Fibroblast cell counts in renal tissues after UUO (8). Several different groups of kidneys were compared to determine the relative contributions of each to the source of fibroblasts. Forty to 80 random high-power fields in cortical kidneys were counted for FSP1⁺ fibroblasts, EMT-derived LacZ⁺ fibroblasts, or GFP⁺ fibroblasts, depending on the group. Mean fibroblast counts are represented by a horizontal line in each column: 12% of normal resident fibroblasts in the kidney come from bone marrow (number of FSP1⁺, GFP⁺ fibroblasts from normal, chimeric recipient kidneys divided by the number of FSP1⁺, GFP⁺ fibroblasts from FSP1.GFP⁺ donor kidneys); local EMT as a source is rare in the absence of fibrogenic stress (number of FSP1⁺, LacZ⁺ fibroblasts from normal kidneys divided by the number of FSP1⁺ fibroblasts from normal kidneys); and during experimental fibrosis, local EMT (number of FSP1⁺, LacZ⁺ fibroblasts from UUO kidneys divided by the number of FSP1⁺ fibroblasts from UUO kidneys) and bone marrow (number of FSP1⁺, GFP⁺ fibroblasts from UUO, chimeric recipient kidneys divided by the number of FSP1⁺ fibroblasts from UUO kidneys) contribute 36% and 15% of fibroblasts, respectively.