Leukocyte infiltration and renal fibrosis after UUO histology. Cortical renal sections were stained for CD45⁺ leukocytes. At 10 days after UUO (a) leukocytes accumulated in the peritubular interstitium in obstructed kidneys compared with unobstructed control kidneys (b). Treatment with BX471 from day 6 to 10 (c), as well as treatment for 10 days (d), reduced infiltration of CD45-positive leukocytes in UUO kidneys compared with a and b. No reduction was noted in UUO kidneys of mice treated with BX471 from days 0 to 5 (not shown). The accumulation of FSP1-positive fibroblasts in the peritubular interstitium 10 days after UUO (e) was reduced when BX471was given for 10 days (f) and from day 6 to 10 (latter not shown). Cortical renal sections were also silver stained to assess interstitial volume and fibrous tissue deposition. Note a marked widening of the interstitial space with deposition of fibrous tissue in areas of dilated tubules in obstructed kidneys at 10 days (g) compared with unobstructed control kidneys (h) of vehicle controls. Treatment with BX471 from days 6 to 10 reduced interstitial volume and matrix deposition (i), as well as BX471 treatment for 10 days (j), compared with g. No reduction was noted in UUO kidneys of mice treated with BX471 at days 0–5 (not shown). Tubular dilatation and tubular epithelial cell damage remained unchanged in all groups (original magnification ×400).