Host LCs are required for the development of TLR-induced cutaneous GVHD. (A) Lethally irradiated Langerin.DTR/GFP mice were reconstituted with a mix of B6 and BALB/c BM, 8 weeks before infusion of 3 × 10⁷ BALB/c Thy1.1⁺ splenocytes. DT or PBS was given intraperitoneally to recipient mice on day −2 and day 4 after splenocyte transfer. MCs were treated topically with imiquimod (Imq) or nil on day 0, day 5, and day 10. (B) Left: Representative contour plots showing depletion of CD11b⁺ GFP⁺ recipient LCs from the epidermis of imiquimod-treated MCs at day 14. Right: Summary data showing the percentage of CD11b⁺ GFP⁺ cells in the epidermis of MCs at day 14, with or without DT and with or without imiquimod (n = 7-9 mice per group); data pooled from 4 independent experiments. **P < .01. ***P < .001. The mean is indicated by the horizontal bar. (C) Summary data of histologic GVHD score as evaluated single blind (n = 5 mice per group); data pooled from 2 independent experiments. *P < .05. **P < .01. The median is indicated by the horizontal bar. (D) Photomicrographs of representative histologic sections (original magnification ×200) of skin histology on day 14 in imiquimod-treated [B6 + BALB/c] → Langerin.DTR MCs given DT or control.