Kinetics of rTT.C-specific CD19⁺ B cells after TT vaccination. The kinetics of the appearance of CD27high or CD27⁺ cells specific for rTT.C in blood, of a representative donor, demonstrates the sequential release of PBs and memory B cells. The rTT.C-specific CD19⁺ B cells at day 0 or days 4, 6, 8, and 11 after booster immunization with TT were identified by labeling of Ag-specific B cells with rTT.C-Dig and anti-Dig FITC. Staining of viable CD19⁺ PBMCs with anti-CD27 Cy5 mAb, rTT.C-Dig, and anti-Dig FITC is shown. Percentages of CD19⁺ B cells are indicated.