Effect of cell-derived growth factors and cytokines on the clonal outgrowth of EBV-infected B cells and established lymphoblastoid cell lines.

Epstein-Barr virus (EBV) is a potent inducer of polyclonal B lymphocyte proliferation and is widely used as a tool for the establishment of B cell lines producing human monoclonal antibodies. However, because of low transformability, low clonability, and the inherent instability of EBV-infected B cells, valuable antibody-producing B cells are often lost during this procedure. We have here examined various cell-derived cytokines for their ability to enhance both the cellular outgrowth of newly infected B cells and the clonability of infected B cells and lymphoblastoid cell lines. Our results show that the murine thymoma cell line EL-4 is superior to peripheral blood mononuclear cells in both cellular outgrowth and cloning experiments, whereas monocyte-derived factors and monocyte cell lines were less capable than peripheral blood mononuclear cells in enhancing cellular outgrowth and cloning. Furthermore, the human T cell hybridoma cell line MP6 that secretes a B cell growth and differentiation factor, recently identified as an isoform of thioredoxin, is also capable of stimulating EBV-infected B cells and lymphoblastoid cell lines. Co-cultivation of EBV-infected B cells with MP6 cells significantly enhanced the cloning efficiency at the 1 cell/well level. The present results also suggest that one potential role of the MP6-derived thioredoxin could be the up regulation of IL-6 receptor expression in EBV-infected B cells.