Essential Immunoregulatory Role for BCAP in B Cell Development and Function

BCAP was recently cloned as a binding molecule to phosphoinositide 3-kinase (PI3K). To investigate the role of BCAP, mutant mice deficient in BCAP were generated. While BCAP-deficient mice are viable, they have decreased numbers of mature B cells and B1 B cell deficiency. The mice produce lower titers of serum immunoglobulin (Ig)M and IgG3, and mount attenuated responses to T cell–independent type II antigen. Upon B cell receptor cross-linking, BCAP-deficient B cells exhibit reduced Ca2+ mobilization and poor proliferative responses. These findings demonstrate that BCAP plays a pivotal immunoregulatory role in B cell development and humoral immune responses

Transient Receptor Potential 1 Regulates Capacitative Ca2+ Entry and Ca2+ Release from Endoplasmic Reticulum in B Lymphocytes〉

Capacitative Ca2+ entry (CCE) activated by release/depletion of Ca2+ from internal stores represents a major Ca2+ influx mechanism in lymphocytes and other nonexcitable cells. Despite the importance of CCE in antigen-mediated lymphocyte activation, molecular components constituting this mechanism remain elusive. Here we demonstrate that genetic disruption of transient receptor potential (TRP)1 significantly attenuates both Ca2+ release-activated Ca2+ currents and inositol 1,4,5-trisphosphate (IP3)-mediated Ca2+ release from endoplasmic reticulum (ER) in DT40 B cells. As a consequence, B cell antigen receptor–mediated Ca2+ oscillations and NF-AT activation are reduced in TRP1-deficient cells. Thus, our results suggest that CCE channels, whose formation involves TRP1 as an important component, modulate IP3 receptor function, thereby enhancing functional coupling between the ER and plasma membrane in transduction of intracellular Ca2+ signaling in B lymphocytes