Notch2 amplification of B cell division and differentiation fates

Abstract The efficiency with which B cells respond to activation signals varies depending on the subset. Whereas marginal zone (MZ) B cells exhibit rapid activation kinetics following stimulation, follicular (FO) B cells adopt delayed effector programs. The development and maintenance of MZ B cells uniquely requires signaling through transmembrane receptor family member Notch2, but whether this signal underlies distinctive response patterns among B cell subsets is not known. To examine the functional consequences of Notch2 signals on B cells with no Notch requirement, we cultured FO B cells on Notch2-ligand expressing OP9 stromal cells and subsequently stimulated them. Notch2-experienced FO B cells displayed a marked enhancement of several aspects of proliferation, including two-fold more rounds of division. Further, sensitivity to BCR cross-linking was enhanced by this signal, enabling cell cycle entry earlier and in response to lower concentrations of anti-BCR. Additionally, Notch2 signals modified responses to TLR stimuli Poly(I:C) and LPS by amplifying the time to first division and the propensity to become a plasma cell. Intriguingly, TLR3 responsiveness appeared to be an entirely Notch2-dependant mechanism. Employing a published mathematical model for dividing lymphocytes, we found Notch2 amplified the division destiny of both graded and quantal patterns of B cell responses. We next examined the timing and magnitude of Myc induction, a mitotic regulator and known Notch target. Remarkably, Myc levels prior to the first division appeared to be a direct predictor of division destiny. Together these observations highlight a novel role for Notch2 in modifying two distinct response patterns and their respective outcomes for B cells. Supported by grants from NIH (T32-AI00763,R01 AI139123,T R01 AI154932)