PRDM1 and influenza: Because we had shown previously that Blimp-1+ B-1PC have reduced or absent CD19-expression (Savage et al., 2017) and found here that these cells are present after influenza infection (Figure 1A–B) and often lacked CD5-expression (Figure 1C), we expanded the analysis to include all IgMb-expressing (B-1 donor-derived) and IgMa negative (recipient-derived) cells, regardless of expression of CD19 or other surface markers (Figure 1H).