Figure 4. Detection and localization of Se epitope-specific T cells using an adoptive transfer system.

(A) CD4⁺ memory T cells (2.5 × 10⁶) from CD45.1⁺ B6 × 129 F1 mice infected intravenously with 10⁸ Listeria monocytogenes-ΔactA (Lm) or intragastrically with 10⁸ Se bacteria 30 days earlier were transferred into CD45.2⁺ B6 × 129 F1 recipients. Five mice received Lm-primed memory cells, five received Se-primed memory cells, and nine did not receive any cells. All recipients were challenged intravenously with 10⁴ Se-Tomato bacteria. Mean splenic CFU (± geometric S.D.) were measured seven days later and analyzed by one-way ANOVA, with Tukey’s multiple comparisons post-test (**** p < 0.0001). The results are derived from two independent experiments. (B)Representative flow cytometry plots of splenic T cells from mice that received Lm-primed (middle), Se-primed (right), or no (left) CD45.1⁺ CD4⁺ memory T cells and were challenged with Se-Tomato bacteria seven days earlier. Mean fold expansion (± S.D.) of transferred cells over controls that received T cells but were not infected is shown in the bar graph. Unpaired student’s T-test was used to compare the responses of the two memory T cell populations (**** p < 0.0001). (C) Spleen sections from a B6 × 129 F1 (CD45.2⁺) mouse that received CD45.1⁺ memory CD4⁺ T cells from CD45.1⁺ Se-infected donors and was challenged intravenously with Se-Tomato bacteria seven days earlier. Sections were stained with the indicated antibodies. Part of the image in the white box is shown enlarged. Scale bars are included on each panel. (D)Quantitative analysis as described in the legend to Figure 3E but applied to images of transferred CD45.1⁺ CD4⁺ T cells from eight different recipient mice. (*** p≤ 0.0004).