Direct evidence of a functional separation of alloreactive T lymphocytes from bystander cells infiltrating rat allografts: Interleukin 2 receptor-positive cells reacting with the monoclonal antibody art 18 mediating second-set rejection

In this study we examined the functional capacity of unseparated, IL-2R positive and IL-2R negative leukocytes infiltrating BN rat hearts or kidneys grafted into allogeneic LEW rats. Upon adoptive transfer into syngeneic LEW recipients, splenocytes or day-3 graft infiltrate cells of either cardiac or renal transplants were ineffective to alter BN cardiac test graft survival (controls 7.8 ± 0.8 day). However, adoptive transfer of day-5 heart infiltrate cells resulted in a delay of test graft rejection (9.4±0.7 day, P<0.001), while day-5 kidney-graft-infiltrating cells produced second set rejection (6.2±0.5, P<0.001). Specificity controls of day-5 cells infiltrating DA heart or kidney grafts rejected at 7.8± 0.8 or 7.7±0.5 days. Following separation into IL-2R positive and negative subpopulations by use of the mAB ART 18, IL-2R positive but not IL-2R negative cells caused second set rejection in both the renal and the cardiac model (6.2±0.4, respectively, 6.3+0.5 days, P <0.001 or P<0.005). Furthermore, in the kidney model IL-2R positive nylon-wool nonadherent cells also caused second set rejection (6.2±0.4, P<0.005) suggesting that IL-2R positive T cells present in the graft at maximal infiltration are the mediators of rejection. Thus, it appears that these cells can be phenotypically and functionally separated from bystander cells.