(HEPATOLOGY 2011;) Liver damage caused by liver graft ischemia/reperfusion (I/R) represents a highly complex cascade of events leading to hepatocellular injury after liver transplantation
(LT). These events are triggered when the liver is transiently Metabolism inhibitor exposed to hypoxic and hypothermic conditions and is reperfused with warm and oxygenated blood. The procedure is unavoidable during transplantation surgery, and every liver graft suffers from some degree of I/R injury. Liver I/R injury represents a serious problem in LT and significantly affects patient and graft outcomes.1, 2 In a large series of living donor and deceased donor LT patients, a longer cold ischemia time was associated with a higher frequency of early graft failure and with a higher rate of acute cellular rejection.3 Moreover, I/R injury contributes to the donor organ shortage because of the higher susceptibility of marginal livers to ischemic insults. To date, there is no specific treatment available to prevent or reduce hepatic I/R injury, and the current treatment is based merely on supportive care. Thus, extensive SB203580 in vivo research efforts to better understand the mechanisms of hepatic I/R injury after LT are warranted. B7 homolog 1 (B7-H1), which is also called CD274 and programmed death 1 (PD-1) ligand, is a recently
identified member of the B7 family with important regulatory functions in cell-mediated immune responses.4, 5 Together with the PD-1 receptor, B7-H1 is known to play an important role in regulating TGF-beta inhibitor local immune responses to infection,6, 7 autoimmunity,8, 9 and alloimmunity.10-;12 PD-1 is a member of the CD28 family, which is expressed by activated CD4 and CD8 T cells, B cells, and myeloid cells.13, 14 In
contrast, B7-H1 is expressed by antigen-presenting cells (APCs), such as dendritic cells (DCs), monocytes, and B cells, upon stimulation.15 Moreover, B7-H1 can be detected in the parenchymal cells of nonlymphoid organs, including hepatocytes.16 A growing number of reports suggest a crucial role for B7-H1 expression in the regulation of local immune responses in the liver. It has been reported that interactions with B7-H1 in the liver selectively delete activated CD8+ T cells.17 Moreover, the spontaneous acceptance of mouse liver grafts is prevented when the grafts lack B7-H1 expression because of the reduced apoptosis of graft-infiltrating host CD8+ T cells.18 In this study, we hypothesized that the hepatic expression of B7-H1 plays crucial roles during innate immune responses induced by hepatic I/R injury, and using B7-H1 knockout (KO) mice, we tested this hypothesis directly in the mouse LT model with prolonged cold preservation (24 hours).