Macrophages and fibroblasts mediate intracellular collagen degradation in vivo. (A) High magnification image of the dermis of a collagen-injected Cx3cr1-GFP transgenic mouse. Example of endocytic vesicle containing collagen and Texas red dextran shown with arrows in a GFP-positive cell demonstrates intracellular collagen degradation by macrophages. (B) Representative high-magnification image of the dermis of a collagen-injected Col1a1-GFP transgenic mouse (GFP-tagged fibroblasts). Example of endocytic vesicle containing collagen and Texas red dextran shown with arrows in a GFP-positive cell demonstrates intracellular collagen degradation by fibroblasts. Bars: (A) 10 µm; (B) 5 µm. (C) Percentage of cells internalizing collagen that are GFP negative and GFP positive in collagen-injected Cx3cr1-GFP transgenic mice. (D) Percentage of Cx3cr1-GFP–positive cells displaying or not displaying intracellular collagen. n = 4 for collagen-injected Cx3cr1-GFP mice. (E) Cell counts in noninjected or collagen-injected dermis, as determined by the counting of Cx3cr1-GFP–positive and GFP-negative cells in z stacks from the injection field. n = 5 for uninjected mice, and n = 4 for collagen-injected mice. (F) Percentage of cells internalizing collagen that are GFP negative and GFP positive in collagen-injected Col1a1-GFP transgenic mice. (G) Percentage of GFP-positive cells displaying or not displaying intracellular collagen. n = 4 for collagen-injected Col1a1-GFP mice. (H) Cell counts in noninjected or collagen-injected dermis, as determined by the counting of Col1a1-GFP–positive and GFP-negative cells in z stacks from the injection field. n = 3 for uninjected mice, and n = 3 for collagen-injected mice. Data are shown as means ± SD.