Mobilization of CD19⁺/CD27high/HLA-DRlow plasma cells after vaccination. In the course of TT/diphtheria vaccination, CD19⁺/CD27^high PBMCs were analyzed for their expression levels of HLA-DR. Living PBMCs were identified according to light scatter properties and PI (gating not shown). The expression level of HLA-DR on CD19⁺/CD27^high PBMCs, found in peripheral blood on day 0 (▦) and day7(▪) after immunization, is shown (A). According to the different expression level of HLA-DR found (A-B) CD19⁺/CD27^high PBMCs were classified in HLA-DR^low/HLA-DR^high (A). Recently generated PBs were identified as intracellular Ig⁺/HLA-DR^high PBMCs specific for rTT.C (B). Based on the enumeration of CD19⁺ lymphocytes by TruCount and flow cytometry, the numbers of recently generated PBs CD19⁺/CD27^high/HLA-DR^low (▪) and CD19⁺/CD27^high/HLA-DR^high PCs (▧) (as identified in panel A) from 3 healthy donors on days 0 and 7 after immunization were then calculated as shown in panel C.