BCR signaling and downstream pathways. The BCR consists of a surface transmembrane Ig receptor associated with the Ig alpha (Igα, CD79A) and Ig beta (Igβ, CD79B) chains. BCR signaling in response to antigen binding induces LYN- and SYK-dependent phosphorylation of tyrosine motifs (phosphorylation denoted by “P” in yellow circle) on CD79A and CD79B. Several protein tyrosine kinases (red symbols) and the lipid kinase PI3Kδ (green symbol) transmit survival and proliferation signals and regulate cell maturation and migration. Small-molecule inhibitors of select kinases in the BCR pathway that have demonstrated significant clinical activitgips2 indAR ed.