Background: Chronic Rejection (CR) is the leading cause of renal allograft dysfunction. Upregulation of growth factors has been shown in CR but the time point at which this occurs in not known. The aim of this study was to examine the time course of upregulation of growth factors and correlate this with the macrophage and myofibroblast interstitial infiltrate.
Methods: Using a rat model of CR (F344 kidney donor to Lewis recipient), infiltration by ED1 + macrophages and proliferation of alpha-smooth muscle actin (alpha-SMA) and desmin-expressing cells was examined using immunohistochemistry. In addition, expression of mRNA for interferon-gamma (IFN-gamma), transforming growth factor-beta (TGF-beta), basic-fibroblast growth factor (b-FGF) and vascular endothelial growth factor (VEGF) was studied using a semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR) technique. Native Lewis rat kidney and Lewis-Lewis isografts were used as controls.
Results: Immunohistochemical staining of ED1 + cells showed a marked increase in the macrophage infiltrate of allografts compared to isografts at all time periods (P = 0.0002) peaking at weeks 8-12 after transplantation. Expression of alpha-SMA was also increased in allografts (P = 0.002). RT-PCR analysis showed that mRNA for TGF-beta was maximally upregulated in allografts in comparison to isografts at week 8 after engraftment (P = 0.05) and declined thereafter, although remained at elevated levels compared to controls. IFN-gamma and b-FGF gene expression was increased in allografts late in the post-transplantation period.
Conclusion: Early infiltration of macrophages and production of TGF-beta1 was followed by later upregulation of fibrogenic growth factors and myofibroblasts associated with interstitial fibrosis and organ dysfunction.