Characterization of hepatic allograft infiltrates in rats pretreated with donor-specific blood transfusion (DST).

A single intravenous injection of 1 ml freshly heparinized donor blood given 7 days prior to transplantation prolonged significantly the survival of subsequent hepatic allografts in fully allogeneic ACI(RT1a)-to-LEW(RT1(1)) rats. The cellular identity of allograft infiltrates was investigated at various times after transplantation using OX8 (CD8) and W3/25 (CD4) monoclonal antibodies. The number of CD8+ cells increased rapidly and reached a peak on Day 3 after transplantation of the untreated allografts. Similarly, the number of CD8+ cells in the allografts from DST-treated rats was maximum on Day 3 and decreased gradually thereafter. The maximum number of CD4+ cells was found on Day 3 in untreated allografts. In contrast, no significant infiltration of CD4+ cells occurred during the first 7 days after transplantation in DST-treated allografts. Thereafter, the number of CD4+ cells increased rapidly and reached a peak on Day 14. CD4+ cells remained persistently elevated in hepatic allografts of rats pretreated with DST, but did not become functionally competent or initiate rejection. These findings suggest that persistent infiltration by CD4+ cells is a characteristic feature of long-surviving hepatic allografts in rats pretreated with DST.