Harvested spleens were processed and stained with antibodies. CD23+IgD+ cells were sorted on a BD FACsAria Fusion. 50,000 cells were used for library preparation. Cells were lysed, then treated with transposition mix (Nextera DNA Sample Preparation Kit) for 30 min at 37 degrees. Library fragments were amplified with 1x NEB Next PCR Master Mix and custom Nextera PCR primers. The number of cycles of PCR amplification was determined by q-PCR. 300-800 bps of libraries were selected using SPRI beads. Libraries were sequenced on a HiSeq 4000 system as paired-end reads.