Fig. 5. Memory CD8⁺ T cells arrest upon cognate Ag recognition presented by DCs but not CCR2⁺Ly6C⁺ monocytes.

(A) Ccr2^CFP mice cotransferred with naïve OT-I Td⁺ and gBT-I GFP⁺ cells and immunized with 10⁴ Lm-Ova-gB were challenged ~6 weeks later with 10⁶ Lm-Ova, and spleens from live mice were exposed and imaged 16 hours later using IVM imaging. A representative image (left) of OT-I (red) and gBT-I (green) T_M cell localization in a cluster (white dotted line) of CCR2⁺Ly6C⁺ monocytes (blue) is shown. Autofluorescence appears in yellow. Also shown (center and right images) are OT-I T_M cell tracks (outside, red and inside, yellow) and gBT-I T_M cell tracks (outside, green and inside, purple) inside/outside the same cluster of CCR2^CFP monocytes. Graphs represent the speed of individual OT-I and gBT-I T_M cells in the monocyte cluster area (left) and inside/outside the cluster. (B and C) Lethally irradiated (1200 rads) B6-K^d recipient mice were reconstituted with (B) B6-K^d or WT B6 (K^b) and Ccr2^DTR K^d BM or (C) Cd11c^DTRK^d or K^d and WT B6 BM. Six weeks after reconstitution, mice were immunized with 10⁴ Lm-gB (B) or Lm-Ova (C) and, 6 weeks later, challenged with 10⁶ Lm-gB 12 hours after DT treatment. Endogenous CD8⁺ T_M cells were monitored using LLO_91–99/K^d, gB_498–505/K^b, or Ova_257–264/K^b Tet. Graphs show the expression of CCL3 and IFNγ among Tet⁺ cells after challenge. Each symbol corresponds to one individual mouse in one of two replicate experiments, and P values are shown. *P < 0.1, **P < 0.01, ***P < 0.001, and ****P < 0.0001.