SPLIT TOLERANCE INDUCED BY ORTHOTOPIC LIVER-TRANSPLANTATION IN MICE

Spontaneous orthotopic liver allograft acceptance associated with micr ochimerism in mice induces tolerance to subsequent skin or heart trans plants from the donor but not third-party animals. Despite in vivo hyp oresponsiveness, in vitro MLC and CTL assays showed continuing antidon or reactivity. Cells isolated from recipients' spleens and grafted liv ers, when tested in MLC and CTL assays, were antidonor reactive out to 3 months to the same degree as splenocytes obtained from either naive or presensitized (with skin or heart) mice. Nevertheless, passive tra nsfer of splenocytes or liver lymphocytes from liver tolerant mice, bu t not naive or sensitized donor strain mice, were able to prolong skin graft survival significantly in naive irradiated recipients. By using a strain combination in which the donor but not the recipient express ed the stimulatory endogenous super-Ag (Mls(f)), it was possible to de termine whether super-Ag-reactive T cells bearing V beta 5 and V beta 11 were deleted or anergic. Phenotypic analysis of cells isolated from recipients' spleens and grafted livers (up to 90 days after transplan t), when compared with naive animals, showed no significant difference in V beta 5 and V beta 11 TCR expression. Additionally, when these is olated spleen cells were tested for antibody-mediated stimulation, bot h anti-V beta 5 and V beta 11 TCR mAb led to marked proliferation of c ells obtained from naive and liver-transplanted recipients, but as exp ected, proliferation was very low in cells from naive donors. These re sults suggest that liver transplantation induces donor-specific tolera nce in vivo, which may not be reflected in in vitro proliferative and cytotoxicity assays (split tolerance). Furthermore, this tolerance doe s not seem to be induced by clonal deletion or anergy of minor-lymphoc yte-stimulating-antigen-reactive T cells in the recipients. recipients .