L. major–specific T_RM cells enhance T cell recruitment after challenge with L. major. Splenocytes from L. major (A–C) or LCMV (D) immune mice were CFSE labeled to track them after transfer. They were injected i.v. into either naive or L. major–immune mice (20 wk after infection) that were then challenged with L. major or PBS in the flank. Recruitment of cells to the challenge site was assessed 20 h later. (A) Representative flow plots of CFSE⁺ CD4⁺ T cells comparing the blood and the flank in naive or immune mice challenged with L. major. (B) Frequency and number of transferred L. major immune CD4⁺ and CD8⁺ T cells in the blood and flank skin of naive and immune mice 20 h after challenge with L. major. (C) Frequency and number of transferred L. major–immune CD4⁺ T cells 20 h after challenge with L. major or injection of PBS in naive or immune mice. (D) Frequency and number of transferred LCMV immune lymphocytes in the blood and flank skin of naive and immune mice 20 h after challenge with L. major. (E) L. major–immune mice were treated with anti-CD4 mAb, and the frequency of CD4⁺ T cells in the skin of untreated or anti-CD4–treated immune mice is shown. (F and G) Naive L. major–immune or L. major–immune mice treated with anti-CD4 mAb (F) or anti-CXCR3 mAb (G) received CFSE-labeled splenocytes from immune mice, and were then infected in the flank with L. major. After 20 h, the frequency and number of the transferred cells in the blood and flank was determined. (H and I) Flank skin from naive or immune mice was grafted onto the flank of naive mice. After 7 d, the recipient mice were injected i.v. with CFSE-labeled immune cells, each graft was infected with L. major, and, 20 h later, cells were isolated from the grafts. (H) Representative flow plots of CFSE⁺ CD4⁺ T cells comparing the blood and naive or immune skin grafts challenged with L. major. (I) Frequency and number of transferred L. major–immune CD4⁺ T cells in naive or immune skin grafts (cells were gated on live, CD45, CD90.2, CD4 cells). All data are from one representative experiment of two or more with three or more mice per experiment, and each bar represents the mean (±SEM) of individual mice (A–G) or combined data from two experiments where each dot represents a mouse (H and I). Immune mice used in all these experiments were 14 to 20 wk after infection. *, P < 0.05; **, P < 0.01; ***, P < 0.001.