Phenotype of rTT.C-specific plasma blasts. Differential expression of various Ags on rTT.C-specific PBMCs from a representative donor 6 days after TT booster immunization. Formaldehyde-fixed PBMCs were gated (A) and stained with anti-CD27 Cy5 mAb, biotinylated anti-CD19 mAb/SA PerCP, rTT.C-Dig, and anti-Dig PE in the presence of saponin. rTT.C-specific CD19⁺/CD27^high or CD19⁺/CD27^high PBMCs with undefined specificity were identified by gating as indicated in panels B and C. Forward scatter, indicating the cell size, expression of HLA-DR, CD20, CD38, CD95, or intracellular IgG is shown for rTT.C-specific CD19⁺/CD27^high (▦) or CD19⁺/CD27^high PBMCs with undefined specificity (▪) (D-I). MFIs are indicated by the numbers in the top corners.