The B cell antigen receptor (BCR) promotes the selective survival or population expansion of germinal-center (GC) B cells of higher affinity, but how this occurs is unclear. In Science, Shlomchik and colleagues show that proliferating GC B cells are refractory to BCR signaling because of enhanced phosphatase activity. GC B cells have less phosphophorylation of the proximal tyrosine kinases Syk and BLNK than do non-GC or naive B cells. This is due to greater activation of the tyrosine phosphatases SHIP-1 and SHP-1, which also show enhanced association with the BCR at steady state and after activation. The diminished signaling ability of GC B cells suggests that the GC BCR may favor antigen presentation over signaling and that the survival advantage of cells with high-affinity BCRs is due to more effective capture of antigen, followed by more efficient competition for T cell–dependent signals.

Science (3 May 2012) doi:10.1126/science.1213368