The time course of cell-mediated lympholysis in rat hepatic allograft recipients pretreated with a single donor-specific blood transfusion

A single intravenous injection of 1 ml freshly heparinized donor blood seven days before transplantation significantly prolonged the survival of subsequent donor-specific hepatic allografts in the fully allogeneic ACI(RT1a-to-LEW(RT1l)) rat combination. The time course of cell-mediated lympholysis was studied in this animal model. The activity of CML in lymphocytes infiltrating into the hepatic allograft (CML-G) and in the spleen (CML-S) was determined by measuring % lysis of donor Con A blast cervical lymph node cells. Preoperative DST resulted in an increased activity of CML-S with a peak (31.6%, E/T = 150) on day 7. This increased CML-S activity after DST rapidly declined during the first days following hepatic transplantation. The activities of both CML-S and CML-G then increased after transplantation and reached peaks on days 15 (48%, E/T = 150) and 20 (2.57%, E/T = 75), respectively. These were much higher than the peak values of CML-S (11.2%, E/T = 150) on day 7 and CML-G (19.5%, E/T = 75) on day 6 in untreated controls and were followed by a subsequent gradual decrease in those activities to preoperative levels by day 113 posttransplant. Phenotypic analysis of lymphocytes infiltrating grafts in DST-treated hosts demonstrated that the CD4/CD8 ratio remained relatively constant (less than 1.0). While the ratio in control grafts increased and reached a peak (2.17) on day 9. Histological examination revealed that mononuclear cell infiltration of grafts reached a peak on day 9 in both DST-treated hosts and controls. This mononuclear cell accumulation gradually subsided in DST-enhanced grafts. The mitotic index of graft hepatocytes reached a peak on day 15 in DST-treated hosts and on day 7 in control. The evidence of prolonged survival of hepatic grafts in recipients pretreated with DST, despite the presence of cytotoxic T cells with increased CML activity in vitro, suggests that effector cytotoxic cell activity may not be necessary for rat liver allograft rejection and that there may be limitations in measuring host cytotoxic activity simply by CML assays.