Circulating Fibrocytes in Ischemia-Reperfusion Injury and Chronic Renal Allograft Fibrosis

Background: Interstitial fibrosis in chronic allograft injury has been suggested as a major cause of the loss of allograft. Methods: To clarify the involvement of circulating fibrocytes (CF) and alpha-smooth muscle actin (SMA)-positive cells in renal allograft injury, we investigated 36 renal transplanted cases at 0 h, 1 h, 2-4 weeks, 4-8 weeks, and 1 year, and 5 normal controls. Double immunofluorescence analysis for both COL1 and CD45 indicating CF (/mm(2)), and the positive area (%) of alpha-SMA and Masson trichrome (MT) stain were detected by an image analyzing system. Results: The mean number of CF was 0 in controls and 4.0 in total transplanted specimens (p < 0.05). CF correlated with the alpha-SMA-positive area in the graft (R-2 = 0.39, p < 0.01), but not with Banff 2005 scores. The number of CF increased in 2-4 weeks; however, decreased 1 year after transplantation. alpha-SMA-positive area gradually increased at 1 year concomitant with the increase of MT-positive area. A similar phenomenon was observed in a case of primary nonfunction kidney from 0 h to 6 weeks after transplantation. The electron microscopy score of fibrosis around peritubular capillaries was correlated positively with COL1-positive area (R-2 = 0.72, p < 0.01), but negatively with infiltrated CF (R-2 = 0.25, p < 0.05). Conclusion: CF were transiently induced, probably due to ischemia-reperfusion injury, but fibrosis only slightly progressed in this process. The alpha-SMA-positive myofibroblasts may accelerate the expansion of fibrosis around peritubular capillaries in chronic allograft injury. Copyright (c) 2012 S. Karger AG, Basel