To investigate which of these signaling mechanisms dominate activation of NF-κB and Bcl-XL in CLL, we stimulated primary CLL cells with either CD40L-transfected 3T3 fibroblasts (3T40), CpG to activate TLR9, or IL-4 combined with anti-IgM to activate BCR signalling25 (Fig. 1A). Here, CD40LG is linked to B-cell chronic lymphocytic leukemia.