Bcl-6⁺ T cells induced by S. enterica infection are PD-1^lo and locate to the T–B border. (A and B) Immunofluorescence stains of spleen sections from C57BL/6 immunized 4 (A) or 35 d (B) previously with S. enterica. Boxed areas indicate the location of the zoomed-in images on the right, in the same order (from top to bottom). (C) Quantification of CD3⁺ Bcl-6⁺ PD-1^lo (left) and CD3⁺ Bcl-6⁺ PD-1^hi (right) cells in the T–B border and GCs at the indicated times after immunizations. (D) Representative flow cytometric plots showing PD-1 versus CXCR5 expression on effector/memory CD4⁺ CD44^hi cells from 80% Bcl6^−/− CD45.2:20% Cd28^−/− CD45.1 (Tc Bcl6^−/−) chimeras or control 80% Bcl6^+/+ CD45.2:20% Cd28^−/− CD45.1 (Tc Bcl6^+/+) fetal liver chimeric mice injected 7 d previously with S. enterica (green gate, non-Tfh effectors; blue gate, PD-1^lo Tfh cells; and red gate, PD-1^hi Tfh cells). These data are representative of two independent experiments with four mice per group in each cohort.