same rate. A small proportion of cells (1 X 10-6 to 10 X 10-6) appeared to produce interferon constitutively. This fraction was increased threefold by u.v. irradiation of the cells, and up to 10-fold by exposing cells to the mutagen ethyl methane sulphonate.

Interferon induction with Newcastle disease virus in FS-4 cells: effect of priming with interferon and of virus inactivating treatments

Inoculation of human FS-4 cells with Newcastle disease virus (NDV) resulted in the induction of two distinct interferon responses, one that peaked at about 5 hr (early response) and one that reached a maximum between 10 to 24 hr after inoculation (second response). The early interferon response was enhanced by previous treatment of the cells with interferon (priming), whereas the second response decreased after interferon treatment in a dose-dependent manner. The early response diminished with decreasing multiplicities of infection, the magnitude of the second response in unprimed cells was relatively independent of the dose of NDV employed. The early interferon response was sensitive to inhibition by actinomycin D for only 1 hr after inoculation. In marked contrast, the second response remained sensitive to inhibition by actinomycin D until 12 hr after inoculation. The ability of NDV to induce the second response was greatly diminished by irradiation of the virus with ultraviolet light or by its treatment with hydroxylamine, whereas the ability to stimulate the early response was relatively resistant to these virus-inactivating treatments. Treatment of NDV with hydroxylamine abolished the virus to induce the second response at the same rate as it destroyed infectivity. The results suggest the existence of at least two distinct mechanisms of interferon induction by NDV; the early response is triggered either by a virion component or by a product of primary transcription, whereas induction of the second response requires the expression of some functions of the virus not needed for triggering the early response.

Production of labile Newcastle disease virus progeny after infection of chicken embryo cells in the presence of caffeine

A study was undertaken to examine the effects of caffeine on Newcastle disease virus (NDV) infection of chicken embryo cells. Addition of 10 mM caffeine to the growth medium produced 95% reduction in progeny synthesis, 63% reduction in RNA synthesis, 45% reduction in protein synthesis, and 25% reduction in hemadsorption ability in NDV-infected cultures when compared with untreated, infected cultures. Purified NDV obtained from caffeine-treated, infected cultures was more sensitive to ultraviolet irradiation and to damage by freezing and thawing than was observed in untreated virus cultures. The SDS-polyacrylamide gel electrophoresis revealed that purified virions contained the same complement of polypeptides, but there was a significant variation in the quantities of several of the NDV polypeptides.

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.

Effect of virus infection and cycloheximide treatment on the labeling of cellular phospholipids with 32 P

The total amount and the relative proportions of labeled phospholipids were studied in chorioallantoic membrane cells (CAM), chick embryo cells (CEC) and L cells which were either infected with Newcastle disease virus (NDV), fowl plague virus (FPV) and mouse encephalomyocarditis (EMC) virus or treated with cycloheximide. In productively infected or nonproductively infected cells, the total amount of labeled phospholipids was not altered, but the relative proportions of individual phospholipids were modified. These modifications were related to the presence of viral proteins. Blocking of protein synthesis for 6 h with 7 microng cycloheximide/ml did not modify the total amount of labeled phospholipids in CAM and CEC. Less label was incorporated into cyclohexidime-treated L cells than in controls. The relative proportions of the labeled individual phospholipids were modified in all three cell types and these modifications were different from those in virus-infected cells.

The production and action of interferon in Chinese hamster cells

The interferon system has been investigated in primary cell cultures established from Chinese hamster embryos and new born pups. Interferon synthesis was induced with Sindbis virus, ultraviolet inrradiated Newcastle disease virus (u.v.-NDV) and with polyriboinosine acid-polyribocytidylic acid complex [poly (rI). poly (rC)]. Only u.v.-NDV induced significant production of interferon, maximum amounts being produced in 'aged' cells. Its apparent mol. wt. was 25000. CHO-KI cells, an established line of Chinese hamster cells, did not synthesize interferon in response to viruses, but were sensitive to its action.

[Synthesis of virus-specific RNA under conditions of homologous and heterologous interference by Newcastle disease virus]

Homologous and heterologous interference by Newcastle disease virus (NDV) was manifested in a marked inhibition of virus-specific RNA synthesis of both the interacting viruses. Inactivation of the interfering NDV by irradiation reduced its capacity to inhibit the synthesis of virus-specific RNA of the homologous virus, leaving its effect on the synthesis of RNA of the heterologous virus unchanged. In contrast, treatment of cell cultures with heparin leading to reduced interferon production eliminated the heterologous interference but did not affect the homologous interference.

Interferon induction by viruses and polynucleotides: a differential effect of comptothecin

The plant alkaloid comptothecin inhibits interferon production induced by Newcastle disease virus (NDV) or ultraviolet-irradiated NDV in chick and human cells, and by Sindbis virus in chick cells. It has no effect on interferon production induced by poly (rI).poly(rC) in chick and human cells. No effect of comptothecin could be detected on the multiplication of NDV, and it is concluded that the inhibition reflects a difference between interferon induction by viruses and by polynucleotides.

The effect of interferon inducers on colony stimulating factor production in L cell cultures

Bone marrow colony-stimulating activity in the culture media of L cell mono-layers treated with Newcastle disease virus or polyriboinosinic:polyribocytidylic acid showed an early increase followed by a marked fall fo activity when compared with non-induced cultures.

Protein synthesis in Newcastle disease virus-infected chicken embryo cells

A double-isotopic label difference analysis of polyacrylamide gels has been used to distinguish between cellular and viral protein accumulation in infected cells and to quantify the kinetics of accumulation of viral polypeptides. This technique, coupled with the determination of total radioactive amino acid incorporation in infected cultures, has revealed the following kinetic patterns. Viral polypeptides are first detected in infected cultures 2.0 to 2.5 h postinfection. The rate of accumulation of radioactive amino acids in viral polypeptides increases to a maximum (30 to 35% of the rate of accumulation in uninfected control cultures), whereas the rate of accumulation of radioactive amino acids in host-cell protein decreases to a minimum (20% of the rate of accumulation in uninfected control cultures) by 5 to 6 h postinfection. All of the viral polypeptides detected late in infection are also present at the earlier times, and the major virion structural polypeptides are present in approximately the same (N/G-2, 53K) or slightly increasing (L, G-1, M) relative amounts. One peak area containing a nonstructural glycopeptide with an apparent molecular weight of 66,000 shows significant alterations in rates of accumulation during infection. Inhibition in the rate of radioactive amino acid incorporation into both trichloroacetic acid-soluble and acid-precipitable material during infection has been demonstrated. However, these two inhibition phenomena can be uncoupled temporally by incubating infected cultures at 36 C instead of the usual 40 C, suggesting that they may not be directly related.

Relationship between the ribonucleic acid synthesizing capacity of ultraviolet-irradiated Newcastle disease virus and its ability to induce interferon

Ultraviolet (UV)-irradiated Newcastle disease virus which has lost its infectivity but has the capacity to induce interferon also has the capacity to induce ribonucleic acid (RNA) synthesis both in vitro and early in infection in vivo. With large doses of UV irradiation, RNA-synthesizing capacity and interferon-inducing capacity are lost in parallel. Limited amounts of base-paired RNA associated with a transcriptive intermediate are involved in this RNA synthesis. These findings suggest the possibility that the single-stranded RNA of the UV-irradiated virus induces interferon by serving as a template for the synthesis of base-paired RNA. UV irradiation of the virus breaks down viral RNA but at a rate which is too slow to be a major cause of the loss of RNA-synthesizing capacity. Evidence is presented which suggests that less of the template RNA of the UV-irradiated virus is copied and that the product which is synthesized is smaller than that synthesized by nonirradiated virus.