TNFSF13B and B-cell chronic lymphocytic leukemia: Co-culture of CLL cells with the combination of GFP-APRIL, GFP-BAFF and GFP-APRIL + CD40L fibroblasts for 24 h resulted in a significant additive effect on the phosphorylation signals of p38 MAPK (pT180/Y182) relative to co-culture with GFP-APRIL + CD40L fibroblasts only (Fig. 1g).