Sedimentation characteristics of newly synthesized Epstein-Barr viral DNA in superinfected cells

The diagnosis of Epstein-Barr virus-associated polymorphic B cell lymphoma in immunocompromised patients: Review of methods

Polymorphic B cell lymphoma and diffuse B cell lymphoproliferation associated with Epstein-Barr virus infection is increasingly reported in immunodeficient patients. Accurate diagnosis of these pathologies is essential because the appropriate treatment regimens for the patients in question differ from those for patients with other lymphoproliferative diseases. Two complementary techniques are currently used in the diagnosis and characterization of Epstein-Barr virus-associated B cell lymphomas and diffuse B cell lymphoproliferation. Immunofluorescence allows specific detection of Epstein-Barr nuclear antigens in lymphomatous tissue. Molecular hybridization with the Bam H1-W and/or Bam H1-NJ probes confirms the presence of the Epstein-Barr virus genome in tumour cells. The Bam H1-NJ probe is also useful in determining the clonality of the tumour and the replication mode, episomal or linear, of the viral genome. The polymerase chain reaction method allows detection of the Epstein-Barr virus genome within 24 h in these tumours and is more sensitive.

Maintenance of growth transformation with Epstein-Barr virus is mediated by secretion of autocrine growth factors in two serum-free B-cell lines

The characteristics of two tamarin (Saguinus oedipus) B-cell lines (sfBIT and sfBT) growth-transformed by Epstein-Barr virus (EBV) that proliferate continuously in serum-free medium are described. sfBIT was established by selecting cells for growth in RPMI 1640 supplemented with insulin, transferrin, and selenium (J. E. Shaw, R. G. Petit, and K. Leung, J. Virol. 61:4033-4037, 1987). sfBT, a subline of sfBIT cells reported here for the first time, required transferrin as the only protein supplement for continuous growth in RPMI 1640. Growth of sfBT cells was linear with human transferrin at 10(-2) to 10 micrograms/ml. Transferrin at 5 micrograms/ml yielded a culture density of 5 X 10(5) to 1 X 10(6) cells per ml, a cell doubling time of 2 to 3 days, and a culture viability greater than 95%. sfBIT and sfBT cells released transforming virus during continuous growth in serum-free culture medium without EBV-inducing agents. The spent medium of both serum-free lines supported cell growth at low culture density (1 x 10(4) to 5 X 10(4) cells per ml), but growth was arrested at low culture density with fresh serum-free medium. A procedure to measure growth-promoting activity (GPA) was established, and it revealed that the GPA of spent medium was greater than that of fresh medium for both serum-free cell lines. When fresh and spent media were dialyzed (molecular weight cutoff, 3,500) and subsequently concentrated by lyophilization, only the GPA of spent medium increased. We conclude that maintenance of growth transformation of tamarin cells latently infected with EBV is mediated by growth factors that are entirely autocrine in origin.

Specific immune serum to the Epstein-Barr virus DNA polymerase

Epstein-Barr virus (EBV) DNA polymerase was released from phorbol ester-treated tamarin (Saguinus oedipus) cells (B95-8) and prepared for use as an antigen by sequential column chromatography with DEAE-Sephadex A-25, DEAE-cellulose, phosphocellulose, and single-stranded DNA cellulose. Proteins from single-stranded DNA cellulose with DNA polymerase activity in 100 mM ammonium sulfate were mixed with complete Freund adjuvant and injected intradermally into rats and rabbits. Immune sera that were screened for specific antibody by indirect immunofluorescence procedures reacted with approximately 3% of the cells in EBV-producer cultures (B95-8 and P3HR-1) but not with EBV genome-negative cells (BJAB). In functional enzyme assays, immune sera or the immunoglobulin fraction inhibited the activity of purified EBV DNA polymerase 90%. Inhibition of enzyme activity was not affected by absorption of immune sera with insoluble matrices of proteins prepared with tamarin and human cells which lacked the EBV genome. Cellular DNA polymerase alpha was not inhibited by immune sera to the EBV enzyme.

P3HR-1 Epstein-Barr virus with heterogeneous DNA is an independent replicon maintained by cell-to-cell spread

We present results of biological experiments which indicate that the subpopulation of Epstein-Barr virus strain P3HR-1 with heterogeneous (het) DNA consists of self-contained replicons which multiply alongside, but independently of, Epstein-Barr virus strain HR-1 containing standard DNA. When a population of HR-1 virions containing het DNA was introduced into X50-7 cells, the input heterogeneous DNA increased in abundance, as did the DNA of the endogenous virus of X50-7 cells. The input standard HR-1 viral DNA, however, was not amplified. When parental HR-1 cells or a cellular subclone containing het DNA were grown for several weeks in the presence of human serum with neutralizing antibody, the het DNA was lost from the culture; standard HR-1 DNA, however, was not affected by antiserum. Furthermore, virions containing het DNA could be serially propagated through cellular subclones of HR-1 cells which lack het DNA. After each serial passage, cells which acquired het DNA released virions with the ability to induce early antigens in Raji cells. These experiments define a novel in vitro life cycle of an Epstein-Barr virus variant which is maintained, not vertically by partitioning to daughter cells in cell division, but horizontally by cell-to-cell spread.

The circular intracellular form of Epstein-Barr virus DNA is amplified by the virus-associated DNA polymerase

Selective DNA extraction and hybridization procedures were used to estimate the relative number of covalently closed circular viral genomes in cultures of Epstein-Barr virus (EBV)-transformed cells. In virus-producing P3HR-1 cultures that were exposed for 11 days to phosphonoacetic acid or to acyclovir, the content of covalently closed circular EBV DNA was reduced ca. 70% relative to a control culture without drug. The EBV plasmid content of Raji, a virus nonproducer cell line, was not reduced by exposure to these compounds. When P3HR-1 cultures were exposed to 12-O-tetradecanoylphorbol-13-acetate, the number of circular genomes per cell increased. These findings indicate that two enzyme activities synthesize circular EBV DNA and that the virus-associated DNA polymerase synthesizes most of the circular EBV DNA in a virus producer culture. It is suggested that the circular genomes synthesized by the viral enzyme are intermediates in the syntheses of linear virus DNA.

Hypomethylation of Epstein-Barr virus DNA in the nonproducer B-cell line EBR

The conversion of the Epstein-Barr virus-negative Ramos cell line has previously been shown to result in an Epstein-Barr virus-positive non-virus-producer cell line, EBR. We report here that Epstein-Barr virus DNA from EBR alone among several cell lines examined was totally unmethylated at three of four sites containing guanine plus cytosine which were tested. This is in direct contrast to reports of high degrees of methylation in the DNAs of other animal viruses, including herpesviruses, isolated from cells in which the viral genome is expressed at a low level.

Dimer-size DNA circles in a leukemic cell immortalized with the Epstein-Barr virus

The intracellular state of the 30 viral genome equivalents of Epstein-Barr virus (EBV) DNA carried in latent form by the CII cell line, established from a chronic lymphocytic leukemia patient, has been partially characterized. The CII line, which has markers confirming its tumor origin, extends the analysis of the intracellular state of EBV DNA to include other, non-Burkitt lymphoid tumor cells. Monomer-size, free, circular EBV genomes, the major intracellular viral DNA species in other EBV-transformed cells, were absent or present in only minor amounts. Instead, EBV DNA sequences were found associated with a circular DNA form twice the size of the 110 x 10(6) Mr EBV genome. Though circular dimers of mtDNA have been found exclusively in human leukemic lymphocytes, the CII line is similar to normal cells in having only monomer-size mtDNA molecules, which can occur either singly or as catenated forms of two or more interlocking 5-micrometer mtDNA circles.