CXCR3, CXCR4, and CCR9 expression on CD19⁺/CD27high PBMCs. Expression of CXCR3, CXCR4, and CCR9 on CD19⁺/CD27^high PBMCs specific for rTT.C (black line) or of undefined specificity (gray line) of 1 representative donor, analyzed 7 days after immunization. rTT.C-specific PBs were identified by gating on formaldehyde-fixed CD19⁺/CD27^high PBMCs (B) stained in the presence of saponin with rTT.C-Dig (A). Frequencies of CXCR3, CXCR4, and CCR9 expressing CD19⁺/CD27^high PBMCs specific for rTT.C (▦) or of undefined specificity (▪) are shown (C-E). Donor 1, C, E, G; donor 2, D, F, H. Percentages indicate frequencies of cells that express the respective markers.