Dermal mast cells activated via TLR7 are critical for the early onset of inflammation and promote emigration of LCs. (A) Total RNA from BMMCs and c-Kit⁺GFP⁺ dermal mast cells isolated from 4get mice was analyzed for the expression of the indicated mRNA species. BMMCs were left untreated or incubated in the presence of 10 μg/mL imiquimod for 16 hours. c-Kit⁺GFP⁺ cells were isolated from naive mice or following daily topical treatment with imiquimod on 2 consecutive days. HGPRT served as housekeeping gene transcript and mouse mast-cell protease 4 as positive control expressed by connective tissue–type mast cells.³³  Representatives of 3 independent experiments with equivalent results. (B) Ears of wild-type (Kit^+/+), mast-cell–deficient (Kit^W-sh/W-sh), and mast-cell–deficient mice that had previously been reconstituted (indicated by an arrow) with BMMCs from either wild-type or TLR7-deficient mice were treated daily with imiquimod (starting on day 0). The contralateral ear of each animal was treated with vehicle. Ear swelling was measured and the indicated values refer to the ear thickness at the beginning of the experiment. (C) At the end of the experiment shown in panel B, epidermal sheets were prepared and stained for MHC class II⁺ LCs. The values shown for LC migration refer to the reduction in LC numbers compared with the untreated contralateral ears. (D) Epidermal sheets from Kit^+/+ and Kit^W-sh/W-sh mice were stained for LCs on day 7 after daily treatment with imiquimod. Shown are the means (± SD) from 4 to 5 mice per condition. *P < .01 versus Kit^+/+.