Fig. (4) Growth curves of the established cell lines (GDLBGCB1 and GDLB-GCB2) in the presence or absence of IL-4 and CD40L stimulation. Removal of IL-4 (●) from the system consisting of CD40L⁺3T3 and IL-4 containing medium (♦) resulted in cell growth arrest. Proliferation of tumor cells also decreased in medium only (Ɨ) or medium containing IL-4 (Ж). Addition of anti-CD40 blocking antibody to this culture system inhibited the proliferation of these cell lines (▲)(Δ), and proliferation of the cells from GDLB-GCB2 was inhibited in a concentration-dependent manner. Each condition was repeated in duplicate, and the cell number was counted two times in each well on days 3, 6 and 9. One case (GDLB-GCB2) was counted until day 12. Abbreviation: IL-4, interleukin-4; CD40L, CD40 ligand; CD40L⁺3T3, NIH Swiss mouse embryonic fibroblast cell line transfected with CD40L.