BCR and B-cell chronic lymphocytic leukemia: CLL cells with both Un-IgVH and high ZAP-70 expression show increased activation of proteins downstream of the BCR such as Akt, mitogen-activated protein kinase (MAPK), and NF-κB.4,6,7 This suggests that alterations in the BCR signaling pathway through increased expression of the tyrosine kinase ZAP-70 are important in CLL disease progression.