Cutting Edge: Recruitment of the CD19/CD21 Coreceptor to B Cell Antigen Receptor Is Required for Antigen-Mediated Expression of Bcl-2 by Resting and Cycling Hen Egg Lysozyme Transgenic B Cells

Abstract

Recruitment of the CD19/CD21 coreceptor is thought to lower the threshold for effective signaling through the B cell Ag receptor. We provide evidence supporting a second role for coreceptor recruitment, and that is to enhance the survival/proliferative potential of the responding B cells. We show that B cell Ag receptor signaling in the absence of coreceptor recruitment induces cellular accumulation of the anti-apoptotic protein Bcl-xL, whereas CD19-mediated signals are required for Bcl-2 accumulation. The expression of both anti-apoptotic proteins correlates with the enhanced responsiveness of both resting and cycling B cells to growth-promoting signals delivered through CD40. These results provide further evidence for the necessity of coreceptor recruitment during Ag-dependent B cell activation and indicate that Ags derived from inflammatory sites function as better thymus-dependent Ags than their counterparts not coated with complement fragments.