Increased apoptosis is specific for acute rejection in rat small bowel transplant

Apoptosis has been associated with several events in solid organ transplantation, including ischemia/reperfusion (IR) injury and acute rejection. To determine whether apoptosis-profiles may distinguish these two conditions, we analyzed apoptosis rates in a rat orthotopic small bowel transplant (SBT) model. SBT was performed in Lewis rats with either freshly harvested or preserved (4 h, in UW at 4°C) syngeneic and allogeneic (Brown-Norway) grafts. Bowel samples were collected 2 h after reperfusion and on small bowel transplant postoperative days (POD) 1, 4, and 7. Apoptosis was detected by measuring levels of histone-associated DNA fragments and caspase 3 expression, and by determining apoptotic body counts. All markers measured 2 h after reperfusion increased profoundly in association with preservation. After a significant decrease on POD 1, apoptosis rates rose again between POD 4 and 7 only in allogeneic grafts. This distinct second increase in apoptosis may be an early and specific sign of acute rejection.