Coexistence of HLA-DR^high plasmablasts and HLA-DR^low plasma cells in steady state. (A) Intracellular Ig^high plasmablasts/plasma cells circulating in steady state were stained for CD62L and β₇ integrin and counterstained for HLA-DR or Ki-67. Plasma cells lacking Ki-67 expression and stained weakly for HLA-DR were also β₇ integrin⁻/CD62L⁻ (gray gate represents histograms and MFI ± SD values), whereas high expression of HLA-DR and Ki-67 on plasmablasts was associated with expression of CD62L or β₇ integrin (black gate represents histograms and numbers). (B) CD38^high bone marrow plasma cells were counterstained for CD62L, β₇ integrin, Ki-67, HLA-DR (open histograms), and isotype controls (shaded histograms), revealing absence of CD62L and Ki-67 expression, a small subset of HLA-DR^high cells, and expression of β₇ integrin. The insert shows bone marrow mononuclear cells (Ki-67, open; control, shaded) positively stained for Ki-67. (C) PBMCs isolated 7 days after tetanus/diphtheria vaccination were migrated toward 10 nM of CXCL12. Migrated icIg^high plasmablasts (black) and nonmigrated icIg^high plasmablasts/plasma cells (gray) and their HLA-DR expression were detected cytometrically. Three different donors are shown.