From plasmablasts to mature PCs. (A) Schematic representation of the 800 genes that were statistically differentially expressed between plasmablasts and the 2 mature PC populations with a ratio of mean expression greater than 2. Relevant genes that were statistically differentially expressed between PPCs and mature PCs but with at least one ratio of mean expression less than or equal to 2 are indicated in parentheses. PBB indicates peripheral blood B cells; TBC, tonsil B cells; TPC, tonsil plasma cells; BMPC, bone marrow plasma cells; and PPC, polyclonal plasmablastic cells. (B) Expression of ILT3 and granzyme B mRNA was studied by RT-PCR on purified CD19⁺ PBB cells, on CD20^-/CD38⁺⁺ sorted PPCs, and on purified CD138⁺ BMPCs. (C) Quantitative RT-PCR confirms SDF1 and MER expression in BMPCs. SDF1 expression in stromal cells and MER expression in monocytes are used as standards. SDF1 and MER transcripts are undetectable in PPCs.