Production of bacterial blight resistant lines from somatic hybridization between Oryza sativa L. and Oryza meyeriana L

Novel bacterial blight (BB) resistance gene(s) for rice was (were) introduced into a cultivated japonica rice variety Oryza sativa (cv. 8411), via somatic hybridization using the wild rice Oryza meyeriana as the donor of the resistance gene(s). Twenty-nine progenies of somatically hybridized plants were obtained. Seven somatically hybridized plants and their parents were used for AFLP (amplified fragment length polymorphism) analysis using 8 primer pairs. Results confirmed that these plants were somatic hybrids containing the characteristic bands of both parents. The morphology of the regenerated rice showed characters of both O. sativa and O. meyeriana. Two somatic hybrids showed highest BB resistance and the other 8 plants showed moderate resistance. The new germplasms with highest resistance have been used in the rice breeding program for the improvement of bacterial blight resistance.

Epstein-Barr virus lytic cycle spreads via cell fusion in a nasopharyngeal carcinoma hybrid cell line

NPC-KT cl.S61, a subclone derived from an epithelial-nasopharyngeal carcinoma hybrid cell line NPC-KT, showed extensive Epstein-Barr virus (EBV) production and cell fusion when the EBV replicative cycle was induced by 5-iodo-2'-deoxyuridine. On the contrary, parental NPC-KT cells produced virus at a lower level and did not show cell fusion. Cell fusion in cl.S61 cells was blocked by 2-deoxyglucose and acyclovir, inhibitors of glycosylation and EBV DNA polymerase, respectively, with a concomitant decrease in the number of cells expressing EBV growth-associated antigens. However, the frequency of virus antigen expression in parental NPC-KT cells was not significantly affected by these drugs. This result suggests that efficient production of EBV from cl.S61 cells is due to the spreading of viral replicative cycle via cell fusion. It was also demonstrated by in situ autoradiography that cl.S61 cells producing virus fused to not only EBV receptor/CR2 positive Raji and BJAB cells, but also to receptor-negative Jurkat cells. The possible mechanism of EBV entry into cells devoid of virus receptor by cell fusion is discussed.

Susceptibility of human-mouse T cell hybrids to HIV-productive infection

Interspecies human x mouse cell hybrids were used to investigate the genetic basis of human permissivity to HTLV-IIIB infection. T cell hybrids between the mouse BW 51.47 T lymphoma line and normal, PHA-IL-2 activated, human peripheral mononuclear cells (PBMCs) were generated. These hybrids preferentially segregated human chromosomes, as assessed by phenotype and karyotype analysis. Viral integration occurred only in those hybrids expressing CD4+ at the cell surface. However, infectious progeny production was demonstrated only in two of the three CD4+ hybrids tested. By segregation analysis, we could correlate the absence of human chromosomes 1, 3, and 9 with the lack of infectious viral progeny.

Increased replication of simian immunodeficiency virus in CEM x174 cells by morphine sulfate

Infection with simian immunodeficiency virus induces cytopathic effects on CEM x174 cells in vitro. Syncytium formation of SIV-infected CEM x174 cells was significantly enhanced in the presence of morphine sulfate, with a concomitant increase in the activity of cellular reverse transcriptase and in the expression of SIV p27 core antigen. Parallel establishment of the viability of the morphine-treated cells indicates that the short-acting opioid protects against cell lysis induced by SIV so that replication and production of SIV particles continued and exceeded those without morphine treatment. This delayed cell lysis induced by morphine as seen in vitro correlated with an in vivo observation that peripheral blood mononuclear cells isolated from morphine-treated rhesus macaques displayed a less degree of programmed cell death by apoptosis during early stages of SIVmac infection. These studies suggest that the modification of the biological properties of HIV-infected cells by morphine sulfate may be one of the mechanisms by which opioids exacerbate the progression of HIV in drug abusers.

The blocks to human immunodeficiency virus type 1 Tat and Rev functions in mouse cell lines are independent

Rodent cells present two blocks precluding the expression of the human immunodeficiency virus type 1 (HIV-1) genome. First, the viral protein Tat is only poorly active in these cells. Second, when the HIV-1 provirus is integrated in the genome of mouse cells, it electively fails to express the viral structural proteins, indicating a block to Rev action. Both defects can be complemented by fusion of the infected mouse cells with uninfected human cells. Because the production of high levels of Rev is dependent on Tat-mediated transactivation and because both Tat and Rev bind the viral transcript, it has been hypothesized that the two blocks found in rodent cells might be linked. In the present work, we demonstrate that overexpression of Rev in mouse cell lines does not relieve their block in HIV-1 structural-gene expression. In addition, we show that this defect is also present in human-mouse cell hybrids which contain human chromosome 12 and support Tat function. On that basis, we conclude that the blocks to HIV-1 Tat and Rev action in mouse cell lines are independent and result from the absence of distinct cellular elements that are critical for HIV-1 gene expression.

Effects of gangliosides on the growth of herpes simplex virus type 1-infected cells derived from neurons and on viral replication

Although it is well-known that herpes simplex virus can establish latent infections in neurons of sensory and sympathetic ganglia, little is known about the viral or cellular factors which regulate the latent state. Experiments were designed to elucidate the effects that can be produced by adding gangliosides, abundant components in neurons but not in most other cell types, to virus-infected cells from mouse trigeminal ganglia and from the neuroblastoma x glioma hybrid cell line NG108-15. The results obtained indicate that gangliosides, when used in combination with acyclovir, efficiently protect the infected cells from lysis in both cell systems, and that they can exert antiviral activity at least in part via suppressing protein kinase C activity.

[The reproductive characteristics of the tick-borne encephalitis virus in interspecific somatic hybrids]

The study dealt with features of tick-borne encephalitis virus reproduction in two series of interspecies somatic hybrids generated by fusion of transformed cells of Chinese hamster (Ag17) with human diploid fibroblasts (KM/3) and with pseudonormal cells of Indian deer (Muntiacus munjak) (KOM). The viral infection in hybrid Ag17 cells ran an acute course with cell damage, but in KM/3 and KOM cells virus multiplication was not accompanied by the development of cytopathic effect. Two other parameters of tick-borne encephalitis virus infection under study: the extent of infectious particles production and electroimmunochemical properties were found to be under control of genomes of different parental cells.

Characterization of multiple mRNA species of simian immunodeficiency virus from macaques in a CD4+ lymphoid cell line

Cytoplasmic poly(A)+ RNA was isolated from CEMX721.174 cells 5 to 10 days after infection with molecularly cloned simian immunodeficiency virus SIVmac239. Expression of SIV RNA was analyzed by Northern (RNA) blot hybridization and by sequencing of cDNA clones. As expected, a splice donor site was demonstrated in the untranslated leader sequence outside the left long terminal repeat. The region between pol and env was found to contain at least two splice donor and six splice acceptor sites. Splice acceptor and donor sites in the intergenic region were suitably positioned for expression of vpx, vpr, tat, and rev. Splice acceptor sites at nucleotides 8802 and 8805 were demonstrated in singly and doubly spliced RNAs with the potential of expressing nef and the second exons of tat and rev. Our results demonstrate a complex pattern of alternative splicing of SIV mRNAs. The results are very similar to what has been observed in human immunodeficiency virus type 1-infected cells, suggesting that both human and simian immunodeficiency viruses are subject to multiple levels of regulation.

Human genes other than CD4 facilitate HIV-1 infection of murine cells

The human CD4 glycoprotein is a specific receptor for the HIV family of retroviruses. When expressed on human cell lines, this molecule binds virus through direct interactions with the gp 120 viral envelope glycoprotein thus allowing virus infection to occur. Subsequent to binding, conformational changes in the viral envelope glycoproteins are thought to facilitate virus entry into the target cell through direct fusion of the virus with the cell membrane. In contrast to the infection observed in human cell lines, infection of murine cell lines even in the presence of the CD4 receptor does not readily occur. We have examined this species tropism of HIV infection. We report that the inability to infect murine cells is not a function of the receptor for HIV or a suppressive function of the murine cellular background. Human CD4 expression, configuration and down-modulation on the murine background are similar if not identical to expression on the human cell background. Utilizing a panel of interspecific cell hybridomas, we have been able to bypass the barrier to infectivity of human CD4-positive murine cells. We demonstrate that there are at least two different restrictions to infectivity on the mouse background which can be complemented by the human genome. One restriction appears to be an extremely early postbinding function likely to be molecules necessary for viral entry into cells, the second restriction is necessary for high levels of virus production. Our mapping studies suggest that fewer than five human chromosomes are necessary for reconstituting infectivity in the murine background. These results have implications for models of HIV-induced pathogenesis and infectivity.

Fusion of Rous-sarcoma-virus-transformed rat cells to morphologically normal human or rat cells results in transcriptional suppression of the provirus that depends on its chromosomal integration site

The fusion of a Rous sarcoma virus (RSV)-transformed rat fibroblast clone to at least 2 different human cell types reproducibly produces phenotypically normal hybrids. Analysis of such hybrids reveals that proviral silence is the result of transcriptional down-regulation, presumably by a trans-acting human molecule. Furthermore, this phenomenon seems to be strongly influenced by the proviral chromosomal integration site and its imposition may entail a mechanism that is required only transiently.

Propagation of hepatitis A virus in hybrid cell lines derived from marmoset liver and Vero cells

To establish monkey liver cell lines with a high susceptibility to hepatitis A virus (HAV), marmoset (Saguinus labiatus) liver cells were fused with Vero cells deficient in hypoxanthine-guanine phosphoribosyltransferase and the resulting hybrid cells were selected in HAT medium. Of four hybrid cell lines obtained (S. 1a/Ve-1 to -4), three (S. 1a/Ve-1, -3 and -4) were equally susceptible to HAV infection. When inoculated with a virus isolated from marmoset liver tissue (10% liver tissue extract) or a faecal virus (10% stool extract) from a human hepatitis A patient, all susceptible cell lines showed a significant elevation of viral antigen activity as seen in radioimmunoassay and/or immunofluorescent antibody assays, at 4 to 6 weeks post-infection (p.i.) with the liver-derived inoculum and at 6 to 8 weeks p.i. with the stool-derived inoculum. In S. 1a/Ve-1 cells, a representative of the susceptible hybrid cell lines, full adaptation of HAV (liver tissue virus concentrate) to cell culture was attained after four serial passages. Thereafter, the virus grew to a plateau titre of 10(8.5) TCID50/ml at 7 days p.i. in a growth experiment. The infected cells showed no cytopathic effects but eventually a persistent infection was established when a saturated level of virus growth was reached.

Several rat cell lines share a common defect in their inability to internalize murine coronaviruses efficiently

Infection of rat cells, Schwannoma RN2, hepatoma HTC or myoblast L6, with the murine coronavirus JHM strain results in a persistent infection characterized by the release of virus over an extended period of time with a limited cytopathology. Several stages of the viral replication cycle have been examined in these cells in comparison to those in mouse L2 cells, which are totally permissive to JHM infection. Although the rat cells bound as much virus as the mouse cells. Their ability to internalize it was 40-fold less efficient than the mouse cells. This lower internalization efficiency was not enhanced by pH shock of infected cells, but was by treatment with polyethylene glycol. In all cell types there appeared to be no major differences in the ability of the internalized virus to replicate the viral RNA as determined by slot-blot analysis with a radiolabelled viral cDNA. A similar genetic mechanism appears to be operative in the lines because somatic cell hybrids formed between these lines in various combinations were also deficient in the ability to internalize bound virus. Taken together these results imply that rat cell lines in general share a common deficiency in their inability to internalize murine coronaviruses efficiently. This low efficiency in viral internalization may explain in part the ability of these lines to sustain persistent infections.

Electrofusion of individual animal cells directly to intact corneal epithelial tissue

An electromechanical process was developed to electrofuse human and nonhuman cultured cells directly to rabbit corneal epithelial tissue in vitro and in situ. This new process was utilized successfully to incorporate functional gonococcal membrane attachment receptors from human lymphoma cells into superficial rabbit corneal epithelium. Thus, cell-tissue electrofusion biotechnology may be employed to establish unique and novel animal models for investigating receptor-mediated processes in vivo.

Human T cell leukemia viruses use a receptor determined by human chromosome 17

Human T cell leukemia viruses (HTLV-I and HTLV-II) can infect many cell types in vitro. HTLV-I and HTLV-II use the same cell surface receptor, as shown by interference with syncytium formation and with infection by vesicular stomatitis virus (VSV) pseudotypes bearing the HTLV envelope glycoproteins. Human-mouse somatic cell hybrids were used to determine which human chromosome was required to confer susceptibility to VSV(HTLV) infection. The only human chromosome common to all susceptible cell hybrids was chromosome 17, and the receptor gene was localized to 17cen-qter. Antibodies to surface antigens known to be determined by genes on 17q did not block the HTLV receptor.

Extinction of JC virus tumor-antigen expression in glial cell--fibroblast hybrids

JC virus (JCV) is a ubiquitous human papovavirus that shares sequence and structural homology with simian virus 40 (SV40). In contrast to SV40, expression of JCV is restricted to a small number of cell types, including human fetal glial cells, uroepithelial cells, amnion cells, and some endothelial cells. To study the control of JCV early region expression, we made heterokaryons and stable hybrids between JCV-transformed hamster glial cells and mouse fibroblasts. Binucleate heterokaryons exhibited extinction of large tumor antigen expression in the hamster nuclei as assayed by indirect immunofluorescence. This extinction was both time and dose dependent: extinction reached maximal levels at 24-36 hr after fusion and was dependent on the ratio of glial cell to fibroblast nuclei in multinucleated heterokaryons. Extinction also was observed in stable hybrids between the glial cells and mouse Ltk- cells. Southern blot analysis showed that the extinguished hybrids contained viral sequences. Reexpression of large tumor antigen was observed in several subclones, suggesting that extinction was correlated with the loss of murine fibroblast chromosomes from these hybrids. The cis-acting region that mediates extinction resides within the viral regulatory region, which contains two 98-base-pair repeats that have enhancer activity. These data demonstrate that cellular factors that negatively regulate viral gene expression contribute to the restricted cell-type specificity of this virus.

[Cytomorphologic study of a line of hybrid somatic cells persistently infected with the scrapie agent]

Virological, cytological and electron microscopic methods were used to study the peculiarities of the scrapie agent persistence in the tissue culture of the mouse and human hybrid cells. A long-term persistence of the scrapie agents in the cells (658 days) has been obtained. The fact of persistence is confirmed by the results of biotest and electron microscopic studies of the mouse CNS. The agent persistence promotes a decrease in the mitotic activity of the infected cells and development of the ultramicroscopic changes in cells similar to the picture of the specific changes in the CNS of mice inoculated by scrapie agent.

Mechanism of interaction between endogenous ecotropic murine leukemia viruses in (BALB/c X C57BL/6) hybrid cells

The germline ecotropic murine leukemia (MuLV) proviruses of BALB/c and C57BL/6 (B6) mice were analyzed to determine the molecular basis of low virus expression in these mouse strains and to determine the mechanism of interaction of these two proviruses. Previous work had demonstrated that the BALB/c endogenous ecotropic provirus was infectious but unable to induce XC cell syncytia formation, and that induced (BALB/c X B6) hybrid cells expressed 10- to 50-fold more XC syncytia than induced parental cells. Two independently isolated DNA clones of the B6 endogenous ecotropic provirus were noninfectious following transfection into cells, and cell lines that expressed this viral genome produced noninfectious MuLV. Nucleotide sequencing of the mutant region of the B6 provirus indicated that the defective nature of this provirus resulted from an amino acid substitution of proline for alanine in the central portion of reverse transcriptase. From the analysis of the virus produced by induced hybrid cells, and the patterns of steady-state viral RNA in induced cells, we propose that the enhanced XC cell syncytia formation observed in hybrid cells is due to trans-complementation of viral proteins and not viral recombination or trans-activation of viral genome expression.

Restriction of human adenovirus replication in Chinese hamster cell lines and their hybrids with human cells

We have found that the replication of human adenovirus (Ad2) is restricted in multiple Chinese hamster cell lines including CHO and V79. The major site of restriction involves differential accumulation of late viral proteins as demonstrated by immunofluorescence assay and polyacrylamide gel electrophoresis with and without prior immunoprecipitation. Synthesis of fiber and penton base are markedly reduced, whereas others, such as the 100K polypeptide, are synthesized efficiently. This pattern of restriction is similar to that previously reported for Ad2 infection of several monkey cell lines; however, the restriction is more marked in the Chinese hamster cell lines. The restriction is most likely due to a deficient cellular function since stable cell hybrids between V79 or CHO and human cells are permissive for virus replication. By analysis of a series of hybrids with reduced numbers of human chromosomes, fiber synthesis was correlated with the presence of the short arm of human chromosome 3. More hybrids showed restoration of fiber synthesis than production of progeny virus, suggesting that more than one unlinked function is required for the latter.

Viral replication in HeLa/fibroblast hybrid cells infected with human cytomegalovirus

Three human hybrid cell lines were generated by the fusion of D 98OR, a HeLa cell variant, and TIG human diploid fibroblasts. Chromosome numbers of the hybrid cells fell between that of D 98OR cells and the combined chromosome number of the two cell lines, with three marker chromosomes identical to those of D 98OR cells. One hybrid, B-3, produced large amounts of human fibronectin as analyzed by immunohistochemistry. Only human cytomegalovirus (HCMV) infected B-3 cells showed positive fluorescence as detected by human antiserum to HCMV. Further cloning of B-3 by limiting dilution resulted in two cloned hybrids with markedly enhanced virus production as compared with B-3 cells. Treatment of these two clones with phorbol ester further enhanced virus production. These cloned hybrids may provide a tool to analyze host cell factors controlling the transcription and replication of HCMV.

[Characteristics of human-mouse hybrid cell lines and the changes induced in them by the poliomyelitis virus]

Cells of the four hybrid lines between continuous mouse cells Rag and human diploid embryonal fibroblasts were polymorphic and had mitotic activity in fully formed monolayers. Most of the these mitoses were pathological. Hybrid cells examined 8 months after hybridization were susceptible to the poliomyelitis virus infection with partial cytopathologic effect, they produced virus antigens and the infectious virus. Small hybrid cells displayed a more pronounced cytopathologic effect than did big, polynuclear and mitotic cells. Hybrid cells that were passaged 1.5 months after infection did not excrete any infectious poliovirus but contained poliovirus antigens.

Superinfection of epithelial hybrid cells (D98/HR-1, NPC-KT, and A2L/AH) with Epstein-Barr virus and the relationship to the C3d receptor

Three Epstein-Barr virus (EBV) genome-positive epithelial/hybrid cell lines (D98/HR-1, NPC-KT, and A2L/AH) were superinfected with EBV derived from P3HR-1 (HR-1), NPC-KT, and B95-8 cells. The HR-1 virus is lytic and induces early antigen in superinfected Raji cells; the virus is not capable of transforming B-lymphocytes. Virus preparations from NPC-KT cells have both transforming and early antigen-inducing properties, while B95-8 virus can only transform B-lymphocytes. It was possible to demonstrate EBV antigens after superinfection of D98/HR-1 cells with both HR-1 virus and NPC-EBV. The NPC-KT hybrid cells, which were originally prepared by fusing human adenoid epithelial cells (Ad-AH) and EBV genome-positive NPC explanted epithelial cells, were susceptible to superinfection with HR-1 virus but not to NPC-EBV. The A2L/AH hybrid cells, which were prepared by fusion between Ad-AH cells and lymphocytes transformed by B95-8 virus, could not be superinfected with any of the virus preparations. In order to further investigate the nature of the EBV receptor as it relates to other cell membrane components, we examined cell surface markers on Ad-AH, NPC-KT, A2L/AH, and D98/HR-1 cells using monoclonal antibodies and by rosette formation. We found that the NPC-KT, A2L/AH, and Ad-AH cell lines express the OKB2 antigen and that the common acute lymphoblastic leukemia antigen is expressed on the A2L/AH cells. We also found that NPC-KT parental cells and a clone of NPC-KT cells express erythrocyte antibody complement b and erythrocyte antibody complement d, as determined by rosette formation, but were negative for C3b and C3d when monoclonal antibodies against these two markers were used. The D98/HR-1 cells were also confirmed to be negative for C3b and C3d. The data suggest that the C3d receptor may be part of the EBV receptor but that the C3d receptor, by itself, is not the only receptor to which EBV can bind.

Effects of temperature on Epstein-Barr virus replication in epithelial/nasopharyngeal carcinoma hybrid cells

The authors studied the replication of Epstein-Barr virus (EBV) in the epithelial hybrid cells derived from nasopharyngeal carcinoma (NPCKT) caused by the effects of sub-optimal incubation at 34, 32 and 28 degrees C, respectively, using an immunofluorescence technique. The intensity of EBV induction by sub-optimal temperatures was in the order of 32 degrees C----28 degrees C----34 degrees C. In particular, 18-24% positive cells for early antigen and viral capsid antigen were observed at around 10 to 14 days after shift-down of the incubation temperature from 37 to 32 degrees C.

Differential expression of murine leukemia virus loci in chemically induced hybrid cells

The time course of murine leukemia virus production after chemical induction was determined in hamster-mouse somatic cell hybrids containing the xenotropic murine leukemia virus induction locus Bxv-1 or the ecotropic locus Akv-2. By using these hybrids, induction could be studied in the absence of secondary virus spread because xenotropic viruses cannot infect hybrid cells and ecotropic viruses cannot infect hybrids which have lost mouse chromosome 5. After induction, hybrids with Bxv-1 produced only a transient burst of virus, whereas those with Akv-2 continued to produce virus for periods in excess of 3 months. The presence or absence of other mouse chromosomes in the hybrid lines did not alter these induction patterns. Thus, endogenous murine leukemia virus loci differ in their response to induction, and both inducibility and the kinetics of virus expression are controlled at or near these proviral loci.

[Characteristics of enterovirus infection in cultures of human and mouse hybrid cells]

Lines of human-mouse hybrid cells susceptible to infection with poliomyelitis types I, II, III, ECHO type 1 and 12, and Coxsackie A7 viruses have been derived. The presence in the hybrid cells of 2 and 3 genomes of the nonpermissive cell partner (mouse) was shown not to inhibit enterovirus reproduction. Hybrid cultures differed in their sensitivity to the mutagenic action of poliomyelitis virus. There was no correlation between poliomyelitis virus yield and the number of chromosome breaks in hybrid cells. Poliomyelitis virus type I-infected hybrid cultures passaged for 11/2 months eliminated this virus and subsequently became less sensitive to reinfection with poliomyelitis virus of all 3 types but retained their original sensitivity to Coxsackie and ECHO viruses.

Replication of murine coronaviruses in somatic cell hybrids between murine fibroblasts and rat schwannoma cells

The replication of the murine coronaviruses MHV3 and JHM has been studied in somatic cell hybrids formed between murine fibroblast L2 cells which support lytic infections with both these agents, and rat RN2 Schwannoma cells which support the replication of JHM in a temperature-sensitive, persistent manner but are restrictive to the replication of MHV3. The results described in this report indicate that the totally permissive state is dominant over the persistent or restricted state since the hybrid cells permit the replication of both these viral agents in a lytic manner.

Studies on mechanism of entry of EB virus into non-B lymphocytes. Establishment of an EB virus-producing human-tupaia hybrid cell line TuH18

With the use of the EB virus-producing lymphoblastoid cell line H18, an attempt was made to infect the monolayer cell culture of nasopharyngeal tissue from the normal tupaia, and an EB virus-producing, human-tupaia hybrid cell line was established. The mechanism of entry of EB virus into cells other than B lymphocytes is discussed in this paper.

Epstein-Barr virus nuclear antigen-positive nasopharyngeal hybrid cells

An epithelial-like hybrid cell line was established by cell fusion of 8-azahypoxanthine-resistant epithelial cells (Ad-AH) with lymphoblastoid cells (A2L), derived from the human nasopharynx. The nasopharyngeal hybrid cells, designated as A2L/AH, were Epstein-Barr virus (EBV)-associated nuclear antigen (EBNA)-positive by the anticomplement immunofluorescence method. Furthermore, the treatment of the hybrid cells with 5-Iodo-2' -deoxyuridine (IUDR) induced early antigen (EA) and viral capsid antigens (VCA), while the treatment of nonproducer lymphoblastoid cells, A2L, induced EA but not VCA. The appearance of IUDR-induced VCA in the hybrid cells suggests that some factor produced by the Ad-AH cells might neutralize a repressed state of VCA and thus activate these antigens with the treatment of IUDR. These established nasopharyngeal hybrid cells might be useful for studies of in vitro nasopharyngeal carcinoma (NPC) since no EBV-carrying NPC cell lines have been established.

Epstein-Barr virus activation of human epithelial-nasopharyngeal carcinoma hybrid cells

The authors used indirect immunofluorescence and electron microscopic techniques to study the effects of 5-iododeoxyuridine (IUDR) and the tumor promotor 12-O-tetradecanoylphorbol-13-acetate (TPA) on the epithelial hybrid cell line (NPC-KT) derived from nasopharyngeal carcinoma. The hybrid cells contained Epstein-Barr virus (EBV)-induced early antigens at a very low level but not Epstein-Barr viral capsid antigens in spontaneous production; the hybrid cells responded significantly to both IUDR and TPA induction. The chemicals induced both early antigens and viral capsid antigens in the NPC-KT cells. Moreover, the virus particles were detected in the altered NPC-KT cells by IUDR treatment. The data suggest that the EBV-induced agents activate the EBV productive cycle in a proportion of nasopharyngeal carcinoma cells.

Effect of (E)-5-(2-bromovinyl)-2'-deoxyuridine on several parameters of Epstein-Barr virus infection

The selective and potent anti-herpesvirus drug, (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVdU), has been examined for its inhibitory effects on several parameters of Epstein-Barr virus (EBV) infection in the lymphoblastoid cell lines Raji, P3HR-1, B-95-8 and P3 hybrid cells (a human embryo oropharyngeal cell line fused with a nasopharyngeal carcinoma cell line). At a dosage of 0.03 to 0.1 mM, BVdU caused a marked inhibition of (i) spontaneous viral capsid antigen (VCA) expression in B-95-8 and P3 hybrid cells, (ii) VCA expression and DNA synthesis in B-95-8 cells induced with croton oil and n-butyrate, (iii) early antigen (EA) expression and DNA synthesis in Raji cells superinfected with EBV, and (iv) VCA expression and DNA synthesis in B-95-8 cells superinfected with EBV. In its inhibitory effects on these various parameters of EBV infection, BVdU appears to be comparable to acyclovir [9-(2-hydroxyethoxymethyl)guanine], another selective anti-herpesvirus drug which has been previously recognized as an effective inhibitor of EBV replication.

Cytoplasmic distinction of avirulent and virulent Rickettsia prowazekii: fusion of infected fibroblasts with macrophage-like cells

L-929 cells with virulent or avirulent Rickettsia prowazekii growing in their cytoplasm were fused with cells of the macrophage-like cell line RAW264.7. Fusion occurred between the two cell types, producing heterokaryons containing R. prowazekii. Both the number of rickettsiae per infected heterokaryon and the percentage of heterokaryons infected with rickettsiae decreased in experiments with the avirulent strain compared to those with the virulent strain. These results indicate that the differential survival of the virulent strain in macrophages is some unknown function of the cytoplasm of the macrophage and that the distinction is not only at the phagolysosome level.

Reciprocal productive and restrictive virus-cell interactions of immunosuppressive and prototype strains of minute virus of mice

Viral and cellular factors responsible for parvovirus target cell specificity have been examined for two serologically indistinguishable strains of the minute virus of mice which infect mouse cells of dissimilar differentiated phenotype. Both the prototype strain and the immunosuppressive strain grow in and form plaques on monolayers of simian virus 40-transformed human fibroblasts, a finding that has allowed the comparison of several aspects of their virus-host cell interactions. Although closely related by antigenic and genomic criteria, both the prototype strain and the immunosuppressive strain are restricted for lytic growth in each other's murine host cell, that is, in T cells and fibroblasts, respectively. The host range of each virus variant appears to be specified by a genetic determinant that is stably inherited in the absence of selection. In the restrictive virus-host interaction lytic growth is limited to a small or, in some cases, undetectable subset of the host cell population, and the majority of the infected cells remain viable, continuing to grow at the normal rate without expressing viral antigens. The susceptible host cell phenotype is dominant in T lymphocyte x fibroblast fusion hybrids, implying that different cell types express different developmentally regulated virus helper functions that can only be exploited by the virus variant that carries the appropriate strain-specific determinant.

Antiviral effects of interferon on a somatic cell hybrid between two Burkitt's lymphoma cell lines of different interferon sensitivities

A somatic cell hybrid between two human Burkitt's lymphoma cell lines, Raji and Daudi, was infected with either Epstein-Barr virus or vesicular stomatitis virus after interferon treatment. Raji cells are resistant to the antiviral effects of exogenously added interferon, whereas Daudi cells are interferon sensitive. The Raji-Daudi hybrid showed an interferon sensitivity that was intermediary to that of the parental cells against both viruses.

Coronavirus 229E susceptibility in man-mouse hybrids is located on human chromosome 15

Human coronavirus 229E, n enveloped, RNA-containing virus, causes respiratory illness in man and is serologically related to murine coronavirus JHM, which causes acute and chronic demyelination in rodents. 229E displays a species-specific host range restriction whose genetic basis was studied in human-mouse hybrids. 229E replicated in human WI-38 cells but not in three mouse cell lines tested (RAG, LM/TK-, and A9). Human coronavirus sensitivity (HCVS) was expressed as a dominant phenotype in hybrids, indicating that mouse cells do not actively suppress 229E replication. HCVS segregated concordantly with the human chromosome 15 enzyme markers mannose phosphate isomerase (MPI) and the muscle form of pyruvate kinase (PKM2), and analysis of hybrids containing an X/15 translocation [t(X;15)(p11;q11)] localized HCVS to the q11 leads to qter region of chromosome 15. HCVS might code for a specific surface receptor, allowing 229E to be absorbed to and received within the host cell.

Epstein-Barr virus in nontumorigenic and tumorigenic nasopharyngeal carcinoma (NPC) somatic cell hybrids

Somatic cell hybrids between mouse fibroblasts and human cells derived from nasopharyngeal carcinoma (NPC) biopsies or NPC tumors propagated in nude mice were examined for the expression of the Epstein-Barr nuclear antigen (EBNA), retention of Epstein-Barr viral (EBV) DNA, and tumorigenicity in nude mice. In all hybrids the expression of EBNA correlated with the detection of EBV-DNA. After more than 2 years in culture, the hybrids examined retained similar amounts of EBV-DNA when compared to previously published data. Retention of EBV-DNA did not correlate with the presence of any particular human chromosome. Use of either rodent cell lines, clone 1D or IT-22, did not affect the retention nor loss of EBV-DNA. For tumorigenicity studies, NPC cells were fused with IT-22 cells and injected into nude mice. Tumor formation did not depend on the presence or absence of EBNA and detectable EBV-DNA sequences; tumorigenicity in these studies could not be correlated with the presence of any particular human chromosome or the origin of the NPC biopsy.

Restriction of C-type viral antigen in H-2/Fv-1 syngeneic mouse somatic cell hybrids

Somatic cell hybrids between an AKR lymphoma or a C3H sarcoma and H-2, Fv-1 syngeneic CBA sarcoma or carcinoma have been examined for expression of the structural components of murine leukemia virus (MuLV) by radioimmunoassay and complement-dependent cytotoxicity assay. Parental AKR and C3H cells contained high concentrations of MuLV core protein p30 in their cell extracts and showed high sensitivity to anti-MuLVgp70 and p30 sera. In contrast, CBA cells expressed little detectable p30 in the extracts, were much less sensitive to anti-gp70 serum, and were almost insensitive to anti-p30 serum. The hybrids between the AKR or C3H cells and CBA cells had a decreased amount of p30 in the extracts and were almost resistant to cytotoxicity by anti-p30 serum, although they maintained high sensitivity to anti-gp70 serum. These findings suggest that the CBA genotype suppresses the production and cell-surface expression of p30 antigen of AKR and C3H endogenous C-type viruses. The suppressive gene is not Fv-1n.

Expression of feline xenotropic RNA tumor virus in hybrids between permissive human and non-permissive mouse cells

Somatic cell hybrids were generated by fusing human (A549) cells, cloned after infection with the feline xenotropic CCC virus, to mouse (3T3) cells which are non-permissive for this virus. Hybrid clones were found to be capable of expressing infectious virus. CCC virus expression, however, was regulated in the hybrid cells in such a way that 20-200 times less virus was released into the culture fluid than by the human parental line. Thus human permissiveness for this virus is co-expressed with murine restriction. Markers for twenty human chromosomes were assayed in the hybrid clones. No single human chromosome was found to be essential and sufficient for CCC virus production, since none of them was consistently present or lost in virus-positive and virus-negative clones, respectively.

Tumorigenicity and intracisternal A-particle expression of hybrids between murine myeloma and lymphocytes

Hybrids of BALB/c lymphocytes and a murine myeloma, a tumor that expresses intracisternal A-particles, were obtained with polyethylene glycol as the fusogen. The karyotype, tumorigenicity, and A-particle expression of the hybrid clones were assessed. All the hybrid clones analyzed were tumorigenic and expressed intracisternal A-particles even when they were the result of a fusion event between two lymphocytes and one myeloma cell in which no loss of chromosomes was detected. The tumors that developed following inoculation of hybrid cells into BALB/c mice (1 x 10(6) cells/mouse) were karyotypically identical to the inoculated cells. It appears that the two myeloma cell phenotypic traits analyzed (tumorigenicity and A-particle expression) are dominant.

Assays for endogenous and exogenous lymphoid leukosis viruses and chick helper factor with RSV(--) cell lines

Japanese quail cells transformed by the envelope-defective Bryan high-titer strain of Rous sarcoma virus [R(-)Q] were used as a source of the Rous sarcoma virus genome in three kinds of assays. (i) The simplest and most sensitive assay for infectious, endogenous viruses of the chicken belonging to subgroup E involved infection of a mixture of R(-)Q cells and turkey cells with the sample and assay of supernatants of these cells for focus formation on subgroup E susceptible cells. (ii) Inactivated Sendai virus-induced fusion of R(-)Q cells with live test cells was found to be a specific method for detection of chick helper factor. Focus formation by supernatant of the fused cells on subgroup E susceptible cells was correlated with the presence of subgroup E envelope glycoprotein on the plasma membranes of test cells. Whole blood cells as well as fibroblasts could be used in this assay. (iii) A method of assay for exogenous lymphoid leukosis viruses in which mixed cultures of R(-)Q cells and C/E cells and assay of supernatants for focus formation on C/E cells was as sensitive as assays presently used for exogenous lymphoid leukosis virus. Because no infectious Rous sarcoma virus was used as part of the procedure, the assays for infectious virus described here yielded pure pseudotypes of the input virus, an advantage for determining purity and subgroup of the input virus.

Genetic mapping of the ecotropic murine leukemia virus-inducing locus of BALB/c mouse to chromosome 5

By means of an approach that combined the techniques of somatic cell genetics and Mendelian breeding studies, the inducibility locus, designated Cv, for ecotropic murine leukemia virus in BALB/c mice, was mapped to chromosome 5, 23 units from the locus for phosphoglucomutase-1, with gene order Cv-Pgm-1-Gus. This low-efficiency inducibility locus is therefore not allelic with the chromosome 7 loci previously described for two other mouse strains with high virus inducibility. These studies provide further evidence that endogenous ecotropic viruses represent viral genomes inserted at different chromosomal sites in the various mouse strains.