Development of plasma cell-prone germinal center B cells

Higher- or lower-affinity GC B cells are directed to plasma cell or recycling GC cell fates; however, how commitment to the plasma cell fate takes place is unclear. By using the level of Bcl6 as a marker, we found that a population of light zone (LZ) GC cells, Bcl6loCD69hi with IRF4 and higher-affinity BCRs or Bcl6hiCD69hi with lower- affinity BCRs, favored the plasma cell or recycling GC cell fate, respectively. Mechanistically, CD40 acted as a dose-dependent regulator for Bcl6loCD69hi cell formation. Furthermore, we found that ICAM1 and SLAM levels on Bcl6loCD69hi cells were higher than on Bcl6hiCD69hi cells, thereby affording more stable TFH-GC B cell contacts, while attenuating this contact down-regulated IRF4. These data support the model that commitment to the plasma cell begins in the GC, and suggest that stability and possibly duration of TFH-GC B cell contacts are key for formation of plasma cell-prone precursor GC cells. mRNA profiles of GC B cell subsets and GC-derived plasmablast were generated by barcode-based digital RNA sequencing.