Differential inhibition of downstream BCR signaling pathways by SYK, BTK, and PI3Kδ inhibitors. (A) CLL cells were preincubated for 2 hours with 1 μM of the indicated BCR inhibitor and then stimulated for 10 minutes with 10 μg/mL soluble goat F(ab′)2 anti-human IgM (sol-aIgM). Cellular extracts were prepared and analyzed by immunoblotting with the indicated antibodies. One representative experiment is shown. Ibr, ibrutinib; Idel, idelalisib. (B) CLL cells were preincubated with 1 μM of the indicated inhibitors and stimulated for 10 minutes with sol-aIgM or 24 hours with imm-aIgM. One representative experiment out of 4 is shown. (C) CLL cells were stimulated with sol-aIgM or imm-aIgM in the presence or absence of the indicated inhibitors (1 μM) and then analyzed as in panel A. One representative experiment out of 3 is shown. (D) CLL cells were preincubated with 1 μM of R406, Ibr, or Idel and stimulated for 24 hours with imm-aIgM prior to harvesting and analysis of β-catenin expression.