Signal transduction by the B-cell antigen receptor (BCR) regulates development, survival, and clonal expansion of B cells. The BCR complex comprises the membrane-bound immunoglobulin molecule and the Ig-α/Ig-β heterodimer, and was shown to form oligomeric structures. Antigen-mediated engagement of the BCR results in the tyrosine phosphorylation of multiple signaling proteins leading to calcium mobilization and the activation of downstream serine/threonine kinases as well as transcription factors. In pervanadate (PV)-treated B cells, comparable pathways are activated on expression of the BCR, indicating that the BCR can signal in an antigen-independent fashion as well. In this chapter, we describe the analysis of antigen-dependent and -independent tyrosine phosphorylation events as well as a method to study calcium mobilization from differentially stimulated B cells. Furthermore, we emphasize the use of phospho-specific antibodies (Abs) and low-molecular-weight enzyme inhibitors in the process of mapping BCR-activated signaling pathways as well as determining activation states of signaling proteins.
