CD40LG and B-cell chronic lymphocytic leukemia: Because our findings indicate that only IgM BCR amounts and aggregation into high-density regions — parameters linked with BCR signaling — associate with in vivo clonal BRs (Figure 1 and Supplemental Figure 3F) and cellular changes associated with BCR signaling (Figures 2 and 3 and Supplemental Figures 4 and 5), we investigated whether autonomous BCR signaling, which is expected to be an ongoing event in CLL clones, differed for the IgM and IgD isotypes.