*2.1. Infiltration of Interstitial Macrophages Correlates with Fibrosis in Obstructed Kidneys*

To investigate the role of macrophage infiltration in renal fibrosis, we compared five mice kidneys harvested seven days after UUO to five mice kidneys harvested 14 days after UUO. Masson trichrome staining indicated that the area of renal tubulointerstitial fibrosis increased with the time of UUO. Moreover, immunohistochemistry showed α-smooth muscle actin (α-SMA)-positive myofibroblasts progressively increased in the day 14 obstructed kidneys as compared to the day 7 ones. Notably, the area of F4/80 (pan-macrophage marker)-positive macrophage infiltrate also correspondingly increased in the day 14 obstructed kidneys (Figure 1), indicating that interstitial macrophages did play an essential role in the development of renal fibrosis.
