Gr-1hi monocytes infiltrate and proliferate in situ in ultraviolet irradiation–inflamed skin. Mice were treated as described in . (a,b) At 1 d after bead injection, all monocytes positive for fluorescein isothiocyanate–labeled beads are mainly Gr-1lo in the absence of clodronate treatment (a) but are Gr-1hi when beads are injected after mice are treated with clodronate-loaded liposomes (b). Data are representative of at least five separate experiments. (c) At 4 d after exposure to ultraviolet irradiation, bead-positive Gr-1hi but not bead-positive Gr-1lo monocytes are present in the skin. (d) Percent propidium iodide–negative CD45.1+ bead-positive cells that infiltrate the epidermis in Gr-1lo and Gr-1hi groups after exposure to ultraviolet irradiation. (e) Gr-1hi monocytes labeled with fluorescein isothiocyanate–positive beads before exposure to ultraviolet light are recruited to the skin, whereas Gr-1hi monocytes labeled with phycoerythrin-positive beads 4 d after exposure to ultraviolet light fail to enter the skin, suggesting that Gr-1hi monocytes do not enter the skin 4 d after skin injury. Numbers in quadrants, beside outlined areas and above bracketed lines indicate percentage of cells in each area. FITC, fluorescein isothiocyanate; FSC, forward scatter; PE, phycoerythrin; UV, ultraviolet. Data in c–e are representative of three separate experiments.