T lymphocytes are known to obtain polarity cues from antigen-presenting cells and to undergo asymmetric division and diversification of daughter cell fates. In Science, Reiner and colleagues show that germinal center B cells asymmetrically segregate the transcription factor Bcl-6, the receptor for interleukin 21 (IL-21R) and the polarity protein PKC-ζ between daughter cells. These three proteins segregate together in all asymmetric divisions and seem to be inherited by the daughter cell that arises from the side of the B cell proximal to the follicular helper T cell. Asymmetrical segregation is enhanced by CD40 signaling and is impaired in the absence of the adhesion molecule ICAM-1. B cells undergoing homeostatic division in unimmunized mice show infrequent polarity. The fate of the daughter B cells that arise from asymmetric divisions during the germinal center reaction remains to be investigated further.

Science (15 December 2011) doi:10.1126/science1213495