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
.