B-Cell Receptor Signaling

The B-Cell Receptor (BCR) signaling pathway involves a complex cascade of events initiated by antigen binding. The signaling pathway begins with the assembly and activation of a crucial molecular complex called the signalosome It is governed by numerous genes that encode the receptor itself, associated signaling molecules, adaptor proteins, kinases, and downstream transcription factors. The core of the BCR complex is the membrane-bound immunoglobulin (which binds the antigen), non-covalently associated with a signaling heterodimer responsible for signal transduction. CD79a molecule contains an ITAM (Immunoreceptor Tyrosine-based Activation Motif) for signal initiation. CD79b molecule contains a second ITAM for signal initiation. Src family tyrosine kinase A phosphorylates the ITAMs on CD79A/B upon antigen binding, initiating the cascade.Other Src-family kinases with similar roles in initial ITAM phosphorylation. Phosphorylated ITAMs recruit the SYK kinase, forming the signalosome, a critical hub that amplifies and branches the signal.