CX3CR1⁺ LPC and CD103⁺ DC display different responsiveness to Flt3L and GM-CSF in vivo. Melanoma cells secreting Flt3L or GM-CSF were injected subcutaneously into CX3CR1^+/GFP mice and animals were sacrificed 6–12 d later. (A) 12 d after injection of Flt3L-secreting tumor cells, confocal microscopy revealed massive expansion of intestinal CD103⁺ DC but not CX3CR1⁺ LPC. Images show representative stainings for CX3CR1/GFP (green), CD103 (red), and CD11c (blue). The boxed region in split channels is shown on the bottom. Arrowheads indicate CD11c⁺CD103⁺ LP DC and arrows mark CD11c⁻CD103⁺ cells, most likely representing T cells. Three mice were analyzed in three independent experiments. Bars, 20 µm. (B) The total number of isolated CD103⁺ DC, CX3CR1^high LPC, and CX3CR1^int LPC in tumor-bearing mice was determined by flow cytometry. Mean (SD) is shown of at least six mice per group analyzed in two (GM-CSF) and three (Flt3L) independent experiments. Results were obtained with an unpaired Student's t test. **, P < 0.01; ***, P < 0.001.