Skin sections were stained with H&E and the epidermal thickness was determined by measuring the average interfollicular distance under the microscope in a blinded manner. For IHC staining, skin cryosections were fixed, blocked, and stained with rat-anti-mouse Gr-1 mAb (1:50) followed by goat-anti-rat IgG secondary Ab (1:200, Southern Biotech) 4 (link). Slides were developed with 3-amino-9-ethylcarbazole (AEC) substrate solution (Vector Laboratories) and counterstained with hematoxylin. Images were acquired at x200 magnification using Aperio ScanScope digital scanners.