Fig. (1) IL4 and CD40L co-stimulation induced short-term proliferation of B cells in vitro from healthy volunteers. CD40L+3T3 stimulating cells and IL-4 induced normal B-cell proliferation for about three weeks. Cells proliferated to about 110 to 120-fold until day 20 and then cell growth ceased on day 26. Abbreviation: IL-4, interleukin-4; CD40L, CD40 ligand; CD40L⁺3T3, NIH Swiss mouse embryonic fibroblast cell line transfected with CD40L.