Specific tolerance induction of allo-Kb-skin grafts by FK506 in the CD8-depleted H-2k recipients required low amounts of Kb-antigen

MHC class I allo-grafts can be directly rejected by recipient CD8 T cells and be indirectly rejected by recipient CD4 T cells. Although the experimental results using the bm mutant and C57BL/6 mice indicated that CD4-mediated rejection of class I-disparate grafts is a relatively weak process and is expected to be more sensitive to additional exogenous immunosuppression, it is unclear that whether this mechanism can be used for inducing a specific tolerance of class I disparate grafts. In this study, we hypothesize that a short course of FK506 may induce a specific tolerance of class I-disparate skin grafts in the CD8-depleted recipients. Kb-transgenic C3H mice, Tg.H-2 Kb-1 and Tg.H-2 Kb-2 mice that express high copies and low copies of Kb-antigen respectively were used as donors. Wild type C3H mice (H-2k) in which either CD4 or CD8 T cells were depleted by administration of anti-CD4 or CD8 monoclonal antibody (mAb) were used as recipients. Results showed that FK506 promoted longer survival of allo-Kb skin grafts in CD8-depleted C3H mice than in CD4-depleted C3H mice. Graft survival from Tg.H-2 Kb-2 mice was significantly longer than Tg.H-2 Kb-1 mice. A short course of FK506 induced long-term survival of skin grafts from Tg.H-2Kb-2 mice, but not from Tg.H-2Kb-1 mice in CD8-depleted C3H recipients, even after FK506 was stopped. These mice also accepted grafts of Tg.H-2Kb-1 mice when challenged with skin grafts from Tg.H-2Kb-1 mice, but promptly rejected third party skin grafts from BALB/c (H-2d) mice. T cells from Kb-tolerant C3H mice did not respond to allo-Kb-antigen in in vitro assays of mixed lymphocyte culture and cell-mediated cytotoxicity. In conclusion we found that a short course of FK506 treatment and low amounts of Kb-antigen induced a Kb-specific tolerance in the CD8-depleted recipients, and this tolerance maintained even after withdrawing the anti-CD8 mAb treatment.