Figure 4.

Cell membrane expressed CD154 is a very effective mitogen for negatively purified B cells. (a) Proliferation of MLN B cell was induced by cell membrane expressed CD154, but not by vector control transfected L929 cells, with or without stimulation via sIg. The results are the average of triplicate cultures where the standard deviation was<10% of the mean. (b) Growth of MLN B cells is supported by cell membrane expressed CD154. Proliferating viable B cells were separated from cultures by gradient centrifugation each week, cell number was counted and then B cells (≈1·5×10⁶ cells/ml) were transferred to new flasks containing γ-irradiated cell membrane expressed CD154 cells. Growth of B-cell number (viable cells only) over 6 weeks is shown (b). Closed circles show the cell number per ml in culture and open circles show the total viable cell number in the cultures.