Cell phenotype (CD23)‐dependent variation in EBV genome copy numbers within lymphoblastoid cell lines (LCL)

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Abstract
Three Epstein‐Barr‐virus‐transformed lymphoblastoid cell lines (LCL) were analysed on the basis of their CD23 expression. Levels of EBV‐DNA were compared in the positive and negative subpopulations. Two lines were further analysed with regard to EBNA, cytoplasmic immunoglobulin (clg) and lytic (EA/VCA) protein expression. Both subpopulations had a similar MHC class‐11 transcription, but the CD23− subpopulation had a lower plating efficiency and a lower rate of DNA synthesis. In the B6, NAD50 and 0467.3 cell lines, CD23− cells contained 2 ± 0.2–6.4 ± 3.0 times less EBV DNA than the corresponding CD23+ population. EBNA was expressed in 81 ± 4.2%‐93 ± 3.8% of the CD23+ cells and in 0–46 ± 8.0% of the CD23− cells. No CD23+ cells in B6 or NAD50 contained any EA/VCA, while 19 ± 2.8%‐24 ± 4.2% of the CD23− cells were positive for the lytic‐cycle‐associated antigens. Of the CD23− cells, 70 ± 8.6%‐86 ± 6.0% were positive for cytoplasmic immunoglobulin compared to 14.7 ± 2.7%‐14.9 ± 1.8% in the corresponding CD23+ population. We have previously shown that only 18% of the clg‐positive cells were EBNA‐positive in the B6 line compared to 94% in the clg population. This was open to 2 alternative interpretations: loss of EBV genomes from a fraction of the cells with subsequent differentiation to secretory immunoglobulin production, or down‐regulation of EBNA expression in differentiating, EBV‐genome‐positive cells. Our present findings speak for the first alternative, indicating that a certain proportion of the cells may lose their EBV genomes in both long‐established and freshly transformed LCLs. This is accompanied by a reduced percentage of EBNA‐positive cells, the disappearance of at least one activation marker (CD23) associated with the virally induced blast transformation, and an increased synthesis of clg.

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