Host LCs are required for licensing CTLs recruited to the skin epidermis. [B6 + BALB/c] →Langerin.DTR/GFP MCs were treated topically with imiquimod (Imq) and with or without DT by intraperitoneal injection on day −2 and day 4 after donor splenocyte transfer. (A) Absolute numbers of Thy1.1⁺ CD62L^low CD4 or CD8 cells in the skin draining LN (n = 8 or 9 mice per group); data pooled from 4 independent experiments. The mean is indicated by the horizontal bar. (B) Summary data showing accumulation of total Thy1.1⁺ cells (left) or Thy1.1⁺ CD8 cells (right) in the epidermis of imiquimod-treated MCs, with DT or PBS (n = 8 or 9 mice per group); data pooled from 4 independent experiments. The mean is indicated by the horizontal bar. (C) Representative contour plots showing frequency of GFP-expressing cells (representing host LCs) and of Thy1.1⁺ cells in epidermal suspensions derived from imiquimod-treated MCs after splenocyte transfer, and after DT or PBS. (D) Thy1.1⁺ CD8 cells were flow-sorted on day 14 from pooled skin epithelia of imiquimod-treated MCs given DT or PBS. Graphs represent mean plus or minus SD mRNA quantification for each transcript in the DT and control groups compared with glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL; n = 3 or 4 mice per group per experiment); data pooled from 3 independent experiments. *P < .05.