WT CD8⁺ T cells form clusters in the MZ of spleen early in the expansion phase. Spleen sections of mice that received a 1:1 mixture of CD45.1⁺ CXCR3^−/− and CD90.1⁺ WT OT-I cells (∼1–3 × 10⁶ cells total) and were infected with VV-OVA were analyzed by immunofluorescent staining. The splenic compartments are represented as follows: T, T cell zone; B, B cell zone; bold dashed line, WP–RP border; thin dashed line, T cell–B cell zone border. Bars, 50 µm. (A and B) Sections were stained for CD90.1 (red, WT OT-I), CD45.1 (green, CXCR3^−/− OT-I), and type IV collagen (blue). Arrows indicate clusters of WT OT-I cells. (B) Representative section from day 2 showing distribution CXCR3^−/− and WT OT-I cells around T cell zone. (C) Ratio of OT-I cells in MZ/RP to those in WP. Data are shown as mean ± SEM. *, P < 0.01. (D) Sections were stained for CD11c (red), OT-I cells (green), and type IV collagen (blue) at day 2 after infection. (E) Sections were stained for CXCL9 (red), OT-I cells (green), and type IV collagen (blue) at day 2 after infection. (F) Sections were stained for IL-12p40 (red), OT-I cells (green), and type IV collagen (blue) at day 2 after infection. Data represent two (A–E) or three (F) independent experiments (n = 3–4 per time point).