| At present, renal allograft transplantation is still a clinically effective means to treat end-stage renal diseases. With the discovery of immunodepressants, achievement ratio and survival time of renal allograft transplantation have been significantly elevated, but chronic allograft dysfunction is still the leading problem that impact on the long-term survival of allograft kidney.Statistical data showed that, at 1 year after kidney transplantation there were up to 6% of grafts presented as chronic allograft dysfunction per year with pathological manifestation characterized by chronic renal allograft fibrosis and intimal fibrous thickening in small arteries.The process of renal allograft fibrosis is divided into three phases:①initial stage: some immune or non-immune factors lead to tissue injury;②fiber formation stage: inflammatory and proliferative response regulated by cytokines, chemokines and growth factors produce extracellular matrix (ECM);③matrix deposition stage: overproduction or decreased degradation of ECM eventually lead to fibrosis. Thus cells being activated and producing a large number of extracellular matrix are the key processes to cause renal fibrosis. Excessive extracellular matrix is produced by fibroblasts proliferation and/or myofibroblasts transformation when injury or inflammation and some other factors exist, new composite collagen fiber deposits in renal tissue. The origin of myofibroblasts had been considered from the stromal fibroblasts itself, but some recent studies showed that renal tubular epithelial cells possibly involved in fibrosis formation by turning into mesenchymal cells (epithelial-mesenchymal transformation,EMT) in renal fibrosis. Someone even proposed that tubular epithelial-mesenchymal transformation was the main source of myofibroblasts in renal fibrosis. Tubular epithelial cells with myofibroblasts transformation are characterized by de novo activation ofα-smooth muscle actin (α-SMA) and the loss of keratin compared with mature epithelial cells.In renal transplantation, many risk factors can cause transplanted kidney injury, most of those are acute rejection but the most severe injuries are chronic renal allograft dysfunction and renal fibrosis. Although combined immunosuppressants were reasonably used, still up to 40% of transplanted kidney presented as post-operative acute rejection. In 1995, it was reported that lymphocytes inside the peritubular walls in acute renal allograft rejection were mainly CD8+ T cells (cytotoxic T lymphocytes). Previous reports and our clinical data demonstrate that serious acute rejection and acute rejection frequent stroke accelerate the time that chronic renal allograft fibrosis presents, indicating that there must be some direct relationship between acute rejection and chronic renal allograft dysfunction.So, we reviewed 203 biopsy specimens with different degrees of renal rejection and/or fibrosis to observe the relationship between epithelial-mesenchymal transformation and T lymphocytes infiltration in different cases of acute rejection providing a basic reasch on renal allograft rejection especially the prevention and the treatment of chronic allograft dysfunction.Specimens were collected from renal allograft biopsy specimens during the july 2005 - September 2007. According to Banff-2007 classification, 55 specimens were chose as our research targets, including 7 cases of non-obvious reactive rejection (fundamental normal), 28 cases of acute T-cell-mediated rejection class IA, 14 cases of acute T-cell-mediated rejection class IB, 6 cases of interstitial sclerosis and tubular atrophy. Of the 55 specimens, 37 are male, 18 are female, the mean age is 41 years.Two makers, monoclone mouse anti-humanα-smooth muscle actin(α-SMA, a smooth muscle and myofibroblast marker) and monoclone CD8 (a cytotoxic/suppressive T lymphocyte marker), were used to observe the relationship between epithelial-mesenchymal transformation and infiltrating CD8+ T lymphocytes by immunocytochemical S-P method.In this study by each pathologic group, the expression ofα-SMA was examined close to atrophic tubular epithelial basement membrane but not in cytoplasm of epithelial cells compared with positive control, that in vascular smooth muscle. However there was no significant difference ofα-SMA expression in atrophic tubules among groups. It is not clear that theα-SMA positive expression close to tubular epithelial basement membrane is a direct evidence of epithelial- mesenchymal transformation or it is a result of tubular basement membrane thickening and interstitial muscle fiber proliferation. Excepting the expression ofα-SMA in tubular epithelial cells in atrophic area, we found that it was examined in a small number of tubular epithelial cells without atrophy in each pathologic group, and positiveα-SMA was expressed in cytoplasm. At the same time apparent lymphocytes were found within and around theα-SMA positive tubular epithelial cells. Theα-SMA expression among pathological groups was different. As the severity of acute T-cell-mediated rejection increased, videlice,the infiltration of lymphocytes and lymphomonocytes augmented, especially the degree of tubular inflammation increased, the quantity ofα-SMA expression in tubular epithelial cells increased. The statistical analysis of between-group comparison demonstrates that the expression ofα-SMA was significantly different between groups of acute T-cell-mediated rejection class IA and IB, class IB and non-obvious reactive rejection, class IB and interstitial sclerosis, tubular atrophy. This difference supports that tubular epithelial cells are sources of myofibroblasts which produce a large amount of extracellular matrix in renal fibrosis by epithelial- mesenchymal transformation.On basis of this observion of theα-SMA expression in different pathologic groups, CD8 T lymphocytes immunocytochemical staining was performed to detect the infiltrating lymphocytes in cases of acute T cell-mediated rejection. The results showed that different percentages of CD8+T cells expression were examined in infiltrating lymphocytes of acute T cell-mediated rejection, and lymphocytes inside the peritubular walls were mainly CD8+T cells. Statistical analysis demonstrates that the percentage of infiltrating CD8+T cells has no significant correlation with the positive expression ofα-SMA in tubular cells in cases of rejection, however some correlated trends of those can be found if more attention have been paid, it is the percentage of CD8+ T cells is less than 10% in lymphocytes in the cases withα-SMA negative expression.All our above research data suggest that in renal allograft rejection, lymphocytes inside the peritubular walls may be directly involved in or cause epithelial-mesenchymal transformation, it is probably a factor connected acute renal allograft rejection with chronic fibrosis.In summary, this study chiefly identifies the existion of tubular epithelial-mesenchymal transformation in acute T cell-mediated renal allograft rejection, and there is an obvious infiltration of lymphocytes within and around the tubular cells with epithelial-mesenchymal transformation; as the severity of acute T cell-mediated rejection increases, tubular epithelial-mesenchymal transformation increases. The percentage of infiltrating CD8+T lymphocytes in acute T cell-mediated rejection has a positive correlation with the degree of tubular epithelial-mesenchymal transformation. |
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