Surface markers and size of lymphocytes in human umbilical cord blood stimulated into deoxyribonucleic acid synthesis by Epstein-Barr Virus

When Epstein-Barr virus persistently infects B-cell lines, it frequently integrates

In this study we used Gardella gel analysis of intact DNA, Southern blotting of digested DNA, and fluorescence in situ hybridization to provide complementary and unequivocal information on the state of the Epstein-Barr virus (EBV) genome in persistently infected cells. The fluorescence in situ hybridization technique allowed us to directly visualize both integrated and episomal EBV DNA at the single-cell level. We show here that circularization of the EBV genome is rarely detected upon infecting activated normal B cells. The virus can persist upon infection of a different proliferating B-cell target, EBV-negative Burkitt's lymphoma tumor cell lines. Analysis of 16 such lines reveal again, that the virus infrequently persists as covalently closed episomes; rather, the virus preferentially persists by integrating into the host DNA (10 of 16 clones). The integrated virus is linear and usually intact, although 3 of 10 isolates have deletions from the left-hand end including the latent origin of replication. At the level of our analysis, no obvious relationship was seen between the integration sites. These studies provide, for the first time, a reproducible in vitro model system to study integration by EBV.

Human monoclonal antibodies to influenza virus: IgG subclass and light chain distribution

Three adults and three children were immunized with inactivated or live attenuated influenza vaccines and 98 IgG monoclonal antibodies derived from EBV immortalization of their blood lymphocytes were studied. All antibodies reacted specifically with influenza A H3N2 or H1N1 whole virus and 73 of 74 tested reacted with the purified HA glycoproteins. The majority (76%) of 77 monoclonal antibodies adequately tested by ELISA or solid phase RIA contained lambda light chains. ELISA analysis of the IgG subclass of the six persons' postimmunization anti-influenza serum activity and of monoclonal antibodies derived from them showed a similar predominance of IgG1.

Isolation of a normal B cell subset with a Burkitt-like phenotype and transformation in vitro with Epstein-Barr virus

Epstein-Barr virus (EBV) is causally linked with endemic Burkitt's lymphoma (BL), a tumor whose homogeneous cell surface phenotype suggests derivation from a particular subset of activated germinal centre B cells in vivo. Endemic BL also shows an unusual form of EBV infection with down-regulation of certain of the virus latent proteins which are constitutively expressed when EBV infects and transforms normal resting B cells in vitro. Here we question whether this virus:cell interaction is unique to malignant BL cells or whether it might be reproduced by in vitro infection of those particular germinal centre cells displaying the BL-like phenotype. Firstly, we show by biochemical means that a subset of normal tonsillar B cells does indeed express the globotriaosylceramide glycolipid BLA and the common acute lymphoblastic leukaemia antigen CALLA, 2 important markers of the BL phenotype. Secondly, using 2-colour immunofluorescence labelling with anti-BLA and anti-CALLA monoclonal antibodies (MAbs), 4 subsets of low buoyant density tonsillar B cells (BLA+ CALLA+, BLA+ CALLA-, BLA- CALLA+, BLA- CALLA-) have been separated by means of a FACS and tested for their susceptibility to EBV-induced growth transformation in a limiting dilution assay. The BLA+ CALLA+ (i.e., BL-like) subset contained the highest proportion of cells already actively in cycle in vivo and gave the lowest yield of transformants, perhaps reflecting the greater efficiency with which EBV transforms resting target cells. Of the cell lines established from the BLA+ CALLA+ population, a significant number retained BLA expression but CALLA was always lost. In 2 further respects, these lines resembled conventional in vitro transformants rather than lines of BL type; thus the cells expressed cellular "activation" antigens (CD23, CD39, CD30, Ki-24) characteristic of the lymphoblastoid phenotype and contained the full spectrum of EBV latent proteins.

Nonrandom X chromosome inactivation in B cells from carriers of X chromosome-linked severe combined immunodeficiency

X chromosome-linked severe combined immunodeficiency (XSCID) is characterized by markedly reduced numbers of T cells, the absence of proliferative responses to mitogens, and hypogammaglobulinemia but normal or elevated numbers of B cells. To determine if the failure of the B cells to produce immunoglobulin might be due to expression of the XSCID gene defect in B-lineage cells as well as T cells, we analyzed patterns of X chromosome inactivation in B cells from nine obligate carriers of this disorder. A series of somatic cell hybrids that selectively retained the active X chromosome was produced from Epstein-Barr virus-stimulated B cells from each woman. To distinguish between the two X chromosomes, the hybrids from each woman were analyzed using an X-linked restriction fragment length polymorphism for which the woman in question was heterozygous. In all obligate carriers of XSCID, the B-cell hybrids demonstrated preferential use of a single X chromosome, the nonmutant X, as the active X. To determine if the small number of B-cell hybrids that contained the mutant X were derived from an immature subset of B cells, lymphocytes from three carriers were separated into surface IgM positive and surface IgM negative B cells prior to exposure to Epstein-Barr virus and production of B-cell hybrids. The results demonstrated normal random X chromosome inactivation in B-cell hybrids derived from the less mature surface IgM positive B cells. In contrast, the pattern of X chromosome inactivation in the surface IgM negative B cells, which had undergone further replication and differentiation, was significantly nonrandom in all three experiments [logarithm of odds (lod) score greater than 3.0]. These results suggest that the XSCID gene product has a direct effect on B cells as well as T cells and is required during B-cell maturation.

Frequency of B-lymphocyte transformation by Epstein-Barr virus decreases with entry into the cell cycle

The relationship between in vitro B-cell activation and transformation by Epstein-Barr virus (EBV) was studied. B cells were fractionated using discontinuous Percoll gradients to purify cells with resting morphology. Activation of resting cells for 24 hr with anti-Ig (mu chain specific) or Staphylococcus aureus Cowan I (SAC) resulted in transition of susceptible cells into the G1 phase of the cell cycle as shown by an increase in cell size, an increase in uridine incorporation and an increase in sensitivity to B-cell growth factor (BCGF). Entry into S phase was achieved by extending the period of activation to 48-96 hr with high concentrations of SAC or anti-mu or using BCGF. SAC-activated cells entered S phase on Day 2 and anti-mu treated cells on Day 3. Control (G0) cells and cell activated for varying lengths of time (G0/G1, G1/S) were exposed to EBV and plated in a limiting dilution assay to determine the frequency of EBV-transformable cells. Control cells and cells activated for 24 hr had a transformation frequency of 1-2%. With continued activation with SAC or anti-mu, however, transformation frequency decreased at a rate paralleling the entry of the population into S phase. Treating cells with low concentrations of anti-mu or SAC in combination with BCGF decreased the transformation frequency to levels lower than anti-mu or SAC alone, further suggesting that entry into S phase is accompanied by a reduction in transformability. These results indicate that resting B cells are highly susceptible to transformation, and that with in vitro activation into the cell cycle B cells become resistant to EBV transformation.

A routine method for the establishment of permanent growing lymphoblastoid cell lines

Permanent lymphoblastoid cell lines are of great practical value in human clinical and experimental genetics. A detailed protocol for routine use is given for the establishment of lymphoblastoid lines from peripheral blood using Epstein-Barr virus and the immunosuppressivum Cyclosporin A. In addition, the biologic basis of this transformation system is briefly summarized.

Epstein-Barr virus susceptibility of normal human B lymphocyte populations

Human blood and tonsil B lymphocytes were fractionated on density gradients and tested for virus binding and penetration into the cells. Epstein-Barr Virus (EBV) transformation was detected by immunofluorescence staining for EBV-determined nuclear antigen (EBNA). EBV bound to and penetrated all B cell populations, but only the high density populations were transformed. Activated B lymphocytes were found in the low density fractions and these cells were resistant to EBV infection. Infected and noninfected B lymphocytes were density-analyzed during in vitro culture. A spontaneous, not virus-induced, density decrease was found to precede the production of EBNA. Cells remaining at high density never expressed EBNA. The results suggest that EBV can transform only small resting B lymphocytes and that a virus-independent activation of the infected cells induces the EBNA production and transformation.