Effects of a phorbol ester on activation and immortalization of leukaemic B cells by Epstein-Barr virus

Immortalization of chronic leukaemic B cells by Epstein-Barr virus (EBV) was investigated. Immortalization resistant and susceptible cell populations were defined by chronic lymphocytic leukaemia (CLL) and prolymphocytic leukaemia (PLL) cells respectively. These cell types could be distinguished by the effects of a phorbol ester on [3H]-thymidine incorporation by EBV-infected cells. A synergistic effect was observed in the non-immortalizing CLL samples, whereas this response was inhibited in the immortalizing PLL. Under the conditions used in the study, TPA did not cooperate with EBV to immortalize CLL cells.

Activation and immortalization of leukaemic B cells by Epstein-Barr virus

We have studied the responses of chronic leukaemic B cells to infection by Epstein-Barr virus (EBV). Our results define one population of B lymphocytes, represented by prolymphocytic leukaemic (PLL) cells, which are highly susceptible to immortalization by EBV. Another B-cell type, represented by chronic lymphocytic leukaemic (CLL) cells, can be readily infected by the virus but is resistant to immortalization. Comparative studies of viral and cellular related events early after infection in these 2 cell types reveal that both express the EB viral nuclear antigen (EBNA) complex, but the immortalization-resistant CLL cells fail to express the latent membrane protein (LMP), which can be detected in PLL cells 48 hr after infection. Circularization of the linear viral genome could be detected at 7 days post infection in the PLL cells, but only in 2 out of 4 CLL cells tested. Both CLL and PLL cells show increased surface expression of CD23 and HLA-DR molecules after infection but, whereas PLL cells show an increase in size, together with RNA and DNA synthesis indicative of cell cycle progression, CLL cells appear to be arrested in the G1/S phase of the cycle. The results suggest that the outcome of infection by EBV is determined by the nature of the target cell rather than by random virus-related events. The correlation between the block in immortalization of CLL cells and their failure to express LMP suggests that expression of this protein is essential for in vitro immortalization of B cells. The failure to detect circularization in some EBV-infected CLL cells suggests that this, as well as LMP expression, may be dependent on prior activation of the B cell by EBV, an event which may vary between the different CLL samples tested.

Early events during the activation of human lymphocytes by the mitogenic monoclonal antibody OKT3

The effects of the mitogenic monoclonal antibody OKT3 on the metabolic changes preceding DNA synthesis during the activation of human peripheral blood mononuclear cells were compared with those induced by PHA. The aspects studied included uridine transport, the incorporation of inositol into phospholipids, Na+-dependent amino acid uptake, and protein synthesis. All four parameters were increased in response to the ligation of the T lymphocyte receptor recognized by OKT3. These changes were apparent as early as the corresponding changes induced by PHA. However, the increases in uridine uptake and inositol incorporation were disproportionately reduced when compared to those caused by PHA, and no evidence of high-dose inhibition was seen in cells activated by OKT3. This suggests that at least some lectin-induced changes in metabolism are mediated through additional mechanisms, probably involving distinct receptors.

Inhibition of proliferation of a murine myeloma cell line and mitogen-stimulated B lymphocytes by the antibiotic amphotericin B (Fungizone)

Amphotericin B at the concentration normally used for routine suppression of fungal infection in tissue culture strongly inhibits the proliferation of NS1/1 myeloma cells and the LPS-induced activation of B lymphocytes from mouse spleen. The proliferation of T lymphocytes induced by concanavalin A (Con A) was less affected by the antibiotic, indicating that B-lymphocyte proliferation was preferentially inhibited. The unexpected sensitivity of B-lymphoid cells to amphotericin B precludes its use as an anti-fungal agent in the production of hybridomas from fusions between these cells.