BACKGROUND:?Although many human inlfammatory and autoimmune diseases were previously considered to be mediated by T helper type 1 (Th1) cells, the recently described Th17 cells play dominant roles in several of these diseases. We and others speculated that allograft rejection after organ transplantation may also involve Th17 cells. Episodes of acute rejection occur in 30%of liver transplants. This study aimed to determine the frequency of circulating Th17 cells in patients who had received liver transplants for benign end-stage liver disease and to identify any association between acute rejection episodes and levels of Th17 cells in the peripheral blood. METHODS:?A prospective study compared Th17 cells from 76 consecutive benign end-stage liver disease patients who had undergone orthotopic liver transplantation from 2007 to 2011 with those from 20 age-matched healthy individuals. Peripheral blood samples were collected at different time points within one year after transplant. Blood samples and liver biopsies were also collected at the diagnosis of acute rejection. Percentages of circulating CD4+IL-17+cells were measured by lfow cytometry. The transplant patients were classiifed into two groups: a rejection group consisting of 17 patients who had an episode of acute rejection, and a non-rejection group comprising the remaining 59 patients with no acute rejection episodes. Percentages of circulating Th17 cells were compared between the two groups and controls. RESULTS:?The levels of circulating CD4+IL-17+T cells in the rejection group were higher during acute rejection than those in the non-rejection group (2.56±0.43% versus 1.79±0.44%, P